Recovery of valuable metals
A continuous flotation process and apparatus for iron-containing sulphides in ores and concentrates of ores are disclosed. The process includes adjusting the pH of an aqueous pulp of the ores or concentrates of the ores to be in the range of 6.5-8.5 and thereafter adding a reducing agent to modify an iron hydroxide film on the surface of iron-containing sulphides in the ores or ore concentrates to enable adsorption of a collector onto iron-containing sulphides. The process also includes adding the collector to the pulp prior to, during, or after adding the reducing agent. The process also includes aerating the pulp to increase the pulp potential to a level sufficient to allow collector adsorption onto the iron-containing sulphides and thereafter bubbling gas through the pulp and subjecting the aqueous pulp to froth flotation to produce a froth containing said sulphide containing minerals.
1. A continuous flotation process for iron-containing sulphides in ores and concentrates of ores includes the following steps:
(a) adjusting the pH of an aqueous pulp of the ores or concentrates of the ores to be in the range of 6.5-8.5;
(b) adding a reducing agent to modify an iron hydroxide film on the surface of iron-containing sulphides in the ores or ore concentrates to enable adsorption of a collector onto iron-containing sulphides;
(c) adding the collector to the pulp prior to, during, or after adding the reducing agent in step (b);
(d) aerating the pulp to increase the pulp potential to a level sufficient to allow collector adsorption onto the iron-containing sulphides;
(e) bubbling gas through the pulp and thereby subjecting the aqueous pulp to froth flotation to produce a froth containing said sulphide containing minerals; and
(f) adding a complexant to the pulp prior to or during step (b) to minimize iron hydroxide reforming a film on the iron-containing sulphides.
2. The process defined in claim 1 includes controlling the addition of the reducing agent in step (b) by reference to the change in pulp potential as the reducing agent is being added in step (b).
3. The process defined in claim 1 wherein step (e) includes separating the froth of floated iron-containing sulphides from the pulp and thereafter recovering valuable metals from the froth.
4. The process defined in claim 1 wherein the iron-containing sulphides contain one or more valuable metals selected from the group that includes nickel, gold, or platinum group metals.
5. The process defined in claim 1 wherein step (a) includes adjusting the pH of the aqueous pulp to be in the range of 7.0-8.0.
6. The process defined in claim 5 wherein step (a) includes adjusting the pH of the aqueous pulp to be in the range of 7.1-7.5.
7. The process defined in claim 1 wherein step (a) includes adjusting pulp pH by adding acid to the pulp.
8. The process defined in claim 1 wherein step (a) includes adjusting pulp pH as the pulp flows through a first tank.
9. The process defined in claim 1 wherein step (a) includes controlling the flow of pulp through the first tank to be plug flow.
10. The process defined in claim 1 wherein step (b) includes controlling the addition of the reducing agent by adding the reducing agent to the pulp to decrease the pulp potential by at least 150 mV.
11. The process defined in claim 10 wherein step (b) includes controlling the addition of the reducing agent by adding the reducing agent to the pulp to decrease the pulp potential by at least 200 mV.
12. The process defined in claim 1 wherein step (b) includes controlling the addition of the reducing agent by adding the reducing agent to the pulp to decrease the pulp potential by no more than 350 mV.
13. The process defined in claim 1 wherein step (b) includes intensively mixing the pulp while adding the reducing agent.
14. The process defined in claim 1 wherein step (b) includes adding the reducing agent to the pulp as the pulp flows through a second tank.
15. The process defined in claim 1 wherein the reducing agent is an oxy-sulphur compound which dissociates in the aqueous media to form oxy-sulphur ions having the general formula
SnO y z−
where n is greater than 1; y is greater than 2; and z is the valance of the ion.
16. The process defined in claim 15 wherein the oxy-sulphur compound is dithionite.
17. The process defined in claim 1 wherein the complexant is selected from the group consisting of citric acid and oxalic acid.
18. The process defined in claim 17 wherein the complexant is citric acid.
19. The process defined in claim 1 includes adding the complexant to the pulp during step (b) of adding the reducing agent to the pulp.
20. The process defined in claim 1 includes adding the complexant to the pulp during step (b) of adding the reducing agent to the pulp as the pulp flows through the second tank.
21. The process defined in claim 1 wherein the collector is selected from the group that includes xanthates, dixanthogen, xanthate esters, dithiophosphates, dithiocarbamates, thionocarbamates, and mercaptans.
22. The process defined in claim 21 wherein the collector is a xanthate.
23. The process defined in claim 1 wherein step (c) includes adding the collector to the pulp during step (b) of adding the reducing agent to the pulp.
24. The process defined in claim 23 wherein step (c) includes adding the collector to the pulp during step (b) of adding the reducing agent to the pulp as the pulp flows through the second tank.
25. The process defined in claim 1 includes controlling the process so that the average residence time of pulp flowing through the second tank is less than 45 seconds.
26. The process defined in claim 25 includes controlling the process so that the average residence time of pulp flowing through the second tank is approximately 30 seconds.
27. The process defined in claim 1 includes controlling the flow of pulp through the second tank to be plug flow.
28. The process defined in claim 1 wherein step (d) includes aerating the pulp downstream of the second tank.
29. A continuous flotation process for iron-containing sulphides in ores and concentrates of ores includes the following steps:
(a) adjusting the pH of an aqueous pulp of the ores or concentrates of the ores to be in the range of 6.5-8.5;
(b) adding a reducing agent to modify an iron hydroxide film on the surface of iron-containing sulphides in the ores or ore concentrates to enable adsorption of a collector onto iron-containing sulphides;
(c) adding the collector to the pulp prior to, during, or after adding the reducing agent in step (b);
(d) aerating the pulp to increase the pulp potential to a level sufficient to allow collector adsorption onto the iron-containing sulphides;
(e) bubbling gas through the pulp and thereby subjecting the aqueous pulp to froth flotation to produce a froth containing said sulphide containing minerals;
(f) adding a complexant to the pulp prior to or during step (b) to minimize iron hydroxide reforming a film on the iron-containing sulphides
wherein the complexant is selected from the group consisting of citric acid and oxalic acid.