Characterization of cyanide in a natural stream impacted by gold mining activities in the Witwatersrand Basin, South Africa

Abstract

Water systems in the Witwatersrand Basin are heavily contaminated with pollutants from gold-mine tailing leachates and spillages. Cyanide speciation was studied in relation to the Natalspruit, a natural stream within a gold mining area of Johannesburg. The part of the studied stream was adjacent to an abandoned gold-mine tailings dump. The results of this study pointed to a variation in surface and groundwater chemistry. The groundwater had low pH and contained elevated concentrations of pollutants including secondary cyanide species, e.g. thiocyanate, cyanate, and ammonium. Metal-cyanide complexes that are weak-acid dissociable (CN WAD) and strong-acid dissociable (CN SAD) cyanides were found to dominate the speciation of cyanide, with iron cyanide complexes being most prevalent in groundwater. Decreases in the concentration of 63% for Cu(CN) 32-, 83% for Ni(CN) 42-, 69% for Fe(CN) 64-, and 47% for Fe(CN) 63- were observed from groundwater to surface water largely due to dilution and dissociation (in the case of the first two complexes). Speciation modeling was used to estimate the concentrations of CN WAD and CN SAD based on total cyanide (CN T), total metal, and total anion concentrations. Other cyanide complexes as well as dominant sulfate complexes were also predicted. © 2011 Taylor and Francis Group, LLC.