University of Ghana http://ugspace.ug.edu.gh STUDIES OF RARE EARTH ELEMENTS AND ASSOCIATED RADIOACTIVITY IN THE COASTAL SAND OF THE CENTRAL AND WESTERN REGIONS OF GHANA THIS DISSERTATION IS SUBMITTED TO THE UNIVERSITY OF GHANA, LEGON IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF Ph.D. DEGREE IN NUCLEAR AND RADIOCHEMISTRY BY JOSHUA AYODEJI ABEY, (10444542) B.Sc. (UNAD, Nigeria), 2009, M.Sc. (OAU, Nigeria), 2014 DEPARTMENT OF NUCLEAR SCIENCES AND APPLICATIONS SCHOOL OF NUCLEAR AND ALLIED SCIENCES-ATOMIC COLLEGE OF BASIC AND APPLIED SCIENCES UNIVERSITY OF GHANA, LEGON JULY, 2017 University of Ghana http://ugspace.ug.edu.gh DECLARATION This dissertation is the result of research work undertaken by JOSHUA AYODEJI ABEY in the Department of Nuclear Sciences and Applications, School of Nuclear and Allied Sciences, University of Ghana, Legon, under the supervision of Prof. Yaw Serfor-Armah, Prof. Samuel B. Dampare and Dr. Dennis K. Adotey. Signature………………………… Joshua Ayodeji Abey (Student) Date ………………………… Signature…………………… Date ………………………… Prof. Yaw Serfor-Armah, Ph.D. (Supervisor) Signature…………….… Date ………………………… Prof. Samuel B. Dampare, Ph.D. (Co-Supervisor) Signature……………… Date ………………………… Dr. Dennis K. Adotey (Co-Supervisor) ii University of Ghana http://ugspace.ug.edu.gh DEDICATION This work is dedicated to the God of Science and Technology who is the Source of my Strength. iii University of Ghana http://ugspace.ug.edu.gh ACKNOWLEDGEMENT My appreciation goes to God Almighty the source of my Existence and Inspiration. My thanks go to my parents, Mr. and Mrs. Abey, for their active role in the financing of my research project. I hereby wish to express my profound gratitude to my supervisor, Prof. Yaw-Serfor Armah, for his support, guidance and supervision of this work which has been able to widen my horizon. The moral support of the co- supervisor, Prof. S.B. Dampare cannot be overemphasized, as he provided critical information with respect to the geological perspective of this study. The contributions of Dr. D.K Adotey, who sacrificed his time during the drafting of the work-plan is highly appreciated. The support of Dr. David Kpeglo in the studies of the naturally occurring radioactive materials (NORMs) is highly appreciated. I sincerely appreciate my brother, Mr. Solomon Abey and his wife, Nosarieme Abey for their moral and financial support during my research. Many thanks to my colleagues: Mrs. Irene Opoku-Ntim, Mrs. Jennifer Ofori, Mrs. Dzifa Banson, Ms. Delali Tulasi and Mr. Hyacinthe Ahimadjie. The relentless support of Messrs Patrick Bayowobie, Oswald Mkanda, Solomon Bello, Randy Davordzie, Philip Gasu, Ms. Afia Boatemaa and Ms. Florence Amoakohene during the course of the research is highly appreciated. I appreciate the support of members of Mt. Sinai Methodist Church, Atomic, for their spiritual mentorship. I acknowledge the support of my beloved Temple Henry and my guardians Mr Alfred Fosu family, Aunty Doris and Mrs. Felicia Darko-Asare. The mentorship provided by Prof. F.O. Asubiojo, Prof. F.M Adebiyi and Prof. P.A Tchokossa of the Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria, is highly appreciated. iv University of Ghana http://ugspace.ug.edu.gh I acknowledge the support of organizations such as the Ghana Atomic Energy Commission (GAEC); Ghana Standards Authority (GSA); Department of Physics, University of Ghana; Ghana Highway Authority; Separations Ltd. South Africa; Ore Research and Exploration Pty Ltd, Australia (OREAS); ALS Global Laboratory, Canada; African Mineral Standard (AMIS), South Africa; Eichrom Technologies U.S.A; and, TRISKEM International, France v University of Ghana http://ugspace.ug.edu.gh ABSTRACT Beach sands are known host of different heavy minerals, which occur mostly as placer deposits and are of great importance to the electronics, metallurgy, medical, defense, and automobile industries. Typical examples of such heavy minerals are the rare earth-associated minerals (e.g. monazite, bastnaesite, xenotime and euxenite). Some of these rare earth elements-containing ores are known to occur in association with naturally occurring radioactive uranium (U-238) and thorium (Th-232). Limited studies are available on identification of rare earth element fingerprints in the coastal sands of Ghana. Also, the relationship between the Naturally Occurring Radioactive Materials (NORMs) and the Rare Earth Elements (REEs) in Ghanaian coastal sands has not been well studied. The study developed an analytical procedure for mapping out the composition of rare earth elements in beach sands via the pathfinder role of naturally occurring radioactivity along the coast of the Central and Western regions of Ghana. This was achieved through: (i) assessment of naturally occurring radionuclides (238Th, 232Th and 40K) using Gamma Spectrometry and ascertaining the presence of REEs-associated minerals using bromoform (density = 2.89 g/cm³) prior to petrography of the heavy mineral concentrates; (ii) investigation of REEs in coarse, medium and fine fractions using Lithium Metaborate Fusion Method using Inductively Coupled Plasma Mass Spectrometry (ICP-MS); (iii) development of chemical method in the separation of selected REEs (Pr, Nd, Sm, Eu); and (iv) establishment of geospatial distribution pattern to aid exploration of REEs minerals. Beach sand samples were collected from 15 locations in the Central region (Gomoa Fetteh, Senya Beraku, Winneba, Mankwadze, Apam, Mumford, Dago, Akra, Ekumpoano, Edumafa, Anomabu, Cape Coast, Elmina, Dutch Komenda and Kafodzizi) and 10 locations in the Western region (Shama, Abuesi, Sekondi, vi University of Ghana http://ugspace.ug.edu.gh Takoradi, Cape Three Points, Egyembra, Axim, Esiama and Sanzule) along the coastline of Southwestern Ghana. The average concentrations of 238U, 232Th and 40K in the beach sands of the Central and Western regions of Ghana were found to contain the United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR) recommended permissible levels (35; 30; and 400 Bq/Kg respectively) for radionuclides; with mean activity concentrations (ranges) of 1.3 ± 0.47 to 31.50± 3.31 Bq/Kg (238U); 0.7± 0.04 to 71.70± 4.55 Bq/Kg (232Th); 73.9± 6.72 to 1775.5± 28.35 (40K) for the Central region. In the Western region, the mean activity concentration ranged fom 1.0 ± 0.03 to 5.6± 0.24 Bq/Kg (238U); 0.8± 0.04 to 3.8± 0.14 Bq/Kg (232Th); and 18.6± 0.23 to 343.2± 18.35 (40K). Beach sand dose rate in the Central region and Western region ranged from 4.13 to 132.39 (nGy/hr) and 1.78 to 19.32 (nGy/hr) respectively; with a total average across the two regions being 11.40 (nGy/hr). The annual effective dose in the Central region ranged from 0.0051 to 0.1624, while that for the Western region ranged from 0.002 to 0.024; total average for the two regions was 0.014 mSv/Yr. High radioactivity levels (Bq/Kg) (238U; 232Th; 40K; Raeq) observed in the beach sands of Dago (31.5±3.31; 71.7±4.55; 1775.5±28.35; 258.21); Akra (4.1±1.13; 2.0±0.51; 81.6±6.39; 12.66); and Ekumpoano (27.2±5.8; 6.2±1.20; 69.7±8.12; 33.67) of the Central region exceeded the individual radioactivity levels of the Western region. Heavy minerals such as Zircon, Rutile and Amphibole were identified in the beach sands of the Central and Western regions. The minerals found are known to concentrate REEs and are indicative of shore-derived minerals. Rare earth elements were found in beach sands at both regions. Total Rare Earth Elements (TREEs) distribution in the beach sands of the Central region ranged as coarse fraction (6.33 to 13.30 ppm); medium fraction (8.56 to 53.15 ppm) and fine fraction (16.67 to 795.01 ppm). The sum of Light Rare vii University of Ghana http://ugspace.ug.edu.gh Earth Elements (LREEs); Heavy Rare Earths (HREEs); and ratio of light to heavy rare earth (LREE/HREE) distribution in the Central region were: coarse fraction (5.56 to 11.77 ppm; 0.64 to 1.53 ppm; 5.81to 9.89); medium fraction (7.72 to 48.13 pm; 0.84 to 5.02 ppm; 5.83 to 9.95); and fine fraction (14.98 to 727 ppm; 1.69 to 74.53 ppm; 4.43 to 10.79). The TREE distribution in the beach sands of the Western region varies as follows; coarse (5.69 to 29.78 ppm); medium (9.51 to 85.58 ppm) and fine fraction (24.3 to 86.28). The sum of light LREEs, HREEs and ratio of light to heavy rare earth (LREE/HREE) distribution in the Western beach sands were: coarse fraction (5.07 to 26.08 ppm; 0.62 to 3.70 ppm; 6.67 to 10.11); medium fraction (8.47 to 76.8ppm; 1.04 to 8.78 ppm; 3.97 to 9.56) and fine fraction (21.6 to 77.46 ppm; 2.7 to 17.63 ppm; 2.76 to 8.78). Despite the prominence of REE- fingerprints in the beach sands of Dago, Akra and Ekumpoano in the Central region, the corresponding increase in radioactivity concentrations at these locations (Dago, Akra and Ekumpoano) suggest strong influence of the geology of these areas. The sharp decrease in the concentration of total REEs in the beach sands of Akra shows an anomaly despite the fact that the sampling points are along the same trend. The geospatial observation of the coastline along the Central region showed that the sampling location at Dago and Ekumpoano are on probable geological faults and have differing geology. The study has also revealed that the radioactivity distribution in the beach sands serves as pathfinders to potential rare earth elements deposits in the Central region. Although heavy REEs were found in relatively higher concentrations in the beach sands of the Western region, the REEs in the fine fractions of the Central region exceeded that of the Western region. Consequently, the renewable energy target which relies on selected rare earth elements is achievable if more resources are committed towards potential sources of the REEs in-land. viii University of Ghana http://ugspace.ug.edu.gh TABLE OF CONTENTS OUTLINE TITLE PAGE .................................................................................................................. i DECLARATION ........................................................................................................... ii DEDICATION ............................................................................................................. iii ACKNOWLEDGEMENTS .......................................................................................... iv ABSTRACT .................................................................................................................. vi TABLE OF CONTENT ................................................................................................ ix LIST OF FIGURES .................................................................................................... xiv LIST OF TABLES ..................................................................................................... xvii LIST OF ACRONYMS .............................................................................................. xix CHAPTER ONE ............................................................................................................ 1 GENERAL INTRODUCTION ...................................................................................... 1 1.1 Background .............................................................................................................. 1 1.2 Problem Statement ................................................................................................... 5 1.3 Objectives ................................................................................................................ 6 1.4 Justification for the Study ........................................................................................ 7 1.5 Extent of the Study................................................................................................... 8 1.6 Arrangement of Chapters ......................................................................................... 8 CHAPTER TWO ........................................................................................................... 9 LITERATURE REVIEW .............................................................................................. 9 2.1 Occurrence and Abundance of Rare Earth Elements ............................................... 9 2.2 Ores of Rare Earth Elements .................................................................................. 11 2.2.1 Carbonatite Associated Rare Earth Deposits .................................................. 13 ix University of Ghana http://ugspace.ug.edu.gh 2.2.2 Alkaline Complexes and Alkaline Pegmatite REE Deposits .......................... 16 2.2.3 Rhyolite Associated REE Deposits ................................................................. 16 2.2.4 Granitic Associated REE Deposits .................................................................. 17 2.2.5 Hydrothermal Related REE Deposits .............................................................. 18 2.2.6 Skarn Deposit of REEs .................................................................................... 19 2.2.7 Heavy Mineral Sands REE Deposits ............................................................... 20 2.2.8 Rare Earth Elements Ores in Placer Deposits ................................................. 21 2.3 Classification of Rare Earth Minerals .................................................................... 21 2.4 Rare Earths and Associated Radioactivity ............................................................. 22 2.5 Properties of Rare Earth Elements ......................................................................... 23 2.5.1 Chemical Properties of Rare Earth Elements ................................................. 23  2.5.2 Physical Properties of Rare Earth Elements ................................................... 26 2.6 Industrial Processing of Rare Earth Ores .............................................................. 29 2.6.1 Acid Digestion of Rare Earth Ores ................................................................. 31 2.6.2 Alkaline Digestion of Rare Earth Ores ........................................................... 33 2.7 Separation of Rare Earth Metals ............................................................................ 33 2.7.1 Solvent Extraction in Rare Earth Processing .................................................. 34 2.7.2 Ion Exchange Resin Separation ....................................................................... 38 2.7.3 Chromatographic Extraction REEs Separation ............................................... 