Lithium-ion batteries as energy storage devices have been widely used in the field of new energy vehicles.In the context of the global energy crisis and the continuous increase in the ownership of new energy vehicles，lithium-ion batteries have also begun to retire in large numbers，which has brought huge economic pressure and environmental burden to society.Therefore，the use of efficient and clean recycling process for waste lithium-ion batteries has become the focus of domestic and foreign scholars.In this paper，the wet recovery process of waste lithium-ion power batteries from pre-treatment，leaching of valuable metal ions from cathode materials and separation of valuable metal ions from leaching solution was reviewed.The leaching process included acid leaching，ammonia leaching and biological leaching.The separation of valuable metals from leach solution included ion exchange process，solvent extraction process，salting-out process，chemical precipitation process and electrochemical process.At the same time，it was also pointed out the development direction of using wet recovery process to recover valuable metals of waste lithium ion batteries.

The current applications of hydrometallurgical and pyrometallurgical technologies in the treatment of fluorine-containing solid wastes such as carbon slag，spent pot lining and aluminum electrolytes were reviewed.The advantages and disadvantages of these two technologies were outlined.Hydrometallurgical treatment involved selecting appropriate reagents to leach fluorine，aluminum，and other elements into the liquid phase under specific conditions，and then preparing aluminum fluoride products through steps such as precipitation and calcination.However，the quality and properties of the products still needed further improvement.Pyrometallurgical treatment focused on converting fluorine into fluorides under high-temperature conditions to achieve fluorine recovery.However，the corrosion of equipment under high-temperature conditions limited its large-scale application.It was of great significance for the continuous development of safe，effective，and high-value utilization technologies for fluorine-containing solid wastes in China's aluminum electrolysis industry.Current work was mainly concentrated on using chemical methods to extract and utilize valuable elements from fluorine-containing solid wastes.In the future，it was necessary to explore other new treatment methods，develop a wider variety of products，and achieve low-cost and large-scale utilization of fluorine-containing solid wastes.

The long-term storage of phosphogypsum is increasingly harmful to the ecological environment and human health.Its recycling is one of the important ways to alleviate such problem.The physical and chemical properties of phosphogypsum and its impact on environment were summarized.On this basis，the research status of phosphogypsum in the fields of traditional building materials，agriculture，chemical industry，environmental protection，and the resource utilization of high value-added products such as nano whiskers，phosphorus and fluorine chemicals were introduced.The reasons that hindered the large-scale utilization of phosphogypsum lay in its low utilization level，lack of systematicness，and imbalance between economic and environmental benefits.In addition，the influence mechanism of impurities in phosphogypsum was not completely clear，and its separation and purification needed to be further studied.Meanwhile，the large-scale application of such technology still needed to improve products performance and reduce costs.Also，it was necessary to carry out research on low-carbon phosphogypsum recycling technology and process，which was consistent with the goal of carbon neutralization.

In ammonia flue gas desulphurization，it is very important to determine the effect of liquid phase impurities on the crystallization of （NH₄）₂SO₄.In this paper，the effects of Fe³⁺ and Al³⁺ on the crystal shape and particle size distribution of （NH₄）₂SO₄ were studied by SEM，XRD and particle size analysis，and the effect mechanism of Fe³⁺ and Al³⁺ on the crystallization of （NH₄）₂SO₄ was revealed by molecular dynamics simulation.The results showed that when the concentration of Fe³⁺ in （NH₄）₂SO₄ solution was less than 200 mg/L or the concentration of Al³⁺ was less than 400 mg/L，the crystallized crystals existed in a regular prismatic shape with average particle sizes of about 168 µm and 169 µm，respectively，the uniformity was relatively high.When the concentration of Fe³⁺ in （NH₄）₂SO₄ solution was higher than 200 mg/L or the concentration of Al³⁺ was higher than 400 mg/L and continues to increase，the crystal shape of （NH₄）₂SO₄ crystal changes to sheet，and the average particle size and uniformity of （NH₄）₂SO₄ crystal showed a decreasing trend.Compared with Al³⁺，the increase of Fe³⁺ concentration had a greater inhibitory effect on the crystallization of （NH₄）₂SO₄.The molecular dynamics simulation showed that the adsorption energy of Fe³⁺/Al³⁺ and （NH₄）₂SO₄ crystal （020） surface was more negative than that of （NH₄）₂SO₄ molecule and （NH₄）₂SO₄ crystal （020） surface，and （NH₄）₂SO₄ was easy to form sheet.With the increase of Fe³⁺/Al³⁺ concentration，the pH of （NH₄）₂SO₄ solution was decreased，the metastable zone of solution was narrowed，resulting in the decrease of supersaturation，and ultimately the crystal size.Therefore，the crystallization properties of （NH₄）₂SO₄ could be reasonably regulated by controlling the concentration of Fe³⁺ and Al³⁺.

