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Purification of Sodium Diuranate Produced from Gabal Gattar (Gii) Mineralization Using Tri Butyl Phosphate

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Purification of Sodium Diuranate Produced from Gabal Gattar (Gii) Mineralization Using Tri Butyl Phosphate Eleventh Arab Conference Oil the PeacefuJ Uses of Atomic Energy. Khartoum. Sudan. 16-20 Decanter 2012 PURIFICATION OF SODIUM DIURANATE PRODUCED FROM GABAL GATTAR (GII) MINERALIZATION USING TRI BUTYL PHOSPHATE JK. F. 2G. G. Mohamed 1w. M. Morsi 1Nuclear Materials Authority 2Faculty of Sciences^ Cairo University ABSTRACT Purification of the prepared sodium diuranate product to almost a ue was properly applied ؟nuclear purity grade, the solvent extraction techni to study the various relevant optimum conditions. For this purpose,organophosphorus solvents has been used; namely tri butyl phosphate (TBP). the produced sodium di-uranate contains only a small amount of the deleterious impurities which can be purified by solvent was dissolved in nitric acid so آ ﻣ ﻷ2 س ue. The prepared ؟exfraction techni that the free acidity of the obtained solution attained 3M and its uranium content assayed 202g/L. Nitrate solution from the TBP route used to prepare UO3 from the former, it was first evaporated at 95°c to decrease its volume to only 25% and which would increase uranium concentration. By proper cooling greenish yellow ؛uranyl nifrate hexa hydrate crystals were formed and which were then let ٠ for air drying before denifration at 280-300°C for 4 hr !.INTRODUCTION Several promising uranium occurrences have been discovered in Geble Gattar uranium prospect area in the Eastern Desert and are indeed hosted in younger granites (G-I to G-XII1) except GV occurrence, which is located in El-Hammamat sedimentary rocks. In this mineralization, uranium is mainly found as secondary minerals which are essentially represented by uranophane and beta uranophane .( and N4ahmoud؛J؛Sayyah and Attawiya) Apart from the recently developed dry refining processes which are almost devoted for producing directly the reactor grade UF6 required for the enrichment processes and in which the refining and conversion procedures are combined, the wet refining processes do not involve conversion. In other words, the latter would only be concerned with uranium relying to nuclear purity in the form of UO3 or ammonium uranyl tri-carbonate (AUTC). In all the wet refining processes solvent extraction technique are applied using different types of organic solvents with special emphasis on TBP and tertiaty amines. In the present work, acrude uranium concentrate or yellow cake (sodium diuranate) prepared from Gattar uranium mineralization is subjected to a solvent extraction purification process (refining) phosphate (TBP). The ؛using the neutral organophosphours tributy target is to optimize the relevant factors in a manner to obtain a purified uranium concentrate that is would be suitable for use as a nuclear fiile. Most countries actually been concerned with TBP using different procedures, however, amines have also been suggested in Japan and Argentina. 2 . EXPERIMENTAL 2.1. Preparation of Gattar Sodium Diuranate In order to obtain a uranium concentrate of the most possible purity, it was found suitable to precede its precipitation by eliminating most iron and aluminum by neutralization ofthe eluate solution till pH 3.5 .This is generally performed by a suitable alkali (NaOH) and the obtained iron cake would then be filtered and washed from possible entrained uranium values. The filtrate obtained after iron cake filtration and washing was farther neutralized till pH 7 using a dilute NaOH solution. At this pH, uranium is preeipitated as sodium di uranate (yellow cake) which was then filtrated, washed and dried at ۴ the prepared crude sodium diuranate as shown ٠ c. The analysis 110 in Table (1). Table(l): Quantitative anaiytical data ofthe prepared sodium diuranate. Element Sodium Diuranate * u% 48.9 Na 88070 Fe 2522 Si 1822 Mg 1020 Ca 621.5 Al 281 Zn 140.8 o 98.5 Mn 8367 p 78.453 Mo 31 Cu 25.6 K 15.55 9.5 ٧ Sr 2.2 * Moisture content =6.28% * Loss of Ignition =23.22% 2.2. Purification ofUranyl nitrate working !iquor uranate was-؛roper sample weights of the prepared sodium d? dissolved in stoichiometric a mounts of HNO3 acid to obtain a neutral solution ofuranyl nitrate; namely Na2U20 7+6HNCb — « U 0 2 (N0 3)2+2NaNCb+3H20 The obtained solution representing the feed for solvent extraction experiments was then filtered to remove the un- reacted residue and completed to volume with double distilled water. The .concentration in this solution attained 202gU/l ﺳ ﺎ س final 2.3. Solvent Extraction ?rocedure The prepared uranyl nitrate feed solution was then subjected to solvent extraction experiments using the above mentioned organic solvent. These experiments were so planned to investigate the optimum conditions for uranium extraction. The relevant extraction conditions were studied; namely contact time, free acid of the aqueous, phase extractant concentration, uranium concentration, temperature as well as O/A ratio. For