Abstract
Amino acids have been extensively used in several processes in the pharmaceutical and food industries. However, treatments for the recovery and re-use of the wastewaters generated from these processes are sparse and little known. The aim of the present work was the study of the influence of different variables on the sorption of L-cysteine from aqueous solution onto the mineral clinoptilolite. For this purpose, L-cysteine (Cys) was sorbed by clinoptilolite (Clino) from aqueous solutions of variable concentrations at various temperatures and pH values. The materials employed were characterized by X-ray powder diffraction (XRD), infrared spectroscopy (IR) and thermal analysis (TG, DTG and DSC) techniques. The results indicated that the sorption process depended strongly on the pH, temperature and concentration of amino acid. L-Cysteine was specifically sorbed onto the surface sites of clinoptilolite probably via its NH+3 moiety. The pH dependence suggests that these sites may be silanolate groups (≡Si – O−). Analysis of the experimental data obtained for the sorption isotherms via the Langmuir model gave a good fit. The calculated thermodynamic parameters (Δ;H0, Δ;S0 and Δ;G0) indicated that the sorption process was exothermic.