39 2.7.4 Molecular Recognition in the Separation of REEs ......................................... 43 CHAPTER THREE ..................................................................................................... 44 MATERIALS AND METHODS ................................................................................. 44 3.1 Profile of the Study Area ..................................................................................... 44 3.1.1 Description of Study Area ........................................................................... 44 3.1.2 Geology of the Coastal Area ........................................................................ 46 3.2 Description of the Selection of Sampling Sites .................................................... 47 x University of Ghana http://ugspace.ug.edu.gh 3.3 Collection of Beach Sand Samples ........................................................................ 52 3.4 Preparation and Analysis of Samples .................................................................... 55 3.4.1 Flow Chart for General Scheme of Analysis .................................................. 55 3.5 Grain Size Distribution of Coastal Sands .............................................................. 57 3.5.1 Instrumentation for Grain Size Analysis......................................................... 57 3.5.2 Experimental Procedure for Particle Size Distribution ................................... 58 3.6 Mineral Identification in Coastal Sands Experiment (Petrography) ...................... 60 3.6.1 Materials for Petrographic Studies .................................................................. 60 3.6.2 Sample Preparation for Mineral Identification ................................................ 61 3.7 Determination of Naturally Occuring Radioactive Minerals (NORMs) ................ 63 3.7.1 Instrumentation for Gamma-ray Spectrometry ............................................... 63  3.7.2 Calibration of γ-ray Detector ........................................................................... 63  3.7.3 Sample Preparation for Gamma-ray Spectrometry .......................................... 66 3.8 Chemical Identification and Quantification of Rare Earth Elements using Inductively Coupled Plasma Mass Spectrometry ................................................... 68 3.8.1 Reagents, Chemicals and the Treatment of Samples ...................................... 68 3.8.2 Sample Digestion for REEs Analysis .............................................................. 69 3.9 Separation of Selected Light Rare Earth Elements (LREEs) ................................. 71 3.9.1 Sr, TRU and LN Resins in the Separation of LREEs ...................................... 71 3.9.2 Digestion of Samples for REEs Separation ..................................................... 72 CHAPTER FOUR ........................................................................................................ 75 RESULTS AND DISCUSSION .................................................................................. 75 4.1 Natural Occurring Radioactive Materials in Beach Sands of the Central and Western Regions of Ghana .................................................................................. 75 4.1.1 Radium Equivalent Activity (Raeq) ................................................................. 86 4.1.2 Absorbed Gamma Dose Rate .......................................................................... 86 xi University of Ghana http://ugspace.ug.edu.gh 4.1.3 Annual Effective Dose Rate (AEDR) ............................................................. 87 4.1.4 Activity Utilization Index (AUI) ..................................................................... 87 4.1.5 Radiation Hazard Indices (RHI) ...................................................................... 88 4.1.6 Gamma Radiation Representative Level Index (RLI) ..................................... 88 4.2 Grain Size Distribution of Coastal Sands in the Central and Western Region of Ghana ................................................................................................................. 91 4.2.1 Distribution in Coastal sands of Central Region ............................................. 91 4.3 Heavy Minerals in Beach Sands of the Central and Western Regions of Ghana .. 95 4.4 Rare Earth Elements Distribution in Coastal Sands of the Central and Western Region of Ghana .................................................................................................... 98 4.4.1 Distribution of Rare Earth Elements in Beach Sands of the Central Region .. 98 4.4.2 Distribution of Rare Earth Elements in Beach Sands of the Western Region .......................................................................................................... 107 4.5 Elemental Concentration (ppm) of Thorium and Uranium in Relation to Rare Earth Elements in Beach Sands of the Central and Western Region of Ghana ... 119 4.5.1 Elemental Concentration (ppm) of Thorium and Uranium in Relation to Rare Earth Elements in Beach Sands of the Central Region of Ghana ......... 119 4.5.2 Elemental Concentration (ppm) of Thorium and Uranium in Beach Sands of the Western Region of Ghana ....................................................................... 121 4.6 Dendogram Hierarchical Clustering Studies of the Rare Earth Elements in Beach Sands of the Central and Western Regions of Ghana. ............................. 123 4.6.1 Hierarchical Clustering of REEs in Beach Sands of the Central Region ...... 123 4.6.2 Hierarchical Clustering of REEs in Beach Sands of the Western Region of Ghana ........................................................................................................... 128 4.7 Geospatial Elucidation of the REEs in the Coastal Environment. ....................... 132 4.8 Rare Earth Elements Separation in Selected Beach Sands .................................. 141 xii University of Ghana http://ugspace.ug.edu.gh CHAPTER FIVE ....................................................................................................... 143 CONCLUSIONS AND RECOMMENDATIONS .................................................... 143 5.1 Conclusions .......................................................................................................... 143 5.1.1 Radioactivity Distribution Assessment (NORMs) ........................................ 143 5.1.2 Rare Earth Elements Fingerprints ................................................................. 145 5.1.3 Geospatial Observation ................................................................................. 146 5.2 Recommendations ................................................................................................ 147 REFERENCES .......................................................................................................... 148 APPENDICES ........................................................................................................... 165 APPENDIX A: Calibration curve for γ-ray spectrometry .................................... 165 APPENDIX B: Particle size data statistics .......................................................... 166 APPENDIX C: Pearson correlation data of LREE and HREE in beach sands ... 179 APPENDIX D: Range of REE distribution in Central and Western region summary data .............................................................................. 180 APPENDIX E: Comparison of activity concentration in beach sands in the Central and Western region with others around the world .......... 181 APPENDIX F: Pie chart representation of YREE in the beach sands of the Western region of Ghana ............................................................. 182 APPENDIX G: Photomicrograph of selected minerals in the beach sands along the coastline of the Central and Western regions. ....................... 199 APPENDIX H: Suggested complex structure of HDEHP, TBP and CMPO with lanthanide in nitric acidic medium ...................................... 202  xiii University of Ghana http://ugspace.ug.edu.gh LIST OF FIGURES Fig. 1.1: Rare earth elements reserves in selected countries in the World. ................... 2  Fig. 1.2: Rare earth elements production in selected countries in the World between 2016 - 2017. ................................................................................................... 2 Fig. 2.1: Classification of elements in the Earth Crust .................................................. 9  Fig. 2.2: Selected radioactive and rare earth associated minerals ............................... 23  Fig. 2.3: Temperature characteristics of the rare earth elements ................................. 28  Fig. 2.4: Separation process for heavy minerals in beach sands ................................. 30  Fig. 2.5: Processes flow chart for rare earth separation. ............................................. 32  Fig. 2.6 (a): Typical cations of ionic liquid ................................................................. 37  Fig. 2.6 (b): Typical anions of ionic liquid ................................................................. 38  Fig. 2.7: Anion exchange separation of rare earth element from rock ........................ 39  Fig. 2.8 (a): Structural complex of TBP interaction with Ln3+ in acidic solution. ...... 42  Fig. 2.8 (b): Inferred structural complex of CMPO interaction with Ln3+ in acidic solution. ........................................................................................... 42 Fig. 3.1: (a) A map showing the Central and Western regions of Ghana, West Africa. (b) Inset showing Africa and a highlight of Ghana (c) Inset showing Ghana and a highlight of Central and Western regions ............................................ 45  Fig. 3.2: GIS representation of the Central region coastline of Ghana ...................... 53  Fig. 3.3: GIS representation of the Western region coastline of Ghana ..................... 54  Fig. 3.4a: Flow chart for general experiment .............................................................. 55  Fig. 3.4b: Flow chart for general experiment .............................................................. 56  Fig. 3.5: Scheme for particle size distriution ............................................................... 57  Fig. 3.6: Statistical analysis scheme for beach sands from the study area .................. 59  Fig. 3.7: Mineral separation from beach sand fractions ............................................. 62  Fig. 3.8: (a) Block diagram for γ-ay spectrometry experiment (b) Laboratory setup . 63  Fig. 3.9: Graphical user interface of a typical spectrum using Genie 2000 software .. 65  Fig. 3.10: Stages in the separation of LREEs .............................................................. 72 Fig. 3.11: Schematics for the separation of LREEs ..................................................... 74 xiv University of Ghana http://ugspace.ug.edu.gh Fig. 4.1: Activity concentration of 238U in the beach sands of the Central region of Ghana ............................................................................................. 79 Fig.4.2: Activity concentration of 232Th in the beach sands of the Central region of Ghana ........................................................................................................ 80 Fig.4.3: Activity concentration of 238U in the beach sands of the Western region of Ghana ............................................................................................. 81 Fig.4.4: Activity concentration of 232Th in the beach sands of the Western region of Ghana ............................................................................................................. 82 Fig.4.5: Activity concentration of 238U and 232Th in the beach sands of the Central and Western regions of Ghana………………………………………...…....83 Fig.4.6: Activity concentration of 238U, 232Th and 40K in the beach sands of the Central and Western regions of Ghana……………………………………..84 Fig. 4.7: Photomicrograph of selected minerals in beach sand of Central and Western regions of Ghana: (Left image) cross polarized light and (Right image) plane-polarized light (a) Staurolite (b) Zircon (c) Rutile (d) Tourmaline (e) Hornblende (f) Kyanite .................................................. 97  Fig. 4.8: Distribution of LREEs (La - Eu) in the coarse, medium and fine fraction of beach sands in the Central Region of Ghana. .......................................... 104  Fig. 4.9: Distribution of HREEs (Gd –Lu) in the coarse, medium and fine fraction of beach sands in the Central Region of Ghana. .......................................... 105  Fig. 4.10: Distribution of total REEs (La – Lu) in the coarse, medium and fine fraction of beach sands in the Central Region of Ghana. ............................ 106  Fig. 4.11: Distribution of LREEs (La - Eu) in the coarse, medium and fine fraction of beach sands in the Western Region of Ghana. ........................................ 113  Fig. 4.12: Distribution of HREEs (Gd - Lu) in the coarse, medium and fine fraction of beach sands in the Western Region of Ghana. ........................................ 114  Fig. 4.13: Distribution of total REEs (La – Lu) in the coarse, medium and fine fraction of beach sands in the Western Region of Ghana. ........................... 115  Fig. 4.14: Distribution of LREEs (La – Eu) in the coarse, medium and fine fraction of beach sands in the Central and Western Regions of Ghana. .... 116  Fig. 4.15: Distribution of HREEs (Gd – Lu) in the coarse, medium and fine fraction of beach sands in the Central and Western Regions of Ghana. .... 117  Fig. 4.16: Distribution of total REEs (La – Lu) in the coarse, medium and fine fraction of beach sands in the Central and Western regions of Ghana. .... 118  xv University of Ghana http://ugspace.ug.edu.gh Fig. 4.17: LREE-HREE U, Th ternary diagram for the Central region of Ghana ..... 120  Fig. 4.18: LREE-HREE U, Th ternary diagram for the Western region of Ghana. .. 122  Fig. 4.19(a): Hierarchical Clustering Studies of REEs and Y in coarse fraction beach sands of the Central region of Ghana. ....................................... 125  Fig. 4.19(b):Hierarchical Clustering Studies of REEs and Y in medium fraction beach sands in the Central region of Ghana. ......................................... 