Selective adsorption of natural zeolite for controlled-release of fertilizer

Abstract

In this study, batch liquid adsorption of NH4+ and K+ ions on clinoptilolite was carried out to obtain equilibrium and kinetic data at room temperature. From the analysis of the kinetic data, conformity to the Elovich model suggested that the adsorption of both cations was governed by a heterogeneous diffusion process. Equilibrium adsorption studies showed that an increase in pH and the initial concentration of NH4+ and K+ ions resulted in faster sorption and greater amounts of both ions being adsorbed. In addition, it was found that K+ ions were adsorbed to a much greater extent compared with NH4+ ions. From the desorption studies using NaCl, quantitative amounts of sorbed NH4+ and K+ ions on clinoptilolite could be desorbed, depending on salt concentration. When NH4+ and K+ ions were equally loaded on clinoptilolite, approximately the same amount of both ions were released from the adsorbent. In contrast, when the lading ratio of NH4+ and K+ ions was relatively high, a much higher amount of sorbed K+ ions was released, suggesting that the desorbed NH4+ ions may also be involved in the release of sorbed K+. The results indicate that clinoptilolite can potentially be used for the controlled release of ions such as NH4+ at desired compositions from fertilizers