CN112391653B - Method for reducing rare earth oxide into rare earth metal simple substance in chloride molten salt system - Google Patents

Method for reducing rare earth oxide into rare earth metal simple substance in chloride molten salt system Download PDF

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CN112391653B
CN112391653B CN202011281058.XA CN202011281058A CN112391653B CN 112391653 B CN112391653 B CN 112391653B CN 202011281058 A CN202011281058 A CN 202011281058A CN 112391653 B CN112391653 B CN 112391653B
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rare earth
earth oxide
oxide
molten salt
cathode
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CN112391653A (en
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季男
黄卫
龚昱
蒋锋
彭浩
佘长锋
朱铁建
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Shanghai Institute of Applied Physics of CAS
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    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
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Abstract

The invention provides a method for reducing rare earth oxide into rare earth metal simple substance in a chloride molten salt system, which comprises the following steps: a. grinding: adding a pore-forming agent into the rare earth oxide for grinding and mixing; b. tabletting: b, tabletting the mixed materials in the step a to prepare a green body; c. and (3) sintering: sintering the green body in a muffle furnace to obtain a rare earth oxide solidified body; d. preparing a cathode: fixing and binding the rare earth oxide solidified body by using metal wires to obtain the required cathode; e. electrolysis: inserting the cathode into a crucible filled with molten chloride salt in a molten state, and electrolyzing by taking graphite as an anode to reduce the rare earth oxide into a rare earth metal simple substance; wherein the chloride molten salt in the step e is added with Li2Chloride fused salt LiCl-KCl of O. The method is simple to operate, can directly electrolyze to obtain the rare earth metal solid, and provides a new method for rare earth smelting and spent fuel post-treatment.

