Process for the recovery of non-ferrous metals from sulphide ores and concentrates

In a method for recovering zinc from material selected from the group consisting of sulphidic ores and concentrates and for rendering copper, lead, silver, and gold in said material more readily recoverable, the improvement comprising:

• (a) roasting said material in a subdivided form in a fluidized bed reactor at a temperature from 620.degree. to 700.degree. C., with 20-60% excess air over the stoichiometric for an average retention time of over 1 hour at a superficial spacial velocity of the gas within the bed of 25-150 cm per sec at reactor temperature resulting in an atmosphere comprising SO.sub.2, SO.sub.3, water vapour, and remaining O.sub.2 and N.sub.2 from the air, to obtain a calcine containing zinc and copper as sulphates and oxysulphates, ferrites, oxides, and unreacted sulphides, iron as hematite, and lead, silver, and gold in forms amenable to recovery;
• (b) leaching said calcine with water or dilute sulphuric acid solution at a temperature below 80.degree. C. in such a manner that sulphates, oxysulphates, and oxides of zinc and copper are leached out from the calcine into the water or dilute sulphuric acid solution;
• (c) subjecting the leach pulp resulting from step (b) to a liquid-solid separation step to yield a leach solution from which zinc and copper can be recovered;
• (d) leaching the solid residue resulting from step (c) with hot, strong sulphuric acid solutions, at a temperature above 80.degree. C. but below the boiling point of the solution and with sulphuric acid solution stronger than used in step (b), in such a manner that zinc and copper ferrites and unreacted sulphides of zinc and copper are converted to sulphates of iron, copper, and zinc which dissolve in the leach solution;
• (e) subjecting the pulp resulting from step (d) to a solid-liquid separation step to obtain a leach solution containing said sulphates of iron, copper, and zinc;
• (f) recycling said sulphates of zinc, copper, and iron obtained in step (e) in part into said fluidized bed reactor in a subdivided form to convert the sulphates of iron to hematite, SO.sub.2 and SO.sub.3 and render the sulphates of zinc and copper to the calcine for recovery by means of steps (b) and (c);
• (g) washing the solid residue resulting from step (e) with water;
• (h) subjecting any pulp resulting from step (g) to a solid-liquid separation step to obtain a washed leach residue containing lead, silver and gold in forms amenable to recovery and a wash liquor containing zinc, copper, and iron sulphates and sulphuric acid;
• and
• (i) recycling said wash liquor resulting from step (h) in part to step (b) and/or in part to said fluidized bed reactor in a subdivided form to convert the sulphates of iron to hematite, SO.sub.2 and SO.sub.3 and enable recovery of the sulphates of zinc and copper by means of steps (b) and (c).