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Klorlama yöntemiyle cevherlerde toryum kazanma veriminin artırılması

Başlık çevirisi mevcut değil.

  1. Tez No: 22266
  2. Yazar: BAYRAM KOPUZ
  3. Danışmanlar: PROF. DR. ALİ NEZİHİ BİLGE
  4. Tez Türü: Doktora
  5. Konular: Nükleer Mühendislik, Nuclear Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1992
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 93

Özet

ÖZET Nükleer reaktörlerde uranyum veya bileşikleri yakıt olarak kullanılmaktadır. Toryum fisil bir malzeme olmamasına ragmen eğer reaktörde ışınlanırsa fisil malzeme olan 233U oluşur. Bu ise yakıt olarak kullanılabilir. Doğada toryum içeren birçok mineral bulunmasına kar şın toryum yataklarındaki başlıca toryum mineralleri Monazit [(Ce,La,Y,Th)P04], Torit (ThSiOO, Thorlanit [(Th,U)02]'tir. Kimyasal çözündürme metotlarına alternatif olarak klorlama yöntemiyle toryum cevherlerinden toryumun ayrılması bu çalışmanın esasını oluşturmaktadır. Bu çalışmada Eskişehir Beylikahır yöresindeki bast- nasit cevherinin doğrudan klorlanmasıyla nadir toprak elementleriyle toryumun birbirinden ayrılması için gerek li değişkenler incelenmiştir. Klorlamada en yüksek toryum ayrışma veriminin sağlanabilmesi için değişkenlerin etkisi incelenmiştir. Bu değişkenler; kullanılan cevherin tane boyutu, cevher kar bon oranı, klorlama sıcaklığı, klorlama süresi, klorlama uygulanacak cevherin tenörü, klorlama uygulanacak cevherin flor içeriği sayılabilmektedir. Klorlamada diğer yöntemlerdeki cevher hazırlama ve çözündürmenin gerektirdiği aşamalar ortadan kalkmış olmaktadır. Yapılan deneysel çalışmalarda en yüksek toryum ayrışma veriminin elde edilmesi için en uygun koşul olarak; klorlama sıcaklığı 1000° C, cevher /karbon oranı 1, klor akış hızı 0.7 l/saat, reaksiyon süresi 1000© C de 1 saat argon atmosferinde, 1000° C de 1/2 saat klor atmosferinde şeklinde belirlenmiş ve bu koşullarda %86'lık toryum verimi elde edilmiştir.

Özet (Çeviri)

