CN102373490A - Method for separating Gd and Eu through fused salt electrolysis - Google Patents

Abstract

The invention provides a method for separating Gd and Eu by molten salt electrolysis. In the electrolytic furnace, the inert metal molybdenum is used as the cathode and placed in the lower part of the electrolytic cell, graphite is used as the anode, and MgCl ₂ , LiCl, KCl, then add the mixture of gadolinium oxide and europium oxide according to 13-20% of the mass of _MgCl2 , control the temperature at 690-780°C, and after the material in the crucible is melted, pass in direct current electrolysis to control the cathode current density 9 -12A/cm ² , the anode current density is 0.4-0.5A/cm ² , the cell voltage is 6.6-7.7V, after 3-5 hours of electrolysis, a magnesium alloy is deposited near the cathode in the electrolytic cell, and gadolinium is mainly transferred to the magnesium alloy Among them, europium is mainly left in the molten salt. The invention can make the process equipment more miniaturized. Moreover, alloy materials can be recovered directly after electrolytic separation.

Description

A kind of molten salt electrolytic separation method of Gd, Eu

technical field

The invention relates to a dry separation method, specifically a method for separating Gd and Eu through molten salt electrolysis, and belongs to the technical field of pyrometallurgy.

Background technique

Rare earth elements widely exist in nature, and there are more than 250 kinds of rare earth minerals, of which more than 50 kinds have industrial value. Due to the very similar properties of rare earth elements, the separation of rare earth elements has become one of the most difficult problems in inorganic chemistry. The basic methods for the separation of rare earth elements include fractional crystallization and fractional precipitation, ion exchange, solvent extraction, and pyrochemical vapor transport.

The molten salt electrolysis method is widely used to produce a large amount of mixed rare earth metals and some single rare earth metals and rare earth alloys because of its continuous operation, simple equipment, economical and convenient, and not limited by reducing agents. Molten salt electrolysis can be divided into chloride molten salt electrolysis and fluoride-oxide molten salt electrolysis. Both approaches have pros and cons:

(1) The chloride molten salt electrolysis method has less corrosiveness of molten salt, is easy to master, and the structural materials of large-scale electrolytic cells are easy to solve. Therefore, it is the basic method for the production of rare earth metals in the modern rare earth electrolysis industry. However, the preparation cost of rare earth chloride is high, the dehydration is difficult, the reactivity is high, and the storage and transportation are difficult.

(2) The fluoride-oxide electrolysis method has the advantages of good storage and transportation of oxides, but compared with the chloride molten salt system, the fluoride-oxide molten salt has a higher melting point, a higher electrolysis temperature, and stronger corrosion of the molten salt.

The biggest feature of the two electrolysis processes is that they can handle rare earth metals with high melting points, and as long as the rare earth oxides are constantly replenished, the electrolysis can be carried out continuously.

There are reports on the separation of rare earths in the prior art, most of which use solvent extraction followed by ion exchange and gas phase transport methods. For example, for example, the patent application number is 89100200.6, and the name is disclosed in the patent document entitled "Separation Method of Rare Earth Elements". A method for continuous separation of rare earth elements by solvent extraction is developed. Through five processes, high-purity light rare earth elements, medium rare earth elements, and heavy rare earth elements are continuously and continuously separated from the raw material solution of rare earth elements with low content of medium and heavy rare earth elements. element and yttrium. Another example is that the patent application number is 95117489.4, and the patent document titled "the technology for preparing high-purity neodymium oxide by ion exchange method" discloses a solution containing NdCl _1-10 %, and a pH of 2-5 as the feed liquid. The ammonium acetate solution (I) of 0.3-0.8 mol/liter and the ammonium acetate solution (II) of 0.9-1.2 mol/liter are used as eluent, and rinse successively, and the pH of ammonium acetate solution (I), (II) is 5.8-6.5. The product solution is collected, precipitated with oxalic acid, and burned to form neodymium trioxide. Another example is the patent application number 200910012454.X, titled "A Method for Separating Rare Earth Oxide from Rare Earth Oxide Using Ammonium Chloride-Potassium Chloride Vapor Phase Transmission", which opened up a new way for the separation of rare earth. In addition, there is also a method for separating rare earths by using the valence-changing properties of rare earths. For example, the patent No. 96205784.3, which is named "Electrolytic Extraction Separation of Rare Earths Device", is a method for the efficient separation of rare earths by using electrolysis, electrophoresis, electrodialysis, and extraction technologies. way.

