Solvent extraction of impurity metals from a valuable metal sulphate solution
The present invention relates generally to a method of extracting cobalt and other impurity metals from a concentrated nickel sulphate solution by a solvent extraction process whereby a cationic solvent extractant is separately pre-equilibrated with a portion of a purified nickel sulphate solution in such a manner that it is loaded with nickel without precipitating insoluble nickel double salts. The nickel loaded extracted is then transferred to an impure cobalt nickel solution where the cobalt and certain other impurity metals exchange with nickel leaving a purified concentrated nickel sulphate solution suitable for hydrogen reduction or electrowinning. The cobalt loaded extractant is stripped with dilute sulphuric acid before being recycled while an aqueous cobalt stripped solution is further processed to recover cobalt.
1. A method of extracting impurity metal ions including any one or more of cobalt, copper, zinc and manganese from an impure valuable sulphate stream in the form of a cobalt/nickel-containing stream in a solvent extractant circuit, the method comprising the steps of:
a) contacting the cobalt/nickel-containing stream in a cobalt solvent extraction circuit with an organic solvent and producing a cobalt-loaded organic extractant and a purified nickel-containing stream;
(b) stripping cobalt from the cobalt-loaded organic extractant and producing a stripped organic extractant;
(c) directly after step (b), loading the stripped organic extractant with nickel from a part of the purified nickel-containing stream from step (a) to pre-equilibrate the organic extractant; and
(d) providing the pre-equilibrated organic extractant as the organic solvent for contacting with the cobalt/nickel-containing stream in step (a).
2. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 1 wherein the impure valuable sulphate stream is a concentrated nickel sulphate liquor obtained by acid pressure leaching of a nickel-cobalt sulphide mineral.
3. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 1 wherein pre-equilibration of the organic extractant with the nickel from a part of the purified nickel-containing stream is effected with the direct addition of an ammonia solution.
4. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 3 wherein the purified nickel-containing stream is preconditioned by dilution with a diluent to achieve a predetermined concentration of the nickel sufficient to avoid formation of insoluble ammonium/nickel sulphate double salts.
5. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 4 wherein the diluent is water.
6. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 1 wherein pre-equilibration of the organic extractant is effected with the direct addition of magnesia or magnesium hydroxide.
7. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 1 further comprising the step of stripping of an impurity loaded organic extractant from the solvent extraction circuit with sulphuric acid to yield the organic extractant for recycle to pre-equilibration.
8. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 7 wherein said step of stripping of said impurity loaded extractant produces an aqueous impurity metal strip solution which is processed to recover one or more of said impurity metal ions.
9. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 1 also comprising the step of electrowinning a high purity electrolyte of the purified nickel-containing stream to recover high purity nickel.
10. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 1 wherein the purified nickel-containing stream or a derivative thereof is subjected to hydrogen reduction.
11. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 1 wherein the organic extractant comprises a phosphinic acid.
12. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 11 wherein the phosphinic acid is bis (2,4,4 trimethylpentyl) phosphinic acid, or a derivative thereof.
13. A method of extracting impurity metal ions from an impure valuable sulphate stream in a solvent extraction circuit as defined in claim 4 wherein the purified nickel-containing stream is diluted with another diluent.