Spout Fluidized Bed Assisted Preparation of Poly(tannic acid)-Coated Urea Fertilizer

[Image: see text] Slow-release fertilizers (SRFs) have been widely used to reduce environment pollution derived from excessive nutrients. Coated fertilizers have been designed and prepared using various materials. However, development of new green coating materials and simple process is still a huge challenge. In this study, tannic acid (TA), a natural polyphenol, was used to prepare poly(tannic acid) (PTA)-coated fertilizers with urea prills as the core, and the technology of the coating process in a spout fluidized bed was developed. PTA coating could be formed rapidly by the fast oxidation of TA by an oxidation solution containing CuSO(4) and H(2)O(2). The coated urea release behavior was systematically studied in water and soil. In both water and soil, the release rate of nitrogen from coated urea is much slower than that from raw urea. Raw urea was completely dissolved within 30 min, while 27% of urea was released from coated urea. The pot experiments indicated that coated urea has a positive effect on the plant growth as well. Our results provide an effective method to prepare environment-friendly SRFs, indicating a promising application in sustainable agriculture.