Contents of the invention

The object of the present invention is to provide a method for electrolytic separation of Gd and Eu by molten salt electrolysis, which has good separation effect, can make process equipment miniaturized, and can directly recover alloy materials after separation.

The purpose of the present invention is achieved like this:

In the electrolytic furnace, the inert metal molybdenum is used as the cathode and placed in the lower part of the electrolytic cell, graphite is used as the anode, and MgCl ₂ , LiCl, KCl, then add the mixture of gadolinium oxide and europium oxide according to 13-20% of the mass of _MgCl2 , control the temperature at 690-780°C, and after the material in the crucible is melted, pass in direct current electrolysis to control the cathode current density 9 -12A/cm ² , the anode current density is 0.4-0.5A/cm ² , the cell voltage is 6.6-7.7V, after 3-5 hours of electrolysis, a magnesium alloy is deposited near the cathode in the electrolytic cell, and gadolinium is mainly transferred to the magnesium alloy Among them, the content of gadolinium in the magnesium alloy is relatively large, accounting for 6.9-10.7%, europium is mainly left in the molten salt, and the content of europium in the magnesium alloy is very small, accounting for 4.4×10 ^-3 to 1.0×10 ^-2 %. The recovery rate of gadolinium is 74.5-89.7%, the distribution coefficient of gadolinium oxide in alloy and molten salt is 2.55-4.01, the distribution coefficient of europium oxide in alloy and molten salt is 1.7×10 ^-3 -3.2×10 ^-2 , The separation factor of gadolinium oxide and europium oxide is 112-2330.

The LiCl and KCl were first dried at 300° C. and 600° C. for 24 hours, respectively.

The mixture of gadolinium oxide and europium oxide is a mass mixture of gadolinium oxide and europium oxide.

What the present invention provides is that the mixture of gadolinium oxide and europium oxide is directly electrolyzed in molten salt, and in the obtained alloy, the elements in the alloy obtained by electrolysis are analyzed by ICP, according to M.Kurata et al. in their article " Distribution behavior of uranium, neptunium, rare-earth elements (Y, La, Ce, Nd, Sm, Eu, Gd) and alkaline-earth metals (Sr, Ba) between molten LiCl-KCI eutectic salt and liquidcadmium or bismuth" in the formula:

β＝D _Gd /D _Eu (3)

和

分别为Gd和Eu在合金与熔盐中的摩尔百分含量；β为分离系数。)分别计算出Gd₂O₃和Eu₂O₃在合金与熔盐中的分配系数D_Gd、D_Eu与的分离系数β。(wherein: D _Gd and D _Eu are respectively the distribution coefficient of Gd ₂ O ₃ and Eu ₂ O ₃ ;

and

are the molar percentages of Gd and Eu in the alloy and molten salt, respectively; β is the separation coefficient. ) to calculate the distribution coefficients _D Gd , _{D Eu} and the separation coefficient β of Gd ₂ O ₃ and Eu ₂ O ₃ in the alloy and the molten salt, respectively.

The molten salt electrolytic separation of the present invention is a method of dry separation. Compared with water separation, the volume of operating materials for dry separation is smaller, which can make the process equipment more miniaturized. Moreover, alloy materials can be recovered directly after electrolytic separation.

In the method for separating gadolinium oxide and europium oxide provided by the present invention, the recovery rate of gadolinium is 74.5-89.7%, the distribution coefficient of gadolinium oxide in alloy and molten salt is 2.55-4.01, and the distribution coefficient of europium oxide in alloy and molten salt 1.7×10 ^-3 -3.2×10 ^-2 , and the separation coefficient between gadolinium oxide and europium oxide is 112-2330. Molten salt electrolysis directly separates gadolinium and europium in rare earth oxides in one step, and prepares an intermediate alloy; continuous electrolytic separation can be realized by continuously adding raw materials.