126  Fig. 4.19(c): Hierarchical Clustering Studies of REEs and Y in fine fraction beach sands of the Central region of Ghana. ........................................ 127  Fig. 4.20(a):Hierarchical Clustering Studies of REEs and Y in coarse fraction beach sands of the Western region of Ghana. ....................................... 129  Fig. 4.20(b):Hierarchical Clustering Studies of REEs and Y in medium fraction beach sands of the Western region of Ghana. ....................................... 130  Fig. 4.20(c): Hierarchical Clustering Studies of REEs and Y in fine fraction beach sands of the Western region of Ghana. ................................................. 131  Fig. 4.21(a): Geospatial representation of the geology in the Central region ........... 134  Fig. 4.21(b): Geospatial representation of the geology in the Central region. .......... 137  Fig. 4.22(a): Geospatial representation of the geology in the Western region of Ghana. ................................................................................................... 138  Fig. 4.22(b): Geospatial representation of the geology in the Western region of Ghana. ................................................................................................... 139  Fig. 4.23: Interconnecting spline linkage of REE geospatial distribution pattern; (a) Western and (b) Central regions of Ghana………………………… 140  xvi University of Ghana http://ugspace.ug.edu.gh LIST OF TABLES Table 2.1: Composition of rare earth elements in the Earths continental crust .......... 11  Table 2.2: Location of selected carbonatite deposits in Africa ................................... 15  Table 2.3: Electronic configuration of rare earth elements and their corresponding ionic radius ................................................................................................. 24  Table 2.4: Selected physical properties of rare earth .................................................. 27  Table 2.5: Percentage composition of monazite in selected beach sands ................... 29 Table 3.1: Selected sampling locations along the coast of the Central region of Ghana. ....................................................................................................... 48  Table 3.2: Selected sampling locations along the coast of the Western region of Ghana. ....................................................................................................... 49  Table 3.3: Geology of selected sampling locations along the coast of the Western region of Ghana......................................................................................... 50  Table 3.4: Geology of selected sampling locations along the coast of the Central region of Ghana......................................................................................... 51  Table 3.5: Arithmetic method of moment statistics .................................................... 59  Table 3.6: Geometric method of moments.................................................................. 59  Table 3.7: Logarithmic method of moments ............................................................... 60  Table 3.8: Original logarithmic graphical measures ................................................... 60  Table 3.9: Modified geometric graphical measures .................................................... 60 Table 4.1: Activity concentration of 238U, 232Th and 40K in beach sands along the coast of the Central region of Ghana .................................................. 76  Table 4.2: Activity concentration of 238U, 232Th and 40K in beach sands along the coast of the Western region of Ghana ........................................................ 77  Table 4.3: Radiological parameters in the Coastal sands of the Central and Western regions of Ghana ......................................................................... 90  Table 4.4: Sediment Name and Textural Group of Selected Coastal Sands along the Central Region of Ghana...................................................................... 93  Table 4.5: Sediment Name and Textural Group of Selected Coastal Sands along the Western Region of Ghana .................................................................... 94  xvii University of Ghana http://ugspace.ug.edu.gh Table 4.6: Rare earth elements concentration (ppm) in coarse fractions of the beach sands of the Central region. ............................................................. 99  Table 4.7: Rare earth elements concentration (ppm) in medium fractions of beach sands in the Central region ............................................................. 101  Table 4.8: Rare earth elements concentration (ppm) in fine fractions of beach sand in the Central region. ....................................................................... 102  Table 4.9: Rare earth elements concentration in coarse fractions of beach sand in the Western region ............................................................................... 108  Table 4.10: Rare earth elements concentration in medium fractions of beach sand in the Western region .................................................................... 111  Table 4.11: Rare earth elements concentration in fine fractions of beach sand in the Western region ....................................................................................... 112  Table 4.12: Elemental concentration (ppm) of thorium and uranium in relation to rare earth elements in beach sands of the Central region of Ghana. .. 120  Table 4.13: Elemental concentration (ppm) of thorium and uranium in relation to rare earth elements in beach sands of the Western region of Ghana . 122  Table 4.14: Summary statistics of the REEs in the Central region of Ghana. .......... 133  Table 4.15: Summary statistics of the REEs in the Western region of Ghana. ........ 136  Table 4.16: Data for Pr, Nd, Sm and Eu concentration (ppm) after chemical separation ............................................................................................... 142  xviii University of Ghana http://ugspace.ug.edu.gh LIST OF ACRONYMS AED Annual Effective Dose CN Coordination Number CS Coarse Sand CMPO Carbamoylmethyl-phosphine oxide CREE Critical Rare Earth Elements DW Dry Weight FS Fine Sand HPGe High Purity Germanium HREE Heavy Rare Earth Elements ICP-MS Inductively Coupled Plasma Mass Spectrometry LN Lanthanide LREE Light Rare Earth Elements MCA Multichannel Analyzer MREE Middle Rare Earth Elements MS Medium Sand NORMs Naturally Occurring Radioactive Materials PTS Petrographic Thin Section RECl Rare Earth Chloride REE Rare Earth Elements REE-TM Rare Earth Elements – Transition Metal TBP Tributylphosphate TENORM Technologically Enhanced Naturally Radioactive Materials TRU Trans-Uranium Resin VCS Very Coarse Sand VFS Very Fine Sand xix University of Ghana http://ugspace.ug.edu.gh CHAPTER ONE GENERAL INTRODUCTION 1.1 Background The demand for Rare Earth Elements (REEs) in critical areas of advanced technology such as renewable energy, electronic, nuclear, glass, petroleum, weapons, metals, magnets, chemical, and automobile industry has led to the increase in exploration and exploitation of known deposits of rare earth elements around the globe (ACC, 2014). It is widely known that the rare earth elements are a group of 15 elements Lanthanum (La) to Lutetium (Lu) that span across the atomic number 57 to 71. Scandium (21Sc) and Yttrium (39Y) share similar chemical properties with the rare earth elements, hence leading to their occurrence in similar geochemical environment. Promethium (61Pm) which is a naturally radioactive element is no longer existent in the earth crust but can be prepared artificially in a cyclotron (Hu et al., 2006; Liao et al., 2005). In the 21st Century, REEs are vital economic resource and considered as “Potential Energy of the Future”. Globally, REEs are playing a critical role in the economics of emerging technologies with industrial value of about US$5.000 billion, which represents 5% of the worlds GDP (CEID, 2015). The market value for REEs is expected to hit about US$20 billion by 2024 (GMI, 2018). The World’s top 5 consumers of REEs are China, Japan, USA, France, and Korea respectively (He et al., 2014). China holds the world’s largest REE reserves and it has been estimated to be about 48% of the world’s total reserves as shown in Fig. 1.1. This makes China the leading producer of REEs in the world as shown in Fig. 1.2 (USGS, 2017a). 1 University of Ghana http://ugspace.ug.edu.gh Fig. 1.1: Rare earth elements reserves in selected countries in the World Fig. 1.2: Rare earth elements production in selected countries in the World between 2016 - 2017 2 University of Ghana http://ugspace.ug.edu.gh Rare earth elements such as Yttrium and Lanthanum are used in YLiFePO4 battery cell for electric vehicles and semiconductor transistors, while Cerium is useful in silicon microprocessor and glass surface polishing. Praseodymium and Neodymium are used as high strength metals in aircraft engines, magnets in consumer electronics such as mobile phones, and microphones. Artificially produced Promethium is used in heart pacemakers and fluorescent bulbs. Samarium, Europium, Terbium, and Yttrium are applied in energy efficient bulbs. Dysprosium, Neodymium, Praseodymium, Samarium and Terbium have found applications in wind turbines. Elements such as Gadolinium, Dysprosium, Holmium and Erbium have also been used as neutron absorbers in nuclear reactor. Ytterbium is used in stainless steel alloying while Lutetium is used as phosphors in Light Emitting Diodes (LED) and catalyst in petroleum refining (Esro et al., 2015; ACC, 2014; Krebs, 2006; Pisecny et al., 2004; Haoqing & Lijun, 2003). Although REEs co-exist with over 200 minerals, they occur appreciably in ores such as monazite (Th(Ln)PO4.H2O), xenotime (Y, Dy, Yb, Er, Gd, PO4), bastnaesite ((La, Y, Ce)CO3F), and churchite YPO4.2(H2O) (Xie et al., 2014; Jordens et al., 2013; Kanazawa & Kamitani, 2006). The REEs, based on similarity in their occurrence, physical and chemical properties, are broadly grouped into two groups which are Light Rare Earth (La, Ce, Pr, Nd, Pm, Sm, Eu) and Heavy Rare Earth (Gd, Tb, Dy, Ho, Er, Tm, Lu). Three-group classification has been observed based on the industrial processing of rare earth as Light-REEs (La, Ce, Pr, Nd); Medium-REEs (Sm, Eu, Gd,); and Heavy-REEs (Tb, Dy, Ho, Er, Tm, Yb, Lu) (Hu et al., 2006; Liang et al., 2013). The REEs have been exploited in countries such as China, Namibia, United States, Australia and in beach placers along the Indian coasts (Varnavas, 1990; Rajendran et al., 2008; Krishnamurthy & Gupta, 2004). 3 University of Ghana http://ugspace.ug.edu.gh Selected beach sand along some coastal areas around the world are known to contain REE associated minerals which occur as placer deposits, due to the transport of mineral bearing fragments from source rocks under wave action (Krishnamurthy & Gupta, 2004). Although some of these REEs occur in addition to some radioactive elements like Thorium and Uranium-bearing ore (USGS, 2010), others are associated withnon-radioactive elements in their ore. Such non-radioactive associations are found in ores such as allanite, bastnaesite, and ion adsorbed clay minerals. REE studies have been conducted on different rocks in Ghana and some have proven to be potential sources of REEs (Hayford et al., 2013; Dampare et al., 2005; Schnetzler et al., 1967). Some analytical methods used in the investigations of REEs include X-ray Fluorescence Spectrometry (XRF), Instrumental Neutron Activation Analysis (INAA), Inductively Coupled Plasma - Mass Spectrometry (ICP-MS), Inductively Coupled Plasma - Atomic Emission Spectrometry (ICP-AES), Atomic Absorption Spectrometry (AAS), and Spectrophotometric method (Liang et al., 2013). The increased demand for REEs in renewable energy technology industries requires not just the identification of REEs in their natural geological matrix but also developing methods for identifying probable large deposit wherein they occur in association with radioactive elements via their fingerprints in coastal sands. This study will focus on the identification of potential REE sources in selected beach sands in the Central and Western regions of Ghana. Since the future of green energy technology rests on the application of rare earth metals, identification of REE distribution and investigating the associated 4 University of Ghana http://ugspace.ug.edu.gh radioactivity will aid in the recognition of potential deposits of REEs and their pattern of distribution in the beach sands. 1.2 Problem Statement The Paris agreement on climate change, of which Ghana is party to, was adopted on 12th December 2015 and signed by over 195 countries at the United Nations Headquarters on 22nd April 2016 in New York. The agreement is poised at sourcing funding and technology to mitigate climate change among supporting member nations; most especially in supporting the development of renewable energy sources towards mitigating climate change in Africa (Hart, 2013; Richard& Benedict, 2009). Ghana is challenged with insufficient energy and high cost associated with power generation. The “Africa 2030: Roadmap for a Renewable Energy Future” report targets the need for the deployment of renewable energy technology towards facilitating industrial growth and a cleaner environment (IRENA, 2015). Rare earth elements magnets are key industrial component in offshore and onshore wind turbines. Existing report by the World Wind Association (WWA) at the end of 2017 showed that wind turbines accounts for about 539,291 Megawatt overall capacity of World’s wind power, with China leading by 188 Gigawatt capacities, and Denmark sourced 43% of its power from wind turbine in the year 2017. Ghana is well known for the exploration, mining, and export of minerals such as gold, diamond, bauxite, and manganese. Gold export accounts for over 90% of the country’s total mineral revenue, with 46% increase export in 2016 compared to 2015 (GCM, 2017). Little or no emphasis is placed on the exploration of the rare earth elements minerals which are important to the green energy future of Ghana. Beach sands are known host of eroded rock materials from inland sources and continental 5 University of Ghana http://ugspace.ug.edu.gh shelf. There is a tendency for beach sands to hold information about probable deposit of rare earth elements. Presence of Naturally Occurring Radioactive Materials (NORMs) in beach sands is indicative of radioactive minerals; these minerals (Monazite and zircon) are pointers to REEs (IAEA, 1989). It is therefore imperative to conduct an investigation on the presence of rare earth elements (REEs) fingerprints and extractability of selected REEs in the beach sands of the Western and Central regions along the coastline of Southern Ghana for future technological applications. 