Patent Application
20150203979
The invention relates to a process for recovering at least one rare earth metals (REM) from the group of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.
Rare earth metals (i.e. Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) are becoming increasingly important in today's society. It is therefore an increased demand in finding improved methods of extracting rare earth metals from various resources such as permanent magnets, in particular Nd containing magnets such as NdFeB—magnets, batteries such as battery cathodes containing AB5, where A is lanthanum, cerium, neodymium and/or praseodymium, and B is nickel, cobalt, manganese and/or aluminium, thin films, lightings and displays, ores, rare earth concentrates from ores.
The rare metals can be present in metallic form but commonly as oxides, e.g. La2O3, CeO2, Pr6O11, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb4O7, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, and Y2O3.
The object of the invention is to provide a process for recovering at least one rare earth metal from the group of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu from a resource containing at least one of these metals.
Another object of the invention is to recover Nd and/or Dy from Nd/Dy containing magnets.
At least one of the objects mentioned above is met by a process for recovering at least one rare earth metals (REM) from the group of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, said process including the steps of:
Thereby at least one rare earth metal from the group of: Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu can be recovered.
The salt melt is preferably heated under protective atmosphere, suitably argon. The atmosphere may also be nitrogen. Furthermore, chlorine gas may be admixed to the nitrogen or argon atmosphere.
For given salt combination of the least two chloride salts, it is preferred that the contents of the salts are within 10% by weight from the lowest eutectic point of the salt combination, more preferably within 5% by weight, most preferably within 1% by weight. However, other contents may be used as long as the liquidus temperature of the salt combination is at least 50° C. lower than the operating temperature during electrolyzing; preferably 100° C. lower than the operating temperature. Preferably the salt composition comprises at least two of the salts selected from the group: NaCl, KCl, LiCl, and CaCl2, preferably at least three of the salts selected from the group: NaCl, KCl, LiCl, and CaCl2.
In preferred embodiment the at least one chloride salt composition includes by weight % of the at least one chloride salt, 3-20 NaCl, 30-70 KCl, 20-60 LiCl, preferably 5-15 NaCl, 40-60 KCl, 30-50 LiCl, more preferably 7-12 NaCl, 45-55 KCl, 35-45 LiCl.
In an alternative embodiment the at least one chloride salt composition includes by weight % of the at least one chloride salt, 10-50 NaCl, 2-20 KCl, 50-80 CaCl2 preferably 25-35 NaCl, 3-10 KCl, 60-75 CaCl2.
In an alternative embodiment the at least one chloride salt composition includes by weight % of the at least one chloride salt, 5-20 NaCl, 20-40 LiCl, 40-70 CaCl2 preferably 7-15 NaCl, 25-35 LiCl, 50-60 CaCl2.
In an alternative embodiment the at least one chloride salt composition includes by weight % of the salt composition, 35-65 KCl, 20-50 LiCl, 5-20 CaCl2 preferably 45-55 KCl, 30-40 LiCl, 10-15 CaCl2.
The flux is AlCl3. The flux can be added before or after forming the salt melt. It may also be added stepwise as it is consumed. In one embodiment at least a fraction up to all of the AlCl3 is generated in situ by reacting chloride ions in the salt melt with an aluminium anode, preferably the aluminum anode is an aluminum melt at the bottom of the crucible.
The REM containing resource may be crushed and/or ground and/or milled before being provided to the crucible. The crushed and/or ground and/or milled may be pelletized before being provided to the crucible.
The REM containing resource may e.g. be:
Rare earth oxides are particularly suitable, for instance rare earth oxides from the group of: La2O3, CeO2, Pr6O11, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb4O7, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, and Y2O3. Resources of particular interest are those containing at least one of Dy, Nd, Pm, Sm, Ho, Er, Tm, Yb and Lu. At present the most interesting elements to recover are Dy and Nd since these elements may be present in high contents in permanent magnets.
