Electrolytic production of Cu-Ni alloys in CaCl₂-Cu₂S-NiS molten salt

An alternative metal/alloy production method, known as direct electrochemical reduction (DER), was introduced for the fabrication of CuNi alloys from mixed sulfides (Cu₂S, NiS) under both galvanostatic and potentiostatic conditions. The influences of the process parameters (e.g., cell voltage and current) on the compositions of the reduced compounds were investigated to yield industrially desirable alloys, namely, CuNi10, CuNi20, and CuNi30. The electrochemical behaviors of Cu₂S and NiS in CaCl₂ melt were examined at a temperature of 1200 °C via cyclic voltammetry (CV). Based on the CV results, the cathodic reduction of Cu₂S occurred in one step and cathodic reductions of NiS occurred in two steps, i.e., Cu₂S⇒Cu for copper reduction and NiS⇒Ni₃S₂ ⇒Ni for nickel reduction. Galvanostatic studies revealed that it was possible to fabricate high-purity CuNi10 alloys containing a maximum sulfur content of 320×10⁻⁶ via electrolysis at 10 A for 15 min. Scanning electron microscopy along with energy-dispersive X-ray spectrometry and optical emission spectroscopy (OES) examinations showed that it was possible to fabricate CuNi alloys of preferred compositions and with low levels of impurities, i.e., less than 60×10⁻⁶ sulfur, via DER at 2.5 V for 15 min.