Separation of nickel and copper from ammoniacal solutions through co-extraction and selective stripping using LIX84 as the extractant

Abstract

Ammoniacal–sulphate leach liquors obtained from a copper–nickel–iron concentrate were processed through solvent extraction for nickel–copper separation. Using the extractant LIX84 (40 vol.% diluted with kerosene, mainly aliphatic), the two metals were co-extracted quantitatively from a leach liquor containing (in kg/m 3) 13.8 Cu, 10.7 Ni, 90 (NH 4)OH and 45 (NH 4) 2SO 4 in two counter-current stages at an aqueous/organic (A/O) phase ratio of 1:2. The ammonia present in the loaded organic phase (1.92 kg/m 3) was removed prior to nickel stripping in a single stage scrubbing step using 6.6 kg/m 3 H 2SO 4 solution. The ammonia removal was ∼99% and the nickel loss to the scrub raffinate was 26.3 g/m 3. From the NH 3-depleted organic, nickel was selectively stripped in four counter-current stages at an A:O phase ratio of 2:1. By using a spent nickel electrolyte containing 57 kg/m 3 of nickel, 12 kg/m 3 each of H 3BO 3 and Na 2SO 4 (pH 1.70), nickel stripping was nearly quantitative. The spent organic retained ∼20 g/m 3 of nickel. There was some copper co-stripping (∼68 g/m 3) which is reported in the nickel-pregnant electrolyte. This copper concentration was reduced to 2.3 g/m 3 in a single stage extraction using the same solvent (40 vol.% LIX84) at an A/O ratio of 5 and the loaded organic was combined with the primary loaded organic for copper stripping. From the ammonia depleted and Ni-free loaded organic phase, copper was stripped in three counter-current stages at equal phase ratio using the spent copper electrolyte containing 30 kg/m 3 Cu and 180 kg/m 3 H 2SO 4. Although the spent organic retained ∼0.6 kg/m 3 copper, this value remained constant on recycling the spent organic in the extraction–stripping–extraction loop. A flow-sheet is suggested for the treatment of the leach liquor based on the above results.