Dissolved oxygen (DO) concentration is one of the key environmental factors affecting the heterotrophic nitrification-aerobic denitrification (HN-AD) process. However, the effect of DO concentration on the HN-AD process remains unclear. Herein, DO concentration was controlled by adjusting the aeration rate. Three different aeration rates of low (0.15 L/min), medium (0.5 L/min), and high (1 L/min) were set to investigate the effect of aeration rate on the nitrogen removal performance and bacterial community assembly of the HN-AD process. At the low aeration rate (0.15 L/min), the NH4+-N and TN removal rates of the reactor reached 8.66 and 8.05 mg/(L·h), respectively. The corresponding aeration costs per unit removal of NH4+-N and TN were 0.21 and 0.22 m3/g, respectively. In contrast, the high aeration rate (1 L/min) significantly increased NH4+-N and TN removal rates, with mean values of 17.11 and 15.54 mg/(L·h), respectively. However, it entailed higher aeration costs per unit removal of NH4+-N and TN, with mean values of 0.70 and 0.77 m3/g, respectively. In the bacterial community of the reactor, Thauera was predominant. The assembly process of the bacterial community was dominated by stochastic processes. Increasing the aeration rate favored the environmental selection, and the proportion of homogeneous selection increased to 22.22%. The high aeration rate (1 L/min) enhanced interconnections among bacterial species. Taibaiella and Bdellovibrio were identified as key species as well as connectors of the networks. The partial least squares path modelling (PLS-PM) showed that beta diversity and sludge properties have contributed to efficient nitrogen removal of the reactor. This study can provide a valuable theoretical basis and technical support for the engineering application of the HN-AD process.

In this study, porous three-dimensional graphene oxide/citric acid/sodium alginate (GO/CA/SA) aerogel microspheres were prepared via a cross-linking and freeze-drying method using graphene oxide (GO), citric acid (CA), and sodium alginate (SA) as raw materials, and were applied for the adsorption of methylene blue (MB). The GO/CA/SA aerogel beads were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TG), scanning electron microscopy (SEM), zeta potential, energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Adsorption experiments revealed that the adsorption capacity of GO/CA/SA for MB reached a very high value of 994 mg g(-1). The adsorption behavior conformed to the Langmuir isotherm model. For a low MB concentration of 100 mg L-1, adsorption onto GO/CA/SA essentially reached equilibrium within 120 min, achieving an adsorption capacity of 175 mg g(-1) and a removal efficiency of 87.5%, following a pseudo-second-order kinetic model. Combined with thermodynamic parameters, the adsorption process was identified as a spontaneous exothermic reaction dominated by chemisorption. Further analysis by XPS, FT-IR, and zeta potential confirms that the adsorption mechanisms of MB onto GO/CA/SA included hydrogen bonding, pi-pi interactions, and electrostatic forces. Moreover, in the presence of the anionic dye methyl orange (MO), the neutral dye rhodamine B (RhB), and humic acid (HA), GO/CA/SA retained good adsorption performance and selectivity toward MB. Using ethanol for desorption, GO/CA/SA were reused for five adsorption-desorption cycles with a MB removal >90% and an adsorption capacity >180 mg g(-1). GO/CA/SA aerogel beads demonstrate great potential as efficient adsorbents for the removal of MB from wastewater.

Iron, a prevalent impurity in dechroming sludge (DCS), poses a major challenge to the recovery and purification of valuable metals such as Cu, Ni, and Zn in wet processing. There is an urgent need for an efficient and selective iron separation technique that minimizes the loss of Cu, Ni, and Zn. In this study, an innovative combined approach of acid leaching and on-line adsorption was developed to selectively recover Fe3 + from DCS. Results indicated that acid leaching with 0.05 mol/L H2SO4 achieved extraction efficiencies of 98.2% for Fe3+, 99.0% for Cu2+, 94.6% for Ni2+, and 96.5% for Zn2+, yielding a leachate containing approximately 93.5 mg/L Fe3+. A phosphonic acid-functionalized resin (X-Fe resin) was then used to selectively remove Fe3+ from the leachate. Batch adsorption experiments demonstrated higher adsorption capacity, rapid kinetics, and good reusability of the resin. Dynamic adsorption tests in the unitary, binary, and ternary systems revealed an affinity order of Fe3+ >Cu2+ >Zn2+ >Ni2+, with competitive substitution favoring selective Fe3+ uptake. EDS-mapping (Energy-Dispersive X-ray Spectroscopy mapping), XPS (X-ray Photoelectron Spectroscopy), and DFT (Density Functional Theory) analysis demonstrated that the high adsorption affinity was due to the more negative binding energy between Fe3+ and the resin. When treating the DCS, the dynamic on-line adsorption process efficiently recovered of 95.3% of Fe-3(+), and the final effluent had less than 5.0 mg/L Fe, meeting the requirements for industrial production standards. This work focuses on an innovative combination process of acid leaching and selective adsorption for iron removal, which offers a sustainable route for purification and resource recovery in a hydrometallurgical process.