According to a preferred embodiment the ocean floor nodule ore is excluded as a REM containing resource because said raw material normally has a very low content of rare earth oxides and since they contain high amounts of base metals such as Mn, Fe and Ni.
The flux AlCl3 acts as a chloride donor dissolving rare earth metal oxides and/or rare earth metals to rare earth metal chlorides in the salt melt. The following chlorides can be formed depending on which are earth oxides or metals that are present in the resource to be dissolved: LaCl3, CeCl3, PrCl3, NdCl3, SmCl3, EuCl3, GdCl3, TbCl3, DyCl3, HoCl3, ErCl3, TmCl3, YbCl3, LuCl3, and YCl3.
When AlCl3 dissolves rare earth metal oxides, aluminium will form Al2O3. When AlCl3 dissolves rare earth metals, Al metal is released which will is highly reactive and is hence likely to react with other reducible chlorides in the salt melt.
In one embodiment the dissolving step d) is performed before the recovering step d). However they may in different embodiments partly or fully overlap as will be described below, in particular in relation to the use of a liquid aluminium anode. To dissolve the REM-containing resource, the salt melt is kept at high temperature usually for a time between about 2 and about 10 hours, preferably 3-8 hours, more preferably 4-8 hours. The amount of REM-containing resource is preferably such that a weight ratio “flux”/“REM in the resource” is between 0.1-3, preferably 0.2-2.0, more preferably 0.3-1.0, most preferably 0.4-0.6. The temperature should be lower than 1000° C., more preferably lower than 900° C. For optimal economy, the temperature is preferably in the range of 550-700° C. during the dissolution, more preferably 580-650° C. To improve viscosity of the salt melt, the temperature of the salt melt is preferably at least 50° C. above the liquidus temperature of the salt melt, more preferably at least 100° C. above the liquidus temperature of the salt melt.
When dissolving a neodymium magnet (Nd2Fe14B) the reactions can be:
The Gibbs energy of neodymium chloride formation is negative, whereas the Gibbs energy for formation of FeCl3 and BCl3 are positive. Therefore formation of NdCl3 is more feasible than that of FeCl3 and BCl3. Neodymium can be recovered from neodymium chloride by electrolysis and/or vaporization.
Recovering To recover the REM-resource from the melt various processes may be used. The salt melt used for extraction may optionally be recycled. Preferably the at least one rare earth metal and other metals can be selectively electro-deposited from the salt melt. However, it is also possible to use vaporization of the metal chlorides and condensing them, or leach the salt phase in water and extracting the metals as hydroxides by hydrometallurgy method. The process can be designed to be continuous by combining the two steps. Residues after processing, such as Al2O3, may be used for landfill, building construction or as a raw material for the refractory industry. The salts can be recovered and reused.
In a preferred embodiment, the REM is recovered by electrolysis by having at least one anode and at least one cathode are connected to the salt melt. In this embodiment the recovering includes the step of electrolyzing the salt melt to form at least one rare earth metal at the cathode. Preferably at least one REM from the group Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu is selectively electrodeposited on the at least one cathode.
In one embodiment the electrolysis is done using conventional anode/s and cathode/s which is further described under “Electrolysis using conventional anode/s and cathode/s”.
In the most preferred embodiment, the electrolysis includes an aluminium anode which facilitates an in situ formation of an aluminium chloride. This is further described under “Dissolving and electrolysis using aluminium anode”.
According to one embodiment a conventional anode and cathode configuration is used, e.g. at least one cathode and at least one anode submerged in the salt melt.
Preferably, two electrodes, e.g. of graphite, are immersed into the melt and connectable to a DC source. The theoretical decomposition voltage for MCl3, where M is a rare earth metal is around 2.5-3 V. Preferably a voltage in the range of 2.5-5 V is used for the electrolysis, more preferably 3-4 V. If AlCl3 remains in the salt melt it may be selectively electrodeposited or co-deposited with the rare earth metal on the cathode.
