Abstract:Driven by"Dual Carbon"goals of carbon peaking and carbon neutrality,the recycling of spent lithium-ion batteries(LIBs),particularly those featuring ternary cathode materials(LiNixCoyMnzC2,NCM),has emerged as a crucial step toward achieving resource circularity and emission reduction.Conventional recycling techniques,such as pyrometallurgical and hydrometallurgical processes,are often hindered by high energy consumption,complex multi-step procedures,and the production of low-value outputs such as basic metal salts.These limitations present significant economic and environmental bottlenecks.Consequently,shifting the paradigm from"metal recovery"to high-value"material regeneration"is imperative.In recent years,utilization routes that directly convert leaching solutions into cathode material precursors have gained significant traction.However,research in this area remains relatively fragmented,lacking systematic consolidation and critical evaluation.This review provides a comprehensive examination of technological progress in the pretreatment of spent ternary LIBs,metal leaching,and leachate purification.It then analyzes three primary high-value utilization pathways derived from metal-rich leachates:co-precipitation,spray pyrolysis,and sol-gel methods.For each pathway,the working principles,technical advantages,and industrialization challenges are elucidated.A comparative analysis is conducted regarding their adaptability to variable waste streams,recovery efficiency(balancing metal yield and product purity),engineering scalability(addressing continuous production and equipment design),and the electrochemical performance of the regenerated materials.Despite their promise,these pathways face common challenges:sensitivity to feedstock composition and the trade-off between reagent consumption and economic viability;technical barriers to process scaling and continuous operation;and a performance ceiling,where regenerated materials often merely restore rather than exceed the properties of their virgin counterparts.To overcome these challenges and accelerate the industrialization of high-value LIB recycling,future research and development should focus on several integrated directions:(1)developing intelligent,adaptive processes capable of handling complex feedstocks through real-time monitoring and machine learning;(2)innovating low-carbon,short-process technologies and integrated reaction-separation systems to minimize energy and reagent use;(3)advancing equipment design and process engineering to enable efficient,stable large-scale production;and(4)exploring intrinsic performance-enhancing strategies during recycling,such as targeted doping or microstructure engineering,to elevate the functionality and value of regenerated cathode materials beyond conventional levels.This review aims to provide a structured reference and actionable insights to facilitate the industrial adoption of high-value recycling technologies for spent lithium-ion batteries.

Abstract:Based on an evaluation of the current development status of the waste battery recycling industry,this study identifies key challenges,analyzes their underlying causes in depth,and proposes targeted management recommendations.To enhance the accuracy of research findings,the study collected extensive industrial data,including information on the construction and operation of recycling service networks,the approval and implementation of recycling projects,and enterprise compliance reporting.Through comparative data analysis,statistical assessment,and field investigations that supplemented and verified information regarding key operational processes,this study conducted a comprehensive evaluation of the industry's resource utilization technologies and environmental protection capabilities.The research reveals that the recycling industry currently faces several issues,including an imbalanced industrial chain,inadequate levels of comprehensive utilization,and prominent safety and environmental risks.Specifically,the industrial chain imbalance is reflected in the low operational efficiency of the collection system,significant overcapacity in comprehensive utilization,and a consequent slowdown in the advancement of production technologies.Particularly noteworthy is the inadequate level of comprehensive utilization,characterized by a distinctly fragmented industrial landscape.Over 60％of projects are limited to pretreatment processes such as crushing and screening,failing to achieve the ultimate goal of resource recovery.Moreover,resource regeneration projects primarily focus on metallic resources such as lithium,nickel,and cobalt,with minimal production capacity dedicated to recycling iron phosphate residues and anode materials.The causes of these problems span multiple dimensions,including policy planning,market conditions,and technical standards.First,the lack of proper implementation planning and control for supportive policies has resulted in a surplus of redundant projects and poor coordination with upstream and downstream industries.Second,the lack of mandatory regulations has led to a proliferation of informal operators,causing idle capacity among compliant enterprises while significantly increasing environmental pollution and product safety risks.Third,the technical requirements for standardized processing necessitate substantial investments in production operations and environmental management;the resulting high costs and low returns directly deter companies from expanding advanced production capacity.This insufficient development of advanced production capacity further constrains improvements in the overall level of comprehensive utilization across the industry.Finally,recent market shifts,including the contraction of downstream applications and falling prices of raw materials,have significantly undermined cost-effectiveness and substantially limited market prospects.To establish an efficient collection and standardized disposal system,this study recommends strengthening institutional policy safeguards,developing standardized documentation to regulate recycling practices,vigorously promoting technological research and development,and enhancing full-chain supervision.Specific pathways include reinforcing mandatory recycling systems,formulating technical standards for the battery health assessment,transportation,and storage,and strengthening off-site supervision via material flow tracking,power consumption monitoring,and satellite remote sensing.

Abstract:The rapid growth of renewable energy,particularly wind power,has led to the large-scale construction and operation of wind farms.By the end of 2024,the global installed wind power capacity had reached 1 136 GW,with China leading the world by contributing over 520 GW.Consequently,the number of decommissioned wind turbine blades is rising at an accelerating rate,indicating an impending surge in waste volume.This anticipated surge of composite waste has elevated the recycling and disposal of wind turbine blades from a niche concern to a pressing global environmental challenge.Wind turbine blades are primarily composed of high-performance composite materials,notably glass fibers,carbon fibers,polymer resins,and various core materials.These components are engineered for durability and strength,which also gives them significant resource value.The recovery and reclamation of these valuable materials are crucial for fostering a circular economy within the renewable energy sector itself.However,the technologies for separating and recycling these materials pose significant challenges and risks of causing secondary pollution.This study systematically analyzes the generation characteristics of waste wind turbine blades to project future waste volumes;comprehensively compares existing recycling technologies from technical,economic,and environmental perspectives,based on the blades'structural and material properties;and discusses future technological developments.Furthermore,by reviewing national and provincial policies,this paper elucidates the current policy landscape and future directions for the recycling sector.Results indicate that,based on a 20-25-year blade service life,global waste blade volumes are projected to surge from approximately 200 000 tons in 2025 to 2.6-6.0 million tons by 2050.China's share is expected to reach 0.9-1.9 million tons by 2050.For the glass and carbon fibers in blades,glass fiber recycling primarily utilizes incineration,co-processing in cement kilns,and mechanical-physical recovery.In contrast,higher-value methods such as pyrolysis and chemical processing are favored for carbon fiber recycling.In terms of resource recovery technologies,thermal treatment processes are relatively mature and have achieved industrial application;however,they offer low economic returns and pose significant challenges in controlling secondary pollution.Although chemical separation technologies are highly efficient and yield valuable recovered products,their complex procedures and high operating costs have prevented widespread industrial adoption.Mechanical-physical methods,typically used as pretreatment steps,are low-cost and widely implemented in industry.However,they require integration with chemical or thermal processes to achieve efficient separation and full-scale recovery.Effectively addressing the recycling of discarded wind turbine blades is crucial for ensuring the long-term sustainability and circularity of the wind power industry itself,requiring joint efforts from both industry and academia.

