銅の電解精製とアノード不動態化

Abstract

In the process of electrorefining of copper, application of higher current density increases the tendency of anode passivation. The passivation disrupts the sound operation of the electrorefining process, reducing the current efficiency and the quality of copper deposited on the cathode. Therefore, anode passivation should be avoided in industrial electrolytic cells. Anode passivation is attributed to the precipitation of copper sulfate, which is saturated locally in the vicinity of the anode surface. When a copper anode contains high concentrations of insoluble impurities that form slime on the anode surface, the tendency of anode passivation increases. Because e-waste often contains such elements that induce anode passivation as well as the harmful elements from the concentrate, the operation of the electrorefining process becomes difficult when the feeding ratio of secondary materials (scraps) is increased. To promote the recycling of metals and reduce energy consumpution in the process, it is essential to develop a passivationprevention technology for low-grade copper anodes. This article outlines the physicochemical basis of anode passivation and reviews earlier research with a focus on experimental techniques. Past research on anode passivation of pure Cu anodes, which was carried out to understand the precipitation of copper sulfate quantitatively, is also reviewed to explain the relationship between passivation and current density.

Effect of Impurity Ions and Additives in Solution of Copper Electrorefining on the Passivation Behavior of Low-Grade Copper Anode

“…As a result of this situation, the concentration of impurities included in crude Cu produced by pyrometallurgy has been increasing. 1,2) Electrorefining of crude Cu obtained by pyrometallurgy produces Cu with a purity of above 99.99 mass%, which is used for electrical wire and rolled products. The anode for this electrorefining is usually crude Cu with a purity above 99 mass%.…”

Fundamental Application of Basket Electrolysis Method for Black-Copper Anode

“…Their average compositions (Table 1(a)) were similar to that of black-copper in industrial use. 3,33,34) For comparison, a Cu alloy block (10 mm © 10 mm © 5 mm, 4.00 g) with the same composition as the shot samples, and a Ag-free Cu alloy in the same shot form (Table 1(b)) were also used. The average compositions and variations were determined four times for three shot samples by chemical analysis, i.e., dissolution in aqua regia and then inductively coupled plasma atomic emission spectroscopy (Spectro Arcos, Spectro Analytical Instruments, Kleve, Germany) measurements.…”

“…This passivation makes treatment of black-copper anodes via conventional processes difficult. 3,4) Among impurity elements, Ag significantly promotes anode passivation. The Ag contents of crude copper is carefully controlled at 10 750 ppm, 5) and it has been reported that crude copper anodes containing Ag at 2600 ppm hardly work because of passivation.…”