Removal of copper and silver from dilute aqueous solutions using mercaptoacetimide of poly(ethyleneimine) and poly(propyleneimine)

Abstract

Two new polymercaptans, poly(ethylene mercaptoacetimide) and poly(propylene mercaptoacetimide), have been prepared by reacting mercaptoacetyl chloride with poly(ethyleneimine) and poly(propyleneimine), yielding resins with high redox capacities, 8.14 and 7.08 meq/g, respectively. The resins have high copper removal capacities — 238 mg/g and 206 mg/g, respectively — in good agreement with theie redox capacities and have extraordinarily high silver removal capacities — 1430 mg/g and 1409 mg/g, respectively — which are even higher than the redox capacities, indicating that other sorption processes, in addition to the mercaptyl redox reaction, take part in the removal of silver. Both Cu(II) and Ag(I) are reduced by the mercaptyl resins, the former to Cu(I) and the latter to Ag(0). The sorbed Cu(I) is easily removed by stripping with dilute HCl and the resulting oxidized form resins are reduced with 10% aqueous bisulfite for a complete redox cycle. The resins are resistent to hydrolysis in dilute HCl media at ambient temperature to permit stripping with dilute HCl. The sorbed silver, which is in the metallic state, is however removed only with hot nitric acid, which also decomposes the resins. Ag(I) has much faster sorption kinetics compared with Cu(II), the sorption being particle-diffusion controlled in both cases.