With the surge in demand for rare earth elements in the modern high-tech industry and the emergence of water pollution during the mining and production of rare earth elements, the development of a green and efficient separation technology for rare earth elements is imperative. Layered double hydroxides can be used for the adsorption of rare earth elements, but the adsorption capacity is unsatisfactory. In this study, magnesium-iron layered double hydroxide (TC-MgFe LDH) modified with carboxyl and amino functional groups on its surface was prepared to enhance the adsorption of rare earth elements. TC-MgFe LDH had a very high adsorption capacity of 179.4 mg g-1 for La3+. The adsorption process followed pseudo-second-order kinetics and the Freundlich isotherm model, confirming the multi-molecular layer chemical adsorption mechanism. XPS, FT-IR spectroscopy and zeta potential analyses revealed that the mechanism of the adsorption process involved coordination and electrostatic interaction. TC-MgFe LDH exhibited good regeneration performance and maintained more than 95% of the initial capacity after three adsorption-desorption cycles. In addition, TC-MgFe LDH maintained stable adsorption of La3+ over a wide pH range and in the coexistence of competitive ions such as Na+ and Ca2+. TC-MgFe LDH shows high potential for the adsorption and enrichment of rare earth elements, and this study can provide insights for the functionalization of LDHs.

This study reported the facile synthesis of CeO2@NH2-MIL-53 composite abrasive via a mild one-pot co-modification strategy, and its chemical mechanical polishing (CMP) performance was systematically evaluated using K9 glass as the model substrate. Comprehensive characterization revealed that the incorporation of NH2-MIL-53 effectively modulated the surface chemical environment of CeO2, leading to increased Ce3 + concentration, enhanced oxygen vacancy formation, and improved wettability and dispersion stability. CMP results demonstrated that the composite abrasives exhibited a markedly enhanced material removal rate compared with pure CeO2, reaching up to 188.52 nm/min while maintaining low surface roughness. Mechanistic analysis indicated that the improved polishing performance originated from the synergistic effect between enhanced chemical reactivity, which facilitated Si-O-Ce bond formation, and improved mechanical action induced by the unique morphology of NH2-MIL-53. These findings provided new insights into the rational design of high-performance CeO2-based composite abrasives and offered a promising strategy for achieving efficient and controllable CMP processes.

Phosphogypsum (PG) is a major by-product of phosphoric acid production. Due to its high concentration of radioactive nuclides (such as ²²⁶Ra), heavy metals (such as Cd, As), and soluble fluorides, it can seep into groundwater and bioaccumulate, thus posing serious environmental and safety risks. This review critically assesses global research on the environmental behavior of these pollutants from 2005 to 2025 and explores advanced stabilization and resource recovery strategies. Although the adoption of traditional recycling in building materials offers a way for large-scale utilization, its long-term feasibility depends on effective fixation mechanisms, such as chemical encapsulation and lattice substitution, to control leaching and radon emissions. The process of resource recovery, especially the recovery of rare earth elements (REEs), must be carefully balanced between extraction efficiency and the risk of secondary pollution caused by acidic waste liquids. Emerging bioremediation and bioreleaching technologies, combined with mineral carbonization, have shown potential in the synergistic stabilization of pollutants and carbon dioxide sequestration. Despite this, challenges still exist, including the heterogeneity of waste, high energy consumption, and the uncertainty of long-term stability. Future progress requires interdisciplinary innovation, integrating AI-optimized processes and sound policy frameworks to prioritize the management of safe, circular and sustainable by-products. This review highlights the potential of transforming by-product gypsum (PG) from an environmental burden into a valuable resource in a bio-based circular economy.

