The overall metal recovery also depends on the metal elution
efficiency of the adsorbed metals. Elution efficiency was defined
in this study, as the ratio of the mass desorbed from the resins to
the mass adsorbed onto the resins. Table 4 compares the elution
of nickel adsorbed on Purolite S950. The effects of variables
including the nature of the complexes, metal (100–2000 mg/L)
and acid concentrations (0.01 and 0.1 M) on metal elution were
considered in this investigation. As shown, nickel complexes
were easily eluted from the resins; elution efficiencies of about
90% were achieved. In general, similar elution efficiencies of
nickel were achieved when adsorbed from various complexes
and metal concentrations. Co-complexes were also found to be
efficiently eluted from the resin (up to 98%) (see Table 5). It
is clear, the nature of the ligand complexed to Co and Ni and
metal concentrations have little effect on the cobalt desorption.
This suggests the exchange reactions are equivalent for the three
complexes considered in this study and that surface interaction
between the resin and the metal complexes are independent of
the metal speciation. Efficient elution of the metal complexes
from the resin suggests the metal complexes interaction with
the resin is based on weak bonds.