The efficient separation of fluorine from rare earths is a critical challenge in the recycling of both rare-earth molten salt electrolytic slag. In this work, a synergistic co-roasting strategy using ferroboron as a reactive additive was developed to enable simultaneous defluorination and resource recovery. Thermodynamic analysis confirmed that NdF3 can react with boron in air to generate volatile BF3 and neodymium borates, facilitating fluorine removal without alkali additives. Experimental results showed that direct roasting of NdF3–ferroboron mixtures at 800°C for 3 h with a B:F molar ratio of 4:3 achieved a fluorine removal efficiency of 95.09

The extraction of ion-adsorbed rare earth deposits in southern China suffers from complex processing flows, severe environmental damage, and clarified solution exhibits high residual rare earth ion concentrations ( 30 ppm). This work innovatively proposed a coupled process of precipitation and membrane separation, using polytetrafluoroethylene hollow fiber membranes to separate and enrich the rare earth magnesium salt precipitates, successfully solving the above-mentioned problems. A systematic investigation was conducted to elucidate the membrane fouling mechanisms, utilizing nine membrane fouling models. The effects of operating parameters on membrane flux variation were investigated, as well as the kinetics of membrane fouling. The experimental results indicate that no rare earth ions were detected in the permeate, and the turbidity of the feed solution decreased from 110 to 1 NTU. The membrane filtration resistance is mainly reversible fouling resistance (Rr = 0.5228). The best fit was achieved with the complete blocking model (R2 = 0.9906) and the intermediate blocking model (R2 = 0.9908), suggesting that the fouling was primarily due to particle adsorption and deep pore blocking. Near-complete flux recovery (> 99

This study presents a submerged electrocatalytic ceramic membrane (ECM) with a 60 nm CoO catalytic layer for the synergistic treatment of rare earth wastewater containing coexisting ammonia nitrogen (NH3-N) and rare earth ions (REIs). The CoO layer, rich in oxygen vacancies and exposing (111) crystallographic facets, enhances electrochemical active sites, as indicated by a double-layer capacitance (8.736 & times; 10(-5) F) and Tafel slope (2183.94 mV & centerdot;dec(-1)). Under 0.5 M NaCl, complete degradation of 50 ppm methylene blue was achieved within 100 min, confirming effective electrochemical self-cleaning. After MgO-based precipitation, membrane filtration enabled full retention of rare earth elements (<0.1 ppm), reduced turbidity from 107 to 1 NTU, and maintained a stable permeate flux of similar to 950 L & centerdot;m(-2)& centerdot;h(-1) over 100 min. Electrogenerated hypochlorite oxidized NH3/NH4+ via chloramine formation and breakpoint chlorination, achieving 100% ammonia-N removal within 90 min. DFT calculations reveal that the chlorine evolution reaction proceeds through the Volmer-Krishtalik pathway, exhibiting the lowest rate-determining step barrier (Delta G = 1.45 eV) with high Cl- selectivity over SO42- and CO32-. The integrated system enables efficient rare earth recovery, rapid nitrogen removal, and robust antifouling, offering a sustainable solution for complex wastewater remediation.

The rare earth elements(REEs)extraction by chemical leaching from ion-adsorption type rare earth ores(IAREO)has led to serious ecological and environmental risks.Conversely,demand for bioleaching is on the rise with the advantage of being environmental-friendly.As one of the organic acids produced by biological metabolism,citric acid was used to leach REEs and explore the performance and process.The results demonstrate that citric acid exhibits higher leaching efficiency(96.00％)for REEs at a relatively low concentration of 0.01 mol/L compared with(NH4)2SO4(84.29％,0.1 mol/L)and MgSO4(83.99％,0.1 mol/L).Citric acid shows a preference for leaching heavy rare earth elements,with 99％leaching efficiency in IAREO,which shows higher capacity than(NH4)2SO4 and MgSO4(as inorganic leaching agents).Kinetic analysis indicates that the leaching process of REEs with citric acid is controlled by both the internal diffusion kinetics and chemical reaction kinetics,which is different from inorganic leaching agents.Visual Minteq calculations confirm that RE-Citrate is the main constituent of the extract solution in the leaching process of the IAREO,thereby enhancing the leaching efficiency of REEs from the IAREO.It suggests that citric acid may be used as a promising organic leaching agent for the environmental-friendly extraction of REEs from IAREO.