The flux, AlCl3, can be added in a single batch or in several batches as the aluminium chloride is consumed, preferably 5-30% by weight of the salt mixture when added in a single batch, more preferably 5-20% by weight of the mixture, most preferably 7-15 wt %. Since the flux is difficult to recover after the extraction process, it is desirable that there is no excessive addition of aluminium chloride.
Accordingly, it is preferable to have a careful control of the content of aluminium chloride in the salt melt. Moreover, as set out under “Dissolving” a sufficient amount of AlCl3 in the melt is preferred in order to get a sufficient formation of REM-chlorides in the salt melt. Accordingly, in a preferred embodiment the amount of AlCl3 is maintained at a sufficient level. This may be done by adding AlCl3 stepwise or continuously as it is consumed and/or by in situ formation of AlCl3 in the salt melt. In situ formation of AlCl3 is discussed under “Dissolving and electrolysis using aluminium anode”. The content of aluminium chloride in the salt melt is dependent on the material to be treated. For neodymium magnets (Nd2Fe14B) the AlCl3/Nd-ratio is 2/1 considering the reaction set out above. In the example 20 wt. % AlCl3was used. Preferably, the amount of AlCl3 is controlled within ±7%, preferably within ±5% or within ±3%.
The electrolysis preferably is carried out in the crucible that holds the salt melt with the dissolved REM containing resource containing at least one rare earth metal from the group of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
During electrolysis chloride ions will be attracted to the anode. With the use of a conventional anode/s, e.g. a graphite electrode/s, chlorine gas will form and evaporate from the salt melt. The chlorine gas is preferably recovered.
Preferably the batch of melt is electrolyzed for 2 to 8 hours. During the electrolysis, the temperature of the salt melt is preferably lower than 1000° C., more preferably lower than 900° C. For optimal economy the temperature is preferably in the range of 550-700 ° C., more preferably 580-650° C. To improve viscosity of the salt melt, the temperature of the salt melt is preferably at least 50° C. above the liquidus temperature of the salt melt, more preferably at least 100° C. above the liquidus temperature of the salt melt.
The dissolving step and the electrolysis step may be performed separately or they may fully or partly overlap.
The at least rare earth metal of the group Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and optionally other dissolved metals, can selectively be electrodeposited on the cathode. After depositing one metal the cathode can be removed and the metal deposited on the cathode can be extracted. To avoid interrupts of the electrolysis, another “clean” electrode can be submerged. Alternatively, the salt melt may have a plurality of electrodes which one after the other is activated as a cathode while the former is deactivated. Thereby, the metals can be selectively deposited at individual electrodes.
After recovering the at least one rare earth metal and possibly other metals, the chloride salts of the salt melt may be recycled. The residue after processing contains Al2O3 and for instance other stable oxides such as SiO2, depending on the contents of the REM containing resource. The residues may for instance be used for landfill, building construction or as a raw material for the refractory industry.
In a preferred embodiment the at least one anode includes aluminium, preferably in the form of an aluminium melt provided at the bottom of the crucible. The aluminium melt form the anode or a part of the anode, for instance by immersing an electrode, e.g. a graphite electrode, in the aluminium melt and connecting it to positive polarity during electrolysis. Alternatively, the crucible is at least partly made in a conductive material being in contact with the aluminium melt, and connecting the crucible positive polarity during the electrolysis. Thereby, the crucible and the molten aluminium operate as an anode. Of course at least one cathode is still required during electrolysis, e.g. one or more graphite electrode/s submerged in the salt melt.
When using an aluminium melt at the bottom of the crucible as the anode or part of the anode, the salt melt and the aluminium are heated to a temperature where both are in liquid phase. To improve viscosity of the salt melt, the temperature of the salt melt is preferably at least 50° C. above the liquidus temperature of the salt melt, more preferably at least 100° C. above the liquidus temperature of the salt melt. The temperature should be at least 660° C. and not more than 1000° C., preferably the temperature is in the range of 700-900° C.
