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For purposeful control of the adsorption process, a comprehensive study of the properties of the original cells and the effect of metal ions on them is necessary. In this regard, the features of the adsorption of Cr(III) ions on the cell surface of Spirulina platensis algae were studied. FTIR spectroscopy revealed that the main functional groups responsible for the binding of Cr(III) ions are carboxyl, hydroxyl, amino, and phosphate groups on the surface of algae. The adsorption data were processed using the Langmuir and Freundlich models. It is shown that the maximum adsorption of Cr(III) ions on the surface of algae cells is 31.25 mg/g. The Freundlich constant 1/n is 0.65. The study of the effect of the concentration of Cr(III) ions on the Zeta-potential of algae cells revealed an abnormal increase in the negative value of the ζ – potential at 10–5 mol/L, caused by the release of an additional amount of anionic functional groups to the surface. A further increase in the concentration of Cr(III) ions in the algae suspension leads to a decrease in the ζ – potential and recharge of the surface at C>10–2 mol/L. It was found that the adsorption of Cr(III) ions also affects the morphology of the cell surface. If before contact with Cr(III) ions, the surface of algae cells is represented as a uniform green grid, after adsorption of Cr(III) ions, the surface becomes green-brown, with swollen spirals. The study of the effect of pH on the adsorption and desorption processes shows an increase in the desorption of Cr(III) ions from the surface of algae during acidification of the medium. The adsorption reaches a maximum value in the pH range of 6–7. In the region of optimal Cr(III)/biosorbent ion ratios, the recovery rate of Cr(III) reaches 98.5–99.3 %.

In order to modify the surface, thermal acid activation of the zeolite of the Chankanai deposit was conducted. It was found that the treatment of the mineral with acid at high temperature leads to a decrease in the content of Ca, Al and Sr in its composition. Adsorption of chitosan on the surface of thermoacid-activated zeolite was also studied. Processing of the adsorption isotherms according to Langmuir and Freundlich models showed that the maximum adsorption of chitosan on the zeolite surface is 30.1 mg/g and the Freundlich constant 1/n is 0.75. On the IR-spectra of chitosan-modified zeolite, a certain shift to the higher frequencies of the peak was found at the oscillation frequency of 1638 cm-1, which can be explained by the contribution of amino groups adsorbed on the surface of the mineral. The shift to the left of the peak at 581 cm-1, typical for aluminosilicate groups, is also an evidence of their interactions with chitosan. When studying the effect of chitosan concentration on the wetting of the modified zeolite powder, it was found that at concentration of 2.10-3 base mol/L, an increase in the wetting angle from 10° to 47° occurs due to surface overcharging. According to the data of adsorption, IR spectroscopy and wetting of the surface, the main mechanism for binding chitosan to the zeolite surface was due to the electrostatic interaction of polymer amino groups with silicate and aluminosilicate groups of the mineral, stabilized by hydrogen bonds between the OH-groups of the polymer and ≡Si-O-groups of the solid phase.

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