Modification of natural zeolite by carbon nanotubes for an improvement in the sorption properties

The possibility of using initial and modified natural minerals as sorbents for manufacture of economically acceptable technological systems for purifying technological aqueous solutions and liquids has been studied. The processes of modifying natural zeolite by carbon nanotubes have been investigated. As a modifying additive, multi-walled carbon nanotubes have been used in the sorbent, obtained by the method of chemical vapor deposition in the argon flow using organometallic compounds. Before use, multi-walled carbon nanotubes were ground. Since the compatibility of the nanocarbon material and the sorbent matrix largely depends on the presence of polar carboxyl groups on the surface of the zeolite and the surface of the material itself, the carbon nanotubes were subjected to the process of functionalization by polar groups. In order to obtain carboxyl groups on the surface of multi-walled carbon nanotubes, it was treated by an oxidizing mixture of concentrated nitric and sulfuric acids. By reaction with triethanolamine on the basis of carboxylated carbon nanotubes, quaternary ammonium salt was grafted onto the surface of the tubes. On the basis of the obtained results a technique for modifying natural zeolite with multi-walled carbon nanotubes was developed by co-precipitating tubes with zeolite in the presence of aluminum sulfate. During the precipitation a fine powder of the sorbent is formed with the inclusion of nanocarbon material. The most stable system is formed by co-precipitation of zeolite and carboxylated nanotubes. Sorption ability of the composite material with respect to heavy metal ions has been studied. For applicaton of modified zeolite in purification systems, the dependence of the extraction ratio of zinc ions on the content of carboxylated nanotubes in the zeolite was studied. Zeolite has a rigid frame structure and it is possible to use ultrasonic intensification of sorption processes for it. The time of ultrasonic treatment was 80 seconds. The extraction ratio of heavy metals depends on the content of carbon nanotubes in the sorption material and reaches 98.0 % for zinc ions with the 0.2 % content of tubes in the modified zeolite.