Application of IR spectra in the studies of heavy metal cations immobilization on natural sorbents

This work presents the results of FTIR spectroscopic studies (MIR) of heavy metal cations (Pb2+, Cd2+, Ag+ and Cr3+) immobilization from aqueous solutions on various forms of natural sorbents. Sorption has been conducted on natural clinoptilolite–montmorillonite mudstone and on its major components which have been separated from this deposit, i.e. on zeolite and smectite (their sodium forms).Based on changes in the spectra due to the immobilization of heavy metal ions, a scale of the sorption and the type of mechanism involved in the process (ion-exchange and/or chemisorption) can be established. Changes in intensities and positions of the bands corresponding to the characteristic ring vibrations have been observed. These rings occur in pseudomolecular 4-4-1 complexes (built of alumino- and silicooxygen tetrahedra) which constitute the secondary building units (SBU) and form spatial framework of the zeolite. The most significant changes have been determined in the region of pseudolattice vibrations. On the other hand, introduction of heavy metal cations into the structure of montmorillonite has caused the modification of band intensities due to stretching vibrations of OH− groups. In both cases, systematic changes connected with the type of cation (its chemical nature) and its concentration in the initial solution have been revealed.Results of IR spectroscopic studies have been compared with those obtained by atomic absorption spectroscopy (AAS), from which the proportion of ion-exchange to chemisorption in the process and the effective cation exchange capacity of the individual samples have been estimated.