Method of rare-earth elements extraction from liquid alloys with zinc

FIELD: metallurgy.

SUBSTANCE: proposed method comprises immersion of alloy into salt melt to change rare-earth element from liquid alloy into melt by oxidation. Note here that said oxidation us performed in zinc chloride melt at 420-550°C while melt zinc ions are used as oxidiser.

EFFECT: higher yield.

2 tbl, 2 ex

 

The invention relates to the field of creation of pyrochemical processing of spent nuclear fuel (SNF).

As working environments for pyrochemical processing of spent nuclear fuel is the most effective use of molten mixtures of chloride salts. The basis of the processing is the selection of SNF components in the system "molten salt to metal. As a metal it is advisable to apply fusible, such as zinc. The distribution of the components between the liquid salt and metal phases can be done by electrolysis, or metabolic redox processes. No-current methods are much simpler in terms of technology. One of the important operations in the organization of technological schemes is the extraction of the rare earth fission products with large yield mass in spent fuel and high total radioactivity of liquid alloys with zinc. To establish such a way that differs efficiency and simplicity, the present invention is directed.

The analysis of the prior art in this field indicates that the closest to the claimed method is a method for extracting rare earth elements from liquid alloys with zinc, comprising immersing the alloy in a molten salt with the subsequent transfer of rare earth elements from the liquid alloy in with the eve of the melt by oxidation (AV Kovalevsky, V.A. Lebedev and

IVAN Nichkov "Anodic dissolution of the alloy of yttrium and rare-earth metals and zinc in the molten mixture of potassium chloride and lithium"in kN.: Physical chemistry and electrochemistry molten salt. Sat. works UPI them. CM. Kirov, No. 220, 1973, s-76). Extraction of yttrium and rare earth metals (REM) of zinc alloys due to their oxidation electric current was carried out at 500, 600 and 700°C in an inert atmosphere at current density 0.010-0.015 A/cm2in the melt KaCl-LiCl.

The main disadvantages of this method are: the need for use as a cathode gas diffusion electrode, olivepomace corrosive gas is chlorine; the complexity of managing electrochemical process when creating the optimal modes of dissolution, partial dissolution of zinc in conjunction with REM. These factors increase the cost and complexity of the entire technology of extraction of rare earth elements from irradiated nuclear fuel.

The present invention is to create an efficient and simple in the technological design of the current-free method for extracting rare earth elements from liquid alloys with zinc, with a large yield mass among the fission products.

This task is solved in that the extraction of rare earths from a liquid alloy with zinc, including the POG is angling alloy in molten salt with subsequent transfer of rare earth elements from the liquid alloy into the melt by oxidation, is carried out in the melt of zinc chloride in the temperature range 420-550°C, and are used as oxidants zinc ions from the melt.

The essence of the proposed method lies in the fact that rare earths can be extracted from the liquid metal alloys with zinc salt phase ZnCl2as a result of metabolic reactions directly with the zinc ions contained in the molten ZnCl2,

For the successful extraction of rare-earth metals from liquid alloys of zinc, contacting the salt and metal phases may be carried out at temperatures from 420 to 550°C. the Lower temperature limit is determined by the melting temperature of the alloy, and the upper high volatility vapors of zinc chloride.

As the melt is necessary to use individual zinc chloride that will allow you to achieve the most effective extraction of REE and will not cause contamination of the molten salt and liquid alloy extraneous components.

The result of the technological operations is the getting of zinc chloride enriched chlorides of rare earth elements and zinc metal with a low residual content of REM, suitable for secondary use as a solvent metal fuel or liquid metal electrodes.

Example 1

The alloy is Zn-La were prepared by fusion of individual metals, the original content of lanthanum in the alloy was varied from 0.2 to 5 wt.%. Exposure of the samples of the alloys in the melt held within a quartz cell, which was placed Lundby crucible with salt and samples. The melt in the cell was under the atmosphere of purified argon at 450°C. the contact Time of the alloys with the molten zinc chloride was 10 hours. The original weight of the electrolyte ZnCl2was equal to 15 g, the mass of the alloy to about 3, After a test melt down the capillary and produced a sample of the electrolyte. Next, the melt was cooled to room temperature, extracted samples alloys, washed and dried them. In a selected sample of the electrolyte was determined by the concentration of lanthanum, passed into the melt of the alloy samples Zn-La in contact with chloride of zinc. Molten salt and the samples of the alloys were analyzed by the method of mass spectrometry with inductively coupled plasma. During each experiment was determined by the content of lanthanum alloys before and after their exposure to the molten ZnCl2.