Abstract:The rapid growth of the photovoltaic and semiconductor industries has dramatically increased the demand for high-purity silicon while generating large amounts of silicon waste during wafer slicing,metallurgical refining,and module decommissioning.Efficient recycling of waste silicon can mitigate environmental pressure and provide a sustainable raw material source for silicon-based industries.This work systematically reviews the purification,recovery,and reuse technologies of waste silicon,focusing on three major categories:silicon cutting waste(SCW),metallurgical-grade silicon refining slag(MGSRS),and end-of-life photovoltaic modules(EoL-PV).The physicochemical characteristics of these wastes,including phase composition,impurity distribution,and structural morphology,are analyzed to establish the relationship between their origins and corresponding purification strategies.Experimental and industrial results reported in recent literature are compared to identify the optimal parameters for impurity removal.For SCW,acid leaching with HF-HCl or HNO3-HF mixtures achieved Fe,Al,and Ca removal efficiencies exceeding 95％under temperatures of 50-60 ℃ and moderate acid concentrations.In MGSRS refining,CaO-SiO2-Al2O3 or Fe2O3-SiO2-based slags effectively removed Ti,C,and Ca impurities through oxidation and selective slagging reactions,yielding silicon purities above 99.8％.Vacuum refining and zone melting remove volatile impurities(e.g.,P)and metallic impurities,respectively;however,removing B remains a challenge due to its segregation coefficient being close to unity.Emerging physical purification methods,including plasma,microwave,and electron-beam treatments,are discussed in terms of heat transfer behavior,impurity volatilization kinetics,and energy consumption.The synergistic combination of chemical and physical refining routes has been shown to markedly improve purification efficiency,shorten processing time,and reduce reagent use.The thermodynamic feasibility and kinetic constraints of impurity reactions are summarized to provide theoretical guidance for multi-step integration.Regarding reutilization,purified silicon waste can be converted into metallurgical-grade,solar-grade,or electronic-grade silicon depending on purity requirements.In addition,secondary utilization pathways include the synthesis of SiC and Si3N4 ceramics,Si-C composite anodes for lithium-ion batteries,and porous silicon for energy storage and photothermal conversion.Life-cycle analyses indicate that recycling 1 t of silicon waste saves approximately 8-10 MW·h of energy and reduces CO2 emissions by more than 5 t compared with primary silicon production.Overall,waste silicon recycling offers substantial environmental and economic benefits,but large-scale industrial implementation is still limited by impurity variability,lack of standardized process control,and the high cost of deep purification.Future work should focus on elucidating the thermodynamic and kinetic mechanisms of impurity removal,optimizing multi-process coupling between refining and solidification,and developing modularized refining-functionalization systems.Establishing unified evaluation criteria and techno-economic models will be key to achieving sustainable,high-value recycling of waste silicon materials.

Abstract:The co-smelting of waste printed circuit boards(WPCBs)and spent automotive catalysts(SACs)represents an innovative"waste-to-resource"strategy for recovering resources from hazardous wastes.Through metallurgical interactions,the copper in WPCBs acts as an efficient scavenger for enriching platinum group metals(PGMs),gold,and silver from SACs.Although this technology provides a sustainable treatment solution for these hazardous wastes through the synergistic recovery of metals,the transformation mechanisms of organic pollutants during the co-smelting process are not well understood.This study systematically investigated the transformation behavior of organic pollutants under optimized metal recovery conditions:a smelting temperature of 1 400 ℃,a holding time of 4 h,a WPCBs-to-SACs ratio of 25％,and a basicity of 1.0.The chemical compositions of SACs and WPCBs was characterized using X-ray diffraction(XRD)and Fourier transform infrared spectroscopy(FTIR).Their elemental contents were determined by X-ray fluorescence spectrometry(XRF)and inductively coupled plasma optical emission spectrometry(ICP-OES).Subsequently,the liquid-phase and gas-phase products from the co-smelting process were collected to assess secondary pollution risks.Gas chromatography-mass spectrometry(GC-MS)was employed to identify the compostion of organic substances.The weight loss characteristics and pyrolysis mechanisms of the materials were further analyzed.The Kissinger-Akahira-Sunose(KAS),Flynn-Wall-Ozawa(FWO),and Friedman methods were used to study the kinetic mechanisms of organic substance decomposition during co-smelting.The reaction kinetic model equations were applied to fit different conversion rate intervals to explore the decomposition mechanisms of organic substances.Additionally,an equivalent weighting method was employed to comprehensively assess the product toxicity,bioaccumulation,persistence,and secondary pollution risks.Analysis of organic substance composition revealed that the liquid-phase products mainly consisted of benzene derivatives(35.77％)and phenolic derivatives(37.26％),with no halogenated pollutants detected.The gas-phase products were primarily composed of small molecules such as H2,CO,CH4,CO2,and aromatics.Therefore,the co-smelting process resulted in the dehalogenation and molecular weight reduction of the products,reducing environmental risks.The metal components in the WPCBs-SACs co-smelting system catalyzed the decomposition of epoxy resins in WPCBs.The metals inherently present in the co-smelting system(e.g.,Cu,Fe,and PGMs)significantly reduced the activation energy for organic substance decomposition,promoting the efficient cracking of complex pollutants.Within the temperature range of 600-800 ℃,the activation energy for organic substance decomposition decreased by 221.64-286.64 kJ/mol.The comprehensive toxicity assessment identified 4-phenylphenol,bisphenol A,phenol,naphthalene,and p-cresol as the organic pollutants with the highest environmental risks in the gas and liquid phases.Building on previous research on the co-smelting recovery of PGMs from WPCBs and SACs,this study comprehensively elucidated the transformation mechanisms of organic pollutants during the smelting process.

