Method and apparatus for accurately determining the solubility of rare earth oxides in high-temperature molten salt

Abstract

This invention provides a method and apparatus for accurately determining the solubility of rare earth oxides in high-temperature molten salt. It relates to the field of rare earth oxide solubility detection technology, and overcomes the measurement errors caused by severe volatilization of molten salt under high-temperature conditions and the presence of undissolved rare earth oxide or rare earth fluoride particles in the obtained samples, which are present in existing technologies. Furthermore, by using rare earth fluorides instead of rare earth oxides, the amount of rare earth oxides dissolved in the rare earth fluoride-alkali metal fluoride mixed molten salt can be accurately measured, avoiding indirect analysis errors and greatly improving the accuracy of rare earth oxide solubility determination results in high-temperature molten salt.

Description

Technical Field

[0001] This invention belongs to the field of detection technology of rare earth oxides in high-temperature molten salt, and particularly relates to a method and apparatus for accurately determining the solubility of rare earth oxides in high-temperature molten salt. Background Technology

[0002] Currently, the main production methods for rare earth metals in my country are metallothermic reduction and molten salt electrolysis. Metallothermic reduction is mainly used for producing medium and heavy rare earth metals, while molten salt electrolysis is mainly used for preparing light rare earth metals. Molten salt electrolysis primarily uses a mixed molten salt system of rare earth oxides, rare earth metals, and alkali metal fluorides. This method relies on the dissolution of added rare earth oxides to provide rare earth metal ions, which are then deposited at the cathode through electrolysis. Therefore, accurately determining the solubility of rare earth oxides in the molten salt system is crucial for optimizing the electrolytic production process. Otherwise, a reasonable feeding regime cannot be established. If the feeding rate is less than the dissolving capacity, it affects current efficiency; if the feeding rate is greater than the dissolving capacity, undissolved rare earth oxides will sink to the bottom of the tank, increasing tank resistance and energy consumption.

[0003] Currently, the solubility of rare earth oxides in molten salt systems is mainly measured using the isothermal saturation method. This method involves adding an excess of rare earth oxides to a graphite crucible containing molten salt, allowing the oxides to dissolve at a certain temperature for a certain period of time until equilibrium is reached, and then using a tool to scoop out the supernatant for chemical analysis to obtain solubility data. This method for determining the solubility of oxides in molten salt has three problems: (1) Due to the intense molecular motion within the molten salt system under high temperature conditions, some undissolved rare earth oxides are suspended in the supernatant. The sample obtained by scooping out the supernatant actually contains undissolved oxides, leading to an overestimation of the detection result. (2) During the experimental operation, because sampling needs to be considered, the apparatus is not easy to seal, and the molten salt volatilizes significantly, resulting in a large error in the results. (3) When the rare earth fluoride and the added rare earth oxide in the system are the same rare earth elements, the current common method is to analyze the content of F, RE and alkaline earth metals in the sample, and subtract the amount of RE in REF3 from the total amount of RE to estimate the solubility of rare earth oxides. This method ignores the fact that RE2O3 will react with REF3 to form REOF, which leads to the calculated result not matching the actual result.

[0004] Therefore, it is necessary to design a method and apparatus for accurately measuring the solubility of rare earth oxides in high-temperature molten salt to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for accurately determining the solubility of rare earth oxides in high-temperature molten salt, avoiding the problems of undissolved rare earth oxides entrained in the supernatant and severe volatilization of molten salt, thereby greatly improving the accuracy of the determination results of the solubility of rare earth oxides in molten salt system.

[0006] To achieve the above objectives, the present invention provides the following solution: a method for accurately determining the solubility of rare earth oxides in high-temperature molten salt, comprising the following steps:

[0007] S1. Add the fluoride mixture to the stepped position of the stepped graphite crucible, place a partition at the stepped position, and then add the fluoride mixture again above the partition. Heat and maintain the temperature inside the resistance furnace using a thermocouple. While heating and maintaining the temperature, inert gas is introduced into the resistance furnace through the protective gas inlet pipe. After maintaining the temperature for the set time, take the molten salt above the partition for analysis to obtain the RE content w of the blank sample. o ;

[0008] S2. Add REOF to the bottom of the stepped graphite crucible, then add a fluoride mixture as a solvent, adding the fluoride mixture to the stepped position of the stepped graphite crucible. Place a partition at the stepped position, and then add another fluoride mixture above the partition. Heat and maintain the temperature inside the resistance furnace using a thermocouple. While heating and maintaining the temperature, inert gas is introduced into the resistance furnace through the protective gas inlet pipe. After maintaining the temperature for the set time, take the molten salt above the partition for analysis to obtain the RE content w. RE′ Then, calculate the solubility of RE2O3 in molten salt according to formula 1-3.