1.3 Objectives The overall objective of this study is to develop an analytical procedure for mapping out rare earth element composition of beach sands via the naturally occurring radioactivity along the coast of Central and Western regions of Ghana. The specific objectives of the study are to: (a) assess the concentrations of naturally occurring radioactive nuclides (238U, 232Th and 40K) in beach sands using γ- ray Spectrometry; and ascertain the presence of REE-associated minerals through Gravity Separation using bromoform and Petrographic Thin Section (after particle size distribution); (b) investigate the lvels of REEs in coarse, medium and fine fractions of beach sands using Lithium metaborate fusion and ICP-MS; hence evaluate the % Y and REE : HREE as a measure of REE abundance; (c) develop a chemical method for the separation of selected (renewable energy Industry) REEs (Pr, Nd, Sm, Eu) using extraction chromatographic technique; and 6 University of Ghana http://ugspace.ug.edu.gh (d) establish the Geospatial distribution pattern of the REE- clusters in the coastal sands to aid exploration of REE minerals. 1.4 Justification for the Study Layton (1958) described the economic geology of some radioactive minerals (monazite, xenotime, and zircon) and reported that relatively high radioactivity concentrations were observed in graphic granites and quartz veins observed during the construction of the Accra-Winneba road, as well as black sands in the Mankwadze, Abrekum and Apam, which are towns proximal to the coastal area of the Central region of Ghana. In recent times, different authors have studied the naturally occurring radioactivity (238U, 232Th and 40K) of sediments in selected areas of the coastal environment of Ghana, and admitted to the rhetoric of safe radiation level in the coastal area (Amekudzie et al., 2011; Botwe et al., 2017; Lawluvi, 2016). While the study of Layton (1958) suggests the probable presence of monazite in some selected areas proximal to the coastal environment, this study will take a critical look at the distribution of naturally occurring radioactive elements in the coastal sands from a perspective of their probable association with rare earth elements (REEs). Assessment of the REEs as they distribute within the coarse, medium and fine fractions of the beach sands will provide information about the prominence of either the light rare earth elements (LREE) or the heavy rare earth elements (HREEs). The rare earth distribution in the beach sands will eventually serve as a pointer to the geology of the environment and probable effect of long-range transport of the beach sands. 7 University of Ghana http://ugspace.ug.edu.gh 1.5 Extent of the Study The study focuses on the collection of beach sand from twenty-five locations based on the geology of the Central and Western regions of Ghana. Acquisition of gamma spectrometry data of the beach sands will ascertain the levels of naturally occurring radioactivity of the beach sands along the Central and Western regions of Ghana. The collected sands will be sorted into different particle sizes and separated into three major fractions as coarse, medium and fine fractions. The three sand fractions from each location will be investigated for rare earth element contents and their trend in their distribution along the sampling location. Extraction chromatographic resins will be used in the separation of selected REEs. Petrographic details of the beach sands will provide information about the composition of minerals in the beach sands. 1.6 Arrangement of Chapters This dissertation is divided into five chapters. Chapter one focuses on a brief introduction of the rare earth elements (REEs), background to the study and objectives of the studies of rare earth elements in beach sands. Chapter two discusses the literature available on the occurrence and coastal depositional environment of REEs and the associated radioactivity. Classification, industrial processing and separation methods of REEs are highlighted, while the instrumental methods for the determination of the REEs are not exempted. Chapter three focuses on the materials and methods involved in the experimental process of the grain size distribution of coastal sands, Gamma spectrometry of the coastal sands, analysis of the rare earth elements in the beach sands and the chemical separation of selected rare earth elements. Chapter four focuses on the discussion of results obtained from the experiments conducted in Chapter three while chapter five deals with conclusions of the study and recommendations for further studies. 8 University of Ghana http://ugspace.ug.edu.gh CHAPTER TWO LITERATURE REVIEW 2.1 Occurrence and Abundance of Rare Earth Elements Rare earth elements traditionally occupy the f-block of the periodic table, having atomic number (Z) in the range 58-71(La - Lu), while the non-lanthanide rare earths are Yttrium and Scandium with Z= 39 and Z=21respectively. The lithophilic nature of rare earth implies that they are enriched in the earth crust (Hedrick et al., 2006). The varying concentration of the rare earth in the earth has been observed to follow a particular pattern whereby we have the light rare earth in higher concentration than the heavier rare earth. According to the Goldschmidt geochemical classification of elements within the earth crust, the elements are broadly divided into chalcophile, siderophile, lithophile and atmophile. Fig. 2.1 shows the Periodic Table representation of the Goldschmidt classification. Fig. 2.1: Classification of elements in the Earth Crust (White, 2013) 9 University of Ghana http://ugspace.ug.edu.gh The lithophile elements (31-elements and REEs) are known to be closely associated with the earth surface, they bond with oxygen in silicates (tetrahedral sites, or octahedral sites, or decahedral sites) and oxides (Albarede, 2011). It is observed that the lithophile elements have closely filled outer electronic shells thereby forming ionic bonds. The trivalent (Ln3+) nature of the rare earth is responsible for their availability in similar geochemical environments. Thus, it has been scientifically proven that in the list of the REEs, Ce and Eu occur mostly in nature as tetravalent (Ce4+) and divalent elements (Eu2+) due to varying oxidation states. Marc (2010) alludes that there is moderate abundance of rare earth in the earth crust, and they are even more abundant than copper, lead, gold and platinum. About 150- 220 mg/kg of REE are known to be found in the earth crust (Long et al., 2012). Table 2.1 shows a composition of estimated rare earth elements concentration in the lower, middle and upper continental crust. The commonly observed opinion about the REEs in the crust is that they share similar properties with those formed in CI Chondrite; this is reflected by similarity in the concentrations of Sm/Nd,143Nd/144Nd, 142Nd/144Nd (Huang et al., 2013a; Caro et al, 2008). However, recent trends suggest high concentration on Sm/Nd in the bulk silicate earth than the chondrite (Huang et al., 2013). The concentration of Ce in the upper (63 ppm), middle (53 ppm) and lower crust (20 ppm) exceeds the concentration for the other REEs (Holland & Turekian, 2004). In other words, Ce is considered not only very reactive, but the most abundant of the REEs and the 25th most abundant element in the earth crust (Gschneidner et al., 2006; USGS, 2017b). Owing to the similarity in geochemical association, lanthanum through to europium are generally referred to as cerium-group (LREE), while gadolinium to lutetium are considered as yttrium-group (HREE) (Mortimer, 1979). 10 University of Ghana http://ugspace.ug.edu.gh Table 2.1: Composition of rare earth elements in the Earths continental crust Element Crust Upper Middle Lower Bulk Sc 14 19 31 21.9 Y 21 20 16 19 La 31 24 8 20 Ce 63 53 20 43 Pr 7.1 5.8 2.4 4.9 Nd 27 25 11 20 Sm 4.7 4.6 2.8 3.9 Eu 1 1.4 1.1 1.1 Gd 4 4.0 3.1 3.7 Tb 0.7 0.7 0.48 0.6 Dy 3.9 3.8 3.1 3.6 Ho 0.83 0.82 0.68 0.77 Er 2.3 2.3 1.9 2.1 Tm 0.3 0.32 0.24 0.28 Yb 2.0 2.2 1.5 1.9 Lu 0.31 0.4 0.25 0.3 Th 10.5 6.5 1.2 5.6 U 2.7 1.3 0.2 1.3 Source:(Holland & Turekian, 2004) 2.2 Ores of Rare Earth Elements Rare earth elements are broadly grouped into the cerium group and yttrium group. The cerium group comprises lanthanum to europium while the yttrium group is mainly made up of gadolinium to lutetium (Mortimer, 1979b). This same classification explains the basis for the division of the rare earth elements into light rare earth (LREE) and heavy rare earth (HREE). 11 University of Ghana http://ugspace.ug.edu.gh In a bid to further explain the REE broad classification in relation to their ore, it is important to look at the description of Guilbert et al. (2007) where the authors have discussed source, character, migration and deposit of ore bearing fluids in relation to their magmatic, metamorphic or sedimentary origin. The largest deposits of rare earth ores in the world are associated with alkaline carbonate intrusive series (Kanazawa & Kamitani, 2006). During the formation of magma (a mobile rock originating from the earth), metallic elements have a tendency of association with the resulting magma which could be intrusive or extrusive (Fabian, 2013). Rare earth elements (REEs) are considered as lithophile elements which are incompatible with the mantle (Sarbas & Töpper, 2013). The REEs are rather expunged during magmatic processes which occur during the partial melting of the mantle, thereby leading to their concentration in silicate phases in the crust (Wyllie, 1988). The rare earth element contents in the primitive mantle, continental crust and upper crust have been estimated and reported (Workman & Hart, 2005; McDonough, 1995; Hart & Zindler, 1986) . Lanthanum has been described as the most incompatible of the rare earth elements, leading to its increased abundance in ores (monazite-La and bastnaesite-La) (McKenzie & O'Nions, 1991). Data obtained from Taylor & McLennan (1985) for the upper continental crust shows a range of 0.32- 64 ppm with the highest concentration in cerium elements. Rare earth associated elements such as uranium and thorium are also enriched in the upper continental crust. Holland & Turekian (2004) and Rudnick & Gao (2003) discussed the enrichment of both uranium (2.7 ppm) and thorium (10.5 ppm) in the upper crust 12 University of Ghana http://ugspace.ug.edu.gh and a gradual decline in their concentrations from the upper crust to the middle (U - 1.3 ppm; Th - 6.5 ppm) and lower crust (U-0.2 ppm; Th -1.2 ppm) (Hacker et al., 2015; Trindade et al., 2013) [Table 2.1]. Rare earth deposits generally are known to be of igneous, hydrothermal and sedimentary origin (Oliveira & Inverno, 2014). Dill (2010) reported a magmatic, structural and sedimentary rare earth deposits classification based on host rock and mineralogical content (Fan et al., 2016). A Recent review by Oliveira & Inverno, (2014) shows a documentation of the works of Weng & Co-workers (2013) in the recent classification of REE deposits which focuses on geological processes associated with the concentration of REEs and mineral formation. 2.2.1 Carbonatite Associated Rare Earth Deposits Rare earth elements found in carbonatites accounts for about 80% of the world's supply of light rare earth elements (LREE) (Hayford et al., 2013; Hofstra et al., 2016; Wang et al., 2017). Available data obtained from airborne geophysical studies have shown that Africa hosts about 35% of the worlds’ carbonatite deposits and about 35 % is found in Asia (Bell, 2009). Carbonatite is known to be associated with magmatic segregation of igneous origin (Jones et al., 2013). This implies that the igneous rock is rich in carbonates and related to alkali forming process, mantle degassing and magma evolution (Guilbert et al., 2007). Carbonatite can be described as a type of intrusive or extrusive rock of igneous origin with varying degree of the Ca-Fe-Mg carbonate melt. Commonly associated minerals found in carbonatites include dolomite, calcite or siderites; others include pyrochlore, monazite, apatite, zircon and perovskite (Sinding-Larsen & Wellmer, 2010). While 13 University of Ghana http://ugspace.ug.edu.gh some carbonatites are rich in REEs, others show increased affinity for the high magnetite-apatite content or high fluorine or barium content (Guilbert & Park, 1986). Geochemical classifications of the carbonatite are mainly (i) Alkali (ii) Ferric iron (iii) Zirconium rich (iv) alkali poor (v) Fe-O-CaO-MgO rich and Zirconium-Poor Carbonatite (Guilbert & Park, 1986). Hayford et al. (2013) in a study conducted on the igneous carbonatite complexes in Kpong area of Ghana, described it as a potential source of REEs having reported a concentration range of 540 – 705 mg/kg for the total REE observed. Table 2.2 shows selected locations in Africa where carbonatite complexes which host REEs are found. Although Africa owns large deposit of carbonatite, deposits found in Bayan Obo (Baotou) China and Mt. Pass (California) in the USA account for some of the largest in the world (Ali, 2014). Studies conducted on the carbonatites of Zambia have shown carbonatites which are not in commercial quantity, but the bastnäsite-(Ce) carbonatite complex of the Nkombwa Hill shows potential for commercial exploitation (Mike, 2010; Sliwa, 1991). The carbonatite in the Songwe hill in Malawi is reported to be enriched in heavy rare earth elements due to the hydrothermal fluid apatite formation which accompanies the carbonatite complex (synchysite-Ce) (Broom-Fendley et al., 2017). 