Synthesis and hydrolysis mechanism of calcium sulfide for H2S production from gypsum waste

Abstract

The copper smelting industry generates significant gypsum waste, primarily composed of calcium sulfate (CaSO₄), which can be utilized as a sulfur source for hydrogen sulfide (H₂S) production. This study explores an optimized process for H₂S generation via hydrolysis of calcium sulfide (CaS), produced by vacuum carbothermal reduction of gypsum. The results show that: 1) CaSO₄ is reduced to CaS under vacuum carbothermal conditions, and subsequent hydrolysis efficiently produces H₂S; 2) key parameters, including reduction temperature, carbon content, and recovery time, significantly influence CaS yield; 3) under optimized conditions (hydrolysis temperature, reaction time, and solid-liquid ratio), H₂S concentrations exceeded 8000 ppm, and high-purity H₂S gas was achieved, meeting industrial requirements for further processing. Thermodynamic analysis and characterization of reaction intermediates provided insights into the underlying mechanisms, highlighting the critical role of temperature and phase composition in optimizing H₂S production. Kinetic analysis further clarified that the hydrolysis process follows a diffusion-controlled mechanism, with the temperature dependence of the reaction rate constant (k) aligning with the Arrhenius equation. This optimized approach offers a sustainable pathway for utilizing gypsum from copper smelting, contributing to sulfur resource recovery, waste reduction, and high-purity H₂S production for industrial applications.