The adsorption of rare earth ions (RE3+) from rare earth ore leachate using ion-imprinted polymers has emerged as an efficient and sustainable strategy. In this study, a "microbead immobilized bacteria (SBC) and ionimprinted polymer (FECY)" interaction system was established. Under optimized process parameters, SBC + FECY was found to exhibit significantly higher adsorption efficiency for yttrium(III) (Y3+) than either adsorbent alone. Addition-sequence experiments demonstrated that SBC likely enhances the adsorption performance of FECY indirectly by regulating ionic concentrations in solution. The characterization results further indicate that SBC and FECY possess a mesoporous structure, which effectively increases the contact area between RE3+ and the adsorbent, thereby conferring excellent adsorption capacity. Based on selective adsorption experiments and characterization data, it was demonstrated that SBC enhances the highly selective adsorption of Y3+ by FECY through ion-imprinted sites, modulating the ionic environment. The quantum theoretical calculations were performed to optimize the composite structure of FECY and Y3+, thereby providing a comprehensive illustration of the adsorption behavior of FECY toward Y3+. Furthermore, transcriptomic analysis revealed that bacteria can sense external environmental changes and modulate the ionic environment at the gene-expression level, thereby influencing their response to ionic stress and their adsorption capacity for impurity ions. After five adsorption cycles, both SBC and FECY exhibited excellent reusability. This study presents a novel strategy for the green and highly selective adsorption of target RE3+ from complex rare earth leachates.

Humic acid (HA) is an environmentally friendly and efficient aid leaching agent, however, the mechanism of HA and ammonium sulfate ((NH4)2SO4) on rare earth (RE) in-situ leaching process and the effect of HA on ammonium reduction remain unclear. Herein, the potential of HA as an aid leaching agent to optimize the dosage of (NH4)2SO4 and reduce the residual ammonium salt was investigated, controlling the ammonia nitrogen pollution. Moreover, the calculation model of (NH4)2SO4 amount and unit consumption equation were established based on mass action law. The result indicated that the leaching efficiency of RE was increased by 3.96 % in the presence of 0.2 g center dot L-1 of HA, suggesting there was a synergistic effect between HA and (NH4)2SO4 during the RE leaching process. This effect was further confirmed by the leaching mechanism. Specifically, when the value of mass action quotient (Kt) increased, the reaction molar ratio (n) was decreased as compared with that of pure ammonium sulfate, indicating HA has a promoting effect on the ion exchange reaction between rare earth ions and ammonium ions. Additionally, it was revealed that the (NH4)2SO4 dosage was reduced by 34 % based on the law of mass action. Notably, the optimal (NH4)2SO4 concentration was lowered from 0.1 mol center dot L-1 for the traditional technology to 0.08 mol center dot L-1 for this work. These findings provided new insights into strengthening the leaching process of weathered crust elution-deposited rare earth ores by HA, which were valuable for elucidating the interaction mechanisms and realizing the source control of ammonia nitrogen pollution.

Rare earth elements (REEs) are critical for advanced materials and green energy technologies, including electric vehicles and renewable energy systems. REEs are leached from primary and secondary resources into aqueous solutions using mineral acids and subsequently separated via solvent extraction (SX). Despite extensive studies, a systematic review of REE extraction from acidic leachates remains lacking. Unlike prior reviews that treat these aspects separately, this review integrates aqueous-phase speciation, extractant coordination behavior, and separation efficiency to provide mechanism-based insights. SX processes in chloride, sulfate, and nitrate media are analyzed, with emphasis on cation-exchange and solvation mechanisms. Key extractants, including organophosphorus compounds (P204, P507, Cyanex 272, Cyanex 572) and carboxylic acids (Versatic 10), are compared. Effects of pH (0.5-4.0), organic-to-aqueous ratios, and the presence of modifiers or additives on extraction efficiency and selectivity are quantitatively assessed. Environmental and economic considerations, as well as technological improvements, are also evaluated to support sustainable REE supply. The analysis links aqueous speciation with extractant selection and process performance, with direct implications for circuit design and operation.

ABSTRACT The growth mechanism of α‐hemihydrate gypsum (α‐HH) in Na 2 SO 4 solution is still undefined. In this work, we constructed the solution‐crystal models to investigate the growth morphology of α‐HH in Na 2 SO 4 solution system by molecular dynamics simulation. The attachment energy (AE) model was used to predict the growth behavior of α‐HH, revealing that the (002), (200), (110), and (1–10) crystal faces are dominant, with the (002) face exhibiting the highest attachment energy and predicted fastest growth rate. Molecular dynamics simulations of α‐HH in Na₂SO₄ solution with varying mass fractions (2%–12%) revealed that the interaction energy between the solution layer and crystal faces follows the order: (002) > (1–10) ≈ (110) > (200). Radial distribution function analysis indicated the presence of hydrogen bonds, chemical bonds, van der Waals forces, and electrostatic interactions between the solution layer and crystal faces. Notably, the diffusion coefficients of Na⁺ and SO₄ 2 ⁻ ions were highest on the (002) crystal face, suggesting enhanced diffusion on this face. These findings provide insights into the structural and morphological transformations during α‐HH crystal growth, offering a foundation for optimizing growth conditions, manipulating crystal size and morphology, and ultimately guiding the production of high‐quality α‐HH crystals.

