EP3781718A1

EP3781718A1 - Method for individual rare earth metals recycling from fluorescent powder e-wastes

Info

Publication number: EP3781718A1
Application number: EP19716844.6A
Authority: EP
Inventors: Ajay Bhagwan PATIL; Rudolf P. W. J. STRUIS; Albert Josef SCHULER; Christian Ludwig
Original assignee: Scherrer Paul Institut
Current assignee: Scherrer Paul Institut
Priority date: 2018-04-19
Filing date: 2019-04-02
Publication date: 2021-02-24
Also published as: WO2019201582A1; EP3556873A1

Abstract

A robust and economically viable process technology is developed for the recycling of critical rare earth elements (REEs) from end of life lamp fluorescent powder (FP) e-waste. This is one of the first efforts to recycle individual pure REEs from municipale-waste components to arrive at commercially promising individual REEs purity, which are knowingly difficult to separate from wastes. The process technology addresses the management of strategically important REEs resources relevant for green energy and smart/hybrid technology. The methodology involves cheap mineral acid for near quantitative REE metal's sequential digestion and extractive (liquid-liquid) separation protocols using the selective extractant ligand molecules and carefully designed hydrometallurgical process conditions to separate Y, Eu, and Tb, to more than 99% purity and Gd, La and Ce to elevated purities each from the metal digested FP waste fractions. The developed technology has potential for scale up on industrial scale, re-use of extractant and organic phase, as well as, extended use for recovering RE metals from other types of e- waste after optimizations. The process can be employed to REE mixtures from e-waste as well as mining tailings origin. The process has the advantage over earlier methods involving inseparably combined digested phosphor fractions as well as over inefficient leaching of Tb from LAP phosphor. It uses less complex organic extractants and lesser stages for the separation of the individually targeted REEs, such as onlyone extraction stage to achieve >99% pure Y from the digested YOX phosphor. It is also one of the first attempts to achieve individual high purity of rare earths raw materials from such a complex waste stream. The novel approach proposed herein with judicial choices of extractants and inventive steps of process hydrometallurgy will help to tap potential in e-waste secondary resources. The environmental benefit is important and possible due to the fact that the organic and acidic feeds are optimized throughout the process and could be re-used within the process.

Description

Method for individual rare earth metals recycling from fluorescent powder e-wastes

The present invention relates to a method for recovering individual rare earth metal content in electronic waste by using a carefully designed digestion and hydrometallurgical process .

Rare earth elements (REEs: 17 elements Y, Sc, La-Lu) have special optical, magnetic and physical properties. They have extended the technological limits of the conventional

electronics. This resulted in the advent of smart technology in the energy, transportation, medicine and diagnostics, advanced defense and space applications. Due to such strategic and advanced uses of the REEs, the European Union and the USA department of defense declared them as critical raw materials with potential supply risk.

Ever increasing use of such raw materials is resulting in stockpile of valuables with the e-waste as a major resource management concern. Due to lack of reliable and economically feasible processing technology, the recovery of such

individual raw materials is neither commercially undertaken in Europe nor in other developed countries. In primary mining production also the majority of EU and USA based companies are outcompeted. The major process difficulties in the primary mining production or the recycling of secondary raw materials are due to difficult separations of the REEs, their dilute content in waste streams, and balance problem (stockpiling of unwanted metals during the mining of the desired ones) that are not addressed by conventional hydrometallurgical processes in state of the art. Recently some emerging techniques

involving ionic liquids or metal organic frameworks have been reported. However, they involve scale up or operational difficulty due to hydrodynamic parameters or due to the costs involved. For e-waste targets, most research groups focus their research on material flows and technical investigations for the mining of REEs or just on the separating phosphors as a composite mixture of rare earths. The diversity and inhomogeneity of e-waste make REE recovery very challenging and general or obvious approaches do not help to resolve the challenging rare earths in the form which can be handed over to the front end manufacturing sector.

