Removal of Cysteine (an Aliphatic Amino Acid) by Natural Clinoptilolite

Amino acids have been extensively used in several processes of the pharmaceutical and food industries. Treatments for the recovery and reuse of the wastewaters generated from these processes are few and little known. This work aims at studying the influence of different variables on the sorption of L-cysteine, contained in aqueous solutions, on clinoptilolite mineral. L-Cysteine (Cys) was sorbed by Clinoptilolie (Clino) from aqueous solutions of variable concentrations, temperatures and pHs. The powder X-Ray Diffraction (XRD), InfraRed (IR) spectroscopy and thermal analysis (TG, DTG and DSC) techniques were applied for characterization of materials. The results indicated that the sorption process depends strongly on pH, temperature and concentration of amino acid. Cysteine is specifically sorbed on clinoptilolite surface sites, probably through its NH3+ moiety. The pH dependence suggests that these sites may be silanolate groups (≡Si-O-).The experimental data of sorption isotherms obtained and analyzed with Langmuir model showed that this model fitted the sorption data. Calculated thermodynamic parameters (ΔH°, ΔS°, and ΔG°) indicate that the sorption processes were exothermic.