Separation and Characterization of Multiple Rare Earth Phases in CaO-SiO2-La2O3 Basic Slag System

Abstract

Bayan Obo, located in Inner Mongolia, China, is renowned for housing the world’s largest deposit of iron-niobium-rare earth polymetallic co-associated minerals. During the process of developing and exploiting this deposit, rare earth elements and other valuable minerals are incorporated into the slag phase, resulting in a significant secondary source of rare earth resources. To effectively recover the rare earth elements, supergravity technology was used to selectively separate the three distinct rare earth phases in the CaO-SiO₂-La₂O₃ basic slag system. The process yielded three rare earth phase pure crystals, namely La₂Ca₃(SiO₃)₆, Ca_xLa_4.67-x(SiO₄)₃O_1-0.5x, and La_xCa_2-x(SiO₄)O_0.5x, which were obtained under specific conditions: a gravity coefficient of G = 1000, separation time of t = 10 min, and crystallization temperature for respective each rare earth phase (1330 °C, 1350 °C, 1600 °C). Comprehensive characterization of these crystals was conducted using Raman spectroscopy, EPMA, and XRF. The results indicated that the La₂O₃ content in the three rare earth phases was approximately 40 wt.%, 75 wt.%, and 20 wt.%, respectively. Notably, the Ca_xLa_4.67-x(SiO₄)₃O_1-0.5× phase exhibited the highest La₂O₃ content, making it the most valuable phase for rare earth enrichment. This study supplements the knowledge of rare earth phases in CaO-SiO₂-La₂O₃ basic slag system, providing a theoretical reference for efficient recovery of rare earth resources and sustainable utilization of RE-bearing slag.

Graphical Abstract