This study examined the recovery of nickel and cobalt from organic acid complexes using a chelating aminophosphonate Purolite S950 resin. These
metal complexes are generated by bioleaching nickel laterite ores, a commercial nickel and cobalt mineral oxide, with heterotrophic organism and
their metabolites or organic acid products. Equilibrium adsorption tests were conducted as a function of Ni and Co concentrations (15–2000 mg/L),
solution pH (0.01 and 0.1 M acids) and three metabolic complexing agents (citrate, malate and lactate). It was shown that the adsorption of the
various Ni- and Co-complexes on Purolite were quite low, 16–18 and 5.4–9 mg/g of resin, respectively, in comparison to the smaller nickel ions
and nickel sulfate. This was attributed to the bulky organic ligands which promoted crowding effect or steric hindrance. The adsorption of these
complexes was further hampered by the strong affinity of the resin to H+ ions under acidic conditions. Mechanisms of adsorption, as inferred from
the fitted empirical Langmuir and Freundlich models, were correlated to the proposed steric hindrance and competitive adsorption effects. Nickel
and cobalt elution from the resin were found be effective and were independent of the type of metal complexes and metal concentrations. This
study demonstrated the relative challenges involved in recovering nickel and cobalt from bioleaching solutions.
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