Characterization and Risk Assessment of Spent Pot Lining of Valco’s Landfill Site at Tema, Ghana

Abstract

Spent Pot Lining (SPL) is a waste material generated in the Primary Aluminium Smelting Industry. Globally, aluminium smelters produce in excess of about 500,000 tonnes of SPL annually, and safely disposing of this unavoidable but hazardous waste product is a challenge faced by the Aluminium Smelting Industry. In many cases, SPL is disposed of in a landfill. SPL contains toxic fluoride and cyanide compounds that are leachable in water. SPL is corrosive (exhibiting high pH due to alkali metals and oxides). In addition, SPL is reactive with water (producing inflammable, toxic and explosive gases). The toxic, corrosive and reactive nature of SPL means that utmost care must be taken in its handling, transportation and storage. SPL is becoming one of the aluminium industry’s major environmental concerns. The concerns stems from the environmental impact of dissolved fluorides and cyanide from SPL landfill leachate. SPL is known to have high energy value ranging from 4444 cal/g to about 5000 cal/g or more as determined in this study. It is therefore being used as a direct fuel in foundries. The high fluoride content in SPL is of immense benefit to the Cement Industry (speeds up the clinkering reaction thereby lowering operating temperatures). In view of the economic importance of SPL, there is intense mining of SPL at VALCO’s SPL landfill site at Tema. Considering the toxic nature of SPL, mining of SPL raises health concerns. In this Study, a conceptual model was developed to help understand the interrelationship between CN- and F- release mechanisms, exposure medium and pathways at the landfill site. In addition, human health risk assessment was conducted to assess possible human health risks posed to scavengers mining the waste. Also, characteristics such as the calorific value and sulphur content in the SPL which are important parameters to consider if the waste is to be used as alternate fuels were determined. Hazard Quotients of 0.73 and 0.72 for F- in soils taken at 30 and 45

cm depths respectively and 0.036 for CN- at both 30 and 45 cm depths versus the recommended limit of < 0.2 set by Health Canada’s Toolkit Model (2004) for health risk assessment. Mean F- and CN- content of scavenger urine samples were 0.66 mg/L and 0.05 mg/L respectively but could not be attributed solely to the SPL mining activity. A calorific value of 6629.65 cal/g and sulphur (S) content of 1.48 % were obtained using the Bomb Calorimeter and X-ray fluorescence (XRF) methods respectively. Fluoride and cyanide levels in the buried SPL were 410.1 mg/kg and 0.082 mg/kg, versus pre-disposal regulatory limit of 2.7 mg/kg F- and 1.4 mg/kg CN- respectively set by USEPA, (2011). Both Background soil F-and CN- levels (179.2 mg/kg F- , 0.032 mg/kg CN-) were low compared to levels in Surface soil (259.6 mg/kg F-, 0.052 mg/kg CN-) at the landfill site. Data obtained suggests that SPL buried at VALCO’s landfill site needs to be treated to forestall soil contamination within the catchment of the landfill site. Calorific value and sulphur content in SPL buried at VALCO’s landfill site suggests that, it could be a source of cheap environmentally friendly alternate fuel but scavengers mining the SPL could also be exposed to some health risks.