陽極スライム中のCu₂O相起源について

銅陽極不働態化の研究 (第2報)

抄録

An electrochemical technique, which has been established previously, was adopted to investigate the origin of a Cu₂O phase often detected in the anode residues in copper electrorefining.
It has been found that a Cu₂O phase in the slime layer originated from the surface of a corroding anode. Therefore, when oxygen content increases in the copper anode, an amount of Cu₂O entering the slime layer correspondingly increases; thus making it thicker. This causes the mass transport of Cu²⁺ ions from the surface of a corroding copper anode to be more restrictive, and, in turn, the tendency of the anode to passivate increases.
Material balance calculations have shown that about 3 to 5% of Cu₂O in the anode enter the slime layers when a large variety of copper anode samples were anodically dissolved under the nominal testing conditions. This ratio was observed to further increase to about 8% when one particular anode sample contained 7300 ppm oxygen.
A Cu₂O phase present in a layer of anode slimes, when contacted with a sufficient amount of oxidizing agent such as dissolved oxygen, is expected to dissolve actively according to the chemical reaction,
Cu₂O+2H₂SO₄+1/2O₂→2CuSO₄+2H₂O (ΔG°=-47.3kcal/mol)
The addition of a small amount of H₂O₂ to Cu electrolyte increases the oxidizing effect, which agrees with the observed fact that the tendency of anodes to passivate dramatically decreases by this addition as well as by sparging O₂ gas in the electrolyte.