SUMMARY The development of a country is defined as the energy consumption per person. One of the oldest energy sources on earth are the fossil fuels. Approximately four fifths of the world's energy is obtained from petroleum, coal, natural gases. Unfortunately these sources are rapidly diminishing and not renewable. The share of nuclear reactors is more than one tenth. The rest of the energy comes from hydroelectric plants. There is not much possibility of increasing the percentage of hydroelectricity. Therefore it is obvious that some alternative source of energy should be used. This could be solar energy, wind energy, fusion energy, and nuclear energy. Solar and wind energies do not con tribute to the total and work on fusion energy is still being done. Therefore the possibility of using nuclear energy is becoming important. The energy consumption in Turkey has increased along with development and population growth. To meet the in creasing demand both capacities of existing plants and should be increased and alternative sources should be built. Therefore local hydroelectricity and lignite sources gained more importance, and nuclear and solar energy are brought up as alternative sources. Petroleum surveys in creased to lessen the amount of import. The existing electricity capacity in Turkey (by the end of 1986) is 10112.7 MWe. of which 62% is thermal and 38% is hydroelectricity. Considering all the sources of energy in Turkey, and assuming that no new sources are discovered, there will be a shortage after the second half of nineties. The only alternative to meet the increasing demand could be nuclear energy. Strickly speaking Turkey can easily use a 1000 MWe reactor today. viPreliminary and side works were carried at Akkuyu in the Mediterranean district about the harbour and infra structure of the reactor since 1975 but no firm has the contract yet. Uranium and uranium compounds are used as fuel materials for nuclear reactors. Thorium which is not a fissile material itself, produces 2330 when irradiated. This in turn can be used as a reactor fuel. Therefore thorium is a secondary nuclear fuel. The nuclear reac tion is as follows g*Th.-*(/i.y) IfTh.--^ » If Pa ==4 » ^u *> so 23 mm. 17 days * The use of thorium in reactors is only possible with enriched fissile material. The product 233U has fission reactions, can produce fission products and energy. If thorium is used as fuel in fast breeder reactors, then there is 1.5 kgs of 233ü or 239pu for each kg of 235U Qr 239Pu. Neutron efficiency of 233ü is higher than both 235U and 239Pu. There is no practical application of thorium fuel technology up till now. Irradiation of 232Th gives an intermediate product 231 Pa, which emits high energy gamma rays that causes some difficulties during recycling of the fuel and is not wanted in the neutron economy. When these technological problems are solved we will have a fuel material that is three times more abundant. Thorium was discovered by Swedish chemist Jons Jacop Berzelius in 1828. In 1885 Carl Auer Von Weisbach discovered thorium oxide gives off a bright light and used it in kerosene lamps. The chemical properties of thorium are similar to those of titanium and zirconium, therefore it can be evaluated with the IV b group. It is the first element in actinide series. The actinides and lanthanides are analogues to each other, and basic chemical properties are very much alike. viiThorium metal and compounds are used in alloys as an alloying element, and in chemical processes. The in creasing use of thorium in industry has led to recovery and use of rare earth elements which are found in the same type of ores. Radioactive 23 2Th, found in nature disintegrates to lead. It is the 35th. element in abundance. That is 3-4 times more than uranium. It is found in both basic and acidic rocks. But basic rocks have six times more thorium. Geochemical properties of thorium are similar to those of zirconium and uranium and therefore it is found in the same ores as complex minerals. The richest thorium ores are found in sedimental rocks near ocean shores as monazite mineral. There are 120 types of thorium bearing minerals. They may be in the form of silicates, oxides, phosphates, and f luorocarbonates. These minerals are rare earth min erals at the same time. Although there are many types of thorium minerals, the main minerals in thorium ores are Monazite [(Ce, La, Y, Th.)P04], Thorite (ThSiOO, and Thorianite [(Th.,ü)02] Commercially 80% of the thorium deposits are monazite minerals. These are sedimental deposits. Thorium ore is mined using various technologies (suction tubes, excavators). Before mining, mineralogical compo sition of the ore is studied to determine the ore prep aration and mining method. The ore which is excavated from sedimentary deposits is first sieved, then according to the density is separated by preconcentration, final concentration, magnetic separation, and electrostatic separation procedures. Other valuable minerals are sep arated from monazite during these operations. The monazite concentrate is leached using different methods. a) Sulfate method: Monazite concentrate is treated with concentrated sulfuric acid at 200-300°C. viiib) Basic leach : This method has three different applications; sodium hydroxide fusion, soda fusion, and leach with sodium hydroxide solution Sodium hydroxide leach is done at 140°C, sodium hy droxide fusion at 400-500 °C, and soda fusion at 800-825°C. Different chemical methods are applied to separate the thorium and the rare earths that are brought into solution. In thorium ores and in each concentration step there is the need to determine thorium and other elements. De termination methods for thorium are a) Mass spectrometer b) Neutron activation analysis (NAA) c ) Fluorometry d ) Photometry e ) Spectrography f) Radiometry g) Amperometric titration h) X-Ray fluorescense analysis (XRF) In this work all analysis were done by XRF and NAA because of the ease and rapidity of the methods. In NAA samples and standards were irradiated, after 20 days of cooling period 233pa peak areas were compared to those of standards and thorium was determined. In XRF two methods were used. One was standard addi tion the second was basic parameter method. Basic par ameter was preferred for thorium, cerium, lanthanides because of the ease and rapidity of the method. In this work chlorination for separation of thorium from thorium ores, as an alternative to chemical dissol ution is tried. Chlorination is known for a long time. The ore was roasted with sodium chloride in early applications. Later volatile and nonvolatile compounds were separated with chlorination. This method has found a wide field ixof application in producing zirconium and titanium chlor ides from their concentrates. These concentrates are mainly ZrSiCU and Ti02 with very low impurity