Rare earth resources are easy to produce low concentration rare earth solution or very low concentration rare earth wastewater in the process of development and extraction, which causes problems such as enrichment difficulties, environmental pollution and resource waste. The sources and characteristics of common low concentration rare earth solutions are introduced, and the principles and research progress of enrichment and recovery technologies of low concentration rare earth solutions in recent years are reviewed, including precipitation, solvent extraction, membrane separation and adsorption separation. The advantages and disadvantages of various enrichment and recovery methods are analyzed, future direction for technological development are also outlined.

The chemical composition, phase composition, and occurrence state of the main minerals in scheelite hydrochloric acid decomposition residue were systematically studied by a comprehensive mineral analysis system (TIMA), X-ray fluorescence spectrometer (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and other methods. The results indicate that the mineral particles in the hydrochloric acid decomposition residue of scheelite exhibit euhedral to subhedral to anhedral blocky structures. The primary phases identified are tungstic acid, fluorite, quartz, cassiterite, pyrite, molybdenite, arsenopyrite, and vivianite, with their respective mass fractions being 66.93%, 28.22%, 1.12%, 1.26%, 0.3%, 0.07%, 0.2%, and 0.04%. The grain size of tungstic acid is above 110 μm, while the grain sizes of fluorite, quartz, cassiterite, pyrite, molybdenite, and arsenopyrite are mainly concentrated between 5~20 μm. These particles are relatively fine and are either closely intergrown with tungstic acid or encapsulated by it.

In response to the issue of low cobalt leaching rate from oxidized copper-cobalt ore in the Kambove mining area of Congo(DRC), the mineralogical characteristics of the ore were analyzed by Mineral Liberation Analysis (MLA), polarized light microscopy, and Scanning Electron Microscopy (SEM). Based on the findings, leaching of cobalt from the ore with sodium pyrosulfite, Fe powder and SO₂ as reducing agents was studied. The influence of different reducing agents and dosage on the leaching effect was investigated. The resluts reveal that the primary copper minerals in the ore are pseudomalachite, malachite, and libethenite, while the main cobalt minerals are copper-cobalt-bearing manganese oxide and heterogenite. The gangue minerals predominantly consist of siltstone, quartz, sericite, and chlorite. The occurrence states of copper and cobalt in the ore are complex, with cobalt minerals being fine-grained and mostly occurring as inclusions. The theoretical leaching rate of cobalt is calculated to be 92.82%. Compared with the three reducing agents, the leaching effect of SO₂ is better. Under the optimal conditions of liquid volume to solid mass ratio of 3∶1, sulfuric acid dosage of 26.7 g/L, SO₂ amount at 1.7 times the theoretical amount, reaction temperature of 38 ℃, and reaction duration of 3 h, the cobalt leaching rate can reach 85.48%, approaching the theoretical maximum. The research results can provide both theoretical and technical support for the efficient utilization of cobalt resources in the Kambove mining area of Congo(DRC).

The recycling of lithium cobaltate from waste lithium-ion batteries is of great significance for alleviating resource shortage and reducing environmental pollution. L-malic acid/ascorbic acid system was used as leaching agent to recover cobalt and lithium from waste lithium cobaltate batteries. The effects of L-malic acid concentration, ascorbic acid concentration, liquid volume to solid mass ratio, reaction temperature and time on the leaching rates of cobalt and lithium in lithium cobaltate were investigated. The leaching mechanism was discussed through kinetic analysis and SEM characterization. The results show that the optimal leaching conditions are L-malic acid concentration of 0.2 mol/L, ascorbic acid concentration of 0.1 mol/L, liquid volume to solid mass ratio of 0.3 mL/1 mg, reaction temperature of 70 ℃, leaching time of 1 h. Under the conditions, the leaching rates of cobalt and lithium are above 98%. The kinetic analysis shows that the leaching process is mainly controlled by external diffusion. The method is efficient and environmentally friendly, and can provide an important technical reference for the green recovery of lithium cobaltate in waste lithium-ion batteries.

To address the issues of high energy consumption, low efficiency, difficult recovery and easy secondary pollution in the pyrometallurgical recovery of lithium from solid waste, the enhanced leaching of lithium from discarded lithium aluminum silicate (Li₂O-Al₂O₃-SiO₂, LAS) glass-ceramics samples using a mixed acid of HF/H₂SO₄ as the leaching agent was studied. The effects of liquid volume to solid mass ratio, sulfuric acid mass concentration, leaching temperature, leaching time, stirring speed and raw material particle size on the leaching rate of lithium were investigated, as well as the effects of liquid volume to solid mass ratio and leaching temperature on the leaching rates of aluminum and silicon. The kinetics of lithium leaching was also explored. The results show that under the optimal conditions of m(sample)∶ V(HF)∶V(H₂SO₄)=1∶2.5∶2, particle size of -0.074 mm, sulfuric acid mass concentration of 900 g/L, leaching temperature of 60 ℃, leaching time of 120 min, and stirring speed of 200 r/min, the leaching rate of lithium can approach 99%. Compared with other influencing factors HF volume to sample mass ratio and leaching temperature have a greater impact on the leaching rate of lithium. In contrast, the HF volume to sample mass ratio and leaching temperature have a greater effect on the leaching of aluminum than that of silicon. The leaching of lithium conforms to the unreacted core shrinkage model, with an apparent activation energy E_a of 39.53 kJ/mol, and the leaching rate of lithium is controlled by the chemical reaction-internal diffusion mixed control. The research results can provide theoretical guidance for the recovery and reuse of valuable elements from discarded LAS glass-ceramics.

