RU2568729C1 - Method of preparing anion-deficient uranyl nitrate solutions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes mixing uranium oxide with water with liquid to solid ratio of 0.1-0.15, adding nitric acid to the obtained pulp while stirring constantly, said nitric acid being added in droplets with molar ratio of the nitrate ion to metal in the solution of 1.6-1.95, filtering the obtained solution and adjusting the density of the solution first, and then pH of the solution at temperature not higher than 12°C by adding urotropin.

EFFECT: efficient production of anion-deficient metastable uranyl nitrate solutions with given characteristics.

5 cl, 4 ex

Description

The invention relates to the preparation of anion-deficient metastable solutions of uranyl nitrate and can be used in chemical technology, in particular, when impregnating uranium into porous graphite billets in order to obtain uranium-graphite fuel elements (fuel elements) or when producing microspheres using the sol-gel method.

A known method of preparing anion-deficient solutions by dissolving uranium oxides in an aqueous solution of thorium nitrate (US patent No. 3838062, IPC C01G 43/00, NCI 252 / 301.1R, publ. 09.24.1974). The solutions obtained in this way with the addition of urotropine and urea can be used for the production of microspherical ceramic fuel by the sol-gel method. However, this method is only suitable for the preparation of mixed solutions of uranium and thorium in the preparation of mixed UO ₂ —ThO ₂ fuel.

The closest in technical essence to the proposed invention is a method comprising dissolving uranium oxides by contacting them with nitric acid and water and filtering. In accordance with the known method, anion-deficient solutions of uranyl nitrate are prepared by dissolving uranium oxides lower than UO ₃ and higher than UO ₂ in dilute nitric acid, the amount of which is calculated with the expectation of obtaining a molar ratio of nitrate ion to uranium equal to 1.5 ( US patent No. 4051060, C01G 43/00, NCI US 252 / 301.1R, publ. 09/27/1977).

The disadvantage of this method is the impossibility of obtaining a metastable anion-deficient solution with predetermined characteristics in terms of the molar ratio of nitrate ion to uranium and pH (pH). So, for example, with a calculated ratio of nitrate ion to uranium equal to 1.5, the solutions obtained by this method have a range of 1.4 ÷ 1.8, which greatly complicates the preparation of metastable solutions, since their preparation requires anion scarce solutions with a strictly specified value of the concentration of uranium and the ratio of the nitrate ion to it when urotropine is added to it. In addition, the estimated amount of acid that is taken at the dissolution stage is estimated approximately and does not take into account the oxygen coefficient of the soluble uranium oxide.

) и водородному показателю (pH) раствора.The problem to which this invention is directed, is to obtain anion-deficient metastable solutions of uranyl nitrate with predetermined characteristics according to the concentration of uranium, the ratio of nitrate ion to it ( $$N{O}_3^{-}/U$$

) and the pH value of the solution.

The task and technical result are achieved by the fact that in the method of preparing anion-deficient solutions of uranyl nitrate, including dissolving uranium oxides by contacting them with nitric acid and water and filtering, according to the invention, uranium oxide is preliminarily mixed with water in a liquid to solid ratio of 0.1 ÷ 0.15, and the dissolution is carried out with constant stirring of the pulp by feeding in it nitric acid, which is introduced dropwise with a molar ratio of nitrate ion to metal in the solution of 1.6 ÷ 4.95, while lichestvo moles of nitric acid per mole of uranium calculated by the formula:

N _u is the number of moles of uranium;

To _o is the oxygen coefficient (O / U);

K is the molar ratio of nitrate ion to uranium,

after filtration, the resulting solution is first adjusted for density, and then adjusted for hydrogen at a temperature of not more than 12 ° C by adding urotropine.

The optimal feed rate of nitric acid is 400 ÷ 500 ml / hour.

The dissolution of uranium oxides and the filtration of the solution is carried out at a temperature of 40 ÷ 75 ° C.

The density adjustment of the solution is carried out by adding water according to the formula:

γ is the density of the solution without the addition of urotropine, g / cm ³ .

The pH adjustment of the resulting solution is carried out by adding urotropin, which is added at a temperature of 5 ÷ 12 ° C, while the number of moles of urotropin (N) per mole of uranium is determined by the formula:

N _u is the number of moles of uranium;

pH * is the pH of the solution after dissolving the uranium oxide and adjusting the density of the solution by adding water.

The optimal range of the rate of nitric acid supply to the pulp, which is 400 ÷ 500 ml / h, is due to the fact that at a higher speed due to the large exothermicity of the uranium oxide dissolution reaction, a local, uncontrolled heating of the pulp to temperatures of 80-100 ° C occurs, leading to partial removal nitric acid and water, which ultimately negatively affects the receipt of a solution with specified characteristics. A decrease in the feed rate of less than 400 ml / h seems to be impractical due to a decrease in the dissolution rate and an increase in the duration of the dissolution process.

