濃厚塩化カルシウム水溶液からの鉛電析

Abstract

CaCl₂ is a low-toxic, inexpensive reagent that dissolves in large amounts in water to form highly concentrated aqueous solutions, or hydrate melts electrolyte. In this work, it was investigated that the concentrated CaCl₂ aqueous solutions (aq) as novel lead (Pb) electrodeposition baths. While PbCl₂ is poorly soluble in water at room temperature, PbCl₂ dissolved up to 0.452 mol kg⁻¹ ([Pb(II)] = 93.7 g kg⁻¹) by the formation of PbCl₄²⁻ complexes in the concentrated CaCl₂ aq due to its high Cl⁻ activity. Electrochemical measurements confirmed that the apparent exchange current density and the limiting current density of Pb electrodeposition decreased with increasing CaCl₂ concentration. Since the diffusion of Pb(II) species was limited due to the high viscosity and ionic strength of the solution, agitation was effective in improving ion transport and electrodeposition rate. The presence of chloride ions in Pb electrolysis is usually detrimental due to the low solubility of PbCl₂, however, the highly concentrated CaCl₂ solution can be a potential candidate electrolyte for PbCl₂-based electrolytic processes.