The kinetics of concentrates of uranium monoxide-oxide dissolution process by nitric acid solutions of 5...9 mole/l in the range of 11...90 °C has been studied. It is stated that initial nitric acid concentration increasing results in some uranium dissolution degree increasing only at the first process stage. Temperature increasing significantly raises uranium dissolution degree at the first stage as well. Uranium dissolution degree increases for all studied temperatures with increasing of the process period. The main feature of the studied process is that while dissolving uranium monoxide-oxide the behavior of iron, molybdenum, silicon additives is adequate to that of uranium. The equation of the reducing sphere describes the uranium leaching process from its nitric acid concentrate

Buynovskiy, A. S.

Kozyrev, A. S.

Makaseev, Yu. N.

Mikhailova, N. A.

Romanov, M. E.

Ryabov, A. S.

Shamin, V. I.

Shikerun, T. G.

Electronic archive of Tomsk Polytechnic University

REFERENCES1. Certificate of federal task program «Development of atomic energyindustrial complex of Russia for 2007–2010 and in perspective till2015». The main program builder is Federal nuclear power engineering agency of the RF. It was stated by the RF Government regulation 06.10.2006 № 605. – Moscow: 2006. – 184 p.2. Yaminskiy V.V., Pchelin V.A., Amelina E.A. et al. Coagulation contacts in dispersed systems. – Moscow: Khimia, 1982. – 185 p.3. Technology of atomic raw material / Ed. by A.P. Zefirov. – Moscow:The main management in atomic energy research at USSR Councilof Ministers, 1959. – 147 p.4. Kovarskiy N.Ya., Ivanenko V.V., Kustov V.N. Complex defining ofsea water microelement composition using electrodeposited magnesium hydroxide // Zhurnal Analiticheskoy Khimii. – 1987. –V. 42. – № 12. – P. 2126–2179.5. Lobanov F.I., Korobov A.S., Kuzmitskiy V.G., Spiridonova N.N.Organization of production of polymer flocculants PRAESTOL inRussia and experience of their application at utility and industrialenterprises of Russia and CIS // Materials of the IId Internationaltheoretical and practical conference devoted to the 1000 anniversaryof Kazan. – Kazan, 2005. – P. 140–142.6. Polyacrilamide / Ed. by V.F. Kurenkova. – Moscow: Khimia, 1992.– 192 p.7. Lazarchuk V.V., Ryabov A.S., Shamin V.I. et al. Using flocculantsfor separation of highly concentrated uranium solutions and fine dispersed solid limes // Theses of the reports of the Vth Russian conference in radiochemistry. Radiokhimia2006. – Dubna, October23–27, 2006 – P. 308–309.8. Catalogue. Agents for drinking water. – 2006. – 21 p. Authorized agent of the company SNF S.A. FLOERGER(r) snf@online.ru;www.koagulant.ruReceived on 07.12.2006Bulletin of the Томsк Pоlytеchnic University. 2007. V. 311. № 318To obtain uranium hexafluoride used for enrichmentaccording to the demands of International standardАSТМ С 78703 uranium refined from soluble and insoluble impurities to the certain limits is required. Concentrates which represent oxides of uranium and impurities afterthermal treatment (U3О8, МоО3, SiО2, Fe3О4, СаО, МgО,Al2О3 etc.) may be used as a material for obtaining uranium of the required purity degree. Dissolution (leaching) ofU3О8 from the concentrates is reasonable to be carried outwith nitric acid as the extractant tributyl phosphate usedfor refining U (VI) from impurities works efficiently in nitrate medium. In the process of triuranium octaoxide dissolution in nitric acid U(IV) is oxidized to U(VI) withoutoxidizer. Nitric acid has low corrosive activity relative toconstructive materials, for example, to steel 12Х18Н10Т.The task of investigations included defining influence oftemperature, nitric acid concentration, time of concentrate dissolution on the degree of extraction of uranium andimpurities from it (iron , molybdenum, silicon) as well asinvestigation of kinetics of uranium and impurities dissolution, calculation of velocity constant and activation energy,choice of limiting process stage.Experimental partTriuranium octaoxide concentrate which representsa darkgrey powder of the following composition: U –83,14 wt. %; U234 – 53 mkg/g; impurities (% of U): Fe– 0,070, SiO2 – 0,170, Mo – 0,031, Ca – 0,004,As≤0,004, B≤0,00003, F≤0,0005, halogens – 0,002, Mg– 0,001, P – 0,006, K – 0,01, Na – 0,010, Th≤0,003,Ti≤0,001, V≤0,001, Zr≤0,001, W≤0,001 was used as asubject of