Magnesium desulphurization wastewater in copper smelting industry contains high concentration of heavy metal ions such as Cu²⁺ and Mg²⁺. The traditional "neutralization—flocculation" process has problems, such as high treatment costs, waste of heavy metal resources and great risk of environmental pollution. In view of the above problems, the two-step precipitation method of "sulfurization and impurity removal—sodium hydroxide precipitation" was studied to recover copper and magnesium from desulfurization wastewater. Firstly, Cu²⁺ was preferentially precipitated by precise placement of sodium hydrosulfide (1.1 times the theoretical amount) to form CuS. Secondly, sodium hydroxide is used to adjust pH and promote Mg²⁺ to produce magnesium hydroxide efficiently. The effects of pH, NaHS dosage, reaction temperature, reaction time and stirring speed on the recovery of copper and magnesium hydroxide were investigated. The results show that the recoveries of copper and magnesium hydroxide can reach over 95% under the optimal conditions. The process technology is feasible, not only reduces the discharge of heavy metals, but also the CuS formed can be used as raw materials for copper smelting production, and magnesium hydroxide can be reused in desulfurization system. A circular economy model of "pollutant treatment—resource regeneration—process closed loop" is constructed, which can provide technical reference for the recycling of wastewater in metallurgical industry.

To address the issue of the efficient separation and recovery of vanadium and gallium from acidic solution system, the physicochemical differences between V(Ⅴ) and Ga(Ⅲ) in the V(Ⅴ)-Ga(Ⅲ)-H₂O system were systematically examined. Through metallurgical thermodynamic simulations, concentration predominance diagrams and species predominance diagrams were generated. Combined with alkali titration experiments and Raman spectroscopy analysis, the optimal lg[C]_T-pH range for vanadium-gallium separation was determined. The results indicate that the ideal pH range is between 2 and 3. In the range, vanadium ions will form large-nucleus anions of vanadium polyoxometalates with a molar fraction of more than 90%, while gallium mainly exists in the form of small-nucleus cations, increasing the chemical state difference between vanadium and gallium in acidic solution system and effectively avoiding the formation of large-nucleus gallium hydroxide precipitates, which is conducive to the separation and recovery of vanadium and gallium in the enriched solution system.

To address the issues of low conversion rate of aromatic amine monomers and high consumption of oxidants in polymerization reactions, the synthesis of polymeric Schiff base nanoparticles using m-phenylenediamine and glutaraldehyde as monomers through aldol-amino condensation reaction and their application in the adsorption and removal of Cu(Ⅱ) from wastewater were investigated. The morphology and structure of the products were characterized, and the thermal stability, acid stability, and adsorption mechanism of the material for Cu(Ⅱ) in wastewater were analyzed. The results show that the amino and aldehyde groups underwent nucleophilic addition to form a Schiff base structure, and the products are spherical nanoparticles with diameters ranging from 100 to 400 nm. The $\mathrm{C}=\mathrm{N}$ structure of the polymeric Schiff base has good thermal stability and acid stability, and the adsorption process of Cu(Ⅱ) conforms to the characteristics of the Langmuir isothermal adsorption model and the pseudo-second-order kinetic model. Under optimized conditions, the equilibrium adsorption capacity of the polymeric Schiff base for Cu(Ⅱ) is 116.30 mg/g, which is superior to that of common biochar, magnetic iron, and other polymer materials. The adsorption mechanism of the polymeric Schiff base for Cu(Ⅱ) is mainly electrostatic interaction and show strong coordination ability.

