Development of polyadsorbents based on polyethylenimine and low molecular weight ligands for the extraction of group II metal ions from wastewater

The object of this study is the physicochemical processes of interaction between Group II metal ions and polyethyleneimine (PEI) and low-molecular-weight ligands (salicylic acid, sulfosalicylic acid, EDTA) with the aim of developing polyadsorbents for the selective extraction of toxic ions from aqueous media. The problem to be solved is the development of effective and selective polyadsorbents for removing toxic metal ions from wastewater. Potentiometric, conductometric, and viscometric analysis methods have established that in binary PEI-M2+ systems, coordination complexes are formed with a molar ratio of PEI:M2+ = 2:1. For systems with Sr2+ and Ba2+ ions, stepwise complexation was identified, with particles of composition 6:1 and 4:1 being formed at the initial stage, respectively. The stability of the complexes formed was established in the following order: Be2+ > Ca2+ > Sr2+ > Ba2+ > Mg2+. Thermodynamic parameters showed that the complexation processes are spontaneous and exothermic, with the decrease in entropy being associated with an increase in order within the system. Stability constants (lgβ0) range from 5.4 (Mg2+) to 10.16 (Be2+). Quantum chemical calculations have shown that the reaction centers in the ligand molecules are: the oxygen atoms of the carbonyl group (H2Sal), the sulfonate group (H3Ssal), and the carboxyl group (H2edta2⁻). It has been established that donor-acceptor interactions predominate in PEI-M2+-H2Sal/H3Ssal ternary systems, while electrostatic interactions dominate in PEI-Zn2+/Cd2+-H2Sal and PEI-Be2+-H2edta2⁻ systems. In sorption tests in model solutions, the ternary complexes PEI-Be2+-H3Ssal and PEI-Hg2+-H3Ssal demonstrated the highest efficiency: the degree of removal of Be2+ reached 97.1%, Hg2+ – 93.4%, while for Mg2+ and Ba2+ it was less than 70%. Modified PEI with H3sal proved to be the most effective adsorbent among those studied. In industrial trials, the developed adsorbents reduced the concentrations of Be2+ and Hg2+ in wastewater to 0.004 and 0.002 mg/l, respectively, which meets the maximum permissible concentrations for discharge into water bodies