this purpose, the following stock solutions ofthe working solvent systems were prepared: * 25% (v/v) TBP (50ml of purified TBP added tol50 ml kerosene). After each extraction experiment the aqueous phase was separated for uranium analysis and the extracted amount was calculated by difference. In addition, a final extraction experiment was performed under the determined optimum conditions and in which uranium and the associated elements were analyzed. In the applied extraction systems and before stripping, the obtained uranium-loaded organic layer was scrubbed to reduce the CO- extracted impurities content by contacting it with nitric acid or ammonium carbonate as follows: *0.1M H N O 3 at an O /A ratio o f l 5 : l in case o f using TBP extractant. Besides distilled water, both acid and alkali reagents were applied for uranium stripping from the scrubbed uranium-loaded namely dilute HNO3 or HC1 acid solution or else؛ organic solvent ammonium carbonate solution. The most efficient solution was then used in the stripping process as follows :- *0.01 MHNO} acid solution at an O/A ratio of 1:1 through five contacts. 3. Analytical Procedures ١ ؛ Analysis of Uranium 3.1 Uranium analysis in the different stream solutions was performed by oxidimetric titration using ammonium metavanadate after a prior uranium reduction. 3.2. Instrumentation and Methods of Analysis The crude uranium concentrate has been analyzed for several elements attaining up to 23 elements using different instrumental ,procedures. These elements inelude Al,A^Ba,Ca.€d ﻟ ﺴ ﺘ ﺎ ﺳ ﻪ1 Most .٢ ^ ,Co,Cr, Cu,Fe, K,Mg,Mn ,Mo,Na,Ni,P,P b,Si,Sr, Ti,Th, u,v of these elements have been analyzed by atomic absorption spectrometry (AAS) however, Al, p. Si, Th have been s^cfrophotometrically analyzed (Absorption Spectrometric Analysis (AAS :،؛Atom .3.3 The behavior of the other elements accompanying uranium whether in the uranium concentrates was analysed using AAS. For this purpose a GBC 932-AA speetrometer supplied with acetylene and nitrous oxide burner heads was used. 4. RESULTS AND DISCUSSION 4.1. Study of Relevant Faetors for TBP Solvent Extraction of Gattar Concentrate Tri butyl phosphate is a neutral organic phosphorous extractant that possesses three-open straight butyl chains attached by a phosphor group. It is a relatively cheap solvent and is characterized by its selectivity for uranium where it reacts with uranium according to the ’ ا following equation U 0 2 (N0 3)2 .2TBP org ٠ TBP org و ه + U 0 2 (N0 3) 2 2 TBP is indeed one ofthe most common extractants in refining of uranium, however, the formed uranyl nitrate -TBP complex is highly stable, and its re-extraction (stripping) into water would therefore require either a large number of transfer stages or else an undesirably large ratio of water to solvent. Due to its relatively high specific gravity (0.98), TBP is usually diluted by an inert diluent; kerosene is actually the most applicable diluent . 4.1.1. Effect of Contact Time on TBP-Uranium Purification Proper solution aliquots ofthe prepared uranyl nitrate solution (202gU/L) in 3M HN03 free acidity) were shaken for equilibration with equal volumes of 25% (v/v) TBP /kerosene under room temperature for different contact times ranging from 1 to 6 minutes. After phases separation, uranium was volumetrically determined in the aqueous phase while its concentration in the organic phase was calculated by difference. From the latter, both the extraction efficiency and the extraction coefficient were calculated. The obtained data are (.2) tabulated in Table (.2) [}[['’cranium purification ٠١١ Table؛،Table (2): Effect ©،'Contact tim؛، uIT assay at equilibrium g/L،,/! D°arv>_ %uO/TI س + ﻣ ﻤ ﺖContact Extracted Org phase Aq phase 42 160 0.26 20.79 1 2 67 135 0.49 33.16 3 78.5 123.5 0.63 3 8.86 48.51 0.94 04 أ 4 5 105 97 1.08 51.98 6 105 97 1.08 51.98 From above data, it is obvious that the extraction efficiency increases with increasing the contact time from 1 to 5 minutes, beyond which it become constant. In other words, as time increases from I to 5 minutes, the extraction efficiency of uranium increases from 20.79 to 51.98%. Therefore, 5 minutes would be considered as the optimum contact time for uranium equilibrium to be attained under the working conditions. Stiochiometrie calculation according to the above mentioned reaction reveals that the working 25% TBP/k (0 .9 4 M) would be actually saturated with 0.47 M u i.e. 111.86 g/L while the experimented data indicate that the obtained organic phase assays 105 g/L. It is interesting in this regard to mention that the relatively low extraction <ﺀ/ه 2 ة distribution coefficient (1.08) equivalent to about efficiency is actually due to the low TBP concentration in the organic phase. 4.1.2. Effect of Free acidity on TBP-Uranium Purification Six solution aliquots of 202 gU/L with free acidities varying from 1 to 6 M HN03 were first prepared and were then subjected to TBP/k extraction experiments for 5 minutes contact time, with solvent concentration 25% (v/v) TBP in kerosene, at an O/A ratio of 1:1 under room temperature.
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