Behavior of phosphorus during the carbothermic reduction of phosphorus-rich oolitic hematite ore in the presence of Na2SO4

• Al2O3 and SiO2 are beneficial to the carbothermic reduction of fluorapatite.
• Na2SO4 renders the reduction of Ca5(PO4)3F by consuming Al2O3 and SiO2 in advance.
• P content in the metallic iron phase decreased with the increasing dosage of Na2SO4.
• Na2SO4 results in the mineralogical separation of Fe and P.

Recently, additives such as Na2SO4 and Na2CO3 have been proven to be capable of enhancing the reduction of phosphorus-rich oolitic hematite ore and the recovery of dephosphorized iron by magnetic separation. In this study, the behavior of phosphorus during the carbothermic reduction of a phosphorus-rich oolitic hematite ore in the absence or presence of Na2SO4 was characterized. Thermodynamic calculations of the reactions of fluorapatite with SiO2, Al2O3, or Na2SO4, phase transformations during reduction and the distributing characteristics of phosphorus in the metallic iron and non-metallic phases of the reduced pellets were investigated. Thermodynamic analysis demonstrates that SiO2, Al2O3, and Na2SO4 influence the reduction of fluorapatite significantly. XRD and SEM-EDS results confirm that when the oolitic hematite ore was reduced in the presence of Na2SO4, reactions between Na2SO4, SiO2, and Al2O3 are prior to the reduction of fluorapatite. Therefore, the phosphorus content of the metallic iron phase in the pellet decreased markedly. With the sodium sulfate dosage varying from 0% to 20%, the mean phosphorus mass content in metallic iron grains decreased from 0.877% to 0.02%. The dephosphorized iron is then recovered by magnetic separation subsequently.

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