Removal of Ions and Acidity from Acid Mine Water Using Transformed Fly Ash

Fly ash obtained from a coal combustion thermal electric power plant was reacted with NaOH at 100 °C for 24 h to synthesize zeolite. Shaker flasks experiments were conducted to assess whether fly ash or fly ash zeolite (FAZ) could be used to treat acidic mine water. The FAZ was used to treat the mine water at doses of 5–60 g/L; the FAZ increased pH from 2.76 to as high as 7.51 and removed most of the Ca and Mg hardness and acidity from the mine water, though it did not affect sulphate concentrations. The cation exchange capacity of the FAZ was regenerated using NaCl. After six regeneration/reuse cycles, the FAZ was less effective but still capable of increasing pH and removing substantial hardness. In contrast, fly ash was not effective in removing hardness or acidity, and instead released ions into the mine water.