Abstract
Production of a low-grade phosphate raw materials-based line of products using economically and environmentally appropriate hydrochloric-phosphorus acid technology is a promising area. A double superphosphate (P2O5 = 46 wt. %) was obtained by isothermal re-crystallization due to removing iron(III) from impurities of the technical monocalcium phosphate (P2O5 = 35 wt. %). The obtained product is represented exclusively by a mobile (water-soluble) phosphorus form. The development of greenhouses and requirements for closed soils impose strict restrictions on the impurities composition in the mineral fertilizers. The current State standards regulate such physico-chemical and physico-mechanical parameters of phosphorus-containing fertilizers as nutrients’ concentration, moisture content, pH of 10% solution, granulometric composition, granules’ strength, friability, heavy metals’ concentration. But they ignore a number of impurities, for example, iron(III), that can lead to phosphorus retrogradation. The simple enough technology makes it possible to obtain cheap effective product –monocalcium phosphate (MCP) – from low-grade ores (phosphorites). This explains the high demand for it among farmers. MCP can also be used in animal husbandry, provided that the sanitary regulations and norms requirements on MPC of controlled impurities are met. The development of the “Green Chemistry” involves the use of water-soluble fertilizers and eliminates the toxic elements content that can accumulate in the soil. The iron(III) extracted from impurity minerals binds to phosphorus and forms FePO4 with the citrate-soluble form of P2O5, thereby reducing its mobile form (P2O5 wat.) in the product. A more concentrated product corresponding to the double superphosphate in the main component (P2O5 wat.) content was produced by isothermal re-crystallization of MCP with ballast impurity. In addition, the final product was purified from iron compounds to trace amounts. Thus, purification of technical MCP by isothermal recrystallization method due to the removal of iron impurities to trace amounts expands the field of its application.
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