The extraction of rare earth elements (REEs) via chemical leaching from ion-adsorption type rare earth ores has led to serious ecological and environmental risks. Organic acid leaching agents possessed advantages in environmental friendliness and differential leaching capabilities. This study investigated the leaching behaviors of REEs from ion-adsorption type rare earth ores using organic acids and focused on the differential leaching properties of light rare earth elements and heavy rare earth elements. The leaching conditions using acetic acid, malic acid, and citric acid were optimized, and the influences of organic acid on mineral properties and soil ecological functions were elaborated. The experimental results indicated that acetic acid, malic acid, and citric acid had unique REEs differential leaching properties, without significantly altering the mineral structure. The leaching efficiency of full-phase, and colloidal sediment phase REEs reached 49.75%, and 28.03% for acetic acid, 52.07%, and 26.65% for malic acid, 51.79%, and 33.07% for citric acid, respectively. Furthermore, the patterns of the soil enzyme activity also confirmed the perspective that the soil ecology had not been affected obviously by the organic acids leaching process and rapidly recovered after leaching. Subsequently, Visual Minteq simulation and Density Functional Theory calculations indicated the differential leaching mechanism of light and heavy rare earths elements depended on the differences in complexation effects of organic acid, and the leaching of colloidal sediment phase REEs was the result of combined effects of acid leaching and complexation competition. The work provided molecular-level insights into the colloidal sediment phase REEs leaching and differential leaching mechanisms of light and heavy rare earths elements by organic acids, contributing to the understanding of REEs extraction processes.

Ionic rare earth purification residue (PR) originates from refining of ionic rare earth ores and is predominantly composed of rare earth elements (REEs), aluminum (Al), and silicon (Si). This is a recyclable secondary resource. It provides substantial challenges due to its classification as low-level radioactive waste (LLW). Recognizing the distinctive properties of PR, this paper describes a highly efficient process for the recovery and enrichment of Al, REEs, uranium (U), and thorium (Th) through a multistep process encompassing alkali digestion, hydrochloric acid leaching, sole extractant enrichment and separation. At a controlled temperature of 70 degrees C, the Al digestion efficiency reached 88.9 %. The alkali digestion residue underwent hydrochloric acid leaching, yielding leaching efficiencies of 99.9 %, 99.4 %, and 99.0 % for REEs, U(VI), and Th(IV), respectively. Notably, the amount of insoluble residue was reduced by 90 %, and it was transformed from LLW into general solid waste residue. Additionally, the utilization of 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (HEHEHP) as the sole extractant provided 100 % extraction efficiencies for U(VI) and Th(IV). After stepwise stripping processes, the purities of both U(VI) and Th(IV) exceeded 90 %. The REEs were precipitated as RE2(C2O4)3 and subsequently calcined to produce rare earth oxides with a recovery of 90.1 % and a purity of 97.4 %. This comprehensive scheme addressed the persistent challenges associated with long-term storage and radiological environmental risk.

The remediation of rare earth metallurgical wastewater, particularly the simultaneous removal of Cl- and ammonia nitrogen (NH4+-N) contaminants, constitutes a significant environmental challenge. This study presents a novel Bi-containing upconversion glass-ceramic (GC) for the efficient collaborative removal Cl- and NH4+-N pollutants. The GC exhibits a porous structure that facilitates deep migration of Cl- and H+ towards its Bi source in GC during the Cl- removal process, achieving Cl- removal rate is close to 100 % at a concentration of 1000 mg/ L. The resulting chlorine-removal precipitates were collected and utilized as near-infrared (NIR) photocatalysts, characterized by a defect-rich heterostructure, excellent upconversion luminescence, and efficient separation efficiency of e--h+ properties. In the degradation of NH4+-N, removal efficiencies of 98 % and 40 % were observed under UV-Vis-NIR and NIR irradiation, respectively. Analysis of potential NH4+-N degradation pathways indicated that center dot O2- and ClO center dot radicals were the primary reactive species. This study demonstrates that Bi-containing GC serves as an effective strategy for efficient collaborative removal Cl- and NH4+-N pollutants from rare earth smelting wastewater.

