2018 Volume 58 Issue 4 Pages 612-619
The reserves of niobium and rare earth element in the mineral resources in Bayan Obo ranked the forefront of the world, the thermodynamic information such as liquidus and phase equilibrium relations in the related slag system phase diagram were important to the comprehensive utilization of niobium and rare earth resources. In the current work, the pseudo-melting temperatures were determined by the single-hot thermocouple technique (SHTT) for the specified content of 10 to 50 pct Nb2O5 in the CaO-SiO2-Nb2O5-10%La2O3 phase diagram system. The 1573 K, 1623 K, and 1673 K liquidus were first calculated based on the pseudo-melting temperatures according to thermodynamic equations in the specific primary crystal area. The phase equilibrium relations at 1573 K and 1473 K were determined experimentally using the high-temperature equilibrium followed by scanning electron microscope, X-ray diffraction, and energy dispersive X-ray spectroscope analysis. The liquid phase, SiO2 phase, CaO·SiO2 phase, and 2CaO·Nb2O5 phase were found in the experiment. Therefore, the phase diagram was constructed for the specified region of the CaO-SiO2-Nb2O5-10%La2O3 system. The experimental results have practical significance for further research on the related slag system, and for the comprehensive utilization of niobium and rare earth resources.