14 University of Ghana http://ugspace.ug.edu.gh Table 2.2: Location of selected carbonatite deposits in Africa Country Location(s) Deposit type Angola Monte Verde, Bonga, Carbonatite Virulundo, Bilundo, Tchivira. Congo Zaire Bingo (Bingu) Carbonatite with residual enrichment Ghana Kpong Alkalic Igneous Kenya Buru, Mrima Hill Carbonatite with residual enrichment Malawi Kangankunde, Kapiri Carbonatite with residual enrichment Nsengwa, Tundulu, Songwe Mali Adiounedj, Anezrouf Carbonatite Morocco Tamazert (OuedTamazert, Carbonatite Tamazeght, BouAgrao) Namibia Lofdal-Bergville, Eureka, Carbonatite Okorusu Complex, Ondurukurme Complex Somalia Dalkainle Carbonatite South Africa Glenover, Goudini, Palabora Carbonatite (Phalaborwa), Sandkopsdrif (Zandkops Drift) Pilanesberg Complex Alkalic Igneous Tanzania Makonde Carbonatite with residual enrichment Wigu Hill, Mbeya (Panda Hill) Zambia Kaluwe, Nkomba Carbonatite with residual enrichment Source:(USGS, 2014b; Orris & Grauch, 2002) 15 University of Ghana http://ugspace.ug.edu.gh 2.2.2 Alkaline Complexes and Alkaline Pegmatite REE Deposits Alkaline intrusives are known for hosting rare earth and several intruding phases like that observed in the beryllium rare earth deposits found in Thor Lake which hosts minerals such as zircon, allanite-bastnaesite (Irving & Richardson, 1992). Characteristic minerals such as apatite, miserite, eudidymite and mosandrites have been found in the alkali igneous deposit of the Kipawa Lake of Ontario, Canada; in addition to zircon and uranium minerals, the host rocks contain peralkaline quartz syenite amphiboles schists (Woolley, 1987). On the basis of the Henriech structural classification, it is known that not all carbonatites are associated with other mafic igneous rock (Traversa et al., 2001; Mitchell, 2005). Carbonatite types are as follows (i) Alkali Ring Complexes (ii) Alkali Non-ring Complexes (iii) Non-Alkalic Rock Association (iv) Pyroclastic Flows (Kinnaird & Bowden, 1991). 2.2.3 Rhyolite Associated REE Deposits Rhyolites are classified as felsic extrusive igneous rocks, which have high silica content which forms lava domes. They are often extruded from the base of the upper crust and are composed of major minerals such as quartz, plagioclase, sanidine and minor minerals such as hornblende and biotite (Barry et al., 1988). Anderson (2007) discussed the crustal partial melting and the extrusion of rhyolitic magma from granitic magma origin. The round top mountain in Texas, U.S.A is considered as a typical rhyolite which has proven to be a reliable host of heavy REEs (HREE) (Pingitore et al., 2014). Miller (2015) described the HREE (Nd-Dy-Y-Tb) deposit 16 University of Ghana http://ugspace.ug.edu.gh discovered in the Foxtrot area of Canada as being hosted by peralkaline volcanic rocks and a potential source of REEs. 2.2.4 Granitic Associated REE Deposits Granites and granitic pegmatites are typical examples of REE hosts (Linnen et al., 2012) describes granitic pegmatites as poised sources of critical metals such as Ta, Nb and REEs which are accumulated alongside high flux elements (Li, B, P, F) which takes place during magmatic processes (Jahns & Burnham, 1969). Families of rare earth associated pegmatites include: LCT (Li-Cs-Ta) pegmatites, NYF (Nb-Y-F) pegmatites and a mixture of LCT- NYF pegmatites: with the NYF-pegmatites having a high tendency for accumulation of REEs and other elements such as Th, U, Be, Sc, Ti and Zr (Cerny & Ercit, 2005; Simmons, 2007). Cerny & Ercit (2005) described NYF-pegmatites as derivatives of A-type granites and I-type granites which hold information about the REEs components in association with Th and U. Ghost lake batholiths found in Northwestern Ontario, Canada are a typical case of granite rare earth elemental pegmatite system. Although quartz and feldspars crystallize from granitic melts, REEs are known to be incompatible with these minerals. Linnen et al. (2012) argue that extreme fractionation originating from the extended crystallization of quartz and feldspar is responsible for increased concentration of REEs in residual melts. Mckeough et al. (2013) explained rare earth enrichment in pegmatites as a result of pegmatite fractionation cum REE partitioning from pegmatite phase to the volatile phase in relation to their host rocks. 17 University of Ghana http://ugspace.ug.edu.gh 2.2.5 Hydrothermal Related REE Deposits Rare earth elements associated with granites of hydrothermal origin mostly occur as veins emanating from heated magmatic water process under high temperature and pressure, resulting in the crystallization of rare earth associated minerals via pre- existing fissures within the host rock (Wenk & Bulakh, 2003). Edwards & Atkinson (1986) described mineral deposits from hydrothermal sources to have emanated from the hot aqueous fluid of unspecified origin. Conditions required for the mineral deposition from hydrothermal sources have been described to include the following; (i) Hot water (brine) for transportation of dissolved minerals, (ii) Available interconnected fissures for fluid passage (iii) Depositional sites availability and (iv) Favorable chemical reaction for deposition (Farooq, 2017). Classification of vein-type hydrothermal deposits based on the various depths occurring at a temperature range of 50 – 500 oC is as follows: hypothermal (i.e. great depths and high temperature), mesothermal (intermediate depth and moderate temperatures), and epithermal (shallow depths and low temperatures). Rare earth minerals (Fe-oxide REE) elements associated with hydrothermal origin have been reported in the South of Australia (USGS, 2014a). Typical minerals associated with some hydrothermal deposits include monazite, bastnaesite, fluocerite, haematite, fluorite and uranite (Deb & Sarkar, 2017). Einaudi & Oreskes (1983) described the Olympic dam granite hosts of REEs as a pink to yellowish-green coarse to medium grained equi-granular biotite granite. Uranium- 18 University of Ghana http://ugspace.ug.edu.gh REEs have been associated with metamorphic-hydrothermal deposits (Oliver et al., 2010). 2.2.6 Skarn Deposit of REEs Skarns basically are composed of the following types (i) Calcic Skarn and (ii) Magnesium Skarn (Ahankoub et al., 2015). The calcic skarn comprise mainly grossular-andradite series, diopside-hedenbergite series, wollastonite, vesuvianite, and scapolite in limestone or marble rocks. The magnesian skarn contains forsterite, serpentine (altered forsterite), diopside, phlogopite, spinel, tremolite and humit in dolomite limestones. Manganonan skarn contains Mn (Ca, Mg, Fe, Al), silicate minerals such as diopside, manganonan, hedenbergite, johansennite, tephrolite in relation to Pb-Zn (Ag) mineralization. Alkaline skarns are subdivided into (i) Hydrothermal Metasomatic Alkaline Skarn (Carbonatite-related), (ii) Alkaline Skarn (alkaline granitoid-related) and (iii) Alkaline Skarn (syenite related) (Obolenskiy et al., 2007; Yiming et al., 2005). The alkaline skarns formed in relation to dolomitic carbonatites are formed via the hydrothermal process. REE Nb-alkaline skarn related to alkali granitoid and carbonatites are found in the eastern Bayan Obo (Fe-Nb-REE) ore deposits; they are formed as a result of volcanic exhalative process (Fan et al., 2016). 19 University of Ghana http://ugspace.ug.edu.gh 2.2.7 Heavy Mineral Sands REE Deposits Deposits of REEs have been found in secondary places such as in beach sands where they occur in association with other minerals. Commercial quantities of heavy minerals extending over a wide range of area are obtainable on different beaches around the world, thus making beach sands a potential source of industrial metals. Rare earth elements associated minerals such as monazite, xenotime, apatite and other accessory minerals (zircon, ilmenite, rutile and leucoxene) are known to occur in beach sands (Cherniak, 2010). The sedimentary processes that lead to the formation of the heavy minerals in the coastal sands are due to the erosion of REE associated minerals from beach rocks (metamorphic, igneous and sedimentary) which are often located onshore. Rock materials weathered from inland sources are carried along by streams and rivers, thereby contributing to the sands and heavy minerals on beaches (Jones, 2009). While attributing the concentration of heavy minerals on the beach sands along the coast to inland contributory sources, sediments from the sea floor are also being eroded and deposited on the shore as a result of the tidal wave (CISCAG, 2011). Sorting of heavy minerals in the beach sands occur due to the reworking of the sands by waves, wind, longshore drifts and wind action, thereby leading to the formation of mineral layers based on particle size alignment in the beach sands (Gosen et al., 2014). Monazite sand of about 60 % and 4.68 Mt rare earth oxides have also been reported in the beach sands of New South Wales, Queensland, Australia (Williams, 2008). Although the associated radioactivity due to thorium poses a challenge to the production of REEs from monazite sands, the radioactive sands are major sources of light REEs. 20 University of Ghana http://ugspace.ug.edu.gh 2.2.8 Rare Earth Elements Ores in Placer Deposits The etymology of the term “placer deposit” originates from the Spanish word placea, which explains the alluvial or glacial deposits of sand or gravel, while the term “alluvial” is derived from the Latin word alluvius which suggests sediments eroded over a long drift via agents of weathering and deposited in marine or non- marine environment (McColl, 2005). A well structured and lithified form of the alluvium is regarded as alluvial deposit. The deposition of heavy minerals can occur in lake sediments which are regarded as lacustrine, river sediments (fluvial), glacial environments (glacial till) and beach sands (placers) (Suresh & Raja, 2014). Granitic rocks are known to have a high content of REEs and could serve as a primary source which is subjected to weathering and the transported fragments serve as the basis for the existence of tertiary and quaternary placers in the marine environment. Monazite and xenotime minerals have been found as placers in beach sands of India, Brazil, U.S.A, Malaysia, Australia and Thailand (Sengupta, 2016). 2.3 Classification of Rare Earth Minerals The rare earth minerals can be classified as carbonates, halides, borates, phosphates, sulphates, arsenates and silicates. The classification of REEs into cerium-group (La- Eu) and yttrium-group (Gd-Lu) is important while considering the association of REEs in minerals. Clark (1983) highlighted the arguments surrounding the role of the coordination number of REEs and how it influences their occurrence in minerals. 21 University of Ghana http://ugspace.ug.edu.gh The Ce-group selective minerals have coordination number (CN) 10-12, minerals with CN 7-9 can inter-switch between the Ce or Y-group, whereas minerals with CN 6 have a selective preference for Y-group REES. Most times, minerals in coastal environment are a product of the disintegrated rocks which host major minerals such as amphiboles, mica, schist and those that host minor minerals such as zircon, allanites, apatite, tourmaline (Mange & Maurer, 1992). Visual inspection of some beach sands shows dark-like color characteristics which suggest the accumulation of heavy minerals. Heavy minerals common to beach sands include garnet, ilmenite, monazite, rutile, sillimanite, zircon, leucoxene, magnetite, haematite, hornblende, augite and tourmaline (Gupta & Desa, 2001; Mange & Maurer, 1992). The phosphate mineral, monazite is prominent among the heavy minerals in beach sands for the accumulation of REEs within its monoclinic crystal structure. The common structural derivative includes Ce-monazite, Nd-monazite, La-monazite; this is dependent on the dominant REE within the monazite crystal (Lima-de-Faria, 2001). 2.4 Rare Earths and Associated Radioactivity Ramasamy and Co-workers (2014) in a study conducted on the level of radioactivity in the beach sands of Kerala in India, reported the radiation level as unsafe. The radiation levels from the beach sands were due to naturally occurring radioactive elements (uranium, thorium and potassium) which are formed in the heavy minerals. Thus we have minerals whose structural configuration supports their coordination with radioactive elements in addition to REEs. Typical rare earth elements found in radioactive minerals include; monazite [(Ce, La, Nd, Th)PO4]; allanite [(Ca, Ce ,Y, 22 University of Ghana http://ugspace.ug.edu.gh La)2 (Al,Fe)3(SiO4)3(OH)]; euxenite [(Y,Ca,Er,La,Ce,U,Th)(Nb,Ta,Ti)2O6]; micro-lite [(Ca,Na)2Ta2O6(O,OH,F)]; pyrochlore [(Ca,Na)2Nb2O6(O,OH,F)]; Samarskite-(Y) [(Y,Ce,U,Fe)3(Nb,Ta,Ti)5O16]; and xenotime [(YPO4)]. Fig. 2.2 shows selected radioactive minerals with a probability of hosting rare earth elements. Frondel & Fleischer (1958) documented a host of minerals which are radioactive in the document “systematic mineralogy of uranium and thorium.” Fig. 2.2 Selected radioactive and rare earth associated minerals 2.5 Properties of Rare Earth Elements 2.5.1 Chemical Properties of Rare Earth Elements Rare earth elements are known to have similar chemical properties. The coherence in chemical properties of REEs influences their occurrence and formation in the similar geological environment. The electronic configuration of REEs in their trivalent state is considered the most stable state as shown in Table 2.3. Ionic radii of the trivalent REEs decrease with increase in atomic number from La (III) to Lu (III). 