Distribution of TR₂O₃, P₂O₅, and Nb₂O₅ between Two Immiscible Melts in the Monazite–SiO₂–NaF–Nb₂O₅–Fe₂O₃ System

Abstract

The monazite–SiO₂–NaF–Nb₂O₅–Fe₂O₃ system in the isotherm at 1200°C is characterized by a wide region of two immiscible melts: a silicate melt and a phosphate–fluoride (salt) melt. The system is reciprocal; in the salt melt, new rare-earth metal (REM) phases form: binary phosphates and fluoride phosphates of REM and Na, which contain neither Fe, nor Nb. Iron has a strong effect on the immiscibility of the melts: in the absence of iron, the segregation region occupies 50% of the area of the diagram; at 5% Fe₂O₃, 57%; and at 10% Fe₂O₃, 70%. REM, P, and Nb oxides are contrastingly distributed between the immiscible melts. Most (95%) of REM and P are concentrated in the phosphate–salt melt, and Nb is concentrated in the iron–silicate melt. If the silicate melt contains no Fe₂O₃, then the Nb₂O₅ content is 4.91%; and at a Fe₂O₃ content of 15.33%, the Nb₂O₅ content is 6.89%, i.e. is 40% higher.