METHOD FOR PREPARING RARE EARTH ALLOYS

Abstract

A method for preparing rare earth alloys by molten salt electrolysis using rare earth oxides as the raw material is provided, where the electrolytic cell used is divided into the anode chamber and the cathode chamber containing melts such as anolyte, catholyte and liquid alloy. The method has the advantages of continuous production, high operability, low requirements on raw material purity and high quality of rare earth alloy products.

Claims

1. A method for preparing rare earth alloys, wherein the method is implemented by using an electrolytic cell divided into an anode chamber and a cathode chamber, wherein an anolyte and an anode are provided in the anode chamber, a catholyte and a cathode are provided in the cathode chamber, a liquid alloy is contained at a bottom of the electrolytic cell, and the anolyte and the catholyte are not in contact with each other but are connected via the liquid alloy; the cathode is a solid consumable cathode or a liquid cathode; and the method comprises: powering on the electrolytic cell to operate, adding a rare earth oxide raw material to the anode chamber, and obtaining a liquid rare earth alloy product in the cathode chamber.

2. The method for preparing the rare earth alloys according to claim 1, wherein in the rare earth oxide raw material, a content of a total rare earth oxide is ?90 wt %, and a single rare earth oxide accounts for 90 wt % or above of the total rare earth oxide; and the single rare earth oxide is one of lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide, lutetium oxide, yttrium oxide, and scandium oxide.

3. The method for preparing the rare earth alloys according to claim 1, wherein a relative purity of a single rare earth metal in the liquid rare earth alloy product is ?99.0 wt %.

4. The method for preparing the rare earth alloys according to claim 1, wherein the anode is a carbon anode or an inert anode.

5. The method for preparing the rare earth alloys according to claim 1, wherein the liquid alloy is a single rare earth metal or consists of a single rare earth metal and one or more of Cu, Co, Fe, Ni, Mn, Pb, Sn, In, Sb, and Bi; and a density of the liquid alloy is greater than a density of the anolyte or a density of the catholyte.

6. The method for preparing the rare earth alloys according to claim 1, wherein the anolyte is a fluoride system or a chloride system; the fluoride system comprises a single rare earth fluoride with a content of 40-95 wt %, LiF with a content of 5-40 wt %, and an additive with a content of 0-40 wt %, wherein the additive is BaF.sub.2 or/and CaF.sub.2; and the fluoride system further comprises the rare earth oxide dissolved the fluoride system or/and a solid rare earth oxide raw material; and the chloride system is CaCl.sub.2, or consists of CaCl.sub.2 with one or more of LiCl, NaCl, KCl, BaCl.sub.2, CaF.sub.2, and LiF.

7. The method for preparing the rare earth alloys according to claim 1, wherein the catholyte comprises a single rare earth fluoride with a content of 40-90 wt %, LiF with a content of 10-50 wt %, and an additive with a content of 0-30 wt %, wherein the additive is BaF.sub.2 or/and CaF.sub.2.

8. The method for preparing the rare earth alloys according to claim 1, wherein the solid consumable cathode is M1, a melting point of the M1 is higher than an electrolysis temperature, and the M1 is allowed to form an alloy having the melting point lower than the electrolysis temperature with a rare earth metal; and when the electrolytic cell is in a normal operation, a current density of the cathode is 0.1-30.0 A/cm.sup.2.

9. The method for preparing the rare earth alloys according to claim 1, wherein the liquid cathode is M2, a melting point of the M2 is lower than an electrolysis temperature, and the M2 is allowed to form an alloy having the melting point lower than the electrolysis temperature with a rare earth metal; and when the electrolytic cell is in a normal operation, a current density of the liquid cathode is 0.1-10.0 A/cm.sup.2.

10. The method for preparing the rare earth alloys according to claim 1, wherein the liquid rare earth alloy product is configured for preparing high-purity rare earth alloy materials or high-purity rare earth metal materials by refining processes; and the refining processes comprise one or a combination of two or more of a vacuum smelting process, a vacuum distillation process, an electrorefining process, a zone smelting process, and a solid state electromigration process.

11. The method for preparing the rare earth alloys according to claim 8, wherein the M1 is one or more of Fe, Ni, Co, Mn and Cu.

12. The method for preparing the rare earth alloys according to claim 9, wherein the M2 is one or more of Al, Mg, Zn, Sn, Pb, and Sb.

