Ion-Exchange Process for Nitrate Removal and Release Using Surfactant Modified Zeolite

Nitrogen (N) loss from irrigated cropland، particularly sandy soils، significantly contributes to nitrate contamination in surface and groundwater and increases N applications to crops. This is because negatively charged nitrate normally does not have much affinity to soil particles. To retard the movement of nitrate، materials should have high affinity for anions، which most naturally occurring minerals do not have. The cation-exchange properties of natural zeolites can be exploited to modify their surface chemistries so that other classes of compounds، particularly anions and non-polar organics are retained. In this study، the ability to remove nitrate from aqueous solutions with different Cl- concentrations using Iranian zeolite (Semnan) modified by hexadecyltrimethylammonium bromide in millimeter and nanometer particle sizes was determined and the equilibrium isotherms were characterized. The nitrate release as affected by time and ionic strength was also evaluated. It was demonstrated that SMZ is capable of adsorbing more than 60 mmol kg-1 and 80 mmol kg-1 nitrate in millimeter and nanometer sizes، respectively، and adsorbed nitrate can be easily released under different ionic strengths. The millimeter and nanometer-sized SMZ showed 26. 7% to 82. 3% and 37. 8% to 85. 5% nitrate removal efficiency، respectively. The average of nitrate released by millimeter-sized SMZ was 6. 92 mmol kg-1 in deionized water while it was 14. 68، 22. 71، and 34. 91 mmol kg-1 in releasing solutions with ionic strengths of 0. 03، 0. 1، and 0. 3 M، respectively