Kinetics of Ion Removal from an Iron‐Rich Industrial Coproduct: II. Sulfate

Abstract

AbstractAn iron‐rich material (IRM) contained copious quantities of salts, including Cl and SO4. A previous study on Cl removal hypothesized that SO4 played a major role in the chemistry of the IRM. Therefore, this study investigated the kinetics of SO4 removal from the IRM, which had a point of zero charge similar to those of some tropical soils. Stirred‐flow (SF) and column studies showed that SO4 removal was a time‐dependent chemical reaction(s). The SF technique facilitated modeling of the chemical kinetics of SO4 removal by providing a uniformly mixed system. The SO4 removal mechanism from the IRM to the ambient solution, in the SF system, was a zero‐order oxidation‐dissolution reaction of the Fe‐sulfide present as a minor constituent in the IRM. The computed value of the rate‐constant was 0.043 µmol min−1. In the column studies, the newly dissolved SO4 was present in the effluent, and was adsorbed on the IRM through a ligand (OH−) exchange mechanism. Calcium hydroxide dissolution, together with the SO4 adsorption, resulted in a pH increase with pore‐volume.