GB791916A - Improved method of extracting copper values from material containing copper - Google Patents

Abstract

Finely pulverized copper-bearing mineral sulphides are leached in an agitated aqueous ammonia solution at above 80 DEG F. and atmospheric pressure into which a free oxygen-bearing gas (such as oxygen with or without an inert gas, oxygen enriched air or air) is passed so as to maintain a partial pressure of oxygen above 5 lbs./sq. inch and thereby solubilize the copper and some other meal values and form polythionates and/or thiosulphates; the solution after removal of insoluble residues is oxidized to ammonium sulphate or sulphamate; the free ammonia content is reduced, e.g. by heating the solution; and metallic copper is precipitated at elevated temperature and pressure with a sulphur-free reducing gas such as hydrogen at above 300 DEG F. and at between 50 and 500 lbs./sq. inch, or carbon monoxide. The leach solution contains sufficient free ammonia to convert copper values to and dissolve them as copper amines, 60-100 gms./litre being satisfactory. Subsequently remaining copper and other metal values such as zinc, nickel, cobalt and cadmium may be precipitated with hydrogen sulphide and returned if desired to the leaching step and crystalline ammonium sulphate may be recovered from the leach solution and a portion can be returned to the leaching stage; alternatively it can be regenerated for recovery of ammonia. Uncombined ammonia can be removed from the leach solution by heating and recovered for re-use. It is desirable to reduce the ammonia content of the solution until a molecular ratio NH3/Cu of about 2.5/1 is reached, whilst maintaining a concentration of about 200 to 400 grams per litre of ammonium sulphate in the solution: sulphuric acid may then be added to reduce the ratio to about 2 : 1 and the copper precipitated as indicated above. Preferred features are the use in the leaching stage of particles from 35 to 325 (Tyler) screen size; 15 to 50 per cent solids by weight of the solution; temperatures of 100 DEG to 300 DEG F.-supplemental heat to that generated autogenously may if necessary be supplied, or cooling coils may be employed; partial pressures of oxygen of 20 to 150 lbs. per sq. inch; generally 96 to 99 per cent of the copper should be extracted in 4 to 11 or 12 hours by these means. If an inert gas is used with the oxygen, a constant withdrawal of gas should be maintained and ammonia recovered therefrom. Counter-or con-current leaching may be employed, using a plurality, e.g. two, stages. An example of the leaching stage refers to a nickel/copper/iron sulphide ore of which copper and nickel are dissolved whilst iron remains in the residue as ferric oxide or hydrate. If present in the sulphidic material, cobalt, zinc and cadmium also are dissolved, but lead remains in the residue. Reference has been directed by the Comptroller to Specification 670,184.