Production of Urea/Acetylated-lignin Sulfonate Matrix as SRFs and an Investigation on the Effect of Hydrodynamic Conditions on Release Rate Using the Biot Number

Introduction: This study aimed to investigate the effect of hydrodynamic conditions on the release rate of urea/acetylated lignin sulfonate (Ac-LS) matrix as slow-release fertilizers (SRFs). Therefore, two models were developed using the mass transfer balance for the determination of finite/infinite volume of fluids and solving finite integral transformation/separation of a variable. The Biot number, validating the hydrodynamic condition, was found in these models. Methods: In this study, the urea/Ac-LS matrix fertilizer was prepared. The morphological, thermal, chemical, and mechanical properties of the LS, Ac-LS, urea, and urea/Ac-LS matrix were analyzed using Fe-SEM, TGA, XRD, and SANTAM. Finally, the nitrogen release of the matrix fertilizer was investigated at 25°C for different impeller speeds. The models were also validated using the experimental data. Results: The results showed that the thermal and mechanical resistance of urea/Ac-LS due to strong interaction increased compared to pure urea or Ac-LS. The results further showed that the external resistance on the mass transfer decreased as the impeller speed increased, and the nitrogen release rate increased as the Biot number increased in both the states, i.e., finite and infinite. Conclusion: It was also observed that the release rate in the finite environment was less than that of the infinite one in the given hydrodynamic condition initially; however, the type of environment did not affect the release rate after a while.