Abstract: A method of removing sodium ions from an alkaline aqueous solution such as a leach solution which contains dissolved sodium tungstate. The method involves passing the solutions through the anode compartment of an electrolytic cell and passing an electrical direct current through the cell causing the sodium ions to pass through the cation selective membrane and tungstic acid to be produced in the anode compartment. Sodium-containing alkali is bled from the cathode compartment at a rate sufficient to prevent build-up of alkali in the cathode compartment. The tungstic acid is typically converted to ammonium tungstate by treatment with ammonia and then the ammonium tungstate further treated for recovery of the tungsten values.

Abstract: A method of treating sulphidic mattes containing from 5% to 60% iron; from 15% to 40% sulphur together with soluble non-ferrous metals such as copper, cobalt, nickel and zinc and also optionally insoluble non-ferrous metals which term includes platinum group metals gold and silver by a leaching process to effect substantial separation of the non-ferrous metals from iron as well as from insoluble residue material. The matte is contacted in a finely subdivided form with sulphate in acid medium at a temperature of from 70.degree. C. to 120.degree. C. and an oxygen partial pressure of from 50kPa to 1,000kPa. The quantity of sulphate present is at least the stoichiometric amount required for dissolving the soluble non-ferrous metals present but is limited to ensure that a substantial proportion of iron which dissolves simultaneously with the soluble non-ferrous metals precipitates out as it is replaced by dissolving non-ferrous metals.

Abstract: A process for treating zinc sulphide materials wherein the sub-divided material is firstly leached, under pressure at less than 119.degree. C., with a sulphate leach solution low in sulphuric acid and having a high iron content together with zinc and impurities in a manner causing iron to precipitate and subsequently leaching the residue and redissolving the iron precipitate with spent electrolyte containing regenerated sulphuric acid resulting from the treatment of the leach liquor obtained from the first leach step and wherein the leach solution from the subsequent leach step constitutes the starting leach solution for the first leach step. The second leach step is carried out in two phases; a first leach phase conducted at elevated pressure and elevated temperature (less than 119.degree. C.) in the presence of oxygen and a second phase at atmospheric pressure and without the supply of free oxygen to the leach solution.

Abstract: A process for treating zinc sulphide materials wherein the sub-divided material is firstly leached, at less than 119.degree. C., with a sulphate leach solution, low in sulphuric acid and having a high iron content together with zinc and impurities in a manner causing iron to precipitate and subsequently leaching the residue and re-dissolving the iron precipitate with spent electrolyte containing regenerated sulphuric acid resulting from the treatment of the leach liquor obtained from the first leach step and wherein the leach solution from the subsequent leach step constitutes the starting leach solution for the first leach step.