Environmental application of mineral sulfides for removal of gas-phase Hg(0) and aqueous Hg2+

Synthesized and commercially available metal sulfides were evaluated for th eir ability to adsorb elemental and ionic mercury. The coinage group metal sulfides adsorb elemental Hg(0) vapor stoichiometrically. The mechanism of Hg(0) uptake by the copper and gold sulfides is a redox process resulting i n the formation of HgS. The mechanism in the case of Ag2S involves redox bu t there is no HgS formation. The relative rates of Hg(0) adsorption increas es in the order CuS > Ag2S > Au2S > AU(2)S(3) corresponding to the metal io n reduction potentials. The relative rate of Hg(0) adsorption for commercial grade CuS is increased by an activation process which involves making a slurry of the metal sulfi de in concentrated oxalic acid followed by drying and then exposure to Hg(0 ). Relative rates of Hg(0) adsorption were also increased by decreasing the particle size of the metal sulfides. Particle sizes were decreased by synt hesis of the metal sulfide in the presence of the particle-size mediating a gent CTAB. The metal sulfides remove ionic mercury from acidic solutions by precipitat ion with the dissolved sulfide forming HgS. In acidic solution there was no evidence of physical or chemical adsorption between Hg(0) and the metal su lfide. The quantity of ionic Hg2+ removal from aqueous solutions is correla ted with the solubility of the metal sulfide. Cu2S was the most soluble met al sulfide tested and thus removed the most ionic mercury from solution by precipitating HgS.