Fixed–bed column studies of nitrate ion adsorption using modified montmorillonite adsorbent

In recent years, due to limited water resources and the extraordinary increase in nitrates in the environment, efforts to remove and control in order to benefit from the natural adsorbents have been made. Although according to the negatively charged surface of bentonite particles, absorbent needs improvement.

In the current study, the adsorption of nitrate columns by the modified calcium montmorillonite adsorbent was investigated. Furthermore, In order to change the surface load and increase the adsorption efficiency, three-step acid leaching, oxidation layering, and loading of the cationic surfactant hexadecyltrimethylammonium bromide on the adsorbent were performed. Molecular interaction and crystallography of pure montmorillonite and synthetic nano-adsorbent (ACZ) were characterized by Fourier transform infrared spectroscopy and X-ray analysis. Moreover, the morphology of ACZ nano adsorbents was evaluated using Transmission electron microscopy and scanning electron microscopy.

Nanoparticle compaction and less access to pores and cavities in the fixed bed column reduced the adsorbent capacity inside the column compared to the discontinuous system.The results showed that an increase in inlet concentration from 80 to 150 mg/L increased the adsorption capacity from 67.39 to 88.25 mg/g. Reducing the inlet flow rate increased the penetration time, interaction, and greater access to the binding sites for nitrate ions and finally improved the column performance and increased the inlet flow rate reduced the adsorption capacity and breakthrough time. Therefore, the adsorption of nitrate ions by the stage of internal mass transfer is controlled and depends on the duration of interaction and the possibility of penetration into the active sites. With increasing the bed height from 4.2 to 9 cm, there was a significant increase in adsorption capacity from 60.608 to 77.167 mg/g. The effect of detergents and recovery showed an absorption column; After 3 leaching steps, acid leaching played an important role in increasing column recovery. Experimental data with correlation coefficients of R2>0.95 corresponded to Thomas and Yoon-Nelson kinetic models.In this study, the ACZ nano adsorbent column for rapid removal of nitrate ions from aqueous solutions was introduced and for use in reusable systems was proposed.