Slow release urea fertilizer synthesized through recrystallization of urea incorporating natural bentonite using various binders

In this study, various slow release urea fertilizers (SRUFs) were prepared by incorporation of urea into local natural bentonite with various binder i.e. corn starch and hydroxypropyl methylcellulose (HPMC). In the preparation, a binder was added to a mixture of natural bentonite and melted urea. Then, the admixture was put into a mould and extruded to obtain SRUF in the form of pellets. The SRUF was dried at 50 °C for 8 h before use. Urea desorption mechanisms of the SRUF was examined through static release experiments. The structural properties of SRUF was characterized through scanning electron microscopy with energy dispersive x-ray (SEM-EDX) analysis and Fourier-transform infrared spectroscopy (FTIR). It was found from static release experiments that the SRUFs more slowly released urea in water than conventional urea fertilizer. After 500 min of the experiment, the slowest release of urea was achieved by SRUF using corn starch. Meanwhile, conventional urea fertilizer completely released urea in water after less than 50 min. Release mechanisms of the SRUF using corn starch and SRUF using HPMC were anomalous transport and Fickian diffusion, respectively.