Mechanism of Adsorption of Ammonia Nitrogen in Saline by Transition Metal Montmorillonite.

In general, ion-exchange adsorption and biological method have higher treatment efficiency for ammonia nitrogen in water, but the existence of salt makes the treatment efficiency of ion-exchange adsorption method decreased due to the competition of salt ions, and the salt also inhibits the activity of microorganisms, which makes the biological method s treatment efficiency decreased. Four transition metals (Co, Ni, Cu and Zn) were used to support montmorillonite, and four transition metal-based montmorillonite were obtained. Compared with montmorillonite, the ammonia-nitrogen removal performance of the four transition metal-based montmorillonite is greatly improved in the range of saline solution pH 9.0 - 11.5. The specific surface area test shows that the transition metal montmorillonite has larger inner space, and its specific surface area is also greatly improved. Moreover, compared with montmorillonite, the modification of transition metals makes the pore size of montmorillonite smaller, which is the exchange between Na+ with smaller ionic radius and transition metal ions with larger ionic radius in the montmorillonite layer. This conclusion is confirmed by energy spectrum analysis, that is, the relative content of Na decreases from 9.46% to 2.75% - 5.48% after the modification of montmorillonite by transition metal. X-ray diffraction analysis also confirmed this point, that is, compared with montmorillonite, NaCl at the characteristic peaks of 31.8°, 45.5°, 56.5° and 75.3°, the intensity of diffraction angles corresponding to the four transition metal-based montmorillonite weakened or even disappeared, indicating that the montmorillonite underwent iso-crystal replacement in the process of metal modification. In the layer, Na+ and other substances were successfully exchanged by Co2+, Ni2+, Cu2+, Zn2+. Scanning electron microscopy shows that the surface structure of montmorillonite is relatively compact, and the surface of transition metal-montmorillonite is porous and uneven, with obvious gullies. These microstructure make metal-montmorillonite have larger specific surface area and more adsorption sites. The four kinds of transition metal-montmorillonite showed a similar trend in the adsorption properties of ammonia nitrogen under the influence of different salt contents, that is, Cu-montmorillonite always maintained the best, which not only had the strongest coordination ability between Cu2+ ion and NH3 molecule, but also had the highest inner hydroxyl group and the largest inner layer spacing. According to the photoelectron spectroscopy analysis, the N1s of Cupric montmorillonite after the removal of ammonia nitrogen indicates that cupric montmorillonite forms a coordination covalent bond with ammonia nitrogen, and there are ion exchange and electrostatic attraction. The adsorption process is more consistent with the quasi-second-order kinetic model. The full spectrum shows that the N element of Cu-montmorillonite increases from 0 to 2.78% before and after removing ammonia nitrogen. [ABSTRACT FROM AUTHOR]