Hindawi Publishing Corporation Journal of Mining Volume 2013, Article ID 698031, 5 pages http://dx.doi.org/10.1155/2013/698031 Research Article Nickel and Zinc Removal from Acid Mine Drainage: Roles of Sludge Surface Area and Neutralising Agents William E. Olds, 1,2 Daniel C. W. Tsang, 2,3 Paul A. Weber, 1 and Chris G. Weisener 4 1 Solid Energy New Zealand Ltd, Private Bag 1303, Christchurch 8024, New Zealand 2 Department of Civil and Natural Resources Engineering, University of Canterbury, Christchurch 8140, New Zealand 3 Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 4 Great Lakes Institute for Environmental Science, University of Windsor, ON, Canada N9B 3P4 Correspondence should be addressed to Daniel C. W. Tsang; dan.tsang@polyu.edu.hk Received 28 June 2013; Accepted 26 September 2013 Academic Editor: Yong Sik Ok Copyright © 2013 William E. Olds et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. During acid mine drainage (AMD) treatment by alkaline reagent neutralisation, Ni and Zn are partially removed via sorption to Fe and Al hydroxide precipitates. his research evaluated the efect 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. he 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 efect on Ni removal. he 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 ). hese results suggest that the surface area of precipitated locs and the selection of neutralising reagent critically afect the sorption of Ni and Zn during AMD neutralisation. 1. Introduction Acid mine drainage (AMD) is one of the major environmen- tal impacts of coal mines that disturb pyritic overburden on the West Coast of the South Island of New Zealand [1]. he formation of acidity associated with AMD is illustrated by FeS 2 + 7 2 H 2 O + 15 4 O 2 ⇒ Fe(OH) 3 +2H 2 SO 4 (1) As part of AMD treatment, acidity neutralisation to pH 6- 7 by alkaline reagent decreases the solubility of Fe and Al, resulting in Fe and Al hydroxide precipitation and removal by sedimentation [2, 3]. However, potentially ecotoxic metals (e.g., Ni, Zn, Cu, Pb, and Cd) require a further increase in pH (to 8 or above) to precipitate as metal hydroxides [4–6]. Incomplete removal and resultant discharge of residual met- als may afect downstream freshwater ish assemblages[7]. Previous studies have reported removal of Ni and Zn dur- ing AMD neutralisation, where these metals were removed to varying degrees via coprecipitation and sorption onto Fe and Al hydroxide precipitates [8–11]. Davies et al. [10] showed a negative correlation between dissolved Zn concentration and Zn incorporation into neutralised AMD loc. Batch experiments showed that, at pH 7 and for ratios of Zn to sorbent of 1 : 10 to 1 : 100, between 70% and 90% of Zn was removed from AMD due to sorption to precipitated metal oxides [12, 13]. A similar trend was shown for Ni removal (at a similar sorbent to metal concentration ratio) where 66% of Ni was adsorbed to hydrous iron oxide at pH 7 [14]. he purpose of this paper is to investigate the importance of the surface area of loc formed during AMD neutralisation by three industrial alkaline reagents (NaOH, Ca(OH) 2 , and CaCO 3 ) for Ni and Zn removal from AMD. As sorption is a solid-liquid interface process, we hypothesise that the