The morphology and size of nanozymes significantly affect their mimetic enzyme catalytic activity.In order to improve the substrate catalytic activity of CeO₂ as a nanozyme and broaden its application range，using cerium nitrate as the precursor and citric acid as the structure-directing substance，CeO₂ quantum dots（CeO₂ QDs） with good crystallinity and small particle size were prepared by one-pot hydrothermal method.The small size effect and rich surface defects of CeO₂ QDs could expose more substrate contact active sites，thereby endowing it with oxidase-liked activity.The optimal CeO₂ quantum dot nanozyme，CeO₂ QDs-6，with the maximum particle size distribution at （4.0±0.6） nm，showed better oxidase enzyme kinetic characteristics than natural enzymes，with the Michaelis kinetic constant as low as 0.165 mmol/L and the maximum reaction rate up to 9.11×10^-8 mol/（L·s）.Based on the antioxidant activity of ascorbic acid，a rapid，sensitive and highly selective CeO₂ QDs-6 ascorbic acid colorimetric detection probe was constructed.Under the optimized conditions，this probe had good ascorbic acid detection performance in the linear range of 1.0~8.0 μmol/L，the lowest detection limit was 148 nmol/L，and showed certain feasibility in the detection of milk samples.

Rice husk ash，a by-product of rice after combustion，mainly contains amorphous silica.Resource recovery and reprocessing of rice husk ash can not only reduce the environmental burden caused by the accumulation，but also obtain the A-type zeolite with high value.Using rice husk ash as silica source，the A-type zeolite was synthesized through hydrothermal reaction.The effects of Si/Al ratio［n（SiO₂）/n（Al₂O₃）］，NaOH solution concentration，reaction temperature and reaction time on the phase composition and microscopic morphology of the synthesized zeolite samples were comprehensively investigated using X-ray diffraction（XRD） and scanning electron microscope（SEM）.The results indicated that the A-type zeolite with single crystal phase，high crystallinity and well-defined cubic morphology could be obtained under the conditions of n（SiO₂）/n（Al₂O₃） of 1.4，NaOH solution concentration of 2.5 mol/L，reaction temperature of 100 ℃ and reaction time of 6.0 h.The A-type zeolite synthesized under optimal hydrothermal conditions was characterized using fourier transform infrared spectrometer（FT-IR），thermogravimetric analysis（TG-DTA） and N₂ adsorption-desorption test.The results showed that the hydrothermal product A-type zeolite exhibited certain thermal stability，had uniform pore size and specific surface area of 44.468 m²/g，making it potentially useful in fields such as adsorption，catalyst carrier.

