Reduction of lime consumption when treating refractory gold ores or concentrates

• US 20060133974A1
• Filed: 10/11/2005
• Published: 06/22/2006
• Est. Priority Date: 12/22/2004
• Status: Active Grant

• Current Assignee: Placer Dome Technical Services Limited
• Original Assignee: Placer Dome Technical Services Limited
• Inventors: Ji, Jinxing, Fleming, Christopher Andrew, Ferron, Cesare Giosue, King, James A.
• Granted Patent: US 7,604,783 B2
• Time in Patent Office: Days
• US Class Current: 423/36
• CPC Class Codes: C22B 11/04 by wet processes extraction of metal compounds by leaching in organic solutions C22B3/16; treatment or purification of solutions by liquid-liquid extraction C22B3/26
• CPC Class Codes: C22B 3/08 Sulfuric acid , other sulfurated acids or salts thereof
• CPC Class Codes: C22B 3/44 by chemical processes treatment or purification of solutions by liquid-liquid extraction C22B3/26, by ion-exchange extraction C22B3/42
• CPC Class Codes: Y02P 10/20 Recycling

Abstract

The present invention is directed to a precious metal recovery process in which basic ferric sulphates and/or jarosites are controlled by a number of mechanisms, including control of the oxidation reaction conditions in the first autoclave compartment, hot curing of the autoclave discharge slurry, and/or contacting of the autoclave feed slurry with the hot cured discharge liquid.

Claims

1. A precious metal recovery process, comprising:

(a) oxidizing an aqueous feed slurry in an autoclave, the feed slurry comprising a precious metal-containing material and sulphide sulphur, 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 reactive iron-containing precipitate;

(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 reactive iron-containing precipitate, and wherein the aqueous discharge slurry comprises an acid;

(c) allowing at least most of the reactive iron-containing precipitate in the aqueous discharge solids to react with the acid to form a dissolved iron-containing species;

(d) after step (c), contacting the discharge solids with an acid consumer;

(e) leaching at least most of the precious metal from the discharge solids to form a dissolved precious metal; and

(f) recovering the dissolved precious metal.

2. The process of claim 1, wherein the reactive iron-containing precipitate comprises basic ferric sulphate, the dissolved iron-containing species comprises dissolved ferric sulphate, and the acid comprises sulphuric acid, wherein the precious metal is gold, wherein in step (c), the temperature of the discharge slurry is maintained at or above 60 degrees Celsius, and wherein, in step (c), the slurry is held in a stirred vessel and further comprising:

(g) after step (c) and before step (d), separating at least a portion of the aqueous discharge liquid from the discharge solids and wherein at least about 50% of the basic ferric sulphates is converted into dissolved ferric sulphate according to the following equation;

2Fe(SO₄)(OH)+H₂SO₄=Fe₂(SO₄)₃+2H₂O.

3. The process of claim 1, wherein the reactive iron-containing precipitate comprises basic iron sulphate, the dissolved iron-containing species comprises dissolved ferric sulphate, and the acid comprises sulphuric acid, wherein the acid consumer is predominantly lime and wherein, in step (d), the pH of the discharge solids is increased from a pH in the range of from about pH 2.0 to about pH 5.0 to a pH in the range of from about pH 9.0 to about pH 11.0, and further comprising:

(g) contacting dissolved ferric sulphate in the aqueous discharge liquid with lime and/or limestone to convert at least most of the dissolved ferric sulphate to ferric hydroxide.

4. The process of claim 2, wherein the acid consumer is lime and/or limestone, wherein, after step (c), the aqueous discharge slurry comprises from about 50 to about 150 g/l dissolved ferric sulphate, no more than about 5 wt % basic ferric sulphates in the solid phase, no more than about 5 wt % jarosites in the solid phase, and from about 10 to about 40 g/l sulphuric acid, wherein the aqueous discharge liquid comprises at least about 70% of the ferric iron in the aqueous discharge slurry after step (c), wherein the separated aqueous discharge liquid comprises no more than about 1 wt % solids, and wherein the separated aqueous discharge solids comprise no more than about 70 vol. % liquid.

5. The process of claim 1, wherein the autoclave comprises multiple compartments and wherein a slurry temperature in the first compartment that is at least about 5°

C. less than a slurry temperature in a second compartment of the autoclave, the second compartment being adjacent to and downstream of the first compartment.

6. The process of claim 5, wherein from about 0.05 to about 0.90 (molar ratio of equivalent CaO to S) of a laterite is contacted with the feed slurry prior to and/or during sulphide oxidation in the first autoclave compartment.

7. The process of claim 5, wherein the slurry temperature in the first compartment is at least about 10°

C. less than the slurry temperature in the second compartment.

8. The process of claim 5, wherein acid consumers are added to the first compartment and wherein the molar ratio of total acid consumers (as equivalent CO₃) to sulphides in the first compartment is no more than about 0.26.

9. The process of claim 8, wherein the molar ratio ranges from about 0.1 to about 0.225.

10. The process of claim 2, further comprising before step (a):

(g) contacting at least a portion of the separated aqueous discharge liquid with the precious metal-containing material, wherein the recycled aqueous discharge liquid comprises the dissolved ferric iron and free sulphuric acid to partially oxidize sulphide sulphur in the material prior to step (a).