) затрудняется растворение оксидов урана, а снижение дефицита ( $$N{O}_3^{-}/U\ge \mathrm{1,95}$$

) приводит к получению очень кислых растворов (pH≥-1,0), что делает затруднительным их корректировку по pH и использование для получения метастабильных растворов, пригодных для импрегнирования урана и применения в золь-гель процессе.The range of the deficit ratio of nitrate ion to uranium in solution (1.6 ÷ 1.95) is due to the fact that with an increase in the deficit of nitric acid ( $$N{O}_3^{-}/U\le \mathrm{1,6}$$

) the dissolution of uranium oxides is difficult, and the deficit is reduced ( $$N{O}_3^{-}/U\ge 1.95$$

) leads to the production of very acidic solutions (pH≥-1.0), which makes it difficult to adjust them to pH and use to obtain metastable solutions suitable for impregnation of uranium and use in the sol-gel process.

The optimum temperature range for dissolving uranium oxides and filtering the solution, equal to 40 ÷ 75 ° C, is due to the fact that with an increase in temperature above 75 ° C, partial removal of nitric acid and water occurs, and with a decrease in temperature below 40 ° C, the formed uranyl nitrate crystallizes.

The dissolution of dioxide (UO ₂ ) and nitrous oxide (U ₃ O ₈ ) of uranium proceeds according to the following equations:

The number of moles of nitric acid per mole of uranium, which is taken to dissolve the uranium oxides, depends on the oxygen coefficient of the oxide (O / U) and the given molar ratio of nitrate ion to uranium. This amount is calculated by the formula (1).

The range of the ratio of solid (uranium oxide) to liquid (water) in the pulp (T: G), equal to 0.1 ÷ 1.15, due to the fact that a decrease in water in the pulp (T: W≤0.1) leads to an increase in viscosity and the deterioration of its mixing, and an increase in water in the pulp (T: W≥0.15) leads to its dilution and a decrease in the rate of dissolution.

The method proposed by the authors was tested in the preparation of anion-deficient metastable solutions for the impregnation of uranium into porous graphite blanks.

Example 1

), равным 1,6, брали 350 г диоксида урана (UO₂) и смешивали с 50 мл воды до получения однородной пульпы (Т:Ж=0,143). 370 мл воды смешивали с 230 мл азотной кислоты с удельным весом 1,352 г/см³ (2,2 моля HNO₃ на моль урана) и по каплям при перемешивании со скоростью 450 мл/час подавали в пульпу. Количество молей азотной кислоты (2,2 моля) на моль урана рассчитывали по формуле (1). Полученную смесь нагревали до 60-70°C. После окончания подачи кислоты (1,5 час) раствор выдерживали при этой температуре в течение 0,5 часа и затем проводили его фильтрование при 40-60°C. Полученный раствор имел плотность при 40°C 1,69 г/см³ (32,0 мас.% урана) и рН=1,99. Добавлением воды раствор корректировали по плотности (1,53 г/см³) и концентрации урана (28 мас.%) по формуле (2). Количество молей уротропина на моль урана определяли по формуле (3), и для рН=1,9 охлажденного до 5°C раствора оно составило 0,85 молей уротропина на моль урана. После добавления уротропина получили анион-дефицитный метастабильный раствор нитрата уранила с pH=3,5 и концентрацией урана 27,1%.To prepare a solution of uranyl nitrate with a ratio of nitrate ion to uranium ( $$N{O}_3^{-}/U$$

), equal to 1.6, took 350 g of uranium dioxide (UO ₂ ) and mixed with 50 ml of water to obtain a homogeneous pulp (T: W = 0.143). 370 ml of water was mixed with 230 ml of nitric acid with a specific gravity of 1.352 g / cm ³ (2.2 mol of HNO ₃ per mole of uranium) and was added dropwise with stirring at a rate of 450 ml / hour to the pulp. The number of moles of nitric acid (2.2 mol) per mole of uranium was calculated by the formula (1). The resulting mixture was heated to 60-70 ° C. After completion of the acid supply (1.5 hours), the solution was kept at this temperature for 0.5 hours and then it was filtered at 40-60 ° C. The resulting solution had a density at 40 ° C of 1.69 g / cm ³ (32.0 wt.% Of uranium) and pH = 1.99. By adding water, the solution was adjusted for density (1.53 g / cm ³ ) and uranium concentration (28 wt.%) According to formula (2). The number of moles of urotropine per mole of uranium was determined by the formula (3), and for pH = 1.9 of a solution cooled to 5 ° C it was 0.85 moles of urotropine per mole of uranium. After the addition of urotropine, an anion-deficient metastable solution of uranyl nitrate with a pH of 3.5 and a uranium concentration of 27.1% was obtained.

