Method for preparing a high-purity hydrated nickel sulphate

A method for producing nickel sulphate, the method including the steps of:

• a) providing a source of nickel sulphide concentrate;
• b) repulping the nickel sulphide of step (a) concentrate;
• c) fine grinding the nickel sulphide concentrate from step (b) to a P80 of 10 microns;
• d) low temperature pressure oxidation (LTPOX) autoclaving of the nickel sulphide concentrate from step (c) to afford a pregnant leach solution (PLS), wherein the nickel sulphide concentrate contains more than 10% nickel;
• e) neutralising the PLS of step (d) using one or more bases selected from the group including ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide;
• f) counter current decantation of the PLS from step (e) to separate solids from the slurry of the PLS;
• g) neutralising the PLS from step (f) using one or more bases selected from the group including ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide;
• h) optionally clarifying the PLS from step (g);
• i) extracting cobalt from the PLS of step (g) or step (h), wherein the cobalt extraction includes an organic extractant that selectively extracts cobalt over nickel into an organic phase to form a cobalt-rich nickel-lean extractant stream and a cobalt-lean nickel-rich raffinate;
• j) extracting nickel from the cobalt-lean nickel-rich raffinate of step (i);
• wherein the nickel extraction includes contacting the cobalt-lean nickel-rich raffinate with an organic phase including an organic extractant to form a nickel-rich organic phase;
• and
• k) direct crystallisation of the nickel-rich organic phase of step (j), wherein the direct crystallisation includes contacting the nickel-rich organic phase with an aqueous strip solution of sufficient H2SO4 concentration to extract nickel from the organic phase and of sufficient Ni2+ concentration to precipitate NiSO4.6H2O crystals and form a nickel-lean organic phase;
• wherein the nickel sulphate is between 21 and 24% nickel and is in the form of nickel sulphate hexahydrate (NiSO4.6H2O).