Study on Ion-Exchange Behavior of Cu-CN Complexes.

Abstract

Simultaneous removal and recovery of cyanide and copper ions using a strong-base anion exchange resin are studied on the basis of formation of Cu-CN complexes at high pH in electroplating wastewater containing cyanide and copper ions. Strong-base anion exchange resin particles, of Dowex1X8-50, were contacted with synthetic aqueous solutions. For different molar ratios between cyanide and copper, ion exchange characteristics of copper-cyanide complexes were studied experimentally in a batch reactor. Treatment efficiencies of packed and fluidized beds were compared under the various conditions. Several regenerants, NaSCN, NaCN, NaOH, NaCl, and EDTA, were used to regenerate the exhausted resin. The rates of regeneration and recovery for the various regenerants were estimated and discussed. Free cyanide ion has a lower selectivity than Cu-CN complexes on the anion exchange resin. This could be explained by the size, ion pairing, and site competition of complexes. In turn, Dowex1X8-50 can exchange about three times of the equivalent capacity for cyanide as complex form under the experimental conditions of this study in a batch reactor. The degree of treatment efficiency suggested in this study is; fluidized bed > semi-fluidized bed > packed bed. NaSCN was the best regenerant among regenerants used for the regeneration of resin saturated with Cu-CN complexes.