23 University of Ghana http://ugspace.ug.edu.gh The ground state configuration of REEs conforms to the expression [Xe]4fn6s2, with the exception of La, Ce and Gd which occurs as [Xe]4fn-15d16s2; where n=1-14 for the f-subshell (Huang & Bian, 2010). Lutetium has a completely filled f-orbital which suggests its stable ground configuration to be [Xe]4f145d16s2. The occurrence of Table 2.3: Electronic configuration of rare earth elements and their corresponding ionic radius (Huang & Bian, 2010) Element Z A Configuration (Ln3+) (r) Lanthanum(La) 57 138.9 [Xe]4f0 1.061 Cerium (Ce) 58 140.1 [Xe]4f1 1.034 Praseodymium (Pr) 59 140.9 [Xe]4f2 1.013 Neodymium (Nd) 60 144.2 [Xe]4f3 0.995 Promethium (Pm) 61 - [Xe]4f4 0.979 Samarium (Sm) 62 150.4 [Xe]4f5 0.964 Europium (Eu) 63 152.0 [Xe]4f6 0.950 Gadolinium (Gd) 64 157.3 [Xe]4f7 0.938 Terbium (Tb) 65 158.9 [Xe]4f8 0.923 Dysprosium (Dy) 66 162.5 [Xe]4f9 0.908 Holmium (Ho) 67 164.9 [Xe]4f10 0.894 Erbium (Er) 68 167.3 [Xe]4f11 0.881 Thulium (Tm) 69 168.9 [Xe]4f12 0.869 Ytterbium (Yb) 70 173.0 [Xe]4f13 0.858 Lutetium (Lu) 71 175.0 [Xe]4f14 0.848 Yttrium (Y) 39 88.9 [Kr] 0.88 Z = Atomic Number; A= Mass Number; [Xe]=1s2 2s2 2p6 3s2 3p6 3d104s24p6 4d10 5s2 5p6; [Kr]= 1s2 2s2 2p6 3s2 3p6 3d104s24p6 r =ionic radius 24 University of Ghana http://ugspace.ug.edu.gh Yttrium ([Kr]4d15s2) with REE ores and similarity in chemical and physical properties is responsible for its grouping with the REEs (Jack et al., 2016). The configuration of the rare earth elements shows clearly that the 4f-orbital which is located within the 6s-orbital is shielded as it accepts electrons while the outer 6s-orbital is constantly filled throughout the lanthanide series. The lanthanide contractions observed in the defective electronic screening between the 4f-orbitals and the nuclear charge of the trivalent (Ln3+) REEs is responsible for the decrease in ionic radii as the atomic number increases in-line with the effective attraction between the nucleus and the outer electron (Huang & Bian, 2010). While REEs exist mainly in their tetravalent states, selected REEs such as Sm, Eu and Yb also form a stable divalent oxidation state, while Ce, Pr and Tb have the tendency to exist in a stable tetravalent state. REEs in their trivalent (Ln3+) states form ionic salts and form complexes ([Ln(H2O)9]3+) in aqueous solution. Compounds formed from the lanthanide trivalent state include LaF3, LaCl3, LaBr3, La2O3, La2O2S,La2S3, while compounds such as SmI2, YbI2 and EuI2 are typical examples of divalent REE salts (Dorenbos, 2000). The typical stable tetravalent complex is formed by Ce in a nitrate complex (NH4)2 [Ce(NO3)6]; other known solids include CeO2, CeF4, PrO2, TbO2 and TbF4 (Alexander, 1975). LREEs form oxides in their trivalent states due to oxidation. However, the LREE due to oxidation are air sensitive, hence they are mostly stored under inert condition. They form three basic crystal structures (A, B and C) under ambient condition due to the polymorphic nature of REE sesquioxides (Ln2O3). La to Nd forms hexagonal (A-type) structures; Sm to Gd monoclinic-(B-type); Tb to Lu cubic-(C-type) structures which 25 University of Ghana http://ugspace.ug.edu.gh can be altered at high temperatures. Sesquioxides of Eu exhibit both B and C-type structure (Gschneidner & Eyring, 1978; Spits︡︠yn et al., 1976). However, Samares (2013) reported A, B, C, X and H as five major crystal structure. The reaction of REE oxides with water vapor forms alkaline hydroxides (Ln(OH)3) which are sparingly soluble in water, with precipitation pH range of 6.82 to 7.62 (Lu to Ce) and have a progressively decreased basicity from Ce to Lu (Neikov et al., 2009). The reaction of REEs with hydrogen leads to the formation of hydrides (LnH2) and at high-pressure forms (LnH3). Trihydrides of Sm to Lu form air-sensitive hexagonal crystal structure. REEs reacts vigorously with acids leading to the production of hydrogen gas, except for the insoluble reaction with HF leading to REE-fluoride (Ln(F)3) formation. Other reactions of REEs with halides have shown that REEs of Cl, Br and I are less stable when compared to REE-fluorides. REEs react with elements such as Sulphur, hydrogen, carbon and nitrogen. Intermetallic compounds have been formed between REE-TM, REE-group IV and REE-group V, examples of such metals include (Ce-Gd)-Ni, Sm-Co and Nd-Fe-B alloys; Re-Ni-Co (Andrej & Janusz, 1994). 2.5.2 Physical Properties of Rare Earth Elements Rare earth elements typically exist as metals with known silvery-white and silvery- gray colour characteristics, with an exception in the yellow color characteristics of Pr and Nd. Table 2.4 shows selected properties such as density, lattice structure, magnetic susceptibility, resistivity and neutron absorption cross section. 26 University of Ghana http://ugspace.ug.edu.gh Table 2.4: Selected physical properties of rare earth (Zhang & Zhao, 2016) REEs Density Metal Magnetic Resistivity ρ Neutron (g/cm3) Lattice susceptibility χmol/10-6 absorption χmol10-6 (cm3/mol) (cm3/mol) σ(barn) (25oC) Sc 2.985 HCP +295.2(α) 66 24.0 Y 4.472 HCP +187.7(α) 53 1.31 La 6.166 DHCP +95.9 57 9.3 Ce 6.773 FCC +2500(β) 75 0.73 Pr 6.475 DHCP +5530(α) 68 11.6 Nd 7.003 DHCP +5930(α) 64 46 Pm 7.260 DHCP Sm 7.536 ** +1278(α) 92 5600 Eu 5.245 BCC +30900 81 4300 Gd 7.886 HCP +185000 134 46000 Tb 8.253 HCP +170000(α) 116 46 Dy 8.559 HCP +98000 91 950 Ho 8.78 HCP +72900 94 65 Er 9.054 HCP +48000 86 173 Tm 9.318 HCP +24700 90 127 Yb 6.972 FCC +67(α) 28 37 Lu 9.84 HCP +183 68 112 BCC: Body-Centred Cubic, DHCP: Double Hexagonal Closed-Packed, FCC: Face- Centred Cubic, HCP: Hexagonal Close-Packed, **: (Rhombohedral at ambient condition; DHCP at 300 oC / 40 Kbar; HCP at 731 oC, BCC at 922 oC) 27 University of Ghana http://ugspace.ug.edu.gh Fig. 2.3 shows the temperature characteristics of REEs. The boiling point distribution in the LREEs decreases from Pr to Eu. The boiling point of Yb in the HREE is lower in relation to the HREE and the LREE. The lowering of the boiling point characteristics has been associated with hybridization. A similar occurrence is obtainable in the melting point of the REEs. Fig. 2.3: Temperature characteristics of the rare earth elements 28 University of Ghana http://ugspace.ug.edu.gh 2.6 Industrial Processing of Rare Earth Ores The major ores of rare earth are monazite, bastnaesite, churchite and xenotime. Table 2.5 shows a typical composition of monazite in the beach sands of Brazil and India (Habashi, 1997). Table 2.5: Percentage composition of monazite in selected beach sands Compound ThO2 U3O8 (RE)2O3 Ce2O3 P2O5 Fe2O3 TiO2 SiO2 India 8.88 0.35 59.37 28.46 27.03 0.32 0.36 1.00 Brazil 6.5 0.17 59.2 26.8 26.0 0.51 1.75 2.2 Source:(Habashi, 1997) Monazite sands in coastal placer environments are usually found in addition with other heavy minerals such as ilmenite, xenotime, zircon, rutile, tantalite, epidote, tourmalime amongst others. The process required for the concentration of monazite from the beach sands is shown in Fig. 2.4. Important processes involved in the beneficiation processing of monazite and include the following; de-sliming, floatation, acid treatment, hypogravity separation and magnetic separation (Adam & Neil, 2014; Jack & Baodong, 2016; Misra et al., 2005). The industrial mining process requires Dredge and Wedge Upgradation Plant (DWUP) which aids the upgrade of the accessory heavy minerals in the beach sands, leading to a higher percentage of heavy minerals and the discarding of quartz. The heavies obtained from the dredge and wedge up-gradation processes are further processed by the Heavy Upgrade Plant (HUP) which promotes the beneficiation of the minerals before the individual minerals separation. Venugopal et al. (2005) discusses 29 University of Ghana http://ugspace.ug.edu.gh more on the mining processes involved in the beneficiation of heavy minerals from beach sands. Fig. 2.4: Separation process for heavy minerals in beach sands (Zhang & Zhao, 2016) 30 University of Ghana http://ugspace.ug.edu.gh 2.6.1 Acid Digestion of Rare Earth Ores Monazite sand which predominantly is associated with LREE is subjected to different physical separation processes such as crushing, screening, grinding, floatation (Zhang & Zhao, 2016). The concentrated monazite could be digested in acids such as H2SO4, HCl, HNO at relatively high temperatures (~200-230 o3 C) to give rare earth phosphate (REPO4), RE2(SO4)3, RECl3 and RE(NO3)3, Th. A two-stage digestion process described by Habashi (1997) demonstrates the use of 93% sulfuric acid (twice the mass of sand) in the digestion of monazite concentrate at the first stage and a second stage acid digestion which requires about 5 hrs fuming sulphuric acid digestion. The mixture is cooled while thorium and rare earth are dissolved in solution by addition of cold water. Thorium is precipitated using aqueous ammonia at a pH of 1.3 while REEs are precipitated at a pH of 2.3 (Habashi, 1997). In a method developed by Lynascorp (2006), mixed oxides of rare earth are digested in H2SO4 and dissolved in water with the addition of MgO which aids in lowering of the pH control, thereby leading to the slight removal of residues (SiO2, ThO2, ZrSiO4) via filtration. The monazite sulphate which contains Ln2(SO4)3 in solution is further subjected to partial neutralization with ammonium hydroxide in a reaction tank at a pH of 1.05-1.1, this helps in the precipitation of thorium concentrate (ThO2) which can be further processed to nuclear reactor grade (Abrao et al., 2001; Habashi, 1997). The precipitates of REEs are obtained at a pH of 2.0 at controlled pH using Na2CO3 and NH4OH. The hydroxide REE-component is reacted with Na2SO4 for further precipitation of LREE and HREE. The filtrate is from the hydroxide precipitation is processed for the removal of uranium. Un-reacted REEs which is precipitated with the 31 University of Ghana http://ugspace.ug.edu.gh thorium cake can be further removed during the thorium purification process. Fig. 2.5 shows the flow process for REE separation adopted by Peak Resources Ltd. Fig. 2.5: Processes flow chart for rare earth separation (Allen, 2016) Bastnaesite ores concentrated via floatation have been processed using acid digestion method under relatively similar conditions as monazite. The LREE-dominant concentrates can either be calcined at temperatures close to 600 oC prior to H2SO4 digestion or digested in concentrated H2SO4 at a temperature close to 200 oC, leading to the loss of CO2, HF and SO2. The resulting sulphates concentrate is leached with water to give REE sulphate [RE2(SO4)3] and CeO2 which is used in glass polishing (Kato et al., 2000). 32 University of Ghana http://ugspace.ug.edu.gh 2.6.2 Alkaline Digestion of Rare Earth Ores The common ores digested on an industrial scale are monazite, bastnaesite, xenotime and ion-adsorbed clay. The conventional mode for alkaline digestion of monazite (<45 μm) requires the use of about 65% of NaOH for 3 hrs in a digester at about 140 oC. The residue obtained contains about Th(OH)4, Na2U2O7 and RE(OH)3 residue while the Na3P04.10H2O is filtered off from the digestate and cooled as crystals (Chayavadhanangkul et al., 2009; Habashi, 1997). Similar digestion method can be applied for bastnaesite; reaction takes place at about 200oC in NaOH prior to acid digestion (IAEA, 1993). The hydroxides obtained from the digestion phase are dissolved in concentrated HCl to give ThCl4, RECl3 and uranium chloride. The use of about 20% NaOH aids the precipitation of thorium and uranium at pH of 5.8 and the RECl3 are precipitated at pH 3.5, radium is removed using barium sulphate solution. Solvent extraction is used in the separation of the individual components of the REEs (Kumar et al., 2014). 2.7 Separation of Rare Earth Metals Separation of rare earth was considered a Herculean task in the early 50s due to the similarity in chemical properties of the REEs. This has led to the development of methods such as fractional crystallization, ion exchange, chelation ion exchange, solvent extraction, ionic liquid separation and molecular recognition separation. 33 University of Ghana http://ugspace.ug.edu.gh 2.7.1 Solvent Extraction in Rare Earth Processing Critical to the separation of REEs is the idea of solvent extraction, which played a vital role in the selective distribution of rare earth between aqueous and organic phase. Solvent extraction has helped in the industrial separation of rare earth elements as a group and on an individual basis (Xie et al., 2014). Organophosphorus compounds are among the solvents which have found applications in the separation of REEs (Dulski, 1999). Commonly available solvents used in the separation process include the following; Di-(2-Ethylhexyl)phosphoric acid (D2EHPA), mono-(2- Ethylhexyl)phosphoricacid (HEHEHP), dibutyl-phosphoricacid, Versatic 10, tributylphosphate (TBP), Tributylphosphine oxide (TBPO), triphenylphosphine oxide, carbamoylmethyl phosphonate (CMP), carbamoylmethyl-phosphine oxide (CMPO), tetraoctyldiglycolamide and Aliquot 336 (Koshimoto et al., 2011; Sun & Waters, 2014). Three classifications of organic extractants used in metal extraction are as follows; chelating, solvating and ion pair extractants. The chelating extractants are reported to have weak acidic properties and form chelate complexes with metals in solution. They are often used in synergy with solvents in order to promote the easy recovery of metal analytes of interest. Examples of commonly available include organophosphoric acids, 2-thenoyltrifluoroacetone (HTTA), oximes and beta-diketones (Santhi et al., 1994; Petrova & Kurteva, 2011). Typical applications include the separate individual HREEs from solution into organic complexes. Rare earth producers follow similar principles and schemes when selecting specific solvent extraction routes. 