Method for recovering metals
View Patent ↗The invention relates to a method and apparatus for recovering metals from metalliferous starting materials comprising steps of i) leaching the metalliferous starting material in chloride-based leaching liquor, ii) withdrawing from the leaching step i) aqueous chloride solution with dissolved metals, iii) recovering metal value from the aqueous chloride solution in a metal recovery process step, iv) neutralizing hydrogen chloride content of the aqueous chloride solution in the metal recovery process step with adding hydrolyzed ammonia to the process solution so as to form ammonium chloride, v) withdrawing ammonium chloride containing process solution to an ammonium regeneration step where calcium-containing reagent is added to generate calcium chloride and ammonia gas and recycling ammonia back to the metal recovery process step iii), vi) regenerating the CaCl 2 -solution with H 2 SO 4 so as to provide a aqueous HCl solution for recycling to the leaching step i).
1. A method for recovering metals from metalliferous starting materials comprising steps of
i) leaching the metalliferous starting material in chloride-based leaching liquor having a chloride concentration between 100 g/l and 350 g/l,
ii) withdrawing from the leaching step i) aqueous chloride solution with dissolved metals,
iii) recovering metal value from the aqueous chloride solution in a metal recovery process step comprising solvent extraction,
iv) neutralizing a hydrogen chloride content of the aqueous chloride solution in the metal recovery process step by adding hydrolyzed ammonia to form an ammonium chloride containing process solution,
v) withdrawing the ammonium chloride containing process solution to an ammonium regeneration step where calcium-containing reagent is added to generate a calcium chloride solution and ammonia gas, and recycling the ammonia gas back to the metal recovery process step iii) to take part in a pre-neutralization,
vi) regenerating the calcium chloride solution with H 2 SO 4 so as to provide an aqueous hydrogen chloride solution for recycling to the leaching step i).
2. The method according to claim 1 , wherein the starting material is selected from the group consisting of laterite ores containing the base metals nickel and cobalt, copper, cobalt, nickel metal-bearing raw materials, oxidized metalliferous material containing nickel, cobalt and copper, nickelferous sulfide material containing at least one other metal selected from the group consisting of cobalt, copper and iron, NiS precipitate, nickel matte, aqueous metal sulfate-containing solution the metals being selected from the group consisting of cobalt, copper, nickel and iron, nickel sulfide concentrate and mixtures thereof.
3. The method according to claim 1 , wherein the temperature in the leaching step is between 80° C. and the boiling point of the solution.
4. The method according to claim 3 , wherein the temperature in the leaching step is between 80 and 104° C.
5. The method according to claim 3 , wherein the temperature in the leaching step is between 80 and 99° C.
6. The method according to claim 1 , wherein the metal value to be recovered is selected from the group consisting of copper, cobalt and nickel.
7. The method according to claim 1 , wherein ground nickel matte is fed as a reducing agent to the chloride-based leaching liquor.
8. The method according to claim 7 , wherein gold and platinum group metals are recovered by precipitating into leach residue and recovering from the leach residue.
9. The method according to claim 1 , wherein pH in the leaching step is between −0.5 and 1.5 so that iron is leached and a leach residue is formed, which is separated after which iron is precipitated at pH 1.5-2.6 with a calcium containing neutralization agent.
10. The method according to claim 1 , wherein pH in the leaching step is between 1.5 and 2.6 so that iron is precipitated during the leaching.
11. The method according to claim 1 , wherein, after metal recovery, there is a total sulfur concentration as sulfate of between 0.1 g/l and 1 g/l, causing iron precipitation.
12. The method according to claim 1 , wherein copper is recovered as a part of step iii) by extraction by contacting the aqueous chloride solution containing copper with hydroxyloxime-based reagent diluted in a hydrocarbon solvent.
13. The method according to claim 1 , wherein the method contains one or more copper solvent extractions and each of them contains 1-3 extraction stages, 1-3 washing stages and 1-3 stripping stages.
14. The method according to claim 1 , wherein a copper extraction step is carried out, whereby copper is obtained in a raffinate, which copper is precipitated as atacamite at pH between 2.5 and 5.
15. The method according to claim 1 , wherein cobalt is recovered as a part of step iii) by solvent extraction by contacting the aqueous chloride solution, which contains cobalt, with one or several extraction reagents diluted in a hydrocarbon solvent and where the extraction is based on cation exchange.
16. The method according to claim 1 , wherein the method contains one or more cobalt solvent extractions and each of them contains 2-6 extraction stages, 1-3 washing stages and 1-4 stripping stages.
17. The method according to claim 1 , wherein the cobalt is recovered as a part of step iii).
18. The method according to claim 1 , wherein nickel is recovered, as a part of step iii), by solvent extraction by contacting the aqueous chloride solution, which contains nickel, with one or several extraction reagents diluted in a hydrocarbon solvent.
19. The method according to claim 1 , wherein the process step iii) contains one or more nickel solvent extractions and each of them contains 2-6 extraction stages, 1-3 washing stages and 1-4 stripping stages.
20. The method according to claim 1 , wherein ammonia is used in a solvent extraction that forms a part of step iii) to pre-neutralize a metal extractant molecule.
21. The method according to claim 1 , wherein ammonia is fed directly to a solvent extraction that forms a part of step iii) to neutralize hydrochloric acid which is formed in extraction reactions.
22. The method according to claim 1 , wherein calcium containing reagent in step v) is calcium oxide and/or calcium hydroxide.
23. The method according to claim 1 , wherein temperature is 25-100° C. and pressure is 7-200 kPa in the ammonium regeneration step.
24. The method according to claim 1 , wherein ammonia is stripped from solution to gas phase by using steam in the ammonium regeneration step.
25. The method according to claim 1 , wherein calcium chloride solution from the ammonium regeneration step is mixed with sulfuric acid solution so that gypsum and hydrochloric acid solution are formed.
26. The method according to claim 1 , wherein the temperature of the step of regenerating the calcium chloride containing solution is between 25° C. and 80° C. and the concentration of the sulfuric acid in sulfuric acid solution is between 25 wt-% and 99 wt-%.
27. The method according to claim 1 , wherein the calcium concentration in the solution after the step of regenerating the calcium chloride containing solution is 10 to 40 g/l.
28. The method according to claim 1 , wherein the copper is recovered, as a part of step iii), by solvent extracting by contacting the aqueous chloride solution containing copper with hydroxyoxime-based reagent diluted into kerosene, acting as a diluent.
29. The method according to claim 1 , wherein copper is recovered, as a part of step iii), by precipitating copper sulfide with hydrogen sulfide.
30. The method according to claim 1 , wherein the cobalt is recovered, as a part of step iii), by extraction by contacting the aqueous chloride solution, which contains cobalt, with an extraction reagent diluted into kerosene, acting as a diluent.
31. The method according to claim 1 , wherein nickel is recovered, as a part of step iii), by extraction by contacting the aqueous chloride solution containing nickel with an extracting reagent.