Studies on the Mediation of Cyanide and Heavy Metals in Effluent and Tailings in a Mining Environment in Obuasi, Ghana

Abstract

Mining is one of the main anthropogenic sources of metal contamination in water and soil. Soil pollution with arsenic and lead due to industrial activities is a major environmental problem. The main objective of this study was to evaluate the heavy metal- and cyanide-mediation techniques for treated effluent and soil adopted by AngloGold Ashanti, Obuasi mine. The concentrations of heavy metals and cyanide in detoxified effluent and amended capped tailings were assessed, using the completely randomized design. The bioavailability of heavy metals in mediated tailings was also determined using Lactuca sativa L. as a test crop. The concentrations of As, determined using the Atomic Absorption Spectrometer. Bacterial degradation resulted in a reduction of cyanide in treated effluent. The concentrations of As and Pb in treated effluent were above the maximum permissible limit (MPL). The capping of tailings led to As concentrations that were above the MPL. Zeolite and beringite were the most effective in the mediation of Pb and As and resulted in decreases of the water soluble fraction in uncapped tailings. The bioavailability of As in beringiteamended uncapped tailings was higher than the MPL. The Pb contents of Lactuca sativa L. after amendment of uncapped tailings with biochar and zeolite were also above the MPL. Bacterial degradation was probably the most efficient cyanide detoxification process. It is recommended that long term studies be conducted to evaluate the most efficient techniques of mediating effluent and tailings.