Sorption ability of the chitosan-modified natural zeolite for Pb 2+ , Cd 2+ , and Cu 2+ cations was investigated. The influence of time and concentration of heavy metals on their sorption from concentrated (85% H 3 PO 4 ) phosphoric acid was determined. At 20 and 40 min of sorption curves, there are a number of maxima probably due to desorption of cations from the sorbent into the acid. According to the results, sorption of the modified zeolite for lead cation is the least in the whole interval of time. In the case of equal concentrations of all cations (C Pb = C Cd = C Cu ), sorption of lead, cadmium, and copper was 94.81-95.09%, 96.55-97.50%, and 97.53-98.14%, respectively. Sorption curves in the case of equal Pb 2+ and Cd 2+ , but higher concentrations of Cu 2+ , are the same for all cations. Sorption of cadmium varies from 95.48% to 97.55%. Copper and lead sorbed in a less amount, in the case of (С Рb = С Cd < С Cu ), their sorption in 10 min was 95.42% and 97.55%, respectively. As in the case of equal concentrations of all cations (C Pb = C Cd = C Cu ), the sorptions of copper, cadmium, and lead were (92.09-96.93%), (92.13-95.37%), and (91.35-94.45%), respectively, in the case of (С Рb = С Cu < С Cd ).Physico-chemical methods of analysis are as follows: Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray powder diffraction patterns, and Brunauer-Emmett-Teller have shown that natural zeolite is activated without destroying the structure and adsorbs lead, as well as cadmium and copper cations.

A B S T R A C TZeolite, a well-known inorganic compound, was used for Pb(II) and Cd(II) sorption. For this purpose, the model system composed with "H 3 PO 4 -Pb 2+ -Cd 2+ " medium was selected and applied with various amounts of both heavy metal salts. The results revealed that sorption capacity of the sorbent was higher for Pb 2+ cation than in the diluted phosphoric acid (20% H 3 PO 4 ) for all periods. The absorption of toxic metal ions was measured by atomic absorption spectroscopy. Different physical and chemical analysis techniques such as Fourier Transform infrared, scanning electron microscope, DTA, and XRD showed that natural state of zeolite in a diluted phosphoric acid (20% H 3 PO 4 ) system underwent protonation and hydroxylation to produce additional OH − groups that are active in the sorption process and no destruction was observed in the structure.