Key Takeaways & Executive Findings
- •• HMPT effectively separates iron and enriches rare earths from Bayan Obo refractory ores, with tailings containing 9.15wt% REO, 5.31wt% monazite, and 23.52wt% fluorite. • Closed-circuit flotation achieved a REO grade of 60.27wt% with 73% recovery, demonstrating the feasibility of rare-earth recovery from HMPT-treated tailings. • Monazite remains stable during HMPT, while bastnaesite transforms into Ce7O12 and CeF3, increasing collector consumption but not significantly affecting flotation performance. • The integration of HMPT, magnetic separation, and flotation offers a promising strategy for comprehensive recovery of iron, rare earths, and fluorite from Bayan Obo ores.
Abstract
Hydrogen-based mineral phase transformation (HMPT) technology has demonstrated its effectiveness in separating iron and enriching rare earths from Bayan Obo refractory ores. However, further research is needed to clarify the phase composition and floatability of rare earths obtained after HMPT owing to the associated phase transformations. This study explored the mineralogical characteristics and separation behavior of rare earths in HMPT-treated iron tailings. Process mineralogy studies conducted via BGRIMM process mineralogy analysis and X-ray diffraction revealed that the main valuable minerals in the tailings included rare-earth oxides (9.15wt%), monazite (5.31wt%), and fluorite (23.52wt%). The study also examined the impact of mineral liberation and gangue mineral intergrowth on flotation performance. Flotation tests achieved a rare-earth oxide (REO) grade of 74.12wt% with a recovery of 34.17% in open-circuit flotation, whereas closed-circuit flotation resulted in a REO grade of 60.27wt% with a recovery of 73%. Transmission electron microscopy and scanning electron microscopy coupled with energy-dispersive spectroscopy revealed that monazite remained stable during the HMPT process, while bastnaesite was transformed into Ce7O12 and CeF3, leading to increased collector consumption. Nonetheless, the HMPT process did not significantly affect the flotation performance of rare earths. The enrichment of fluorite in the tailings highlighted its further recovery potential. The integration of HMPT with magnetic separation and flotation presents an efficient strategy for recovering rare earths, iron, and fluorite from Bayan Obo ores.
1. Introduction
The Bayan Obo region is a world-class polymetallic deposit rich in iron, rare earths, and fluorite. Despite its abundant mineral resources, comprehensive recovery remains challenging owing to the ore's complex composition and the limitations of current recovery technologies [1–3]. As mineral resources become increasingly scarce, the recovery of low-grade and refractory deposits has gained critical importance [4–6]. Accordingly, the rare-earth and fluorite resources at Bayan Obo, recognized as vital strategic materials, have attracted significant attention [7–10].
Flotation is an effective method for recovering valuable metals from ores and has also been widely applied to mineral-type rare-earth ores [11–14]. In the 1950s, flotation was employed for the large-scale development of the Mountain Pass rare-earth mine in the United States. A significant breakthrough occurred in the early 1990s at the Bayan Obo deposit, where the successful application of hydroxamic acid collectors in rare-earth flotation enabled the production of high-grade rare-earth concentrates. This advancement established China as the world's largest producer and consumer of rare-earth elements, as the nation contributed approximately 54% of the global output [15–19]. The Baotou Steel (Group) Corporation's concentrator implemented a process flow of “weak magnetic–strong magnetic–continuous flotation”, facilitating the comprehensive utilization of iron and rare-earth resources. However, this method achieves relatively low utilization rates for rare earths and fluorite, with rare-earth concentrate recovery limited to approximately 50%, and approximately 20% of fluorite resources remain uncommercialized and underutilized.
The Bayan Obo deposit, a world-renowned polymetallic resource, has long faced challenges in resource utilization owing to its complex mineral composition, intricate mineral associations, and similar beneficiation properties. Conventional beneficiation techniques, such as magnetic separation and flotation, often lead to the unintended recovery of non-target minerals, thereby reducing the quality of target concentrates and hindering the recovery of other valuable minerals. To address these challenges, researchers have explored mineral phase transformation techniques to improve recovery efficiency. For example, Zhou et al. [20] investigated the carbothermal reduction method for processing Bayan Obo ore. This process involved roasting a mixture of coal and CaO at temperatures between 1100 and 1200°C, converting refractory iron into metallic iron. This transformation enabled the effective separation of iron and rare earths via magnetic separation.
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Jilai Ning, Peng Gao, Yang Wang, Zihao Li, Shuai Yuan, Yongsheng Sun, Wenbo Li, Zhidong Tang (2025). Mineralogical characterization and flotation properties of rare earths in refractory iron tailings subjected to hydrogen-based mineral phase transformation. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3053-y
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Frequently Asked Questions
What is hydrogen-based mineral phase transformation (HMPT) and how does it apply to rare earth recovery?
HMPT is a technology that uses hydrogen to induce phase transformations in minerals, enabling the separation of iron and enrichment of rare earths from refractory ores. In this study, HMPT was applied to Bayan Obo iron tailings, resulting in tailings with significant rare-earth content (9.15wt% REO) that could be further processed by flotation.
What are the main valuable minerals in the HMPT-treated iron tailings?
The main valuable minerals identified were rare-earth oxides (9.15wt%), monazite (5.31wt%), and fluorite (23.52wt%). These minerals are targets for recovery through flotation and other beneficiation processes.
How effective is flotation in recovering rare earths from HMPT-treated tailings?
Flotation tests showed that open-circuit flotation achieved a rare-earth oxide (REO) grade of 74.12wt% with a recovery of 34.17%, while closed-circuit flotation achieved a REO grade of 60.27wt% with a recovery of 73%. This demonstrates that flotation is effective, though recovery rates vary with circuit configuration.
What happens to bastnaesite during HMPT and how does it affect flotation?
During HMPT, bastnaesite is transformed into Ce7O12 and CeF3, which increases collector consumption during flotation. However, this transformation does not significantly affect the overall flotation performance of rare earths, as monazite remains stable and contributes to recovery.
What is the significance of fluorite enrichment in the tailings?
The enrichment of fluorite (23.52wt%) in the tailings highlights its potential for further recovery. This is important because fluorite is a strategic mineral, and its recovery alongside rare earths and iron can improve the economic viability of processing Bayan Obo ores.
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