id11580781 pdfMachine by Broadgun Software - a great PDF writer! - a great PDF creator! - http://www.pdfmachine.com http://www.broadgun.com Inorganic ISSN : 0974 - 746X Volume 8 Issue 2 CHEMAn InSdiaTn JRourYnal Full Paper ICAIJ, 8(2), 2013 [61-68] An upgrading procedure for the uranium concentrate product of Gattar pilot plant via ammonium carbonate M.F.Cheira*, R.A.Ghazala, K.F.Mahmoud Nuclear Materials Authority, P.O. Box 530 El Maadi, Cairo, (EGYPT) E-mail : [email protected] ABSTRACT KEYWORDS An impure crude uranium concentrate is produced at Gattar pilot plant in Uranium; which the ore material is processed by acid heap leaching followed by ion- Ammonium carbonate; exchange resin. Before proper refining of such a concentrate by the well Purification; developed solvent extraction techniques, it was found necessary to apply Yellow cake; a prior upgrading procedure to diminish the associated impurities. Ammonium Precipitation. carbonate is used for this purpose and the two relevant factors that would minimize the latter are studied, namely the (NH4)2CO3 concentration and the required time for effective settling of the precipitated impurities. Accordingly, it has been possible to increase the uranium assay in the working concentrate from about 36 up to 68% while that of Fe and V for example have been decreased from 1.22 and 1.53 % down to only 0.01and 0.029 % respectively. In refining of the upgraded product by solvent extraction, such impurities and the other remaining elements would be easily decreased to the permissible limits. 2013 Trade Science Inc. - INDIA INTRODUCTION cess in which solvent extraction technology is applied to produce nuclear grade products; namely uranium tri- One of the most important steps in the manufacture oxide (orange oxide; UO3) or else the ammonium ura- of the nuclear fuel cycle is the uranium refining and con- nyl tricarbonate[2]. The latter products would then be version which goes from the yellow cake to three dif- converted to UO2 and metallic uranium. The applied ferent uranium products, namely uranium dioxide (UO2), solvents include trialkyl phosphates, trialkyl phosphine natural metallic uranium (U) and uranium tetrafluoride oxides, dialkyl phosphoric acid as well as high-molecular (UF4). The refining step is indeed a process of minimiz- weight long-chain tertiary amines. ing the concentration of the harmful impurities which Uranium precipitated from its bearing solution over always defect nuclear fuel fabrication and performance. a wide pH range, acid or alkaline, depending upon the Uranium refining is currently carried out through two solution type and precipitant used[3-6]. In the produc- main technological routes. The first route is a dry refin- tion of yellow cake by precipitation techniques, the most ing process which employs fractional distillation of im- commonly used method was ammonium hydroxide pre- pure uranium hexafluoride for the production of reactor cipitation to form ammonium diuranate[7]. Although the [1] grade UF6 . The second refining route is a wet pro- yellow cake produced either by NH4OH or by MgO/ 62 An upgrading procedure for the urani.um concentrate product of Gattar pilot ICAIJ, 8(2) 2013 Full Paper Mg (OH)2 was of high quality, hydrogen peroxide was as the hexa-flouride much more difficult besides exert- [8-13] used to precipitate uranium as uranium trioxide . The ing a penalty if its content expressed as V2O5 exceeds pH of the solution, temperature and duration of pre- 2 weight percent of the concentrate[19]. Vanadium can cipitation as peroxide are of vital importance in the pro- actually be removed by addition of ammonium carbon- duction of pure uranium peroxide[14]. In all the wet re- ate where it would be converted to the yellow ammo- fining processes solvent extraction technique are ap- nium metavanadate precipitate at a pH value that ranges plied using different types of organic solvents with spe- from 5 to 10; viz: [15, 16] cial emphasis on TBP and tertiary amines . 2NaVO + (NH ) CO In Egypt, several promising uranium mineralizations 3 4 2 3 2NH VO + Na CO have been discovered in both the Eastern and western 4 3 2 3 Deserts as well as in Sinai and which are either associ- Choice of (NH4)2CO3 versus Na2CO3 has actually ated with igneous or sedimentary host rocks. Among behind its efficiency in precipitating vanadium. In the these, that of Gabal Gattar in North eastern Desert rep- meantime, metathesis (double replacement reaction) with resents an interesting uranium prospect that is mainly a concentrated solution of ammonium sulphate can also hosted in younger granites (G-I to G-XIII) except the be occasionally used to lower the sodium content, a GV occurrence which is located in El-Hammamat sedi- matter which allows for partial conversion of the so- mentary rocks. In this mineralization, uranium is mainly dium diuranate into ammonium diuranate, viz: found as secondary minerals which are essentially rep- Na U O + (NH ) SO resented by uranophane and beta uranophane[17,18]. 