inquiry. Apparent and metric densities of thepowder are 1, 65 and 6, 83 g/cm3, respectively. Powderparticle size determined at sedimentometer ВС3 didnot exceed 50 mkm. Grainsize composition: 3 % offractions of 0...10 mkm, 18 % of fractions of10...20 mkm, 35 % of fractions of 20...30 mkm, and 22 %of fractions of 30...40 mkm and of 40...50 mkm each.Influence of nitric acid concentrations (5...9 mole/l), temperature (11...90 °С) and time on dissolutiondegree of uranium oxides and impurities was studied atlaboratory setup (Fig. 1). Reactor (3) was filled up withnitric acid of specified concentration. The solution wasstirred with mechanical mixer. Solution temperature inUDC 546.791.02.238:66.061THE RESEARCH OF URANIUM MONOXIDEOXIDE DISSOLUTION PROCESS IN NITRIC ACIDA.S. Kozyrev, T.G. Shikerun, А.S. Ryabov, V.I. Shamin, N.A. Mikhailova, M.E. Romanov, *A.S. Buynovskiy, *U.N. MakaseevFederal Unitary Enterprise of Siberian Group of Chemical Enterprises, SeverskЕmail: shk@seversk.tomsknet.ru*Seversk State Technological Academy (SSTA), SeverskЕmail: nmd@ssti.ruThe kinetics of concentrates of uranium monoxideoxide dissolution process by nitric acid solutions of 5...9 mole/l in the range of11...90 °C has been studied. It is stated that initial nitric acid concentration increasing results in some uranium dissolution degree increasing only at the first process stage. Temperature increasing significantly raises uranium dissolution degree at the first stage as well. Uranium dissolution degree increases for all studied temperatures with increasing of the process period. The main feature of the studied process is that while dissolving uranium monoxideoxide the behavior of iron, molybdenum, silicon additives is adequate to that of uranium. The equation of the reducing sphere describes the uranium leaching process from its nitric acid concentrates.the reactor was maintained by thermostat (2) with accuracy ±1 °С. Having obtained the specified temperature,batch of concentrate U3O8 (10 g) was introduced intoacid solution and time reading was maintained.Fig. 1. Diagram of laboratory setup: 1) mechanical mixer motor;2) electric thermostat; 3) dissolution reactor; 4) hydraulic lock; 5) controller of mixer number of revolutions;6) thermometer; 7) samplerMass content of uranium and impurities in concentrate and solution samples was defined by the techniques of accredited laboratory of radiochemical plant atSGCE, Seversk.Uranium content in the samples was defined by chelatometric method; relative definition error is 3, 0 %.Impurity content in uranium solution was determined by chemicalspectral method [1]. Total error of definition is Mo 40...85 % depending on molybdenumcontent in the sample (at different dissolution conditions), Fe – 60...80 %, Si – 80...95 %.Dissolution degree of uranium oxides and impuritieswas determined as a part of the element passed into solution by the moment of sampling relative to the initial amount of the element in the batch of concentrate U3O8 in %.Results and discussionIt was stated that dissolution degree of U3O8 during theprocess changes nonmonotonically (Fig. 2, 3). For example, during the first 5...10 s 70...80 % of uranium (VI) passes into solution 5 mole/l НNО3 at temperature 90 °С andСhemistry19Fig. 2. Influence of temperature and time of reaction in the solution of 5 mole/l HNO3 on dissolution degrees: а) U3O8; б) ferric oxide; в) molybdenum oxide; г) silicon oxideDissolution degree ?,%Time, s Dissolution degree ?,%Time, sDissolution degree ?,%Time, s Dissolution degree ?,%Time, s then during 180 s dissolution degree achieves 98,2 %. Increasing process duration the dissolution degree of U3O8rises for all studied temperatures. Dissolution occurs slowly at 11 °С. So during 30 s 4,4 % of uranium (VI) is extracted into solution, during 180 s it is 37,1 %, and during1200 s it amounts to 96,8 %. Increasing the temperatureuranium dissolution degree rises significantly at the sameresponse time. Changing nitric acid concentration from 5to 7...9 mole/l results in increasing dissolution degree ofU3O8 at the initial stage of the process (in 10 s it increasedby 5 % and 9,7 % respectively). But by the end of the process (in 180 s) dissolution degree of U3O8 becomes equalfor all studied concentrations – 98,2 %.Impurities behavior at dissolution of triuranium octaoxide concentrate of nitric