Effect of Additives and Cl⁻ Ions on the Physical and Chemical Properties of Cobalt Deposits Obtained by Electrowinning

The optimization of the cobalt electrowinning process is crucial to enhance the quality of metallic deposits, as cobalt plays a fundamental role in the manufacturing of high-tech materials. Thus, the effect of the additives sodium lauryl sulfate (SLS), boric acid, and Cl⁻ ions on the physical and chemical properties of cobalt deposits obtained by electrowinning are scarce in the literature. The present study investigated the effect of additive concentrations on current efficiency (CE), specific energy consumption (SEC), and the physical and chemical properties of cobalt deposits (crystalline phases, grain and crystallite sizes, morphology, purity, and microhardness) produced through electrodeposition tests in presence of a cobalt sulfate solution at 200 A m⁻², 60 °C, and pH 4. The results indicated that the presence of 0.05 g L⁻¹ of SLS in the solution led to the best values for CE (95.5 pct) and SEC (1.80 kWh kg⁻¹), as well as the production of uniform deposits. Cracks were identified in the cross-sectional area of the metallic deposits under all evaluated conditions, with the detection of oxygen in these areas, except for Cl⁻ ions. Higher concentrations of SLS and boric acid resulted in the production of deposits with low microhardness and less fragility, attributed to the increased of crystallite and grain sizes. The predominant crystalline phase for all deposits was hexagonal close-packed (HCP), but the presence of SLS and Cl⁻ ions led to the rise of significant percentages of the face-centered cubic (FCC) phase. Furthermore, the increase of Cl⁻ ions concentration led to an increase of residual deformations in the crystalline structure of cobalt deposits, while the increase of SLS and boric acid concentrations led to a decrease of these residual deformations.