Sorption of sulfide on a macroporous, quaternized poly(4-vinyl pyridine) in alkaline medium

A newly available, macroporous anion-exchange resin Reillex™ HPQ, which has about 70% of the pyridine rings quaternized by the addition of methyl groups, has been used in the chloride form for the sorption of sulfide from alkaline aqueous medium. Comparative data on sulfide sorption capacity and kinetics in alkaline media are presented for this new resin and a common anion exchange resin Dowex-1-X8, both used in chloride form. The sulfide sorption capacities of HPQ(Cl⁻¹) and Dowex-1(Cl⁻¹), activated by treatment with mixed NaCl/HCl solution, are found to be 4.8 and 2.5 mmol S/g (dry), respectively, compared to the respective total exchange capacities of 4.6 and 5.6 mEq/g (dry), indicating that sulfide is predominantly sorbed as univalent HS⁻ on HPQ(Cl⁻) and as bivalent S²⁻ on Dowex-1(Cl⁻) this is attributed to the occurrence of nearly 30% of the pyridine sites in HPQ(Cl⁻) in protonated form, contributing to lower pH inside the resin phase as compared to external medium. The chloride/sulfide exchange kinetics, in conditions of particle diffusion control and infinite solution volume, are predicted with good approximation by the Nernst-Planck model. Both the chloride and sulfide counterions taking part in the exchange process diffuse very slowly in the resin, the diffusion coefficients being in the order of 10⁻¹⁰ cm²/s, though chloride ions have relatively higher diffusivity than the sulfide ions.