WO2014044527A1 - Method for obtaining at least one rare earth metal chloride and a rare earth metal - Google Patents

Description

description

Process for obtaining at least one rare earth metal chloride and a rare earth metal

The invention relates to processes for obtaining at least one rare earth metal chloride and for obtaining a rare earth metal from a base material containing at least one rare earth metal compound.

The basic material used here are ores or clay minerals which contain soluble and / or insoluble rare earth metal compounds, as well as other recyclable materials which contain rare earth metals, such as Nd-Fe-B magnets and the like. In particular, ionic adsorption stones are used as clay minerals.

In the processing or treatment of such base material usually large amounts of chemicals, especially in the form of acids and alkalis, are used. Since the processing or treatment of ores or clay minerals is often carried out directly at the site of occurrence, it is usually necessary to transport the chemicals by tanker over long distances and to remote areas. The high consumption of partly environmentally hazardous

Chemicals entail high costs and high environmental risks.

WO 2011/091231 A1 discloses a processing of ore minerals, wherein inter alia a transfer of rare earth elements into an aqueous solution is described.

Overall, the usual process steps in the extraction of rare earth metal compounds from a base material can be summarized as follows: In general, the base material is crushed and concentrated enriched with the rare earth metal phase. Rare earth elements usually do not occur singly in ores or clay minerals, but are found in association with a plurality of other rare earth elements which are to be found adjacent in the periodic table of the chemical elements. The concentrate is now chemically digested, with insoluble rare earth metal compounds, usually in the form of carbonates or phosphates, are converted into soluble rare earth metal compounds. For this purpose, concentrated acids or bases, such as sulfuric acid H ₂ S0 ₄ or sodium hydroxide NaOH, are used in a high-temperature process. This is followed by a transfer of the soluble rare earth metal compounds in an aqueous phase.

Also from crushed recycled material containing rare earth metals can be rare earth metal compounds chemically dissolve. In both cases, an aqueous base solution containing the dissolved rare earth metal compound (s) and, if appropriate, further soluble compounds, which may comprise unwanted heavy metals, for example, is formed. By changing the pH of the base solution, in particular by adding a base, the unwanted heavy metal compounds can largely be precipitated and separated.

The actual separation of the basic solution, in which the individual rare earth elements are selectively separated as precisely as possible, is usually carried out by means of a liquid-liquid extraction. By means of a suitable extractant, the rare earth metal ions dissolved in the aqueous base solution are converted into an electrically neutral species which accumulate in an organic phase. Depending on the extraction medium used, rare earth metal ions can be selectively enriched in the organic phase and separated off in succession. That's the way to go also chemically closely related rare earth elements separate from each other.

Typical cationic extractants used here are di-2-ethylhexyl phosphoric diesters (abbreviation: P204), or 2-ethylhexyl phosphonic acid (2-ethylhexyl) esters (abbreviated to P507). Due to its nonpolar properties, such an extractant is predominantly in the form of dimers in the organic phase. The extraction process is based on the fact that hydrogen atoms deprotonate the extractant, whereby the charge resulting from the cleavage of the protons is compensated by the formation of electrically neutral value metal complexes, in particular rare earth metal complexes. The rare earth metal complexes accumulate in the organic phase.

The extraction reaction is described below by way of example for a rare earth element, abbreviated to Ln:

Ln ³⁺ + 3 (HA) ₂ ~ LnA ₃ (HA) ₃ + 3H ⁺ The upper bar in the reaction equation means that the corresponding species is present in the organic phase. The ionic species are present in the aqueous phase of the base solution. The extraction equilibrium depends strongly on the adjusted pH of the base solution.

Although selective extraction of rare earth elements can be accomplished via the reaction equation, an extraction step is usually not sufficient to achieve sufficient separation of the elements. Therefore, it is customary to use a multistage extraction unit comprising one or more extraction columns or cascades of extraction stages, wherein typically a total of 100 to 500 extraction stages are used. The rare earth metal elements transferred and separated into the organic phase are then separated again from the organic phase by a so-called "stripping." When cationic extractants are used, acid is usually added thereto and the extractant is regenerated at the same time and may be reused There remains one or more aqueous extract solutions, each containing substantially a single rare earth metal element or a mixed concentrate containing a plurality of rare earth metal elements, particularly in the form of rare earth chloride.

From the respective extract solution, the contained rare earth metal element is precipitated in succession as sparingly soluble rare earth metal carbonate or oxalate, separated off, dried and converted at high temperatures into a rare earth metal oxide or calcined.

The rare earth metal oxide is now usually reduced in a complicated process, either by reduction with a less noble element or by fused-salt electrolysis. After a direct reduction of the rare earth oxides is difficult, they are usually first converted back into rare earth metal chlorides or fluorides, which are then reduced to the rare earth metals.

