Effect of Technological Parameters on the Electrowinning of Cobalt from Cobalt(II) Chloride Solutions

Abstract

The effect of technological parameters such as current density, temperature, cobalt concentration, and pH of electrolyte solutions on current efficiency and cobalt morphology during the electrowinning of cobalt from a cobalt chloride solution was observed in an electrowinning cell with a capacity of 500 mL. The experimental results revealed that the cathode current efficiency increased either when the cobalt concentration in the electrolyte solution was increased from 14 to 70 g/L, when the pH of the electrolyte solutions was increased from 0.5 to 2, or when the electrolyte temperature was increased from 30 °C to 60 °C. However, the cathode current efficiency decreased when the current density was increased from 0.8 to 8 A/dm2. The highest current efficiency (96%) was obtained at a current density of 0.8 A/dm2 in the electrolyte solution with a cobalt concentration of 70 g/L and at a temperature of 60 °C and a pH of 1.5. The scanning electron microscopy micrographs revealed that the cobalt deposit morphology tended to be homogeneous and more compact at a low current density. However, cobalt deposits with large particle sizes and a tendency to be more porous and incompact were formed in the electrolyte solution with a relatively low cobalt concentration. The cobalt deposit morphology that was formed in the electrolyte solution with a low pH tended to become more porous. Furthermore, when the electrolyte temperature was increased to 60 °C, the cobalt deposit morphology that was formed in electrolyte solutions with a cobalt concentration of 30 g/L changed from a mixed small needle-like and oval shape to a large needle-like shape, whereas the cobalt deposit morphology in electrolyte solutions with a cobalt concentration of 70 g/L changed from a small needle-like shape to a circular and more compact shape.