Process for preparing a high-purity nickel sulphate solution

A process for preparing a high-purity nickel sulphate solution, comprising the steps of:

• i. providing an aqueous feed solution comprising nickel, cobalt, calcium, and magnesium, and if present, zinc, manganese, cadmium, and/or copper;
• ii. in a first solvent extraction circuit, extracting cobalt, calcium and, at least in part, magnesium, and if present, zinc, copper, cadmium, and manganese, from said aqueous feed solution using a first organic phase comprising a first alkylphosphorus extractant (I) and a first diluent, thereby obtaining an aqueous raffinate solution comprising nickel and a residual magnesium content and a cobalt-rich and calcium containing organic phase;
• iii. in a second solvent extraction circuit, extracting the residual magnesium content from said aqueous raffinate solution using a second organic phase comprising a second alkylphosphorus extractant (H), different from said first alkylphosphorous extractant (I), and a second diluent, thereby obtaining an aqueous nickel sulphate solution having reduced magnesium content relative to the aqueous raffinate solution and a magnesium-enriched organic phase;
• and
• iv. stripping said cobalt-rich organic phase obtained in step ii. with an aqueous solution comprising a mineral acid,
• wherein said first alkylphosphorus extractant (I) and said second alkylphosphorous extractant (II) comprise nickel, and
• whereby said first organic phase and said second organic phase provided in steps ii. and iii. comprise said first and said second alkylphosphorus extractant, respectively, in an amount of 5 to 50 vol. %, relative to the total volume of said organic phases, and said diluents in an amount of 50 to 95 vol. %, relative to the total volume of said organic phases.