Usually, the separation of the rare earth metal elements from a ore or clay mineral and the subsequent reduction of the obtained rare earth metal compound to the rare earth metal at different locations and in different plants. Even though the formation of the oxide complicates the process chain, the easily transportable rare-earth metal oxide has become established at the interface between these plants.) Even when recycling materials containing rare earth metals, the pathway via the rare earth metal oxide is usually chosen due to the separation of the processing site and the reduction site , It is an object of the invention to provide an alternative process for obtaining at least one rare earth metal chloride from a base material containing at least one rare earth metal compound. It is a further object of the invention to provide an alternative method for obtaining a rare earth metal.

The object is achieved for the process for obtaining at least one rare earth metal chloride from a base material comprising at least one rare earth metal compound comprising the following steps:

a) transferring the at least one rare earth metal compound in solution to form an aqueous base solution containing at least one soluble rare earth metal compound and optionally other soluble compounds;

b) carrying out an extraction, wherein an aqueous

Extract solution is separated from the base solution comprising the at least one soluble rare earth metal compound in the form of at least one rare earth metal chloride; and

c) separating the extract solution into process water and dry rare earth metal chloride.

The object is achieved for the method for obtaining at least one rare earth metal from a base material containing at least one rare earth metal compound, comprising the following steps:

a) transferring the at least one rare earth metal compound in solution to form an aqueous base solution containing at least one soluble rare earth metal compound and optionally other soluble compounds;

b) carrying out an extraction, wherein an aqueous

Extract solution is separated from the base solution having the at least one soluble rare earth metal compound in the form of at least one rare earth metal chloride;

c) separating the extract solution into process water and dry rare earth metal chloride; and

d) reducing the dry rare earth metal chloride to the rare earth metal. The extraction can be carried out in both methods as a liquid-liquid extraction or by ion exchange as a liquid-solid extraction. The residual base solution remaining after the extraction has been carried out may contain further rare earth metal chloride, so that the base residual solution can be subjected independently to step c) or steps c) and d).

The processes have the advantage of being able to save considerable amounts of chemicals which are saved for the conventional formation of rare earth metal oxide, which is subsequently reduced to rare earth metal. The complexity of the processes is lower, allowing for a fast and efficient recovery of rare earth metal or rare earth metal chloride.

In step c) it is preferred to first form a wet rare earth metal chloride which is dried in a neutral or reducing atmosphere to form the dry rare earth metal chloride.

In order to accelerate the dehumidification of the moist rare earth metal chloride, it has been proven that the drying at low pressure, in particular at a pressure in the range of

20 to 80 kPa, is performed. A gas purging, in particular with an inert gas or a reducing gas, such as HCl gas, accelerates the dehumidification and counteracts an undesirable formation of oxychlorides. The extract solution is successively preferably subjected to predrying, distillative drying and filtration in step c) to form the wet rare earth metal chloride. This contributes to an optimization of the separation process in terms of time and costs.

The pre-drying of the extract solution to a pre-dried extract solution is carried out in particular with separation of a first part of the process water by means of electrodialysis and / or nanofiltration and / or reverse osmosis and / or evaporation due to heating.

The distillative drying of the predried extract solution originating from the predrying to a distillatively predried extract solution is carried out with separation of a second process water portion, wherein the temperature of the predried extract solution is increased to a boiling temperature of the predried extract solution. Typically, such a pre-dried extract solution boils under normal pressure at a temperature in the range of about 120 to 130 ° C. The energy required to heat the predried extract solution to boiling temperature is preferably provided by waste heat from other process steps or regenerative energy sources.

The distillative drying coming from the distillative pre-dried extract solution is preferably cooled with precipitation of the rare earth metal chloride to an extract suspension. In particular, the extract suspension is cooled to ambient temperature. Optionally, a heat exchanger device can be used in order to be able to continue to use the waste heat. Filtration, in particular, the cooled

 Extract suspension is filtered, carried out by means of a segregator unit, in particular in the form of a filter press or a centrifuge, wherein the moist rare earth metal chloride and a third process water part are formed. The third process water part contains usually still solved

Rare earth metal chloride and is preferably partially fed back into the process.

Preferably, the third process water part is partially recycled and mixed with further extract solution or alternatively with already predried extract solution. The formed mixture of third process water part and

Extract solution and / or pre-dried extract solution is in Follow in the process water and the wet rare earth metal chloride separately. However, the third process water part is not completely recycled to avoid contaminants in the third process water part

concentrate and affect the process.

