Removal of dissolved Zn(II) using coal mine drainage sludge: implications for acidic wastewater treatment.

The mechanism for the removal of Zn(II) by using coal mine drainage sludge (CMDS) was investigated by spectroscopic analysis and observations of batch tests using model materials. Zeta potential analysis showed that CMDS(25) (dried at 25 °C) and CMDS(550) (dried at 550 °C) had a much lower isoelectric point of pH (pH(IEP)) than either goethite or calcite, which are the main constituents of CMDS. This indicates that the negatively charged anion (sulfate) was incorporated into the structural networks and adsorbed on the surface of CMDS via outer-sphere complexation.