A process for the coproduction of zinc and sulphuric acid from zinc sulphide ores

Claim 2

A process according to claim 1 wherein the concentration of solids in the leach solution is from 1:4 to 1:1.

Claim 3

A process which comprises in combination: a. roasting a zinc bearing material selected from the group consisting of iron-containing zinc sulphide ore and iron-containing residues from a zinc manufacturing process at a temperature in the range 500*C to 800*C in an atmosphere which contains oxygen and sulphur dioxode to convert the zinc bearing material to a calcine comprising the bulk of the zinc originally present in the zinc bearing material in the form of zinc sulphate; b. leaching said calcine with water or an aqueous solution at a temperature in the range of 10*C to 100*C, using a solids: liquid ratio up to 2:1 to yield a leach slurry; c. subjecting said leach slurry to a solids/liquid separation process to yield a leach solution which comprises as dissolved zinc sulphate at least 70 percent of the zinc contained in said calcine, and a residue, which contains silicaceous gangue, and any insoluble iron and lead compounds; d. electrolysing said leach solution to yield, as a product, metallic zinc and, as an intermediate, spent electrolyte liquor, which is an aqueous solution of sulphuric acid and zinc sulphate; e. concentrating sulphuric acid in said spent electrolyte liquor so that its liquid phase contains at least 600 g/l of H2SO4 and the bulk of the zinc sulphate is precipitated; and f. separating this precipitate from the liquor and so obtaining sulphuric acid as a product, the precipitated zinc sulphate being redissolved in the free liquor to the electrolysis step and recycled in subsequent operations, said zinc bearing material being roasted to step (a) in teo steps, wherein the first step comprises reasting said material in an atmosphere comprising oxygen and sulphur dioxide at a temperature in the range from 500* to 800*C to convert the bulk of the zinc into zinc sulphate and the second step comprises maintaining the roast at a temperature in the range from 400* to 700*C in an atmosphere from which sulphur dioxide has been substantially purged to decompose water-soluble iron compounds.