Salt composition and physicochemical processes in the volume of fertilizer granules at the storage stage

Abstract

The results of studies of the salt composition and physicochemical processes occurring in separate layers (volume) of granules of complex fertilizers based on ammonium phosphates at the stage of storage in the interval up to 180 days are given. The data of chemical and physicochemical studies, as well as the analysis of microphotographs and element-by-element composition of granules showed the absence of a significant gradient of concentrations of individual components in the volume of granules when they arrive from the technological process. The course of secondary conversion processes in the volume of granules during 3 and 6 months of storage was established, leading, in particular, to a significant decrease in the content of ammonium dihydrogen phosphate in the product from 25.41-27.91 to 1.23-3.25 % and urea, as well as the formation of newdouble salts and adducts: (Kχ,(NH4)1-χ)•H2PO4, CO(NH2)2•NH4Cl. The change in the phase composition of the product during long-term storage and the associated chemical interaction between the layers of individual granules is accompanied by an increase in caking. It is established that during 3 and 6 months of storage, the content of the liquid phase increases, which leads to a partial decrease in the content of individual components. The most active process of sorption of water vapor proceeds in the 1st (outer layer) of granules, while fluctuations in its content in deeper layers are within the margin of error. The dependence of the caking of the product on the type of injected nitrogen-containing component and the forms of nitrogen content in it has been established. The results of the study made it possible to recommend ways to reduce caking and improve the physical and mechanical properties of complex fertilizers during their storage and transportation: increasing the molar ratio at the ammoniation stage to values corresponding to the formation of diammonium phosphate; increasing the ratio of ammonium to the amide form of nitrogen; an increase in the proportion of granular urea in the composition of the fertilizer, followed by the complete exclusion of prilled urea.