ABSTRACT

Selective precipitation is examined here as a technically feasible approach for improving the efficiency for recovering non-ferrous metals from industrial waste effluents in the presence of contaminants such as aluminum, chromium or iron. Precipitation provides probably the lowest cost alternative for the non-selective removal of metals from industrial waste waters to meet EPA standards for effluents. Consideration of the pH dependence of hydroxide precipitation of mixed metal systems such as copper or nickel in the presence of aluminum, chromium or iron would seem to provide an opportunity to conduct staged hydroxide precipitation of the contaminants, aluminum, chromium or iron below about pH 5-6 delaying precipitation of the copper or nickel to a pH above 6. Unfortunately freshly precipitated aluminum, chromium and iron hydroxides provide considerable capacity for adsorption/ion exchange leading to mixed coprecipitates of the trivalent contaminants and the divalent copper or nickel frustrating efficient separations. Recent experimentation with iron precipitated in the presence of selected anionic surfactants in a moderate pH range 3.5-4.5 permitted efficient separation from copper or nickel which remained in solution pending a secondary separation process. 1