Hydrogen reduction of spent copper electrolyte

The recovery of copper powder and the removal of arsenic from spent copper electrolyte by means of hydrogen reduction aimed at purifying the spent copper electrolyte were studied. About 90% of the copper in the electrolyte could be recovered in the form of pure copper powder after 20 min reduction at 180° at a hydrogen pressure of 20 kg cm^?2 (2.0 MPa). An induction period, due to slow hydrogen reduction of As⁵⁺ to As³⁺, could be eliminated as a result of the addition of copper powder as a reductant. Arsenic, antimony and bismuth in the liquor have been found to catalyze the hydrogen reduction of copper. When the copper concentration in the treated solution reached a certain low level, copper arsenide, Cu₃As₁ was formed on the surface of copper through hydrogen reduction of As³⁺ ions. This reaction was very slow and a long reaction time was required for complete removal of arsenic. Therefore, in order to purify spent copper electrolyte, some arsenic removal technique (e.g., solvent extraction) should be combined with hydrogen reduction.