Application of ferric chloride both as oxidant and complexant to enhance the dissolution of metallic copper

In acidic ferric chloride solutions, Fe3+ is oxidant and Cl− is complexant, which would accelerate the dissolution of metallic copper. Based on the thermodynamic analysis, the dissolution of metallic copper in acidic solutions containing ferric chloride was investigated in detail. The related parameters such as pH, ferric chloride concentration, excess Cl− concentration, stirring speed, solid/liquid ratio and temperature were systematically studied. The dissolution rate of copper increased significantly as the pH value decreased from 2 to 0. The presence of FeCl3 accelerates significantly the dissolution of copper. Increasing stirring speed from 150 to 400 rpm and increasing temperature from 1 to 50 °C enhanced the dissolution rate of copper remarkably. Increasing solid/liquid ratio from 0.001 to 0.004 g/mL decreased the dissolution rate. Excess Cl− concentration, which comes from the addition of NaCl, had a slight effect on the dissolution of metallic copper. The copper dissolution rate in acidic solutions of FeCl3 fits the following conversion-time expression: 1 − 2 3 R − ( 1 − R ) 2 3 = k t , where R is the fraction reacted of copper powder, k is the reaction rate constant, t is the dissolution time. The activation energy was found to be 24.9 kJ/mol and inward diffusion was considered to the rate-controlling step.