Sorption purification of solutions from heavy metal ions using zeolite modified by carbon nanotubes

The processes of heavy metal ions sorption - copper and zinc, with the use of natural zeolite modified by multi-walled carbon nanotubes (MWCNT) with functionalized surface of polar groups (carboxyl, carbonyl, hydroxyl) by ultrasonic action have been investigated. The most effective is the functionalization of the carbon nanotube surface by carbonyl groups (MWCNT-COOH) in the treatment of native MWCNT with a compound of concentrated sulfuric and nitric acids. Carbonyl and hydroxyl groups are also fixated on the surface of nanotubes. The processes of adsorption of zinc and copper ions from solutions on the original and modified zeolite have been studied. For the intensification of sorption processes the application of ultrasonic treatment is the most effective. In this case, the diffusion restrictions in the adsorption layer are removed, the concentration is equalized by mixing the liquid. The dependence of the degree of extraction of ions of zinc and copper from the content of MWCNT-COOH in the zeolite has been studied. At the optimum concentration of 0.1 wt. % MWCNT-COOH, the degree of extraction for zinc is 97.8 %, for copper it is 96.4 %. A further increase in the concentration of nanotubes in zeolite insignificantly increases the degree of extraction. The optimal duration of ultrasonic treatment is 100 s. Under these conditions with the use of unmodified zeolite, the degree of extraction of zinc and copper ions amounts to 72.4 and 68.3 per cent, respectively. Without the influence of ultrasound the results that are close in degree of extraction can be obtained by zeolite treatment of solutions of zinc and copper salts for 2-4 h. The adsorption isotherms at various concentrations of the zinc and copper cations in a solution have been represented, and the basic parameters of the processes have been determined. Modification of zeolite by carbon nanotubes increases the degree of extraction by 20-25 %, the sorption capacity for zinc by 3 times, for copper it increases by 3.5 times. In the case of modification with the use of ultrasonic influence the specific surface of the sorbent increases by 2.3 times. The spent zeolite can be regenerated by treatment with acids for not less than 6 cycles with reduction of extraction degree to 25 %. The scheme of obtaining and sorption purification with the use of modified zeolite by nanotubes has been suggested.