Research Status of Electrolytic Preparation of Rare Earth Metals and Alloys in Fluoride Molten Salt System: A Mini Review of China
Abstract
:1. Introduction
2. Comparison of Pyrometallurgical Methods for Rare Earth Metals
REC2(s) = RE(s) + 2C(s)
Metal | Melting Point/K | Boiling Point/K | The Temperature at 133.3 Pa Vapor Pressure/K | Evaporation Rate at 133.3 Pa Vapor Pressure/[g/(cm2·h)] | REF3 Melting Point/K | RE2O3 Melting Point/K | Mineral Characteristics Group | Main Preparation Method |
---|---|---|---|---|---|---|---|---|
La | 1193 | 3743 | 2490 | 53 | 1763 | 2490 | Light rare earth | Molten salt electrolysis |
Ce | 1071 | 3743 | 2420 | 53 | 1710 | 2415 | ||
Pr | 1204 | 3403 | 2241 | 56 | 1668 | 2400 | ||
Nd | 1283 | 3303 | 2032 | 60 | 1647 | 2484 | ||
Sm | 1345 | 2173 | 1237 | 83 | 1579 | 2603 | Lanthanum or carbonthermal reduction | |
Eu | 1095 | 1713 | 1110 | 90 | 1549 | 2668 | ||
Gd | 1584 | 3273 | 2295 | 59 | 1504 | 2663 | Heavy rare earth | Calcium thermal reduction |
Tb | 1633 | 3073 | 2212 | 60 | 1445 | 2663 | ||
Dy | 1682 | 2873 | 1712 | 71 | 1427 | 2664 | ||
Ho | 1743 | 2873 | 1799 | 69 | 1416 | 2673 | ||
Er | 1795 | 3173 | 1879 | 68 | 1413 | - | ||
Tm | 1818 | 2003 | 1368 | 83 | 1431 | 2684 | Lanthanum or carbonthermal reduction | |
Yb | 1097 | 1703 | 924 | 108 | 1430 | - | ||
Lu | 1929 | 3603 | 2371 | 61 | 1455 | - | Calcium thermal reduction | |
Y | 1796 | 3203 | 1355 | 43 | 1425 | - |
Method | Main Raw Materials | Product Components | Production Efficiency | Production Process |
---|---|---|---|---|
Calcium thermal reduction method [21,22] | REF3, Ca | The purity of rare earth metals is between 95.5% and 99.95%. | The yield of rare earth metals is about 95–98%. | Low investment, short process, and a large amount of slag generated from calcium thermal reduction. |
Lithium thermal reduction [23] | RECl3, Li | The purity of rare earth metals can reach more than 99.9%. | The yield of rare earth metals reaches more than 95%. | The quality of the prepared rare earth metals is better than that of calcium thermal reduction. Rare earth chlorides are very hygroscopic compounds. |
Carbonaceous reduction [24,25] | RE2O3, C | Not indicated | The yield of metals reaches 59.37% | High processing cost and discontinuous production. |
Lanthanum thermal reduction [26,27,28] | RE2O3, La | The purity of rare earth metals reaches over 99.9%. | The recovery of rare earth metals reaches over 90%. | High temperature and pressure conditions require high-quality materials and performance of the equipment. |
Chloride system molten salt electrolysis method [29,30] | RECl3-MCl(M = Li, K) | Electrolytic rare earth metals with a purity of 95–98% | The yield of rare earth metals is about 85–90%. Single rare earth current efficiency is around 70%. | Generates toxic chlorine gas, low metal recovery. |
Fluoride system molten salt electrolysis method [30] | REF3-RE2O3-LiF | Electrolytic rare earth metals with a purity of 95–98% | The yield of rare earth metals is about 90–95%. Current efficiency is about 70–80%. | The current efficiency and rare earth metal yield are high; the electrolysis temperature is high, and the anode produces greenhouse gases such as CO2, CF4, and C2F6. |
