Process for reduced alkali consumption in the recovery of silver
First Claim
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1. A process for the enhanced recovery of silver from autoclave discharge, comprising:
- oxidizing an aqueous feed slurry in an autoclave to form an aqueous discharge slurry, 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, the solid-phase reactive sulphate comprising iron and silver;
removing, from the autoclave, the aqueous discharge slurry comprising discharge solids and aqueous discharge liquid, the discharge solids comprising silver and at least most of the solid-phase reactive sulphate and wherein a liquid phase of the aqueous discharge slurry comprises an acid;
hot curing the aqueous discharge slurry to allow at least most of the iron-containing solid-phase reactive sulphates in the discharge solids to react with the acid in the aqueous discharge slurry to form liquid-phase iron-containing reactive sulphate, wherein, after the hot curing step, at least a portion of the solid-phase reactive sulphate comprises silver and the discharge solids have a total solid-phase reactive sulphate content of no more than about 2 wt %;
after the hot curing step, contacting the discharge solids with a strong acid consumer while maintaining a temperature of the discharge solids to greater than about 80°
C. to convert at least most of the remaining iron-containing solid-phase reactive sulphate to a nonreactive iron-containing species and to decompose at least most of the silver-containing solid-phase reactive sulphate to a soluble form of silver, wherein an amount of the strong acid consumer used is no more than about 100 kg/tonne of the discharge solids, and wherein after the contacting step no more than about 25% of the iron in the discharge solids is in the form of solid-phase reactive sulphate; and
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.
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Citations
32 Claims
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1. A process for the enhanced recovery of silver from autoclave discharge, comprising:
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oxidizing an aqueous feed slurry in an autoclave to form an aqueous discharge slurry, 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, the solid-phase reactive sulphate comprising iron and silver; removing, from the autoclave, the aqueous discharge slurry comprising discharge solids and aqueous discharge liquid, the discharge solids comprising silver and at least most of the solid-phase reactive sulphate and wherein a liquid phase of the aqueous discharge slurry comprises an acid; hot curing the aqueous discharge slurry to allow at least most of the iron-containing solid-phase reactive sulphates in the discharge solids to react with the acid in the aqueous discharge slurry to form liquid-phase iron-containing reactive sulphate, wherein, after the hot curing step, at least a portion of the solid-phase reactive sulphate comprises silver and the discharge solids have a total solid-phase reactive sulphate content of no more than about 2 wt %; after the hot curing step, contacting the discharge solids with a strong acid consumer while maintaining a temperature of the discharge solids to greater than about 80°
C. to convert at least most of the remaining iron-containing solid-phase reactive sulphate to a nonreactive iron-containing species and to decompose at least most of the silver-containing solid-phase reactive sulphate to a soluble form of silver, wherein an amount of the strong acid consumer used is no more than about 100 kg/tonne of the discharge solids, and wherein after the contacting step no more than about 25% of the iron in the discharge solids is in the form of solid-phase reactive sulphate; andthereafter recovering at least most of the silver from the discharge solids. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 24, 27, 30)
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11. A process for the enhanced recovery of silver from autoclave discharge, comprising:
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oxidizing, in an autoclave, sulphide sulphur in an aqueous feed slurry, to form an aqueous discharge slurry, the aqueous 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 a solid-phase reactive sulphate, the solid-phase reactive sulphate comprising iron as basic ferric sulphate and silver as argentojarosite; removing, from the autoclave, the 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; hot curing the aqueous discharge slurry to allow greater than about 90% of the basic ferric sulphate in the discharge solids to react with the sulphuric acid to form ferric sulphate dissolved in the aqueous discharge liquid, the discharge solids having, after the hot curing step, a total solid-phase reactive sulphate content of no more than about 2 wt %; 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; contacting the separated discharge solids with a strong acid consumer to decompose the remaining basic ferric sulphate to an iron oxide, and to decompose the argentojarosite, wherein a total amount of lime equivalent acid consumer contacted, in the contacting step, with the discharge solids ranges from about 20 to about 60 kg/tonne of the discharge solids and wherein after the contacting step no more than about 25 % of the iron in the discharge solids is in the form of solid-phase reactive sulphate; thereafter contacting a lixiviant, at a pH greater than about pH 7.0, with the discharge solids to dissolve at least most of the silver and gold in the discharge solids; and recovering the dissolved silver and gold. - View Dependent Claims (12, 13, 14, 25, 31)
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15. A process for the enhanced recovery of silver from autoclave discharge, comprising:
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oxidizing sulphide sulphur in an aqueous feed slurry in an autoclave to form an aqueous discharge slurry, the aqueous 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 a solid-phase reactive sulphate, the solid-phase reactive sulphate comprising iron as basic sulphate and silver as argentojarosite; removing, from the autoclave, the aqueous discharge slurry comprising discharge solids and aqueous discharge liquid, the discharge solids comprising at least most of the solid-phase reactive sulphate, and wherein a liquid phase of the aqueous discharge slurry comprises sulphuric acid; hot curing the aqueous discharge slurry to allow greater than about 85% of the iron-containing solid-phase reactive sulphate in the discharge solids to react with the sulphuric acid to form liquid-phase reactive sulphate as dissolved ferric sulphate in the aqueous discharge liquid, the discharge solids after the hot curing step having a total solid-phase reactive sulphate content of no more than about 2 wt %; 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; contacting the separated discharge solids with lime to decompose at least most of the silver containing argentojarosite, wherein an amount of the lime used is no more than about 100 kg/tonne of the discharge solids, and wherein after the contacting step no more than about 25% of the iron in the discharge solids is in the form of solid-phase reactive sulphate; thereafter contacting a lixiviant, at a pH greater than about pH 7.0, with the discharge solids to dissolve at least most of the silver in the solids; and recovering the dissolved silver. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 26, 28, 29, 32)
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Specification