Example 2

брали 400 г закиси-окиси урана (U₃O₈) и смешивали с 60 мл воды до получения однородной пульпы (Т:Ж=0,15). 300 мл воды смешивали с 290 мл азотной кислоты (2,1 моля HNO₃ на моль урана) и по каплям при перемешивании со скоростью 500 мл/час подавали в пульпу. Количество молей азотной кислоты (2,1 моля на моль урана) рассчитывали по формуле (1). Полученную смесь нагревали до 40-60°C. Полученный раствор после фильтрации имел плотность при 40°C 1,69 г/см³ (32,3 мас.% урана) и рН=0,5. Добавлением воды корректировали раствор по плотности (1,60 г/см³) и концентрации урана (29,7 мас.%) по формуле (2). Количество молей уротропина на моль урана определяли по формуле (3), и для рН=0 охлажденного до 5°C раствора оно составило 1,5 молей уротропина на моль урана. После добавления уротропина получили анион-дефицитный метастабильный раствор нитрата уранила с рН=2,8 и концентрацией урана 25,1 мас.%.To prepare a solution of uranyl nitrate with the ratio $$N{O}_3^{-}/U=1.95$$

400 g of uranium oxide (U ₃ O ₈ ) were taken and mixed with 60 ml of water until a homogeneous pulp was obtained (T: W = 0.15). 300 ml of water was mixed with 290 ml of nitric acid (2.1 mol of HNO ₃ per mole of uranium) and was added dropwise with stirring at a speed of 500 ml / hour to the pulp. The number of moles of nitric acid (2.1 moles per mole of uranium) was calculated by the formula (1). The resulting mixture was heated to 40-60 ° C. The resulting solution after filtration had a density at 40 ° C of 1.69 g / cm ³ (32.3 wt.% Uranium) and pH = 0.5. By adding water, the solution was adjusted according to density (1.60 g / cm ³ ) and uranium concentration (29.7 wt.%) According to formula (2). The number of moles of urotropin per mole of uranium was determined by formula (3), and for pH = 0 of a solution cooled to 5 ° C, it was 1.5 moles of urotropine per mole of uranium. After the addition of urotropine, an anion-deficient metastable solution of uranyl nitrate with a pH of 2.8 and a uranium concentration of 25.1 wt.% Was obtained.

Example 3

использовали 350 г диоксида урана, который смешивали с 40 мл воды до получения однородной пульпы (Т:Ж=0,11). 420 мл воды смешивали с 260 мл азотной кислоты (2,48 моля HNO₃ на моль урана) и по каплям при перемешивании со скоростью 450 мл/час в течение 1,25 часа подавали в пульпу. Количество молей азотной кислоты (2,45 моля) на моль урана рассчитывали по формуле (1). Полученную смесь нагревали до 60-75°C. Полученный раствор имел плотность при 40°C 1,63 г/см³ (30,5 мас.% урана) и рН=0,8. Добавлением воды раствор корректировали по плотности (1,5 г/см³) и концентрации урана (27 мас.%) по формуле (2). Количество молей уротропина на моль урана определяли по формуле (3), и для рН=0,6 охлажденного до 5°C раствора оно составило 1,3 молей уротропина на моль урана. После добавления уротропина получили анион-дефицитный метастабильный раствор нитрата уранила с рН=2,5 и концентрацией урана 25,3 мас.%.To prepare a solution of uranyl nitrate with the ratio $$N{O}_3^{-}/U=1.88$$

used 350 g of uranium dioxide, which was mixed with 40 ml of water to obtain a homogeneous pulp (T: W = 0.11). 420 ml of water was mixed with 260 ml of nitric acid (2.48 mol of HNO ₃ per mole of uranium) and was added dropwise with stirring at a speed of 450 ml / hour for 1.25 hours into the pulp. The number of moles of nitric acid (2.45 mol) per mole of uranium was calculated by the formula (1). The resulting mixture was heated to 60-75 ° C. The resulting solution had a density at 40 ° C. of 1.63 g / cm ³ (30.5 wt.% Uranium) and pH = 0.8. By adding water, the solution was adjusted for density (1.5 g / cm ³ ) and uranium concentration (27 wt.%) According to formula (2). The number of moles of urotropine per mole of uranium was determined by formula (3), and for pH = 0.6 of a solution cooled to 5 ° C, it was 1.3 moles of urotropine per mole of uranium. After the addition of urotropine, an anion-deficient metastable solution of uranyl nitrate with a pH of 2.5 and a uranium concentration of 25.3 wt.% Was obtained.

