Key Takeaways & Executive Findings
- •• Thermal decomposition of bastnaesite in an inert atmosphere is strongly temperature-dependent and elevates the REO grade from 72.90 wt% to 86.83 wt% while increasing Ce oxidation. • Decomposition induces lamellar cracking, increased specific surface area, and particle fragmentation, significantly modifying surface chemistry and raising initial pulp pH to nearly 11.00. • Flotation of decomposed bastnaesite requires a much higher SHA collector dosage, rising from 20 mg·L−1 for raw ore to 250 mg·L−1, due to enhanced chemical adsorption and internal pore distribution. • Optimal flotation recovery is achieved at pH 8.00–9.00, but post-decomposition pH adjustment is difficult; these insights guide the development of tailored reagents for bastnaesite roasting products.
Abstract
This study aimed to elucidate the influence of thermal decomposition under an inert atmosphere on the phase composition, microstructure, and flotation performance of bastnaesite. Experiments showed that decomposition was strongly temperature-dependent. After complete decomposition, the release of CO2 increased the rare earth oxide grade from 72.90wt% to 86.83wt%, accompanied by an increase in the Ce oxidation degree. Major decomposition products included rare earth oxyfluoride (REOF), rare earth trifluoride (REF3), and Ce7O12, with some products showing low crystallinity. The decomposition damaged the particle structure, resulting in the extensive lamellar cracking, a significant increase in specific surface area, and partial fragmentation of the particles. Flotation tests revealed that optimum recovery was achieved at pH 8.00–9.00. However, thermal decomposition increased the initial pulp pH to almost 11.00, making pH adjustment difficult. Salicylhydroxamic acid (SHA) was adsorbed on the surfaces by both physical and chemical interactions, with chemical adsorption being significantly enhanced after decomposition. During flotation, SHA was distributed not only on particle surfaces but also in internal pores after decomposition. Due to the phase and microstructural changes, the required dosage of SHA increased from 20 mg·L−1 for the raw ore to 250 mg·L−1. These results provide insights into the development of reagents suitable for the flotation of bastnaesite roasting products.
1. Introduction
Rare earth elements (REEs) are critical to the advancement of a wide range of modern technologies, including clean energy systems, electronics, aerospace, and defense [1]. Their unique electronic, magnetic, and optical properties underpin the production of permanent magnets, batteries, catalysts, and high-performance alloys [2]. With the global shift towards a low-carbon economy and the growing demand for sustainable technologies, securing a stable and reliable supply of REEs has become increasingly important [3]. Among various REEs minerals, bastnaesite serves as an important source of light rare earth elements, particularly Ce, La, Pr, and Nd [4]. Major deposits such as Bayan Obo in China and Mountain Pass in the United States are dominated by bastnaesite mineralization [5]. The relatively high rare earth oxide (REO) grade, favorable beneficiation characteristics, and widespread occurrence of bastnaesite make it the primary target for REEs extraction.
Flotation is the predominant method for selective recovery of bastnaesite. Extensive efforts have been made to improve flotation performance, particularly through the development of efficient collectors such as hydroxamic acids, fatty acids, and their derivatives, which have strong affinities for REEs cations on the mineral surface [6–7]. Optimization of collector molecular structures, dosages, and adsorption mechanisms has been essential to improving both selectivity and recovery. In parallel, the use of depressants and dispersants has improved the separation efficiency between bastnaesite and common gangue minerals such as barite, calcite, and fluorite [8–9]. More recently, research has expanded to include bastnaesite-bearing tailings and complex REEs ores, with advanced flotation techniques such as carrier flotation and ultrasonic or microbubble assisted flotation being explored to further improve recovery efficiencies [10–12]. Despite these advances, most studies have focused on the flotation behavior of untreated or slightly modified bastnaesites. Investigations into the flotation properties of bastnaesite following thermal treatment, particularly under controlled atmospheres, remain limited. Given the sensitivity of bastnaesite to thermal conditions, a detailed understanding of the effects of thermal decomposition and phase transformation on its flotation behavior is both necessary and timely.
Roasting is widely used as a pretreatment method for REEs concentrates and complex REEs-bearing ores. It can convert REEs minerals into more leachable compounds, thereby facilitating subsequent leaching processes. He et al. [13] demonstrated that selective mineral phase transformation in a N2 atmosphere enabled efficient separation of bastnaesite and monazite in mixed rare earth concentrates, achieving a leaching rate of 93.7wt% for bastnaesite while the leaching rate for monazite remained as low as 3.2wt%. Roasting can also selectively decompose bastnaesite to improve flotation separation from monazite in mixed concentrates. Yang et al. [14] prepared (Ce,La)2O3 by calcination roasting and investigated the flotation separation of rare earth oxides from roasted concentrates.
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Qiang Zhang, Yongsheng Sun, Peng Gao, Zhao Cao, Yuexin Han (2025). Thermal decomposition of bastnaesite in an inert atmosphere and influence on flotation behavior. Journal of Mineral Metallurgy and Materials Science. https://doi.org/10.1007/s12613-025-3251-2
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Frequently Asked Questions
How does thermal decomposition affect bastnaesite flotation?
Thermal decomposition in an inert atmosphere changes the phase composition and microstructure of bastnaesite, increasing the REO grade and specific surface area. It also raises the initial pulp pH to almost 11.00, making pH adjustment difficult, and requires a much higher SHA collector dosage, from 20 mg·L−1 for raw ore to 250 mg·L−1 for decomposed material.
What are the main products of bastnaesite thermal decomposition?
The major decomposition products include rare earth oxyfluoride (REOF), rare earth trifluoride (REF3), and Ce7O12, with some products exhibiting low crystallinity. The release of CO2 during decomposition increases the rare earth oxide grade and the Ce oxidation degree.
Why is pH adjustment difficult after bastnaesite roasting?
Thermal decomposition raises the initial pulp pH to almost 11.00, while the optimum flotation recovery is achieved at pH 8.00–9.00. This large pH shift makes it difficult to adjust and control the pulp pH during flotation.
How does SHA adsorption change after thermal decomposition?
After thermal decomposition, SHA adsorption is enhanced significantly, particularly chemical adsorption. SHA becomes distributed not only on particle surfaces but also in internal pores created by decomposition, increasing the collector demand and the required dosage from 20 mg·L−1 to 250 mg·L−1.
What is the optimal pH for bastnaesite flotation recovery?
Flotation tests show that optimum recovery is achieved at pH 8.00–9.00 for both raw and thermally decomposed bastnaesite, although decomposition increases the initial pulp pH to almost 11.00, complicating pH control.
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