Interactions between components of complex fertilizers. Chemical and physico-chemical interactions at the stages of mixing, granulating and drying during their production

Abstract

The main direction of fertilizers assortment optimization is increasing of the complex fertilizers production, which makes it possible to reduce the cost of their soil application up to 70% and to optimize mineral nutrition of plants. In order to optimiz the process, as well as to predict the properties of final products, possible interactions occurring at separate stages should be taken into account. Processes taking place at the stages of sulfuric and phosphoric acid decomposition of phosphate raw materials as well as at the stage of ammonization have been properly studied and described in literature. However, the information on chemical transformations occurring during complex fertilizers production with the introduction of different kinds of nitrogen and potassium-based components at the stages of mixing, granulating and drying is insufficient to justify an optimal technological regime, qualitative descriptions and mineralogical composition of products. So when urea is introduced as nitrogenous component, it may be present in the product, either alone or in the form of the double salt CO(NH2)2·NH4Cl, as well as the adduct CaSO4·4CO(NH2)2 depending on the conditions of the process. Introduction of magnesium in the quantity of 2 to 10% to the composition of complex fertilizers is accompanied by additional chemical interactions and essential changes in product composition. This chapter presents data on chemical and physico-chemical transformations occurring at the stages of mixing, drying and granulation of complex NPK, NP (S, Ca, Mg) fertilizers on the basis of ammonium phosphate and superphosphates, with the introduction of different types of nitrogenpotassium and magnesium-containing components, based on the studies conducted by the author, as well as under his supervision. Due to the complexity of chemical and mineralogical composition of industrial complex fertilizers, for better understanding of the ongoing transformations, the chemical processes initially have been studied on the model mixtures based on individual salts. For further research the following basic brands of fertilizers have been selected: 7:15:19; 10:15:15; 20:15:10; 16:12:20; 12:12:12; 13:13:13; 15:15:15. It has been established that the chemical processes and phase composition of complex fertilizers obtained on the basis of acid processing of phosphate raw material with the subsequent introduction of nitrogen-potassium-and magnesium-containing components are significantly different from the composition of mixed fertilizers and mixed complex fertilizers obtained by the method of compacting as well as by bulk-blending technology. Depending on the brands of the received fertilizers, potassium in the products is presented in the forms of syngenite K2Ca(SO4)2·H2O, double dihydrophosphates or potassium ammonium sulfate, as well as potassium chloride when introducing it in excess. It has been established that exchange interaction leading to the formation of double sulfates of magnesium ammonium-, hydro-and dihydrophosphates of magnesium as well as dual hydrogen magnesium-ammonium. The polyhalite formation is confirmed by the magnesium compounds participation in the processes of potassium chloride conversion. These processes have a considerable impact not only on the chemical and mineralogical composition but also on the technological and physical-mechanical properties of the fertilizers.