An aqueous solution containing cu2+, e.g., from the ammoniacal leaching of cu ore or scrap, is adjusted to contain 2-4 moles nh4oh/mole cu by adding nh3. The resulting solution is put into an autoclave, pressurized at approximately 200 psig with CO, and heated at approximately 120 deg. C for 30 min to reduce the cu2+ to cu+. The pressure is then released, the solution is cooled to approximately 90 deg. C, and aqueous naoh is added to precipitate cu2o and evolve nh3. The solution is reheated to expel nh3, and the cu2o is filtered off, washed, and dried in vacuo. The cu recovery is almost quantitative.
U.S. Pat. 3,833,717; Sept. 3, 1974 Chem. Abstr. 81:139,061M