34 University of Ghana http://ugspace.ug.edu.gh Reddy et al. (1997) recorded success in the separation of selected lanthanides (Nd(III), Eu(III) and Lu(II)) using mixed ligand chelating organic extractant. Observed were the complex formation of Ln(BFA)3 in benzene from a mixture of 4,4,4-trifluoro-1-phenyl-1,3- butanedione (HBFA) and neutral oxo-donors such as 2-Ethylhexylsulphoxide (B2EHSO) and triphenyl phosphine oxide (TPhPO). Relatively similar studies were obtained in the works of Yamada & Freiser (1981) in the separation of Pr, Eu and Yb in a mixture of chloroform and 1,10-Phenanthroline or 7-dodecenyl-8-quinolinol. Inoue & Co-workers (1985) employed a similar method in the separation of Pr, Eu, and Yb, but a slight change in the extraction component using N-benzoyl-phenylhydroxylamine,N-m-tri-fluoromethyl-benzoylphenyl- hydroxylamine (HL) as stand-alone or in association with 1,10-Phenanthroline. This can be extended to include: La, Pr, Eu, Ho and Yb. Similar studies were found in the works of Atanassova & Dukov (2006) where 4-(2-pyridylazo)-resorcin was used in the separation of La, Nd, Eu, Ho and Lu. Solvating extractants are employed in the removal of metal ions from the aqueous phase into the organic phase, thereby substituting for the hydrate water. Most solvating extractants can be used independently in extraction processes or combined in order to provide synergy in the REE separation process (Komorova & Tran, 1992). Typical solvating reagents applied in the separation of REEs and trans-uranium elements include phosphorus esters such astri-n-butyl-phosphate (TBP), dibutyl butyl phosphonate (DBBP); phosphine oxides as tri-n-octylphosphine oxide (TOPO, Cyanex 921), benzyldi-butylamine (BDBuN). Ion pair extractants provide ligands which form metal-ligand pair interactions. The idea behind the interaction emanates from the reaction of the lanthanide metals with 35 University of Ghana http://ugspace.ug.edu.gh acidic ligands which produce anions which form complex aqueous anionic system. On the other hand, ligands produce cations which form aqueous anionic metal complexes to form ionic pairs. Typical ion pair extractant used as anion exchanger includes; primary amines- (Primene JMT, N1923); and quatenary amines (Aliquat® 336, Adogen® 464). Selected Cation exchanger extractants used in rare earth separation include phosphoric acids-(ethylhexylphosphoric acid (D2EHPA)),Phosphonic acids- (ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHEHPA, HEHEHP, P507, PC88A), Phosphinic acids-(di-2-ethylhexylphosphinic acid (P229);, di-2,4,4- trimethylpentylphosphinic acid (Cyanex 272)), monothiophosphorous acids-(di-2,4,4- trimethylpentyl-monothiophosphinic acid (Cyanex 302)),dithiophosphorus acids-(di- 2,4,4-trimethylpentyl-dithiophosphinic acid (Cyanex 301)) (Koshimoto et al., 2011; Williams, 2001; Xie et al., 2014; Yamada & Freiser, 1981). Ionic liquid extractants in recent times have found application as a form of green solvent utilized in the separation of REEs. The ionic liquids are regarded as “green solvents” even though other scientists question the safety of ionic liquid (Robin & Kenneth, 2002; William, 2002). In a bid to understand the functionality of ionic liquids, it is important to emphasize that RTILs comprise mostly of anionic and cationic group co-existing in a liquid state. Commonly synthesized ionic liquids have heteroatoms incorporated within their cations; such cations include pyridinium, imidazolium, ammonium, phosphonium, pyrrolidinium, isoquinolinium, sulphonium, imidazolium and cholinium cations (Zhang et al., 2006). Fig. 2.6a, and Fig. 2.6b show commonly used cation and anion ionic liquids. Although cations are mostly asymmetrical, they account for the low 36 University of Ghana http://ugspace.ug.edu.gh melting point of RTILs, while anions are known to contribute to the overall distinctive properties of the ionic liquids. Recent studies consider the development of Task-Specific Ionic Liquids (TSILs) in REE extraction. Nockemann & Co-workers (2006) are known to have studied the use of protonated betaine cation and bis-trifluorosulfonyl)imide anion [Hbet] [TF2N] in the selective dissolution of REE content in red phosphor [Y2O3: Eu] leaving other halophosphate in solution (Dupont & Binnemans, 2015). [Hbet] [TF2N] has also been reported in the selective recovery of Scandium(III) from aqueous solutions (Onghena & Binnemans, 2015). Araque et al. (2015) in their study tried to further elucidate ionic liquid structure in general and it’s coupling to transport and dynamics. Fig. 2.6 (a): Typical cations of ionic liquid 37 University of Ghana http://ugspace.ug.edu.gh Fig. 2.6b: Typical anions of ionic liquid (Olivier-Bourbigou et al., 2010; Zhang et al., 2006; Ye et al., 2013) 2.7.2 Ion Exchange Resin Separation The ion exchange chromatographic system has been established in the separation of REEs in the last five decades. The ion exchange system can be classified into cations(strong; moderate; weak), anion-(weak; strong), chelating, or bi-functional exchange system (Vértes, 2011). The development in ion exchange resin separation technique for REEs as reported in the works of Reddy et al., (1997), shows the separation of selected lanthanides (Nd(III), Eu(III) and Lu(II)) using mixed ligand chelating organic extractant. Observed were the complex formation of Ln(BFA)3 in benzene from a mixture of 4,4,4-trifluoro-1-phenyl-1,3-butanedione (HBFA) and neutral oxo-donors such as 2-ethylhexylsulphoxide (B2EHSO) and triphenyl phosphine oxide (TPhPO). 38 University of Ghana http://ugspace.ug.edu.gh The large volume solvent chromatography works of Gilbert (1980) shown in Fig. 2.7 utilized the Biorad AG1-XB anion exchange resin in the separation of REEs and LREEs from geological samples. Digested Sample + Eluent + 50 mL of 5mL of A A + 8 mL 0.05M Elute Dy – Lu (8mL of B) HNO3 + 1 mL B Elute Nd-Gd (55mL of C) 8 X 0.6 cm Bio-Rad Elute La – Ce (5mL of HNO3-1M) AG1XB (Nitrated) 4 X 0.45 cm BioRad AG1XB (Nitrated) A : 90% glacial acetic acid + 10% 5M HNO3 B: 90% methanol + 10% 15.4M HNO3; C : 90% methanol + 10% 0.05M HNO3 Fig. 2.7: Anion exchange separation of rare earth element from rock (Gilbert, 1980) 2.7.3 Chromatographic Extraction Resin in REEs Separation Eichrom technologies in the 1990’s developed a solid-liquid system that allows the use of selective extraction chromatographic resins for the separation of lanthanides and actinides from acidic solution. The resins combine the use of solvating extractants supported on a polymeric solid substrate for the sorption of lanthanides and actinides in different oxidation states from fission products (Horwitz et al., 2005 ; Alexandratos & Ripperger, 1998). The commercially developed Eichrom resins utilized in the separation of lanthanides and actinides from geological matrix include; actinide ™, DGA ™ ,LN ™ , RE ™, TEVA ™ , TRU ™ and UTEVA ™ resin. 39 University of Ghana http://ugspace.ug.edu.gh Horwitz et al. (2006) compared the use of solvent-extraction with chelating- extraction process in the recovery of metals. The use of large volumes of solvents and multiple solvent extraction stages was considered a disadvantage in the recovery of metals from solution (Horwitz et al., 2006; Ostapenko et al., 2015). On the other hand, extraction chromatographic system combines the solvent extraction capability and chromatographic properties, thereby reducing the turnaround time in the separation process. The trans-uranium (TRU) chelation extraction resin developed by Eichrom Industries is applicable in actinide-lanthanide sorption and desorption. The chromatographic material is composed of 13% octyl(phenyl)-N,N-di isobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in 27% n-tributyl phosphate (TBP) and supported on Amberchrom CG-71ms substrate (Pin & Zalduegui, 1997). The TRU resin has found application in the sorption and desorption of Fe, Th, Pa, U, Np, Pu, Am and Cm; and dating of the extraction process. TRU has been used in the separation of Eu in a mixture of radioactive waste and a recovery (> 80%) (Maischak & Fachinger, 2001). Fig. 2.8a and Fig. 2.8b shows a typical complex formed during the interaction between lanthanides, TBP and CMPO; A suggested TBP-CMPO and Lanthanide complex is suggested (Appendix H). Pin & Gannoun (2017) reported the separation of Sm, Nd, Th, U and other LREEs using a coupled TRU and Ln resin system. The LN resin is made up of di-(2-ethylhexyl)-phosphoric acid adsorbed Amberchrom CG-71ms substrate (Pin & Zalduegui, 1997). The separation of Nd and Sr for isotopic studies was achieved using a combination of Sr-resin, TRU-resin and LN-resin with a high rate of recovery (Míková & Denková, 2007). Ostapenko et al. (2015) in a study of the behavior of REEs on the extraction chromatographic resin (DGA, LN, TRU) 40 University of Ghana http://ugspace.ug.edu.gh reported optimum conditions for the separation of Ce(III) and La(III) from nitric acid solution. The challenge associated with the interference of Fe in the separation of the LREEs was resolved via the reaction of digested rock samples with ascorbic acid (Míková & Denková, 2007). The separation of the lanthanides using LN resin has recorded huge success with respect to the isotope determination of Nd/Sm in geological matrices (Saji et al., 2016). The impregnated di(2-ethylhexyl)orthophosphoric acid (HDEHP) extractant was used in the separation of LREE from basaltic rocks. The affinity of the LN resin in the extraction of REEs increases with increase in mass number (Lehto & Hou, 2011). Gharibyan et al. (2014) in a study compared the extraction of other derivatives of the LN, LN2, LN3 extraction resin. Although DGA resin is mostly applied in the extraction of actinides, it has shown strong retention of Yttrium, while elution is achieved using nitric acid or hydrochloric acid (Horwitz et al., 2005). The DGA resin is impregnated on an inert substrate using straight chain or branched C8 groups of N,N,N’,N’-tetra-n-octyldiglycolamide (DGA Resin, Normal) or N,N,N’,N’-tetrakis-2-éthylhexyldiglycolamide extractant. 41 University of Ghana http://ugspace.ug.edu.gh Fig. 2.8a: Structural complex of TBP interaction with Ln3+ in acidic solution. (Braatz et al., 2017) Fig. 2.8b: Inferred structural complex of CMPO interaction with Ln3+ in acidic solution 42 University of Ghana http://ugspace.ug.edu.gh 2.7.4 Molecular Recognition in the Separation of REEs The recent search for environmentally friendly and selective separation mode for REEs led to the development of SuperLig® resins by the Ucore and IBC Advanced Technologies, Inc. The technology promised >99% recovery of REEs as a group or individual elements from pregnant leach solutions, faster flow rate when compared to ion exchange and solvent extraction system, minimal waste generation, minimal elution solvent and improved turn around in separation time (Littlejohn, 2007). The SuperLig® relies on the development of a predesigned selective host ligand species bound chemically to a solid support and packed in a column. Pregnant leach solution of REE concentrates is passed through the column and eluted with dilute nitric acid solution. The question that arises is; how does this MRT technology differ from chelation extraction? What type of selective host ligands is used? The works of Izatt et al. (2016), shows that an organic metal selective ligand compound such as 18- crown-6 ether is attached to a solid silica gel support via a tether. Kruchten & Godfried (1998) in a patent described the solid support mostly used as silica, polystyrene and acrylates which can be covalently combined with immobilized crown ethers in a single step process. The methods of Horwitz et al. (2005) and the works of Izatt et al. (2016) used relatively similar method of chelating extraction procedures and column chromatographic system. 43 University of Ghana http://ugspace.ug.edu.gh CHAPTER THREE MATERIALS AND METHODS This chapter of the study involves the description of the study area, geology, climate, vegetation and topology of the area. The sample preparation techniques and analysis methods are described. Rare earth elements determinations with respect to their particle size distribution are described. The description of the experimental procedure for the determination of activity concentration of the coastal sands is also reported. 3.1 Profile of the Study Area 3.1.1 Geographical Location Ghana is located in the Western part of Africa. It has a total land area of 238,533 square kilometers with border countries such as Burkina Faso to the north, Ivory Coast to the west and the Atlantic Ocean (Gulf of Guinea) to the south (Norton, 2003). The total coastline of Ghana is about 550 kilometers and can be classified as intermediate to low tide terrace (McGlade et al., 2002). Ghana has about ten regional capitals, of which three of these regional capitals form a border with the Atlantic Ocean (Gulf of Guinea). The three regions are Greater Accra, Central Region and Western Region. Figure 3.1 shows a map of Central and Western regions of Ghana. The Central region is one of the administrative regions of Ghana with Cape Coast as its Capital and it occupies a land area of about 9,826 square kilometers (Conafric, 2000). The Central region forms border with the Western region on the West Ashanti, 44 University of Ghana http://ugspace.ug.edu.gh and Eastern region to the North and Greater Accra to the East. The Southern part of the Central region forms border with the Atlantic Ocean (Gulf of Guinea) with a beach length of about 168 kilometer extending from Awutu (5°29'33.6"N 0°22'08.4"W) to Komenda (5°02'01.4"N;1°34'08.3"W) (NewsGhana, 2017). The Western region of Ghana has a land area of approximately 2,3921 square kilometers. It forms a border with Ivory Coast (Côte d’Ivoire) at the west, Ashanti and Brong-Ahafo at the north and the Atlantic Ocean (Gulf of Guinea) to the south (Ghana Imigration, 2017). The coastal stretch for the Western region extends from Komenda (5°02'01.4"N; 1°34'08.3"W) to New Town (5°05'29.6"N; 3°06'31.3"W). Fig. 3.1: (a) A m ap sho wing th e Centr al and W estern regions of Gha na, We st Afric a (b) Inset showing Africa and a highlight of Ghana (c) Ins et showing Ghana and a highlight of Central and Western regions 45 University of Ghana http://ugspace.ug.edu.gh 3.1.2 Geology of the Coastal Area The geology of the coastal area is considered as actively young and due to the lithostratigraphy, the basement rocks which comprise Sekondian, Accraian, Amisian and Apollonian group (IBP, 2008). The geology of Ghana is known to comprise of the Voltaian Basin, while the Birimian supergroup occupies a depth of 15000 km. The Birimian consist of sedimentary rocks containing basalts, sandstones and older shales whose origin can be associated with volcanoes of old origin (Yendaw, 2004). The isolated and spatially restricted coastal sedimentary basins of Ordovician to Cretaceous age are responsible for the opening of the Atlantic Ocean (Paul, 2003). The basement rock of the coastline is known to have occurred as the lithostratigraphic opening of the Atlantic in which Dickson (1969) described the Birimian and Tarkwaian as series of economic importance to Ghana. The metavolcanic Paleoproterozoic rock from the Birimian supergroup and accounts for the major part of the Geology of Ghana. A Paleozoic and Cretaceous to Tertiary sediments are found along the coast (van, 2002). There is an occurrence of a mix of conglomerates, volacnistic sediments, micaceous sandstones, mudstones, interbedded shales and granitoid which characterize the detrital sediments along the coast of Ghana (Yendaw, 2004). A list of the selected locations and coordinates in the Central and Western regions are shown in Table 3.1 and Table 3.2, while a description of the geology of the locations is shown in Table 3.3 and Table 3.4 46 University of Ghana http://ugspace.ug.edu.gh 3.2 Description of the Selection of Sampling Sites Geological map provided by the Ghana Survey Department served as a pointer in the identification of the coastal geology. Geospatial pre-selection of 25 target locations were considered for sampling along the coast and the hand held GPS was used in locking the positions where the samples were collected. The target area for each sample was defined based on the geology of the coastal area. Fifteen locations were selected in the Central region and ten locations were selected in the Western region. The sand samples were collected along the beach face at depths of 30 cm and 100 m by 100 m distance back shore using a composite sampling method. This was repeated for all the twenty-five locations selected along the Central and Western regions during the period of January to June 2016. The samples were collected based on the geology of the coastal area as shown in Table 3.3 and Table 3.4. The common geology of the coastal environment includes deposits transported from the Dahomeyan, Birimian sediments, Birimian volcanics, Tarkwaian, Togo formation, Sekondian, Eocene & Cretaceous, Tertiary and recent sediments (GSD, 2009; Schluter, 2008). 