Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iib metal
Patent
1996-04-24
1999-01-12
Bos, Steven
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iib metal
C01G 900, C22B 1900
Patent
active
058583157
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for the extraction of zinc from zinc sulphide concentrates, comprising the following operations: spent electrolyte so as to produce a leachate which is rich in zinc and substantially iron-free, which is separated, and a zinc ferrite residue, which is separated, portion of the zinc ferrite residue produced in the operation (b) with a solution of sulphuric acid returning from electrolysis at 60.degree.-95.degree. C. in atmospheric conditions and in the presence of finely dispersed oxygen so as to produce a leachate which is rich in zinc and in iron, which is separated, and a leaching residue which is depleted in zinc, which is separated, the quantities of concentrates and of zinc ferrite which are used in this operation (c) being such that the molar ratio of the iron contained in the ferrite and the reactive sulphur contained in the concentrates is at least approximately 0.2, which is rich in zinc and in iron, produced in the operation (c), solution conditioned in the operation (d) so as to produce a solution which is rich in zinc and depleted in iron and a ferriferous precipitate, which is separated, and into the neutral leaching in (b).
The following should be understood here by sulphides, chiefly zinc and iron and, in smaller proportions, copper, silver and/or lead; autoclaves, that is to say at a pressure equal to or differing by less than 20 kPa from atmospheric pressure; and sulphide concentrates and in the leaching residue which is rich in zinc (an expression employed later) and which can be oxidized by ferric sulphate according to the reaction: consists of all the sulphur present in the form of sulphide less the pyrite sulphur).
Using the process of the invention, a leachate which is rich in zinc and substantially iron-free, a leaching residue which is depleted in zinc and a ferriferous precipitate are therefore obtained. This leachate can be purified and subsequently electrolysed in order to extract the zinc from it. The leaching residue which is depleted in zinc, and which contains sulphur, lead sulphates, silver compounds, undissolved sulphides (pyrites) and gangue, can be subjected to an appropriate treatment in order to extract the sulphur and the valuable metals from it. The ferriferous precipitate can be stored or, when it is pure enough, can be employed as pigment or as source of iron in the steel industry.
BACKGROUND
A process similar to that as defined above is described in document EP-A-0451456. In this known process, all of the calcine produced in the operation (a) is leached in the operation (b) and all of the ferrite produced in the operation (b) is leached in the operation (c), while employing a concentrate:ferrite ratio such that approximately 15 to 20% of the trivalent iron, required for the oxidation according to reaction (I) of the reactive sulphur present in the concentrate, originates from the leaching of the ferrite according to the reaction +ZnSO.sub.4 +4H.sub.2 O (II) reactive sulphur is obtained by the reaction +H.sub.2 O (III) rich in zinc and in iron has a sulphuric acid content of 10-25 g/l and an Fe.sup.3+ content of less than 10 g/l, which is apparently unobtainable in a single leaching stage. This is why the leaching in (c) is carried out in two stages.
In the first stage, the zinc ferrite and a leaching residue which is rich in zinc, produced in the second stage, are treated with the solution of acid returning from electrolysis so as to produce a primary leachate containing 50-90 g/l of H.sub.2 SO.sub.4 and the leaching residue which is depleted in zinc, which are separated. No oxygen is employed in this first leaching stage, this being to make it possible to use in this stage simpler types of reactors than in the second stage. The involvement of reaction (III) is therefore not brought about in the first stage.
In the second stage, the concentrates are treated with the said primary leachate in the presence of finely dispersed oxygen so as to produce, by reactions (I) and (III), a leachate which is ri
REFERENCES:
patent: 3976743 (1976-08-01), Landucci et al.
patent: 4004991 (1977-01-01), Veltman et al.
patent: 4107265 (1978-08-01), Von Ropenack et al.
patent: 4510028 (1985-04-01), Bolton et al.
De Nys Thierry S. A.
Terwinghe Francois M. I. G.
Van Put John W.
Bos Steven
N.V. Union Miniere S.A.
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