The first process water part and / or the second process water part are used again elsewhere in the process, preferably for the formation of hydrochloric acid. The hydrochloric acid formed is used in particular in step a) for transferring the rare earth metal compound in solution and / or used in step b) in the extraction. In particular, the hydrochloric acid is formed from the purge gas for drying the humid rare earth metal chloride in the form of HCl gas and the first and / or second process water part. After this

Reaction is exothermic, the resulting heat energy is preferably dissipated via a further heat exchanger device and fed back elsewhere in the process. Figures 1 to 3 are intended to exemplify the methods of the invention for the recovery of rare earth and rare earth metal chloride. As shown: a process for the extraction of rare earth metal; a process for obtaining rare earth metal chloride; and

3 shows another method for obtaining rare earth metal chloride.

1 shows a method for obtaining at least one rare earth metal 150 from a base material 100 containing at least one rare earth metal compound. The base material 100 is usually crushed and in terms of

Value metal content of concentrated form, for example in the form of a pulp or as a heap, provided. In a dissolving reactor 20, with addition of dissolving chemicals, _n

Here, adding a concentrated acid such as hydrochloric acid or sulfuric acid 110, the rare earth metal compound converted into a soluble rare earth metal compound. As a rule, the pulp or the heap is heated at the same time. There is an aqueous base solution 130 containing the soluble rare earth metal compound and optionally further soluble

Compounds such as heavy metal compounds easily separable via a change in the pH of the base solution 130 are formed. The insoluble residue 120 of the base material 100, which is largely freed from rare earth elements, is discharged from the process.

The base solution 130 is collected in a collecting vessel 30, which may also be formed by a tube only, and fed into an extraction unit 40 comprising one or more extraction columns or cascades of extraction stages in which a liquid-liquid extraction takes place. The extraction unit 40 here comprises a plurality of extraction reactors 41, 42, wherein a cationic extraction agent 50 is added to the base solution 130 in a first extraction reactor 41 of the extraction unit 40. An aqueous extract solution 1 based on the soluble rare earth metal compound is separated from the base solution 130. The residual base solution 60 is transferred to a second extraction reactor 42 of the extraction unit 40 and another extractant 51 is added. A further aqueous extract solution 1 "based on a further soluble rare earth metal compound in the form of another rare earth metal chloride is separated off from the residual base solution 60. If appropriate, further soluble extractive metal compounds contained in the further residual base solution 61 are removed via further subsequent extraction reactors.

Often, groups of rare earth metal chlorides based on different rare earth metals are separated together, and only subsequently a largely pure sorting into the individual rare earth metal chlorides, if necessary, made. In the following, the further process will be described further only with reference to the extract solution 1, but in practice, of course, a similar treatment of further extract solutions 1 "or of the base residual solution also takes place.

The extract solution 1 is transferred to a separation unit 70, in which a separation of the extract solution 1 in process water 140 and dry rare earth metal chloride 15 takes place. Within the separation unit 70, preferably moist rare earth metal chloride 11 (cf. FIG. 2) is first formed, which is dried here as a purge gas 13 while supplying HCl gas. Moist purging gas 14 is removed from the separation unit 70. The dry rare earth metal chloride 15 is reduced to the rare earth metal 150 in a reduction unit 80.

FIG 2 shows a process for recovering rare earth metal chloride 15 to which a rare earth metal 150 recovery process of the present invention may also be based.

The same reference numerals as in FIG. 1 designate the same elements. Here, a possible detailed structure of the separation unit 70 is explained in more detail. Here, it comprises a predrying unit 2 for receiving the extract solution 1, which is designed, for example, as a nanofiltration system. In the predrying unit 2, a first process water part 3 is separated from the extract solution 1 and there remains a pre-dried extract solution 4, which is fed to a distillation unit 5 for distillative drying. By means of the distillation unit 5, the predried extract solution 4 is boiled and a second process water part 6

distilled off. The first process water part 3 and second process water part 6 can be reused as process water 140 elsewhere in the process. The distillatively predried extract solution 7 formed is cooled to ambient temperature, which takes place here in a heat exchanger unit 8. The recovered thermal energy 81 can be used elsewhere in the process. Upon cooling, the rare earth metal chloride precipitates out as a solid and an extract suspension 10 is formed which subsequently in a separation unit 17 into the moist rare earth metal chloride 11 and a third process water part 9 is separated. The third process water part 9 usually still contains dissolved rare earth metal chloride, so that this is preferably partially recycled and mixed with extract solution 1 and / or predried extract solution 4, the separation unit 70 passes through again.

The obtained moist rare earth metal chloride 11 is then dried in a drying unit 12 at a temperature in the range of 80 to 400 ° C with gas purging with HCl gas as the purge gas and a reduced pressure, in particular in the range of 20 to 80 kPa (absolute). Particularly advantageous in this case is a slow increase in the drying temperature over the drying time. In this case, preferably a higher pressure for the drying is selected at a low drying end temperature, and a lower pressure for the drying is selected at a high drying end temperature. During drying, residual moisture and water of crystallization are expelled. The resulting dry rare earth metal chloride 15 is packed airtight and can be reduced by means of a reduction unit 80 directly to rare earth metal 150 (see FIG. 1).

