At room temperature(5~35 ℃),rare earths,fluorine and iron in Pr-Nd metal polished waste were recovered and recycled by screening,wet magnetic separation,acidification,oxalic acid precipitation and roasting.The obtained Pr-Nd oxide and Pr-Nd fluoride exhibit high purity,and the recovery rates of rare earths,fluorine,and iron are also high.The recovery rate of rare earths exceeds 96%,fluorine 90%,and iron 93%.The waste acid produced in the process of recovering the acid insolubles and the dust and washing water produced in the process of washing sieve oversize can be recycled in the treatment of the next batch.The whole process not only realizes the secondary resource utilization,but also produces no waste residue,saving the production costs and solving the problem of waste residue in environmental protection.The recovery and treatment method of Pr-Nd metal polished waste proposed by this process is simple and easy to operate and industrialize.

The existing processes of rare earth metal smelting are analyzed.Molten salt electrolysis with fluoride system,calcium thermal reduction and lanthanum thermal reduction can be used to produce different rare earth products in accordance with their properties.A feasible scheme for automatic feeding and discharging in the electrolysis process is proposed.A complete set of equipment consisting of a bale breaker,automatic feeding equipment and control system is adopted in the feeding process,realizing mechanized charging,automatic feeding,and information-based statistical analysis.The vacuum siphon or manipulator could be used for the discharging process.The treatment scheme of “three wastes”,especially the waste gas,is proposed with nearly all dust being recovered,fluorine being solidified into calcium fluoride for comprehensive utilizayion,and waste gas being emitted in compliance with standards.

In response to the problems of large differences in raw materials,long process flow,low vanadium recovery rate(mostly below 60%),and high cost in extracting vanadium from stone coal boiling roasting materials,a process route of mixing acid,curing and leaching-oxidation neutralization-ion exchange-vana-dium precipitation with ammonium salt-calcination was adopted to extract vanadium.The experimental results show that under the conditions of sulfuric acid dosage of 20% of the raw material weight,curing temperature of 100 ℃,and curing time of 6 h,the vanadium leaching rate of stone coal boiling roasting material reaches 90.2%.The final product V₂O₅ powder quality is stable and reliable,which reaches the level of industry standards.This process has a short process flow,low engineering construction investment,high vanadium recovery rate,and low vanadium smelting cost,achieving good economic and technical indicators.

The concentrated sulfuric acid curing leaching was used in extracting vanadium from Xiangxi stone coal,the effects of sulfuric acid dosage,decarbonization temperature,curing time,curing temperature,and leaching time on leaching rate of vanadium were researched by single factor experiments and orthogonal experiments.The experiment results show that the leaching rate of vanadium is 83.2% under the conditions of decarbo-nization temperature of 600 ℃,sulfuric acid dosage of 24%,curing temperature of 180 ℃,curing time of 8 h and leaching time of 8 h.The vanadium extraction process does not produce harmful gases and reduces environmental pollution.

Taking the leaching solution of retired ternary lithium-ion battery materials as the research object,the process of iron removal from the leaching solution was studied.The effects of the terminal pH value of the leaching solution after iron removal,reaction time,reaction temperature,and oxidant addition coefficient β(n_{NaClO_(3})∶n_Fe) on the removal of iron from the leaching solution of ternary lithium-ion battery materials were investigated.The optimized process parameters are as follows:terminal pH value 4.5,reaction time 2.5 h,reaction temperature 85 ℃,and β=1.1.Under these optimized conditions,the iron removal rate is greater than 98%,and nickel content in slag is less than 0.2%.The research results provide a scientific basis for the comprehensive utilization of retired ternary lithium-ion battery materials.

The effects of reaction temperature,H₂SO₄ concentration,SO₂ flow rate and reaction time on the preparation process of Se by SO₂ reduction of SeO₂ were investigated,the kinetics of the process was stu-died,and the optimal process conditions and kinetic restrictive control links were obtained.The results show that under the conditions of the reaction temperature of 40 ℃,H₂SO₄ concentration of 1 mol/L,SO₂ flow rate of 60 mL/min,and reaction time of 30 min,the reduction rate of Se reaches 99.73%,preparing Se with a purity of 99.85%.By controlling the conditions,different forms of Se can be obtained:amorphous red Se at low temperatures and well-crystallized black Se at high temperatures.The preparation process of Se by SO₂ reduction of SeO₂ conforms to the Avrami model,controlled by diffusion with an apparent activation energy of 1.98 kJ/mol,and described by the kinetics equation of-ln(1-X)=0.178×e^-238/Tt^1.276.

