Recovery of non-ferrous metals by thermal treatment of solutions containing non-ferrous and iron sulphates

A method for recovering zinc from a strong sulphuric acid solution containing zinc and iron as sulphates or from zinc sulphide ores or concentrates, comprising:

• (a) roasting said sulphate or zinc sulphide ore or concentrate in a subdivided form in an inert fluidized bed reactor at a temperature from 600 to 750.degree. C. with 20-150% excess air for an average retention time of 1-12 hours 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 ferrite and sulphates, oxysulphates and oxides of zinc, plus hematite;
• (b) leaching said calcine with water or dilute sulphuric acid solution in such a manner that the sulphates, oxysulphates, and oxides of zinc are leached out in part 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 suitable for purification-metal recovery steps for zinc;
• (d) leaching the solid residue resulting from step (c) with strong sulphuric acid solution in such a manner that the ferrite and unreacted sulphides of zinc are converted to the sulphates of iron and zinc;
• (e) subjecting the pulp resulting from step (d) to a liquid-solid separation step to obtain a leach solution containing said sulphates of iron and zinc;
• and
• (f) recycling said sulphate solution obtaining in step (e) in a subdivided form into an inert fluidized bed in such a manner that the dry calcine contains zinc sulphate and iron sulphate and/or hematite, said inert fluidized bed being fueled by the off gas from roasting step (a).