An Experimental Study of the Melt Immiscibility and Distribution of Rare Earth Elements, Р₂О₅, and Nb₂O₅ between Immiscible Melts in the Monazite–SiO₂–NaF–Nb₂O₅ System

Abstract

This study was made with the aim of developing a process for liquation fusion of rare earth–rare metal ocherous ores of carbonatite weathering crust deposits. The formation of two immiscible melts, silicate and phosphate–salt, in the monazite–SiO₂–NaF–Nb₂O₅ system was studied. The melt liquation field in the isotherm occupies 50% of the diagram area at 1200°C, 39.0% at 1100°C, 20.0% at 1000°C, and <5% at 900°C. The silicate melt can be readily quenched into a glass containing fine spherical droplets of the phosphate–salt melt. The phosphate–salt melt is always in the crystalline state. The phosphate–salt melt and phosphate–salt spheres contain double phosphates and fluoride phosphates of rare earth elements (REEs) and sodium. Nb₂O₅ concentrates in the silicate melt. REE oxides, Nb₂O₅, and other components are distributed between the two coexisting melts in the contrast fashion. Rare earth oxalate and hydroxide concentrates were obtained from the phosphate–salt melt, and commercial niobium product containing ≤0.50% Р₂О₅, from the silicate melt.