• ISSN 1008-505X
  • CN 11-3996/S
TIAN Hong-yu, DONG Jing-jing, XIE Chen-shuo, CUI Jing, DUAN Jian-hang, ZHANG Tian-jiao, DAI Jia-ying, WANG Shuo, ZHANG Li-li, WEI Zhan-bo, WU Liang, GUO Wu-song, LIU Zhi-guang, ZHANG Min. Using discrete element simulation and microstructure observation to study the urea surface modification and nutrients release performance of coated urea[J]. Journal of Plant Nutrition and Fertilizers, 2023, 29(5): 900-911. DOI: 10.11674/zwyf.2022495
Citation: TIAN Hong-yu, DONG Jing-jing, XIE Chen-shuo, CUI Jing, DUAN Jian-hang, ZHANG Tian-jiao, DAI Jia-ying, WANG Shuo, ZHANG Li-li, WEI Zhan-bo, WU Liang, GUO Wu-song, LIU Zhi-guang, ZHANG Min. Using discrete element simulation and microstructure observation to study the urea surface modification and nutrients release performance of coated urea[J]. Journal of Plant Nutrition and Fertilizers, 2023, 29(5): 900-911. DOI: 10.11674/zwyf.2022495

Using discrete element simulation and microstructure observation to study the urea surface modification and nutrients release performance of coated urea

  • Objectives Surface modification is a key step towards realization of nutrient-release control of coated urea production. We tested several abrasives, and studied the basis for modification in improving the coating property.
    Methods In this study, large granular urea (3–5 mm, N 46%) was used as the fertilizer core, while the tested abrasives included brown-fused alumina, white-fused alumina, zirconia beads, alumina porcelain beads, and aluminum porcelain column. By measuring the repose angle of polished urea after polishing with the abrasives, alumina porcelain beads with a bulk density of 1.336 g/cm3 and a diameter of 6 mm were chosen as the abrasive in the later research stage. 1 kg urea and 1.5 kg alumina porcelain beads were loaded into a drum granulator, discrete element software (EDEM) was used to simulate the motion, collision, force and distribution of particles in system of abrasive friction and urea particle self-friction. The surface and sectional structure and the roughness of modified urea were scanned using electron microscopy. The microstructure of the coating was observed using atomic force microscopy (AFM). The nutrient release characteristics of polished and ordinary urea, coated with 3%, 5% and 7% of nano-SiO2 modified castor oil-based polyurethane, were determined by static water dissolution method.
    Results According to the simulation of EDEM, the urea particles near the bottom moved fast (1.125 m/s), and those at the edge moved slowly (0.00309 m/s), causing the segregation of small pAccording to the simulation of EDEM, the urea particles near the bottom moved fast (1.125 m/s), and those at the edge moved slowly (0.00309 m/s), causing the segregation of small particles at the bottom of the drum during the mixing process. The self-friction force of pure urea was about 0.035N, while the total friction force when mixed with the abrasive increased to about 0.042 N. This enlarged force increased the collision number of urea-abrasive mix system by 13.0% than that of the self-friction system, thus creating more efficient modification. The modification significantly reduced the surface average roughness (Ra) by 79.2% within 1 μm2 of detection area. From the electric micro-morphology images we could see, common urea surface was rough, film material filled into the low parts causing extra consume of film materials and obstructing the close bonding of coating layer with the urea chip, thereby the coating film was fragile during transportation or long-time storage and lost controlling capacity of nutrient release. While the modified urea surface was smooth, preventing the waste of film materials. The film layer was even in thickness and uniform in intersecting surface, and closely bonded with the core. The nutrient release period of urea coated with 5% nano-SiO2 modified castor oil-based polyurethane increased by 6 times, from 24 days before polishing to 169 days after polishing.
    Conclusions According to the simulation of EDEM discrete element software, the mixture of alumina porcelain beads and urea greatly increased the modification efficiency, reduced the surface roughness of urea significantly. The surface microstructure of the modified urea core of controlled release fertilizer was significantly improved, the amount of coating material was reduced, and the nutrient release period was prolonged under the same coating rate.
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