The growing demand for rare earth elements has intensified environmental concerns in mining areas, particularly with respect to soil contamination by heavy metals and nutrient imbalances. This study investigated the potential of coal gangue-based silicon fertilizers (CG-SF) for the remediation of ion-type rare earth tailings soil (RETS). CG-SF was applied at various concentrations in controlled pot experiments, with ryegrass cultivation used as a bioindicator of soil health. The results demonstrated that CG-SF significantly improved the soil physicochemical properties, increased pH, CEC, and OM content, while enhancing water retention and nutrient availability. Additionally, CG-SF reduced the bioavailability of heavy metals by promoting their immobilization in stable soil fractions. Soil enzyme activities, particularly dehydrogenase, were stimulated, indicating enhanced microbial activity and nutrient cycling. The results of PiecewiseSEM suggested that silicon fertilizer primarily facilitated the ecological restoration of ion-type rare earth mining areas by enhancing the growth of ryegrass and improving soil chemical properties. This study highlights the dual benefits of CG-SF in recycling industrial waste and providing a sustainable, cost-effective solution for soil remediation in mining areas. The findings underscore its potential for large-scale application in ecological restoration and sustainable land management.

The 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (HEHEHP) extractant exhibits a strong affinity for uranium (U(VI)) and thorium (Th(IV)), facilitating their extraction but complicating their stripping. After prolonged cycling, the HEHEHP organic phase accumulates significant amounts of U(VI) and Th(IV), which not only degrades the extractant’s recyclability but also poses radiological hazards to the working environment and personnel. This study systematically investigates the stripping process and mechanisms for removing U(VI) and Th(IV) from the HEHEHP organic phase using sodium carbonate (Na₂CO₃) as the stripping agent. Experimental results demonstrate that Na₂CO₃, owing to its high alkalinity and strong CO₃2⁻ dissociation, exhibits excellent U(VI) stripping efficiency. A novel approach combining "complete saponification with sodium hydroxide (NaOH) followed by low-concentration Na₂CO₃ stripping" was proposed, achieving efficient U(VI) stripping and separation. The optimal stripping conditions were determined as follows: a Na₂CO₃ concentration of 0.25 mol/L, an organic-to-aqueous phase ratio of 1:2, and a temperature of 30 °C. Under these conditions, a two-stage cross-flow stripping process achieved a U(VI) stripping efficiency of 99.35

Excessive fluoride and Al-F complex- ions severely impede the efficient extraction of rare earth elements (REEs) from rare earth chloride (RECl3) solution. Herein, hydrated calcium chloroaluminate (Ca2Al(OH)6Cl2H2O) was prepared via a facile neutralization precipitation method and applied as a defluoridant to remove fluoride and aluminum to address the challenges in RECl3 solution. Under the optimized conditions (initial pH = 2.0, 15 g L-1 dosage, and 2 hours), the F concentration was reduced to 15.3 mg L-1, achieving a defluoridation yield of 96.4% and a dealumination yield of 85.4% by using Ca2Al(OH)6Cl2H2O. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses reveal that the defluoridation mechanism primarily involves in situ hydrolysis coprecipitation of Al-F complex ions. Based on the study of reaction kinetics, the defluoridation rate equation was -d[F]/dt = 7.389 exp(-2.96/RT)CF00.916CCA0.972. The activation energy of the hydrolysis coprecipitation defluoridation was 2.96 kJ mol-1, indicating a relatively rapid reaction rate. This work provides an effective strategy for the simultaneous removal of fluoride and aluminum, eliminating their hazards in REE extraction and facilitating the recovery of aluminum resources.

