Lignite is an abundant and low-cost carbon precursor for sustainable energy storage, yet its direct carbonization yields materials with limited porosity and electrochemical activity. In this work, a two-step strategy combining ammonolysis pretreatment with temperature-controlled KOH activation was proposed to convert lignite into high-performance electrode materials, focusing on the mechanistic role of activation temperature. The results demonstrated that the activation temperature critically modulates the hierarchical pore architecture, nitrogen configuration, defect density, and graphitic ordering. At lower temperatures (400–500 °C), KOH predominantly reacts with oxygen-containing functional groups, generating micropores while preserving abundant heteroatoms and defects, which contribute to pronounced pseudocapacitance. In contrast, higher temperatures (600–900 °C) promote metallic potassium intercalation and carbon skeleton etching, facilitating the formation of a hierarchical porous network alongside enhanced graphitization, thereby favoring electric double-layer capacitance. Optimal performance is achieved at 500 °C, which features a well-balanced hierarchical pore structure, obvious carbon detects, and high nitrogen and oxygen content (1.6 and 30.6 at. %) enriched in electrochemically active pyridinic-N and pyrrolic-N. Consequently, KCSPN‑5 delivers a high specific capacitance of 320.4F/g at 0.5 A/g in a three‑electrode system, with excellent rate capability (61.4 % at 100 A/g) and outstanding cycling stability (93.1 % after 10,000 cycles). Kinetic analysis reveals a mixed charge storage mechanism with a b‑value of 0.742, confirming the synergistic contributions of surface‑controlled pseudocapacitance and diffusion‑controlled processes. This work establishes a rational temperature-guided activation protocol for upgrading lignite into high-value carbons and provides fundamental insights into the temperature-dependent interplay among porosity, defects, and heteroatom doping.

The large-scale generation of waste graphite not only poses environmental challenges but also provides an opportunity for resource recovery. This study proposes a sustainable strategy that utilizes the graphite cutting waste produced during the production of large graphite electrodes through chemical intercalation, microwave-assisted expansion, and in situ urea nitrogen doping techniques to prepare nitrogen-containing micro-expanded graphite (NMG) composite materials. Structural analysis reveals that the nitrogen-doped amorphous carbon layer formed on the expanded graphite (EG) matrix effectively suppresses excessive expansion while preserving its typical worm-like interlayer morphology and porous structure. XPS confirms successful nitrogen doping with predominant pyridinic-N configuration, introducing abundant defect sites and enhancing lithiophilicity. As an anode for LIBs, NMG delivers an exceptional initial discharge capacity of 1907.5 mAh g-1 at 20 mA g-1 and maintains 798.2 mAh g-1 after 50 cycles, nearly twice that of purified waste graphite (G). Remarkably, after 1000 cycles at 1 A g-1, it retains 650.4 mAh g-1 with 89.9% capacity retention, indicating an electrochemical activation process. Kinetic analysis reveals that the superior performance originates from synergistic diffusion-controlled intercalation and surface-dominated pseudocapacitance, with nitrogen-doped defect sites and hierarchical pore architecture promoting rapid ion/electron transport and surface faradaic reactions. This work demonstrates a viable pathway for value-added upcycling of waste graphite while providing insights into designing high-performance anodes through integrated defect engineering and heteroatom doping.

Controlled shrinkage of open pores during carbonization enables closed pore formation in hard carbons as the anode for sodium ion batteries, though excessive open pores resist conversion and degrade electrochemical performances. Employing Mg2+ as a pore-forming agent chelated by humic acid, we constructed tailored closed pore architectures through pre-carbonization at 600 degrees C followed by 1500 degrees C treatment. The resulting hard carbons exhibit tunable interlayer spacing and disorder, with closed pores of uniform size (1.10-1.18 nm) yet distinct surface areas (307.4-408.3 m2/g). The optimized hard carbons deliver a high reversible capacity (262 mAh/g at 20 mA/g), excellent rate capability (52 % retention at 1000 mA/g), and cycling stability (75 % after 1000 cycles at 500 mA/g). Intercalation capacity correlates with pseudo-graphite carbon content, while porefilling capacity scales with closed pore surface area. This study paves the way for rational engineering of closed pores in hard carbons.

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.