11. A precious metal recovery process, comprising:

(a) oxidizing sulphide sulphur in an aqueous feed slurry in an autoclave, the feed slurry comprising a precious metal-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 basic iron sulphate in a solid phase;

(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 basic iron sulphate, and wherein the aqueous discharge slurry comprises sulphuric acid;

(c) allowing at least most of the solid-phase basic iron sulphate in the aqueous discharge solids to react with the sulphuric acid to form ferric sulphate dissolved in the aqueous discharge liquid;

(d) thereafter separating the aqueous discharge liquid from the discharge solids, wherein at least most of the dissolved ferric sulphate is in the separated aqueous discharge liquid and wherein the separated aqueous discharge solids comprise sulphuric acid;

(e) contacting the separated discharge solids with an acid consumer to consume at least most of the sulphuric acid and dissolved metal sulphates to form a neutralized discharge solids;

(f) contacting a lixiviant, at a pH above about pH 7.0, with the neutralized discharge solids to dissolve at least most of the precious metal; and

(g) recovering the dissolved precious metal.

12. The process of claim 11, wherein the precious metal is gold, wherein in step (c), the temperature of the discharge slurry is maintained at or above 60 degrees Celsius, and wherein, in step (c), the slurry is held in a stirred vessel.

13. The process of claim 11, wherein the acid consumer is predominantly lime and/or limestone and wherein, in step (e), the pH of the discharge solids is increased from a pH in the range of from about pH 0.5 to about pH 5.0 to a pH in the range of from about pH 9.0 to about pH 11.0, and further comprising:

(h) contacting dissolved ferric sulphate in the aqueous discharge liquid with lime and/or limestone to convert at least most of the dissolved ferric sulphate to ferric hydroxide.

14. The process of claim 11, wherein the acid consumer is lime and/or limestone, wherein, after step (c), the aqueous discharge slurry comprises from about 50 to about 150 g/L dissolved ferric sulphate, no more than about 5 wt % basic ferric sulphates in the solid phase, no more than about 5 wt % jarosites in the solid phase, and from about 10 g/L to about 40 g/L sulphuric acid, wherein the aqueous discharge liquid comprises at least about 80% of the dissolved ferric iron in the aqueous discharge slurry after step (c), wherein the separated aqueous discharge liquid comprises no more than about 1 wt % solids, and wherein the separated aqueous discharge solids comprise no more than about 70 wt % liquid.

15. A precious metal recovery process, comprising:

(a) inputting a precious metal-containing feed slurry into a first compartment of a multi-compartment autoclave, the precious metal-containing feed slurry comprising a precious metal-containing material comprising sulphide sulphur;

(b) providing, in the first compartment a slurry temperature that is at least about 5°

C. less than a slurry temperature in a second compartment of the autoclave, the second compartment being adjacent to and downstream of the first compartment;

(c) 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 basic iron sulphate, wherein at least most of the sulphide sulphur is oxidized to sulphate sulphur, wherein the aqueous discharge slurry comprises sulphuric acid, and wherein the discharge slurry comprises less than 10 wt. % (dry basis) of the basic iron sulphate;

(d) contacting the discharge solids with an acid consumer to consume at least a portion of the sulphuric acid and dissolved metal sulphates; and

(e) contacting a lixiviant, at a pH above about pH 7.0, with the discharge solids to solubilize at least most of the precious metal; and

(f) recovering the solubilized precious metal.

16. The process of claim 15, wherein at least most of the iron in the discharge slurry is in the form of hematite.

17. The process of claim 15, wherein at least most of the basic iron sulphate in the aqueous discharge solids is basic ferric sulphate and further comprising before the lixiviant contacting step:

(g) allowing at least most of the basic ferric sulphate in the aqueous discharge solids to react with the sulphuric acid to form ferric sulphate solubilized in the aqueous discharge liquid; and

(h) separating at least most of the aqueous discharge liquid from the discharge solids, wherein at least most of the solubilized ferric sulphate is in the separated aqueous discharge liquid and wherein the separated aqueous discharge solids comprise sulphuric acid; and

(i) contacting the separated discharge solids with an acid consumer to consume at least most of the sulphuric acid and dissolved metal sulphates.

18. The process of claim 15, wherein the slurry temperature in the first compartment is at least about 10°

C. less than the slurry temperature in the second compartment.

19. The process of claim 15, wherein the slurry temperature in the first compartment ranges from about 5 to about 30°

C. less than the slurry temperature in the second compartment.

20. The process of claim 15, wherein from about 0.05 to about 0.90 (molar ratio of equivalent CaO to S) laterite is contacted with the feed slurry prior to or during sulphide oxidation in the first autoclave compartment.

21. The process of claim 15, further comprising before step (a):

(i) contacting at least a portion of the separated aqueous discharge liquid with unoxidized precious metal-containing material, wherein the recycled aqueous discharge liquid comprises dissolved ferric sulphate and free sulphuric acid to partially oxidize sulphide sulphur in the unoxidized material.

22. The process of claim 15, wherein acid consumers are added in the first compartment and wherein the molar ratio of total acid consumers (as equivalent CO₃) to sulphides in the first compartment is no more than about 0.26.

23. The process of claim 22, wherein the molar ratio ranges from about 0.1 to about 0.225.