Molecular Assembly Of Inorganic-Polyamine Materials For The Separtaion Of Rare Earth Metal Ions

"There is oil in the Middle East, there is rare earth in China". China has the most abundant rare earth resources, at present, it has been the largest producer and supplier in the world. In the 21st century, rare earths are important materials in high-tech areas, especially in photoelectric, magnetic functional materials, which have aroused worldwide attention. Sole, the high pure rare earth is a base to exploit and study on the application of rare earth materials. Because they have very similar physical and chemical properties, rare earth elements tend to occur together in Earth's crust, moreover, there are many impurity elements in rare earth mixtures obtained by decomposing rare earth minerals, making their separation extremely difficult. Thus, in the process of the separation of rare earth elements, we must consider not only the separation of rare earth elements among 17 elements, which have very similar physical and chemical properties, but also the separation of many impurity elements, which occur together with rare earth elements in Earth's crust. It is a challenging task to separate rare earths from rare earth ores. The most important separation processes today make use of combinations of liquid-liquid and solid-liquid extraction. Liquid-liquid extraction has been the favored route for a fast separation velocity and a big production capacity. Because of the limits of two or three vents in this separation method, most only can obtain the vent number the pure rare earths via a separation process. Thus, in order to obtain all rare earths, it is needed that intermediate concentration rare earths reentry into an organic phase that is in contact with an acidic solution of the extractor, and many extraction cycles are required. Liquid-liquid extraction may involve environmental drawbacks such as relics of solvents or extractants in water; furthermore, their technical and economic efficiencies are limited by the treatment of dilute effluents. The solid-liquid extraction includes ion exchange and extraction chromatography. The ion exchange process is not suitable for industrial production because of the very long periods required to accomplish significant separation. The extraction resin with the extraction carrier as the stationary phase instead of the ion exchanger, rare earths are extracted, counter-extracted and exchanged time after time while they are flowing along with the mobile phase through a packed bed, the effluent is sectionally collected, and simultaneously obtains many pure rare earths at one time. However, the extraction chromatography combines the selectivity and the flexibility of liquid-liquid extractions with the versatility, the high efficiency and the simplicity of chromatographic columns. Extraction chromatographic separation overcomes the defects of solvent extraction, which are easy emulsification, solvent pollution and difficulty in phase separation. Extraction chromatographic separation may separate effectively rare earths for their difficult separation by using ion exchange or liquid-liquid extraction. In extraction chromatographic separation, extraction resins influence clearly production capacity, separation velocity and separation efficiency of rare earth. The extraction resin with a fast separation velocity and high separation efficiency is a key to separate rare earth. Conventional poly (styrene-divinylbenzene) resin with organophosphorus compounds as an extractant, seems to have favourable properties such as the high selectivity, but their very complicated methods of synthesis, high cost, small specific surface area of resins, slow sorption and desorption, small exchange capacity of resins, low mechanical strength, extractants loss with flow phase, large resin bed volumes, high back pressure and easily degradation have limited their application in industrial scale separation processes; moreover, extractants may be inducted into the closed pores of resin grains, and result in desorption difficulty of rare earth ions adsorbed into closed pores; water is difficult to wet surfaces of the nonpolar poly (styrene-divinylbenzene) resin; one organophosphorus extractant only provides several coordinating atoms; the resin swells in a packed bed.Because characteristics of inorganic materials, it is extremely difficult to change or modify the configuration, according to the practicably need to control size, configuration, physical and chemical properties. Whereas, organic materials have excellent molecular tailorable and modificatory function, but have the defects of consistency and stability. How to combine each other properties both inorganic materials and organic materials, and to construct plasticity, stabilization, ruggedization of novel hybrid materials in configuration, has become an important challenging task in inorganic chemistry and materials science. In recent years, how to recombine, assemble, hybridize and reinforce functional properties of materials has become an investigating hotspot by using molecular design and engineering thoughts; especially, in order to obtain functional properties as an aim, how to design and control carefully inorganic-organic materials has become a challenging task in this area.In this dissertation, using molecular design, inorganic polyamine materials are molecularly assembled for the adsorption and separation of rare earth ions. When rare earth