Key Takeaways & Executive Findings
- •• • Oxidation roasting at elevated temperatures, extended time, and higher O2 concentration increased Ce oxidation degree and REO grade beyond 85.00%, directly enhancing rare earth enrichment but requiring higher collector dosage for >85.00% flotation recovery. • • Thermal decomposition produced Ce7O12 and REF3 phases, creating a complex crystal structure and long, nearly parallel cracks that penetrated particles, increasing porosity and causing fragmentation—this improves wettability but complicates flotation selectivity. • • Dissolved rare earth ion concentration rose significantly during flotation, with surface hydrolysis forming rare earth hydroxyl compounds, which altered the chemical adsorption of SHA and necessitated higher reagent addition. • • SHA adsorption occurred both internally and externally due to surface cracking, increasing collector consumption; this implies that flotation optimization must account for porous particle architecture to avoid excessive reagent costs.
China Advanced Materials & Deep-Tech Radar
Get verified English translations, SEM micrographs & open-access PDF alerts from China's leading state key laboratories delivered to your inbox every Monday at 08:00 EST.
Abstract
Oxidation roasting of bastnaesite was conducted to evaluate its impact on surface characteristics and flotation behavior. Experiments varied temperature, time, and O2 concentration. Increasing temperature promoted thermal decomposition, yielding Ce7O12, RE2O3, and REF3 as main phases. The Ce oxidation degree and REO grade of roasted products exceeded 85.00%. Roasting induced long, narrow, nearly parallel cracks within particles, increasing porosity and causing partial fragmentation. During flotation, dissolved rare earth ion concentration increased significantly, and surface hydrolysis formed rare earth hydroxyl compounds. Complete decomposition raised the required collector dosage to achieve recovery above 85.00%. This increase is attributed to enhanced particle wettability, altered collector adsorption, and deeper penetration into the porous structure. The findings provide a basis for optimizing flotation circuits treating roasted bastnaesite, particularly in iron-bearing rare earth deposits where pyrometallurgical pretreatment is employed.
1. Introduction
Rare earth elements (REEs) are indispensable in electronics, renewable energy, and advanced manufacturing, with global demand rising sharply. Primary sources include bastnaesite, monazite, and ion-adsorption clays, but REEs rarely form independent deposits; they are often recovered as by-products from iron-bearing deposits such as Bayan Obo (China), Mount Weld (Australia), and Pea Ridge (USA). The complex mineralogy and heterogeneous distribution of these ores impede simultaneous recovery of iron and REEs. Pyrometallurgical pretreatment, particularly reduction roasting, converts hematite to magnetite, facilitating iron removal via magnetic separation and enriching REEs in tailings. However, residual REE recovery from tailings remains challenging, and conventional flotation of bastnaesite after such pretreatment suffers from poor selectivity and high reagent consumption.
Hydrogen-based mineral phase transformation (HMPT) has emerged as a promising route for iron and REE recovery from iron-bearing REE ores. Pilot-scale trials on Bayan Obo ore achieved iron concentrate grades of 65.26% and recoveries of 85.29%, leaving REEs enriched in tailings. Subsequent flotation of these tailings is hindered by altered surface properties induced by roasting. This study investigates oxidation roasting of bastnaesite to elucidate phase transformations, microstructural evolution, and surface chemistry changes that govern flotation behavior. By systematically varying temperature, time, and O2 concentration, the work establishes quantitative links between roasting conditions, Ce oxidation degree, REO grade, and collector dosage requirements, providing a technical basis for optimizing flotation circuits in industrial REE recovery from roasted feeds.
Loading authentic research manuscript (Pages 1–5)...
Qiang ZHANG, Yong-sheng SUN, Zhao CAO, Peng GAO, Wen-bo LI (2026). Effects of oxidation roasting on surface characteristics and flotation behavior of bastnaesite. Transactions of Nonferrous Metals Society of China (中国有色金属学报). https://doi.org/10.1016/S1003-6326(26)67066-5
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntelare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the impact of oxidation roasting on the required collector dosage for bastnaesite flotation?
Complete decomposition of bastnaesite during oxidation roasting increased the required collector dosage to achieve a flotation recovery above 85.00%. This increase is attributed to enhanced particle wettability, altered collector adsorption mechanisms, and deeper penetration of the collector into the porous structure created by roasting-induced cracks.
How does the formation of cracks during roasting affect particle size and flotation performance?
Oxidation roasting induces long, narrow, nearly parallel cracks that penetrate particles, increasing porosity and causing partial fragmentation into finer sizes. While finer particles can improve liberation, the increased porosity enhances wettability and allows collector to adsorb internally, which raises reagent consumption and may complicate flotation selectivity.
What are the main phases formed during thermal decomposition of bastnaesite?