Nano-sized tungsten carbide powder is an important raw material for the preparation of ultrafine nano-cemented carbide.However,due to its large specific surface area,agglomeration is easy to occur,hindering the full play of its inherent excellent performance.To reduce the agglomeration of the nano-sized tungsten carbide powder,two surfactants,Triton X-100 and OP-10,were used for dispersion.Sedimentation experiment,absorbance test,particle size analysis and transmission electron microscope were used to study the dispersion performance of nano-sized tungsten carbide in absolute ethanol.The results show that when the mass fractions of Triton X-100 and OP-10 are 2% and 1.5% with ultrasonic times of 30 min and 50 min,respectively,the dispersion effect of the nano-sized tungsten carbide suspension reaches the best.Under the same ultrasonic time and with the same concentrations,OP-10 exhibits better dispersion effect than Triton X-100.Infrared analysis shows that Triton X-100 and OP-10 mainly reduce the agglomeration by adsorbing onto the surface of nano-sized tungsten carbide.

The NiMoS₄@MoS₃ composite electrode material based on nickel foam was successfully prepared using the three-step hydrothermal method.The phase structure and micromorphology of the electrode material were studied by X-ray diffraction(XRD) and scanning electron microscope(SEM) and its electrochemical performance was tested by cyclic voltammetry(CV),galvanostatic charge and discharge(GCD),and electrochemical impedance spectroscopy(EIS).The results show that charge and discharge duration of the NiMoS₄@MoS₃ electrode reaches 5 600 s with specific capacitance of 4 744 mF/cm² at 1 mA/cm².In addition,the composite electrode shows relatively symmetrical redox peaks in the CV curve and symmetrical charge and discharge platform in the GCD curve,indicating its excellent charge and discharge efficiency and stability.The research provides a new insight for the design and preparation of high-performance electrochemical energy storage materials.

Using La(NO₃)₃·6H₂O and H₃BO₃ as raw materials,C₂H₅NO₂ as combustion agent,and Nd(NO₃)₃·6H₂O as modifier,Nd³⁺ doped LaBO₃ phosphors were synthesized by solution combustion method.The products were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM),ultraviolet-visible diffuse reflection spectrum(UV-Vis DRS),and fluorescence spectrum(PL).The results show that the prepared powders are all orthorhombic lanthanum borate and the phosphors prepared under the optimized conditions of calcination temperature of 875 ℃ and Nd³⁺ doping amount of 3% have the best luminescent performance,showing good light absorption performance in both ultraviolet and visible light regions and emitting blue-green light,which can be widely used in the fields of laser illumination and LED lighting.

Taking the Bayan Obo rare earth tailings as raw materials,alkali melt-activated rare earth tailings as silicon source and sodium metaaluminate as aluminum source,A-type molecular sieve was direct synthetized by hydrothermal method to realize the secondary utilization of rare earth tailings.The effects of the amount of alkali addition on the silicon activation of rare earth tailings and the amount of sodium metaaluminate addition on the synthesis of the molecular sieve were studied,and the phase composition,micro-morphology,and pore structure of the synthesized molecular sieve were analyzed by XRF,XRD,SEM-EDS,and BET.The results show that when the alkali-ore mass ratio is 3,the tailings are fully activated and the crystalline silicon species are transformed into soluble active Si element,of which the dissolution rate is 84%.Under the template-free condition,the A-type molecular sieve can be synthesized from alkali melt-activated rare earth tailings with different SiO₂/Al_2O₃ molar ratios,presenting a regular spherical structure with large specific surface area and pore volume,with the pore structure in microporous form.When SiO₂/Al₂O₃ molar ratios is 1.5,the synthesized A-type molecular sieve has the maximum specific surface area of 215.5 m²/g.Fe,Mg and Si in the tailings react with Al to form ferric aluminum anthophyllite impurities,which reduce the crystallinity of the A-type molecular sieve.