PROCESS FOR REDUCED ALKALI CONSUMPTION IN THE RECOVERY OF SILVER
First Claim
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1. A precious metal recovery process, comprising:
- (a) oxidizing an aqueous feed slurry in an autoclave, the feed slurry comprising a silver-containing material and sulphide sulphur, wherein at least most of the sulphide sulphur is oxidized in the autoclave to sulphate sulphur and wherein at least a portion of the sulphate sulphur is in the form of a solid-phase reactive sulphate;
(b) removing, from the autoclave, an aqueous discharge slurry comprising discharge solids and aqueous discharge liquid, the discharge solids comprising at least a portion of the silver and at least most of the solid-phase reactive sulphate and wherein a liquid phase of the aqueous discharge slurry comprises an acid;
(c) allowing at least most of the solid-phase reactive sulphate in the aqueous discharge solids to react with the acid to form liquid-phase reactive sulphate, wherein, after step (c), at least a portion of the solid-phase reactive sulphate comprises silver and the discharge solids have a sulphate content of no more than about 2 wt %;
(d) after step (c), contacting the discharge solids with an acid consumer while maintaining a temperature of the discharge solids of at least about 80°
C. to convert at least most of the solid-phase reactive sulphate to a nonreactive iron-containing species; and
(e) thereafter recovering at least most of the silver from the discharge solids.
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Abstract
The present invention is directed to a precious metal recovery process in which basic ferric sulphates and/or jarosites are controlled by hot curing of the autoclave discharge slurry followed by decomposition of argentojarosite using strong acid consumers.
91 Citations
23 Claims
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1. A precious metal recovery process, comprising:
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(a) oxidizing an aqueous feed slurry in an autoclave, the feed slurry comprising a silver-containing material and sulphide sulphur, wherein at least most of the sulphide sulphur is oxidized in the autoclave to sulphate sulphur and wherein at least a portion of the sulphate sulphur is in the form of a solid-phase reactive sulphate;
(b) removing, from the autoclave, an aqueous discharge slurry comprising discharge solids and aqueous discharge liquid, the discharge solids comprising at least a portion of the silver and at least most of the solid-phase reactive sulphate and wherein a liquid phase of the aqueous discharge slurry comprises an acid;
(c) allowing at least most of the solid-phase reactive sulphate in the aqueous discharge solids to react with the acid to form liquid-phase reactive sulphate, wherein, after step (c), at least a portion of the solid-phase reactive sulphate comprises silver and the discharge solids have a sulphate content of no more than about 2 wt %;
(d) after step (c), contacting the discharge solids with an acid consumer while maintaining a temperature of the discharge solids of at least about 80°
C. to convert at least most of the solid-phase reactive sulphate to a nonreactive iron-containing species; and
(e) thereafter recovering at least most of the silver from the discharge solids. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A precious metal recovery process, comprising:
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(a) oxidizing, in an autoclave, sulphide sulphur in an aqueous feed slurry, the feed slurry comprising a precious metal-containing material, wherein at least most of the sulphide sulphur is oxidized to sulphate sulphur, wherein the precious metal comprises silver and gold, and wherein at least a portion of the sulphate sulphur is in the form of solid-phase reactive sulphate;
(b) removing, from the autoclave, an aqueous discharge slurry comprising discharge solids and aqueous discharge liquid, the discharge solids comprising at least a portion of the precious metal and at least most of the solid-phase reactive sulphate, and wherein a liquid phase of the aqueous discharge slurry comprises sulphuric acid;
(c) allowing at least about 90% of the solid-phase reactive sulphate in the aqueous discharge solids to react with the sulphuric acid to form ferric sulphate dissolved in the aqueous discharge liquid, the discharge solids having, after step (c), a total reactive sulphate content of no more than about 2 wt %;
(d) thereafter separating the aqueous discharge liquid from the discharge solids, wherein at least most of the dissolved ferric sulphate and remaining acid are in the separated aqueous discharge liquid;
(e) contacting the separated discharge solids with an acid consumer to decompose the solid-phase reactive sulphate to iron oxides, wherein a total amount of lime equivalent acid consumer contacted, in step (e), with the discharge solids ranges from about 20 to about 60 kg/tonne of the discharge solids;
(f) thereafter contacting a lixiviant, at a pH above about pH 7.0, with the discharge solids to dissolve at least most of the silver and gold in the solids; and
(g) recovering the dissolved silver and gold. - View Dependent Claims (12, 13, 14)
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15. A precious metal recovery process, comprising:
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(a) oxidizing sulphide sulphur in an aqueous feed slurry in an autoclave, the feed slurry comprising a silver-containing material, wherein at least most of the sulphide sulphur is oxidized to sulphate sulphur and wherein at least a portion of the sulphate sulphur is in the form of solid-phase reactive sulphate;
(b) removing, from the autoclave, an aqueous discharge slurry comprising discharge solids and aqueous discharge liquid, the discharge solids comprising at least a portion of the silver and at least most of the solid-phase reactive sulphate, and wherein a liquid phase of the aqueous discharge slurry comprises sulphuric acid;
(c) allowing at least about 85% of the solid-phase reactive sulphate in the aqueous discharge solids to react with the sulphuric acid to form liquid-phase reactive sulphate in the aqueous discharge liquid, the discharge solids after step (c) having a sulphate content of no more than about 2 wt %;
(d) thereafter separating the aqueous discharge liquid from the discharge solids, wherein at least most of the liquid-phase reactive sulphate and remaining acid are in the separated aqueous discharge liquid and at least most of the silver in the discharge solids is in the form of argentojarosite;
(e) contacting the separated discharge solids with lime to decompose at least most of the argentojarosite to iron hydroxides and gypsum;
(f) thereafter contacting a lixiviant, at a pH above about pH 7.0, with the discharge solids to dissolve at least most of the silver in the solids; and
(g) recovering the dissolved silver. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23)
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Specification