Production of complex and mixed fertilizers by the acidic processing of phosphorites

One way to increase the utilization of phosphate raw materials is the liquid phase circulation method, which is used in the production of double superphosphate. The currently used traditional processes employ phosphorites of varied quality and chemical/mineral composition, which are degraded with excessive quantities of phosphoric acid. The main steps in this cycle method include neutralizing monocalcium phosphate (MCP), sulfating the main circulating solution, separating phosphogypsum, and returning to the acid production cycle. Calcium dihydrophosphate (monocalcium phosphate-double superphosphate) crystallizes and is separated from the main circulating solution. The formation of double superphosphate, which has a P₂O₅ value of 50–59%, indicates that the maximum (98–99%) phosphate mineral breakdown has been achieved in this case. On the one hand, all procedures are equivalent to chamber or chamber-flow methods; on the other hand, they use large rates of acidic reagent (300–800%). Like the flow approach, they are all carried out in the liquid phase and all include a significant amount of phosphoric acid. This cyclic method has the advantage of being able to process the selected kind of phosphate raw material with phosphate/sulfuric acid in a single cycle, yielding high-quality double superphosphate.

By processing phosphate raw materials primarily with mineral acids (sulphate, nitric, and phosphate), phosphorus fertilizer with a higher nutritional value is produced. In this article, the effects of phosphorite treatment in an acidic environment on the production of complex and mixed fertilizers are discussed. In addition, a scanning electron microscope was used to examine the surface microstructure.