Treatment of phosphate waste generated during thermal processing of phosphorites of the Central Kyzylkum

This article presents the results of nitric acid treatment of phosphate waste, specifically mineralized mass (MM) and slurry phosphorite (SP), produced during the thermal processing of phosphorites from Central Kyzylkum (CK). MM with the following composition (in wt%) was used in the laboratory studies: 14.60 P2O5 tot, 3.07 P2O5 avail, 43.99 CaO, 1.01 MgO, 14.11 CO2, 1.04 Al2O3, 0.89 Fe2O3, 1.58 SO3, 1.30 F, 1.02 Н2О; CaO : P2O5 = 3.01; and 10.82 % as insoluble residue. The SP used had the following composition (in wt%): 11.57 P2O5 tot, 1.33 P2O5 avail, 41.08 CaO, 0.61 MgO, 20.91 CO2, 1.84 Al2O3, 1.48 Fe2O3, 0.46 SO3, 1.52 F; CaO : P2O5 = 3.55; and 14.09 % as insoluble residue. The study examined the effects of nitric acid concentration and dosage on the main components of activated phosphate fertilizers, as well as the influence of nitric acid concentration on the relative content of the available P2O5 avail and СаОavail in samples of nitrogenphosphate fertilizers (NPF) produced from SP and MM. The laboratory findings were used to establish the optimal concentrations and dosages of nitric acid for producing fertilizers that meet the applicable agricultural requirements. The compositions of the NPF were as follows (in wt%): when using MM: P2O5 tot of 20.13–20.58, P2O5 avail (by citric acid) of 10.47–11.72, CaOtot of 38.87–39.12, СаОavail of 22.30–24.15, CaOaq of 3.17–3.31, N of 1.27–1.35, with the degree of Р2О5 transition to the liquid phase within 2.01–2.06 %; when using SP: P2O5 tot of 18.29–18.58, P2O5 avail (by citric acid) of 9.33–10.03, CaOtot of 39.62–39.96, СаОavail of 21.98–24.56, CaOaq of 3.16–3.32, N of 1.27–1.36, with the degree of Р2О5 transition to the liquid phase within 2.07–2.12 %.