Continuous electrowinning of nickel from dilute sulfate solutions

Significant amounts of nickel products used in different chemical processes and general applications leave them a valuable source of nickel at the end-of-life. Production of nickel from secondary sources is generally performed through hydro-electrometallurgical methods. The resulting solutions from treatment of secondary nickeliferous resources are generally of low Ni concentration and electrowinning of them is challenging, particularly since Ni concentration in commercial operations is usually more than 80 g/L. In this paper, the continuous electrowinning of nickel from dilute sulfate solutions has been investigated. The effects of four variables of temperature, specific flow rate of electrolyte, current density, and nickel concentration on current efficiency and specific energy consumption were studied by a two-level full factorial design. From the statistical analysis of the results, it was found that current efficiency increases by rising all variables, while specific energy consumption decreases with specific flow rate of electrolyte, current density, and nickel concentration. By using the obtained statistical models, the optimum conditions to achieve a nickel deposit with high current efficiency as well as lowest energy consumption are determined to be 55 °C of temperature, 3 A/dm2 of current density, 3 h−1 of electrolyte specific flow rate, and 30 g/L of nickel concentration.