Nickel and Zinc Removal from Acid Mine Drainage: Roles of Sludge Surface Area and Neutralising Agents

Abstract

During acid mine drainage (AMD) treatment by alkaline reagent neutralisation, Ni and Zn are partially removed via sorption to Fe and Al hydroxide precipitates. This research evaluated the effect of surface area of precipitates, formed by neutralisation of AMD using three alkalinity reagents (NaOH, Ca(OH) 2 , and CaCO 3 ), on the sorption of Ni and Zn. The BET surface area of the precipitates formed by neutralisation of AMD with NaOH (173.7 m 2 g −1 ) and Ca(OH) 2 (168.2 m 2 g −1 ) was an order of magnitude greater than that produced by CaCO 3 neutralisation (16.7 m 2 g −1 ). At pH 6.5, the residual Ni concentration was 0.32 and 0.41 mg L −1 for NaOH and Ca(OH) 2 neutralised AMD, respectively, resulting in up to 60% lower Ni concentrations than achieved by CaCO 3 neutralisation which had no effect on Ni removal. The residual Zn concentration was even more dependent on precipitate surface area for NaOH and Ca(OH) 2 neutralised AMD (0.33 and 1.02 mg L −1 ), which was up to 85% lower than the CaCO 3 neutralised AMD (2.20 mg L −1 ). These results suggest that the surface area of precipitated flocs and the selection of neutralising reagent critically affect the sorption of Ni and Zn during AMD neutralisation.