13. The method for preparing the rare earth alloys according to claim 5, wherein the anolyte is a fluoride system or a chloride system; the fluoride system comprises a single rare earth fluoride with a content of 40-95 wt %, LiF with a content of 5-40 wt %, and an additive with a content of 0-40 wt %, wherein the additive is BaF.sub.2 or/and CaF.sub.2; and the fluoride system further comprises the rare earth oxide dissolved in the fluoride system or/and a solid rare earth oxide raw material; and the chloride system is CaCl.sub.2), or consists of CaCl.sub.2) with one or more of LiCl, NaCl, KCl, BaCl.sub.2, CaF.sub.2, and LiF.

14. The method for preparing the rare earth alloys according to claim 5, wherein the catholyte comprises a single rare earth fluoride with a content of 40-90 wt %, LiF with a content of 10-50 wt %, and an additive with a content of 0-30 wt %, wherein the additive is BaF.sub.2 or/and CaF.sub.2.

15. The method for preparing the rare earth alloys according to claim 10, wherein the refining processes comprise the vacuum distillation process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to illustrate the equipment used in the present invention and the working principles and methods thereof more clearly, FIGS. 1A-1C show a schematic cross-sectional view of the electrolytic cell used in the present invention. For ordinary technical personnels in this field, other figures can also be obtained according to FIGS. 1A-1C without any creative effort.

[0040] FIGS. 1A-1C are schematic structural diagrams of the electrolytic cell of the present invention, where FIG. 1A is a schematic structural diagram of the electrolytic cell with a solid consumable cathode, in which a collector containing liquid rare earth alloy product is located in the middle of the cathode chamber, FIG. 1B is a schematic structural diagram of the electrolytic cell with another solid consumable cathode, in which a collector containing liquid rare earth alloy product is located at the bottom of the cathode chamber, and FIG. 1C is a schematic structural diagram of the electrolytic cell with liquid cathode.

[0041] Reference numerals: 1partition, 2anode, 3electrolytic cell, 4anolyte, 5liquid alloy, 6catholyte, 7collector with liquid rare earth alloy, 8cathode, and 9liquid cathode.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] In order to make the objectives, technical solution and advantages of the present invention become more apparent, a detailed description of the technical solution of the present invention will be provided below. Obviously, the described embodiments are only a few, but not all embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by a person skilled in the art without creative efforts fall within the scope of the present invention.

[0043] The method for preparing rare earth alloys of the present invention is to perform molten salt electrolysis reactions at 800-1100? C. and add the rare earth oxide raw material into the anode chamber, oxidation reactions occur on the surface of the anode, and rare earth ions (in a dissolved state or/and an undissolved state) in the anode chamber are reduced to rare earth metal atoms at the interface between the liquid alloy and the anolyte and enter the liquid alloy; in the cathode chamber, rare earth metal atoms in the liquid alloy are oxidized to rare earth ions at the interface between the liquid alloy and the catholyte and enter the catholyte, the rare earth ions in the catholyte are reduced to rare earth metal atoms at the cathode, and the rare earth metal atoms enter the liquid cathode to form the rare earth alloy product, or undergo alloying reactions with the solid consumable cathode to produce the liquid rare earth alloy product.

[0044] According to the present invention, the anolyte and the catholyte are physically separated by the electrolytic cell, while both the anolyte and the catholyte are in contact with the liquid alloy. Therefore, in order to effectively realize the separation of the catholyte and the anolyte, a structure of the electrolytic cell is as shown in FIGS. 1A-1C, where FIG. 1A is a schematic structural diagram of the electrolytic cell with a solid consumable cathode, in which a collector containing liquid rare earth alloy product is located in the middle of the cathode chamber, FIG. 1B is a schematic structural diagram of the electrolytic cell with another solid consumable cathode, in which a collector containing liquid rare earth alloy product is located at the bottom of the cathode chamber, and FIG. 1C is a schematic structural diagram of the electrolytic cell with liquid cathode.

[0045] The electrolytic cell is spatially divided into the anode chamber and the cathode chamber by the insulating partition 1. The anode chamber contains the anolyte 4, the anode 2 is inserted into the anolyte 4, the cathode chamber contains the catholyte 6, the cathode 8 is inserted into the catholyte 6 or the liquid cathode 9, and the bottom of the electrolytic cell contains the liquid alloy 5 in contact with the anolyte 4 and the catholyte 6, respectively, but not with the anode 2 or the cathode 8 or the liquid cathode 9.

[0046] If the cathode 8 is a solid consumable cathode, the collector 7 is required to hold the liquid rare earth alloy product, and if the liquid cathode 9 is used, the cathode 8 is an inert metal material.

