MEMBRANE EXTRACTION OF SILVER BY DI(2-ETHYLHEXYL)DITHIOPHOSPHORIC ACID

A membrane-based process for silver recovery from waste solutions was derived. Silver diffused from the feed solution through the supported liquid membrane containing di(2-ethylhexyl)dithiophosphoric acid (DTPA) as a carrier into the receiver solution, which contained thiourea at a low pH. Silver transfer rate and diffusion coefficient in the membrane were found to be up to 1.5 X 10(-9) mol/cm2-sec and 2 X 10(-6) cm2/sec, respectively. The membranes used demonstrated an ability to work in contact with waste solutions from silver reclamation eluants until silver had been transferred even against a very high concentration gradient. The dependencies of silver transfer rate on such factors as pH in the receiver and feed phases, DTPA and thiourea concentrations, were investigated.