Resource And Application Of Rare Earth Elements

The main work of this thesis is:â… .The status and function of the rare-earth element (REE) resource in our national economy constructionThe top 5 countries that has the most rare earth elements in the world are China, Commonwealth of Independent States (CIS) USA, Australia and India. China has found the industry reservoir existed in REO of 36 million tons, approximately 80% of the known reservoir volume globally, top of the world. It has such important role in military strategy, equivalent to the role of petroleum in mid-east.The world trade of rare earth elements is focused at the developed countries, especially in USA, Japan and France. China has always kept the special role as an export country.Therefore our country is the biggest rare earth resources country,the rare earth production country,the rare earth expense country and the rare earth supply country.â…¡.The state of rare earth element resourcesThe world rare earth element ore deposit is divided into twelve types:fluoride mineral,simple oxide mineral, complex oxide mineral,tantlum nibolic acid salts and titumim tantalum nibolic salt mineral,carbonate mineral,phosphate arsenate and vanadate mineral,sulfate mineral,borate mineral,complex acid salt mineral,polyacid salt mineral,silicate mineral,titanium or zirconium silicate and aluminum silicate mineral. The types of rare-earth elements are most in the earth.The world rare earth element ore deposit includes three types: endogenetic deposit,metamorphic deposit and exogenic deposit.1.Endogenetic deposit includes three types:ore deposit is related to alkali rock-alkaline-ultrabasic rock( 9 types),ore deposit is related to alkali rock-carbonate rock(5 types) and granitoids(8 types).The sum total is 22 types.2.Metamorphic deposit includes three types: ore deposit is related to migmatite(2 types) ,ore deposit is related tometamorphic conglomerate (1 types)and skarn(1 types). The sum total is 5 types.3.Exogenic deposit includes three types: ore deposit is related to phosphate rock (1 types) ,ore deposit is related placer deposits(2 types)andweathering crust deposits (3 types). The sum total is 6 types.â…¢. The example of application of rare earth element---solids catalyst preparation and application1. SO₄^2-/MxOy type of solid catalyst formation mechanismSO₄^2-/MxOy type of solid catalyst is based on complexion of SO₄^2- and MxOy, the electrical cloud of M-O bond is significantly shifted, that forms the complex of SO₄^2- and metal oxide. The preparation methods of SO₄^2-/MxOytype of solid catalyst are precipitation, solidification, gelation, and hydrolysis, etc.2.The impact of preparation condition on reactivity of catalysts(1) Type of soluble metal saltsThe major impact of metal salts is on the diameter of the formed metal oxide gel particles, therefore, the relative surface area of oxide is changed. For example, in the reaction of acetic acid/ethanol using SO₄^2-/Fe₂O₃ catalyst, using three different raw material, Fe(OH)₃,Fe(NO₃)₃·9H₂O, and FeCl₃·6H₂O, results showed that using FeCl₃·6H₂O as raw material, the catalyst reactivity is the highest, and Fe(NO₃)₃·9H₂O results the lowest catalyst reactivity.(2) Choice of precipitation reagents and pH valuesDifferent precipitation reagents and pH value in the precipitation process has significant impact on catalyst particle size, relative surface area, pore diameter distribution and formation of reactivity center, the suitable pH should be around 8-10.(3) Form of metal oxidesIn preparation of solid catalyst, amorphous oxides are commonly used, crystallized oxides usually do not result solid catalyst.(4) maceration extract type and densityUsing different density's H₂SO₄,(NH₄)2SO₄ or(NH₄)2S2O8 solution to the catalyst has different influence on the relative surface,micoaerture,the acid strength and activeness of the catalyst.If use (NH₄)2SO₄ as maceration extract its density should twice as H₂SO₄. Possible because hydrolysate NH3 which is worked as nucleophilic agent, has decomposition to the catalyst structure. In enhancement catalysis performance promoter action aspect, (NH₄)₂S₂O₈ is stronger than H₂SO₄ in enhancement catalysis performance. But H₂SO₄ is stronger than (NH₄)2SO₄ in this aspect. In brief we should according to the catalyzed performance to choose maceration extract. Moreover no matter which type of maceration extract should be chosen the density is an important influence factor. If density is too low, oxide surface bound too few, the catalytic activity is low; If the density is too high, then the superficial metal oxide will dissolve and form the sulfate, so the superficial passageway and the bulge fuse mutually, then reduces the relative surface and the pore volume greatly it does not favor the preparation of catalyst. Regarding the different oxide or the different reacting system, the choice of the maceration extract has the different density scale:generally ZrO₂ is 0.25～0.5mol/ generallyL, Fe₂O₃ is 0.25～0.5mol/L, TiO₂ is 0.5～1.0mol/L and so on.(5) roasting temperatureRoasting temperature has more effect on the formation, distribution, relative surface, the hole structure of the solid catalyst particles. Along with roasting temperature elevating, the relative surface of catalyst drop. The experiment proved the roasting temperature in 723～923K is suitable.