[0009]

[0010]

[0011]

[0012] In the formula

[0013] w0 represents the percentage content of RE in the blank sample;

[0014] Represents the solubility of RE;

[0015] w REOF (%) represents the solubility of REOF;

[0016] Represents the solubility of RE2O3;

[0017] M RE Represents the molar mass of RE;

[0018] M REOF Represents the molar mass of REOF;

[0019] This represents the molar mass of RE2O3.

[0020] An apparatus for accurately determining the solubility of rare earth oxides in high-temperature molten salt includes a resistance furnace, a furnace lid at the top of the resistance furnace, a stepped graphite crucible inside the resistance furnace, a crucible lid at the top of the stepped graphite crucible, a step in the middle of the inner sidewall of the stepped graphite crucible, a partition at the top of the step, a protective gas inlet pipe through the furnace lid, a protective gas outlet pipe through the bottom of the sidewall of the resistance furnace, and a thermocouple inside the resistance furnace electrically connected to a temperature controller.

[0021] Preferably, the partition plate has a plurality of equally spaced diffusion holes.

[0022] Preferably, the partition is a pure tungsten partition.

[0023] Preferably, the upper inner diameter of the stepped graphite crucible is 2 mm larger than the lower inner diameter.

[0024] Preferably, the diameter of the partition is 1 mm smaller than the upper inner diameter of the stepped graphite crucible.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] This invention effectively prevents undissolved rare earth oxides from suspending in the supernatant by setting steps in a stepped graphite crucible and placing a partition inside. This solves the problem of inaccurate measurements caused by undissolved rare earth oxides in the supernatant. Furthermore, by adding a crucible lid to the stepped graphite crucible, the volatilization of molten salt during high-temperature processing is reduced, thus minimizing inaccuracies in rare earth oxide solubility testing. Additionally, using REOF instead of RE2O3 as an additive simplifies the analytical process. Only the increase in RE content in the supernatant needs to be measured to calculate the solubility of RE2O3 based on the stoichiometric ratio of the reaction REF3 + RE2O3 = 3REOF, significantly improving the accuracy of the results. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a cross-sectional view of the device of the present invention.

[0029] Among them, 1. Protective gas inlet pipe; 2. Furnace cover; 3. Resistance furnace; 4. Crucible cover; 5. Stepped graphite crucible; 6. Partition plate; 601. Diffuser hole; 7. Protective gas outlet pipe; 8. Thermocouple; 9. Temperature controller. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Reference Figure 1 This invention provides a method for accurately determining the solubility of rare earth oxides in high-temperature molten salt, comprising the following steps:

[0033] S1. Add the fluoride mixture to the stepped position of the stepped graphite crucible 5, place the partition 6 at the stepped position, and then add the fluoride mixture again above the partition 6. Heat and keep the inside of the resistance furnace 3 through the thermocouple 8. At the same time as heating and keeping the temperature, inert gas is introduced into the resistance furnace 3 through the protective gas inlet pipe 1. After keeping the temperature for the set time, take the molten salt above the partition 6 for analysis to obtain the content w0 of RE in the blank sample.

[0034] S2. Add REOF to the bottom of the stepped graphite crucible 5, then add a fluoride mixture as a solvent, adding the fluoride mixture to the stepped position of the stepped graphite crucible 5. Place a partition 6 at the stepped position, and then add another fluoride mixture above the partition 6. Heat and maintain the temperature inside the resistance furnace 3 through thermocouple 8. While heating and maintaining the temperature, inert gas is introduced into the resistance furnace 3 through the protective gas inlet pipe 1. After maintaining the temperature for the set time, take the molten salt above the partition 6 for analysis to obtain the RE content w. RE′ Then, calculate the solubility of RE2O3 in molten salt according to formula 1-3.

[0035]

[0036]

[0037]

[0038] In the formula

[0039] w0 represents the percentage content of RE in the blank sample;

[0040] Represents the solubility of RE;

[0041] wREOF (%) represents the solubility of REOF;

[0042] Represents the solubility of RE2O3;

[0043] M RE Represents the molar mass of RE;

[0044] M REOF Represents the molar mass of REOF;

[0045] This represents the molar mass of RE2O3.

[0046] The inert gas can be either nitrogen or argon.

[0047] An apparatus for accurately determining the solubility of rare earth oxides in high-temperature molten salt, used to implement a method for accurately determining the solubility of rare earth oxides in high-temperature molten salt, the apparatus includes an electric resistance furnace 3, a furnace cover 2 at the top of the electric resistance furnace 3, a stepped graphite crucible 5 inside the electric resistance furnace 3, a crucible cover 4 at the top of the stepped graphite crucible 5, a step in the middle of the inner side wall of the stepped graphite crucible 5, a partition 6 at the top of the step, a protective gas inlet pipe 1 passing through the furnace cover 2, a protective gas outlet pipe 7 passing through the bottom of the side wall of the electric resistance furnace 3, and a thermocouple 8 inside the electric resistance furnace 3, the thermocouple 8 being electrically connected to a temperature controller 9.