Closed pores are widely acknowledged as a crucial structural feature for enhancing the sodium storage performance of hard carbon. However, the formation process of closed pores and the corresponding sodium storage mechanism remain unclear. Herein, coal-based hard carbon is selected as a model material to systematically establish the formation process of closed pores. This work confirms that existence of microcrystalline sheets is an essential prerequisite for closed pore formation, with the intrinsic parameters of these sheets playing a pivotal role in boosting the abundance of closed pores. The optimal coal-based hard carbon sample displays a considerable reversible capacity of 242.3 mAh g- 1 at 0.02 A g- 1 (149.0 mAh g- 1 for plateau capacity), excellent rate performance (188.5 mAh g- 1 at 1.0 A g- 1) and outstanding cycling stability (84.6% capacity retention after 1000 cycles at 0.5 A g- 1). Importantly, kinetic analysis further clarifies a three-stage sodium storage mechanism of hard carbon: defect adsorption, microcrystalline insertion and closed pore filling. Gaining a profound insight into closed pore formation process and sodium storage mechanism of coal-based hard carbon enables the rational design of high-performance anodes and lays a solid foundation for accelerating the application of high-energydensity sodium-ion batteries.

Spent carbon anode (SCA), a hazardous waste from aluminum electrolysis, possesses high recycling value as a low-cost precursor for carbon materials. In this study, an electrochemical upcycling method using mesh-integrated bulk SCA as the electrode was proposed to directly treat bulk SCA. This method eliminates the energy-intensive crushing and grinding pretreatment required due to the extremely high hardness of bulk SCA. More importantly, it achieves a deashing rate of 93.53%, significantly outperforming conventional acid leaching methods, and directly converts the tightly stacked carbon structure of SCA into thinly exfoliated graphene oxide sheets. The electrochemical upcycling mechanism was elucidated. Sufficient electrochemical exfoliation of SCA enables the release of fine impurities; meanwhile, hydroxyl radicals generated from water electrolysis attack impurity components, while H⁺ promotes impurity dissolution. These synergistic effects guarantee the recovery of high-purity carbon material from SCA. As the electrolyte concentration increases, the extents of exfoliation and oxidation gradually decline. The carbon recovery rate, deashing rate, and element leaching rate first rise and then fall, with the 20EPC sample exhibiting the optimal comprehensive performance. The 20EPC electrode delivers a specific capacitance of 195.3 F/g at 1 A/g, and the assembled symmetric supercapacitor achieves an energy density of 9.5 Wh/kg at a power density of 636.8 W/kg, with 93.8% capacitance retention after 10,000 cycles. This work provides a facile and efficient strategy for the upcycling of bulk SCA toward purification and high-value utilization, and also paves a new way for the recycling of other waste carbonaceous resources.

Copper ions pose significant hazards to human health and the environment, making the development of efficient adsorption processes for their removal crucial. In this study, low-ash coal was used as the precursor, and the "core-shell" structured coal-based activated carbon magnetic adsorption material (IOCBAC) was prepared by the adsorption/conversion loading process, and its adsorption performance for copper ions in wastewater was investigated. Batch adsorption experiments show that the adsorption properties of IOCBAC after the fifth load is the best with the loading cycle number. In addition, the adsorption process is single molecular layer chemisorption. Continuous adsorption experiments show that the highest equilibrium adsorption capacity of IOCBAC can reach 328.7 mg/g, and the best conditions are: co = 100.00 mg/L, v = 0.065 m/s, m = 0.3 g. The adsorption mechanism primarily involved ion exchange, hydrogen bonding, and complexation interactions. Besides, the IOCBAC regeneration experiment showed that the concentration of NaOH had a significant impact on its regeneration properties, but the equilibrium adsorption capacity could still reach 136.65 mg/g after 5 cycles, which had a good regeneration and recycling properties. Meanwhile, the introduction of magnetism makes the recycling efficiency higher. This study provides a new path for wastewater treatment and high value-added utilization of coal.

