Kinetics of Ion Removal from an Iron-Rich Industrial Coproduct: II. Sulfate
1994
Salingar, Yigal | Sparks, Donald L. | Pesek, John D.
An 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.
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