Description

Method for reducing rare earth oxide into rare earth metal simple substance in chloride molten salt system
Technical Field
The invention belongs to the field of rare earth smelting and spent fuel post-treatment, and particularly relates to a method for reducing rare earth oxides into rare earth metal simple substances in a chloride molten salt system.
Background
University of George Zheng Chen, Derek J. Fray and Tom W. Farthing in CaCl in 20002Successfully in the molten salt, the direct reaction of TiO is realized2The metal Ti is reduced by electrolysis, and the electrolytic method is called FFC sword bridge method (FFC-Cambridge). The process method directly electrolyzes and reduces the metal oxide in the molten salt into the metal simple substance. The electrolyte, CaCl, selected by the research object of the FFC cambridge process at present2The molten salt system is the most common, and CaCl is also selected2-CaO，CaCl2NaCl and the like as investigated. However, the fused salt has the problems of high melting point and over-high use temperature. Excessive use temperatures not only increase energy and material costs, but also can make the cathode more compact, impeding the migration of oxygen ions in the oxide cathode. Therefore, LiCl system molten salts with lower melting points, such as LiCl-Li, are also selected2O, LiCl and LiCl-KCl-CaCl2Etc. also have good O2-Ion solubility.
In recent years, electrochemical reduction of oxide spent fuel has been extensively studied. The oxide spent fuel not only contains actinide oxide to be recovered, but also fission products to be separated, such as oxides like lanthanide and the like. In the electrolytic reduction process, actinide oxides are reduced into metals, while the reduction behavior of lanthanide and other fission product oxides can directly influence the composition of electrolytic reduction products, and further influence the subsequent electrolytic refining process and the decontamination factor of the refining products. Therefore, the electrochemical behavior of the lanthanide series and other fission product oxides during electrolytic reduction is also of concern. In the FFC process, no one has studied a method for reducing rare earth oxide into a metal simple substance by electrolysis by using LiCl-KCl with a low melting point as an electrolyte.
Disclosure of Invention
The invention aims to provide a method for reducing rare earth oxide into a rare earth metal simple substance in a chloride molten salt system, so as to solve the problems that in the prior art, the FFC cambridge method causes the cost of energy and materials to be increased and the redox reaction is interrupted due to overhigh temperature of molten salt.
In order to solve the technical problems, the invention adopts the following technical scheme:
the method for reducing rare earth oxide into rare earth metal simple substance in a chloride molten salt system is provided, and comprises the following steps: a. grinding: adding a pore-forming agent into the rare earth oxide for grinding and mixing; b. tabletting: b, tabletting the mixed materials in the step a to prepare a green body; c. and (3) sintering: placing the green body into a muffle furnace for sintering to obtain a rare earth oxide solidified body; d. preparing a cathode: the sintered rare earth oxide solidified body is fixedly bound by metal wires to obtain the required productA cathode; e. electrolysis: inserting the prepared cathode into a crucible filled with molten chloride salt, and electrolyzing by taking graphite as an anode to reduce the rare earth oxide into a rare earth metal simple substance; wherein the chloride molten salt in the step e is added with Li2Chloride fused salt LiCl-KCl of O.
Preferably, in the chloride fused salt LiCl-KCl, the mass ratio of LiCl to KCl is 0.7-1.9, and Li is added2The content of O is 0.1 to 2 wt%. Also preferably, Li2The content of O is 1-2 wt%.
Preferably, the rare earth oxide in steps a, c and d is any one of lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, promethium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide and lutetium oxide.
Preferably, the pore-forming agent in step a is polyethylene glycol, polyvinyl alcohol, ethanol, ammonium bicarbonate or carbon powder.
Preferably, the content of the pore-forming agent is 1-5 wt%.
Preferably, the sintering temperature in the step c is 600-800 ℃ and the time is 4-8 h.
Preferably, the metal wire selected in step d is a molybdenum wire, a copper wire or a stainless steel wire.
Preferably, the step e adopts a two-electrode electrolysis mode, the electrolysis temperature is 550-650 ℃, the bath voltage is 2.80-3.40V, and the electrolysis time is 12-24 h.
Preferably, step e is performed under an inert gas atmosphere, such as an argon atmosphere.
Preferably, the process further comprises a drying step between milling and tabletting.
It is well known in the art that rare earth oxides are not conductors and therefore do not conduct electricity in LiCl-KCl molten salt systems, but the present invention successfully addresses this problem by utilizing the FFC cambridge method. According to the invention, a method is provided, comprising: grinding, tabletting, sintering, cathode preparation, electrolysis and the like, wherein the grinding step is to fully mix the pore-forming agent and the rare earth oxide, and the granularity of the ground mixed powder is more beneficial to the later step; the tabletting step is to facilitate the sintering and electrolysis of the formed material; the sintering step is to prepare a cathode with certain porosity, so that later electrolysis is facilitated, and the sheet body is firmer and is not pulverized in later high-temperature molten salt.
According to the method provided by the invention, Li is creatively added into a LiCl-KCl molten salt system2O, by Li2The addition of O provides an oxygen ion conduction path for the rare earth oxide during electrolysis, the reduced metal lithium byproduct promotes the reduction of the rare earth oxide, and the problem that the solid rare earth oxide cannot be directly subjected to electrolytic reduction in a LiCl-KCl molten salt system is solved, so that the electrolytic reduction of the solid rare earth oxide in the molten salt to the rare earth metal simple substance is successfully realized, and the electrolysis temperature is reduced.
In conclusion, the invention provides a method for reducing rare earth oxide into a rare earth metal simple substance in a chloride molten salt system, can well solve the problems of high temperature, energy and material cost and the like in the traditional FFC process, is simple to operate, can directly electrolyze to obtain rare earth metal solid, and provides a new method for rare earth smelting and spent fuel post-treatment.
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FIG. 1 is a diagram of an experimental apparatus for carrying out the electrolytic reaction of the present invention;
FIG. 2 shows LiCl (42g) -KCl (58g) -Li at 550 deg.C2Sm in O (0.1 wt%) molten salt2O3XRD pattern of the product after the cathode is electrolyzed for 12h under the bath voltage of 3.00V;
FIG. 3 is LiCl (50g) -KCl (50g) -Li at 650 deg.C2Gd in O (1 wt%) molten salt2O3XRD pattern of the product after cathode electrolysis for 20h under 2.80V cell voltage;
FIG. 4 shows LiCl (42g) -KCl (58g) -Li at 600 deg.C2Dy in O (2 wt%) molten salt2O3XRD pattern of the product after 24h of cathode electrolysis at 3.40V.
Detailed Description
The present invention will be further described with reference to the following specific examples. It should be understood that the following examples are illustrative only and are not intended to limit the scope of the present invention.
According to a preferred embodiment of the present invention, an experimental set-up is provided for carrying out the redox reaction of the present invention. As shown in fig. 1, the experimental apparatus includes: through stainless steel top cap 4 confined tubular resistance furnace 11, along the argon gas import 1 and the argon gas export 3 that vertical direction runs through stainless steel top cap 4 and set up, along circulating water entry 5 and circulating water export 6 that horizontal direction runs through stainless steel top cap 4 and set up, place corundum crucible 7 in tubular resistance furnace 11, load the electrolyte 8 in corundum crucible 7, be fixed in two stainless steel electrode pole 2 bottoms respectively and stretch into graphite anode 9 and rare earth oxide negative pole 10 in electrolyte 8.
The first embodiment is as follows:
according to the preferred embodiment, there is provided a method for reducing rare earth oxides to elemental metals in a molten chloride salt system, comprising the steps of: grinding: 2g of Sm2O3Adding 2wt% of polyethylene glycol for grinding; and (3) drying: drying the ground material; tabletting: tabletting the dried material to prepare a green body; and (3) sintering: placing the blank into a muffle furnace, and sintering at 650 ℃ for 8h to obtain Sm2O3A cured body that is a matrix; preparing a cathode: sm is sintered2O3Punching the solidified body, and fixing and binding the solidified body by using metal wires to obtain a cathode; electrolysis: the prepared cathode was inserted into a container containing LiCl (42g) -KCl (58g) -Li in a molten state2O (0.1 wt%) molten salt was electrolyzed at 550 ℃ for 12 hours by a constant cell voltage method (3.00V) using graphite as an anode.
And (3) characterization: and (4) washing and drying the electrolysis product, and carrying out XRD (X-ray diffraction) characterization analysis on the dried product. As shown in FIG. 2, it was found that Sm was significantly produced in the XRD pattern with a small amount of LiSmO2And entrained salts.
Example two:
a method for reducing rare earth oxide into metal simple substance in a chloride molten salt system comprises the following steps: grinding: collecting 2g Gd2O3Adding 3 wt% of polyethylene glycol for grinding; and (3) drying: drying the ground material; tabletting: tabletting the dried material to prepare a green body;and (3) sintering: placing the blank into a muffle furnace, and sintering at 700 deg.C for 7h to obtain Gd2O3A cured body that is a matrix; preparing a cathode: gd after sintering2O3Punching the solidified body, and fixing and binding the solidified body by using metal wires to obtain a cathode; electrolysis: inserting the prepared cathode into a container filled with LiCl (50g) -KCl (50g) -Li in a molten state2O (1 wt%) molten salt was electrolyzed at 650 ℃ for 20 hours by a constant cell voltage method (2.80V) using graphite as an anode.
And (3) characterization: and (4) washing and drying the electrolysis product, and carrying out XRD (X-ray diffraction) characterization analysis on the dried product. As shown in FIG. 3, it was found that metallic Gd was significantly produced in the XRD pattern, together with the intermediate product (LiGdO)2) And entrained salts.
Example three:
a method for reducing rare earth oxide into metal simple substance in a chloride molten salt system comprises the following steps: grinding: 2g of Dy is taken2O3Adding 5wt% of polyethylene glycol for grinding; and (3) drying: drying the ground material; tabletting: tabletting the dried material to prepare a green body; and (3) sintering: putting the blank into a muffle furnace, and sintering at 800 ℃ for 6h to obtain Dy2O3A cured body that is a matrix; preparing a cathode: dy after sintering2O3Punching the solidified body, and fixing and binding the solidified body by using metal wires to obtain a cathode; electrolysis: the prepared cathode was inserted into a container containing LiCl (42g) -KCl (58g) -Li in a molten state2O (2 wt%) molten salt was electrolyzed at 600 ℃ for 24 hours by a constant cell voltage method (3.40V) using graphite as an anode.
And (3) characterization: and (4) washing and drying the electrolysis product, and carrying out XRD (X-ray diffraction) characterization analysis on the dried product. As shown in FIG. 4, it was found that the XRD pattern was clearly accompanied by the formation of metallic Dy and incomplete electrolysis of Dy2O3And entrained salts.

