Element leachability from a coal stockpile and associated coastal sand deposits

The mobilities of major and trace elements in stockpiled sub-bituminous coal and the coastal sand on which the stockpile has been built have been evaluated by batch leaching tests using demineralised water and controlled-pH (acidic) solutions. The results were compared with those from column leaching tests on the coal with similar liquids, and with a column test in which the coal was placed above a bed of the coastal sand material.Batch testing showed that most trace elements, especially As, Cr, Cu, Mo, Pb, Sb, Sr, V and Zn, were released in higher concentrations from the sand than from the coal. Some elements were released in greater concentrations from the coal (although values were still low), while a few were released in low but approximately equal concentrations from both materials. Comparison of the column and batch test results suggests that most of the elements in the leachate from the column in which coal was underlain by sand were derived from the sand component. The column tests further indicate that concentrations of many elements mobilised from the coal are likely to be reduced by interactions associated with percolation through the sand bed.