ions are desorbed from adsorbed inorganic polyamine materials, they may regenerate adsorption capacity for recycled use, and do not produce contamination. Inorganic polyamine materials molecular assembly endows with a good selection and combination of rare earth ions, which improves the adsorption capacity and separation efficiency of rare earth ions in solution. To develop and exploit these inorganic polyamine materials-novel extraction resins, is very important to accelerate improvements in the overall yield of rare earth, to make efficient use of rare earth resources for their sustainable development in China, they can not be regenerated.In this paper, there are two kinds of hybrid polyamine materials. Firstly, using both surfactant-mediated synthetic method and ionic imprinting technique, the amino group is grafted on the pore wall of mesoporous materials, a novel ordered hybrid inorganic-polyamine material is prepared via the acid-catalyzed hydrolysis and polycondensation of TEOS and AAPS. Secondly, using anchor reagent Cl₃SiCHCH₂, low molecular weight chitosan is grafted on the surface of bentonite, a novel chitosan polyamine-bentonite hybrid material is prepared via the covalent combination of polyamine ligands and bentonite. The composition and pore structures of these two kinds of hybrid materials are characterized with FT-IR, TG-DTA, XRD and MIP. The mostly investigated contents and obtained results are outlined as follows:1. Using both CTAB surfactant-mediated synthetic method and ionic imprinting technique, the amino group is grafted on the pore wall of mesoporous materials via a covalent combination, a novel ordered hybrid inorganic-polyamine material is prepared via the acid-catalyzed hydrolysis and polycondensation of TEOS and AAPS. This novel ordered mesoporous inorganic-organic hybrid material is used to the separation of rare earth ions for the first time. The optimal technological conditions are determined by orthogonal experiments to prepare mesoporous hybrid La³⁺ imprinted inorganic-polyamine material, namely, TEOS:AAPS:CTAB: H₂O: La(NO₃)₃ mole ratio is 1: 0.25: 0.15: 230: 0.1, reaction solution pH is 2, and the hydrolysis temperature is 60℃in initial reaction stage. The mesoporous hybrid La³⁺ imprinted inorganic-polyamine material is prepared under this optimal technological conditions, its average granularity is 11.19μm, its specific surface area is 513.4 m²/g, its average pore radius is 4.62 nm and the La³⁺ adsorption capacity is 176 mmol/g in 1.0×10^-3 mol/L La³⁺ solution.2. Using ionic imprinting technique and anchor reagent Cl₃SiCHCH₂, low molecular weight chitosan is grafted on the surface of bentonite, a novel hybrid chitosan polyacrylamide-bentonite material is assembled through radical copolymerization of MA and AM, Hoffmann reaction is carried out to prepare the novel hybrid chitosan polyamine-bentonite material. It is first application on the separation of rare earth ions. The optimum technological conditions are obtained to assemble La³⁺ imprinted chitosan polyamine -bentonite material, namely, 1 g dried silylated bentonite, 0.5 g chitosan, 0.4 g MA, 1.6 g AM, 1 g LaCI₃, 3 g H₂O, 0.02 g K₂S₂O₈, reaction temperature is 70℃and reaction time is 4 h; moreover, in Hoffmann reaction, 6 g NaOH, 8.1 g 5% NaOCI, reaction temperature is -10℃and reaction time is 6 h. The La³⁺ imprinted chitosan polyamine-bentonite material is assembled under this technological conditions, its granularity distribution is asymmetric, its average granularity is 66.77μm, its specific surface area is 83.52 m²/g, its average pore radius is 4.53 nm and the La³⁺ adsorption capacity is 11.6 mmol/g in 1.0×10^-3 mol/L La³⁺ solution. The organic compound, such as chitosan, polyamine and methacrylic acid, grafted on bentonite arrives at 34 %. 3. Cyclic voltammetry is applied to electrochemically recognize La³⁺ or Ce³⁺, Y³⁺ using carbon paste electrodes modified with chitosan. A pair of well-defined sensitive redox peaks, representing the adsorptive complexes of the rare earth ion and tribromoarsenazo, are found using scanning potentials from -0.80 to 0.00 V vs. SCE. These peak potentials and peak currents are used to determine quantitatively these rare earth ions. The linear detection range and detection limit of La³⁺ or Ce³⁺, Y³⁺ are determined, respectively; linear fit relations of RE(III) are calculated. The optimal pH range 1.5～3.0 is obtained for these rare earth ions detection. Some common metal ions such as alkali and alkaline cations do not effect determination of the rare earth ion. This simple, effective method can be used to electrochemical recognition of rare earth ions.4. Keeping the rare earth ion concentrations constant, permit developing a simple, effective method to evaluate quantitatively the ionic recognition of the imprinted polymers using electrochemical recognition of rare earth ions. Based on the distribution coefficient in a solid-liquid extraction process, the recognition ratio is given by R = K_{impr int ed}/K_{nonimpr int ed} . In the sameelectrochemical cell, keeping the concentrations of rare earth ions constant, the recognition ratio R is calculated by the peak current in the cyclic voltammograms. In this study, the recognition ratios of La³⁺ imprinted chitosan polyamine-bentonite material, Ce³⁺ imprinted chitosan polyamine -bentonite material, La³⁺ imprinted inorganic-polyamine material and Ce³⁺ imprinted inorganic-polyamine material are 1.91, 2.65, 2.10 and 1.78, respectively.