Arsenic leaching in mill tailings at the AngloGold Ashanti- obuasi mine, Ghana: Management of contamination in the related water environment

Abstract

The study investigated arsenic (As) leaching prior to stabilization in mill tailings at the AngloGold Ashanti (AGA)-Obuasi mine in Ghana, using the toxicity characterisation leaching procedure (TCLP). Total As concentrations and pH values in TCLP leachate and related water bodies, as well as the concentration mass-time for As reduction in groundwater, were monitored. The corning pH/C107 meter and the varian atomic absorption spectrometer (AAS) were used to determine pH values and total As concentrations, respectively, in TCLP leachate and water samples. Sample blanks and matrix spikes ensured quality assurance. Statistical analysis was done using the SPSS 16.0 and stata 11.0. The range of total As concentrations and pH values in TCLP leachate were 0.45-8.73 mg/l and 4.3-8.4, respectively, while the results in the water bodies ranged from 0.04-7.23 mg/l and 5.8-8.4, in stream water; 0.01-2.62 mg/l and 5.4-8.0, and also less than 0.01 and 4.2-7.0 mg/l in the unsaturated and saturated ground water zones, respectively. The unsaturated ground water zone was established as the most convenient for As leaching study. Two-tailed 80% upper confidence level (ULC) for As in TCLP leachate was 2.45 mg/l. Arsenic was mostly mobilised within pH range of 6.3-8.2 and 5.8-7.6 in stream water and ground water, respectively. The mobile As required 26, 32, and 45 months degrading to compliance values of 0.10, 0.05 and 0.01 mg/l, respectively, in the groundwater.