Synthesis and surfactant modification of clinoptilolite and montmorillonite for the removal of nitrate and preparation of slow release nitrogen fertilizer

Abstract

This article introduces the synthesis of clinoptilolite and montmorillonite, and their surfactant modification by using solutions of hexadecyltrimethylammonium bromide (CH3(CH2)15N(Br)(CH3)3, HDTMAB) and dioctadecyldimethylammonium bromide ((CH3(CH2)17)2N(Br)(CH3)2, DODMAB). The feasibility of using surfactant modified silicates (SMSs) as a potential adsorbent for nitrate and for slow release of nutrient has been investigated. Adsorption isotherms of NO3− on SMSs have been measured at aqueous concentration of 160–280mgL−1. The SMSs show much higher adsorption capacity than the unmodified materials as determined by Langmuir adsorption isotherm. The surfactant modification and increased surfactant loading concentration enhance the nitrate anion retaining capacity of silicates (montmorillonite (16.05mgg−1)<clinoptilolite (30.58mgg−1)<DODMAB loaded clinoptilolite (75.19mgg−1)<DODMAB loaded montmorillonite (76.92mgg−1)<HDTMAB loaded montmorillonite (80.65mgg−1)<HDTMAB loaded clinoptilolite (125.00mgg−1)). The adsorption data fitted well with the Langmuir and Freundlich isotherms. The slow nutrient release studies have been performed by thin layers-funnel analytical test and soil column percolating system. The obtained results indicate that SMSs are very good adsorbent for NO3− and a slow release of nitrogen is achievable as it releases NO3− still after 15–20 days of leaching study.