Key Takeaways & Executive Findings
- •• Hydrogen-based mineral phase transformation (HMPT) at 525 °C, 12.5 min, and 30% H2 concentration yields an iron concentrate with 64.09% TFe grade and 95.33% recovery. • Flotation optimization produces a rare earth concentrate with 65–70% REO grade and 60–65% REEs recovery. • HMPT enhances magnetic properties of solid waste, enabling effective magnetic separation of iron minerals. • Hematite is reduced to magnetite and bastnaesite decomposes to REE oxides and fluorides, while monazite, fluorite, and barite remain largely unchanged.
Abstract
The storage of solid waste in Bayan Obo has resulted in significant resource wastage and environmental concerns. In this study, an efficient process was developed to recover iron and rare earth elements (REEs) from this waste by processes of hydrogen-based mineral phase transformation (HMPT), magnetic separation, and flotation. Under optimal HMPT conditions (525 °C, 12.5 min, and 30% H2 concentration), an iron concentrate with a TFe grade of 64.09% and a recovery of 95.33% was obtained. The magnetic properties of the solid waste were greatly enhanced by HMPT, allowing the effective magnetic separation of iron minerals. Further optimization of the flotation process resulted in a REEs concentrate with a rare earth oxide (REO) grade of 65%–70% and a REEs recovery of 60%–65%. Hematite was reduced to magnetite during HMPT, and bastnaesite was decomposed to REEs oxides and fluorides, and the particle structure was significantly destroyed. However, changes in monazite, fluorite, and barite were minimal.
1. Introduction
Iron and rare earth elements (REEs) are the cornerstones of modern industry and technology, playing an indispensable role in the construction, manufacture, and production of high-tech devices such as powerful magnets, batteries, and electronic components [1,2]. As technology advances, the global demand for these critical materials continues to grow, and the scarcity of iron and REEs mineral resources has become increasingly apparent [3]. However, as these resources are exploited on a large scale, high-quality mineral reserves are gradually diminishing. This situation highlights the urgent need to develop sustainable and innovative processing technologies to effectively recover iron and REEs from refractory mineral resources and ensure their stable supply [4].
The Bayan Obo deposit is a globally recognized source of iron and REEs that have been extensively mined for several decades. During the 1950s and 1960s, a significant portion of the mined ore was discarded due to technical and economic limitations, resulting in over 20 million tons of solid waste [5]. The total iron (TFe) grade of these wastes is about 20% to 33%, and the rare earth oxide (REO) grade is approximately 6%. In essence, the deposit has become an artificial mine where continuous dumping has resulted in a significant waste of valuable resources. Over time, prolonged exposure to weathering, water leaching, and oxidation has significantly altered the physical and chemical properties of the ore, making efficient beneficiation difficult. Traditional beneficiation methods have not provided satisfactory technical or economic results due to these changes [6]. In addition, the extensive storage of these ores poses a significant environmental risk. Long-term exposure causes metal elements to leach into nearby surface and groundwater, resulting in soil and water contamination [7]. Developing these solid wastes as resources could help alleviate supply pressures and mitigate environmental impacts.
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ZHAO Na, ZHANG Qiang, MA Hongwei, SUN Yongsheng, GAO Peng, CAO Zhao, ZHANG Zhenyue (2024). Advancing the recovery of iron and rare earth elements from the solid waste at Bayan Obo. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2024.12.006
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Frequently Asked Questions
What is the optimal condition for hydrogen-based mineral phase transformation (HMPT) in this study?
The optimal HMPT conditions are 525 °C, 12.5 minutes, and 30% H2 concentration, yielding an iron concentrate with 64.09% TFe grade and 95.33% recovery.
How does HMPT affect the magnetic properties of the solid waste?
HMPT greatly enhances the magnetic properties of the solid waste, allowing effective magnetic separation of iron minerals.
What are the final grades and recoveries for rare earth elements (REEs) after flotation?
After flotation optimization, a REEs concentrate with a rare earth oxide (REO) grade of 65%–70% and a REEs recovery of 60%–65% is obtained.
What mineral transformations occur during HMPT?
During HMPT, hematite is reduced to magnetite, and bastnaesite is decomposed to REEs oxides and fluorides, with significant destruction of particle structure. Monazite, fluorite, and barite remain largely unchanged.
Why is recovering iron and REEs from Bayan Obo solid waste important?
The solid waste at Bayan Obo contains significant iron and rare earth resources, and its recovery addresses resource wastage and environmental concerns, contributing to sustainable supply of critical materials.
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