Study On Silica Coated Diammonium Phosphate For Slow-release Fertilizer

In this thesis,we used the by-product silica which is from the preparation of potassium fluoride with defluorization from wet process phosphoric acid to prepare two types of slow-release materials with the function of water-absorption and water-retention.Then we prepared two types of coated slow-release fertilizers with the materials and diammonium phosphate granular fertilizer.This research mainly consists of following three parts:first,we explored the suitable process for the preparation of composite coating material with silica/corn starch/polyvinyl alcohol and silica/polyethylene glycol/VAE latex.Second,the influence of different content of each component on the swelling rate,water absorbencies and maintaining ability was studied,the optimum formula were determined.Then,the examples were characterized by FT-IR and SEM.Third,we prepared the coated slow-release fertilizer with different coating rates by using the composite coating materials to coat the diammonium phosphate granular fertilizer.And its release performance in water,water retention behaviors in the soil,compressive properties were tested.Simultaneously,we calculated the raw material price changes caused by the coating.The main conclusions were drawn as followings:（1）Considering the water absorbencies and maintaining ability of the silica/corn starch/polyvinyl alcohol composite material,the optimum ratio of raw materials were as that:water weighting 200,corn starch weighting 20,polyvinyl alcohol weighting 5,silica weighting 5,glycerin weighting 3⁵,and glyoxal added 2.5%of corn starch quality.（2）The FT-IR characterization of the silica/corn starch/polyvinyl alcohol composite material showed that new hydrogen bond were generated between SiO₂and CST/PVA.The result revealed the influence of SiO₂ on the properties of the material.And the SEM characterization showed that the material had a dense structure and a certain degree of barrier to moisture.（3）Considering the film-forming properties of the silica/polyethylene glycol/VAE latex composite material,the optimum ratio of raw materials were as that:water weighting 200,polyethylene glycol weighting 5¹5,VAE latex weighting 5¹5,silica weighting 15²5,CMC weighting 1³,aluminium phosphate weighting 0.5¹.5,glycerin weighting 2⁴.（4）The two kinds of composite coating materials had the water-absorption and water-retention properties.Meanwhile,the strength of water-absorption and retention of the materials could be controlled by adjusting the content of each component in the composite coating material.And the coated slow-release fertilizers have the ability of water-retention in soil which is important for saving agricultural water and improving water utilization.（5）Conductivity method can be used to quickly and accurately determination of nutrient dissolution rate of the coated slow-release fertilizers.The slow-release performance of coated slow-release fertilizers increased with the increase of coating rate.Using the two kinds of the composite coating materials mentioned in the thesis can produce products that meet the national standards for slow-release fertilizer GB/T23348-2009.（6）Compared silica/corn starch/polyvinyl alcohol composite coated fertilizer with silica/polyethylene glycol/VAE latex composite coated fertilizer under the same coating rate,the former has stronger water retention in the soil and lower cost on the raw materials.