Method of preparing a gold-containing solution and process arrangement for recovering gold and silver

1. A method of preparing a gold-containing solution from gold-bearing raw materials, wherein the method comprises

(a) a gold leaching step, wherein the gold-bearing raw material is subjected to oxidative chloride leaching in an aqueous leaching liquor in the following conditions:

(i) the aqueous leaching liquor contains dissolved cupric ions (Cu 2+ ), chloride (Cl − ) and bromide (Br − ),

(ii) pH is within a range wherein the cupric ion does not precipitate, and

(iii) the oxidation potential is at least 450 mV Pt vs. Ag/AgCl, to provide a gold-containing solution optionally further containing silver,

(b) a liquid/solid separation step, wherein the gold-containing solution is separated from undissolved solid material;

(c) a gold recovery step, wherein gold is recovered from the gold-containing solution from step (b) to obtain a gold-bearing organic solution and a gold-depleted leach solution containing Cu 2+ , Cl − and Br − ; and

(c′) an evaporation step, wherein gold-depleted leach solution from step (c) containing Cu 2+ , Cl − and Br − is evaporated for removing excess water; and

(d) a circulation step, wherein the gold-depleted leach solution obtained from the evaporation step containing Cu 2+ , Cl − and Br − is circulated to the leaching step (a).

2. The method as claimed in claim 1 , wherein the gold-bearing raw material is selected from ores, concentrates, scraps, recycled materials, leach residues, tailings, flotation tailings, and refractory gold materials, which refractory gold materials have been pretreated by pressure oxidation, roasting and/or bacterial leaching.

3. The method as claimed in claim 1 , wherein free-milling gold ores/concentrates and pretreated refractory gold concentrates are used as the raw material and they have been selected from sulfidic and oxidic materials.

4. The method of claim 1 , wherein the gold-bearing raw material is selected from refractory gold concentrates and the pretreatment of the refractory gold concentrates used as the raw material has been performed by a method selected from pressure oxidation, bioleaching and roasting.

5. The method of claim 4 , wherein the pretreatment of the refractory gold concentrates used as the raw material has been performed by pressure oxidation.

6. The method of claim 1 , wherein the gold-bearing raw material is selected from refractory gold concentrates which have been pretreated by pressure oxidation.

7. The method of claim 1 , wherein the oxidative chloride leaching is performed at atmospheric pressure.

8. The method of claim 1 , wherein the oxidative chloride leaching is performed at the temperature of at least 50° C.

9. The method of claim 1 , wherein the pH value wherein the cupric ion does not precipitate is less than 2.6.

10. The method of claim 1 , wherein the oxidative chloride leaching is performed by providing an oxidizing source.

11. The method as claimed in claim 10 , wherein the oxidizing source is an oxygen feed, an oxygen-enriched air feed or an air feed to the solution.

12. The method of claim 1 , wherein the oxidation potential is 450-800 mV Pt vs. Ag/AgCl.

13. The method of claim 12 , wherein the oxidation potential is 450-700 mV Pt vs. Ag/AgCl.

14. The method of claim 1 , wherein the concentrations of Cu 2+ , Cl − and Br − in the leaching liquor are 10 110 g/l Cu 2 +, 50-300 g/l Cl − and 1-100 g/l Br − expressed as NaBr.

15. The method of claim 1 , wherein the acid concentration of the leaching liquor is 5-20 g/l HCl.

16. The method of claim 1 , wherein the gold recovery step (c) is performed by liquid-liquid extraction.

17. The method according to claim 16 wherein the extractant contains a diester of 2,2,4-trialkyl-1,3-pentanediol or 2-ethylhexanol or both.

18. The method of claim 1 , wherein the method further comprises a gold stripping step, wherein gold is stripped from the gold-bearing organic solution obtained in step (c) to obtain an aqueous gold-bearing solution.

19. The method of claim 1 , wherein the method comprises a further gold recovery step, wherein gold is recovered from the gold-bearing organic solution or from an aqueous gold-bearing solution.

20. The method as claimed in claim 19 , wherein the said further gold recovery step is performed by a method selected from reduction with oxalic acid, ascorbic acid or glucose, adsorption on activated carbon, cementation and direct burning of the gold-bearing organic reagent.

21. The method of claim 1 , wherein a part of the leaching solution is fed to the evaporation step or wherein all of the leaching solution is fed to the evaporation step.

22. The method as claimed in claim 21 , wherein 5-99 wt-% of mass of the leaching solution is fed to the evaporation step after gold recovery step.

23. The method of claim 1 , wherein the method further comprises a silver recovery step, where silver is recovered from at least part of the gold-depleted leach solution obtained from the gold recovery step (c).

24. The method as claimed in claim 23 , wherein the silver recovery step comprises a method selected from liquid-liquid extraction and precipitation.

25. The method as claimed in claim 24 , wherein the silver recovery step comprises liquid-liquid extraction with triisobutylphosphine sulphide, stripping with an aqueous thiosulfate salt solution and cementation of silver from the thiosulfate solution with metal powder.

26. The method as claimed in claim 24 , wherein the silver recovery step comprises sulfide precipitation.

27. The method as claimed in 23 , wherein the gold-depleted leach solution from step (c) is returned to the leaching step (a) after the silver recovery step.