RU2052385C1 - Method for separation of zirconium and hafnium - Google Patents

Abstract

FIELD: atomic power. SUBSTANCE: method for separation of zirconium and hafnium includes preparation of aqueous solution of zirconium and hafnium by dissolving, and, then, precipitation is effected, and sediment is separated from solution. In so doing, dissolving is carried out in the presence of aminopolycarboxylic acid or its salt, and precipitation is effected by introduction into solution of fluoride of alkali metal or aluminum. Aminopolycarboxylic acid or its salt is used in form of ethylenediaminetetraacetic or nitrileacetic acid or their salts. EFFECT: higher efficiency. 2 cl

Description

 The invention relates to the chemical technology of rare and trace elements and can be used in the technology for producing pure zirconium and pure hafnium or alloys of each of these metals with other elements, in particular for producing zirconium alloys with a hafnium content of less than 0.01% for nuclear fuel elements.

A known method of separating zirconium and hafnium from a nitric acid solution by extraction of zirconium with tributyl phosphate in an inert diluent at a concentration of hafnium in the aqueous phase [1]
This method, as well as other versions of the extraction method, is characterized by a high cost of extractants and fire hazard of production. In addition, the separation of zirconium and hafnium by the extraction method is poorly combined with the processes of opening zircon and obtaining pure metal by reduction from its tetrafluoride.

The closest to the invention is a method of separating zirconium and hafnium by fractional crystallisation [2] According to the method fluorozirconate, containing about 2% hafnium were dissolved in water at 80-90 ^{° C,} then cooled to 19 ^{° C} and crystallized to 93% geksaftortsirokonata potassium. The precipitate is separated from the mother liquor and again they are dissolved and crystallized. The first and second mother liquors enriched with hafnium are taken out of the cycle, and the subsequent ones are used to dissolve the crystals. After carrying out 16-18 stages of crystallization, zirconium is extracted up to 80% with a hafnium content of about 0.01% in it and metal zirconium of the required degree of purification is obtained.

 The disadvantage of this method is the low separation coefficient of zirconium and hafnium in each cycle, and therefore, the multi-stage process and low productivity of process equipment.

 The aim of the invention is to increase the separation coefficient of zirconium and hafnium in each technological cycle.

The essence of the invention lies in the fact that in the known precipitation method, the separation of zirconium and hafnium (including obtaining an aqueous solution containing zirconium and hafnium, precipitation of the precipitate enriched with zirconium, and separation of the precipitate from the mother liquor), the dissolution is carried out in the presence of aminopolycarboxylic acids or their salts, and the precipitation carried out by introducing a solution of an alkali metal or ammonium fluoride, as well as the fact that the dissolution is carried out in the presence of ethylenediaminetetraacetic acid (EDTA) or its salt: disodium (Na ₂ H ₂ EDTA) ikalievoy (C ₂ H ₂ EDTA) or its copper complex / Cu (Na ₂ EDTA) /, nitrilotriacetic acid (NTA) or its salts.

 A pattern was found for an anomalous increase in the solubility of alkali metal or ammonium hexafluoroerogaphnate as compared with the solubility of hexafluorozirconate in their mixed solution in the presence of aminopolycarboxylic acids or their salts, which leads to a significant increase in the separation coefficient of zirconium and hafnium from 1.54 in the fractional precipitation method to 10 or more.

The mechanism of separation of zirconium and hafnium in aqueous solutions by crystallization in the presence of aminopolycarboxylic acids or their salts is based on the fact that hafnium compounds form a greater number of hydrogen bonds than zirconium complexes. The consequence of this is an increase in their solubility in aqueous solution. The addition of an aminopolycarboxylate anion to an aqueous solution leads to an increase in the number of H-bonds not only through fluoride ions (M-FH ₂ O), but also through oxygen atoms of the carboxylate groups of aminopolycarboxylate anions, for example COOH.N ₂ O. Then, when introduced into the solution alkali metal or ammonium fluoride fluorozirconate is formed, which due to low solubility precipitates, hafnium remains in the liquid phase.