Abstract:Lithium ore smelting slag is a major bulk solid by-product generated from conventional pyro-hydrometallurgical lithium extraction processes.Developing efficient resource utilization and high-value conversion technologies for this material is crucial for reducing China's dependency on external lithium resources,ensuring the stability and security of the new energy industry chain,and promoting green,low-carbon development.Current research has employed various techniques,such as combined pyro-hydrometallurgy and alkali roasting,to enhance lithium leaching kinetics and enable the co-recovery of associated critical metals such as rubidium(Rb),cesium(Cs),and aluminum(Al).Specifically,pyro-hydrometallurgical approaches can achieve lithium leaching efficiencies exceeding 97％,while subsequent processing of recovered lithium salts via molten-salt electrolysis or thermal reduction,followed by vacuum refining,can yield lithium metal with purity exceeding 98％,potentially reducing energy consumption and environmental pollution.Additionally,solvent extraction and electrochemical methods have shown considerable potential for selective lithium recovery.For associated metals such as Rb,Cs,and Al,high-temperature roasting followed by acid leaching can achieve Rb recovery efficiencies of up to 93.09％,although this method faces challenges regarding energy consumption and product purity.Beyond metal recovery,lithium slag demonstrates significant potential in the production of value-added construction and functional materials such as high-performance ternary geopolymers,cement,and molecular sieves.For instance,under optimized mix designs,incorporating 5％lithium slag as a supplementary cementitious material can reduce energy consumption and achieve 28-day compressive strengths exceeding 80 MPa,demonstrating excellent engineering applicability.Furthermore,lithium slag can be synthesized into environmentally friendly materials such as ternary geopolymers and NaX zeolites.The former exhibits high immobilization efficiency for various heavy metals,while the latter possesses a well-defined structure and superior adsorption performance.Despite these advances,several challenges persist,including incomplete lithium extraction,low recovery efficiencies of critical metals,and the lack of standardized processing systems.Accordingly,this review systematically analyzes the physicochemical characteristics of lithium smelting slag,including its chemical composition and occurrence modes.It summarizes mainstream recovery techniques for valuable metals(Li,Rb,Cs)and evaluates recent advances in producing high-value-added products.Finally,the study outlines a sustainable technology framework centered on"source reduction,low-carbon processing,and end-stage high-value conversion,"emphasizing rapid activation,multi-component selective separation,and full-process system integration.This work aims to provide theoretical guidance and mechanistic insights to support the development of green recycling technologies for lithium ore smelting slag.

Abstract:In recent years,sodium-ion batteries have attracted much attention due to their low cost,high safety,and excellent low-temperature performance.Among the candidate electrode materials,Prussian blue-based cathode materials show great potential for application due to their high energy density.However,there is currently no universally established technology for the recovery of valuable resources and the zero-discharge treatment of wastewater from the production of these materials.Addressing the limitations of traditional technologies,this study proposes a novel process characterized by"targeted precipitation-multi-membrane synergy-directional recycling"to enable resource recovery and zero-discharge wastewater treatment.The system involves two metathesis reactions and a two-stage membrane filtration process.In the first metathesis reaction,calcium chloride is used as a precipitating agent to react with sodium sulfate and sodium citrate in the wastewater.The optimal dosage of calcium chloride was determined to be 21 mg/mL through parametric optimization experiments.After solid-liquid separation,a filtrate containing sodium ferrocyanide and a mixed filter residue composed of calcium sulfate and calcium citrate were obtained.In the second metathesis reaction,sodium carbonate was used as a conversion agent for the mixed filter residue.The optimal conditions were determined to be:a sodium carbonate to calcium citrate ratio of 3∶1,a 25％sodium carbonate solution,pH 10.5,a reaction temperature of 75 ℃,and a reaction time of 30-40 min.The filtrate then undergoes two-stage membrane filtration,during which ferrocyanide and chloride ions are effectively retained.Specifically,sodium ferrocyanide is recycled as a raw material for Prussian blue cathode production,while the remaining solution is treated by reverse osmosis to separate salts,and the resulting purified water is reused.Concurrently,the filter residue containing calcium sulfate and calcium citrate is repeatedly washed and separated to yield a residue mainly composed of calcium sulfate and calcium carbonate.Finally,the filtrate is evaporated and crystallized to yield a white powder mainly composed of sodium citrate.The recovery rate of sodium citrate exceeds over 99.6％,and sodium ferrocyanide can be directly reused in the production process under the optimized conditions.This work provides essential data and methodological guidance for resource recovery and zero-discharge wastewater treatment in the production of Prussian blue cathode materials for sodium-ion batteries.

