Metallic bismuth morphology and microstructure control during the membrane electro-deposition in methane-sulfonic acid system

Abstract

As the mainstream process for bismuth hydrometallurgical extraction, the “chloride leaching – membrane electro-deposition” technology faces disadvantages such as strong volatility of reaction solution, serious occupational health harms, and unsatisfactory morphology of metallic bismuth. In this paper, the green methane-sulfonic acid (MSA) is proposed as hydrometallurgical medium to replace conventional chloride solution. During the bismuth membrane electro-deposition, the effects of additive type and its concentration, temperature, cathode current density, and electrolyte composition on the morphology and microstructure of cathodic bismuth are systematically investigated. Compared to sodium dodecyl sulfate, Trilon M, Lugalvan BNO 12, the addition of calcium lignosulfonate (CL) significantly suppressed the formation of “triangular cone” shaped bismuth grains, and therefore the surface smoothness of cathodic bismuth was greatly improved. Potentiodynamic polarization reveals that CL concentration increasing induced the negative shift of deposition potential (φdep), and this contributed to obtain fine-grained bismuth deposits. The current density and bismuth concentration significantly affected the surface morphology of bismuth deposits. At a current density of 180 A/m2, flat and dense bismuth deposit (99.97% purity) could be produced from 0.5 g/L CL-assisted electrolyte at 35 °C for 8 h. In contrast to the electro-deposition method in chloride solution, the proposed process has green (less volatility and biodegradability), efficient (current efficiency 98.80 %) and energy-saving (electric energy consumption 712.53 kWh/t Bi) features, and has important application in the hydrometallurgical treatment of bismuth-containing materials.