%0 Journal Article
%T Nickel and Zinc Removal from Acid Mine Drainage: Roles of Sludge Surface Area and Neutralising Agents
%A William E. Olds
%A Daniel C. W. Tsang
%A Paul A. Weber
%A Chris G. Weisener
%J Journal of Mining
%D 2013
%R 10.1155/2013/698031
%X 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 CaCO3), on the sorption of Ni and Zn. The BET surface area of the precipitates formed by neutralisation of AMD with NaOH (173.7£¿m2£¿g£¿1) and Ca(OH)2 (168.2£¿m2£¿g£¿1) was an order of magnitude greater than that produced by CaCO3 neutralisation (16.7£¿m2£¿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 CaCO3 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 CaCO3 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. 1. Introduction Acid mine drainage (AMD) is one of the major environmental impacts of coal mines that disturb pyritic overburden on the West Coast of the South Island of New Zealand [1]. The formation of acidity associated with AMD is illustrated by 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¨C6]. Incomplete removal and resultant discharge of residual metals may affect downstream freshwater fish assemblages [7]. Previous studies have reported removal of Ni and Zn during AMD neutralisation, where these metals were removed to varying degrees via coprecipitation and sorption onto Fe and Al hydroxide precipitates [8¨C11]. Davies et al. [10] showed a negative correlation between dissolved Zn concentration and Zn incorporation into neutralised AMD floc. 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
%U http://www.hindawi.com/journals/jmin/2013/698031/