Laboratory Evaluation of the Treatment of Alkaline Leachate with Coal Washery Discard

This paper presents a laboratory investigation into the utilisation of a New South Wales coal washery discard (CWD) as an inexpensive and readily available material for reducing groundwater alkalinity i n situ. It is part of a larger study examining the potential for Australian CWD to be used as a permeable reactive barrier material for the removal of various inorganic and organic contaminant species from groundwater. Batch test results indicate that both fine and coarse CWD can reduce the pH of an alkaline contaminant solution from pH 11-12.5 to pH 8.5. The geochemical equilibrium model MINTEQA2 has been used to assist in the identification of the major attenuation mechanisms. It appears that the kaolinite and siderite within the CWD are dissolving and relatively insoluble secondary minerals (aluminium and iron hydroxides) are being formed. This process is time-dependent, and requires a higher residence time for contaminant solutions with a higher initial pH. Results indicate that CWD has the potential to be an economical and environmentally sustainable groundwater treatment material.