Abstract:With the continuous rapid growth in the volume of spent lithium-ion batteries,developing an environmentally friendly,cost-effective,and efficient recycling process for cathode materials has become a key scientific challenge for the sustainable development of the new energy industry.Conventional hydrometallurgical recycling technologies typically rely on strong acids combined with external reducing or oxidizing agents,which lead to high reagent consumption and operating costs while generating large volumes of metal-containing wastewater,posing significant environmental and disposal challenges.Therefore,it is of great scientific and practical significance to develop a novel recycling process that eliminates the need for external chemical additives while enabling the synergistic recovery of multiple components.In this study,an additive-free recycling strategy based on an intrinsic synergistic redox mechanism is proposed for a mixed system of spent LiFePO4(S-LFP)and LiMn2O4(S-LMO).This approach fully utilizes the electrochemical potential difference between different electrode materials to drive spontaneous electron transfer reactions under mildly acidic conditions,with acid consumption reduced by nearly half compared to conventional methods.Specifically,Fe2+ions are first leached from S-LFP and act as intrinsic reducing agents in the solution;these Fe2+ions subsequently reduce Mn3+to Mn2+in S-LMO,thereby promoting the efficient co-leaching of Mn and Li.This process achieves the synergistic recycling of the spent materials,reaching nearly 100％leaching efficiency for Mn and Li under mild conditions(20 ℃,40 min),demonstrating excellent reaction kinetics and synergistic effects.Concurrently,Fe species are selectively converted into insoluble FePO4 precipitates,allowing for easy solid-liquid separation.The resulting FePO4 can directly serve as a precursor for the regeneration of LiFePO4(R-LFP).The leachate is further processed by adjusting the pH with ammonia to precipitate Mn(OH)2,followed by the addition of Na2CO3 to obtain Li2CO3,thereby achieving the full recovery and reuse of Fe,Mn,Li,and P elements.The regenerated R-LFP exhibits a uniform spherical morphology with a narrow particle size distribution and a well-preserved crystal structure.Electrochemical testing reveals that the regenerated material delivers an excellent discharge capacity of 135.0 mA·h/g and a capacity retention of 99.4％after 200 charge-discharge cycles,indicating outstanding cycling stability and structural reversibility.This work systematically elucidates the self-driven redox mechanism between spent electrode materials and achieves closed-loop recovery of all constituent elements along with the regeneration of high-value-added materials.The entire process relies solely on spontaneous electron transfer between the waste materials,without the need for external oxidizing or reducing agents,significantly lowering energy consumption,reagent usage,and secondary pollution.The proposed synergistic redox strategy overcomes the limitations of conventional hydrometallurgical processes and provides a new theoretical foundation and practical pathway for the green,efficient,and sustainable recycling of multi-component spent lithium-ion batteries,showing great potential for large-scale industrial application.

Abstract:Fiber-reinforced polymers(FRPs),composed of reinforcing fibers and resin matrices,exhibit outstanding characteristics such as low density,high strength,corrosion resistance,and superior mechanical performance.With the large-scale application of FRPs in the renewable energy industry,such as wind turbine blades(WTBs),nacelles,photovoltaic brackets,electric vehicle components,and battery storage enclosures,the decommissioning of large-scale FRP structures has become an increasingly pressing issue.The complex composition of end-of-life materials,the inherent difficulty in separating thermosetting resins,and the underdeveloped recycling infrastructure make it crucial to achieve efficient and environmentally friendly recycling,prevent environmental pollution,and facilitate circular resource recovery.This article focuses on recycling solutions for FRPs in the renewable energy sector,systematically reviewing recycling technologies and highlighting innovations in three main process types:mechanical,pyrolytic,and chemical recycling.Mechanical recycling technologie,through intelligent precision cutting and automatic sorting,effectively reduce fiber damage and enhance the application potential of recycled materials.Pyrolysis recycling technologies encompass high-temperature pyrolysis,fluidized bed pyrolysis,and microwave-assisted pyrolysis.By precisely controlling the temperature and reaction atmosphere,they significantly reduce thermal damage to fibers,yielding a fiber performance retention rate of over 90％;the resulting pyrolysis oil and gas are reused as valuable resources.Chemical recycling technologies,such as chemical swelling and supercritical fluid processes,achieve efficient fiber recovery by selectively breaking the chemical bonds at the resin-fiber interface.This study further highlights the development trends in fiber repair and interfacial modification technologies.Intermediate repair techniques,such as sol-gel coating,plasma surface treatment,and electrochemical oxidation,improve the interfacial performance between regenerated fibers and resin matrices by 15％to 40％,significantly enhancing the overall mechanical properties and durability of regenerated composite materials.In terms of high-value utilization pathways,regenerated fibers have been successfully applied in lightweight automotive components,aerospace structures,and components for ultra-large offshore wind components,through innovative additive manufacturing technologies and the combined use of interfacial compatibilizers,significantly promoting the large-scale application of regenerated materials in high-end sectors.In addition,by treating by-products such as pyrolysis oil and gas through catalytic cracking,hydrodeoxygenation,and Fischer-Tropsch synthesis,high-value-added aromatic chemicals,fuel oils,and high-purity hydrogen can be obtained,further enhancing the economic benefits of resource recovery.Lastly,the article proposes recommendations for full value-chain integration,the development of standardized systems,and intelligent digital control,emphasizing the need to establish a circular ecosystem that spans front-end pretreatment,intermediate-stage repair and regeneration,and back-end high-value applications to support the sustainable development of the renewable energy industry.

Abstract:The recovery of valuable metals from spent lithium iron phosphate(LFP)black mass has garnered significant attention,with hydrometallurgy serving as the dominant recycling strategy.The leachate derived from hydrometallurgical processes typically contains impurity ions such as copper,aluminum,and fluoride,necessitating purification prior to the recovery of valuable metals.In particular,the efficient removal of aluminum ions while minimizing lithium loss via physical adsorption and chemical co-precipitation remains a critical challenge.While neutralization precipitation is a conventional method for aluminum removal,the resulting precipitate exhibits non-negligible lithium adsorption.Alternatively,cryolite precipitation can be employed in more acidic environments to produce highly crystalline aluminum-bearing precipitates with lower lithium adsorption;however,in lithium-rich solutions,it tends to form lithium-containing cryolite(Na1.5Li1.5AlF6),leading to significant lithium losses.To address this limitation,this study proposes a novel hydrometallurgical approach to recover lithium from Na1.5Li1.5AlF6.The process involves converting Na1.5Li1.5AlF6 into a solid mixture of Na3AlF6 and LiF in a NaF solution,followed by selective dissolution.Specifically,a sulfuric acid medium containing sodium sulfate was developed to selectively dissolve LiF while inhibiting Na3AlF6 dissolution via the common ion effect.Experimental results demonstrated that complete conversion of Na1.5Li1.5AlF6 was achieved under the following conditions:NaF concentration of 45 g/L,70 ℃,liquid-to-solid(L/S)ratio of 15 mL/g,and a reaction time of 3 h.The resulting filtrate could be recycled after NaF replenishment.Subsequently,selective leaching of LiF was achieved with an initial sulfuric acid concentration of 90 g/L,Na+concentration ≥ 8 g/L,20-30 ℃,L/S ratio of 15 mL/g,and a duration of 1 h.Through this two-step process,effective aluminum-lithium separation was realized,with aluminum enriched in the solid Na3AlF6 phase and lithium transferred to the liquid phase for subsequent recovery.This work provides a viable strategy for the efficient extraction of lithium from cryolite precipitates in spent battery recycling.

