Effect of reversed micelles in Co/Ni separation by Cyanex 272

Abstract

The extraction and separation of cobalt and nickel from aqueous sulphate solutions using Cyanex 272 reagent (Cytec Industries) in isooctane and D-70 (Shell Chemicals) was studied. The extractant was pre-neutralised with concentrated ammonia water, which forms a one-phase solution at an ammonia/reagent molar ratio of 1:1. The extraction experiments were carried out in a vigorously agitated co-current column reactor with fast phase separation in which the contact time could be varied between 2 and 90 s. The extraction kinetics of Co and Ni are very fast. During the first 10 s of phase contact about 90% of the metals are extracted into the organic phase. At the shortest contact time, when a small amount of cobalt and nickel had been extracted, the organic phase contained reversed micelles enclosing water, metal ions and ammonia. With increasing cobalt loading, the reversed micelles broke up and the concentration of water and nickel decreased in the organic phase. To achieve a high cobalt/nickel separation, the cobalt/extractant molar ratio should be 1 to 4 when the degree of neutralisation of the Cyanex 272 is equal to about 50%. In a system with 10 wt.% Cyanex 272 in D-70 diluent and 3.5 g/L Co and 30 g/L Ni in the aqueous feed, the highest separation factor (5000) was obtained when the feed phase volume ratio was 1:1 and the degree of neutralisation ( N) was 45%. The pre-neutralised reagent was in that case in the form of a two-phase (liquid–liquid) solution.