[0048] The resistance furnace 3 is a tubular resistance furnace. One end of the thermocouple 8 extends into the inside of the resistance furnace 3 to measure the temperature inside the resistance furnace 3, and the other end is connected to the temperature controller 9 located outside the resistance furnace 3 via a wire. The temperature controller 9 is used to control the set heating / cooling and heat preservation programs, and displays the temperature inside the resistance furnace 3 in real time. When the temperature inside the resistance furnace 3 reaches the set temperature, the heat preservation program is started.

[0049] To further optimize the design, the partition plate 6 is provided with several equally spaced diffusion holes 601.

[0050] The protective gas enters through the protective gas inlet pipe 1 and exits through the protective gas outlet pipe 7. This arrangement effectively prevents the stepped graphite crucible 5 and crucible lid 4 from burning out. The crucible lid 4 is placed on top of the stepped graphite crucible 5, which effectively prevents the volatilization of the molten salt inside the stepped graphite crucible 5 and ensures the accuracy of rare earth oxide solubility measurement. A partition 6 is placed inside the stepped graphite crucible 5, and the partition 6 has several diffusion holes 601. This arrangement allows the rare earth oxides at the bottom to diffuse into the molten salt above the partition 6 after dissolving, and also greatly reduces the number of undissolved rare earth oxide particles suspended in the molten salt above the partition 6, ensuring more accurate determination of the solubility of rare earth oxides in the molten salt.

[0051] The design was further optimized, and partition 6 was made of pure tungsten.

[0052] Further optimization of the design: the upper inner diameter of the stepped graphite crucible 5 is 2mm larger than the lower inner diameter.

[0053] The design was further optimized so that the diameter of the partition 6 was 1 mm smaller than the upper inner diameter of the stepped graphite crucible 5.

[0054] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0055] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for accurately determining the solubility of rare earth oxides in high-temperature molten salt, characterized in that, An apparatus for accurately determining the solubility of rare earth oxides in high-temperature molten salt is used. The apparatus includes a resistance furnace (3), a furnace cover (2) at the top of the resistance furnace (3), a stepped graphite crucible (5) inside the resistance furnace (3), a crucible cover (4) at the top of the stepped graphite crucible (5), a step in the middle of the inner side wall of the stepped graphite crucible (5), a partition (6) at the top of the step, and a plurality of equally spaced diffusion holes (601) on the partition (6). A protective gas inlet pipe (1) is provided through the furnace cover (2), a protective gas outlet pipe (7) is provided through the bottom of the side wall of the resistance furnace (3), and a thermocouple (8) is provided inside the resistance furnace (3). The thermocouple (8) is electrically connected to a temperature controller (9). The method for accurately determining the solubility of rare earth oxides in high-temperature molten salt specifically includes the following steps: S1. Add the fluoride mixture to the step position of the stepped graphite crucible (5), place the partition (6) at the step position, and then add the fluoride mixture again above the partition (6). Heat and keep the inside of the resistance furnace (3) through the thermocouple (8). At the same time as heating and keeping the temperature, inert gas is introduced into the resistance furnace (3) through the protective gas inlet pipe (1). After keeping the temperature for the set time, take the molten salt above the partition (6) for analysis to obtain the content w0 of RE in the blank sample. S2. Add REOF to the bottom of the stepped graphite crucible (5), then add a fluoride mixture as a solvent. Add the fluoride mixture to the stepped position of the stepped graphite crucible (5), place a partition (6) at the stepped position, and then add the fluoride mixture again above the partition (6). Heat and keep the inside of the resistance furnace (3) through the thermocouple (8). While heating and keeping the temperature, inert gas is introduced into the resistance furnace (3) through the protective gas inlet pipe (1). After keeping the temperature for the set time, take the molten salt above the partition (6) for analysis to obtain the RE content. Then, calculate the solubility of RE2O3 in molten salt according to formula 1-3. 1 2 3 In the formula w0 represents the percentage content of RE in the blank sample; Represents the solubility of RE; Represents the solubility of REOF; Represents the solubility of RE2O3; Represents the molar mass of RE; Represents the molar mass of REOF; This represents the molar mass of RE2O3.

2. The method for accurately determining the solubility of rare earth oxides in high-temperature molten salt according to claim 1, characterized in that, The partition (6) is a pure tungsten partition.

3. The method for accurately determining the solubility of rare earth oxides in high-temperature molten salt according to claim 1, characterized in that, The upper inner diameter of the stepped graphite crucible (5) is 2 mm larger than the lower inner diameter.

4. The method for accurately determining the solubility of rare earth oxides in high-temperature molten salt according to claim 3, characterized in that, The diameter of the partition (6) is 1 mm smaller than the upper inner diameter of the stepped graphite crucible (5).

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