Emulsion liquid membrane extraction of silver from photographic waste using CYANEX 302 as the mobile carrier

Abstract

The recovery of precious metals such as silver from photographic wastes is required in order to save raw materials and to protect the environment from hazardous compounds especially heavy metals. Several technologies have been used such as precipitation, electrolysis, and ion exchange processes which offer some advantages as well as drawbacks over others. Recently, emulsion liquid membrane extraction has been recognized to be a potential process for industrial wastes treatment and recovery of heavy metals. This process has the ability to selectively separate and rapidly concentrate metals through its very thin layer liquid membrane having large interfacial area. An attempt was made to recover silver from liquid photographic wastes using Cyanex 302 as a mobile carrier. The important variables affecting the emulsion liquid membrane (ELM) extraction process including extraction time, surfactant concentration, carrier concentration, stripping agent solution, level of agitation and the phase treatment ratio between the emulsion and feed phase were investigated. The results showed that Cyanex 302 is more than 80% selective towards silver compared to other metals in the photographic waste. The highest silver extraction was obtained by using 0.05 M Cyanex 302, 3% (w/v) Span 80, 250 rpm stirring speed, 1.0 M thiourea in 1.0 M H2SO4 as stripping agent, 1:5 of treat ratio, and kerosene as the diluent.