content. Chlorination method was used on complex ores and on spent fuels for separation of fission products both laboratory and pilot plant scale. Thorium and uranium can be sepa rated from each other, and the fission products without being brought into the solution by chlorination in thorium and uranium containing fuels. Monazite concentrates of thorium ores were subjected to chlorination. Studies of separating complex tin, chromium, lead, and other elements by chlorination are being carried out recently. Most of these studies are patented. In one of these studies basnasite ore besides monazite, was chlorinated in an electric arc furnace, and therefore rare earth chlorides were recovered. Thorium recovery rates are not mentioned. Iron, manganese, chromium and other elements formed chlorides were separa ted. In this study direct chlorination of Eskişehir Bey- likahir thorium ore and optimum parameters for separation of rare earths and thorium are examined. Chlorination process requires high temperatures for metal oxides and chlorine reaction, therefore the ore should be mixed with carbon, since the reducing effect of carbon will lower the reaction temperature. Experiments were carried out on three different per cent thorium ore of the Eskişehir Beylikahır area. The ore was reduced to 75 urn. The optimum ore/carbon ratio was found to be one, and the ore was mixed with carbon in a drum type mixer with the speed of 8-10 rotations per minute. Water containing some sugar was added to this mixture for binding. It was dried at 100 °C and caked. A chlorination furnace was designed for samples treated this way. The furnace can be opened like a book and heating can be controlled in three regions. It has an inner quartz tube in which the samples are placed. The diameter of the quartz tube is 57 mm and its length is 100 cm. The samples are placed in quartz boats which are made of a quartz tube of 18 mm diameter cut in half lengthwise. The length of this boat is 12 cm. The samples are heated to chlorination temperature and areheld at this temperature for one hour under argon atmos phere. Chlorine gas for different periods were passed and separation efficiency of thorium was determined. The parameters effecting separation of thorium are: a) Particle size of the ore used b) Ore to carbon ratio c) Chlorination temperature d) Chlorination time e) Thorium content of the ore to be chlorinated f ) Fluoride content of the ore to be chlorinated The highest thorium recovery is realized when the ore to carbon ratio is 1. With smaller values thorium recovery rapidly decreases, for higher values there is i small decrease of the recovery. In many studies with the monazite particle size reduction is not applied since monazite consists of fine particles. In this study because the structure of the ore is different, it is found with impurities. It should be ground to very fine particles in order to be mixed with carbon. After determination of the optimum carbon ratio, the effect of chlorination temperature on thorium recovery was studied. The optimum chlorination temperature for basnasite was found to be 1000 °C The other parameter was to determine the chlor ination time. 1, 2, 3, 4, hours of chlorination were tried, 3 hours was found to give the highest recovery. The increase in recovery after 4 hours of chlorination is negligible. The sample was kept at chlorination temperature for one hour in argon atmosphere and then chlorinated for later experiments. The recovery rate of 86% for half an hour of chlorination was found sufficient for completion of the reaction. This means an 1.5 hour shorter chlorination atmosphere period and also reduction of total chlorination time from 3 hours to 30 minutes. An important factor on percent recovery is the flow rate of chlorine. Low flow rates give low efficiencies while for highest efficiency the optimum flowrate is 0.7 1/h. At higher flow rates there is a decrease in xithe efficiency. The reason for this is at high flow rates, liquid chlorides which form of the ore surface stop the main reaction. The first applications of chlorination were done on low content ores and concentrates. The general opinion was that chlorination of ores below a minimum concentra tion is not efficient. This study has shown that the composition of the ore is more important than the concen tration. The low thorium content ore S14 used in this study gave a higher thorium recovery while the ore S15 which has higher thorium content gave a much lower recov ery because of the high fluoride content (5.28%). The highest thorium containing ore S16 gave the highest re covery because of low fluoride content (1.9%). To prove that an increase in the fluoride content would result in a decrease in thorium separation effi ciency, fluoride was added to S14 and S16 samples in the form of CaF2 to make up to 5.28% which is the fluor ide content of S15. S15 ore was added to S14 and S16 and the effect on thorium separation was studied. The results showed considerable decrease in thorium separ ation. Some experiments were run on duplicate and triplicate mixtures, and an addition of fluoride showed a drop of separation efficiency. All experiments were done at the optimum conditions determined before. These studies have shown that chlorination can be useful in processing the Eskişehir Beylikahxr thorium ore with a high rare earth elements content. A mineralogical survey of the area is necessary to determine the places with low fluoride content because these are suitable for chlorination. Chlorination pro cess involves crushing of the ore, mixing with carbon, and chlorinating at 1000 °C. The reaction is a solid gas reaction. It is possible to separate volatile compounds by condensation. The resultant solid products will be richer in rare earths content. It will also contain F, Si, and Ca. These elements won't react with chlorine under experimental circumstances. Other elements are volatilized and separated with thorium. There is no need for ore preparation and leaching steps in chlorination as in other processes. Our experiments were carried out at 1000 °C for thorium and higher temperatures weren't tried. It is xiipossible to separate rare earth elements as anhydrous chlorides at higher temperature using electric arc fur nace. Using this process instead of leaching we have eliminated addition of acids, bases and solutions to the ore and therefore have avoided filtration problems at every step and increase in mass because of 8-10 moles of cyrstal water of some salts. The optimum conditions for highest thorium separ ation efficiency were: Chlorination temperature Ore / carbon ratio Chlorine flow rate Reaction time 1000°C 1 0.7 1/hour 1 hour in argon atmosphere at 1000 °C 1/2 hour in chlorine atmosphere at 1000 °C Thorium recovery % : 86 Xiii

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