Thermal decomposition of bastnaesite during oxidation roasting primarily forms Ce7O12, RE2O3, and REF3. The Ce oxidation degree and REO grade of the roasted product exceeded 85.00%, indicating substantial conversion. The resulting complex crystal structure influences surface properties and flotation behavior.
How does surface hydrolysis affect flotation of roasted bastnaesite?
During flotation, the surface of roasted bastnaesite undergoes apparent hydrolysis, forming rare earth hydroxyl compounds. This increases the concentration of dissolved rare earth ions and alters the chemical adsorption of the collector (SHA), necessitating higher collector dosages to maintain recovery above 85.00%.
What are the implications of these findings for industrial-scale REE recovery from iron-bearing deposits?
The study shows that oxidation roasting enhances REE enrichment but increases flotation reagent costs due to surface and structural changes. Industrial operations must balance roasting conditions to achieve >85.00% REO grade and Ce oxidation degree against higher collector consumption, and consider modified flotation circuits that account for porous, cracked particles to optimize economics.
Related Chinese Research & Cross-Citations
Assessment of zinc migration behavior and toxicity characteristics in redox smelting of zinc leaching residue
The redox smelting of zinc leaching residue (ZLR) was investigated to determine the migration behavior and toxicity characteristics of zinc under varying anthracite addition, temperature, and holding time. The ZLR, containing 10–20 wt.% Zn, 0.5–5 wt.% Pb, and 0.1–0.5 wt.% Cd, generates TCLP leachate concentrations of Zn up to 4589.0 mg/L, far exceeding regulatory limits. Experimental results reveal that CaSO4 in the residue promotes the transformation of ZnFe2O4 into a ZnS–FeS eutectic, which hinders zinc recovery and elevates environmental risk due to its lower thermodynamic stability relative to (Fe,Zn)2SiO4, ZnFe2O4, and (ZnO)slag. At temperatures above 1573 K, the ZnS–FeS eutectic is oxidized by O2/(O)slag to ZnO(s), subsequently dissolved into the slag as chemically dissolved Zn, and finally reduced to Zn(g) by CO. Pre-desulfurization or increased oxygen potential enhances zinc volatilization. Under optimized conditions, the zinc recovery ratio reached 99.13%, and the residual zinc content in the slag decreased to 0.22 wt.%, substantially below the industrial range of 1.0–3.0 wt.%. A novel strategy integrating desulfurization pretreatment with redox smelting is proposed, which lowers the required smelting temperature and improves zinc recovery efficiency, offering a more economical and environmentally sustainable solution for ZLR treatment.
Single Crystal NCM811 Cathode Material Prepared by Rapid Solvothermal Method
Polycrystalline LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes undergo intergranular cracking and structural collapse during extended cycling, limiting their commercial viability. This study reports single-crystalline NCM811 synthesized via a rapid ethanol–water solvothermal method. The solvothermal duration was varied, and the 60 min sample (NCM-60) exhibited optimal electrochemical performance. X-ray diffractometry confirmed an α-NaFeO2 structure with R-3m space group and high crystallinity. NCM-60 delivered a reversible capacity of 157.28 mA·h/g at 1C and a capacity retention of 55.06% after 200 cycles, significantly outperforming polycrystalline NCM (PC-NCM). Cross-sectional scanning electron microscopy revealed no apparent cracks in NCM-60 after 200 cycles, whereas PC-NCM exhibited severe intergranular fracture. The results demonstrate that shortening solvothermal time reduces precursor particle size and crystallinity, but 60 min yields the best balance. Pre-oxidation of the carbonate precursor before lithiation is recommended to mitigate CO2 evolution and lithium–nickel disorder during high-temperature sintering. This rapid solvothermal route offers a scalable pathway to single-crystal NCM811 with enhanced cycling stability and mechanical integrity.
Efficient separation of heavy metals from gypsum residue and secondary zinc oxide fume based on synergistic sulfidation
Synergistic sulfidation roasting of heavy metal gypsum residue and secondary zinc oxide fume was proposed by using the research idea of 'waste to treat waste'. Thermodynamic studies indicated that the sulfidation of zinc oxide could be effectively enhanced by increasing the dosage of calcium sulfate and carbon powder in the range of 500−800 °C. The synergistic sulfidation experiments of heavy metal gypsum residue with secondary zinc oxide showed that the sulfidation rate of zinc reached 90.39% and the grain size of ZnS increased from 5 to 10 μm under the conditions of temperature 700 °C, carbon powder 30%, Na2CO3 10%, mass ratio of gypsum residue to secondary zinc oxide 1.4:1, roasting time 2 h and cooling rate 1 °C/min. Meanwhile, 76.32% F, 72.11% Cl and 93.41% As were removed. TG/DTG−DSC, 3D FTIR spectra and SEM analysis showed that the conversion of CaSO4 to CaCO3 and the avoidance of CO2 and SO2 production were achieved under optimized conditions. This study achieves efficient sulfidation of zinc as well as growth of ZnS grains, laying the theoretical and technological foundation for subsequent recovery of ZnS by flotation.