FIG. 3 shows another method for obtaining rare earth metal chloride 15, to which a rare earth metal 150 recovery method according to the invention can likewise build up. The same reference numerals as in FIG. 2 designate the same elements. The predrying unit 2 is formed here by a heated evaporation plant. Furthermore, here the first process water part 3 and the second process water part 6 are brought together with the moist purge gas 14 and from it hydrochloric acid 16 is formed. The resulting excess additional thermal energy 91 is dissipated via a further heat exchanger unit 90. The from the cooling of the

Extract suspension 10 in heat exchanger unit 8 recovered thermal energy 81 and the further thermal energy 91 are used here for heating the predrying unit 2 and / or the distillation unit 5.

The cooled hydrochloric acid 16 is - depending on the need for dissolving chemicals, in this case hydrochloric acid 110 - supplied to the dissolving reactor 20 and / or used for the extraction in the extraction unit 40.

The methods shown in the figures merely show examples of how rare earth metal chloride or rare earth metal can be formed. Thus, separation unit 70 may include other than the illustrated units to separate an extract solution into process water and dry rare earth metal chloride.

Claims

claims A process for recovering at least one rare earth metal chloride from a base material (100) comprising at least one rare earth metal compound comprising the steps of: a) transferring the at least one rare earth metal compound in solution, wherein an aqueous base solution (130) containing at least one soluble rare earth metal compound and optionally further soluble substance compounds are formed; b) carrying out an extraction, wherein an aqueous  Extract solution (1, 1 ") is separated from the base solution (130) having the at least one soluble rare earth metal compound in the form of at least one rare earth metal chloride; c) separating the extract solution (1, 1 ") in process water (3, 6, 9, 140) and dry rare earth metal chloride (15). 2. A process for recovering at least one rare earth element from a base material (100) comprising at least one rare earth metal compound, comprising the following steps: a) transferring the at least one rare earth metal compound in solution to form an aqueous base solution (130) containing at least one soluble rare earth metal compound and optionally further soluble compounds; b) carrying out an extraction, wherein an aqueous  Extract solution (1, 1 ") is separated from the base solution (130) having the at least one soluble rare earth metal compound in the form of at least one rare earth metal chloride; c) separating the extract solution (1, 1 ") in process water (3, 6, 9) and dry rare earth metal chloride (15); d) reducing the dry rare earth metal chloride (15) to the rare earth metal (150). 3. The method according to claim 1 or claim 2, wherein in step c) a wet rare earth metal chloride (11) is formed which is in neutral or reducing Atmosphere to the dry rare earth metal chloride (15) is dried. 4. The method according to claim 3, wherein the drying is carried out at reduced pressure, in particular at a pressure in the range of 20 to 80 kPa. 5. The method according to claim 3 or 4, during which a gas purging takes place during the drying. 6. The method according to claim 5, wherein the gas purging is carried out with a purge gas (13) in the form of HC1 gas. 7. The method according to any one of claims 3 to 6, wherein the extract solution (1, 1 ") in step c) is successively subjected to pre-drying, distillative drying, and filtration to produce the wet rare earth metal chloride (11). 8. The method according to claim 7, wherein the pre-drying of the extract solution (1, 1 ") to a pre-dried extract solution (4) with separation of a first process water part (3) by means of electrodialysis and / or nanofiltration and / or reverse osmosis and / or evaporation due to heating. 9. The method according to any one of claims 7 or 8, wherein the distillative drying of the predried Extract solution (4) to a pre-dried by distillation  Extract solution (7) with separation of a second process water part (6), wherein a temperature of the pre-dried extract solution (4) to a boiling temperature of the predried Extract solution (4) is increased. 10. The method according to any one of claims 8 or 9, wherein the first and / or second process water part (3, 6) is used to form hydrochloric acid (16) which is used in step a) for transferring the rare earth metal compound in solution and / or is used in the extraction in step b) ,  11. The method according to claim 9, wherein the extractively pre-dried extract solution (7) with precipitation of the rare earth metal chloride to a Extract extract (10) is cooled. 12. The method according to any one of claims 7 to 11, wherein the filtration takes place by means of a separator unit (17), in particular in the form of a filter press or a centrifuge, wherein the moist rare earth metal chloride (11) and a third process water part (9) are formed. 13. The method according to claim 12, wherein the third process water portion (9) is partially recycled and mixed with further extract solution (1) and / or pre-dried extract solution (4), wherein the formed  Mixture in step c) is separated into the process water and the rare earth metal chloride (15).