Abstract:End-of-life(EOL)photovoltaic(PV)modules are becoming an important secondary resource stream,and their safe,efficient recycling strongly depends on the performance of sorting technologies during the pretreatment stage.This review examines sorting technologies for EOL PV modules with the aim of clarifying the roles,application ranges,and limitations of traditional physical sorting and intelligent sorting,and identifying technical directions for improving recycling efficiency and reducing secondary pollution.Based on recent research and engineering practice reports,the paper classifies current sorting routes into traditional physical processes—such as high-voltage electrostatic separation,eddy current separation,magnetic separation,and gravity separation—and intelligent sorting systems driven by machine vision,deep learning algorithms,and precision positioning equipment.The literature is synthesized to compare these routes in terms of separable material types,particle-size ranges,dependence on manual parameter adjustment,and the distinguishability of materials with subtle differences in properties such as conductivity,density,or surface characteristics.Reported data on recovery and purity of product streams,operating stability,and control complexity are used to summarize the typical roles of different sorting technologies within complete EOL PV recycling flowsheets.The results of the review indicate that traditional physical sorting is suitable for the basic separation of glass and metallic fractions and has advantages in process simplicity and robustness,but it is generally restricted to fragments in the range of 2-20 mm and to systems in which materials exhibit pronounced differences in physical properties.These routes have limited capacity to handle laminated structures and components with similar compositions,and they usually require frequent manual tuning to maintain stable recovery and purity.Intelligent sorting technologies can identify wafers,glass,ribbons,and backsheets at the single-particle level by analyzing intrinsic optical and morphological features,expanding the applicable size range and reducing reliance on manual operation.Studies further suggest that coupling intelligent recognition and actuation modules with electrostatic,magnetic,or gravity separation units improves overall separation precision and decreases the risk that hazardous or high-value components may enter inappropriate product streams.From the comparative analysis,the main technical bottlenecks are identified as the narrow applicability and low adaptability of traditional physical processes,along with the high equipment cost,the requirement for large,high-quality datasets,and system integration challenges associated with intelligent sorting.The review concludes that future development should focus on upgrading conventional lines through the integration of intelligent perception and control,designing modular intelligent sorting units that can be flexibly combined with different pretreatment and separation processes,and coordinating technological innovation with policy measures and standardization.These directions are expected to support higher-efficiency,lower-pollution sorting systems and promote the sustainable and high-value utilization of EOL PV modules.

Abstract:To ensure the safety,reliability and longevity of battery systems,accurate estimation of the State of Health(SOH)of lithium-ion batteries is essential.As an internal state variable,SOH is difficult to measure directly with sensors and is therefore often estimated through indirect methods.The accuracy of SOH estimation largely depends on the quality of the extracted health features that are correlated with battery aging.This review systematically analyzes and evaluates mainstream feature extraction methodologies for lithium-ion battery SOH estimation.It clarifies the link between macroscopic aging phenomena(capacity fade and impedance rise)and microscopic electrochemical degradation mechanisms,such as loss of active material(LAM)and loss of lithium inventory(LLI).A comprehensive survey is conducted on five primary feature categories:(1)Voltage-current curve features,derived from standard charging protocols(e.g.,Constant Current-Constant Voltage,CC-CV),including temporal indicators and capacity metrics within specific voltage windows.(2)Differential curve features,such as Incremental Capacity Analysis(ICA)and Differential Voltage Analysis(DVA),identifying electrochemical phase transitions whose peak attributes(height,position,area)serve as health indicators.(3)Pulse power characterization features,obtained from Hybrid Pulse Power Characterization(HPPC)tests,reflecting DC internal resistance(DCR)and variations in the open-circuit voltage(OCV)versus state of charge(SOC)curve.(4)Electrochemical impedance spectroscopy(EIS)features,extracted from raw impedance data,including parameters fitted using equivalent circuit models(ECM)and deconvolution results from distribution of relaxation times(DRT)analysis.(5)Multi-physics field features,which utilize non-electrical signals from thermal,ultrasonic,and mechanical sensors,providing additional diagnostic dimensions.Publicly available datasets(e.g.,NASA,CALCE,Oxford)are also reviewed as benchmarks.The analysis finds that voltage-current curve features are computationally efficient but typically require full charging cycles.While ICA/DVA offer deep mechanistic insight by linking peak changes to LAM and LLI,their susceptibility to noise and current rate complicates online implementation.HPPC-derived features effectively track impedance growth but require accurate OCV correction.EIS provides the most comprehensive diagnostic information,with ECM offering physically meaningful parameters and DRT excelling at decoupling overlapping processes,though measurements are time-intensive.Multi-physics features capture structural and thermal degradation,offering complementary perspectives.A key finding is that no single feature can reliably provide robust and high-precision SOH estimation under complex and variable real-world conditions.Given the limitations of single features,future research is expected to focus on:(1)establishing standardized public benchmarks and evaluation protocols to enable objective comparison and accelerate technological progress;(2)fusing multi-physics features(electrical,thermal,mechanical)to develop more comprehensive and robust health indicators;and(3)integrating physical models with data-driven methods,such as physics-informed neural networks(PINNs),to enhance model interpretability,data efficiency,and generalization.

