Nickel sulphide precipitation process
The invention provides hydrometallurgical processes by which dissolved nickel may be removed from water at ambient temperature and low system pressure.
1. A continuous process for precipitating nickel ions from aqueous solutions, the process comprising:
a) providing a pregnant aqueous solution comprising dissolved nickel ions at a concentration of less than 1 g/L and dissolved oxygen;
b) removing oxygen from said pregnant aqueous solution to provide a de-aerated feed water;
c) contacting the de-aerated feed water with a dissolved sulphide source in a contactor to form solid nickel sulphide, the contacting being performed under contactor conditions that comprise a contacting temperature of between 0° C. and 50° C., a contacting pressure of between 0.5 atmosphere and 1.5 C. atmosphere, and a contacting pH of between 6 and 9;
d) separating the solid nickel sulphide from the pregnant solution to provide a nickel sulphide sludge and a barren water solution, wherein the nickel sulphide sludge has a mean nickel particle size of at least 5 microns and the barren water solution has a dissolved nickel concentration of less than 10 parts per million; and,
e) recycling at least a portion of the nickel sulphide sludge to the contactor under conditions such that said recycled portion seeds nickel sulphide particle growth to provide the mean nickel particle size of at least 5 microns.
2. The process of claim 1 , further comprising dissolving a coagulant in the pregnant aqueous solution so that a dissolved coagulant is present when contacting the pregnant solution with the dissolved sulphide.
3. The process of claim 2 , wherein the coagulant is an aluminium salt or aluminium chloride.
4. The process of claim 1 , wherein the coagulant dose range is controlled to modulate contactor conditions.
5. The process of claim 1 , wherein the contacting pH is about 8.3.
6. The process of claim 1 , wherein the mean hydraulic residence time for the step of contacting in the contactor is less than 1 hour.
7. The process of claim 1 , wherein the mean hydraulic residence time for the step of contacting in the contactor is less than 30 minutes.
8. The process of claim 1 , wherein the mean hydraulic residence time for the step of contacting in the contactor is about 20 minutes.
9. The process of claim 1 , wherein the contacting temperature is less than 35° C.
10. The process of claim 1 , wherein the process is carried out without heating.
11. The process of claim 1 , wherein the contactor temperature is an ambient temperature.
12. The process of claim 1 , wherein the contactor pressure is within 0.5atmosphere of ambient pressure.
13. The process of claim 1 , wherein the contactor pressure is an ambient pressure.
14. The process of claim 1 , wherein the pregnant aqueous solution comprises a dissolved metal selected from the group consisting of cobalt, copper, iron, zinc, arsenic, mercury, lead and manganese.
15. The process of claim 1 , wherein the contactor conditions comprise a contactor oxidation reduction potential, and the contactor oxidation reduction potential is of between −50 and −400 mV with respect to a Ag/AgCl electrode.
16. The process of claim 1 , wherein the contactor conditions comprise a concentration of contactor solids, and the concentration of contactor solids is less than 50 g/L.
17. The process of claim 1 , wherein the sulphide source is selected from the group consisting of a sulphide salt formed from hydrogen sulphide, a hydrogen sulphide, a gaseous sulphide, an alkali metal sulphide and an alkaline earth metal sulphide.
18. The process of claim 17 , wherein said sulphide salt is selected from the group consisting of sodium hydrosulphide, calcium hydrosulphide, sodium sulphide, and calcium sulphide.
19. The process of claim 1 , wherein the concentration of the sulphide in the contactor is in stoichiometric excess over the concentration of dissolved nickel.
20. The process of claim 1 , wherein the nickel sulphide sludge recycle to the contactor is carried out so as to maintain a concentration of nickel sulphide particles in the contactor in the range of 5 to 50 g/L.
21. The process of claim 1 , wherein the dissolved nickel concentration in the barren water is 0.01 to 10 mg/L.
22. The process of claim 1 , further comprising maintaining the contactor pH below about 9 so as to inhibit the formation of solid nickel hydroxide in the contactor.
23. The process of claim 1 , further comprising conditioning the recycled nickel sulphide sludge in a conditioning reactor to peptize the nickel sulphide particles in the sludge before recycling the nickel sulphide sludge to the contactor.
24. The process of claim 23 , further comprising adding a sulphide to the conditioning reactor.
25. The process of claim 1 , wherein the barren water is used to dissolve a sulphide salt to provide the dissolved sulphide.
26. The process of claim 1 , wherein the barren water solution has a dissolved metal concentration that is at least about 95% less than the dissolved metal concentration of the pregnant aqueous solution.
27. The process of claim 1 , wherein the barren water solution has dissolved copper concentration of 0.04 milligrams per liter or less, a dissolved cadmium concentration of 0.003 milligrams per liter or less, and a dissolved zinc concentration of 0.05 milligrams per liter or less.
28. A process for precipitating nickel ions from aqueous solutions, the process comprising:
a) providing a feed solution comprising dissolved nickel ions at a concentration of less than 1 g/L and dissolved oxygen;
b) removing oxygen from the feed solution to provide a de-aerated feed water;
c) contacting the de-aerated feed water with a dissolved sulphide source, in a contactor to form a solid nickel sulphide product;
d) separating the solid nickel sulphide from the feed solution to provide a nickel sulphide sludge product having a mean nickel particle size of at least about 5microns and a barren water solution; and,
e) recycling at least a portion of the nickel sulphide sludge product to the contactor under conditions such that said recycled portion seeds nickel sulphide particle growth to provide the mean nickel particle size of at least 5 microns.
29. The process of claim 28 , wherein said feed source comprises wastewater.
30. The process of claim 28 , wherein the process is carried out without heating.
31. A process for precipitating nickel ions for aqueous solutions, the process comprising:
a) providing:
i) an aqueous feed solution, wherein said feed solution comprises dissolved nickel ions at a concentration less than 1 g/L and oxygen;
ii) a dissolved sulfide source capable of reacting with said nickel ions; and
iii) a contactor;
b) removing oxygen from said feed solution prior to introduction of said feed solution into said contactor; and
c) precipitating said nickel ions with said dissolved sulfide source in said contactor, wherein a solid nickel sulphide is created.
32. The process of claim 31 , further comprising:
d) separating said solid nickel sulfide in a clarifier under conditions such that a nickel sulfide sludge and a barren water solution are created.
33. The process of claim 31 , further comprising:
d) recycling at least a portion of the nickel sulphide product to the contactor.