In order to build a new material with high efficiency for nitrogen removal，iron species were introduced into the sol-gel process in this work.SiFe-x，a ferrosilicon adsorption material with iron content of 3%~5%（mass ratio），was successfully prepared，and its adsorption and denitrification performance was studied through a fixed bed.The ferrosilicon adsorption material was characterized and analyzed using characterization methods such as X-ray diffraction（XRD），X-ray fluorescence spectrometer（XRF），nitrogen adsorption isotherm，and temperature programmed ammonia adsorption（NH₃-TPD）.The material was compared with amorphous silicon aluminum materials with relatively similar elemental composition and pore size to investigate the effect of acidity on nitride adsorption and removal performance.The results indicated that the adsorption capacity of nitrides was positively correlated with the amount of acid，but higher acid strength could make it difficult to remove nitrides，thereby reducing the regeneration efficiency of the adsorbent.SiFe-4 material had a high nitrogen saturation adsorption capacity（20.8 mg/g），and after 4 cycles of adsorption regeneration，it still retained an adsorption capacity of 15.4 mg/g，with a regeneration efficiency of 74.04%.The appropriate amount of acid and relatively low acid strength enabled SiFe-4 to balance adsorption capacity and regeneration ability，and outperform traditional mesoporous/microporous inorganic adsorption materials currently reported.It had certain application potential in the field of adsorption denitrification.

In order to study the influence of the preparation process on the polishing performance of rare earth polishing powder，cerium chloride was used as the cerium source and ammonium bicarbonate was used as the precipitant to prepare the precursor of rare earth polishing powder by the parallel addition method.This precursor could get the final polishing powder product after high temperature roasting treatment.During the study，the preparation parameters were carefully explored，including the concentration of rare earth solution，adding rate，stirring rate，precipitation temperature，the amount of polyethylene glycol dispersant（PEG-1000） used，aging temperature and aging time.After systematic experiments and analyses，the optimal preparation conditions were determined：the concentration of the rare earth chloride solution was 225 g/L，the drop acceleration rate was 2.5 mL/min，the stirring rate was 500 r/min，the precipitation temperature was 45 ℃，the amount of dispersing agent was 2%，the aging temperature was 45 ℃，and the aging time was 4 h.Under the optimal conditions，the particle size D₅₀ of the precursor was 1.229 μm，and the particle size D₅₀ of the final polishing powder was 1.087 μm.In addition，the homogeneity R of the polishing powder reached 1.85，and the polishing etching amount reached 0.473 2 mg/（cm²·min）.Compared with the traditional method of producing polishing powder，the present method eliminated the process of ball milling or air flow pulverization，and directly obtained the rare earth polishing powder that met the customer's demand.The preparation process of this research not only improved the production efficiency，but also optimized the quality and performance of the product，which was of great practical significance and application value for industrial applications.

In order to enhance the industrial application value of Stellera chamaejasme Linn and expand the utilisation space of cesium salt resources in the salt lake，Stellera chamaejasme Linn was activated with cesium chloride as the activator and chemical activation method was used to prepare Stellera chamaejasme Linn activated carbon with uniform pore size.Iodine and methylene blue were used as adsorbents to test the adsorption performance of activated carbon.The experiments were carried out by fully automated specific surface area analyser（BET），X-ray diffractometer（XRD），Raman spectrometer，scanning electron microscope（SEM），Fourier-transform infrared spectroscopy（FT-IR），and X-ray electron spectroscopy（XPS） to examine the specific surface area of the activated carbon，the surface morphology，the surface functional groups and the pore structure.The test results showed that the wolfsbane activated carbon prepared in this study was an amorphous activated carbon.The surface functional groups of the activated carbon were mainly carbon-containing and oxygen-containing functional groups.The specific surface area of this activated carbon was 549.42 m²/g，the iodine adsorption value was 530.4 mg/g，the methylene blue adsorption value was 133.7 mg/g，and the predominant pore size was 1.01 nm，and the pore volume was 0.25 cm³/g，and it was microporous activated carbon，and the carbon yield was 17.71%.This study provided a theoretical basis for the utilisation of Stellera chamaejasme Linn resources and cesium salt resources in Qinghai.

