Effect of Impurity Ions and Additives in Solution of Copper Electrorefining on the Passivation Behavior of Low-Grade Copper Anode

Cu electrorefining using a low-grade copper anode is desirable from the standpoint of electric power savings. Cu electrolysis was carried out in an unagitated sulfate solution with a low-grade copper anode, and the effect of impurity ions and additives in the solution on the passivation of the anode was investigated. The time when anode passivation firstly occurs shortened significantly in a solution containing 0.596 mol·dm¹³ of Ni²⁺ ions as impurity and shortened somewhat in a solution containing As⁵⁺(0.053 mol·dm¹³) or Bi³⁺(0.0005 mol·dm¹³) ions. Sn²⁺(0.0004 mol·dm¹³) and As³⁺(0.053 mol·dm¹³) ions slightly decreased the time to passivation, but Sb³⁺(0.004 mol·dm¹³) ions did not. The viscosity coefficient of the solution increased when the 0.596 mol·dm¹³ of Ni²⁺ ions were added to the solution, while the diffusion coefficient of Cu²⁺ ions decreased. The compound of the AsSbO or AsBiO system was formed in anode slime when the As⁵⁺(0.053 mol·dm¹³) or Bi³⁺(0.0005 mol·dm¹³) ions were added to the solution, which seemed to increase the compactness of slime. The time to passivation was slightly longer in thiourea-free solution but shortened when the concentration of thiourea was increased from 0.525 to 2.24 mmol·dm¹³. The time to passivation was constant in solutions containing 0 to 1.13 mmol·dm¹³ of Cl¹ ions, but significantly decreased as the concentration of Cl¹ ions increased above 1.13 mmol·dm¹³. Cl¹ ions formed CuCl at the upper area of anode slime, which increased the compactness of slime and promoted the passivation.