PRI me R 1. Metal waste of fuel production in the amount of 10 g, containing about 99% zirconium, 1% niobium and 3.4 · 10 ^-2 % hafnium is dissolved in an aqueous solution (1 l) of hydrofluoric acid (20 g / l) in the presence of an equivalent with respect to the amount of zirconium is the disodium salt of ethylenediaminetetraacetic acid (20 g / l) at 20-25 ^C. to the resulting solution was added powdered potassium fluoride in an equivalent relative to the amount of zirconium (12 g) is precipitated fluorozirconate potassium with the concentration of hafnium in solution. The precipitate is separated by filtration, it is dried and analyzed for hafnium content by spectral and neutron activation methods. According to the analysis results, the amount of hafnium in the precipitate does not exceed 3 · 10 ^-3 %. The content of hafnium in the mother liquor is analyzed by the neutron-activation method, the amount of hafnium according to the analysis results is about 99% of the content in the initial solution. Thus, the separation coefficient of zirconium and hafnium, achieved by this method, more than 10.

≈ 10
П р и м е р 2. В водный раствор (1 л) фтористоводородной кислоты (30 г/л), содержащей 10 г циркония, 10 г гафния и 10 г нитрилтриуксусной кислоты вводят 15 г порошка фтористого калия и проводят осаждение фторцирконата калия. Осадок отделяют и анализируют как в примере 1. Содержа-ние циркония в осадке по результатам анализа составляет 9,2 г, а гафния не более 0,8 г. Содержание гафния в маточном растворе по результатам анализа составляет 9,1 г.K≥

≈ 10
PRI me R 2. In an aqueous solution (1 l) of hydrofluoric acid (30 g / l) containing 10 g of zirconium, 10 g of hafnium and 10 g of nitrile triacetic acid, 15 g of potassium fluoride powder are introduced and potassium fluorozirconate is precipitated. The precipitate is separated and analyzed as in example 1. The content of zirconium in the precipitate according to the analysis is 9.2 g, and hafnium is not more than 0.8 g. The content of hafnium in the mother liquor according to the analysis is 9.1 g.

 Thus, the separation coefficient of zirconium and hafnium in this method is more than 10.

≥ 10
П р и м е р 3. В водный раствор (1 л), содержащий фтористоводородную кислоту (30 г/л), цирконий (10 г), гафний (10 г) и этилендиаминтетрауксусную кислоту в количестве 20 г/л при температуре 20-25^оС вводят порошок фтористого калия в количестве 14 г, проводят осаждение фторцирконата и анализ осадка и раствора как в примере 1. Количество гафния в осадке не превышает 0,9 г, таким образом коэффициент разделения составил
K

≈ 11
П р и м е р 4. В водный раствоp (1 л), содержащий фтористоводородную кислоту (20 г/л), цирконий (9,9 г), гафний (0,04 г) и медный комплекс динатриевой соли этилендиаминтетрауксусной кислоты (Na₂CuC₁₀H₁₂O₈N₂) в количестве 5 г/л вводят порошок фтористого натрия в количестве 12 г и проводят осаждения фторцирконата натpия. Затем анализиpуют состав осадка как в примере 1. Количество гафния в осадке не превышает 3 · 10^-3% Коэффициент разделения составляет
K

≈ 13

П р и м е р 5. В водный раствор (1 л), содержащий цирконий (19 г), гафний (1 г) и фтористоводородную кислоту (20 г/л) и нитрилтриуксусную кислоту (10 г) вводят 20 г порошка фтористого калия и проводят осаждение фторцирконата калия. Осадок отделяют и анализируют как в примере 1. Анализируют маточный раствор методом нейтронно-активационного анализа. Содержание гафния в растворе составило 0,95 г. Коэффициент разделения составил
K

20
П р и м е р 6. Раствор приготавливают как в примере 5. Осаждение проводят введением стихиометрического количества (16 г) фтористого аммония. Полученный осадок отделяют, а маточный раствор анализируют методом нейтронно-активационного анализа. Содержание гафния в растворе составило 0,92 г. Коэффициент разделения составил
K

