Process for preparing a high-purity nickel sulphate solution

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

• i. forming an aqueous mixed metal sulphate solution by reacting sulphuric acid with a raw material feed comprising nickel, manganese, cobalt and magnesium in an aqueous medium;
• ii. extracting manganese from said aqueous mixed metal sulphate solution at a temperature between 2° and 45° C. using a first organic phase comprising a first alkylphosphorus-based extractant (I) and a first diluent, wherein said first alkylphosphorus-based extractant (I) comprises an alkylphosphoric acid and/or nickel salts thereof, thereby obtaining a first aqueous raffinate comprising nickel, cobalt and a magnesium content, and a manganese-rich organic phase;
• iii. extracting cobalt from said first aqueous raffinate at a temperature between 45 and 65° C. using a second organic phase comprising a second alkylphosphorus-based extractant (II) and a second diluent, wherein said second alkylphosphorus-based extractant (II) comprises an alkylphosphinic acid, and/or nickel salts thereof, thereby obtaining a second aqueous raffinate comprising nickel and a residual magnesium content and a cobalt-rich organic phase;
• and
• iv. extracting magnesium from said second aqueous raffinate solution using a third organic phase comprising a third alkylphosphorus-based extractant (III) and a third diluent, wherein said third alkylphosphorus-based extractant (III) comprises an alkylphosphinic acid, and/or nickel thereof, thereby obtaining a high-purity nickel sulphate solution and a magnesium-enriched organic phase.