Treatment of electroplating rinse solution by continuous membrane extraction and diffusion dialysis

This paper studies the recovery and concentration of Zn2+ and Cu2+ metal io ns from industrial rinse water containing a mixture of Zn2+, Cu2+, Ca2+, Mg 2+, K+, and Na+ salts. Transport and separation experiments were performed in a continuous membrane extraction (CME) system, i.e. in the membrane syst em composed of two contactors with a cation-exchange polymer membrane (Neos epta CMX) and an organic liquid (liquid membrane) circulating between. The organic solution was composed of kerosene and di-(2-ethylhexyl)-phosphoric acid or salicylaldoxyoxime (Acorga P-50) as the active extractant/carrier. The feed solution has been taken from a rinsing tank working in an industri al electroplating plant. Sulfuric acid (1 M) was applied as the stripping m edium for metal ions. The total flux of target metals (Zn2+ and Cu2+) in th e MI-IS with Acorga P-50 or D2EHPA was 97.1% and 71.4%, respectively. The p roduct of the CME process can be further de-acidified by diffusion dialysis with the use of an anion-exchange membrane (Neosepta AFN-7). The coefficie nts of separation, enrichment, and up-hill transport characteristics indica te that the CME system with Acorga P-50 can be considered a part of a techn ology for the efficient recovery of Cu2+ and Zn2+ in metal finishing plants .