The acid leaching residue (ALR) of ionic rare earth (IRE) concentrates containing radioactive elements such as thorium (Th) is classified as low-level radioactive waste. ALR holds valuable strategic resources such as rare earth and Th, while improper long-term heaping storage of ALR poses a substantial environmental risk. This paper proposes a comprehensive process involving low-temperature roasting, hydrochloric acid leaching, single extractant enrichment, and stepwise stripping to recover rare earth elements and thorium from ALR. The achieved leaching efficiencies are 80.11% of LnY, 99.43% of Sc(III), and 98.67% of Th(IV) after the carbonization of the organic phase in the ALR through low-temperature roasting. Despite large amounts of acid and impurities present in the leachate, 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (HEHEHP) still exhibits nearly 100% extraction efficiency for Sc(III) and Th(IV). The effective separation of LnY, Th(IV), and Sc(III) was achieved by implementing fractional extraction enrichment of Th(IV) and Sc(III), followed by Th(IV) removal through H2SO4 and Sc(III) removal via NaOH from the loaded organic phase. This scheme successfully achieves a recovery of RE and Th and offers a viable solution for the safe disposal of ALR.

Coal gangue is a typical industrial waste, which will bring environmental challenges and resource depletion when piled up in large quantities, and heavy metal pollution is a prominent problem. In this study, Ca3(PO4)2 and calcium superphosphate fertilizer (CSF) were utilized to passivate coal gangue at different pollution levels, and its passivation mechanism was discussed. The results show that both Ca3(PO4)2 and CSF can effectively passivate coal gangue and effectively reduce moderate or high levels of coal gangue pollution to a slight or clean level. The passivation effect of CSF is slightly better than that of Ca3(PO4)2. Through characterization of coal gangue before and after passivation and simulation with Visual MINTEQ and PHREEQC software, it is found that Ca3(PO4)2 can provide PO32-, while CSF releases HPO3-, which is ionized to generate more PO32-, and finally forms insoluble or slightly soluble phosphate with heavy metals. Leaching experiments show that the treated samples contain obviously more stable heavy metal components, and the leaching risk is lower than that of untreated coal gangue. In summary, this method proves its effectiveness in fixing heavy metals in coal gangue and provides an effective method for the harmless treatment of coal gangue.

Coal gangue, a typical industrial waste with high silicon content but low resource utilization, has significant potential as a raw material for silicon fertilizer preparation. This study explored the preparation mechanisms of coal gangue-based silicon fertilizers, focusing on the effect of various carbonate additives on the release of effective silicon. Results demonstrated that adding 20% Na2CO3, followed by roasting at 700 degrees C for 2 h, achieved a silicon fertilizer with an effective silicon content of 22.63 %. Mechanistic studies, including activation energy experiments, Hydrocarbon System Calculator (HSC), and Density functional theory (DFT) simulations, revealed that Na2CO3 preferentially decomposes to generate Na-O particle cluster, which break Si-O bonds, significantly enhancing silicon release and conversion efficiency. Additionally, the preparation cost of silicon fertilizer is 522 yuan per ton, highlighting the advantages of Na2CO3 in economic feasibility and energy efficiency compared to K2CO3 and CaCO3. Future research should focus on further optimizing process parameters, exploring alternative low-cost additives, and scaling up the proposed method for industrial applications. This study provides theoretical insights and practical guidance for the efficient and sustainable utilization of coal gangue resources, offering a promising approach for industrial applications and sustainable agricultural development.

At present, in the mining process of ionic rare earths, the separation of rare earth element (REEt) from aqueous solution still relies on natural sedimentation, which has the disadvantage of low efficiency. Additionally, there will be a significant amount of rare earth ions (similar to 30 ppm) remaining in the supernatant. In this work, the use of flat ceramic membranes to separate REEt from aqueous solution is innovatively proposed. Firstly, the performance of REEt separation by flat ceramic membrane process was determined. It was found that the flat ceramic membrane process had good interception performance for REEt separation, and the concentration of rare earth ions in the supernatant was close to 0 ppm. Then, the impacts of different operating conditions (including operating time, backwash duration and concentration times) on the membrane fouling process were investigated. It was demonstrated that the shorter the operating time, the less the degree of membrane fouling. The operation of back washing was greatly beneficial to renew membrane flow. The change of reversible pollution resistance was calculated, the process of membrane pollution was analyzed by four pollution models, and the pollution mechanism was discussed in detail. Furthermore, the recovery of membrane flow after chemical cleaning and non-agent cleaning, and the changes in reversible fouling resistance under different concentration multiples were also studied. It is proved that the immersed flat ceramic membrane has the characteristics of low membrane fouling, high solid-liquid separation efficiency, and good stability for the separation and enrichment of rare earth particles, which shows great potential in industrial applications.

