Anodic dissolution of electronegative component during the process of metal codeposition in a flow-through porous cathode

Abstract

Possible magnitude of the electronegative component (M₂) dissolution during a two metal (M₁ and M₂) codeposition inside a porous electrode is studied theoretically (by modeling) and experimentally. Model calculations based on the substituting of the pure metal (M₂) dissolution rate for its selective dissolution rate from the alloy gave an overestimated evaluation of the effect. The dissolution effect is shown to be small when the porous electrode is filled up with metal deposited from a solution large single portion; however, it increased significantly when the solution is divided into smaller portions. Experimental studies of Ag and Cu deposition dynamics in thiosulfate solution showed that the turning from a direct-flow to a circulation mode results in significant increase in the Cu mass and widening its deposition zone up to the porous electrode entire thickness. When the 2nd and 3rd portions of the solution are subjected to electrolysis, the solution is temporarily enriched with Cu ions, which evidences the copper partial dissolution whose scale is close to calculated estimates. The explanation of specific features of Cu dissolution in repeated cycles of the metal recovery was suggested and experimentally proved.