Abstract:With the rapid expansion of the electric vehicle industry,the volume of spent lithium-ion batteries(LIBs)has witnessed a sharp increase,underscoring the significance of recycling and reutilizing spent graphite anodes for sustainable development.Although spent graphite retains a relatively stable layered framework after cycling,it exhibits structural defects,residual electrolyte components,and surface contaminants.These issues limit its direct reuse in new batteries but create opportunities for targeted regeneration and functional transformation.This review provides a comprehensive overview of recent advances in the repair,regeneration,and functional utilization of graphite anodes from spent LIBs.Repair and regeneration aim to restore the electrochemical activity of degraded graphite by removing impurities,repairing structural defects,and reconstructing the electrode-electrolyte interface.Low-to-medium-temperature graphitization,enabled by the introduction of transition metal catalysts that reduce the migration energy barrier of carbon atoms,allows the graphitization process to occur at lower temperatures and with reduced energy consumption.Surface treatments focus on constructing protective coatings on damaged graphite to cover defect regions,improve structural integrity,and stabilize the electrode-electrolyte interface,thereby suppressing undesired side reactions.Rapid heating treatments,such as microwave irradiation and Joule heating,generate localized high temperatures within seconds,enabling efficient removal of surface residues and repair of near-surface defects in an energy-saving and environmentally friendly manner.Functional utilization leverages the intrinsic defects,porous structures,and the ability of spent graphite to incorporate heteroatoms or metals.By tailoring surface morphology and introducing functional elements,spent graphite can be converted into advanced functional materials for diverse applications.Specifically,defect sites and residual heteroatoms can serve as catalytic centers for electrocatalysis and pollutant degradation,while the engineered porous structures and surface functional groups enhance the adsorption of heavy metals and organic contaminants in aqueous environments.Furthermore,strategies such as defect engineering,heteroatom doping,and composite formation enhance ionic transport and capacitive performance,facilitating the development of porous carbons,doped graphene,and graphite-based composites for supercapacitors as well as sodium-ion and potassium-ion batteries.From an environmental and economic perspective,graphite regeneration and utilization provide distinct advantages over conventional recycling methods.Repair and regeneration reduce greenhouse gas emissions and minimize secondary pollution,while functional utilization mitigates waste and generates economic value by producing functional materials with ecological benefits.Despite notable progress,large-scale recycling of spent graphite remains challenging due to high energy consumption,complex processing steps,and the limited availability of efficient,scalable technologies.In addition,the diversity of waste sources complicates the establishment of standardized pretreatment and regeneration procedures.Future research should focus on developing intelligent and universal recycling technologies,along with the construction of integrated closed-and open-loop pathways,to achieve resource-efficient,environmentally compatible,and value-added reutilization of spent graphite.The coordinated implementation of these strategies is expected to enhance efficiency,reduce costs,and maximize the resource potential of spent graphite,thereby supporting a sustainable and circular lithium-ion battery industry.

Abstract:Driven by the global energy transition and the"dual-carbon"goals,the efficient recycling of spent lithium-ion batteries(LIBs)is of great significance for securing critical metal resources and mitigating environmental impacts.Pressurized technology,which alters reaction thermodynamic equilibria and enhances kinetics under elevated temperature and pressure,offers a promising approach for spent LIB recycling and has garnered significant attention in this field.This review systematically summarizes recent advances in the application of pressurized technology for recycling spent LIBs,with a particular focus on three key areas:valuable metal extraction,synthesis of high-value materials,and direct regeneration of electrode materials.In terms of valuable metal extraction,technologies such as pressurized acid leaching,ammonia leaching,and oxidative leaching exhibit remarkable effectiveness in enhancing the extraction of valuable metals.These methods significantly improve the leaching efficiency and selectivity of critical metals such as lithium,cobalt,and nickel.The high-temperature,high-pressure environment accelerates reaction rates,enables reactions that are non-spontaneous under ambient conditions,and reduces reagent consumption.Beyond metal extraction,pressurized technology,primarily the hydrothermal method,facilitates the short-path,high-value utilization of spent LIBs.Purified leachates can be directly employed as precursors for the synthesis of functional materials,such as cathode precursors and metal oxides,thereby upgrading waste into valuable products.Regarding direct regeneration,hydrothermal repair presents a compelling alternative to traditional energy-intensive solid-state calcination.This approach allows for an effective relithiation of degraded cathodes such as LiFePO4,LiCoO2,and ternary materials(e.g.,NMC)under milder conditions.The liquid-phase environment ensures uniform lithium-ion diffusion,leading to more homogeneous repair,superior recovery of electrochemical performance,lower energy consumption,and specific capacities comparable to those of pristine materials.Furthermore,to address current challenges such as the difficulty of in-situ characterization and the lack of suitable characterization technologies for pressurized processes,this review also highlights advancements in in-situ characterization techniques.The integration of specialized reactors with powerful tools such as synchrotron radiation X-ray diffraction(XRD),X-ray absorption spectroscopy(XAS),and Raman spectroscopy enables real-time observation of phase transitions,valence changes,and crystal growth during pressurized processes,offering unprecedented insights into reaction mechanisms.Despite the promising laboratory-scale successes,the industrial application of pressurized technologies still faces challenges,including insufficient thermodynamic data for novel and mixed materials,inadequate mechanistic understanding,lack of robust in-situ characterization techniques,and high equipment costs.Future development should prioritize establishing comprehensive thermodynamic databases,developing multi-dimensional and multi-scale in-situ characterization methods,innovating reactor designs for lower energy consumption and cost,integrating pressurized processes with clean energy sources to reduce the carbon footprint,and developing low-cost,corrosion-resistant materials for reactors.This review concludes that pressurized technology holds significant potential for enabling closed-loop and sustainable recycling of spent LIBs.

Abstract:With the widespread application of lithium-ion batteries in electric vehicles and the energy storage sector,the large-scale retirement of these batteries has created an urgent demand for effective recycling solutions.However,there is a lack of in-depth analysis regarding the waste generation characteristics associated with different recycling paths,and the potential environmental threats posed by wastewater,waste gas,and solid waste generated during the recycling process have not been quantitatively evaluated.This study investigates the recycling processes of spent lithium cobalt oxide(LCO)and nickel-cobalt-manganese(NCM)batteries.It provides a detailed overview of the recycling methods and waste generation pathways for these two types of batteries.Comprehensive environmental impact assessments(EIA),life cycle assessments(LCA),and economic analyses were conducted to quantify both environmental and economic impacts.Based on the analysis of the waste generation pathways,waste produced during the recycling process of both types of batteries consists mainly of heavy metal ions and substances contributing to chemical oxygen demand(COD)in the wastewater.This is primarily due to the use of hydrometallurgical treatment processes.The results of the environmental impact assessments indicate that the recycling of LCO batteries has a lower impact than that of NCM batteries.The LCA results are consistent with the EIA findings and reveal that marine ecotoxicity represents the most significant environmental impact,accounting for 93.8％and 86.3％of the total environmental impact for LCO and NCM batteries,respectively.Furthermore,the LCA shows that hydrogen peroxide and kerosene contribute 78.3％and 59.9％to the total environmental impact for LCO and NCM battery recycling,respectively,highlighting the substantial impact of key input materials.Economic analysis indicates that the proportion of environmental investment is higher for LCO batteries,suggesting a relatively lower burden for end-of-pipe treatment.In contrast,the total operating cost of NCM battery recycling is higher,reflecting the complexity and difficulty in separating their metal components.Sensitivity analysis results show that hydrogen peroxide and kerosene have the most significant influence on the environmental performance of LCO and NCM battery recycling,with sensitivity coefficients of 3.91％and 3.79％,respectively.In conclusion,the comprehensive evaluation reveals that LCO battery recycling is more environmentally friendly,while NCM battery recycling offers higher resource recovery value.

