Influence of Electrolyte on an Energy-Saving Copper Recycling Process Using Ammoniacal Alkaline Solutions

In order to make the energy-saving copper recycling process more economical by reducing the power consumption during copper electrowinning, the influence of the bath composition on the saturated concentration of cuprous ion, the electric conductivity, the cathodic current efficiency and the power consumption were studied in an ammonia-ammonium chloride-cuprous/cupric ion solution. The saturated cuprous ion concentration increased with the ammonia and ammonium chloride concentrations. The electric conductivity of the solution increased in proportion to the ammonium chloride concentration, because ammonium chloride acts as a supporting electrolyte. When the ammonia concentration increased from 3 to 10 kmolm3 or when the cuprous ion concentration increased from 0.5 to 2 kmolm3, the cathodic current efficiency decreased by 5–10 % at a current density higher than 500Am2. This results from an increase in the cupric ion concentration formed by the unavoidable oxidation and the disproportionation of cuprous ions. The low current efficiency, however, had little influence on the power consumption compared to the influence of the electric conductivity that was the dominant factor determining the power consumption. Actually, when the concentration of ammonium chloride increased from 2 to 4 kmolm3, because of its function of increasing the electric conductivity of the solution, the power consumption was reduced by half. Based on this study, a suitable bath composition for the energy-saving copper recycling process was determined to be 3–10 kmolm3 ammonia, 4–5 kmolm3 ammonium chloride and 1–2 kmolm3 cuprous ions. [doi:10.2320/matertrans.47.2871