Recovery of nickel and cobalt from laterite leach solutions using direct solvent extraction Part 2: Semi- and fully-continuous tests

摘要

In Part 1 of this paper, two synergistic solvent extraction systems consisting of Versatic 10/LIX63/TBP andVersatic 10/4PC were assessed in batch tests for the separation and purification of nickel and cobalt fromsynthetic laterite leach solution after iron removal. In Part 2, semi- and fully-continuous tests are reportedfor the Versatic 10/LIX63/TBP system, with conditions optimised for separating nickel and cobalt frommanganese, magnesium and calcium.Semi-continuous extraction tests were conducted using the synergistic organic system consisting of 0.50 MVersatic 10, 0.45 M LIX63 and 1.0 M TBP in Shellsol D70. With a pH profile of 5.5/6.1/6.5 for the three stagesEX1/EX2/EX3 at 40 ℃, the nickel and cobalt extractions were 99.9% with only 5 mg/L nickel and <1 mg/Lcobalt left in the raffinate. With two stages of scrubbing and a pH profile of 5.4/5.0 at 40℃, about 2 mg/L manganese and less than 1 mg/L magnesium and calcium were left in the scrubbed organic solution. Withtwo stripping stages and an 0/A ratio of 10 at 40 ℃ using 50 g/L H_2SO_4 as strip solution, the strippingefficiencies of nickel and cobalt were over 95%.A fully-continuous pilot plant was operated for 280 h. With an 0/A ratio of about 2 and a pH profile of 5.5/5.8/6.0/6.3 for the four stages EX1/EX2/EX3/EX4 at 40 ℃, both nickel and cobalt were almost completelyextracted. The nickel and cobalt concentration in the raffinate was lower than detection limit of 0.2 mg/L Themanganese, magnesium and calcium concentrations in the loaded organic solution were 34, 8 and 1 mg/L,respectively. Using a pH profile of 5.4/5.0 for SC1/SC2 at an 0/A ratio of 10 and 40℃, the manganesescrubbing efficiency was over 96% and the concentrations of manganese and magnesium in the scrubbedorganic solution were <5 mg/L and that of calcium 1 mg/L. Using three strip stages and a strip solutioncontaining 50 g/L H_2SO_4 and 55 g/L Ni at an O/A ratio of 10 and 40℃, over 98% Ni and 99% Co were strippedwith only 64 mg/L Ni in the stripped organic solution. The nickel concentration in the loaded strip liquor was86 g/L, giving a ΔNi of 31 g/L. The loaded strip liquor contained less than 1 g/L acid.