2 2 7 4 2 4 + 2- After successful laboratory scale studies for ura- (NH4 )2U2O7 + 2Na + SO4 nium recovery from the G. Gattar mineralized younger On the other hand, the ferric sulphate, in the leach granite occurrences, it was decided to construct an ex- solution could substantially react with all the phosphate perimental pilot plant at the site for testing the studied in solution to form ferric phosphate (FePO4) precipi- flowsheet. In this pilot plant, a crude uranium concen- tate as well as the applied carbonate to precipitate fer- trate (yellow cake) is currently produced through acid ric hydroxide at pH 10 according to the following reac- heap leaching followed by concentration and purifica- tion: tion through anion-exchange recovery unit. In the heap Fe (SO ) + 6(NH ) CO +6H O leaching of the ore material, uranium is leached by 20- 2 4 3 4 2 3 2 3(NH4 )2SO4 + 6(NH4 )HCO3 +2Fe(OH)3 40 g/l H2SO4 acid and from the obtained leach liquor uranium is then recovered through its adsorption by a Concerning, the other associated impurities includ- special anion exchange resin. Uranium is afterwards ing calcium, magnesium, aluminum, zinc, etc. they could eluted from the loaded resin with 1M NaCl solution actually be precipitated to a large extent by increasing acidified with about 0.05M sulfuric acid solution fol- the pH up to 10 during application of the suggested lowed by precipitation with NaOH solution as sodium procedure of ammonium carbonate leaching. diuranate. However, analysis of the latter has revealed From the above giving, it was found greatly inter- that it is actually a highly impure low grade product ( esting to apply a suggested procedure for upgrading 36 % U) besides the presence of several harmful ele- G. Gattar crude yellow cake via its proper treatment ments (metals and nonmetals). This low quality con- with ammonium carbonate. The latter would indeed centrate can be attributed to the difficult working con- upgrade the working concentrate to a level suitable ditions as well as to the relatively poor quality of the for the required final refining and conversion tech- adopted resin. For example it has been ascertained that niques. In this regard, the two relevant factors in this vanadium which assays up to the extent of 1.53% in the treatment and that would minimize the different asso- obtained concentrate is considered a serious highly un- ciated impurities would involve the (NH4)2CO3 con- desired contaminant. This is due to the fact that it would centration and in turn the leach solution pH besides render the subsequent conversion of the concentrate the required time for effective settling of the precipi- into uranium metal or other uranium compounds such tated impurities. Accordingly, it has been possible to Inorganic CHEAMn IIndSiaTn JRournYal ICAIJ, 8(2) 2013 M.F.Cheira et al. 63 Full Paper minimize the latter and increase the uranium assay in pH 7 2Na4UO2 (SO4 )3 3(NH 4 )2CO3 the obtained uranium concentrate by this treatment from about 36 up to 68%. The present work thus pro- (NH 4 )2U 2O7 4Na2SO4 2(NH 4 )2 SO4 3CO2 vides indeed a relatively simple and inexpensive pro- pH >7 (NH 4 )2U 2O 7 6(NH 4 )2CO 3 3H 2O cess for a considerable decrease of the impurities as- sociated with uranium in the prepared G. Gattar pilot 2(NH 4 )4UO 2 (CO 3 )3 6NH 4OH plant crude yellow cake with ammonium carbonate In each experiment, the obtained precipitate was solution. left to settle down after which the slurry was subjected to filtration and the precipitate was thoroughly washed EXPERIMENTAL while the obtained filtrate and washing were completed to a known volume before being directed for the analy- Material characterization sis of both uranium and impurities. On the other hand, The highly impure working yellow cake (sodium the final filtrate obtained at pH 10 has then been sub- diuranate) which is produced at G. Gattar pilot plant jected to adjust its pH to 12 using 30% sodium hy- has first been chemically analyzed using both qualitative droxide to form the upgraded sodium diuranate pre- and quantitative analytical procedures. The latter have cipitate as follows: pH 12 involved several analytical wet and instrumental tech- 2(NH ) UO (CO ) +14NaOH niques. 4 4 2 3 3 Na U O +6Na CO +8NH OH+3H O For the upgrading procedure suggested in the 2 2 7 2 3 4 2 present work, a proper 1L sulphate solution has been Analytical procedures prepared by dissolution of 10 g of the crude concen- trate in 30 g/l sulphuric acid solution. During dissolution Inductively Coupled Plasma Optical Emission Spec- the gross amount of silica and other insolubles have been trometry (ICP-OES) and X-ray fluorescence techniques removed as insoluble residue which was then filtered were used to qualitatively identify the composition of and washed until having 1 litre clear solution of the both the working uranium ore concentrate and the ob- working crude uranium concentrate.