Additional Reduction Processes

Electrowinning may be used to recover copper from leaching solutions containing more than approximately 25 g/L (3.4 oz/gal) of copper (Harlan process). The electrolytic cells are equipped with insoluble lead-antimony anodes and 99% Ni cathodes. The copper powder does not adhere, but falls to the bottom of the cells. Temperature of the electrolyte is 60 °C (140 °F); cathode current density varies from 1350 to 2700 A/m2 (125 to 250 A/ft2). When the copper concentration falls below 15 g/L (2 oz/gal), the electrolyte is drained and used for ore leaching. Particle size of the powder prior to furnace processing is 1 to 25 /'m, with excellent purity (>99.9%). The power requirements for electrowinning of copper are approximately ten times as large as those for electrorefining of copper with soluble anodes.

Copper may be concentrated from low-content leach solutions by solvent extraction, followed by stripping with dilute sulfuric acid into an aqueous solution and electrowinning. Carboxylic acid and hydroxylamine-based compounds have been found to be selective solvents of low water solubility, to have good stability, and to be compatible with inexpensive diluents. Direct powder precipitation with hydrogen or ammonia is an alternative to stripping the metal from the organic solvent into an aqueous solution.

Metals can be precipitated from their acid or basic solutions by reduction with hydrogen. Sulfuric acid, ammoniacal ammonium carbonate, and ammoniacal ammonium sulfate solutions have been used to produce copper powder by this method. Sulfuric acid leaching of a cement copper and hydrogen reduction of the filtered solution in an autoclave at 120 to 140 °C (250 to 280 °F) and 3 MPa (425 psi) is reported to produce a precipitate with a purity of about 100% Cu. Drying and furnace processing in a reducing atmosphere at 540 to 790 °C (1000 to 1450 °F) increases particle size, due to agglomeration of the very fine powder.

0 0

Post a comment