Nano Sulfur-Coated Diatomite for Enhanced Chromate Removal by Sulfide Reduction

Site remediation of chromate-contaminated soil and groundwater by reductive immobilization desires that the system's reaction kinetics be substantially improved especially when the media's pH is high. The objectives of the current study were to prepare a sulfur-coated diatomite catalyst and examine its capability in catalyzing chromate reduction by sulfide in the pH domain of 8-10. Results showed that nano sulfur particles can be readily coated on an otherwise hydrophilic diatomite surface post sequential treatments of acid and base cleaning and cetyl trimethyl ammonium bromide, by mixing the modified dolomite in a colloidal solution of nano-sulfur particles generated through an in situ reaction of thiosulfate and HCI. Sulfur-coated diatomite thus synthesized was not able to reduce chromate, but could improve the reaction kinetics of chromate-sulfide at pH 8-9, although only a limited improvement was observed at pH 10. Systems with higher loading rates of sulfur coated diatomite also had faster reaction kinetics. Two potential mechanisms that involved either sulfide-adsorbed sulfur particles on the diatomite surface and/or polysulfide formation due to an interfacial chemical reaction of the coated-elemental sulfur and sulfide in solution were invoked to interpret the observed phenomena. Findings of this study have significant implications for in situ reductive immobilization by the sulfide of chromate-contaminated sites, particularly those having slow reaction rates due to an elevated pH.