≈ 13
Результаты примеров осуществления способа показывают, что проведение растворения и осаждения соединений циркония в присутствии приведенных аминополикарбоновых кислот и их солей наблюдается (в 5-10 раз) увеличение коэффициента разделения циркония и гафния по сравнению с известными осадительными методами. При промышленном использовании способа это позволит получить ядерно чистый цирконий (содержание гафния менее 0,01 ат.), сократив количество ступеней кристаллизации (до двух-трех вместо 20-30), в несколько раз повысить производительность технологического оборудования. Кроме того, с помощью предложенного способа может быть одновременно получен металл с высоким содержанием гафния, который может быть использован для других целей.K

≥ 10
PRI me R 3. Into an aqueous solution (1 l) containing hydrofluoric acid (30 g / l), zirconium (10 g), hafnium (10 g) and ethylenediaminetetraacetic acid in an amount of 20 g / l at a temperature of 20- 25 ^о С, potassium fluoride powder in the amount of 14 g is introduced, precipitation of fluorozirconate and analysis of the precipitate and solution are carried out as in example 1. The amount of hafnium in the precipitate does not exceed 0.9 g, so the separation coefficient is
K

≈ 11
PRI me R 4. Into an aqueous solution (1 l) containing hydrofluoric acid (20 g / l), zirconium (9.9 g), hafnium (0.04 g) and a copper complex of disodium salt of ethylenediaminetetraacetic acid (Na ₂ CuC ₁₀ H ₁₂ O ₈ N ₂ ) in an amount of 5 g / l, sodium fluoride powder in an amount of 12 g is introduced and sodium fluorozirconate is precipitated. Then analyze the composition of the precipitate as in example 1. The amount of hafnium in the precipitate does not exceed 3 · 10 ^-3 % The separation coefficient is
K

≈ 13

PRI me R 5. Into an aqueous solution (1 l) containing zirconium (19 g), hafnium (1 g) and hydrofluoric acid (20 g / l) and nitrile triacetic acid (10 g), 20 g of potassium fluoride powder and potassium fluorozirconate is precipitated. The precipitate is separated and analyzed as in example 1. Analyze the mother liquor by neutron activation analysis. The hafnium content in the solution was 0.95 g. The separation coefficient was
K

20
PRI me R 6. The solution is prepared as in example 5. Precipitation is carried out by introducing a stiometric amount (16 g) of ammonium fluoride. The precipitate obtained is separated, and the mother liquor is analyzed by neutron activation analysis. The hafnium content in the solution was 0.92 g. The separation coefficient was
K

≈ 13
The results of examples of the method show that the dissolution and precipitation of zirconium compounds in the presence of the aminopolycarboxylic acids and their salts (5-10 times) increase the separation coefficient of zirconium and hafnium compared with the known precipitation methods. With the industrial use of the method, this will make it possible to obtain nuclear-grade zirconium (hafnium content less than 0.01 at.), Reducing the number of crystallization steps (to two or three instead of 20-30), and to increase the productivity of technological equipment several times. In addition, using the proposed method can be simultaneously obtained metal with a high content of hafnium, which can be used for other purposes.

 The proposed method with great economic effect and without any changes in technological schemes can be applied in the processing of metal waste from zirconium production.

 In addition, on the basis of this method, a fundamentally new, high-performance, safe and environmentally friendly technology for producing nuclear-pure zirconium, which has a demand in the world market, can be created.

Claims (2)

 1. METHOD FOR SEPARATING ZIRCONIUM AND HAFNIUM, including preparing an aqueous solution of zirconium and hafnium by dissolution, precipitation and separation of the precipitate from the solution, characterized in that the dissolution is carried out in the presence of aminopolycarboxylic acid or its salt, and the precipitation is carried out by adding alkali metal or ammonium fluoride to the solution.  2. The method according to claim 1, characterized in that ethylenediaminetetraacetic or nitrile acetic acid or their salts are used as aminopolycarboxylic acid or its salt.