Claims (3)

1. A method for reducing rare earth oxide into rare earth metal simple substance in a chloride molten salt system is characterized by comprising the following steps:
a. grinding: adding 2-5 wt% of pore-forming agent polyethylene glycol into rare earth oxide for grinding and mixing, wherein the rare earth oxide is any one of samarium oxide, gadolinium oxide and dysprosium oxide;
b. tabletting: b, tabletting the mixed materials in the step a to prepare a green body;
c. and (3) sintering: sintering the green body in a muffle furnace at the sintering temperature of 600-800 ℃ for 4-8 h to obtain a rare earth oxide solidified body;
d. preparing a cathode: fixedly binding the sintered rare earth oxide solidified body with a metal wire, wherein the metal wire is a molybdenum wire, a copper wire or a stainless steel wire, and thus obtaining the required cathode;
e. electrolysis: inserting the prepared cathode into a crucible filled with molten chloride molten salt, taking graphite as an anode, and adopting a two-electrode electrolysis mode, wherein the electrolysis temperature is 550-650 ℃, the bath voltage is 2.80-3.40V, the electrolysis time is 12-24 h, and the rare earth oxide is reduced into a rare earth metal simple substance;
wherein the chloride molten salt in the step e is added with Li2Chloride fused salt LiCl-KCl of O, the mass ratio of LiCl to KCl is 0.7-1.0, and Li is added2The content of O is 1-2 wt%.
2. The method of claim 1, wherein step e is performed under an inert gas blanket.
3. The method of claim 1, further comprising a drying step between the grinding step and the tableting step.
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CN115020693A (en) * 2022-06-10 2022-09-06 上海空间电源研究所 Fused salt lithiating agent for thermal battery and preparation method of anode material of fused salt lithiating agent
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