M. Preda, P. Scott, C. McCombe, and C. Gimber (Australia)
Acidic mine pit lake, coal ash, neutralisation
Acidic mine pit lake water was treated with various proportions of alkaline coal ash. The pH variations were monitored over almost a month and chemical analyses were conducted on selected samples. This preliminary study of the neutralising effect of fly ash on highly acidic pit water has produced promising results. The pit water had an initial pH of 2.7, which increased to more than 7.2 after 28 days, in the case of several experimental tests, where 200 ml of water were mixed with more than 100 g of ash. Considering the significant pH increase and the composition of the water before and after ash addition, it is hypothesised that the weathering of silicates is the main process that ensures the neutralisation of the pit water. The neutral pH leads to the immobilisation of most trace metals initially present in significant concentrations in the pit water. It was also observed that the concentration of major metals and anions increased, while cyanide was not significantly influenced. It is recommended to scale up the laboratory tests to determine long-term effects and the most efficient quantity of ash to be added to attain neutral pH.
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