Sorption of iron and zinc ions from non-aqueous solution by shea butter ( Butyrospermum parkii) seed husks

Abstract

Studies have been conducted on the equilibrium and dynamic adsorption of Fe(II) and Zn(II) ions from aqueous and non-aqueous (methanol-water and isopropanol-water) solutions of the ions by shea butter ( Butyrospermum parkii) seed husks. The equilibrium sorption of Fe(II) and Zn(II) ions at 30°C was enhanced by methanol in a 50% (v/v) mixture of methanol-water solution of the ions, but depressed by the same volume mixture of isopropanol-water. The rate of equilibrium sorption, k, for Fe(II) ion from 50% (v/v) isopropanol-water and methanol-water mixtures showed a negative temperature dependence in the range 30–50°C, yielding values which were not higher than 1·35 × 10 −3 min −1 at 30°C in the latter mixture and a corresponding t 1/2 of 513 min. For Zn(II) ion, k showed a positive temperature dependence in the solvent mixtures with values of up to 3·0 × 10 −3 min −1 at 70°C in 50% (v/v) isopropanol-water mixture. The dynamic sorption of Zn(II) and Fe(II) ions from aqueous solutions at 30°C increased with initial metal ion concentration in the range 50–100 ppm, yielding values for the amount of ion sorbed of 2·42 and 2·44 mg/g sorbent, respectively, at 100 ppm. The values for dynamic sorption of Fe(II) and Zn(II) ions at 30°C from aqueous solution and from the non-aqueous solutions were comparable. However, the values for dynamic sorption of Fe(II) and Zn(II) ions from the same solutions at 30°C were much higher than the ones for equilibrium sorption by factors of up to 2 and 15, respectively.