Binding of chromium and copper ions from aqueous solutions by shea butter ( Butyrospermum parkii) seed husks

The adsorption of Cu(II) and Cr(III) ions from aqueous solution by shea butter ( Butyrospermum parkii) seed husks has been investigated. The amount of ions adsorbed by the husks was dependent on the contact time, the initial metal ion concentration and temperature. The adsorption isotherms showed distinct features, exhibiting maxima and then minima at critical contact time of about 40 min. The rates of sorption, k, of Cu(II) ions at different temperatures were low, that is not greater than 10.4 × 10 −3 min −1 with half-times, t 1 2 ranging from 67 to 693 min. The effects of agitation and counter-ion on the sorption process were investigated. Sorption was enhanced by a factor of 2 by agitation but was independent of its speed. For the counter-ions, sorption of Cu(II) ion from aqueous solution of different salts was in the order CuCI 2 > CuSO 4 > Cu(NO 3) 2 at low substrate-ion contact times. Addition of isopropanol to aqueous solutions of Cu(II) and Cr(III) ions enhanced the amount of Cu(II) ion adsorbed by the seed husks but depressed that of the Cr(III) ion. Carboxymethylation of the seed husk reduced its adsorptive capacity for Cr(III) ion by 60%.