ABSTRACT
A novel metal cyanide separation technique has successfully combined a gas membrane and an ion exchanger to recover the metal and cyanide content of metal cyanide-bearing wastewaters. These wastewaters have an alkaline pH generally above and under these conditions cyanide ions bind the metal to form complex anions such as Zn(CN)42- and Cd(CN)42-. This chapter focuses on some operating problems observed in practical application of the process to real metal cyanide rinsewater. The synthetic metal cyanide solutions were made from analytical grade reagents. Sodium cyanide and cuprous cyanide solid were dried in the oven at a temperature of 120°C and then stored in the desiccator. Solution containing copper cyanide complexes, produced stable cuprous cyanide precipitates upon acidification. Indeed the precipitation of CuCN is the basis of quantitative analysis for copper in the literature on cyanides in mineral extraction. The pH dependence and mass transfer data supported the suspicion that hydrogen cyanide was formed in the reaction rather than cyanogen.