Description of drawings

Fig. 1 is the SEM surface scan photograph of embodiment 3 gained alloy;

Fig. 2 is the distribution figure of the Mg element analyzed by the EDS energy spectrum of embodiment 3 gained alloy;

Fig. 3 is the distribution figure of the Gd element analyzed by the EDS energy spectrum of embodiment 3 gained alloy;

Fig. 4 is a distribution diagram of the Eu element analyzed by the EDS energy spectrum of the alloy obtained in Example 3.

Detailed ways

The following examples describe the present invention in more detail:

The basic technical scheme of the present invention is: use MgCl ₂ +LiCl+KCl as the electrolyte system, the mass percentages of MgCl ₂ , LiCl, and KCl are 10-16%, 42-45%, and 42-45% respectively; _2. 13-20% of the mass is added with mixed rare earth oxide (the mass of gadolinium oxide and europium oxide are equal), and the temperature is controlled at 690-780°C. After the material in the crucible is melted, direct current electrolysis is introduced to control the cathode current density 9-12A/cm ² , the anode current density is 0.4-0.5A/cm ² , the cell voltage is 6.6-7.7V, after 3-5 hours of electrolysis, magnesium rare earth alloy is deposited near the cathode in the electrolytic cell. The recovery rate of gadolinium was 74.5-89.7%. The distribution coefficient of gadolinium oxide in alloys and molten salts is 2.55 to 4.01, the distribution coefficient of europium oxide in alloys and molten salts is 1.7×10 ^-3 to 3.2×10 ^-2 , and the separation coefficient of gadolinium oxide and europium oxide is 1112 ~2330. Gadolinium is mainly transferred to the alloy, and the content of gadolinium in the alloy is 6.9-10.7%, but the content of europium in the alloy is very small, 4.4×10 ^-3 to 1.0×10 ^-2 %, and europium is mainly left in the molten salt It shows that the effect of the separation experiment is quite ideal, achieving the purpose of separation of gadolinium and europium.

Embodiment ₁ : with MgCl ₂ +LiCl+KCl as the electrolyte system, the mass percentages of each component are 16%, 42% and 42% respectively, then add europium oxide and gadolinium oxide mixed rare earth oxide by 13% of the mass of MgCl , to The inert metal molybdenum (Mo) is used as the cathode, and graphite is used as the anode. At an electrolysis temperature of 690°C, the cathode current density is 9A/cm ² , the anode current density is 0.4A/cm ² , and the cell voltage is 6.6-7.1V. After 3 hours of electrolysis , Mg alloy is deposited near the cathode in the electrolytic cell, and the contents of Mg, Li and Gd in the alloy are 84.9%, 10.6% and 8.5% respectively. The content of gadolinium in the alloy is more than 8.5%, but the content of europium in the alloy is only 7.6×10 ^-3 %, and the recovery rate of gadolinium is 78.6%. The distribution coefficient of gadolinium oxide in alloy and molten salt is 3.53, the distribution coefficient of europium oxide in alloy and molten salt is 3.2×10 ^-2 , and the separation coefficient of gadolinium oxide and europium oxide is 112.

Embodiment 2: with MgCl ₂ +LiCl+KCl as the electrolyte system, the mass percentages of each component are 16%, 42% and 42% respectively, then add europium oxide and gadolinium _oxide mixed rare earth oxide by 13% of the mass of MgCl , to The inert metal molybdenum (Mo) is used as the cathode, and the graphite is used as the anode. At an electrolysis temperature of 720°C, the cathode current density is 9A/cm ² , the anode current density is 0.4A/cm ² , and the cell voltage is 6.5-6.9V. After 4 hours of electrolysis , Mg alloy is deposited near the cathode in the electrolytic cell, and the contents of Mg, Li and Gd in the alloy are 77.2%, 15.9% and 6.9% respectively. The content of gadolinium in the alloy is more than 6.9%, but the content of europium in the alloy is only 1.0×10 ^-2 %, and the recovery rate of gadolinium is 74.5%. The distribution coefficient of gadolinium oxide in alloy and molten salt is 2.55, the distribution coefficient of europium oxide in alloy and molten salt is 4.1×10 ^-3 , and the separation coefficient of gadolinium oxide and europium oxide is 626.