Example 4

брали 400 г закиси-окиси урана (U₃O₈) и смешивали с 50 мл воды до получения однородной пульпы (Т:Ж=0,125). 300 мл воды смешивали с 250 мл азотной кислоты (1,8 моля HNO₃ на моль урана) и по каплям при перемешивании со скоростью 500 мл/час подавали в пульпу. Количество молей азотной кислоты (1,8 моля) на моль урана рассчитывали по формуле (1). Полученную смесь нагревали до 50-70°C. Полученный раствор имел плотность при 40°C 1,75 г/см³ (33,7 мас.% урана) и рН=1,5. Добавлением воды раствор корректировали по плотности (1,63 г/см³) и концентрации урана (30,6 мас.%) по формуле (2). Количество молей уротропина на моль урана определяли по формуле (3), и для рН=0 охлажденного до 10°C раствора оно составило 1,0 молей уротропина на моль урана. После добавления уротропина получили анион-дефицитный метастабильный раствор нитрата уранила с рН=3,8 и концентрацией урана 28,3 мас.%.To prepare a solution of uranyl nitrate with the ratio $$N{O}_3^{-}/U=\mathrm{1,6}$$

400 g of uranium oxide-uranium oxide (U ₃ O ₈ ) were taken and mixed with 50 ml of water until a homogeneous pulp was obtained (T: W = 0.125). 300 ml of water was mixed with 250 ml of nitric acid (1.8 mol of HNO ₃ per mole of uranium) and was added dropwise with stirring at a speed of 500 ml / hour to the pulp. The number of moles of nitric acid (1.8 mol) per mole of uranium was calculated by the formula (1). The resulting mixture was heated to 50-70 ° C. The resulting solution had a density at 40 ° C of 1.75 g / cm ³ (33.7 wt.% Of uranium) and pH = 1.5. By adding water, the solution was adjusted for density (1.63 g / cm ³ ) and uranium concentration (30.6 wt.%) According to formula (2). The number of moles of urotropine per mole of uranium was determined by formula (3), and for pH = 0 of a solution cooled to 10 ° C, it was 1.0 moles of urotropine per mole of uranium. After the addition of urotropine, an anion-deficient metastable solution of uranyl nitrate was obtained with a pH of 3.8 and a uranium concentration of 28.3 wt.%.

The technical advantages of the method proposed by the authors in comparison with the prototype (US patent No. 4051060, C01G 43/00, NCI US 252 / 301.1R, publ. 09/27/1977) consist in obtaining a metastable anion-deficient solution with predetermined characteristics in density, molar ratio of nitrate ion to uranium and pH (pH). In addition, the technological process of preparing the solution is reduced and simplified, because the laborious operation of analyzing the solution for the content of uranium and nitrate ion is excluded, the resulting solution acquires the property of metastability - stability at a certain temperature (at least 12 ° C). Such a solution can be used in the impregnation of uranium into porous, for example graphite, billets upon receipt of uranium-graphite fuel elements.

Claims (5)

1. A method of preparing anion-deficient solutions of uranyl nitrate, including dissolving uranium oxides by contacting them with nitric acid and water and filtering, characterized in that the uranium oxide is mixed with water in a ratio of liquid to solid 0.1 ÷ 0.15, dissolution carried out by feeding into the pulp with stirring nitric acid, which is introduced dropwise at a molar ratio of nitrate ion to metal in a solution of 1.6 ÷ 1.95, while the number of moles of nitric acid per mole of uranium is calculated by the formula
n = N _u (2-0.7K _o + K),
Where
N _u is the number of moles of uranium;
To _about - oxygen coefficient (O / U);
K is the molar ratio of nitrate ion to uranium,
after filtration, the resulting solution is first adjusted for density, and then adjusted for hydrogen at a temperature of not more than 12 ° C by adding urotropine. 2. The method according to p. 1, characterized in that the nitric acid is administered dropwise at a rate of 400 ÷ 500 ml / h 3. The method according to p. 1, characterized in that the dissolution of uranium oxides and filtering the solution is carried out at a temperature of 40 ÷ 75 ° C. 4. The method according to p. 1, characterized in that the solution is adjusted for density by adding water, while the concentration of uranium in the solution is adjusted to the required formula
Cu = 27 (γ-0.5) wt.%,
Where
γ is the density of the solution without the addition of urotropine, g / cm ³ . 5. The method according to p. 1, characterized in that urotropin is added at a temperature of 5 ÷ 12 ° C, while the number of moles of urotropin per mole of uranium is determined by the formula
N = 1.5 N _u -0.35pH *,
Where
N _u is the number of moles of uranium;
pH * is the pH of the solution after dissolving the uranium oxide and adjusting the density of the solution by adding water.