Patent GB-424375-A (GB)
Title: An improved method of recovering ore values
IPC: C22B1/02
Filed: 1933-05-16
Abstract: In a process of extracting metals from a complex ore, the ore, when it contains little or no sulphur, is mixed in finely divided condition with an alkaline earth metal compound and a sulphur-bearing material, and roasted under oxidizing conditions, the roasting being so controlled as to temperature and agitation of the material that the roasted product contains alkaline earth metal sulphate interspersed therethrough and is in a non-sintered and permeable condition, whereupon the ore metal oxides contained in the roasted material are solubilized by treatment with liquid or gaseous reagents or both, and extracted from the residue gangue and alkaline earth material.  The roasted ore should contain not less than 5 per cent of alkaline earth sulphate.  Suitable added sulphur-bearing material is sulphide ore or the sulphates of hydrogen, zinc, aluminium, copper, manganese, sodium, potassium or iron.  When complex sulphide ores are treated, addition of further sulphide material is unnecessary and roasting is carried on under oxidizing conditions to burn off most of the sulphur.  At least 5 per cent of alkaline earth sulphate must be present in the roasted material.  The alkaline earth material may consist of calcium, barium, strontium or magnesium oxides, hydroxides or carbonates or mixtures thereof.  Limestone, dolomite, witherite and strontianite are specified.  When magnesium compounds are used, the magnesium sulphate produced is washed out with water prior to solubilizing and extracting the metal oxides.  Mixing of the ground ore and alkaline earth is preferably effected in the presence of water. Any sulphate present in the raw ore is thereby converted to insoluble sulphate prior to roasting.  The roasting operation is preferably carried out at a low temperature, and the material is thoroughly agitated.  The heat may be obtained wholly from the combustion of the ore, or it may be obtained wholly or in part from a gas, oil or other flame.  Reference is made to ores containing zinc, lead, silver, copper, gold, manganese, tin, iron, antimony nickel, cadmium, caesium, lithium, chromium, zirconium, &c.  An example relates to the treatment of a sulphide ore containing chiefly zinc and iron.  Calcium oxide is added in amount corresponding to the molecular equivalent of zinc. Roasting is effected at 550--700 DEG C. in a long inclined rotary tube provided with agitating flanges. The product may be treated with liquid reagents such as dilute hydro-chloric or sulphuric acid, or with ammoniacal ammonium sulphate or carbonate.  Zinc is dissolved by the last reagent, probably as tetra-amino zinc carbonate, copper present being left in the residue. Ammonia is expelled by heat, the zinc carbonate precipitated being subsequently calcined to oxide.  The solution may be evaporated to precipitate copper if present.  Alternatively, the roasted product may be treated with sulphur-oxygen gases, or with hydrogen chloride or chlorine or both.  The chloridized product may be heated in the presence of sufficient oxygen to convert ferric chloride to ferric oxide and chlorine, whereafter zinc chloride is leached from the material.