Usually, the performance of the sorbing materials can be
evaluated in terms of uptake (qA) and affinity toward the solute. In
this study, and although it was not possible to estimate the
maximum value of qA for the CC sorbent, clearly this material has a
higher uptake capacity toward Hg2+ than the CS. However, in terms
of affinity, parameter which is characterized by a steep rise of the
isotherm curve close to its origin, the CS sorbent performs better
than the CC. In this particular case, and although there is no
experimental data for CC below CA,e of 15.5 mg/L to support this
statement, the theoretical isotherms curves of the two sorbents
intersect at CA,e circa14 mg/L (Fig. 4), point where theoretically the
performance of the two sorbents is the same in terms of qA. So, the
modelling of the equilibrium data suggest that for lower CA,e, the CS
has a better performance than CC, while for values higher than
14 mg/L the CC sorbent is clearly better. This highlights the
importance of choosing the right sorbent according with purpose
of the process. For instance, if the sorbent is supposed to work at
low residual sorbate concentrations, with the goal for example of
limiting the maximum concentration in an effluent, the CS sorbent
is the best choice while, if the purpose is to saturate the sorbent as
much as possible, independently of the residual concentration in
solution, the CC sorbent is better since it uptakes more Hg2+ at
higher residual concentrations.