Abstract:With the continuous increase in global demand for stainless steel and special alloy steels,the output of high-carbon ferrochrome slag,a by-product of high-carbon ferrochrome smelting,has risen steadily.Currently,the predominant treatment method for high-carbon ferrochrome slag is landfilling,which occupies large areas of land and presents significant environmental risks.Due to the presence of Cr2O3 in the slag,trivalent chromium(Cr3+)can be partially oxidized into hexavalent chromium(Cr6+)during weathering,posing potential hazards to ecosystems and human health.This study analyzes the chemical composition and mineralogical characteristics of high-carbon ferrochrome slag,revealing that its major crystalline phases include forsterite(Mg2SiO4),cordierite(Mg2Al4Si5O18),and spinel phases such as Mg(Al,Cr)2O4.Notably,most chromium is immobilized within the spinel phases,which greatly reduces its leaching potential and environmental impact.Based on these mineral features,this paper reviews recent global research progress on its application in construction materials(such as cement,concrete,and lightweight aggregates)and functional materials(such as ceramics,glass-ceramics,and refractories).Studies have shown that high-carbon ferrochrome slag possesses high hardness,a stable crystal structure,and a low chromium leaching risk,making it suitable for the preparation of construction materials such as cement mortar,concrete,and lightweight aggregates.In addition,when combined with other minerals or solid wastes,high-carbon ferrochrome slag can form high-temperature-resistant phases such as cordierite,spinel,and forsterite through appropriate sintering and modification processes,thereby meeting the requirements for the production of high-performance ceramics and glass-ceramics.However,industrial-scale applications of high-carbon ferrochrome slag in these fields remain limited.Future research should focus on several key areas.First,regarding the synergistic utilization of multi-source industrial wastes,high-carbon ferrochrome slag can be combined with fly ash,blast furnace slag,and titanium-bearing slags to explore waste-to-resource strategies through coupled reaction mechanisms and heat treatment processes.This can enhance composite material properties and mitigate chromium leaching risks.Second,concerning waste heat utilization and metal recovery,dry-type heat recovery technologies should be prioritized due to the high tapping temperature and sensible heat of molten high-carbon ferrochrome slag.Furthermore,combining techniques such as carbonization,crushing,screening,magnetic separation,and secondary smelting can improve the recovery rate of ferrochrome alloy,thereby increasing energy efficiency and resource utilization while reducing the environmental hazards posed by chromium.Third,it is essential to establish comprehensive life cycle assessment(LCA)systems and long-term environmental impact evaluation standards to ensure the safety and sustainability of the products.These efforts will contribute to promoting the comprehensive utilization of high-carbon ferrochrome slag toward low energy consumption,high-value utilization,and environmental sustainability.

Abstract:Anaerobic digestion is an important approach for reducing the volume of urban sludge and achieving resource recovery.However,conventional anaerobic digestion is limited by the diffusion of hydrogen and formic acid,which can easily lead to metabolic blockage,eventual acidification,and system collapse.Direct interspecies electron transfer(DIET)has been proven to effectively mitigate these issues and enhance the efficiency of anaerobic digestion.Previous studies have shown that the addition of a small amount of glycerol can enrich electroactive microorganisms and promote DIET.However,the use of exogenous glycerol increases operational costs.To address this,the present study combined alkali pretreatment and yeast fermentation to produce glycerol in situ from urban sludge,thereby promoting DIET and supporting efficient methane production.The results showed that the optimal duration for alkaline pretreatment was 10 hours,which increased the soluble sugar content by 43.4％compared to untreated sludge.The optimal inoculation ratio for yeast fermentation was 10％,and the optimal fermentation duration was 9 hours,during which glycerol accounted for 2.43％of the total chemical oxygen demand(COD)of the sludge.Anaerobic digestion performance was evaluated based on indicators such as methane yield,volatile solids(VS)removal rate,and organic matter conversion efficiency.Compared with the control group,the yeast fermentation group and the combined alkaline pretreatment and yeast fermentation group achieved increases in methane production of 11.8％and 15.4％,respectively.The VS removal rate was similar across all groups(approximately 45％),while the organic matter conversion efficiency for the yeast fermentation group and the combined group increased by 5.80％and 9.30％,respectively.Furthermore,analysis of the electron transfer coefficient(ETC)revealed the intrinsic mechanism of system enhancement.Compared to the control group,the discharging ETC in the yeast fermentation group and the combined pretreatment group increased by 11.1％and 16.8％,respectively.Similarly,the charging ETC in these groups increased by 11.1％and 17.3％,respectively.Finally,microbial community analysis indicated that Methanothrix soehnenii GP6 and Fastidiosipila sanguinis were enriched in the combined pretreatment group,suggesting their potential involvement in DIET.

