Processes of Ion Exchange Sorption and Desorption of Cu2+ and Zn2+ Ions on a Composite Sorbent.

The results of an experimental study of the processes of ion exchange sorption and desorption of copper and zinc ions on a composite sorbent are presented. The sorbent is obtained from modified sawdust and chitosan at a molar ratio of 1 : 0.4. The average particle size is 1.6 mm. The sorbent has a macroporous structure and contains carboxyl, phenolic hydroxyl groups and amino groups capable of ion exchange with heavy metal ions from solutions. The experimental study is а passing the initial solution through a stationary annular sorbent layer and reading the output curves of ion exchange. The sorbent with a volume of 9.8×10–4 m3 was placed in an annular adsorber between the inner and outer gratings. In the study of the direct ion exchange process, solutions of copper and zinc sulfates with a concentration of 0.05 N with volume velocity 8.1×10–6 m3/s and a sorbent in Na- form were used. Sorbent was regenerated from heavy metal ions with 0.08 N sodium hydroxide solution with volume velocity 3.2×10–6 m3/s. The full exchange capacities of the sorbent, the degree of regeneration of the sorbent and the specific consumption of the regeneration solution were calculated based on the output curves of ion exchange. The analysis of experimental data showed a decrease in the exchange capacity of the sorbent during its repeated use. After five sorption-desorption cycles, the value of the total dynamic exchange capacity of the sorbent decreased for copper ions by 30% and for zinc ions by 25%. The decrease in the exchange capacity is associated with a decrease in the amount of carboxyl and phenolic hydroxyl groups in the sorbent, as well as with the compaction of its structure and, consequently, a decrease in the availability of functional groups. [ABSTRACT FROM AUTHOR]