The effects of cations（Na⁺，Ca²⁺，Mg²⁺） on crystal structure，settling performance，dewaterability and ion exchange properties of the chloride removal precipitates were studied in order to improve their recovery potential.It was found that in terms of crystal structure，the FS layers formed in MgCl₂ and CaCl₂ solutions were more widely spaced，the FS was more unstable，and the interlayer ions were prone to ion exchange.In addition，the FS products in MgCl₂ showed the largest grain size，which could be attributed to the grain boundaries with doping of Mg²⁺ to change the grain boundary mobility and thereby the local grain growth rate by several orders of magnitude.In addition，differences in FS settling performance produced by the three solutions existed due to differences in Zeta potential.The dosing of PAM could increase the settling velocity by increasing the average particle size of the precipitates，but it did not improve the settling performance much.PAM significantly improved the settling performance of the chloride removal sludge of MgCl₂.The addition of 200 mg/L PAM to the dechlorinated precipitate in MgCl₂ solution reduced SV₁₂₀ from 100.0% to 43.0%.Among the three mechanical dewatering methods，vacuum，plate and frame，and centrifugal，the chloride removal sludge of NaCl was suitable for vacuum dewatering，while the dechlorinated sludge of CaCl₂ and MgCl₂ was suitable for plate and frame dewatering，and the addition of PAM could reduce the bound water content of the sludge cake.

Aiming at the agglomeration and sintering problems generated during the roasting process of ultrafine cerium oxide precursor，a new idea of using multifunctional reticulated framework polyethylene glycol（PEG） to prepare the precursor cerium carbonate salts of ultrafine cerium oxide powder was proposed，and the thermal decomposition process and kinetic analysis of the precursor were studied by using the TG-DSC thermal analyser and the effect of the roasting temperature，the rate of heating and the holding time on the particle size，morphology and crystal structure of the ultrafine cerium oxide were investigated.The effects of temperature，morphology and crystal structure were investigated.The experimental results showed that the thermal decomposition of the precursor was divided into three stages.The first stage at 25~258 ℃ was the stage of demineralised water，with a weight loss of 2.94%.The second stage was at 258~422 ℃ with a weight loss of 11.86%，and the precursors Ce（CO₃）₂O·H₂O and Ce₂（CO₃）₂O·H₂O were decomposed into CeCO₃OH and CeO₂.The third stage was at 422~630 ℃，the residual PEG was volatilised by high temperature oxidative decomposition，and part of the rare earth cerium carbonate salt CeCO₃OH was decomposed to produce perfectly crystalline cerium oxide with a weight loss of 10.29%.Using the Freeman-Carroll method，the activation energy（E） of the second reaction stage was determined to be 166.68 kJ/mol，and the number of reaction stages（n） was 19.27.The activation energy（E） of the third reaction stage was determined to be 101.95 kJ/mol，and the number of reaction stages（n） was 14.75.It was found that under the roasting system with a roasting temperature of 1 000 ℃，a temperature rise rate of 300 ℃/h and a holding time of 3 h，the mean particle size D₅₀≤0.50 µm of the ultrafine ceria powder could be obtained.

The electrolyte is crucial to the energy density and stability of lithium-ion batteries.However，the lithium salt commonly used in commercial electrolytes，lithium hexafluorophosphate（LiPF₆），is prone to decomposition at temperatures above 60 ℃，which increases the risk of combustion or explosion of the battery under extreme high temperatures.A series of novel flame-retardant electrolyte systems were developed，which used lithium hexafluorophosphate（LiPF₆） and lithium difluorophosphate（LiPO₂F₂） as lithium salts，with ethylene carbonate（EC） and diethyl carbonate（DEC） as mixed solvents，and trimethyl phosphate（TMP） as a flame-retardant additive.The flame-retardant performance was evaluated by self-extinguishing time and infrared spectroscopy analysis，the thermal stability was analyzed by differential scanning calorimetry-thermogravimetric（DSC-TG） experiments，and the electrochemical performance was assessed through electrochemical charge-discharge testing，cycle performance testing，and impedance testing.The results showed that the electrolyte with 3% TMP added did not spread when burned，demonstrating excellent flame-retardant properties.The addition of the lithium salt LiPO₂F₂ to the electrolyte had improved the thermal stability of the electrolyte.The results indicated that the electrolyte（LiPF₆+LiPO₂F₂）+（EC+DEC）+3%TMP in a LiCoO₂/Li battery achieved a first discharge specific capacity of 132.9 mA·h/g and a coulombic efficiency of 99.63% at 25 ℃ and 0.5C rate.After 100 cycles at 80 ℃ and 1.0C rate，the discharge specific capacity was 110.8 mA·h/g，with a capacity retention rate of 92.49%.

