We developed a novel slow-release nitrogen fertilizer with the aim of increasing the efficiency of urea use,recycling phosphogypsum,and reducing related pollution.Phosphogypsum was used as a granulating agent and carrier for urea to prepare a novel fertilizer core,which was coated with paraffin wax.SpanTM 80 was added to the paraffin to improve the wetting and adhesion between the paraffin coating and the fertilizer core.Paraffin-coated urea particles were prepared as a control sample using this method and their urea-release behavior was investigated.The results showed that less than 35% of urea from the paraffin-coated phosphogypsum-granulated urea was released over 28 days of submersion in water.The urea release was sustained much longer than that of paraffin-coated urea (only 7 days due to the expansion of brittle cracks in the coating).The release patterns of all coated fertilizers followed a logistic model.The release efficiency of paraffin-coated fertilizers could be improved by increasing the particle size of the fertilizer cores and improving adhesion between the paraffin coating and fertilizer core.
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