Green Electrorefining of Crude Lead with High-Quality Deposits in an Additive-Assisted Methanesulfonic Acid System
The conventional electrorefining process of crude lead (Pb)─employing a bone glue (BG)- and calcium lignosulfonate (CL)-synergistically assisted fluosilicic acid (H2SiF6) system─suffers the undesired environment burden caused by the high saturated vapor pressure and low stability of H2SiF6. Herein, we propose an additive-assisted methanesulfonic acid (MSA) system for green and efficient electrorefining of crude Pb based on the low volatility and high stability of MSA. Combinations of MSA with additives are evaluated and screened using photographic images, SEM observations, XRD, white light interference, etc. The electrochemical analysis of cyclic voltammetry and chronoamperometry elucidates the Pb deposition behavior in the Lugalvan BNO12-assisted MSA system, in which a three-dimensional nucleation model is applicable. Using MSA as the solvent and β-naphthol ethoxylate (Lugalvan BNO12) as the assisted additive, the bench-scale operation of crude Pb electrorefining experimentally achieves an electric energy requirement (W) of 87 kWhe/t Pb and a cathodic current efficiency (η) of 99.6%. This is very competitive with the W of 120 kWhe/t Pb and η of 95.0% for the BG-CL-assisted H2SiF6 system. Also, the bench-scale operation obtains a plat and dense deposit sample with a Pb purity of >99.99%. The distribution behavior of elements shows that most of the Pb element is recovered in the form of the cathodic Pb, elements Sn, Zn, and Fe mainly accumulate in the electrolyte, and elements As, Sb, Bi, Ag, and Cu remain in the anode slime. This work opens new directions for more technically and economically feasible Pb electrorefining.
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