Phase Equilibria in the System CaO-SiO2-La2O3-Nb2O5 at 1400 °C

Jiyu Qiu,Chengjun Liu,Zhengyue Liu

doi:10.3390/met11121892

Abstract

CaO-SiO2-La2O3-Nb2O5 system is of great significance for the pyrometallurgical utilization of Bayan Obo tailing resources. In the present work, the phase equilibrium of this quaternary system at 1400 °C was determined by a thermodynamic equilibrium experiment. On the basis of the recently determined CaO-La2O3-Nb2O5 phase diagram, some boundary surfaces of primary phase fields of CaO-SiO2-La2O3-Nb2O5 phase diagram were modified; then, the 1400 °C isothermal surface in the primary phase fields of SiO2, CaNb2O6, Ca2Nb2O7, and LaNbO4 was constructed, respectively. On this basis, CaO-SiO2-Nb2O5 pseudo-ternary phase diagrams with w(La2O3) = 5%, 10%, 15%, and 20% were determined, respectively. Considering the importance of equilibrium crystallization reaction type, we proposed a new rule named Tangent Line Rule to judge the univariant reaction type in the quaternary phase diagram. By applying Tangent Line Rule and Tangent Plane Rule previously proposed, some univariant and bivariant crystallization reaction types in the CaO-SiO2-La2O3- Nb2O5 phase diagram were determined, respectively. The current work can provide original data for the establishment of a thermodynamic database of Nb-bearing and REE-bearing slag system; the proposed Tangent Line Rule will promote the application of a spatial quaternary phase diagram.

Highlights

Bayan Obo deposit in northern China is a famous polymetallic ore deposit in the world
An important reason is that the coexistence of complex mineral phases makes it difficult to predict the property of slag system at high temperatures [3], which has delayed the development of related processes
Approximate 1 g sample was placed in the platinum crucible in a MoSi2 furnace (Precondar Co., Ltd, Luoyang, China), and heated to 1600 ◦ C and kept for 3 h for the sample to achieve homogeneous so that it can achieve equilibrium faster in the subsequent process; after that, the sample was cooled to 1400 ◦ C and kept for 24 h

Summary

Introduction

Bayan Obo deposit in northern China is a famous polymetallic ore deposit in the world. More than 71 kinds of elements existing in over 170 types of mineral phases have been detected in this deposit [1]. Among these valuable elements, niobium (Nb) and rare earth elements (REE) are two typical elements with huge reserves: the proven reserves of Nb and REE rank second and first in the world, respectively [2]. Niobium (Nb) and rare earth elements (REE) are two typical elements with huge reserves: the proven reserves of Nb and REE rank second and first in the world, respectively [2] Such a considerable amount of mineral reserve did not bring the expected metal production—. Due to the special composition of tailings, CaO-SiO2 -La2 O3 Nb2 O5 slag system has proved to be a basic system in related pyrometallurgical processes

Methods

Results

Conclusion