[0047] In addition to the electrolytic cell shown in FIGS. 1A-1C, the structure of the electrolytic cell can also be designed in many forms, such as a U-shaped electrolytic cell. Further, the shape of the electrolytic cell can be varied, for example, the bottom of the electrolytic cell is not limited to a flat bottom, but can also be a trapezoidal bottom and a round bottom.

[0048] Rare earth electrolytic cells capable of achieving physical separation of the anolyte and the catholyte, and the mediation function of liquid alloy, can be applicable to the method of the present invention.

[0049] In scale applications, the electrolytic cell may be operated in series or in parallel with each other.

Example 1

[0050] A pre-alloyed LaNi alloy with the Ni content of 25 wt % was contained at the bottom of the electrolytic cell, the inert anode made of 65.8 wt % La.sub.2O.sub.3+33.7 wt % Ni.sub.2O.sub.3+0.5 wt % In.sub.2O.sub.3 ceramic material was used as the anode, and a pure nickel rod was used as the cathode. Lanthanum oxide was used as the raw material with the REO content of 96.3 wt % and the La.sub.2O.sub.3/REO of 97.1 wt %. The anolyte was 60 wt % LaF.sub.3+27 wt % LiF+13 wt % BaF.sub.2, the above lanthanum oxide raw material was added, and the catholyte was 65 wt % LaF.sub.3+35 wt % LiF. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 950? ? C. and heat preservation for 2 h, the current density of the cathode was controlled at 0.1 A/cm.sup.2 by current conduction, the above lanthanum oxide raw material was periodically added after the start of electrolysis, and the lanthanum-nickel alloy with the La/REM of 99.95 wt % was obtained after electrolysis.

[0051] The obtained lanthanum-nickel alloy can be prepared as a rare earth hydrogen storage alloy for use in hydrogen fuel electrolytic cells/nickel-hydrogen batteries, and can also be used as a scavenger or modifier for steel or nonferrous metal melts, such as for deoxidation of nickel-containing stainless steels.

Example 2

[0052] Metal Ce was contained at the bottom of the electrolytic cell, graphite was used as the anode, and the liquid aluminum cathode inserted with a conductive tungsten rod was used as the cathode. Cerium oxide was used as the raw material with the REO content of 96.2 wt % and the CeO.sub.2/REO of 98.6 wt %. The anolyte was 65 wt % CeF.sub.3+35 wt % LiF, the above cerium oxide raw material was added, and the catholyte was 65 wt % CeF.sub.3+35 wt % LiF. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 860? ? C. and heat preservation for 2 h, the current density of the cathode was controlled at 0.1 A/cm.sup.2 by current conduction, the above cerium oxide raw material was periodically added after the start of electrolysis, and the aluminum-cerium alloy with the Ce/REM of 99.94 wt % was obtained after electrolysis.

[0053] The obtained aluminum-cerium alloy can be used as an intermediate alloy for the production of cerium-containing aluminum alloy materials.

Example 3

[0054] A pre-alloyed PrFe alloy with the Fe content of 10 wt % was contained at the bottom of the electrolytic cell, graphite was used as the anode and a pure iron rod was used as the cathode. Praseodymium oxide was used as the raw material with the REO content of 97.6 wt % and the Pr.sub.6O.sub.11/REO of 95.9 wt %. The anolyte was 45 wt % PrF.sub.3+20 wt % LiF+35 wt % BaF.sub.2, the above praseodymium oxide raw material was added, and the catholyte was 50 wt % PrF.sub.3+50 wt % LiF. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 1000? C. and heat preservation for 2 h, the current density of the cathode was controlled at 2.0 A/cm.sup.2 by current conduction, the above praseodymium oxide raw material was periodically added after the start of electrolysis, and the praseodymium iron alloy with the Pr/REM of 99.87 wt % was obtained after electrolysis.

[0055] The obtained praseodymium iron alloy can be used as the additive in the production of neodymium iron boron permanent magnetic materials.

Example 4

[0056] A pre-alloyed NdFe alloy with the Fe content of 15 wt % was contained at the bottom of the electrolytic cell, graphite was used as the anode and a pure iron rod was used as the cathode. Neodymium oxide was used as the raw material with the REO content of 98.3 wt % and the Nd.sub.2O.sub.3/REO of 98.7 wt %. The anolyte was 83 wt % NdF.sub.3+10 wt % LiF+7 wt % BaF.sub.2, the above neodymium oxide raw material was added, and the catholyte was 80 wt % NdF.sub.3+20 wt % LiF. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 1050? C. and heat preservation for 2 h, the current density of the cathode was controlled at 6.0 A/cm.sup.2 by current conduction, the above neodymium oxide raw material was periodically added after the start of electrolysis, and the praseodymium iron alloy with the Nd/REM of 99.92 wt % was obtained after electrolysis.