(6) ageing temperatureThe activity of catalyst in low temperature is stronger than in normal temperature.3.preparing trip-protic rare earth solid catalyst S₂O₈^2-/Pr₂O₃―ZrO₂―TiO₂10%solution of ZrOCl₂andTiCl₄ and 2% praseodymium nitrate and the little surface active agent polyethylene glycol mix together. Then the mixing solution is cooled to 0℃and add 0℃6mol/ L NH₄Cl solution in it. After no longer has the precipitation, join 6mol/L NH₃·H₂O in it causing its precipitation complete and get the complex hydroxide recipitation. We should adjust the pH value at 8¹0.then chenhua for 24 hours in low temperature. The system should be filtered and washed about 8¹0 times. Till no cl- has been checked out. We get the pure hydroide precipitation. Stoving the precipitation. Stoving it at 110℃in drying oven. Abrade it pass through 100 item sieve, soaked it by (NH₄)₂S₂O₈ solution according to every 1g proportion per 15mL maceration extract after 24 hours filter and staving again. Then roasts for 3 hours in the muffle furnace.Cool it and obtain the tri-protic rare earth solids catalyst . 4. Application of tri-protic rare earth solids catalyst --ethyl phenylacetate catalyzed synthesis(1) reagents: Phenylacetic acid, absolute ethyl alcohol, strong sulfuric acid, glacial acetic acid, ZrOCl2·8H₂O, ammonium persulfate, ammonia, praseodymium nitrate, ammonium chloride, TiCl4 and so on.All of them are analytically pure; Salicylic acid is chemistry pure.(2) ester synthesisPut phenylacetic acid, absolute ethyl alcohol and the self-made catalyst into the flask. measuring its acid value after mixing evenly.Then stirs and elevates temperature gradually till the temperature achieve to about 82℃. When the first drop of backflow fluid appears begin to record, take 0.5mL mixing solution from the reacting system at regular interals,titrate it by NaOH and use phenolphthalein as indicator to determine its acid value and caculate esterification rate.According to the GB1668 - 81 methods measure the change of acid value.(3) the influence of reaction condition on esterification rateThe reaction condition influences esterification rate dramatically. For example the mole rate of acid and alcohol, the reaction time, the amount of catalyst, the reaction temperature, the amount of dropping water agent etc.The most appropriate reaction conditions are as follows:roasting temperature is 500℃, soaking density is 1.5mol/L, preparing tri-protic rare earth solid catalyst at 0℃, the amount of catalyst used is 1.5g per 0.1mol phenylacetic acid, the reaction time is 5 hours, the mole amount of phenylacetic acid and anhydrous alcohol is 1: 5 .The main conclusions and new insights:1.Based on the investigation of the rare earth element resource mineral and ore deposit type the thesis proposed the significance of comprehensive utilization for associated rare earth element and its trace meaning in geological disaster. 2. It is the first time to prepare the solid catalyst ---S₂O₈^2-/ Pr₂O₃-ZrO₂-TiO₂ and get the most appropriate reaction conditions: preparing the complex hydroxide deposit at 0℃chenhua for 24h, soaked Pr₂O₃-ZrO₂-TiO₂ by (NH₄)2S2O8 solution according to every 1g proportion per 15mL for 24 hours,after filtrating roasts for 3 hours in the muffle furnace at 500℃.3.Use TG-DTG,XRD,TEM and IR methods to analysis and indicate the catalyst S₂O₈^2-/ Pr₂O₃-ZrO₂-TiO₂ .Result indicates that the catalyst is in nanometer grade and the average diameter is 17 nm. The crystal structure exists on the surface of catalyst and the reaction is surface catalysis.The basement of the catalyst and SO₄2- form bridge coordination and carry high catalysis ability.With the introduction of Pr₂O₃ restarded the crystallize of ZrO₂.Because the bonding strength of rare earth elements'4f orbital is weak it can active reactant molecules and form products at the same time the product is easy to remove form the catalyst.The catalysis ability of rare earth element is better. The solid catalyst also has the good catalyzed performance and environmental protection ,both union can play supplementary role.The increase of active centre type plays guangpu catalyst role.Simultaneously it is thought that the positive ions for the basement are not widespread and have the specific selectivity.The selective essence is decided by the ion values of atom structure.Every oxides with lower value ion are not work as the basement of catalysts.Because they can not form bridge coordination bond.Hence the oxides which can work as catalyst basement must carry more then +3 values.4.Ester synthesis is taken place by phenylacetic acid, absolute ethyl alcohol and nano-catalyst S₂O₈^2-/ Pr₂O₃- ZrO₂-TiO₂ .Result indicates that the catalyst has strong catalysis activity to ester synthesis reaction. The most appropriate reaction conditions are the mole amount of phenylacetic acid and anhydrous alcohol is1: 5.the amount of catalyst used is 1.5g per 0.1mol phenylacetic acid, the reaction time is 5 hours.Esterification rate is above 88% .The reaction time is short ,the yield is high ,the catalyst is good reproducibility and easy to separate,friendly to the environment.Compared with other catalysts in labtory condation it showes that the ester ratio is obviously higher than other kinds of catalysts.