Recovery and Concentration of Precious Metals from Strong Acidic Wastewater

Generally, trace precious metals remaining in wastewaters generated from the refining process of precious metals are not recovered, due to a relatively high processing cost as well as various technical problems. Recovery of precious metals from wastewaters is very important for the conservation of resources and the protection of environment. However, wastewaters containing a large amount of ammonium ion (NH4 þ) cannot be treated by general neutralization operation, due to formation of metal ammine complexes with increasing pH. In this study, the possibility of recovering precious metals and other valuable metals from wastewaters by various traditional metallurgical processes such as cementation, neutralization and reduction, were investigated. A recovery of 99% Copper (Cu), 96% Palladium (Pd), and 85% Gold (Au) by cementation using Iron (Fe) powder, and 99.6% Cu, 99.5% Pd by cementation using Aluminum (Al) powder was achieved. However, complete recovery of all valuable metals by a one-step cementation process was not possible. On the other hand, precious metals and other valuable metals including Copper and Indium, etc., were precipitated by combining neutralization, deammoniation and reduction processes. Results showed that the recovery of Platinum (Pt) in the reduction process was improved by adding deammoniation step. Finally, precious metals are concentrated in the crude copper metal by fusion process. The recovery of Au, Ag, Pd was more than 91%, and that of Pt was about 71%. [doi:10.2320/matertrans.M2010432]