[0057] The obtained neodymium iron alloy can be used for preparing neodymium iron boron permanent magnetic materials.

Example 5

[0058] A pre-alloyed SmCo alloy with the Co content of 20 wt % was contained at the bottom of the electrolytic cell, graphite was used as the anode, and a pure cobalt rod was used as the cathode. Samarium oxide was used as the raw material with the REO content of 92.4 wt % and the Sm.sub.2O.sub.3/REO of 98.8 wt %. The anolyte was CaCl.sub.2) and the catholyte was 80 wt % SmF.sub.3+20 wt % LiF. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 950? C. and heat preservation for 2 h, the above samarium oxide raw material was added before the start of electrolysis, the current density of the cathode was controlled at 1.5 A/cm.sup.2 by current conduction, the above samarium oxide raw material was added again during electrolysis, and the samarium cobalt alloy with the Sm/REM of 99.94 wt % was obtained after electrolysis.

[0059] The obtained samarium-cobalt alloy can be used for preparing samarium-cobalt permanent magnetic materials, or samarium, which is an easily evaporable component, is separated by vacuum distillation process (900? C., <10 Pa), and after condensation, high-purity metal samarium (Sm/REM?99.99 wt %) is obtained.

Example 6

[0060] A pre-alloyed EuPb alloy with the Pb content of 80 wt % was contained at the bottom of the electrolytic cell, graphite was used as the anode and the liquid tin cathode inserted with a conductive tungsten rod was used as the cathode. The raw material was europium oxide with the REO content of 96.9 wt % and the Eu.sub.2O.sub.3/REO of 92.3 wt %. The anolyte was CaCl.sub.2)NaCl in a molar ratio of 3:1 and the catholyte was 70 wt % EuF.sub.3+30 wt % LiF. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 850? C. and heat preservation for 2 h, the above europium oxide raw material was added before the start of electrolysis, the current density of the cathode was controlled at 5.0 A/cm.sup.2 by current conduction, the above samarium oxide raw material was added again during electrolysis, and the tin-europium alloy with the Eu/REM of 99.64 wt % was obtained after electrolysis.

[0061] The obtained tin-europium alloy can be vacuum distilled (900? ? C., <10 Pa) to separate europium which is an easily evaporable component, and then high-purity metallic europium (Eu/REM?99.95 wt %) can be obtained after condensation.

Example 7

[0062] A pre-alloyed DyCu alloy with the Cu content of 52 wt % was contained at the bottom of the electrolytic cell, graphite was used as the anode, and a pure iron rod was used as the cathode. Dysprosium oxide was used as the raw material with the REO content of 98.8 wt % and the Dy.sub.2O.sub.3/REO of 99.1 wt %. The anolyte was 90 wt % DyF.sub.3+10 wt % LiF, the above dysprosium oxide raw material was added, and the catholyte was 66 wt % DyF.sub.3+34 wt % LiF. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 1050? C. and heat preservation for 2 h, the current density of the cathode was controlled at 3.5 A/cm.sup.2 by current conduction, the above dysprosium oxide raw material was periodically added after the start of electrolysis, and the dysprosium iron alloy with the Dy/REM of 99.95 wt % was obtained after electrolysis.

[0063] The obtained FeDy alloy can be used for the preparation of rare earth functional materials such as neodymium-iron-boron materials and giant magnetostrictive materials.

Example 8

[0064] A pre-alloyed YbSn alloy with the Sn content of 70 wt % was contained at the bottom of the electrolytic cell, a 25 wt % Ni-35 wt % Fe-10 wt % NiO-2 wt % Yb.sub.2O.sub.3-28 wt % NiFe.sub.2O.sub.4 metal ceramic composite inert anode was used as the anode, and a pure copper rod was used as the cathode. Ytterbium oxide was used as the raw material, with the REO content of 98.8 wt % and the Yb.sub.2O.sub.3/REO of 98.7 wt %. The anolyte was CaCl.sub.2)LiClBaCl.sub.2 in a molar ratio of 80:15:5 and the catholyte was 75 wt % YbF.sub.3+25 wt % LiF. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 850? C. and heat preservation for 2 h, the above ytterbium oxide raw material was added before the start of electrolysis, and the current density of the cathode was controlled at 3.0 A/cm.sup.2 by current conduction, the above ytterbium oxide raw material was further added during electrolysis, and the copper ytterbium alloy with the Yb/REM of 99.91 wt % was obtained after electrolysis.