To address the issue of resource utilization of fluoride-containing waste residues generated during the treatment of fluoride-containing wastewater from semiconductor manufacturing enterprises, a chemical transformation method is employed to convert fluoride residues into calcium fluoride, thereby achieving resource utilization of these residues. The transformation effects of different agents, including ammonium fluoride, hydrofluoric acid-ammonium fluoride, and acetic acid-ammonium fluoride were studied, focusing on the effects of the type of transformation agent, solution pH and fluoride concentration on the calcium fluoride content in the transformed residue. The results indicate that transformation rate is the highest for converting fluoride residues into calcium fluoride using acetic acid-ammonium fluoride as the transformation agent yields. Under conditions of liquid volume to solid mass ratio of 10 mL/1 g, acetic acid dosage of n(CH₃COOH)/[2×n(CaCO₃)]=1.2, ammonium fluoride dosage of n(NH₄F)/[2×n(Ca)+4×n(Al)+6×n(Si)-n(F^-)_{fluoride residue})]=1.1, stirring time of 1 h and solution pH between 3.5 and 4.0, the calcium fluoride content can reach 88.72%, with transformation rate of 38.11%. The stepwise transformation using acetic acid-ammonium fluoride can eliminate the inhibiting effect of calcium fluoride formed on the surface of calcium carbonate on the further acid dissolution of the inner layer of CaCO₃, thereby increasing the content of CaF₂ and the transformation rate of the fluoride-containing residues. It can provide a technical reference for the resource utilization ot fluorine-containing slag.

Aiming at the difficulty in separating and recovering copper and cobalt from iron-cobalt-copper alloys, a process was proposed to leach iron and cobalt from the alloy with low-concentration sulfuric acid, separate copper, and then separate iron and cobalt by oxygen pressure hydrolysis to prepare iron oxide. The effects of various factors on the low-concentration acid leaching and the separation of iron by oxygen pressure hydrolysis were investigated. The results show that the leaching rates of iron and cobalt are 98.57% and 99.21%, respectively, and the copper leaching rate is only 0.3% after 4 times of leaching, under the conditions of sulfuric acid concentration of 30 g/L and liquid volume to solid mass ratio of 10∶1. Under the conditions of oxygen partial pressure of 0.4 MPa, reaction temperature of 180 ℃, stirring speed of 400 r/min and reaction time of 120 min, the hydrol ysate is mixture of FeOOH and Fe₂O₃, the iron content is more than 58%, the iron immersion rate was about 92%, the cobalt recovery rate is more than 99.5%, and the sulfuric acid yield is 96.41%. The method realizes the separation of iron, cobalt and copper in iron, cobalt and copper alloys, and recycles the sulfuric acid produced during the hydrolysis process, which can offset the sulfuric acid consumption in the leaching process and greatly increase the cobalt concentration in the solution. The results of this study have important reference value for the wet separation of iron-based alloys containing valuable metals such as copper and cobalt.

Biometallurgy has drawn the attention of the academic community in recent years as an effective way to achieve in-situ resource utilization (ISRU) in future interstellar bases. However, the mechanism of interaction between Streptomyces and minerals is still unclear under the effect of microgravity. To investigate this issue, simulating the leaching of elements from minerals by Streptomyces sp. R76 under microgravity using clinostats was studied. The results show that the simulated microgravity environment significantly accelerated Streptomyces sp. R76's development, differentiation, and metabolic capacity, which is primarily manifested in the early development and differentiation of aerial hyphae and spores, as well as the increase in organic acid. Streptomyces sp. R76 can produce lactic acid and citric acid at concentrations of 8.6 and 0.17 mmol/L under simulated microgravity and 5.8 and 0.04 mmol/L under gravity, respectively. When Streptomyces sp. R76 is co-cultured with minerals, the leaching rate of rare earth elements under simulated microgravity is 3‰, the leaching rate of calcium is 0.11‰.The leaching rate of rare earth elements under gravity is only 0.33‰ and the leaching rate of calcium is 0.08‰.The lactic acid and citric acid produced by Streptomyces sp. R76 under microgravity conditions are important factors in promoting the leaching of calcium, silicon, and rare earth elements from minerals.

Preparation of a novel imidazole-based functional resin using polystyrene-divinylbenzene copolymer as the support by chloromethylation reaction and imidazole modification was studied. Adsorption properties and selectivity for uranium by the resin from acidic waste solution were systematically investigated. The results show that the equilibrium adsorption capacity of imidazole-based functional resin is 58 mg/g for uranium containing acidic solution with pH=5 and uranium mass concentration of 90 mg/L. Additionally, the resin has good tolerance to nitrate and chloride ions and high adsorption selectivity for uranium. When the mass concentrations of nitrate and chloride are 20 g/L and 5 g/L, respectively, the uranium adsorption capacity can also reach 57 mg/g. When the mass concentrations of uranium and interfering ions in the solution were both 90 mg/L, the adsorption capacity of imidazole-based functional resin for uranium can reach 44 mg/g, while the adsorption capacity of any single interfering ion (A1³⁺, Ca²⁺, Mg²⁺, Zn²⁺, Mn²⁺, K⁺, Na⁺) is less than 5.4 mg/g. Furthermore, 0.5 mol/L HNO₃ is used as desorption, the desorption rate is 99.83%.When the imidazole-based functional resin is used to adsorb the actual uranium-containing acid waste liquid from a mine, the adsorption capacity of uranium is 40.2 mg/g, which is superior to that of common 201×7 anion exchange resin.

