Patent GB-746633-A (GB)
Title: Improved method of extracting zinc from zinc bearing material
Inventor: FORWARD FRANK ARTHUR
IPC: C22B19/00
Filed: 1954-03-11
Abstract: Zinc is recovered from zinciferous mineral sulphides by dispersing the finely divided sulphide in strong aqueous ammonia solution, which may also contain ammonium sulphate, and which must contain at least the stoichiometric equivalent of sulphur to the metal values to be extracted and dissolved, and agitating the mixture at an elevated temperature and pressure whilst feeding an oxygen containing gas thereto, thereby dissolving the zinc values to form a solution from which metal values other than zinc are precipitated and the zinc subsequently precipitated.  The leaching is preferably carried out at 60 to 135 DEG C. under an oxygen partial pressure of about 5 to 50 pounds per square incr above the normal pressure generated at the reaction temperature.  Metals such as zinc, copper, nickel, cobalt, cadmium and silver are extracted from the starting material and dissolved.  Oxidizable iron values are converted to hydrated iron oxides, which are insoluble and are separated from the solution with the undissolved residue; the latter may contain lead and also precious and noble metals in a recoverable form.  Depending on the degree of leaching the pregnant leach solution may contain thiosulphates and/or polythionates, or these may have been converted to sulphates or sulphamates.  Copper may be recovered from the filtered leached solution either as a sulphide or metal. If the copper content of the starting material is low the solution may be boiled to reduce the ammonia concentration thereby precipitating copper as sulphide provided sufficient thiosulphates and polythionates formed during the leaching to combine with the copper, are present in the leach solution.  Alternatively if the copper content of the ore is high the leaching is continued for a time sufficient to oxidize the thiosulphate and polythionate content of the solution to sulphate and sulphamate and the solution after filtration is boiled to reduce the ammonia concentration towards a mol ratio of ammonia to copper plus zinc of about 3.6 to 1 or lower. The copper is then precipitated as metal by passing in a reducing gas such as carbon monoxide or hydrogen at a temperature of 232 DEG C. under a pressure of about 750 pounds per square inch.  Metals other than zinc are removed from the solution by adding zinc dust or by electrolysis.  The remaining solution contains all the zinc values and may be acidified with sulphuric acid to a pH of about 2.6 whereby on cooling zinc ammonium sulphate precipitates and is recovered. Alternatively zinc values can be precipitated from the copper free solution by adding ammonia and sulphur dioxide to convert the zinc values to zinc sulphite which is precipitated, separated, heated to drive off the sulphur dioxide which is recovered for re-use, and thus converted to zinc oxide; precipitation of the zinc values can also be effected by treating the copper free solution with carbon dioxide to produce zinc carbonate which is separated and which may be heated to produce zinc oxide and carbon dioxide which may be recycled.  If silver be present in the initial material it is dissolved during leaching and may be precipitated by the addition of sodium chloride before the zinc separation.  The solution remaining after zinc precipitation contans ammonium sulphate which may be crystallized and recovered or alternatively recycled to the leaching stage or employed for the regeneration of ammonia.  Specifications 670,184 and 722,373 are referred to.ALSO:Zinc is recovered from zinciferous mineral sulphides by dispersing the finely divided sulphide in strong aqueous ammonia solution, which may also contain ammonium sulphate, and which must contain at least the stoichiometric equivalent of sulphur to the metal values to be extracted and dissolved, and agitating the mixture at an elevated temperature and pressure whilst feeding and oxygen containing gas thereto, thereby dissolving the zinc values to form a solution from which metal values other than zinc are precipitated and the zinc is subsequently precipitated.  The leaching is preferably carried out at 60 to 135 DEG C. under an oxygen partial pressure of about 5 to 50 pounds per square inch above the normal pressure generated at the reaction temperature.  Metals such as zinc, copper, nickel, cobalt, cadmium and silver are extracted from the starting material and dissolved.  Oxidizable iron values are converted to hydrated iron oxides, which are insoluble and are separated from the solution with the undissolved residue; the latter may contain lead and also precious and noble metals in a recoverable form. Specifications 670,184, [Group III], and 722,373 are referred to.