Concentration of heavy metal ions from aqueous media under dynamic conditions using a composite sorbent based on chitosan and silica

Abstract

Objectives. The study set out to investigate the sorption, toxicological, and regeneration properties of a composite sorbent based on chitosan hydrogel and unsuspended silicon dioxide (chitosan–colloidal silica), which manifest themselves under dynamic conditions of purification of aqueous solutions, as a means of removing heavy metal ions.Methods. The total dynamic exchange capacity of a chitosan–colloidal silica composite sorbent was evaluated under dynamic sorption conditions by passing solutions containing Zn(II), Cd(II), Cu(II), and Cr(III) ions having a concentration of 240–251 mg/L through a fixed sorption bed. The method for determining acute toxicity using daphnia (Daphnia magna Straus) is based on the direct calculation of the mortality of daphnia exposed to toxic substances contained in the test aqueous extract in comparison with a reference culture in samples that do not contain toxic substances. The regeneration ability of the sorbent was assessed by counting the number of sorption–desorption cycles using 0.1 M NaOH and 0.1 M NaHCO3 eluents, as well as aqueous solutions of H2O2 (1 and 3%).Results. The effectiveness of the chitosan–colloidal silica composite sorbent in the process of dynamic purification of aqueous media to remove Cu(II), Zn(II), Cd(II), and Cr(III) ions was established. After determining the times of ion breakthrough and saturation of the developed sorbent, its dynamic exchange capacity was calculated by processing the kinetic curves of sorption of heavy metal ions under dynamic conditions. The results of regeneration of the sorbent were presented in the context of the possibility of its reuse. It is shown that the sorbent can withstand up to five sorption–desorption cycles while maintaining a level copper cation extraction above 90%.Conclusions. Analysis of the kinetic curves demonstrated that the driving force behind the removal of heavy metals from aqueous media by means of the obtained sorbent is the external diffusion mass transfer of ions from the mobile phase of the solution. Biotesting of samples showed that the developed chitosan-based sorbent does not have acute toxicity.

Keywords

• heavy metals
• adsorption
• composites
• chitosan
• biotesting
• regeneration