Process for extracting nickel from gasifier slag

A process (1000) for extracting nickel from gasifier slag, said process (1000) comprising the following steps:

• i. leaching (300) a pulverized gasifier slag (280) with a chelating agent (360) and water at a first predetermined temperature for a first predetermined time, followed by filtering (350) to obtain a first leachate solution comprising an aqueous nickel-chelating agent complex and a first solid residue (380);
• ii. precipitating (400) said first leachate solution comprising said aqueous nickel-chelating agent complex by using a first acidic solution (460), followed by filtering (450) to obtain a precipitated chelating agent (490) and a second leachate solution (470) comprising nickel-containing aqueous solution;
• iii. leaching (500) said first solid residue (380) in a second acidic solution (560) at a second predetermined temperature for a second predetermined time under continuous stirring followed by filtering (550) to obtain a third leachate solution comprising an aqueous nickel-acid complex and a second solid residue (580);
• iv. treating (600) said third leachate solution comprising said aqueous nickel-acid complex by using an organic solvent (790) to obtain a first biphasic mixture comprising an organic layer of a nickel-solvent complex (670) and an aqueous layer (690);
• v. separating (650) said organic layer (670) of a nickel-solvent complex and treating (700) by using a third acidic solution (760) to obtain a second biphasic mixture comprising a nickel-containing aqueous phase and said organic solvent phase (790);
• vi. separating (750) nickel-containing aqueous phase from said second biphasic mixture to obtain a separated nickel-containing aqueous phase (770);
• vii. treating (800) said second leachate solution (470) obtained in step ii) and said separated nickel-containing aqueous phase (770) obtained in step vi) by using an alkali hydroxide (860) under continuous stirring to obtain a slurry comprising a precipitate of nickel hydroxide (870) and an aqueous solution (890);
• and
• viii. separating (850) said nickel hydroxide precipitate (870) followed by drying (900) and calcinating (950) at a third predetermined temperature for a third predetermined time period to obtain nickel (970) in the form of nickel oxide.