47 University of Ghana http://ugspace.ug.edu.gh Table 3.1: Selected sampling locations along the coast of the Central region of Ghana. Site Code Location Coordinates CR1 Gomoa Fetteh 5°25’03.97’’N, 0°27’51.50”W CR2 Senya Beraku 5°23’22.25’’N, 0°29’20.93’’W CR3 Winneba 5°20’33.18’’N, 0°37’02.80’’W CR4 Mankwadze 5°18’53.21’’N, 0°41’04.56’’W CR5 Apam 5°16’55.86’’N, 0°43’50.19’’W CR6 Mumford 5°16’02.15’’N, 0°45’11.57’’W CR7 Dago 5°13’57.46’’N, 0°47’23.86’’W CR8 Akra 5°12’26.45’’N, 0°53’00.42’’W CR9 Ekumpoano 5°12’26.05’’N, 0°53’23.28’’W CR10 Edumafa 5°12’10.97”N, 0°57’54.98’’W CR11 Anomabu 5°10’17.54’’N, 1°07’38.49’’W CR12 Cape Coast 5°06’11.20’’N, 1°40’36.45’’W CR13 Elmina 5°04’52.95’’N, 1°21’06.62’’W CR14 Dutch Komenda 5°03’20.63’’N, 1°28’26.50’’W CR15 Kafodzizi 5°02’10.68’’N, 1°33’22.90’’W 48 University of Ghana http://ugspace.ug.edu.gh Table 3.2: Selected sampling locations along the coast of the Western region of Ghana. Site Code Site Name Coordinates WR1 Shama 5°00’58.30’’N, 1°37’40.07’’W WR2 Abuesi 4°58’14.64’’N, 1°39’12.03’’W WR3 Sekondi 4°55’59.14’’N, 1°42’41.65’’W WR4 Takoradi 4°53’16.10’’N, 1°44’52.11’’W WR5 Cape Three Point 4°45’01.41’’N, 2°05’40.58’’W WR6 Egyembra 4°49’00.15’’N, 2°10’56.53’’W WR7 Axim 4°53’27.33”N, 2°14’45.55”W WR8 Esiama 4°55’43.52’’N, 2°20’29.25’’W WR9 Sanzule 4°57’29.74’’N, 2°27’00.49’’W WR10 Atuabo 5°00’39.92’’N, 2°42’22.22”W 49 University of Ghana http://ugspace.ug.edu.gh Table 3.3: Geology of selected sampling locations along the coast of the Western region of Ghana (GSD, 2009) Site Code Location Characteristic Geology WR1 Shama - Biotite, (+/- Hornblende, +/- muscovite), granitoids, undifferentiated. WR2 Abuesi - Biotite, (+/- Hornblende, +/- muscovite), granitoids, undifferentiated. WR3 Sekondi - Sandstone (5-formations) and interbedded shale, (2- formations undifferentiated) . WR4 Takoradi - Sandstone (5-formations) and interbedded shale, (2- formations undifferentiated) . WR5 Cape Three - Hornblende-biotite granitoids, undifferentiated (strongly Points foliated) [embedded]- volcaniclastic sediment dominant. WR6 Egyembra - Hornblende-biotite tonalite WR7 Axim - Dacitic to rhyolitic flow/subvolcanic rock and minor interbeded volcaniclastics: [tab-trace] conglomerate, mature quartz pebble and quartzose sandstones. WR8 Esiama - Limestone, marl, mudstone with intercalated sandy beds (includes minor cenozoic sediments in the Tano basin area). ; Argilitic/politic sediment dominan +/- kerogen (graphite) WR9 Sanzule - Limestone, marl, mudstone with intercalated sandy beds (includes minor cenozoic sediments in the Tano basin area). WR10 Atuabo - Limestone, marl, mudstone with intercalated sandy beds (includes minor cenozoic sediments in the Tano basin area). 50 University of Ghana http://ugspace.ug.edu.gh Table 3.4: Geology of selected sampling locations along the coast of the Central region of Ghana (GSD, 2009) Site Code Location Characteristic Geology CR1 Fetteh - Minor quartzite; bordered with, quartzite, minor mica schist . CR2 Senya - Quartzite, minor mica schist; bordered with minor quartzite of . CR3 Winneba - Biotite granite, with Archean continental signature), Winneba type . CR4 Mankwadze - Amphibolites, partly of contact metamorphic origin CR5 Apam - Amphibolites, partly or contact metamorphic origin. Birimian protoliths affected by Eburnean tectono metamorphic overprint. CR6 Mumford - Detrital sediment, mainly sandstone and conglomerate, undifferentiated CR7 Dago - Wacke sediment dominant; bordered with detrital sediments, mainly sandstone and conglomerate, undifferentiated. CR8 Akra - Biotite, granitoids, with volacnistic sediments and undifferentiated mica schists. CR9 Ekumpoano - Wacke sediment dominant; bordered with detrital sediments, mainly sandstone and conglomerate, undifferentiated. CR10 Edumafa - Conglomerates, micaceous sandstones, arkose, mudstones. CR11 Anomabu - Sediment, volacnistic sediment, undifferentiated locally mica schists. CR12 Cape Coast - Biotite granitoids, undifferentiated; bordered with volacnistic sediments/ sediment, undifferentiated locally mica schists . CR13 Elmina - Sandstones (5-formations) and interbeded shale (2- formations) undifferentiated. CR14 Dutch - Sandstones (5-formations) and interbeded shale (2- Komenda formations) undifferentiated. CR15 Kafodzizi - Sandstones (5-formations) and interbeded shale (2- formations) undifferentiated. 51 University of Ghana http://ugspace.ug.edu.gh 3.3 Collection of Beach Sand Samples Ghana geological map was referred to the identification of the sample location along the coastal area. This was supported by the use of Google Earth Software (ver. 7.1.8.3036) freeware which provided a 2-dimensional detail of the coastal stretch. Most of the beaches are characterized by low lands and low tide. A spatial pre-selection of 25 target locations were considered for sampling along the coast. Within 1-km2 of each target area, sand samples were collected at the most representative setting. Visual inspection of the defined area was conducted in order to understand the setting of the beach. The sand samples were collected along the beach face at depths of 30 cm and 100 m by 100 m distance back shore using a soil auger. Composite sampling was adopted during the sampling process, this was repeated for all the twenty five locations selected along the Central and Western regions during the period of January – June 2016. The target area for each sample was defined based on the geology of the coastal area. Fig. 3.1 shows a representation of the sampling points as defined on the map of Ghana. Coordinates were picked using hand-held GPS and details were recorded in the field logbook. Geospatial identification of the sampling area was achieved using Shuttle Radar Topography Mission (SRTM) 1 Arc-Second Global data (USGS, 2015). The Environmental Systems Research Institute (ESRI) software package Ver. 10.2, which was licensed to the Remote Sensing Geospatial Information Services (RSGIS) Unit, University of Ghana, was used in the generation of 3-dimensional Imagery of the coastal stretch. The geospatial images for the Central and Western regions shown in 52 University of Ghana http://ugspace.ug.edu.gh Fig. 3.2 and Fig. 3.3 were generated using ArcMap and ArcScene packages from ESRI. The samples collected were transferred to a clean facility at the laboratories of the Ghana Atomic Energy Commission (GAEC) for air drying and oven drying in readiness for further processing. Fig. 3.2: GIS representation of the Central region coastline of Ghana 53 University of Ghana http://ugspace.ug.edu.gh Fig. 3.3: GIS representation of the Western region coastline of Ghana 54 University of Ghana http://ugspace.ug.edu.gh 3.4 Preparation and Analysis of Samples 3.4.1 Flow Chart for General Scheme of Analysis The experimental design for this study is illustrated by the flow chart for the scheme shown in Fig. 3.4a and Fig 3.4b. Fig. 3.4a: Flow chart for general experiment Removal of shells, debris and plant materials as well as particle size distribution was done at the laboratories of the Ghana Research Reactor Centre (GRRC) of the Ghana Atomic Energy commission (GAEC). Determination of Naturally Occurring Radioactive Materials (NORMs) and Heavy Mineral Separation of the beach sands were performed at the γ-ray spectrometry laboratory of the Radiation Protection Institute (RPI) and the Nuclear Chemistry and Environmental Research Centre (NCERC), GAEC respectively. Chemical separation of selected REEs using 55 University of Ghana http://ugspace.ug.edu.gh Extraction Chromatography was carried out at the Radiochemistry Laboratory of the Radiation Protection Institute (RPI). Petrographic Thin Section was carried out at the laboratories of the Department of Earth Science, University of Ghana. Chemical Identification and Quantification of REEs by Inductively Coupled Plasma Mass Spectrometer (ICP-MS) was done at the laboratories of ALS, Canada and the Metal Contaminant Laboratory of the Ghana Standards Authority. ICP -MS: In ductively Coupled Plasma Mass Spe ctromete r NO RMs: Naturally Occurring Radioactive Materials PSD: Particle Size Distribution PT S: Petrographic Thin Section RECG: Rare Earth Coarse Grain RE FG: Rare Earth Fine Grain REMG: Rare Earth Medium Grain * P ulverisation (<75 μm) Fig. 3.4b: Flow chart of general experimental framework 56 University of Ghana http://ugspace.ug.edu.gh 3.5 Grain Size Distribution of Coastal Sands 3.5.1 Instrumentation for Grain Size Analysis ASTM sieve (63, 125, 250, 500, 1000 and 2000 µm), Retsch© vibratory sieve shaker AS 200, Ohaus CS2000 weighing balance, Newtronic oven, Stainless steel weighing tray, 4 inch brush with natural soft bristle, boar bristle brush, HP computer with Microsoft Excel spreadsheet program and GRADISTAT ver. 4.0 software. Fig. 3.5 shows the chart used in grouping of the beach sands into three groups needed for the analysis Fig. 3.5: Scheme for particle size distribution 57 University of Ghana http://ugspace.ug.edu.gh 3.5.2 Experimental Procedure for Particle Size Distribution In a bid to characterize the coastal sands collected along the Central and Western regions of Ghana, a representative sample per target area is collected, stored in a grip sealed low density polyethylene plastic bag and tagged with an identifier. The samples were oven dried at about 100 °C for 24 hours. Cooling was achieved in a desiccator and about 500 g of the sample was run through a set of sieves (63, 125, 250, 500, 1000 and 2000 µm) with the largest pore size at the top and the smallest at the base. The loaded sieves were clamped on the Retsch Vibratory Sieve Shaker AS-200 and agitated intermittently at 5 minutes and a total time of approximately 15 minutes. The sand retained on each sieve was weighed, recorded in the data book and transferred into a labelled grip sealed low density polyethylene plastic bag. The statistical data acquired during the course of the experiments were calculated using particle size- based statistical software Gradistat Ver. 4.0. Statistical details were arrived at using the Folk & Ward (1957) method of grain size analysis. The statistical data obtained aids in the comparison of the different sediments and their distribution along the coast. Information on the mean, mode(s), sorting (standard deviation), skewness, kurtosis, and cumulative percentiles can be acquired as a result of the use of Gradistat. Fig. 3.6 shows a flow process of the acquisition of the statistical data. 58 University of Ghana http://ugspace.ug.edu.gh Skewness Very Coarse Sand 1mm < x < 2mm Kurtosis Sorting Coarse Sand 0.5 100 KeV 3.7.3 Sample Preparation for Gamma-ray Spectrometry The coastal sands were air dried in a clean room for 48 hours and oven-dried at 105oC for about 4 hrs. About 1 kg of sand samples were sieved through a 2 mm pore size mesh packed into a 1 litre Marinelli beaker. The weight of the beaker and sand sample was recorded and the beaker was tightly sealed and stored for about 28 days prior to acquisition of the gamma data (IAEA, 1989). 66 University of Ghana http://ugspace.ug.edu.gh The essence of the 28 days storage was to ensure that secular equilibrium is attained between the long-lived parent radionuclides and short-lived daughter radionuclides in the U-238 and Th-232 decay series. Counting of the naturally occurring radioactive materials in the sand sample was carried out in a well shielded high purity germanium (HPGe) detector for a period of 36000 seconds. Gamma activity measurement is observed as Gaussian peaks and the peak areas which correspond to radionuclides of interest were used in the estimation of the activity concentrations of the respective radionuclides. The activity concentrations were determined on dry weight basis and reported in Bq/Kg. The activity concentrations of the coastal sands were determined by computing the equation below on a Microsoft Excel sheet and developing it for the activity concentration calculation. The key radionuclides of interest in the coastal sand samples are U-238, Th-232 and K-40. Their progenies were identified and their average area was recorded and used in the estimation of the activity concentration of the analytes of interest. ----------------------------------------------------------------------(eq 6) The parameters required are as follows; Asp: Activity concentration of sample N: Net counts of the radionuclide in the samples Td : Delay time between sampling and counting P: Gamma emission probability (gamma yield) 67 University of Ghana http://ugspace.ug.edu.gh η: Absolute counting efficiency of the detector system Tc : Sample counting time m: Mass of the sample (kg) or volume (l) eλpTd: Decay correction factor for delay between time of sampling and counting λp: Decay constant of the parent radionuclide. 3.8 Chemical Identification and Quantification of Rare Earth Elements using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) 3.8.1 Reagents, Chemicals and the Treatment of Samples The selected reagents used in this experiment include: ISO 3696- grade water obtained from ReAgent Chemicals Ltd. U.K., and about 125 mL of multi-element standard (Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Sc, Tb, Th, Tm, U, Yb and Y) of concentration 10 μg/mL, were obtained from Inorganic Ventures, Virginia U.S.A. TRU-resin, LN-resin, SR-resin were obtained from TRISKEM International, France; via Separations Pty, Randburg, South Africa. Lithium metaborate was obtained from Chengdu Chemphysics, Sichuan, China (Mainland). OREAS 460 certified reference material was supplied by ORE Research & Exploration, Australia. AMIS0185 was supplied free by African Mineral Standard, Modderfontein, South Africa. Electronic grade HF, analytical reagent (AR) grade HClO4, HNO3, HCl, were obtained from Fisher Scientific Chemicals. The beach sand samples retrieved from the particle size sorting process were grouped into three fractions viz: (i) coarse fraction (0.5 mm < x < 2 mm) (ii) medium fraction 68 University of Ghana http://ugspace.ug.edu.gh (0.25 mm