During the electrolysis metals/s from metal chloride/s is deposited at the cathode. At the contact surface between the salt melt and the aluminium melt chloride ions are reacting with aluminium, thereby forming AlCl3. This means that during steady state the salt melt can be wholly or partly self-supporting in regards of the flux, AlCl3 and also that emission of chlorine gas is reduced. Lesser amounts of chlorine gas may form even when using an aluminium melt as the anode or part of the anode. This gas may be recovered.
An initiating chloride donor is provided to start the reactions in the salt melt. The initiating chloride donor may be aluminium chloride and/or at least one metal chloride that can be electrolyzed, i.e. so that chloride ions forms AlCl3 at the contact surface between the salt melt and the aluminium melt.
In one embodiment, the initiating chloride donor includes a metal chloride of the same type as provided in the chloride salt composition, e.g. at least one metal chloride selected from the group consisting of chlorides of Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, and Ra.
In a preferred embodiment, the initiating chloride donor includes aluminium chloride added to the mixture before heating it or to the salt melt, said aluminium chloride being added up to 20% by weight of the salt mixture, preferably 1-15% by weight, more preferably 5-10% by weight.
When using aluminium melt as the anode or part of the anode the steps dissolving and recovering by electrolysis are expedited simultaneously, preferably for at least 2 hours.
As the rare earth metal is deposited, additional REM containing resource can be stepwise or continuously added to the salt melt. The electrolysis and dissolving operation can for instance be performed for 2-8 hours; where after metals deposited at the cathode/s is collected, and the electrolysis can be restarted. To avoid interrupts of the electrolysis, another “clean” electrode can be submerged. Alternatively, the salt melt may have a plurality of electrodes which one after the other is activated as a cathode and while the former is deactivated. Thereby the metals can be selectively deposited at individual electrodes.
The voltage is suitably within the range of 2.5-5V, preferably 3-4 V. The rare earth metal may be co-deposited with aluminum or they may be selectively electrodeposited.
The residue after processing may contain Al2O3 and for instance other stable oxides such as SiO2, depending on the contents of the REM containing resource; in particular if the REM containing resource contains REM oxides Al2O3 may form when chlorinating the REM oxides. The residues may for instance be used for landfill, building construction or as a raw material for the refractory industry
Neodymium refining from neodymium magnet was performed in a salt bath containing LiCl, KCl and NaCl. Eutectic composition of the three salts was found from the ternary phase diagram and desired amounts of sodium chloride, lithium chloride and potassium chloride powders were mixed together carefully and the mixture was put in a dryer (T=110° C.) for 24 hours. The Neodymium magnet (Nd2Fe14B) was crushed and added together with aluminum chloride as fluxing agent to the mixture. The AlCl3/neodymium ratio was 2/1 and the AlCl3/salt ratio was 20 wt %. The whole mixture was weighted before each experiment. The masses of the each material are shown in the table 1.
The powders were poured in an alumina crucible and the crucible was put in the vertical furnace.
The time to reach the target temperature which was 850° C. was about 6 hours. Then the graphite electrodes were dipped into the salt bath and the electrolysis was started. The voltage was first set on 4 but due to the high current it was decreased to 3.2 in order to avoid constant current condition. The saturation current of the equipment which was used in this experiment was 5. By fixing the voltage on 4 the current increased to 4.99 (saturation current). Hence the voltage was decreased to 3.2 V. The electrolysis was done during 5 hours.
After the experiment, a thick deposited layer on cathode was observed. The deposited layer contained over 40% by weight of Nd and over 20% by weight of Al. The amount of Fe was below 5% by weight. It should be noted that the essentially all Fe remained in the salt melt although the theoretical decomposition voltage of FeCl3 is below 1 V. From the experiment it can be concluded that Nd can be recovered from the salt melt by electrolysis.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1250932-9 | Aug 2012 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2013/050970 | 8/14/2013 | WO | 00 |
