Effect of zinc oxide and zinc oxide nanoparticles coating on urea diffusion and its release kinetics for design and development of slow-release fertilizer: an experimental and numerical investigation

Urea is the most applied nitrogenous fertilizer with 46% nitrogen (N) among available synthetic fertilizers. On the other hand, uncoated urea is subjected toward quick nutrient loss due to its higher solubility. This problematic issue could be addressed by applying slow-release fertilizer. The main aim behind this research was to model and simulate the nutrient release pattern from coated urea using zinc oxide (ZnO) as a micronutrient Zn source. A multidiffusional model was adopted for the simulation of prill fertilizer. During this study, finite element method and 2D geometry were utilized for prilled urea fertilizer using COMSOL multiphysics software. The second phase consisted of release kinetic study by using the experimental release data. In the present research, synergism was observed between the simulation and experimental results of nutrient release, with an error of 0.041. The dissolution curves of urea for simulation and experimental studies followed sigmoidal behavior. The results findings indicated that a second-order equation could be used to express the nutrient release from Zn coatings (ZnO or ZnO-NPs). Second-order kinetics express that nutrient release from Zn-coated urea was controlled by diffusion. Additionally, the second-order kinetic constant increases with raise in coating percentages which enhanced the mass transfer resistance.