Clean and efficient preparation of metallic bismuth from methane-sulfonate electrolyte in the membrane electrolysis cell

As a prevailing hydrometallurgical extraction system for bismuth sulfide concentrate, the acidic chloride solution has superior applicability to raw materials and high recovery ratio of metallic bismuth. Nevertheless, it has disadvantages of being easily volatile and strongly corrosive, as well as large energy consumption and poor deposition morphology during chloride electrolysis. Methane-sulfonic acid (MSA) solution is widely considered as the next generation of green hydrometallurgical system, due to its excellent physicochemical properties such as high metal salts solubility, low volatility, and biodegradability. In this study, membrane electrolysis technique was adopted based on the acidic bismuth methane-sulfonate leaching solution, and the influence of electrolyte composition, cathode current density (CCD), and temperature parameters on the bismuth conversion ratio (BCR) and deposition rate (BDR), techno-economic indicators and cathodic bismuth morphology were studied. The results show that the CCD affects the deposits morphology significantly, and the bismuth metal is partially dark and composed of loose ellipsoidal particles at high current density. Under the optimal conditions (70 g/L Bi3+ ions, 5 g/L Fe2+ ions, 110 g/L MSA, 35 °C, 180 A/m2), high-purity metallic bismuth (Bi 99.97 %) with silver-white luster is obtained. The BCR and BDR are 9.43 % and 0.46 kg/(h·m2), respectively. The cathodic current efficiency (CCE) reaches over 98 %, and specific energy consumption (SEC) is less than 715 kWh/t Bi. Compared with the traditional chloride system, the MSA-based membrane electrolysis medium has advantages of environmental friendliness, low occupational risks, low carbon and energy consumption, and can thus provide a sustainable green solution for bismuth hydrometallurgy.