Recovery of phosphates(V) from wastewaters of different chemical composition

Phosphate(V) ions were recovered from wastewaters of different chemical compositions in a continuous reaction crystallization of struvite. Two real wastewaters were represented by an effluent sample from the phosphorus mineral fertilizer industry and by liquid manure derived from a cattle-breeding farm. Two other wastewaters were prepared under laboratory conditions. Impurities present in the wastewaters caused the precipitation of solid products of distinctly different quality. The mean size of struvite crystals varied from ca. 18 to ca. 40 mu m. Homogeneity within their populations, quantified by the coefficient of variation CV, varied from satisfactory (CV ca. 75%) to unfavorable (CV ca. 100%), which resulted in the elongation of necessary filtration time. Calcium ions in wastewater precipitated as amorphous hydrated calcium phosphates ACP. Their content in the products varied from 33.4 up to 73.1 mass %. Also 28.32 - 32.74 mass % of P2O5, 6.35 - 14.12 mass % of MgO and 4.35 - 16.94 mass % of CaO were confirmed in the products, together with hydroxides of some metals and salts of other impurities. Based on the chemical composition of the products derived from the investigated wastewaters, their application in agriculture as valuable mineral fertilizers is recommended.