Improvements in preconcentration of non-ferrous metal values

摘要

Non-ferrous metals, specifically copper, nickel, cobalt and zinc are recovered as a sulphate solution from a high sulphur, low arsenic, sulphide concentrate containing ferrous and non-ferrous metal values by a combined roasting and oxidative sulphuric acid leaching process. The ore or part of it is first roasted under temperature and rate condition optimum for sulphur re moval to such a degree (predetermined for the reactants and reaction conditions) that its sulphur content after roasting is such as to provide, with the assistance of any available sulphur in the leach liquor, oxidizable sulphur at least stoichiometrically equivalent to the non-ferrous metal values as sulphate and to produce on oxidation a leach liquor containing not more than 10 per cent sulphuric acid. The term "high sulphur" ore means one which would under the leaching conditions, produce more than 10 per cent sulphuric acid. "Low arsenic" ore means one where the arsenic is stoichiometrically equivalent to less than 5 per cent of the iron present. The thus roasted ore, if necessary after a sulphur content adjustment, is then leached under super-atmospheric pressure in the presence of oxygen, after which the non-ferrous metal sulphate solution is separated from the insoluble, iron-containing residue. The roasting of the ore, which should not reduce the sulphur content low enough to form insoluble ferrites, may be effected to bring the sulphur content to the predetermined amount or alternatively the sulphur content of the roasted concentrate is adjusted to the desired value by adding unroasted concentrate or an oxidizable sulphide. Alternatively the sulphur content of the leach solution may be adjusted by sulphuric acid addition. The sulphur content is preferably so chosen that on exothermic oxidation, sufficient heat is provided to maintain the operating temperature of the leaching, normally between 250 and 650 DEG F. The leaching acid should contain from 3 to 5 per cent sulphuric acid and is preferably obtained from the residual liquor from the non-ferrous metal recovery system. The oxygen may be supplied as air or free oxygen above or below the liquid gas interface and its partial pressure may be between 50 and 300 p.s.i.g. The process is illustrated in the figure. According to a typical example, a nickel copper flotation concentrate containing a major proportion of iron and 28.9 per cent sulphur was roasted at 1200 DEG F. to a sulphur content of 8 per cent. The sulphur dioxide produced is recovered. The roasted concentrate was slurried in water containing sulphuric acid and heated in an autoclave to 450 DEG F. at 600 p.s.i.g. with oxygen. Almost complete extraction of nickel, copper and cobalt occurred with less than 3 per cent iron dissolving. Specification 695,517 is referred to.