Evaluation of biosorbents as an alternative for mercury cyanide removal from aqueous solution

Abstract

Worldwide, artisanal gold miners currently use and lose over 2000 t/year of mercury, which causes massive social and environmental problems. The combined use of mercury and cyanide by artisanal processing centers have exacerbated the bioavailability of the pollutant. Biosorbents have the capability to adsorb mercuric species in solution, and due their low cost and extensive availability close to mines, they can be used to detoxify effluents. In this study, four biosorbents were evaluated for mercury cyanide removal from simulated gold mining effluents: banana peel, passion fruit peel, eggshells, and chicken feathers. For each treatment, the adsorption capacity, equilibrium isotherms, and kinetic modeling were studied. Only banana peel showed favorable adsorption of Hg(CN)2, with a 94 % removal percentage within 90 min. The pseudo-first order model resulted in the same adsorption capacity as the experimental data (0.47 mg/g). The Sips isotherm model fitted the experimental data, indicating that the adsorption was monolayer-based. Banana peel was found to be more selective for mercury than for gold cyanide. Conversely, the excess of free cyanide had a negative effect on the adsorption efficiency.