Recovery elemental sulfur from calcium sulfide prepared by red gypsum in sulfuric acid wastewater treatment

Red gypsum comes from TiO2 production industry by sulfate method, which comes from the low acidic liquid stream treatment using lime or limestone. At present, RG main is treated by outdoor stacking, which induces additional costs and raises environmental concerns. It will be of interest to see the transformations of RG to obtain elemental sulfur and calcium cyclic utilization in the acidic liquid stream treatment. Calcium sulfide was prepared by calcining RG at 900 degrees C for 10 min and pure gypsum at 900 degrees C for 20 min, respectively. The decomposition of RG was easy than pure gypsum because of Fe2O3 catalysis. And srebrodolskite was observed in the samples from RG calcined at 800 to 1100 degrees C, respectively. Hydrogen sulfide was produced when CaS reacted with sulphuric acid wastewater and rod-like gypsum crystals were observed. And then, pellets of elemental sulfur, with 1.5-5 mu m in diameter, were obtained by the H2S oxidation in Fe(III) chelate solution, which achieved elemental sulfur recovery and calcium cyclic utilization.

Automated summary

Red gypsum, a byproduct of the sulfate method in TiO2 production, is currently treated by outdoor stacking, which incurs additional costs and environmental concerns. This study investigates the transformation of red gypsum for the cyclic utilization of elemental sulfur and calcium in acidic liquid stream treatment.