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Affinity of clinoptilolite-based zeolites towards removal of Cd from aqueous solutions

Cd removal from aqueous solutions using as-received and pretreated forms of two different clinoptilolite samples (denoted GC and BC) was investigated and dissimilar sorption affinities were revealed. Equilibrium behavior of systems were modeled using six different adsorption isotherms. The maximum sorption capacities, as obtained from the solubility-normalized Dubinin-Astakhov model for as-received samples, were determined as 0.18meq/g and 0.12meq/g for GC and BC, whereas 0.72meq/g and 0.41meq Cd/g was determined for their pretreated forms, respectively. Examination of the release of exchangeable cations into the solution at equilibrium and the change of pH were discussed in terms of varying prevalence of ion exchange, dissolution of the sorbent and adsorption.