Anodic slimes formation in copper electrowinning

Abstract

The slime formation in acidic electrolytes of copper with several metallic impurities has been studied. On Pb-Ca-Sn anode surface firstly the formation of PbSO₄ takes place, then, it is transformed in PbO₂, which covers the anode surface. It was experimentally established the formation of a manganese dioxide double layer at the anode. This layer was always composed of a thick external layer of non-adhering and easily removable scales, and of a thin internal layer, which adheres relatively well to the surface of the electrode. It was found that the manganese dioxide present in the slime is of different nature: a non-adhering layer produced by electrolysis (ε-MnO₂) on the PbO₂ surface and a pure chemical precipitate in the solution (β- MnO₂). Lead sulfate was found on the β-MnO₂layer when iron was in the electrolyte. When arsenic or antimony was present in the electrolyte, the slime was lead sulfate and amorphous compounds of those ions. Slime of Chilean electrowinning (EW) plants is also discussed.