Example 9

[0065] A pre-alloyed YCo alloy with the Co content of 28 wt % was contained at the bottom of the electrolytic cell, the inert anode made of 60 wt % Ni-30 wt % Fe-5 wt % Y-5 wt % Mn alloy material was used as the anode, and a pure manganese rod was used as the cathode. Yttrium oxide was used as the raw material with the REO content of 98.3 wt % and the Y.sub.2O.sub.3/REO of 98.9 wt %. The anolyte was 75 wt % YF.sub.3+15 wt % LiF+10 wt % CaF.sub.2, the above yttria raw material was added and the catholyte was 90 wt % YF.sub.3+10 wt % LiF. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 1050? C. and heat preservation for 2 h, the current density of the cathode was controlled to be 30.0 A/cm.sup.2 by current conduction, the above yttrium oxide raw material was periodically added after the start of electrolysis, and the manganese-yttrium alloy with the Y/REM of 99.86 wt % was obtained after electrolysis.

[0066] The obtained manganese-yttrium alloy can be used as the additive for magnesium alloy production to improve its mechanical properties and processing properties.

Example 10

[0067] A pre-alloyed YCo alloy with the Co content of 28 wt % was contained at the bottom of the electrolytic cell, graphite was used as the anode, and the Mg liquid cathode inserted with a conductive tungsten rod was used as the cathode. Yttrium oxide was used as the raw material with the REO content of 98.3 wt % and the Y.sub.2O.sub.3/REO of 98.9 wt %. The anolyte was 65 wt % YF.sub.3+35 wt % LiF, the above yttria raw material was added, and the catholyte was 65 wt % YF.sub.3+25 wt % LiF+10 wt % BaF.sub.2. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 880? C. and heat preservation for 2 h, the current density of the cathode was controlled to be 0.5 A/cm.sup.2 by current conduction, the above yttrium oxide raw material was periodically added after the start of electrolysis, and the yttrium magnesium alloy with the Y/REM of 99.93 wt % was obtained after electrolysis.

[0068] The obtained yttrium magnesium alloy can be used as the intermediate alloy for the production of magnesium alloy materials.

Example 11

[0069] A pre-alloyed ScCu alloy with the Cu content of 80 wt % was contained at the bottom of the electrolytic cell, the inert anode made of CaRuO.sub.3 ceramic material was used as the anode, and the liquid aluminum cathode inserted with a conductive tungsten rod was used as the cathode. Scandium oxide was used as the raw material with the REO content of 91.8 wt % and the Sc.sub.2O.sub.3/REO of 99.3 wt %. The anolyte was CaCl.sub.2)KCl in a molar ratio of 4:1 and the catholyte was 40 wt % ScF.sub.3+30 wt % LiF+20 wt % BaF.sub.2+10 wt % CaF.sub.2. The electrolytic cell was placed in an atmosphere filled with dry argon and the temperature was raised by programs to 950? C. and heat preservation for 2 h; the above scandium oxide raw material was added before the start of electrolysis, and the current density of the cathode was controlled at 1.0 A/cm.sup.2 by current conduction; the above scandium oxide raw material was periodically added after the start of electrolysis, and the aluminum scandium alloy with the Sc/REM of 99.97 wt % was obtained after electrolysis.

[0070] The obtained aluminum scandium alloy can be used as the intermediate alloy for the production of aluminum alloy materials.

Comparative Example 1

[0071] This Comparative example 1 differs from Example 1 in that: the bottom of the electrolytic cell does not contain the LaNi alloy, the anolyte and the catholyte are both 65 wt % LaF.sub.3+35 wt % LiF, and other conditions are the same. A lanthanum-nickel alloy with La/REM of 97.79 wt % was obtained after electrolysis.

[0072] It is concluded that in the absence of the liquid alloy, the separation and purification effect based on the electrochemical reaction at the liquid alloy/molten salt electrolyte interface doesn't exist, and the rare earth alloy produced from electrolysis of rare earth oxides in the electrolytic cell with an ordinary partition has a lower purity, a significantly higher content of non-rare earth impurities such as Fe and O, and other rare earth impurities such as Ce and Pr.

Comparative Example 2

[0073] This Comparative example 2 differs from Example 7 in that the cathode is tungsten as an inert cathode material, and other conditions are the same. After electrolysis, solid dysprosium metal with Dy/REM of 99.91 wt % was obtained, and the content of non-metallic impurity F was high.

[0074] The above is only the specific implementations of the present invention, but the protection scope of the present invention is not limited here. Any change or equivalent made by a person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope of the present invention. Accordingly, the scope of protection of the present invention shall be subject to the scope of protection of the claims.