High selectivity and affinity of synthetic Phillipsite compared with natural Phillipsite towards ammonium (NH4+) and its potential as a slow release fertilizer

Phillipsite (PHI) was synthesized in Na-K form, ion exchanged with NH4NO3 and compared with its natural counterpart. Zeolites were then characterized before and after ion exchange by X-ray diffraction, X-ray fluorescence, Thermogravimetric analysis and scanning electron microscopy. Ammonium exchanged Phillipsites were introduced as a soil amendment (2, 4 and 8% zeolite to soil loadings) to study the growth of maize (Zea mays) and compared with a control comprising NPK fertilizer added to soil. The affinity of the zeolite mineral Phillipsite for NH4+ in the presence of other cations is demonstrated by soil nutrient status. Results demonstrated that synthetic Phillipsite had a very high affinity towards NH4+ when introduced as a soil amendment, compared with its natural counterpart. Results were promising for ion exchange reactions in a zeolite-soil system, whereby cations present in soil exchanged for K+ more freely than NH4+ present in the synthetic Phillipsite framework.