acid repeats the characterof dependence of U3O8 dissolution degree on temperature and dissolution duration. Within two hours dissolution degree of molybdenum oxide amounted to45...50 %, ferric oxide – 40...47 % and silicon oxide –8...9 % (Fig. 4–9).Dissolution process of uranium concentrates generally consisting of uranium oxides and attendant impurities refers to the heterogeneous one behaving by thetype S+L>S+L+G, where S is solid; L is liquid; G isgaseous state of reactants. Undissolved concentrate residue should be considered as a solid reaction product.Soluble nitrates of uranyl and impurities in various ionicforms [2, 3] pass into solution that subsequently mayimpede uranium extraction refining [4–6]. Nitric oxides NO, NO2 are gaseous reaction products.To describe the kinetics of heterogeneous processesvarious equations are applied in terms of reaction conditions [7–10]. For the process which rate depends bothon agents diffusion to the response surface and on reaction velocity on the phase interface the equation of reducing surface was used:where α is the degree of conversion (reaction), parts; kis the velocity constant, с–1; τ is the time of reaction, s.Processing the experimental data the dependence ofdissolution degree on the time was made in coordinates1–(1–α)1/3; t and adequacy of applying chosen equationwas estimated by correlation factor. The experimentaldata in these coordinates are well linearized, chosenequation describes the change of concentrate dissolu1/31 (1 ) ,kα τ− − = ⋅Bulletin of the Томsк Pоlytеchnic University. 2007. V. 311. № 320Fig. 3. Influence of HNO3 concentration and reaction time at 90 °С on dissolution degree: а) U3O8; б) ferric oxide; в) molybdenum oxide; г) silicon oxideDissolution degree ?,%Time, s Dissolution degree ?,%Time, s Dissolution degree ?,%Dissolution degree ?,%Time, s Time, s tion degree on time at different temperatures ratherauthentically and kinetic parameters of the process maybe defined by this equation. Reaction velocity constantwas calculated for each temperature by slope ratio of aline in coordinates 1–(1–α)1/3; t and temperature dependence of reaction velocity constant was made in coordinates lnk; 1/Т. On linear section of the lnk=f(1/Т)the parameters lnk0 and Е/R were found by the leastsquare technique and activation energy Е and preexponential factor k0 were searched from them.The results of calculation of kinetic parameters ofU3O8 dissolution process are given in Tables 1, 2 and theirmathematical treatment using the equation of reducingsurface is represented by diagram in Fig. 4, a and 5, a.Fig. 4. Dependence 1–(1–α)1/3=k; t for: а) U3O8; б) ferric oxide;в) molybdenum oxideThe analysis of the given data shows that the equation of reducing sphere describes rather authenticallyU3O8 dissolution process from its concentrates by nitricacid with initial concentration (5...9) mole/l in temperature range of 28...90 °С at S:L=1:2 (S is solid in mass,L is liquid in volume). Reaction order determined bythis model is close to a unit and apparent activation energy amounted to Еа=52 kJ/mole. Dissolution degree ofU3O8 is determined to a large degree by process temperature. In the researched temperature range 37...90 °СU3O8 dissolution degree changes from 0 to 0,8 fractions.At temperature 11 °С within 60 s from the beginning ofthe process the breakdown time is noted. It might besupposed that in the range of relatively low temperatures there is more complicated response mechanism.Fig. 5. Dependence of lnk on 1/Т for: а) U3O8; б) ferric oxide;в) molybdenum oxideThe experimental data on dissolving the investigated impurities were similarly treated. The results showed that whensolving uranium concentrate the behavior of ferric oxide impurities (Fig. 4, б and 5, б), molybdenum (Fig. 4, в and 5, в)and other impurities is adequate to U3O8 behavior.Final results of processing experimental data in theform of parameters of kinetic equations for dissolutionof triuranium octaoxide and impurities contained inconcentrate are presented in Table 3.lnK(1/?)·103(1/?)?103lnK(1/?)