PNNL

Abstract

Chromate (CrVI) reduction by sulfide was conducted in anaerobic batch experimental systems. The molar ratio of the reduced CrVI to the oxidized S-II was 1:1.5 during the reaction, suggesting that the product of sulfide oxidation was elemental sulfur. Under the anaerobic condition, the reaction was pseudo first order initially with respect to CrVI, but the rate was dramatically accelerated at the later stage of the reaction. The rate acceleration was due to catalysis by elemental sulfur nanoparticles; dissolved species such as monomeric elemental sulfur and polysulfides appeared to be ineffective catalysts. Elemental sulfur nanoparticles were capable of adsorbing sulfide and such adsorbed sulfide exhibited much higher reactivity toward CrVI reduction than the aqueous-phase sulfide, resulting in the observed rate acceleration.