| Due to the electron shell of rare earth elements has a unique structure and physicochemical properties.It has excellent optica,electrical,magnetic,thermal and other characteristics.So they have been widely used in superconductor,aerospace,electronics,sensors,and catalysis,has gradually penetrated intoall areas of society.With the development of the economy,the demand for rare earth elements has increased dramatically worldwide.However,a small amount of the rare earth element in the global occurrence,uneven distribution and non-renewable.Find and extract rare earth element has important for scientific and technological development of the country.Studies show that the symbiotic ore and coal gangue contains large amounts of rare earth elements,rare earth elements in some parts of coal gangue content of up to industrial exploitation of taste.So it has great development value.After the coal was burned,these rare earth elements entered the coal ash.Our country is a large coal country,producing hundreds of millions of tons of fly ash every year.The coal ash was piled up in large quantities,not only occupying a lot of land,causing air pollution,but also prone to geological hazards such as debris flow.At the same time,it also caused a waste of resources.Therefore,the discovery and extraction of rare earth elements from fly ash could"turn harm into benefit,turn waste into treasure".It also could be provide a source for scattered metal resources,which is of great practical significance for the protection and efficient utilization of mineral resources in our country.Organometallic skeleton materials(MOFs)is a kind of material with super-large specific surface,which has the advantages of multi-hole,and could be adjustable aperture and modification regulation.And it has a good adsorption effect on metal ions.Today membrane separation technique has become a set of effective,environmentally friendly and precise.membrane separation technique has become new separation technology.On the basis of the excellent selectivity and recognition performance of MOFs materials for metal ions.In order to achieve La?Ce?Nd efficient and green extraction and separation from fly ash acid leaching solution.We aim at the rare earth elements contained in coal ash,which is produced in the process of coal resource development.And this paper proposes a post-modification design to synthesize MOFs with specific molecular recognition properties and load film formation.Specific studies are as follows:(1)This article has been explored leaching rare earth elements La?Ce?Nd fly ash by alkali-melting-acid leaching.The effects of roasting time,leaching time,temperature,acid concentration and solid-liquid ratio on leaching rate were investigated.We conducted a kinetic analysis of the leaching process and leaching principle.The results show:Mix fly ash raw material and sodium carbonate evenly according to 1:1 mass ratio.Roasting 180 min in850?t ube furnace.We can get the activated fly ash material.the best La?Ce?Nd leaching rate can be obtained by leaching 120 min with HCl 5 mol/L at a solid-liquid ratio of 1:25 at 90?,which is 56.4%,99.99%,99.99%.Moreover,the results of kinetic analysis show that the leaching of rare earth La?Ce?Nd in fly ash is controlled by diffusion.(2)This article has been synthesized DGA-UiO-66-NH2 new materials were prepared by post-modification MOFs by diglycolic anhydride(DGA),which ion selectivity was investigated by fluorescence spectrum analysis.And we have been prepared DGA-UiO-66-NH2@PVDF composite membrane by blending method.We have studied adsorption properties of the membrane material on La?Ce?Nd in fly ash acid-impregnated simulation solution,and investigated the effects of pH value,MOFs loading,adsorption time and initial concentration on the adsorption capacity.And the adsorption mechanism was explored by establishing the kinetic model of adsorption process and the model isothermal adsorption line.The results show:The selectivity of membrane materials to Ce is the best,the second to La,and the worst to Nd.Under the environment of 25?,the solution pH=4,30%load of adsorbed material and the adsorption time is 150 min,and the optimum initial concentration of La?Ce?Nd rare earth ions is 150 mg/L,258 mg/L,120 mg/L,and we could get the maximum adsorption capacity was 253.52?g/g,425.35?g/g,233.8?g/g.The kinetic analysis shows that the adsorption processed accords with the pseudo-first-order model.By fitting the adsorption isotherms,it is found that the Langmuir model was more suitable.And the adsorption process was monolayer adsorption.(3)This article has been synthesized PMIDA-UiO-66-NH2 new materials were prepared by post-modification MOFs by N-(Phosphonomethyl)iminodiacetic acid(PMIDA),which ion selectivity was investigated by fluorescence spectrum analysis.And we have been prepared PMIDA-UiO-66-NH2@PVDF composite membrane by blending method.We have studied adsorption properties of the membrane material on La?Ce?Nd in fly ash acid-impregnated simulation solution,and investigated the effects of pH value,MOFs loading,adsorption time and initial concentration on the adsorption capacity.And the adsorption mechanism was explored by establishing the kinetic model of adsorption process and the model isothermal adsorption line.The results show:The selectivity of membrane materials to Ce is the best,the second to La,and the worst to Nd.Under the environment of 25?,the solution pH=3.5,40%load of adsorbed material and the adsorption time is 120 min,and the optimum initial concentration of La?Ce?Nd rare earth ions is 62.5 mg/L,107.5mg/L,50mg/L,and we could get the maximum adsorption capacity was 193.44?g/g,403.57?g/g,190.16?g/g.The kinetic analysis shows that the adsorption processed accords with the pseudo-first-order model.By fitting the adsorption isotherms,it is found that the Langmuir model was more suitable.And the adsorption process was monolayer adsorption. |
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