The rare earth (RE) metallurgical industry generates substantial radioactive wastewater containing trace thorium (Th), posing potential environmental and public health risks. This study developed a phosphoryl-functionalized polyaniline/activated carbon composite electrode (P-PANI/AC) for high-efficient Th(IV) electrosorption. Phosphoryl group integration enhanced PANI conductivity, improved hydrophilicity, and introduced selective Thbinding sites through P--O and >N- functional groups. The optimized P-PANI/AC had high Th adsorption capacity (238.3 mg (Th)/g (electrode) at pH 3.0, 2.4 V) which is doubling that of PANI/AC (108.0 mg (Th)/g (electrode)). Remarkable selectivity towards thorium was achieved with separation factor of Th/RE up to 6381, surpassing all existing electrodes. Kinetic and isotherm analyses revealed a hybrid adsorption mechanism combining intraparticle diffusion and monolayer chemisorption via Faradaic processes. Practical applicability was demonstrated by effective Th reduction from 3.14 mg/L to 0.035 mg/L within 36 h, and regenerating the electrode using 0.5 mol/L H2SO4. FT-IR, Raman and XPS analyses confirmed Th coordination chemistry (P=O -> Th and >N- -> Th), while DFT calculations revealed strong coordination driving ultra-selective Th adsorption. This work would establish a novel paradigm for radioactive wastewater remediation through rational electrode interface engineering.

Samarium is a rare earth element that exhibits variable valence states of + 2 and + 3. In this work, we present the reduction products obtained through calciothermic reduction of SmF3 at various molar ratios of Ca to SmF3. The crystal structure, morphology, elemental distribution, and chemical valence of the reduction products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The results show that SmF2.028 and CaF2 are the sole reduction products obtained under molar ratios of 0.5, 1, 1.5, and 2 for Ca to SmF3, whereas some unreacted metallic Ca is detected in the products at a molar ratio of Ca to SmF3 of 2. The samarium ions in the reduction products exhibit mixed valence states with a relative content of approximately 9:1 for Sm3+ and Sm2+. Notably, the large amount of adsorbed oxygen present in the products oxidizes Sm2+ to Sm3+.

Ion-adsorption type rare earth ores (IREO) in China serve as the primary source of medium and heavy rare earth globally. With the rapidly growing demand for rare earth elements (REEs) and the dwindling supply of premium IREO, enhancing the recovery of REEs, especially the ion-unexchangeable REEs with ultra-low content and ambiguous speciation from IREO or its tailing, has become a critical trend and challenge. This study identified the occurrences of ion-unexchangeable REEs, primarily detected in Fe-enriched minerals, xenotime, and monazite of IREO using TESCAN integrated mineral analyzer (TIMA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) analysis. To extract these elusive REEs, a bioleaching technique utilizing Aspergillus niger (A. niger) metabolites was proposed, achieving a leaching yield of 31.4 wt%. Complementary sequential chemical extraction methods (SCEM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations further elucidate the underlying mechanism, involving the carboxylic acid produced by the metabolic process of microbes that dissolves goethite by disrupting Fe-O bonds and liberating REEs, which complexed with carboxylate (R-COO-), to promote further dissolution. This work offers insight into enhancing the recovery of ion-unexchangeable REEs from IREO or its tailing, paving the way for sustainable and efficient rare earth mining practices.