Despite the critical importance of both closed pores and ultra-micropores for determining the plateau capacity of hard carbons as anodes for sodium-ion batteries, their formation mechanisms along with the individual contribution to sodium storage are poorly understood owing to their prevalent co-existence. Herein, hard carbons featuring exclusively closed pores or ultra-micropores were synthesized by modulating the pre-carbonization temperatures (400-800 degrees C) prior to carbonization of potassium humate at 1500 degrees C. The potassium species act as in-situ pore forming agents to generate open pores with the specific surface area (SSA) based on CO2 adsorption/ desorption test lower than 534.4 m2/g in the intermediates along with the smaller lateral microcrystal size, which can be effectively converted into closed pores upon post-carbonization treatment. In contrast, intermediates with higher SSA larger than 789.5 m2/g and larger lateral microcrystals just shrunk into predominantly ultra-micropores. The hard carbon with rich closed pores of 0.2131 cm3/g shows a reversible capacity of 277 mAh/g at 20 mA/g with the plateau capacity of 211 mAh/g and pore filling capacity of 119 mAh/g. The hard carbon with abundant ultra-micropores of 0.0316 cm3/g shows a reversible plateau capacity of 191 mAh/g at 20 mA/g with the pore filling capacity of 153 mAh/g. The intercalation capacity of hard carbons scales with the proportion of pseudo-graphite carbon, and the pore filling capacity of hard carbons rich in closed pores is determined by the average diameter of these pores, while the ultra-micropores especially in 0.6-0.7 nm contribute to filling of sodium ions. This work provides a fundamental basis for achieving hard carbons with engineered properties.

Flotation foam stability is a critical factor influencing flotation performance, especially for cationic collectors. However, cationic collectors often generate over-stable foam, leading to a series of problems such as the difficult transportation of flotation products and foam overflow, which impair flotation efficiency. Previous research has shown that the stability of flotation foam is influenced by both flotation reagents and mineral particles. In this study, the influence of mineral particles on foam properties was investigated to reveal the formation mechanism of alkyl ether amine foam stability. The modified Bikerman method was used to evaluate foam stability and drainage behavior. Furthermore, the changes in the velocity of bubbles during their collision and adhesion on mineral surfaces were directly investigated using high-speed photography, providing insights into the bubblemineral interactions. The results show that the properties of mineral particles are key determinants of their ability to stabilize flotation foam. Quartz particles confer significantly greater stability compared to dolomite and apatite. Fine-grained quartz particles demonstrate the strongest foam-stabilizing effect. Quartz particles exhibit the most effective foam stabilization, attributed to their stronger interaction with foaming agent, which promotes more robust attachment to bubble and enhances their retention within the foam structure. The findings of this study provide valuable insights into the mechanisms by which fine mineral particles influence flotation foam stability.

This study successfully fabricated flexible and self-supporting FeCo@CNFs anode materials for sodium-ion batteries with a three-dimensional interwoven network structure through electrospinning and carbonization processes.The material constructs a composite architecture consisting of nitrogen-doped carbon nanofibers embedded with FeCo nanoparticles. Without requiring conventional binders or conductive additives, the interconnected porous fiber network of FeCo@CNFs not only offers efficient pathways for electron/ion transport but also effectively alleviates volume variation during sodium ion insertion/extraction. Electrochemical tests reveal that the FeCo@CNFs-3 electrode delivers a reversible capacity of 301 mAh g-1 at a current density of 20 mA g-1 , retains 94 % of its capacity after 500 cycles even at a high current density of 500 mA g-1 , and exhibits outstanding rate capability (maintaining appreciable capacity at 2000 mA g-1). The remarkable electrochemical performance originates from the synergistic enhancement between FeCo nanoparticles and the carbon fiber skeleton: the nitrogen-doped carbon fibers provide continuous conductive pathways, while the FeCo nanoparticles further enhance the electrode conductivity and promote Na+ reaction kinetics. This study offers an effective structural design strategy for developing high-performance self-supporting anodes for sodium-ion batteries.

At present, the process of purifying and preparing high-purity quartz from quartz ore faces challenges such as the scarcity of high-quality natural quartz ore, the need to improve impurity removal efficiency, and environmental pollution caused by traditional processes. Therefore, this review first introduces the reasons for the formation of different types of impurities (gangue mineral impurities, inclusion impurities, and lattice impurities) in quartz, as well as the methods and difficulties in removing different types of impurities. Then, a comprehensive summary of the current research progress and purification mechanism of quartz purification technology was conducted, including physical purification (crushing, grinding, magnetic separation, gravity separation, flotation, etc.), chemical purification (acid leaching, chlorination roasting, sulfation roasting, vacuum roasting, etc.), and coupled purification processes (biological assisted technology, microwave-assisted technology, ball milling assisted technology, etc.). In addition, in response to the phenomenon that calcination can efficiently promote impurity removal, the mechanisms of phase transition and vacuum calcination promoting impurity removal during the calcination process were emphasized, and efficient impurity removal process methods corresponding to different types of impurities were also proposed. This review has great reference value for the preparation of high-purity quartz.