The fragility of the global rare earth supply chain and the urgent demand for sustainable exploitation have driven intensive research into green and high-efficiency extraction technologies. Bioleaching technology, distinguished by its environmental compatibility and resource adaptability, has emerged as a transformative alternative to conventional chemical leaching methods. This study focuses on the multiphase utilization of ion-adsorption rare earth ores by leveraging Penicillium sp. fermentation broth to promote MgSO4-mediated leaching through a biologically enhanced chemical process. The objectives were to elucidate the rare earth leaching mechanisms under bio-promoted chemical processes and to optimize strain cultivation and leaching parameters. Untargeted metabolomics was applied to delineate dynamic changes in differential metabolites before and after leaching, while Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were utilized to clarify metabolite-mineral interfacial interactions. The results demonstrated that the composite system achieved a rare earth recovery rate of 93.79 % under optimal conditions (liquid-to-solid ratio of 4:1, 6-hour leaching), significantly outperforming conventional chemical leaching. Metabolomic analysis revealed a multifunctional interaction network involving organic acid-mediated proton attack, lipid molecule-driven interfacial modification, and benzenoid compound-regulated redox balance. This study demonstrates that the fermentation broth of Penicillium sp. significantly enhances MgSO4-mediated leaching efficiency of ion-adsorption rare earth ores, thereby offering a sustainable pathway to address resource and environmental challenges in rare earth industries.

The growth mechanism of alpha-hemihydrate gypsum (alpha-HH) in Na2SO4 solution is still undefined. In this work, we constructed the solution-crystal models to investigate the growth morphology of alpha-HH in Na2SO4 solution system by molecular dynamics simulation. The attachment energy (AE) model was used to predict the growth behavior of alpha-HH, revealing that the (002), (200), (110), and (1-10) crystal faces are dominant, with the (002) face exhibiting the highest attachment energy and predicted fastest growth rate. Molecular dynamics simulations of alpha-HH in Na2SO4 solution with varying mass fractions (2%-12%) revealed that the interaction energy between the solution layer and crystal faces follows the order: (002) > (1-10) approximate to (110) > (200). Radial distribution function analysis indicated the presence of hydrogen bonds, chemical bonds, van der Waals forces, and electrostatic interactions between the solution layer and crystal faces. Notably, the diffusion coefficients of Na+ and SO42- ions were highest on the (002) crystal face, suggesting enhanced diffusion on this face. These findings provide insights into the structural and morphological transformations during alpha-HH crystal growth, offering a foundation for optimizing growth conditions, manipulating crystal size and morphology, and ultimately guiding the production of high-quality alpha-HH crystals.

With the increasing demand for enhanced precision and superior surface quality of optical components, chemical mechanical polishing (CMP)-the sole technique capable of achieving global flatness-has gained significant prominence in the optical industry. Cerium oxide (CeO2) nanoparticles, serving as the primary abrasive in optical polishing formulations, are pivotal due to their distinctive physicochemical properties that critically influence polishing efficacy. Nonetheless, the reversible redox cycling between Ce4 + and Ce3+ within the conventional CeO2 lattice, alongside the generation and annihilation of oxygen vacancies, results in relatively low concentrations of Ce3+ ions and oxygen vacancies, thereby constraining the surface reaction kinetics and adversely impacting CMP performance. Consequently, enhancing the chemical activity of CeO2 to improve its polishing capabilities has emerged as a central focus of contemporary research. This investigation examined the effect of aluminum ion (Al3+) doping on the chemical reactivity and polishing performance of CeO2. The findings demonstrated that the incorporation of Al3+ ions induced charge imbalance and lattice expansion within the CeO2 crystal structure, which promoted the formation of a substantial number of oxygen vacancies and Ce3+ ions, thereby markedly augmenting its chemical activity. CMP trials revealed that an Al3+ doping concentration of 1 % optimized the synergistic interaction between chemical reactivity and mechanical abrasion in the CeO2 polishing slurry. Under these conditions, the material removal rate (MRR) for K9 glass substrates reached 458.67 nm/min, representing a 483 % increase compared to the 78.57 nm/min MRR observed with undoped CeO2 polishing slurry. Furthermore, profilometer measurements indicated that the surface roughness of the polished K9 glass, within a test area of 336.71 x 281.51 mu m(2), was reduced to as low as 0.2904 nm. TEM analysis revealed a reduction in the surface damage layer thickness from 20.25 nm to 9.79 nm following polishing. The mechanism analysis results showed that during the polishing process, a softening layer was generated on the K9 glass surface, and then the highly chemically active cerium-based abrasive combined with the Si-O bonds in the softening layer to form strong Ce-O-Si bonds. Under the action of mechanical force, the softening layer was carried away from the glass surface by the cerium-based abrasive. Collectively, this work provided a solid foundation for subsequent researchers to explore how metal ion doping could enhance the CMP performance of CeO2.

