KINETICS OF ION REMOVAL FROM AN IRON-RICH INDUSTRIAL COPRODUCT .2. SULFATE

An iron-rich material (IRM) contained copious quantities of salts, inc luding Cl and SO4 A previous study on Cl removal hypothesized that SO4 played a major role in the chemistry of the IRM. Therefore, this stud y investigated the kinetics of SO4 removal from the IRM, which had a p oint of zero charge similar to those of some tropical soils. Stirred-h ow (SF) and column studies showed that SO4 removal was a time-dependen t chemical reaction(s). The SF technique facilitated modeling of the c hemical kinetics of SO4 removal by providing a uniformly mixed system. The SO4 removal mechanism from the IRM to the ambient solution, in th e 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 mu mol 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 hydroxi de dissolution, together with the SO4 adsorption, resulted in a pH inc rease with pore-volume.