The accumulation of boron during the recovery of rare earth elements (REEs) from spent Neodymium-Iron-Boron (Nd-Fe-B) magnets affects the extraction of REEs and causes environmental pollution through the boroncontaining wastewater. Given that boron is a globally scarce strategic resource, this study proposes a method for the selective separation and recovery of boron from spent Nd-Fe-B magnets leaching solution. The synergistic extraction of boron adopting 2-ethylhexanol (EHA) and 2-ethyl-1,3-hexanediol (EHD), and the extraction mechanism were investigated. Under optimized conditions (30 % EHA-20 % EHD-50 % sulfonated kerosene, 1:1O/A phase ratio, pH 3.3, 10 min), the two-stage countercurrent extraction achieved a remarkable 99.9 % extraction efficiency with minimal loss of REEs. Slope analysis, Raman, FT-IR, and NMR combined with DFT were used to elucidate the extraction mechanism. Specifically, some of the boric acid molecules complexed with the OH groups of EHD to form stable six-membered ring complexes, while another part bound with both EHA and EHD to form linear complexes containing six-membered rings. Employing 0.4 mol/L NaOH as the stripping agent, the two-stage countercurrent stripping process achieved a stripping efficiency of 99.8 %. Subsequently, borax pentahydrate products exceeding 99 % purity were obtained via evaporative crystallization from the stripping solution. Notably, the raffinate contained only similar to 5 mg/L of boron, which could be further reduced below the discharge standard via the REEs recovery process, allowing for safe emission. This work offers a novel approach for the selective separation and recovery of boron from spent Nd-Fe-B magnets, eliminating its adverse effects on REEs extraction and the environment, while simultaneously recovering a valuable resource.

Coal gangue, a solid waste generated during coal mining and washing processes, has caused significant environmental burdens in China. This study aims to optimize and investigate the leaching mechanisms of heavy metals, such as Pb, Zn, and Cu, in coal gangue. The effectiveness of different eluents in removing heavy metals from coal gangue was evaluated by combining experimental methods with software simulations. The leaching conditions (EDTA-2Na concentration of 5 g/L, pH 3, solidliquid ratio of 1:10, leaching time of 4 h, 300 r/min) were optimized to achieve efficient and economical removal of heavy metals. Box-Behnken Design was used to show the key factors of eluant concentration and solid-liquid ratio. The leaching amounts of Pb, Zn, and Cu from coal gangue using EDTA-2Na as a leaching agent were 86 mg/kg, 430 mg/kg, and 66 mg/kg, respectively. The release mechanism and kinetic behavior of heavy metals in the leaching process were studied. The study provided information about leaching mechanisms of heavy metals from coal gangue by experiments and simulations of Visual MINTEQ and DFT that EDTA-2Na enhanced the leaching of heavy metals from coal gangue by enhancing ion exchange and complexation.

Due to the complexity of the internal pore structure of petroleum coke loose particle-packed beds, measuring their thermal conductivity has always been a challenging problem. This work independently developed an experimental apparatus for testing the thermal conductivity of petroleum coke particle-packed beds and constructed a forward calculation model for the heat transfer process, which was based on one-dimensional unsteady heat transfer. Using the Sparse Nonlinear OPTimizer (SNOPT) algorithm, a mathematical relationship between the thermal conductivity lambda of the coke bed, temperature T, and equivalent particle diameter dp was established through inverse modeling. Concurrently, a digital model of the petroleum coke particle packed bed was derived utilizing three-dimensional computed tomography (CT) scanning technology, and a pore-scale gas-solid radiation heat transfer model was formulated based on CFD simulation technology, thereby further elucidating the heat transfer mechanism within the petroleum coke particle packed bed. The research results indicate that the temperature predicted by the established thermal conductivity model aligns well with experimental data. Further CFD simulation studies demonstrate that a smaller particle size leads to a larger temperature difference between the wall and the center of the packed bed, while a higher gas velocity results in a smaller temperature difference, with a linear correlation observed between these two factors. At high temperatures, thermal radiation between particles in the porous petroleum coke-packed bed plays a dominant role. The research outcomes can offer significant theoretical support for a profound analysis of the heat transfer behavior of petroleum coke-packed beds within a vertical shaft calciner.