Production of H_2S with a Novel Short-Process for the Removal of Heavy Metals in Acidic Effluents from Smelting Flue-Gas Scrubbing Systems

摘要

Direct sulfidation using a high concentration of H_2S (HC-H_2S) has shown potential for heavy metals removal in various acidic effluents. However, the lack of a smooth method for producing HC-H_2S is a critical challenge. Herein, a novel short-process hydrolysis method was developed for the on-site production of HC-H_2S. Near-perfect 100% efficiency and selectivity were obtained via CS_2 hydrolysis over the ZrO_2-based catalyst. Meanwhile, no apparent residual sulfur/sulfate poisoning was detected, which guaranteed long-term operation. The coexistence of CO_2 in the products had a negligible effect on the complete hydrolysis of CS_2. H_2S production followed a sequential hydrolysis pathway, with the reactions for CS_2 adsorption and dissociation being the rate-determining steps. The energy balance indicated that HC-H_2S production was a mildly exothermic reaction, and the heat energy could be maintained at self-balance with approximately 80% heat recovery. The batch sulfidation efficiencies for As(Ⅲ), Hg(Ⅱ), Pb(Ⅱ), and Cd(Ⅱ) removal were over 99.9%, following the solubilities (K_(sp)) of the corresponding metal sulfides. CO_2 in the mixed gas produced by CS_2 hydrolysis did not affect heavy metals sulfidation due to the presence of abundant H~+. Finally, a pilot-scale experiment successfully demonstrated the practical effects. Therefore, this novel on-site HC-H_2S production method adequately achieved heavy metals removal requirements in acidic effluents.