Starch wastewater contains abundant organics, high turbidity and various pollutants, which cannot be effectively treated by traditional coagulation. To address this problem, we synthesized Fe3O4-CPAM composite magnetic flocculant via in-situ coprecipitation, and mainly optimized its preparation and application processes. The composite exhibits an inverse spinel structure and superparamagnetism, with a saturation magnetization of 28.42 emu/g and an average crystallite size of 30.1 nm. pH and magnetic field strength are the dominant factors influencing flocculation performance. Under optimal conditions, the removal efficiencies of COD and turbidity reach 96.67% and 97.52%, respectively. It also performs well in real starch wastewater, with COD and turbidity removal rates of 89.42% and 93.07%. Compared with conventional coagulation (68.07% for COD and 72.69% for turbidity removal), this method features lower reagent dosage, easy flocculant recovery and higher treatment efficiency, and has promising application prospects for starch wastewater treatment.

Carbon dots (CDs) as green corrosion inhibitors are garnering widespread interest for mitigating metal corrosion during acid pickling owing to their small size effect and tunable surface chemistry. Herein, an efficient ultrasonic-assisted oxidative strategy was developed to tailor the organic macromolecules of lignite into lignite-based (L-CDs). The obtained L-CDs feature dispersed nanoparticles with average size of 1.98-2.63 nm composed of reasonable sp2/sp3 carbon component (1.28-1.55), and a high density of oxygen-containing groups existing in the form of carbonyl, carboxyl, and hydroxyl groups. Due to their unique microstructural characteristics, the L-CDs demonstrate a remarkable corrosion inhibition efficiency of 96.8% at 200 mg l-1. A compact protective film is formed by mixed physical-chemical adsorption on the steel surface, which blocks corrosive ions from attacking the substrate, thereby suppressing the anodic iron dissolution reaction. This work proposes a sustainable route for the scalable fabrication of low-cost and effective CDs inhibitors for carbon steel.

The preparation of ultra-low ash coal is crucial for the high-value and clean utilization of coal resources. However, long-flame coal features a low metamorphic grade and abundant surface oxygen-containing functional groups, making it difficult for conventional single collectors to generate stable hydrophobic sites. Consequently, deep ash removal remains highly challenging, requiring combined reagents to improve ultra-low ash coal preparation. In this study, typical low-ash long-flame coal from northwest China was ground using high-hardness ceramic balls, and a novel collector-enhanced flotation system was developed based on No. 3 oil combined with acidic, ester, ketone, aldehyde or ether reagents. Experimental results indicate that the mixture of No. 3 oil and 5% ethyl oleate achieves optimal separation performance. Ultra-low ash coal was successfully obtained with a yield of 86.76%, ash content of 0.87%, and combustible matter recovery of 87.23%. Macroscopic and microscopic analyses reveal that the ester co-collector reduces oil droplet size. Its polar groups adsorb onto coal surface oxygen-containing functional groups via hydrogen bonding, and together with the non-polar chains of No. 3 oil, form a double-layer composite structure. This construct forms stable hydrophobic sites, prolongs droplet wetting time, and strengthens the separation of coal from inorganic minerals. This work addresses the technical gap in deep flotation of ultra-low ash long-flame coal and offers an economical approach for efficient and clean utilization of low-rank coal.

Flame retardants are indispensable for the safe use of various polymers. In recent years, inorganic layered flame retardants have emerged as highly promising alternatives to halogen-based counterparts, owing to their eco-friendliness and excellent drip-resistant characteristics. In this review, we systematically classify emerging nanomaterials (e.g., carbon-based, layered structures, and Mxenes, etc.) and elucidate their dual-phase flame-retardant mechanisms (condensed-phase char formation and gas-phase radical quenching) with unprecedented synergy. Notably, we highlight innovative modifications that overcome limitations in dispersion efficiency and environmental toxicity while enhancing fire resistance. Furthermore, this work underscores multifunctional integrations, where materials like hexagonal boron nitride (h-BN) and Ti 3 C 2 T X MXenes simultaneously improve thermal conductivity, mechanical strength, and flame retardancy. Finally, we identify unresolved challenges (e.g., cost-effective production) and forecast trends such as smart fire-warning systems, offering a roadmap for next-generation flame-retardant materials.

