GB263642A - Process for the extraction of precious metals from the slimes of copper refineries - Google Patents

Abstract

263,642. Baraboshkin, N., and Trust Uralkupfer. Jan. 26, 1926. Treating slimes to remove volatile and undesired constituents.-A method for the treatment .of slime from the electrolytic refining of copper for the recovery of gold and silver consists in the separation of copper by any suitable method, subsequent roasting of the product for the removal of volatile compounds of selenium, tellurium and other elements at a temperature rising from 500‹ C. to 900‹ C., and finally fusion of the roasted product with flux to form a fusible slag with the other impurities of the slime. The raw slime, after separation of the anode deposit by screening or sliming, is allowed to settle in a lead-lined tank. Commercial sulphuric acid is then added in proportion equivalent to the copper content. The mixed mass is heated and stirred in iron or copper pans heated by hot gases or by superheated steam for several hours at a temperature not above 250‹ C. All the copper is converted into soluble form, while the silver remains insoluble, as the formation of soluble silver salts begins above 300‹ C. The mass is charged into a tank containing hot water and stirred to dissolve the copper. The residue is filtered and washed with hot water, the solution and washing water being used until saturated with copper sulphate which is crystallized on cooling. The filtered slime is transferred to a roasting furnace and heated to 500‹ C.-600‹C. in an air current for about four hours. Volatile impurities such as selenium and tellurium are driven off and are condensed as oxides. The roasted product is mixed with soda ash and pyrolusite or other flux to produce a fusible slag and smelted in a reverberatory or electric furnace. The flux may be added to the washed slime before roasting. The slag is removed and the remaining metal refined by blowing or by using oxidizing fluxes such as nitre.