Removal of nickel from neutral mine drainage using peat-calcite, compost, and wood ash in column reactors.

The effectiveness of compost, peat-calcite, and wood ash to remove Ni from a circum-neutral-contaminated mine water was tested in continuous flow experiments. Materials were compared in 4.8-L columns at hydraulic residence times (HRT) of ∼ 16.5 h over the course of 2.5-4 months. During this period, all columns successfully treated over 400 L of synthetic contaminated neutral drainage (4.05 mg/L Ni), mainly through sorption processes. Mid-column results (HRT ∼ 9 h) indicated that wood ash was the most effective material for Ni removal, and chemical extractions revealed that retained Ni was less mobile in this spent material. The pH-increasing properties of wood ash played a major role in this material's performance, but a pH correction would be required in the initial stages of full-scale treatment to maintain the effluent within regulatory limits (6-9.5). Scaled to full-sized, mid-column results indicated that treatment cell sizes, designed for the 1-year treatment of a high discharge (10 m/h)-contaminated effluent (4.05 mg/L Ni), would be the smallest with wood ash (< 500 m), followed by compost (600 ± 140 m) and peat-calcite (720 ± 50 m).