Solvent extraction is one of the main methods for rare earth separation and purification, but emulsification often occurs in industrial production due to improper control of process conditions. In order to solve the problem, the extraction of rare earth with the surfactant Span 80 as the regulator, P507 as the extractant and kerosene as the diluent was studied. The effects of aqueous pH, stirring speed and water-oil phase ratio on the extraction rate of Er³⁺ and the mass concentration of oil in the raffinate were investigated, and the process parameters were optimized by response surface method. The optimization results show that under the optimal conditions of aqueous pH=3.5, stirring speed of 130 r/min and water-oil phase ratio of 4∶1 for 5 min, the extraction rate of Er³⁺ can reach 95.42%, and the oil concentration in the raffinate is only 1.68 mg/L. The predicted value is in good agreement with the experimental results. The addition of Span 80 can effectively prevent emulsification, and the regulation effect is obvious.

In order to reduce the content of impurities such as Cu, Fe, Zn and reduce the loss of Ni in crude nickel sulfate solution of copper electrolysis by-products, the process of selective precipitation of copper by Na₂S₂O₃—deep extraction of zinc removal iron—evaporation crystallization was studied for deep purification of the solution, and the key process parameters were optimized. The results show that the precipitation rate of Cu can reach 99.89% and the loss rate of Ni is only 1.22% using Na₂S₂O₃ as precipitator under the optimum conditions of Na₂S₂O₃ excess coefficient of 2.0, solution pH of 5.0, reaction temperature of 85 ℃ and reaction time of 2 h. Using P204 as extracant, the extraction rates of Zn and Fe can reach 99.87% and 99.98%, respectively, and the loss rate of Ni is 2.24% under the optimal conditions of pH=3.0, P204 volume fraction of 25%, saponification rate of 50%, V_O/V_A=1.5/1, extraction temperature of 25 ℃ and extraction time of 10 min. Electroplating grade nickel sulfate crystal products are obtained by evaporation and crystallization of the deeply purified nickel sulfate solution. The quality can meet the national standard GB/T 26524—2023 Class Ⅱ indicators, and can be used as high-quality raw materials for electroplating and other industrial uses.

To address the issue of low ion exchange adsorption performance of natural zeolite caused by the presence of impurities, which makes it ineffective in adsorbing ammonia nitrogen in wastewater, the modification of natural zeolite using inorganic acids, inorganic bases, and inorganic salts was studied. The effects of different initial ammonia nitrogen mass concentration, zeolite particle size, zeolite dosage and reaction time on ammonia nitrogen adsorption performance of natural zeolite were investigated. The adsorption effects of zeolite under different modification conditions on ammonia nitrogen were compared. The results indicate that the ammonia nitrogen adsorption rate of natural zeolite gradually decreases with the increase of zeolite particle size and initial ammonia nitrogen mass concentration, and gradually increases with the increase of zeolite dosage and reaction time. The ammonia nitrogen adsorption effect of zeolite modified by sodium chloride is significantly better than that of zeolite modified by inorganic acids and inorganic bases, as well as other inorganic salts. When the sodium chloride concentration is 0.8 mol/L, the ammonia nitrogen adsorption rate can reach 78.0%, which is 1.64 times that of natural zeolite.

The design and optimization of extraction mixing tank is one of the key factors affecting the extraction efficiency of rare earth. The mixing performance of semi-open curved-blade disc-type stirring impeller(semi-open BWY), semi-open straight-blade disc-type stirring impeller(semi-open BPY), closed curved-blade disc-type stirring impeller (closed BWY) and closed straight-blade disc-type stirring impeller(closed BPY) paddle in the mixing tank was studied by experiment and numerical simulation. The negative pressure, power, discharge flow rate and flow field distribution generated by the four types of impellers at different rotational speeds were investigated. Taking closed BPY as an example, the six parameters of blade diameter, blade width, blade arc length, inner ring diameter, suction port diameter of the mixing tank, and the height between the blade and the suction port were analyzed in detail. The correlation equations of negative pressure, power number, turbulent kinetic energy dissipation rate and displacement number were established. The results show that under the same power conditions, reducing the blade diameter, inner ring diameter, suction port diameter, height between the blade and the suction port and blade width, as well as increasing the blade arc length, can enhance the mixing suction capacity, but it can reduce the blade displacement.

In order to accurately simulate the variation process of gold leaching rate, a multistage leaching model was designed, and the reaction rate prediction model based on the Forward Neural Network (FNN) and Radial Basis Function (RBF) was constructed.The validity of the model was verified by numerical simulation and comparative test. The results show that the error between the predicted value and the actual value of the gold leaching rate is between 2.1% and 2.6%, which is effective and accurate.