Embodiment 3: with MgCl ₂ +LiCl+KCl as the electrolyte system, the mass percentages of each component are 10%, 45% and 45% respectively, then add europium oxide and gadolinium oxide mixed rare earth _oxide by 20% of the mass of MgCl , to The inert metal molybdenum (Mo) is used as the cathode, and graphite is used as the anode. At an electrolysis temperature of 750°C, the cathode current density is 12A/cm ² , the anode current density is 0.5A/cm ² , and the cell voltage is 7.2-7.7V. After 5 hours of electrolysis , Mg alloy is deposited near the cathode in the electrolytic cell, and the contents of Mg, Li and Gd in the alloy are 71.1%, 18.2% and 10.7% respectively. The content of gadolinium in the alloy is more than 10.7%, but the content of europium in the alloy is only 4.4×10 ^-3 %, and the recovery rate of gadolinium is 89.7%. The distribution coefficient of gadolinium oxide in alloy and molten salt is 4.01, the distribution coefficient of europium oxide in alloy and molten salt is 1.7×10 ^-3 , and the separation coefficient of gadolinium oxide and europium oxide is 2330.

Embodiment 4: With MgCl ₂ +LiCl+KCl as the electrolyte system, the mass percentages of each component are 10%, 45% and 45% respectively, then add europium oxide and gadolinium oxide mixed rare earth oxide _by 20% of the mass of MgCl , to The inert metal molybdenum (Mo) is used as the cathode, and the graphite is used as the anode. At an electrolysis temperature of 780°C, the cathode current density is 12A/cm ² , the anode current density is 0.5A/cm ² , and the cell voltage is 6.8-7.2V. After 4 hours of electrolysis , Mg alloy is deposited near the cathode in the electrolytic cell, and the contents of Mg, Li and Gd in the alloy are 77.5%, 12.8% and 9.7% respectively. The content of gadolinium in the alloy is more than 9.7%, but the content of europium in the alloy is only 7.2×10 ^-3 %, and the recovery rate of gadolinium is 85.3%. The distribution coefficient of gadolinium oxide in alloy and molten salt is 4.00, the distribution coefficient of europium oxide in alloy and molten salt is 2.7×10 ^-3 , and the separation coefficient of gadolinium oxide and europium oxide is 1509.

The accompanying drawings of the description are the SEM surface scanning photos of the alloy obtained in Example 3 and the distribution diagrams of Mg, Gd and Eu elements analyzed by EDS energy spectrum. The drawings illustrate that the content of gadolinium (10.7%) in the alloy is far greater than that of europium (4.4×10 ^-3 %), and the content of europium is negligible, that is, the mixed rare earth oxide of gadolinium oxide and europium oxide can be separated by molten salt electrolysis.

Claims (3)

1. A method for molten salt electrolytic separation of Gd and Eu, characterized in that: in the electrolytic furnace, the inert metal molybdenum is used as the negative electrode and placed in the lower part of the electrolytic cell, and the graphite is the anode, which is respectively 10-16% according to the mass percentage , 42-45%, and 42-45% by adding MgCl ₂ , LiCl, KCl, and then adding a mixture of gadolinium oxide and europium oxide according to 13-20% of the mass of MgCl ₂ , and controlling the temperature at 690-780°C. After the material in the crucible is melted, direct current electrolysis is applied, the cathode current density is controlled to 9-12A/cm ² , the anode current density is 0.4-0.5A/cm ² , the cell voltage is 6.6-7.7V, and after 3-5 hours of electrolysis , a magnesium alloy is deposited near the cathode in the electrolytic cell, gadolinium is mainly transferred to the magnesium alloy, and europium is mainly left in the molten salt. 2. A method for separating Gd and Eu by molten salt electrolysis according to claim 1, characterized in that: said LiCl and KCl are firstly dried at 300°C and 600°C for 24 hours respectively. 3. The method for separating Gd and Eu by molten salt electrolysis according to claim 1 or 2, characterized in that: the mixture of gadolinium oxide and europium oxide is a mass mixture of gadolinium oxide and europium oxide.

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