Abstract:

The capacity of synthetic 4A zeolite molecular sieve treated with molten salts to occlude ammonium nitrate and potassium nitrate has been determined, and the salt-occluded zeolite 4A has been characterized with XRD, IR and TG-DTA methods. In a laboratory setting, the KNO₃ treated zeolite 4A contained 15.01% of K(calculated as K₂O)and 9.23% of NO^-₃, and the NH₄NO₃-treated zeolite 4A contained 10.78% of NO^-₃ and 0.94% of NH⁺₄. Molten salt treatment resulted in changes of overall and relative intensities of peaks in X-ray diffractograms of zeolite 4A. The presence of occluded salts in zeolite 4A was confirmed by a decrease of water IR absorption band intensities around 1，640 cm^-1, which was expected with salt occlusion, and two absorption bands, strong around 1,390 cm^-1 and weak around 825 cm^-1, which are identified as V3 and V2 modes of nitrate ions, and weight losses and sequential endo and exothermal responses of KNO₃ and NH4NO₃ in TG-DTA curves- Occlusion of molten salts in zeolite 4A had little or no effects on its framework. This study shows that the capacity of 4A zeolite molecular sieve to store nutrients can be greatly increased by salt occlusion and the salt-occluded zeolite 4A is a potential candidate as slow-release fertilizer

Key words: 4A zeolite molecular sieve, salt occlusion, potassium nitrate, ammonium nitrate, slow-release fertilizer