Abstract:This study investigates the pyrolysis characteristics of reed bamboo and red fir wood to predict their fast pyrolysis product yields.Initially,the physicochemical properties of the raw biomass,including their thermogravimetric behavior,were analyzed.Fast pyrolysis experiments were subsequently performed in a horizontal fixed-bed reactor to examine the influence of temperature,residence time,and feedstock particle size on the yields of solid,liquid,and gaseous products.Finally,a neural network-based model was developed to rapidly and accurately predict the three-phase product yields under various reaction conditions,integrating data from this study with previously reported findings for different biomass types.The results reveal that the pyrolysis of reed bamboo and red fir wood proceeds through four main stages:drying;decomposition of hemicellulose and cellulose;decomposition of lignin;and subsequent low decomposition of the char residue.During the primary decomposition stage,macromolecules like cellulose break down into smaller molecules,with levoglucosan as a major product.As the pyrolysis temperature increases from 350 to 650℃,the solid char yields for both biomass types decrease significantly.At higher temperatures,secondary cracking of pyrolysis vapor is intensified,leading to a lower liquid yiled and a higher gas yield due to the formation of non-condensable gases.Furthermore,extending the pyrolysis residence time enhanced the extent of reaction,promoting further cracking of chemical bonds within the char matrix and residual polymeric materials,thereby releasing more volatile gases.Consequently,the solid yield decreases and the gas yield increases.Additionally,an increase in feedstock particle size impedes intra-particle heat transfer,resulting in incomplete pyrolysis.As a result,higher solid char yields and lower liquid and gas yields are observed,as the particle core does not reach the optimal pyrolysis temperature.An artificial neural network(ANN)model was developed using a combined dataset comprising 28 experimental runs from this study and 62 data points from the literature.The data were split into training and testing sets with a 7∶3 ratio.The model architecture comprised a single hidden layer with 14 neurons,utilizing the logistic-sigmoid activation function.The RMSprop optimizer was employed for training,with a learning rate of 0.000 9 and a smoothing parameter of 0.9.The developed ANN model demonstrated high accuracy,with regression coefficients(R)for the predicted solid,liquid,and gas yields at 0.971,0.966,and 0.974,respectively.When validated against the experimental data from this study,the average relative errors between the predicted and actual yields for the three phases were 5.25％,5.44％,and 5.23％,respectively,confirming the model's strong predictive capability.

Abstract:To rapidly predict changes in residual oil content after the pyrolysis of oily sludge and to guide the optimization of pyrolysis process parameters,this study collected a dataset comprising 228 samples and employed machine learning methods to predict the oil content in the oily sludge pyrolysis residues.Several factors were used as input variables,including final pyrolysis temperature,pyrolysis time,heating rate,nitrogen flow rate,initial oil content,water content,and residue content of the oily sludge.The oil content in the pyrolysis residues was used as the output variable.Methodologically,this study applied four advanced machine learning algorithms in an innovative manner:Gradient Boosting Decision Trees(GBDT),eXtreme Gradient Boosting(XGB),Support Vector Machines(SVM),and Random Forests(RF),to construct high-precision prediction models for the oil content in pyrolysis residues.These models were rigorously trained and cross-validated on a dataset comprising 228 samples to ensure their generalization ability and prediction accuracy.The results showed that the coefficients of determination(R2)for the GBDT,XGB,SVM,and RF models on the test set reached 0.871 6,0.866 7,0.835 6,and 0.917 1,respectively,providing initial validation of the effectiveness of these machine learning models in predicting oil content in oily sludge pyrolysis residues.To further improve the predictive performance of the models,this study introduced the Bayesian Optimization Algorithm(BOA)to fine-tune the hyperparameters of the models.After BOA optimization,the R values of the four models significantly increased to 0.901 2,0.900 1,0.896 5,and 0.920 4,respectively.Among them,the Bayesian-Optimized Random Forest(BO-RF)model exhibited the best predictive performance,demonstrating high consistency on the test set and extremely high accuracy in predicting the dynamic trends of oil content in oily sludge pyrolysis residues.Furthermore,through feature importance analysis,it was found that the final pyrolysis temperature,initial oil content in the sludge,and pyrolysis duration were the most critical factors influencing the oil content in the residues.In summary,by introducing advanced machine learning algorithms combined with a Bayesian optimization strategy,this study successfully constructed high-precision prediction models for the oil content in oily sludge pyrolysis residues.The BO-RF model,in particular,offers an effective and accurate approach for predicting oil content.This achievement contributes to enhancing the pyrolysis process of oily sludge,boosting resource utilization efficiency,and advancing sustainable waste treatment methods.It provides strong support for the pyrolysis treatment of oily sludge at both theoretical and practical levels,opening up new perspectives and approaches for environmental management and resource recovery research.

Abstract:CO2-enhanced oil recovery(CO2-EOR)improves oil displacement efficiency and facilitates effective CO2 sequestration.However,in practice,the minimum miscibility pressure(MMP)between CO2 and crude oil often exceeds the formation's fracture pressure.Thus,reducing the MMP is critical for enhancing oil recovery efficiency.This study experimentally investigates how alcohol-treated CO2 affects the interfacial tension(IFT)and MMP in CO2-alkane systems.Initially,the effects of pressure and temperature on the IFT of the CO2-n-hexadecane system were systematically examined.Results show that,at constant temperature,IFT decreases with increasing pressure due to the enhanced solubility of CO2 in n-hexadecane.Below 3 MPa,IFT decreases with rising temperature,whereas above 3 MPa,it increases.This highlights that IFT is influenced by both temperature and CO2 solubility.Comparative analysis reveals that CO2-n-hexadecane systems exhibit consistently higher IFT than CO2-n-dodecane systems.This is attributed to the longer carbon chain and stronger intermolecular forces of n-hexadecane,which reduce its miscibility with CO2.Subsequently,the effect of alcohol-treated CO2 on IFT was assessed.In the high-pressure region(＞6 MPa),CO2 treated with ethanol or isopropanol significantly reduced IFT,while the effect was negligible at lower pressures.This behavior stems from increased CO2-alcohol solubility at high pressure,enhancing alcohol interaction at the interface and reducing IFT.The CO2-n-dodecane system treated with ethanol also demonstrated notable IFT reduction,with a progressive decrease as pressure increased.The absence of abrupt changes suggests a steady interface modification,facilitated by ethanol's high solubility in n-dodecane and the shorter carbon chain of n-dodecane,which promotes alcohol adsorption and alignment at the interface.Finally,MMPs of the CO2-n-hexadecane system under different treatments were determined via linear extrapolation.Alcohol-treated CO2 notably reduced MMP,especially at elevated temperatures.At 70℃,ethanol and isopropanol treatments reduced MMP by 20.16％and 24.28％,respectively,whereas at 100℃,the reductions were 13.74％and 22.67％.Isopropanol was more effective than ethanol,likely due to its longer hydrocarbon chain and stronger interfacial adsorption capacity.This study elucidates the mechanisms by which alcohol-treated CO2 interacts with alkane systems to reduce IFT and MMP,offering valuable experimental insights for optimizing CO2-EOR applications.