Hard carbon (HC) is widely recognized as one of the most promising anode materials for sodium-ion batteries (SIBs) due to its abundant precursor sources, inherent safety, and exceptional sodium storage performance. However, the complex microstructures of hard carbon anode materials have led to ongoing controversies regarding their sodium storage mechanisms, which partially hinder their commercialization. This review innovatively employs a bibliometric analysis assisted by VOSviewer software to investigate the microstructure, sodium storage mechanisms, precursor diversity, and commercialization potential of hard carbon anode materials. Firstly, the microstructural models of hard carbon and four typical sodium storage mechanisms are comprehensively reviewed. Subsequently, the hard carbon anode materials synthesized from diverse precursors and their variations in electrochemical performance are summarized systematically, with the aim of identifying highly promising precursors and efficient synthesis methods. Moreover, this review summarizes the current commercialization progress of hard carbon anodes in global markets and provides forward-looking perspectives on their future development. This pioneering systematic review is used for the first time to compile and evaluate the anode materials in the field of sodium-ion batteries, with the expectation of providing an important reference for advancing the development.

In hydrometallurgical gold extraction, iodide (I-) is a promising alternative lixiviant to cyanide (CN-) for both primary ore processing and secondary resource recycling; however, reliance on iodine (I2) as oxidant renders the system unstable, poorly controllable, and costly. Herein, we proposed an aqueous copper(III) periodate/potassium iodide system that operates efficiently across acidic to alkaline conditions and enables fast gold leaching at near-neutral pH (5.5): 94.1% in 60 min from a roasted refractory gold concentrate and 96.6% in 20 min from waste mobile phones printed circuit boards. Mechanistically, high-valent copper(III) periodate displays pronounced pH-dependent bifunctionality in assisting iodide during leaching: under alkaline conditions, it serves as the dominant oxidant that directly dissolves gold; whereas as pH decreases, it primarily behaves as a catalyst that drives in-situ generation of triiodide (I3-), a more effective oxidant in iodide gold leaching. Additionally, the leachate can be reused for three consecutive cycles without reagent replenishment, and leached diiodoaurate(I) ions (AuI2-) can be easily recovered by commercial activated carbon, indicating good industry compatibility.

The controlled construction of three-dimensional electrocatalysts for cost-effective oxygen evolution reaction (OER) and urea oxidation reaction (UOR) in overall water splitting is of great importance for sustainable development. Constructing heterojunctions and further tailoring their structures is an effective strategy for regulating the electronic structure of catalysts and optimizing their active sites. In this study, a three-dimensional spherical NiO–Cr2O3/NF–P catalyst was prepared via solvothermal treatment and calcination, where P-doping optimizes the electronic structure and induces additional oxygen vacancies. In alkaline electrolyte, the obtained NiO–Cr2O3/NF–P exhibits activity and stability for OER/UOR, contributing to reduced voltage requirements on the anode side during water splitting. This work offering a novel strategy for the development of low-cost, high-performance electrocatalyst materials.

Sodium-ion batteries have emerged as a sustainable alternative to lithium-ion batteries owing to their low cost and high safety. Among various promising anode materials, hard carbon has garnered extensive attention regarding its abundant sources and superior stability. However, its relatively low reversible specific capacity remains a major bottleneck, inevitably hindering further commercial applications. To address this issue, a profound understanding of the sodium storage mechanism and microstructure design of hard carbon is urgently needed. This review systematically summarizes four representative sodium storage models to clarify the microstructural features of hard carbon, namely microcrystalline, closed pore and defect. The corresponding microstructure engineering strategies and their impacts on sodium storage behavior are elaborated in detail. Furthermore, ultramicropore is proposed as a unique microstructural feature favorable for sodium storage. By analyzing the trade-offs among different strategies, the integrated design of microstructure engineering for hard carbon is put forward. This work is intended to provide fundamental guidance for the rational design of highperformance hard carbon anodes, thereby promoting the commercial application of sodium-ion batteries.