Removal and Recovery of Ni and Zn from Contaminated Neutral Drainage by Thermally Activated Dolomite and Hydrothermally Activated Wood Ash

Abstract

Raw and activated dolomite or wood ash were comparatively evaluated in column reactors for the simultaneous removal of Ni and Zn in synthetic contaminated neutral drainage (CND) over 119 days. Dolomite was thermally activated by charring, while wood ash was subject to alkaline fusion followed by hydrothermal treatment. Column testing was performed using CND with 51.5 mg/L Ni and 46.5 mg/L Zn, at pH 6. Testing was considered complete when metal concentrations in the final effluent reached 0.5 mg/L to meet Canadian regulations on discharge. Results showed that thermally activated wood ash was the most efficient among all tested materials as it removed 64 mg/g Ni and 61.6 mg/g Zn. Based on these results, thermally activated wood ash could be considered a promising option for Ni and Zn treatment in CND, although final pH correction of treated effluent might be necessary. At the end of the testing period, metals could be recovered by dissolution with concentrated acid and by hydrometallurgical processes from spent activated dolomite and wood ash, respectively. As spent material could be used for recovery of treated metals, sludge management issues could be alleviated.