In the process of contact alloy Zn-La with molten ZnCl2the process of exchange displacement REM in salt electrolyte in the course of the oxidation-reduction reactions

During the flowing reaction is a lanthanum-containing chloride melt on the basis of ZnCl2. The results of chemical analysis of the CPF is Bob before and after contact with chloride of zinc are given in table 1. It also contains information about the concentration of lanthanum in the received salt water and the magnitude of the degree of extraction of lanthanum alloy. According to the results obtained after 10 hours of exposure to the melt of zinc chloride source alloy Zn-La enriched in zinc and significantly depleted by lanthanum. The content of lanthanum in the resulting electrolyte ZnCl2- ZnCl3varies depending on the source of the REE content in the alloy.

Table 1
The results of experiments on the extraction of lanthanum alloys Zn-La at 450°C for 10 hours
The initial content of La in the alloy, wt.%The final content of La in the alloy, wt.%The content of La in Plav ZnCl2-LaCl3, wt.%The degree of extraction La, %
0.16<0.0010.03>99
0.370.0060.0898
0.860.170.1787
4.2 0.531.0189

The average rate of dissolution of lanthanum alloy Zn-La 5 wt.% is 4.22 mg/(cm2·h), for alloy Zn-La 0.5 wt.% - 0.35 mg/(cm2·h). Loss of lanthanum in the process of exchange of displacement is less than 0.3%, which corresponds to the allowable errors in chemical analysis.

Example 2

Alloys Zn-Nd were prepared by fusion of individual metals, the original content of neodymium in the alloy was varied from 0.2 to 5 wt.%. Exposure of the samples of the alloys in the melt held within a quartz cell, which was placed Lundby crucible with salt and samples. The melt in the cell was under the atmosphere of purified argon at 450°C. the contact Time of the alloys with the molten zinc chloride was 10 hours. The original weight of the electrolyte ZnCl2was equal to 15 g, the mass of the alloy to about 3, After a test melt down the capillary and produced a sample of the electrolyte. Next, the melt was cooled to room temperature, extracted samples alloys, washed and dried them. In a selected sample of the electrolyte was determined by the concentration of neodymium, passed into the melt of the alloy samples Zn-Nd in contact with chloride of zinc. Molten salt is analyzed by the method of mass spectrometry with inductively coupled plasma. During each experiment was determined from the content of neodymium in the alloys before and after their exposure to the molten ZnCl 2.

In the process of contact alloy Zn-Nd with molten ZnCl2the process of exchange of displacement of the neodymium salt electrolyte in the course of the oxidation-reduction reactions

During the proceeding of the reaction is formed podesteria chloride melt on the basis of ZnCl2. The results of chemical analyses of the alloys before and after contact with chloride of zinc are given in table 1. It also contains information about the concentration of neodymium in the received salt water and the magnitude of the degree of extraction of neodymium alloy.

Table 2
The results of experiments on the extraction of neodymium alloys Zn-Nd at 450°C for 10 hours
The initial Nd content in the alloy, wt.%End the Nd content in the alloy, wt.%The content of Nd in Plav ZnCl2- NdCl3, wt.%The degree of extraction of Nd, %
0.18<0.0010.04>99.5
0.470.0020.1199.6
0.880.0070.2199.2
4.720.060.1698.7

According to the results obtained after 10 hours of exposure to the melt of zinc chloride source alloy Zn-Nd enriched in zinc and significantly depleted by neodymium. The content of neodymium in the resulting electrolyte ZnCl2-NdCl3varies depending on the source of the REE content in the alloy.

Thus, the possibility of deep extraction of rare earth fission products from alloys based on zinc during exchange reactions with the molten zinc chloride.

The technical result consists in the fact that the depth of the extraction of lanthanum and neodymium alloys with zinc in molten zinc chloride at temperatures 420-550°C is more than 99%.

The method for extracting rare earth elements from a liquid alloy with zinc, comprising immersing the alloy in a molten salt with the subsequent transfer of rare earth elements from the liquid alloy into the melt by oxidation, characterized in that the oxidation of rare earth elements is carried out in the melt of zinc chloride in the temperature range 420-550°C, and as the oxidant used zinc ions from the melt.



 

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