RU2457265C2 - Method of purifying zirconium from hafnium - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of separating zirconium and hafnium involves sublimation by heating the starting zirconium tetrafluoride containing hafnium tetrafluoride and desublimation of the formed vapour. Before sublimation, fluoride vapour is passed over or through a layer of zirconium dioxide containing not more than 0.03 wt % hafnium. The height of the layer when passing zirconium dioxide through the layer is equal to 140-150 mm and 1950-2100 mm when passing zirconium dioxide over the layer.

EFFECT: separation of zirconium and hafnium in a single step in a single apparatus; the process itself is wasteless since the hafnium dioxide formed during the reaction is an intermediate product for producing hafnium metal.

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Description

The invention relates to a chemical technology for producing nuclear-pure zirconium, specifically to a technology for purifying zirconium from hafnium, and can be used in ore processing plants and in the nuclear industry.

The problem of purification of zirconium from hafnium is complicated by the fact that their chemical properties are similar due to the similarity in the structure of atoms. For their separation, complex multistage purification is used: crystallization, ion exchange, multiple precipitation, extraction.

A known method of purification of zirconium from 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 [K. Bolshakov et al. Technology of rare and trace elements. M .: Higher school, 1969. t.2, p.475].

This method, as well as other versions of the extraction method, is characterized by the high cost of extractants and the fire hazard of production, the need to use many mechanical and pneumatic devices. In addition, the purification of zirconium from hafnium by the extraction method is poorly combined with the processes of opening zircon and obtaining pure metal by reduction from its tetrafluoride.

Another method of purification of zirconium from hafnium can be the sublimation-sublimation method [Ozherelyev, O.A. Sublimation purification of fluorides of zirconium, hafnium, titanium [Text] / OA Ozherelyev. - Novosibirsk: Nauka, 2005 .-- 135 p. - Bibliography: 131-134. - 500 copies. - ISBN 5-02-032459-0, p. 47]. The disadvantage of this method is the low coefficient of purification (separation), as a result of which 6 purification steps are necessary to obtain zirconium tetrafluoride with a hafnium content of 0.02 wt.%, Even at the optimum temperature and pressure of the process.

The objective of the invention is to provide a method for cleaning zirconium from hafnium in one step in the absence of technological waste using a minimum amount of equipment.

This object is achieved in that the method of purification of zirconium from hafnium involves the sublimation of the initial zirconium tetrafluoride (TFC) containing hafnium tetrafluoride (TFH), and the desublimation of the formed vapor, with fluoride pairs being passed over or through a layer of zirconium dioxide containing 0.02- 0.03 wt.% Hafnium, while the layer height when passing through a layer of zirconium dioxide is 140-150 mm, and when passing over a layer of zirconium dioxide the length of the layer is 1950-2100 mm.

The invention is as follows.

Hafnium tetrafluoride is able to enter into an exchange reaction with zirconium dioxide

Calculations show that the change in Gibbs energy in the temperature range (700–1300) K, that is, at sublimation temperatures of TFC and TGF, has negative values.

In addition to reaction (1), reactions can occur in the system

The solid phase formed by reaction (2) begins to liberate vaporous zirconium tetrafluoride at a temperature of 1023 K. The hafnium oxofluorides formed by reaction (3) behave similarly. Based on this, it follows that at temperatures above 1023 K zirconia will selectively interact with hafnium tetrafluoride. In this case, hafnium will be concentrated in the solid phase (in zirconium dioxide), and zirconium will be concentrated in the vapor phase depleted in hafnium. These assumptions were verified experimentally. In the casing of one apparatus under conditions (pressure and temperature) providing sublimation of zirconium tetrafluoride containing hafnium tetrafluoride, a mixture of their vapors was passed through a layer of zirconium dioxide. Vapors were enriched in zirconium tetrafluoride according to equation (1) and desublimated on the cooled surface of the condenser. The experimental results are shown in table 1.

Table 1 - The dependence of the effective cleaning coefficient on the height of the layer of zirconium dioxide The concentration of hafnium in zirconia wt.% Layer height. mm The hafnium coefficient in the initial TFC, wt.% The concentration of hafnium in desublimate, wt.% The degree of desublimation,% Cleaning ratio 0 1,58 1.20 93.52 1.32 ± 0.18 eighteen 1,58 0.08 96.13 1.98 ± 0.20 0.02-0.03 21 2.17 1.15 97,20 2.09 ± 0.18 35 1.01 0.68 97.43 2.96 ± 0.26 53 2.01 0.53 98.13 3.79 ± 0.30

The experiments showed that the effective coefficient of purification (separation) is higher when passing a mixture of vapors through a layer of zirconium dioxide compared with this value for simple sublimation. In addition, with increasing zirconia layer height, the separation efficiency of zirconium and hafnium tetrafluorides increases.

In order to obtain zirconium tetrafluoride that meets the technical specifications (hafnium content of not more than 0.02%) by this method, a series of experiments was carried out consisting in the multiple passage of steam of the same TFC sample through a layer and above a zirconia layer at a temperature of 1073 K. The experimental results are shown in table 2.

Table 2 - Hafnium concentration in TFC desublimate depending on the organization of the sublimation process The concentration of hafnium in zirconia, wt.% Height (length) of the dioxide layer, mm The concentration of hafnium in desublimate, wt.% Vapors passed through a zirconia layer 0 1.78 eighteen 1,04 36 0.65 54 0.35 0.02-0.03 72 0.20 90 0.16 108 0.10 126 0,078 144 0,034 Vapors passed over a layer of zirconium dioxide 0 20.50 150 17.90 300 14.00 450 12.40 600 10.00 750 7.90 900 3.45 0.02 1050 1.86 1200 0.97 1350 0.72 1500 0.53 1650 0,096 1800 0,078 1950 0,053 2100 0,020

Experiments have shown that when using zirconia with a lower hafnium content, the hafnium content in desublimate also decreases. Zirconium tetrafluoride with a hafnium concentration of 0.02%, corresponding to the technical conditions, was obtained using zirconia containing 0.02-0.03 wt.%. hafnium. Depending on the organization of the process, to obtain nuclear-grade zirconium tetrafluoride, its vapors, initially containing up to 2% hafnium, must be passed either through a layer of zirconium dioxide 140-150 mm high or above a layer of zirconium dioxide up to 2100 mm long.

Thus, the proposed method of purification of zirconium from hafnium allows the purification process to be performed in one step in one apparatus. The process itself is waste-free, since hafnium dioxide formed as a result of reaction (1) is an intermediate product for the production of hafnium metal.

Claims (1)

The method of purification of zirconium tetrafluoride from hafnium fluoride, including sublimation of the initial zirconium tetrafluoride containing hafnium tetrafluoride and desublimation of the vapor generated by heating, characterized in that the fluoride vapor is passed over or through a layer of zirconium dioxide containing not more than 0.03 wt.% hafnium, while passing them through a zirconia layer, the layer height is 140-150 mm, and when passing them above a zirconia layer, the layer length is 1950-2100 mm.