?103lnK 1-(1-?)1/3Time, s 011 CFunction 1-(1-?)1/3Time, s 011 CTime, s Function 1-(1-?)1/3Сhemistry21Table 1. Calculation of rate constant of U3O8 dissolution process by solution HNO3Table 2. Computation of apparent activation energy of U3O8dissolution process by solution HNO3To process the obtained experimental data the otherequations were also checked [2, 3]. However, using theequation of reducing sphere turned out to be the mostadequate.To decrease the volume of gases escaping the reactordissolver and nitric acid consumption for dissolution thefollowing technique was developed. According to thistechnique uranium oxide powder is placed under waterlayer at the ratio of water layer height to height of uranium oxide layer is not less than 1,3 and nitric acid withconsumption 0,30...0,36 t of HNO3 per 1 t/h of uraniumis introduced under the layer of uranium oxides.Table 3. Results of calculation of kinetic parameters of U3O8dissolution process and impurities contained in uranium concentrate in the range of temperatures of20...90 °С Order of dissolution process of uraniumoxides and impurities is the firstFor increasing the degree of separation of liquid andsolid phases the method of uranium concentrate dissolution with obtaining uranium solutions (VI) with concentration 700...800 g/l at weight ratio of nitric acid touranium 0,75...0,84 at temperature 85...100 °С was developed. The obtained pulp is diluted in uncooled stateto the required uranium concentrations (VI) and nitricacid by weak nitrate solutions. After that aqueous phaseis separated from insoluble residue.Conclusion1. Kinetics of U3O8 concentrates dissolution by nitric acidsolutions with concentration 5...9 mole/l at 11...90 °Сwas investigated and process kinetic equation is defined.2. The method of uranium oxide dissolution at 100 °Сand nitric acid concentration 12...16 mole/l obtainingconcentrated uranium solutions (VI) 700...800 g/l andfurther dilution to 400...500 g/l was developed.3. To decrease the volume of gases escaping the reactordissolver and reduction of nitric acid consumption the procedure of U3O8 concentrates dissolution supplying nitric acid under the layer of oxidepowder was developed.ElementDegree of element dissolution, in fractionsEа, kJ/mole k0, с–1U 0...0,8 52 (1,7±0,4).106Mo 0...0,5 48 (2,1±0,6).105Fe 0...0,4 49,5 (2,4±1,3).105Si 0...0,1 51,3 (3,6±0,7).105Temperature1/Т .103Reactionvelocityconstant,k.104, с–1ln kCorrelation factorApparentactivationenergy,kJ/mole°С К28 301 3,32 15 –6,5020,964 5237 310 3,23 29 –5,84345 318 3,14 70 –4,96267 340 2,94 179 –4,02390 363 2,75 418 –3,175Temperature, °СTime, sDissolutiondegree ofU3O8, infractionsFunction1–(1–α)1/3Reactionvelocityconstant,k.104, с–1Correlation factor280 0 015 0,94230 0,044 0,014860 0,056 0,0191180 0,371 0,1431300 0,805 0,4201370 0 029 0,95930 0,1685 0,014860 0,344 0,019190 0,607 0,1431120 0,81 –450 0 070 0,98915 0,337 0,128030 0,582 0,252460 0,81 0,4251670 0 0179 0,9665 0,428 0,169915 0,700 0,330825 0,849 0,467835 0,859 –900 0 0418 0,8865 0,711 0,338910 0,803 0,4181Bulletin of the Томsк Pоlytеchnic University. 2007. V. 311. № 322REFERENCES1. OST 95 101172003. Uranium. Chemicalspectral technique of measuring impurity content.2. Solubility and properties of solutions of molybdenum and tungstencompounds: Reference book / Z.G. Karov, M.V. Mokhosoev; Managing editor A.N. Kirgintsev. – Novosibirsk: Nauka, 1993. – 131 p.3. Blokhin A.A., Solodukhin S.S., Kopyrin A.A. State diagram of molybdenum (VI) and tungsten (VI) in solutions at their joint presence // Zhurnal Neorganicheskoy Khimii. – 2003. – V. 48. – № 3. – P. 508–511.4. Fedorov Yu.S., Zilberman B.Ya. Secondary extraction properties ofactinoid solvates and zirconium // Radiokhimiya. – 1999. – V. 41. –№ 6. – P. 508–513.5. Suleimanov E.V., Chernorukov N.G., Golubev A.V. Thermochemistry of uranomolybdate of alkali metals // Radiokhimiya. – 2006. –V. 48. – № 1. – P. 67–69.6. Fedorov Yu.S., Blazheva I.V., Zilberman B.Ya. Combined extractionof Cr(VI) and U(VI) by tributyl phosphate // Radiokhimiya. – 2000.– V. 42. – № 1. – P. 69–73.7. Rosovskii A.Ya. Topochemical reactions kinetics. – Moscow: Khimiya, 1974. – 128 p.8. Bare P. Heterogeneous process kinetics. – Moscow: Mir, 1976. –400 p.9. Delmon B. Heterogeneous reaction kinetics. – Moscow: Mir, 1972.– 374 p.10. Emmanuel N.M., Knorre D.G. Chemical kinetics course. The 3d issue. – Moscow: Visshaya Shkola, 1974. – 400 p.Received on 07.12.2006

The research of uranium monoxide-oxide dissolution process in nitric acid

The research of uranium monoxide-oxide dissolution process in nitric acid

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