The anodic small-molecule electrooxidation reaction, which is both thermodynamically and kinetically more favorable than the oxygen evolution reaction, when coupled with the hydrogen evolution reaction, has garnered increasing attention and achieved significant progress. This method presents a promising avenue for hydrogen production at industrial current densities (≥ 200 mA/cm2) via water electrolysis while enabling the synthesis of value-added products or the removal of pollutants. However, the correlations among anode small-molecule types, catalyst design, reaction mechanisms, and electrolytic cell configuration remain unclear at industrial current densities. In this review, the characteristics and challenges of hydrogen production via coupling with various small-molecule oxidation reactions at industrial current densities are discussed for the first time, emphasizing key advances in catalyst design–substrate correlations, reaction mechanisms, and electrolytic cell configuration. Additionally, the challenges and future prospects of this field are explored.

The water environmental pollution caused by residual butyl xanthate (BuX-) in mineral processing wastewater is becoming increasingly severe, and the development of high-efficiency adsorbents is crucial for achieving its advanced removal. In this study, a functionalized amorphous nickel-iron layered double hydroxide (A-Ni/Fe LDH) was successfully constructed via an L-cystine-assisted hydrothermal method and its effectiveness for removing BuX- was also evaluated. Characterization results show that A-Ni/Fe LDH possessed an amorphous structure with functional groups such as amino groups and sulfonic acid groups. Results of adsorption experiments indicate that the maximum adsorption capacity of A-Ni/Fe LDH for BuX- reached 1884 mg/g. The adsorption behavior conformed to the Sips isotherm model and the pseudo-second-order kinetic model. Thermodynamic study indicates that the adsorption process is a spontaneous exothermic process dominated by chemical adsorption occurring on a heterogeneous surface. The adsorption mechanism of BuX- on A-Ni/Fe LDH consists of coordination complexation, hydrogen bonding and electrostatic attraction. A-Ni/Fe LDH maintains excellent adsorption capacity and selectivity in the presence of various coexisting ions (e.g., Ca2+, Mg2+, SO42-, H2PO4- , and HPO42-) and humic acid. In addition, the material exhibited good regeneration performance, with a removal efficiency over 90 % after three cycles. This study not only provides a novel approach for effective removal of xanthate-based pollutants but also offers new insights into the amorphization and functionalization design of layered double hydroxides.

Lead (Pb) contamination in phosphate mining wasteland soils severely inhibits plant growth and compromises ecological safety, thereby necessitating long-term remediation strategies to restore ecosystem functions. Pot experiments were conducted to evaluate the synergistic effects of microbially induced carbonate precipitation (MICP) and magnesium polypeptide (MP) amendments on celery growth and the restructuring of rhizosphere microbial communities. Under Pb stress (200 mg/kg), Pb accumulation in celery was significantly reduced by the combined MICP-MP treatment, with concentrations decreasing to 4.49, 0.26, and 1.93 mg/kg in roots, stems, and leaves, respectively; concurrently, plant growth and development were promoted. Correlation analysis revealed that the remediation-induced enhancement of soil physicochemical properties acted as a primary environmental driver, showing a significant negative correlation with exchangeable Pb content. The transformation of Pb from high-risk, bioavailable exchangeable forms to low-risk, stable fractions, such as carbonate-bound and Fe/Mn oxide-bound forms, was successfully promoted by the treatment, concomitant with enhanced soil physicochemical properties and biological activity. Furthermore, rigorous compositional analysis demonstrated that the MICP-MP treatment significantly enriched beneficial bacterial taxa, such as Nocardiopsis and Planococcus. These shifts in community composition played a key role in enhancing the soil bacterial community's adaptation to Pb stress. In summary, Pb-induced phytotoxicity was alleviated, and rhizosphere microbial stability and assembly were modulated by the MICP-peptide combination, providing new insights into plant-microbe interactions under heavy metal stress.