Controlled nitrogen release fertilizer based on zeolite clinoptilolite: Study of preparation process and release properties using molecular dynamics

Abstract

Natural zeolite clinoptilolite was modified with ammonium chloride to prepare a novel controlled release fertilizer. Zeolite as a carrier of fertilizing medium forms a “barrier” to the spontaneous release of the fertilizer into soil. Two particle size fractions of zeolites in interval up to 50 ​μm and interval up to 200 ​μm were used. Ammonium chloride solution, in varying concentrations, was then added to the dried and treated zeolite to bond with NH4+. This bonding process happens as ion-exchange. Ideal conditions for creating a zeolite fertilizer were studied using both adsorption isotherms and kinetics models. The main characteristic of the controlled release fertilizer, its release speed or rate, was studied by the diffusion process. Molecular dynamics was used to study the diffusion of water, NH4+ and combination of both through zeolite pores. It was confirmed that water enters zeolite and pushes NH4+ out. Diffusion coefficients were obtained using inner-particle diffusion model (IPD). Diffusion coefficients of real samples were obtained from slopes of change of electrical conductivity of solution over time. Diffusion coefficients, represented by slopes, were compared with different conventional controlled or slow release fertilizers. Best overall result was achieved when bonding and release slowing agent (paraffin) was used.

Keywords

• Zeolite
• Controlled release fertilizer
• Adsorption isotherms
• Kinetics models
• Diffusion
• Molecular dynamics