3. Research Status of Fluoride Molten Salt System
3.1. Preparation of Individual Rare Earth Metal
3.1.1. Lanthanum Metal
3.1.2. Cerium Metal
3.1.3. Praseodymium Metal
3.1.4. Neodymium Metal
3.2. Preparation of Rare Earth Alloys
3.2.1. RE–Mg Alloys
3.2.2. RE–Al Alloys
3.2.3. RE–Ni Alloys
RE | Molten Salt | Electrode | Electrolysis Time | Temperature | Applied Current Density/Current/ Potential (vs. Pt) | RE Alloys |
---|---|---|---|---|---|---|
Ce [40] | 52.66 wt.% LiF-47.34 wt.% CaF2-CeF3 | Ni | 60 min | 1093 K | −1.5 V | CeNi5 |
Eu [76] | 55.56 wt.% LiF-44.44 wt.% CaF2-EuF3-AlF3 | W | 20 min | 1113 K | −1.1 V | EuAl4 |
Nd [76] | 55.56 wt.% LiF-44.44 wt.% CaF2-NdF3-AlF3 | W | 20 min | 1133 K | −1.33 V, −1.49 V, −1.69 V, −1.88 V | Nd3Al11, NdAl3, NdAl2, Nd3Al |
Ce [77] | 55.56 wt.% LiF-44.44 wt.% CaF2-CeF3-AlF3 | W | 20 min | 1113 K | −1.25 V, −1.43 V, −1.79 V | Ce3Al11, CeAl3, (Ce3Al, CeAl) |
Sm [77] | 55.56 wt.% LiF-44.44 wt.% CaF2-NdF3-AlF3 | W | 20 min | 1113 K | −1.45 V | SmAl3 |
Sm [78] | LiF-CaF2-Sm2O3-AlF3 | W | 180 min | 1223 K | −731.4 mA/cm2 | SmAl2, SmAl3 |
Sm [96] | 52.66 wt.% LiF-47.34 wt.% CaF2 | Ni | 60 min | 1120 K | −200 mA/cm2 | Sm3Ni, SmNi2 |
Nd [97] | 52.66 wt.% LiF-47.34 wt.% CaF2-NdF3 | Ni | 120 min | 1113 K | 35 mA/cm2, 0.65 V | NdNi2, NdNi3 |
Gd [97] | 52.66 wt.% LiF-47.34 wt.% CaF2-GdF3 | Ni | 120 min | 1113 K | 35 mA/cm2, 0.65 V | GdNi2, GdNi |
Sm [97] | 52.66 wt.% LiF-47.34 wt.% CaF2-SmF3 | Ni | 120 min | 1113 K | 35 mA/cm2, 0.7 V | SmNi2, SmNi3 |
Dy [98] | 55.56 wt.% LiF-44.44 wt.% CaF2-DyF3 | Ni | 60 min | 1113 K | −15 mA/cm2 | Dy2Ni17, DyNi4 |
Dy [98] | 55.56 wt.% LiF-44.44 wt.% CaF2-DyF3 | Ni | 60 min | 1113 K | −15 mA/cm2 | Dy2Ni17, DyNi4 |
Nd [99] | 57.84 wt.% LiF-42.16 wt.% CaF2-NdF3 | Ni | 75 min | 1123 K | 0.15 V,0.35 V (vs. Li+/Li) | NdNi2, NdNi3 |
Nd [99] | 57.84 wt.% LiF-42.16 wt.% CaF2-NdF3 | Ni | 50 min | 1123 K | 0.60 V (vs. Li+/Li) | NdNi5 |
Pr [102] | 57.84 wt.% LiF-42.16 wt.% CaF2-PrF3 | Ni | 90 min /180 min | 1123 K | 0.2 V, 0.36 V, 0.6 V(vs. Li+/Li) | PrNi2, PrNi3, PrNi5 |
Dy [113] | 57.84 wt.% LiF-42.16 wt.% CaF2-DyF3 | Fe | 30 min | 1123 K | 0.1 V (vs. Li+/Li) | DyFe2 |
3.2.4. Nd Alloys
3.3. Discussion and Summary
3.3.1. Electrolysis Parameters
3.3.2. Treatment of Anode Gases
3.3.3. Design of Rare Earth Cell
4. Prospects
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Molten Salt System | Electrolysis Temperature | Electrolytic Raw Materials | Time of Electrolysis | Cathodic Current Density/(A/cm2) | Metal Quantity | Current Efficiency |
---|---|---|---|---|---|---|
65 wt.% LaF3–23 wt.% LiF–12 wt.% BaF2 [41] | 1223 K | La2O3 | 60 min | 7 | 36.8 g | 85.21% |
1223 K | Tetragonal crystal system LaOF | 60 min | 7 | 38.1 g | 88.23% | |
1223 K | Rhombic hexagonal crystal system LaOF | 90 min | 7 | 46.7 g | 86.51% | |
70 wt.% LaF3–LiF–BaF2 [43] | 1223 K | La2O3 | 70 min | 8 | 45.3 g | 93.38% |
LiF–LaF3 [44] | 1243–1253 K | Fluorescence-level purity La2O3 | 20 min | 5 | 71.8 g | 81.57% |
Electrolyte System | 38 wt.% NdF3–35 wt.% LiF–27 wt.% CaF2 [64] | 89 wt.% NdF3–11 wt.% LiF [56] | 90 wt.% NdF3–10 wt.% LiF [59] | (88.9–90 wt.%) NdF3–LiF [62] |
---|---|---|---|---|
