Revealing electrochemical behavior for high-quality and efficient bismuth deposition

Abstract

Methanesulfonic acid (MSA, CH3SO3H) emerges as a sustainable and stable medium for membrane-assisted electrodeposition in bismuth (Bi) recovery. The incorporation of calcium lignosulfonate (CL) within the MSA-based system markedly improves the electrodeposition quality and efficiency of Bi, although the exact electrochemical mechanism and kinetics of CL's influence remains unclear and warrant further investigation. Our study focuses on the impact of CL on the electrochemical behavior through quantum chemical calculations, molecular dynamics simulations, electrochemical analyses and in-situ electrochemical optical microscopy. Within the primary solvation shell, Bi3+ associates closely with water and CH3SO3− ions, while CL is embedded in the secondary shell, forming a complex interaction network with Bi3+, H2O, and CH3SO3−, culminating in a solvation complex of Bi(CH3SO3)1.68·0.02CL·6·72H2O. This complex disrupts intra-solution hydrogen bonding, reduces water activity and undesirable side reactions, and thus promotes the electrodeposition efficiency. At the cathode's double electric layer, de-solvated Bi(CH3SO3)2+·nH2O ions are preferentially discharged and reduced. The pronounced physical adsorption of CL at the interface facilitates a three-dimensional electro-crystallization nucleation and growth process, yielding a uniform, smooth, and compact Bi deposit. Our findings not only extend the electrochemical understanding but also provide practical insights for optimizing Bi recovery in the CL-MSA system, with implications for the electrochemical recovery of other metals like lead and tin.