One-step direct desulfurization of cuprous sulfide for copper recovery via electrolysis in deep eutectic solvent

Abstract

Cuprous sulfide (Cu2S) is the main composition of chalcocite and widely used in the catalyst. Deep eutectic solvents (DESs) are eco-friendly electrolytes for the separation and recycling of metals and their compounds in addition to environmental protection. In this work, choline chloride-ethylene glycol (ChCl-EG) DES is innovatively used towards one-step desulfurize cuprous sulfide to recycle copper for the first time. Cyclic voltammetry is employed to investigate the effect of initial potential, scan rate and temperature on the electrochemical behavior of Cu(I) in ChCl-EG DES. The effect of essential parameters (applied voltage, temperature and NH4HCO3 ratio) on the chemical composition and microstructure of the product are discussed. Pure polycrystalline nano-Cu with an average size of ≈16.15 nm can be obtained with the current efficiency of 96.58% at the optimized parameters of 2.5 V, 353 K, 40% NH4HCO3 and 10 h. The structure of Ch+ is unbroken and the main existence form of Cu(I) is CuCl2− in the electrolyte. Mechanism analysis indicates the reduction of Cu2S to Cu is step-by-step with the feasible process of Cu2S→Cu1.96S→Cu7.2S4…→Cu. The S element is possibly converted and stabilized as the sulfate (SO42−) in the DES. All these findings are expected to provide new feasibility for the direct extraction and recycling of Cu from Cu2S with high current efficiency and less hazardous.