Pulse electrodeposition as a new approach in electrowinning of high purity cobalt from WC–Co scraps. Part I: The effect of frequency and duty cycle

• Obtaining of pure cobalt deposit by pulse electrodeposition without any additives.
• Obtaining optimum conditions for electrochemical dissolving the WC–Co scraps in an acidic solution.
• Obtaining a dense and ductile electrodeposit which can be easily detached from the surface of cathode.

The high price of cobalt is the reason for the necessity of its recovery from recycled cutting tools, catalysts and so forth. In this research, the effect of frequency and duty cycle in pulse electrowinning of cobalt from WC–Co scraps has been studied. The scraps was first dissolved in a solution containing 1 N hydrochloric acid and 0.1 M citric acid in anodic potential in the range of 0.05–0.3 VAg/AgCl so that a solution with 22 g L−1 cobalt was acquired. Electrodeposition was performed on a stainless steel cathode in frequencies of 30, 50, 70, 100 and 135 Hz; duty cycles of 10%, 30% and 50%; and peak current density of 250 A m−2; and electrolyte temperature of 60 °C. The surface of the deposits was observed with SEM and its purity was measured using the ICP method. The studies showed that increased frequency reduces the crystal size and the purity of the deposit increases up to 99.1 wt% under the same conditions. Increasing the duty cycle raises the cobalt crystal size and the highest purity of deposit is obtained at a duty cycle of 30%. The optimum conditions in terms of economics and purity involve electrodeposition at a frequency of 70 Hz and duty cycle of 30%, where deposits with a purity of 94.13 wt% are obtainable.