Chromium slag is the waste residue produced in the process of chromite production，which contains water-soluble and insoluble hexavalent chromium and has potential harm to the ecological environment and human health.Therefore，it is of great significance to study the efficient and low-cost detoxification process of chromium slag for realizing its resource utilization and green development.In this paper，an efficient detoxification process was proposed for the pyrolysis of chromium slag and rice husk.Chromium slag and agricultural waste rice husk were mixed for pyrolysis，and Cr（Ⅵ） in chromium slag was reduced to non-toxic trivalent chromium［Cr（Ⅲ）］ by using reducing gas and biochar generated by the pyrolysis of rice husk.The effects of rice husk/chromium slag mass ratio，pyrolysis temperature，pyrolysis time and pyrolysis heating rate on the detoxification effect of chromium slag were investigated.The results showed that under the conditions of rice husk consumption of 1.00 g/g，pyrolysis temperature of 500 ℃，pyrolysis time of 20 min and heating rate of 10 ℃/min，Cr（Ⅵ） content in chromium slag was decreased from 1 058.85 mg/kg to 52.54 mg/kg.Compared with the pyrolysis process of powder mixture，the pyrolysis process of chromium slag-rice husk compendization reduced the Cr（Ⅵ） content in chromium slag to 52.54 mg/kg.The detoxification rate was increased to 96.74%，and the chromium slag after detoxification reached the Cr（Ⅵ） hazardous waste identification standard stipulated in the national standard GB 5085.3—2007“Identification standards for hazardous wastes—Identification for extraction toxicity”.X-ray diffraction（XRD） analysis was conducted on the chromium slag after detoxification，and the results showed that the material was the same before and after detoxification.The research results could provide a new technical idea for the harmless treatment of calcined chromium slag without calcium.

The magnesium hydroxide/graphene oxide composites（MG） were prepared by direct precipitation method using self-made graphene oxide（GO） dispersion as solvent，magnesium sulfate heptahydrate as precursor，and ammonia as precipitant，and the composites were characterized by scanning electron microscopy with energy dispersive spectrometer（SEM-EDS），automatic specific surface and pore size analyzer（BET） and Fourier transform infrared spectrometer（FT-IR）.The experimental results showed that the specific surface area of MG products prepared by direct precipitation was 140.55 m²/g，which was larger than that of magnesium hydroxide（MH），and the open pores generated by MG flower-like structure were larger，and the Zeta potential of MG was 11.9 mV，which was conducive to the adsorption of methyl orange（MO） by MG.At the same time，the effects of MO wastewater concentration，reaction time and pH value on the MO adsorption performance were investigated，and the adsorption isotherm and adsorption kinetics of the MG adsorption process were analyzed.The adsorption experiments showed that when the pH was 7，the adsorbent dosage was 0.67 mg/mL，the adsorption time was 120 min，and the initial concentration of MO was 700 mg/L，the removal rate of MO was 97.63%，and the equilibrium adsorption capacity of MG reached 1 025.17 mg/g.The adsorption process was more in line with the quasi-first-order kinetic model，and the Langmuir model could better describe the adsorption process，and the maximum adsorption capacity was 1 297.16 mg/g.Therefore，the MG prepared in this paper could efficiently and rapidly adsorb and remove MO，and had certain potential in the treatment of printing and dyeing wastewater.

Considering the complex instrumentation and high operator requirements required for the determination of trace lead in zinc oxide produced by direct methods，a simple carrier coprecipitation pre-concentration-xylenol orange spectrophotometric method was proposed.By using strontium chloride as a carrier to precipitate and separate lead in sulfuric acid medium，then converting lead sulfate into lead carbonate with potassium carbonate，dissolving lead carbonate into lead ions with nitric acid and finally forming a purple red complex with xylenol orange，a spectrophotometric method for the determination of trace lead was established.The effects of solution pH，the concentration of chromogenic reagents and the interfering ions on the method were investigated.The results showed that the absorbance value of the generated complex was changed linearly with the concentration of lead ions.The linear concentration range was 1.45~14.49 μmol/L，the linear equation was ΔA=0.059 24c -0.017 15，and the correlation coefficient R² was 0.990 3.The relative deviation between the measured values of lead in direct zinc oxide obtained by this method and those obtained by atomic absorption spectroscopy was between -1.7% and -1.2%.Compared with the atomic absorption spectroscopy method specified in the current standard GB/T 4372.2—2014 “Direct method for chemical analysis of zinc oxide part 2：Determination of lead oxide content”，this method had the advantages of simple instrument and easy operation，and could be used for industrial promotion.

