Effect of particle size and surfactant concentration on nitrate absorption efficiency and release by modified zeolite with HDTMA in aqueous solution

Nitrate anion can be repelled by the negative charges on clay mineral's surface and leached from soil profile to surface and groundwater. Natural clays are not effective adsorbents and entrapment media for anions, low water soluble, non polar and non ionic organic molecules. However, the natural clays may be modified using organic cations (surfactant) to adsorb and trap varieties of non ionic, anionic compounds and enhanced anions retention capacity that are detrimental to our aqueous environments. The objective was to study the adsorption efficiency and desorption of nitrate in aqueous solutions by modified Iranian zeolite clinoptilolite (Semnan) with hexa decyl tri methyl ammonium bromide (HDTMA-Br), a cationic surfactant.
The micro and nano zeolite was separated by centrifuge method. The micro and nano-zeolites were first modified by hexa decyl tri methyl ammonium bromide (HDTMA-Br). In this study, adsorption efficiency in initial concentrations of nitrate by modified zeolite with surfactant loading of 100 and 200% external cation exchange capacity)(ECEC) was investigated in a completely randomized factorial design. The nitrate release as affected by time at 4 and 14 mM of nitrate in surfactant loading 200% ECEC were also evaluated. The external cation exchange capacity (ECEC) of zeolite was determined by replacing the Na in non zeolitic exchange sites with tert butyl ammonium ions. Structure and morphology of zeolite was determined using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and atomic force microscope (AFM).
The results showed that adsorption efficiency of nitrate by nano organo zeolite with surfactant loading of 200% ECEC in 3, 6, 14, 20 and 30 mM nitrate were 92, 88, 77, 67 and 56 %, whereas in micro-zeolite were 75, 67, 50, 41 and 33 % respectively. Adsorption efficiency of nitrate by micro organo zeolite with surfactant loading of 100 % ECEC were 53, 46, 35, 28 and 20 % respectively. In nano-organo zeolite, nitrate desorption were 2.6 to 5.7 % and 8.9 to 12.2 % in 3 and 14 mM, respectively, whereas for micro organo zeolite were 21% and 33 % in 3 and 14 mM of initial nitrate concentration, respectively.
Results of this research showed that the particular separation of zeolite, initial nitrate concentration and level of surfactant loading had a highly effect on adsorption efficiency and cleaning of nitrate in aqueous solutions. Moreover, nano-organozelite showed high adsorption efficiency of nitrate and good quality to trap and retain of nitrate.