Fabrication Of Green Porous Adsorbent Materials And Study On Behavior And Mechanism Of Rare Earth Selective Separation And Recovery

Rare earth elements, because of their unique physicochemical properties, have wide applications, especially in the green technologies, such as wind turbines, hybrid electric vehicles,energy-efficient lighting system and catalysts. The environment has accumulated a large number of rare earth waste. These wastes contain a lot of rare earth elements and other heavy metal elements, if not the correct recycling treatment,environment problems will come. Therefore, it is of great economic value and environmental value to study the separation and recovery of rare earth elements from rare earth wastes for the sustainable utilization of rare earth. The separation of rare earth elements in industry is basically by solvent extraction method. Solvent extraction strategies have already been used for industrial separation and recovery in hydrometallurgy widely as they achieve acceptable enrichment needed by multiple extraction steps. The main drawback is that a large amount of organic solvents used in the extraction process will produce a large amount of organic waste and radioactive waste. Solid-liquid extraction is a novel separation technology. Its extraction process will not be a lot of organic waste. It is considered a simpler, green separation extraction technology. However, the selectivity of solid-liquid extraction for rare earth adsorption and separation is poor. So, it is especially necessary to design rare earth adsorbents with high selectivity and high adsorption capacity.In this paper, based on the perspective of functional selectivity of adsorbent materials, porous materials were selected as the research objects, and their nanostructures were diversified by a variety of different template methods. The methods of preparing functionalized porous materials were explored and the behavior and mechanism of functionalized porous materials for rare earth elements were studied. Porous material system based on the selective separation by solid-liquid extraction method was constructed.1. Preparation of organic-inorganic hybrid mesoporous silica and selective separation of rare earth ions(1) We present the preparation of novel organic-inorganic hybrid mesoporous silica materials modified by maleic anhydride, which can be used in the recovery of rare earth metals through extraction of their ions from an aqueous solution. Our novel maleic anhydride functional hybrid materials demonstrate enhanced selectivity for heavy rare earth metals, which vastly improves the separation process and reduces recovery costs. In addition, the directly modified hybrid materials have been found to exhibit higher distribution coefficients for rare earth elements compared to other materials. The adsorption followes a pseudo-second order model, with particularly rapid adsorption observed in the case of Gd3+. The resulting adsorption isotherms of the materials are better represented by the Langmuir model than the Freundlich model.The one step modified material exhibits a Gd3+ capture capacity of 76.89 mg g-1. In addition, the proposed materials demonstrate a high degree of reusability over a number of cycles,thus enhancing their potential for application in rare earth metal recycling.(2) A straightforward,one-pot approach for novel ion imprinted mesoporous silica materials (IMS) are developed by co-condensation. IMS are used for the recovery of .dysprosium through solid-liquid extraction .in an acidic system. The dysprosium adsorption of IMS are efficiently modeled using the pseudo-second order rate equation. The initial kinetics of adsorption are fast and almost complete adsorption after 3-4 h. Adsorption isotherms are efficiently modeled using the Langmuir equation. The adsorption capacity of IMS toward dysprosium is 22.33 mg g-1 at pH=2.0, which is apparently greater than the adsorption capacity of non-imprinted materials at pH=5.0. The value of imprint factor at pH=2.0 is higher than other pH obviously. The distribution coefficient relative to dysprosium is 539 mL g-1, which is significantly higher than that of other rare earth ions. IMS demonstrates enhanced selectivity towards dysprosium compared to non-imprinted materials in acidic solution via solid-liquid extraction, which substantially improves selective extraction process and provides a greener alternative to liquid-liquid extraction. In addition, the materials demonstrat a high degree of reusability over a five extraction-stripping cycles, enhancing their potential for application in real rare earth metal recycling in acidic system.2. Preparation of ionic imprinted chitosan films and selective separation of rare earth ions(1) A detailed investigation of the formation and properties of imprinted mesoporous carboxymethyl chitosan films by the chiral nematic liquid crystal phase of cellulose nanocrystals (CNCs) is presented. Imprinted mesoporous carboxymethyl chitosan films exhibiting an ordered chiral nematic structures structure are used as adsorbents for efficient and selective adsorption of gadolinium ions. Saturation adsorption capacity of imprinted mesoporous carboxymethyl chitosan films for Gd3+is 25.37 mg g-1. By highly selective imprinted cavities, imprinted films possess significant selectivity of Gd3+ than other rare earth ions. Moreover, imprinted mesoporous carboxymethyl chitosan films could be easily and rapidly retrieved without the need of additional centrifugation or filtration, greatly facilitating the separation process. Reusability tests demonstrat the materials could be repeatedly used without significant loss in adsorption capacity, enhancing their potential application for recovery of Gd3+.(2) We successfully prepared three-dimensionally interconnected macroporous imprinted chitosan films (3DIM-IFs) by template-assisted assembly. Imprinted chitosan films exhibiting an interconnected macroporous structure are used as adsorbents for efficient and selective adsorption of gadolinium ions (Gd3+). Saturation adsorption capacity of 3DIM-IFs for Gd3+ is up to 51.36 mg g-1 at 298 K, which is obviously higher than adsorption capacities for most reported Gd3+ imprinted adsorbents over recent years. Due to highly selective imprinted cavities, imprinted films possess significant selectivity of Gd3+ than other rare earth ions. Moreover,3DIM-IFs can be easily and rapidly retrieve without centrifugation or filtration,greatly facilitating the separation process. Reusability tests demonstrate the materials can be repeatedly used without significant loss in adsorption capacity, enhancing their potential application for recovery of Gd3+.3. Preparation of .dual-template docking oriented ionic imprinted mesoporous films and selective separation and recovery of rare earth ions(1) In this paper, we present free-standing ionic imprinted mesoporous film materials for facile and highly efficient targeted separations of mixtures of rare earth salts by dual-template docking oriented ionic imprinting (DTD-OII) method.Compared with conventional imprinting, this novel strategy does not need additional processes, but provides significantly improved imprinted efficiency and binding properties. It opens an avenue to the facile and efficient synthesis of ionic imprinted mesoporous materials. Our free-standing dual-template docking oriented ionic imprinted mesoporous films (IMFs) exhibit excellent recovery of Nd through solid-liquid extraction in an acidic system. The adsorption capacity of optimized films toward Nd is 34.98 mg g-1 at pH=3.0. The distribution coefficient relative to Nd is 636 mL g-1, which indicates films possess significantly selectivity of Nd than that of other rare earth and interfering ions. In addition, efficient dual-template docking oriented ionic imprinting makes films demonstrating a high degree of reusability over a five extraction-stripping cycles, enhancing their potential for industrial application in rare earth recycling.(2) We present ionic imprinted mesoporous bilayer films (IIBFs) as an ideal adsorbent for selective separation of neodymium (Nd) and dysprosium (Dy) from sintered neodymium magnets. IIBFs were prepared according to a strategy called dual-template docking oriented ionic imprinting (DTD-OII). Due to different imprinted compositions of bilayer films, IIBFs exhibit fast binding equilibrium and Janus properties for selective adsorption of different rare earth ions, which makes our imprinted mesoporous films a specialized adsorbent for adsorption of Nd and Dy at the same time. The adsorption capacities of optimized IIBFs are 17.50 mg g-1 for Dy3+and 12.15 mg g-1 for Nd3+ at pH=4.0. Moreover, we grafted thermo-responsive polymer on the one surface of IIBFs to .realize controlled release of Nd and Dy by temperature. In addition, IIBFs demonstrate a high degree of reusability over a five extraction-stripping cycles by DTD-OII, which develops their promising applications for the REE recycling and separation industry.