Graphitic carbon nitride supported nano-Ag（Ag/g-C₃N₄） composites were prepared by photoreduction method using AgNO₃ and g-C₃N₄ as precursors and polyvinylpyrrolidone as inhibitor.The Ag/g-C₃N₄ composites were characterized by X-ray diffraction（XRD），Fourier transform infrared spectroscopy（FT-IR），photoluminescence spectroscopy（PL），ultraviolet-visible diffuse reflectance spectroscopy（UV-vis DRS），transient photocurrent spectroscopy（TPC） and electrochemical impedance spectroscopy（EIS）.The crystal phase，functional groups，spectral absorption range，photoelectron-hole recombination and charge transfer resistance of Ag/g-C₃N₄ composites were systematically characterized and analyzed.The photocatalytic activity and stability of Ag/g-C₃N₄ composites under visible light were investigated by using methylene blue（MB） dye solution as the target substrate.The results showed that the construction of Schottky heterojunction between nano-Ag and g-C₃N₄ and the plasma resonance effect effectively promoted the separation of photoelectron-holes and broadened the spectral absorption range.The low charge mass transfer resistance promoted the charge transfer and effectively improved the photocatalytic activity.The degradation rate of MB dye solution by Ag/g-C₃N₄ composite reached 98.9% within 60 min of visible light irradiation，and the degradation rate of MB dye solution still reached 98.3% after 5 cycles，showing good stability.The coexistence of inorganic salt ions such as HCO₃^-，CO₃^2- and NO₃^- would affect the photocatalytic reaction.Highly active photoelectrons reduced O₂ to superoxide radicals，and the generated superoxide radicals were involved in the photocatalytic degradation of MB dye solution.

MoS₂/g-C₃N₄ composites were prepared by solvothermal method using MoS₂ and g-C₃N₄ as precursors.X-ray diffraction（XRD），N₂ adsorption-desorption（BET），UV-vis diffuse reflectance spectroscopy（UV-vis DRS），steady-state fluorescence spectroscopy（PL），transient photocurrent spectroscopy（TPC） and electrochemical impedance spectroscopy（EIS） were used to characterize the phase crystal form，specific surface area and pore size，spectral response range and intensity，photogenerated carrier recombination，visible light absorption and conversion ability and charge transfer resistance of MoS₂/g-C₃N₄ composites.MoS₂/g-C₃N₄ composite loaded photocatalytic concrete was prepared by cement coating method and applied to the removal of nitrogen oxides（NO _x ）.The results showed that the construction of heterojunction between MoS₂ and g-C₃N₄ broadened the spectral absorption range，improved the visible light absorption and conversion ability，realized efficient photogenerated carrier separation，and reduced the surface/interface resistance，which was conducive to the improvement of photocatalytic performance.The MoS₂/g-C₃N₄ composite loaded photocatalytic concrete showed excellent visible light removal NO _x activity and stability.The initial NO _x concentration of 200 mg/L，visible light irradiation for 180 min，MoS₂/g-C₃N₄ composite loading of 4% photocatalytic concrete showed the best NO _x removal activity，NO _x removal rate reached 84.63%，and the NO _x removal rate was only reduced by 2.85% after 10 cycles.The load of MoS₂/g-C₃N₄ composite blocked the partially fully connected and semi-connected pores of concrete，and the combination between aggregate and cement was closer，which reduced the water permeability of concrete and improved the compressive strength of concrete，showing good freeze-thaw resistance.