Investigation of mercury cyanide adsorption from synthetic wastewater aqueous solution on granular activated carbon

Mercury (Hg) is one of the most harmful metals to human health. Combined with cyanide (CN−), Hg forms a stable complex (Hg(CN)2) that is difficult to remove from solution. Artisanal gold mining effluents containing mercury cyanide complexes are discharged into rivers and streams, which can be potentially bioavailable to aquatic organisms. In this study, activated carbon adsorption was evaluated for its capacity to remove mercury cyanide from solution. A solution with Hg(CN)2 and free cyanide was prepared at pH 12, corresponding to 1 mg/L Hg2+ and 0.5 mg/L CN. Analysis in batch mode showed that 180 min were required to achieve adsorption equilibrium. The adsorbent dosage was fixed at 0.1 g of activated carbon, which represented an adsorption capacity of 0.14 mg/g, equivalent to adsorption of 81 % Hg(CN)2. The free cyanide concentration did not affect the adsorption of mercury cyanide. Experimental data indicated that the adsorption follows pseudo-second order kinetics and equilibrium results corresponded to the Freundlich adsorption isotherm.