Low-Ammonium Synergistic Leaching of Ionic Rare Earth Ore with Acetic Acid–Ammonium Sulfate System
Conventional ammonium sulfate leaching of ionic rare earth ores generates 4–6 t of ammonia-nitrogen wastewater per ton of rare earth and drives mining-area soil pH to 3.5–4.0, creating an acute environmental compliance risk. This study evaluates a low-ammonium synergistic lixiviant comprising 0.020 mol/L (NH4)2SO4 and 0.010 mol/L acetic acid (HAc) at pH 4–5, 30 °C, and 1 h contact time. Comparative leaching experiments establish a rare earth element (REE) leaching efficiency of 88.92%, a 13.36% absolute increase over single 0.020 mol/L (NH4)2SO4 leaching. To achieve the same ~90% efficiency benchmark, the conventional single-salt system requires 0.030 mol/L (NH4)2SO4; the synergistic system therefore reduces ammonium consumption by 33.3%. Surface characterization indicates a dual mechanism: H+ attenuates electrostatic interactions between RE3+ and silicate surfaces, enhancing NH4+–RE3+ exchange, while CH3COO− forms soluble RE3+/Al3+ complexes that prevent Al(OH)3 passivation and sustain surface reactivity. The protocol offers a directly deployable route to cut reagent cost and ammonia-nitrogen load without sacrificing recovery, addressing the principal bottleneck restraining sustainable ionic rare earth ore exploitation under China's dual-carbon and rare earth total-amount control policies.
Achieving strength-ductility tradeoff in near alpha titanium alloy via multi-stage heat treatment-induced nano-martensite phase transformation
A multi-stage heat treatment (MSHT) strategy, comprising a high-temperature short-duration water quench (WQ) followed by low-temperature long-duration furnace cooling (FC), was applied to a near-alpha Ti-0.3Mo-0.8Ni-2Al-1.5Zr alloy to overcome the strength-ductility tradeoff. The WQ state produced lath nano-martensite alpha-prime, residual beta-prime, and equiaxed recrystallized alpha. Subsequent FC decomposition transformed alpha-prime/beta-prime into homogeneously dispersed nano-scale alpha+beta precipitates, while equiaxed alpha coarsened via grain boundary migration. The WQ condition exhibited an ultimate tensile strength (sigma_UTS) of 610 MPa and elongation to failure (epsilon_f) of 18.2%. The WQ+400FC condition achieved a peak sigma_UTS of 791.5 MPa with epsilon_f = 16.7%, yielding a strength-ductility product (sigma_UTS * epsilon_f) of 13.2 GPa*%, a 19% improvement over the WQ state. Texture analysis revealed a duplex texture in WQ: weak {0001}//Z0 and strong {0110}//Y0, inherited after FC. The 400FC sample showed the highest lattice strain inhomogeneity, with peak kernel average misorientation (KAM) of 1.5 degrees and grain orientation spread (GOS) of 0.96 degrees, correlating with the excellent sigma_UTS. Non-basal slip systems exhibited higher Schmid factor (SF) values after heat treatment, contributing to ductility. Burgers orientation relationship (BOR) reconstruction confirmed variant selection during beta to alpha-prime transformation, with only four predominant alpha-prime variants instead of the twelve theoretically possible.
Adjusting mechanisms for ultrafine-grained microstructures during hot deformation of Ni−38Cr−3.8Al alloy via pre-ageing precipitation
The influence of pre-ageing temperature on dynamic recrystallization (DRX) and microstructure evolution during hot compression of Ni−38Cr−3.8Al alloy was investigated. Five samples with varying pre-precipitation states were fabricated. Pre-ageing treatment precipitates α-Cr phases in lamellar and particle forms. During subsequent hot deformation, pre-precipitated α-Cr lamellae undergo dissolution fragmentation and spheroidization, transforming into finer particles due to elevated temperature and high-density dislocations. At 560 °C, an incomplete discontinuous precipitation (DP) state restrains DRX, producing necklace-like microstructures. Above 640 °C, a complete DP state with fully lamellar structures promotes DRX, yielding ultrafine-grained (UFG) microstructures. Coarse α-Cr particles enhance DRX through particle-stimulated nucleation (PSN) and discontinuous DRX mechanisms, while dissolved α-Cr lamellae promote DRX via continuous DRX. DRX kinetics analysis indicates that increasing pre-ageing temperature accelerates DRX, evidenced by reduced critical strain and peak strain, and increased DRX volume fraction. To achieve UFG microstructures during hot deformation, fully lamellar structures should be precipitated during pre-ageing. These findings provide a processing pathway for tailoring microstructures in high-Cr nickel-based alloys.