Electrode | Anode: graphite Cathode: tungsten rod | Anode: graphite electrolyzer Cathode: 6–8 mm diameter molybdenum rod | Anode: graphite Cathode: 28 mm diameter tungsten rod | Anode: graphite block Cathode: tungsten plate |
Electrolysis temperature | 1303 K | 1308 K | 1343–1353 K | 1293 K |
Cathode current density | 10.97 A/cm2 | 7 A/cm2 | 0.85–1.39 A/cm2 | 1.95 A/cm2 |
Tank voltage | not indicated | 4.50–5.50 V | 4–6.50 V | 4.80–6 V |
Electrolyzer structure | Anode and cathode up plug rare earth cell | Anode and cathode up plug rare earth cell | Anode and cathode up plug rare earth cell | Bottom cathode rare earth cell |
Current efficiency | 52.7% | 62% | 57.60–87.10% | 75.36–85.75% |
Rare earth direct yield | 38.60% | 88.50% | Not indicated | 95.20% |
Rare Earth Metals/Rare Earth Alloys | Electrolyte | Raw Material | Electrolysis Temperature | Cathode Current Density | Current Efficiency | Metal Yield |
---|---|---|---|---|---|---|
La [41] | 65 wt.% LaF3–23 wt.% LiF–12 wt.% BaF2 | La2O3 | 1233 K | 7 A/cm2 | 85.21% | 99.29% |
La [43] | 70 wt.% LaF3–LiF–BaF2 | La2O3 | 1223 K | 8 A/cm2 | 93.38% | 99.29% |
La [44] | LaF3–LiF | La2O3 | 1263 K | 5 A/cm2 | 81.57% | not indicated |
Ce [50] | 63 wt.% CeF3–21 wt.% LiF–16 wt.% BaF2 | CeO2 | 1173 K | 6.25 A/cm2 | 53 % | 94.70% |
Pr [55] | PrF3–LiF | Pr6O11 | 1213–1233 K | 6 - 8 A/cm2 | 70-80% | 90% |
Nd [56] | 89 wt.% NdF3–11 wt.% LiF | Nd2O3 | 1308 K | 7 A/cm2 | 62% | 88.50% |
Nd [64] | 38 wt.% NdF3–35 wt.% LiF–27 wt.% CaF2 | Nd2O3 | 1303 K | 10.97 A/cm2 | 52.70% | 38.60% |
Nd [59] | 90 wt.% NdF3–10 wt.% LiF | Nd2O3 | 1343–1353 K | 0.85–3.79 A/cm2 | 57.60–87.10% | not indicated |
Nd [62] | 88.9 wt.% NdF3–11.1 wt.% LiF | Nd2O3 | 1233–1293 K | 1.95 A/cm2 | 74.30–85.75% | 93.10–95.20% |
Nd–Mg [74] | NdF3–LiF–BaF2–Na3AlF6 | Nd2O3 | 1323 K | 6–7 A/cm2 | 60–72.60% | 84.2–95.2% |
Y–Ni [102] | 85 wt.% YF3–15 wt.% LiF | Y2O3 | 1273 K | 10 A/cm2 | 72.80% | not indicated |
Pr–Nd [114] | 90 wt.% (Pr, Nd)F3–10 wt.% LiF | REO (RE = Nd, Pr) | 1273–1373 K | 4.5–6.5 A/cm2 | 57.40-85% | not indicated |
Pr–Nd [116] | 65 wt.% NdF3–15 wt.% BaF2–20 wt.% LiF | REO (RE = Nd, Pr) | 1303 K | 8–13 A/cm2 | 57% | 90% |
Pr–Nd–(6–8 wt.%) Dy [121] | (87.50–90.91 wt.%)REF3–LiF | REO (RE = Pr, Nd, Dy) | 1263–1353 K | 4–8 A/cm2 | 76.59% | 93.20–98.12% |
Pr–Nd–(10–15 wt.%) Gd [122] | 17.85 wt.% GdF3–69.03 wt.% (Pr, Nd)F3–13.12 wt.% LiF | REO (RE = Pr, Nd, Dy) | 1283–1373 K | 5 - 9 A/cm2 | 75.50–79.60% | 93.20–98.00% |
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Liao, C.; Que, L.; Fu, Z.; Deng, P.; Li, A.; Wang, X.; Chen, S. Research Status of Electrolytic Preparation of Rare Earth Metals and Alloys in Fluoride Molten Salt System: A Mini Review of China. Metals 2024, 14, 407. https://doi.org/10.3390/met14040407
Liao C, Que L, Fu Z, Deng P, Li A, Wang X, Chen S. Research Status of Electrolytic Preparation of Rare Earth Metals and Alloys in Fluoride Molten Salt System: A Mini Review of China. Metals. 2024; 14(4):407. https://doi.org/10.3390/met14040407
Chicago/Turabian StyleLiao, Chunfa, Lianghua Que, Zanhui Fu, Pan Deng, Alin Li, Xu Wang, and Shumei Chen. 2024. "Research Status of Electrolytic Preparation of Rare Earth Metals and Alloys in Fluoride Molten Salt System: A Mini Review of China" Metals 14, no. 4: 407. https://doi.org/10.3390/met14040407