In the case of lamp phosphor e-waste, it usually comprises a combination of different fractions, such as phosphors like HALO (White) (Sr, Ca) _i0 (P0₄) e (Cl, F) ₂ : Sb³⁺, Mn²⁺, YOX (Red)

(Y₂0₃ :EU³⁺), LAP (Green) (LaP0₄ : Tb, Ce) and BAM (Blue)

(BaMgAlioOi7 : Eu²⁺) ; together with some fine glass powder,

Mercury (Hg) traces and several non-RE metals coming from the shredding of the end of life lamps. In earlier attempts for the technology development of the individual rare earth

separation from phosphor waste, the following problems

occurred and they have to be solved to make the rare earth metals recycling realistic and economically feasible:

1. The glass content in such e-waste has not been given appropriate consideration, because heating of such glass content above T=500°C for the removal of Hg results in melting of glass and forms a vitrified form of the waste that makes the further digestion or leaching difficult.

2. Appropriate attention is not given to non-rare earth impurities (e.g. Ca, Ba, and Sr) arriving from HALO phosphor which comprises the nearly 40-50 weight % of the phosphor waste and their combined digestion with the YOX, i.e. the Y and Eu containing phosphor fraction, makes the separation process steps larger and thus expensive.

3. The use of sulphuric acid (H₂SO₄) under higher temperature and oxidative conditions, such as in presence of H2O2 and prolonged digestion times, makes the process tedious for the larger scale operation. 4. Such methods also involve use of multiple extractants or lexiviants or ligand or liquid ion exchangers with more (10- 20) extraction stages, hence, also rendering the Y separation an expensive method.

5. In such extraction stages (or mixer settler batteries used) , the use of kerosene as main diluent can result in the problem of third phase (or gel) formation leading to overall process chemical engineering failures. Therefore, in earlier reports, the use of additional chemical substances named phase modifiers, such as isodecanol along with main diluent kerosene, was proposed.

6. Such processes have not proposed the rational approach to separate Gadolinium (Gd) , which is the rare earth component having good commercial value and present in substantial amounts in phosphor wastes.

7. Purity established in earlier inventions is based on the % composition compared with the non-rare earth impurities chosen for detection. However, the commercial convention considers the % rare earth content in composition compared with the other detected rare earth impurities and the overall non-rare earth matrix is limited to less than one overall mass percent.

Therefore, it is the objective of the present invention to provide a robust separation technology solution that allows reaching high grade individual REE materials from e-waste in an easier and commercially feasible method overcoming the above mentioned problems in this field. This robust separation technology may also be applicable to REE mixtures of different origin including mining tailings after optimizations. Our novel approach of sequential leaching to avoid retrieving a solution mixture of HALO and YOX phosphors by carefully

optimized steps and impurity specific targeting of the complex e-waste feeds by extractive means was found very successful. The inventive contribution focused for the first time on the individual separation of rare earths up to commercially

acceptable purities with judicious and not obvious process parameters and set up.

This objective is achieved according to the present invention by a method for recovering individual rare earth metal content in electronic waste with top down approach from waste to value, comprising the steps of: a) Mechanical shredding or segregation of the electronic

waste in order to arrive at a separated fluorescent powder ; b) Thermal Hg removal by capturing into carbon filter under inert conditions and maintaining the temperatures less than 500°C to avoid the glass dissolution and vitrification to avoid problems in the further digestion of metals; c) Sequentially digesting the separated fluorescent powder at different mineral acid conditions in order to separate different phosphors, preferably HALO

(Sr, Ca) io (P0₄) ₆ (Cl, F) ₂ : Sb³⁺, Mn²⁺, YOX (Y₂0₃ :Eu³⁺), LAP

(LaP0₄ : Tb, Ce) and BAM (BaMgAlioOn : Eu²⁺) and glass powder with increasing concentration of the acid to get the advantages of the minimum acid requirements and decreasing the mass flux of waste in subsequent process steps to reduce the process costs; d) Treating the different phosphors according to one or more of the following steps: dl) Hydroxide washing and nitrate conversion of the separated phosphors of interest (YOX, LAP and BAM) to avoid additional process stages such as oxalate precipitation and cost

intensive calcination at very high temperatures, preferably in the range of 1000°C, in between processing stages.; d2) Controlled dissolution at different HC1 mineral acid solution conditions, preferably 0.5M to 1M HC1 conditions, to remove heavier lanthanides or rare earths including Y, from the Y, Gd and Eu containing YOX fraction; d3) Controlled dissolution at different nitrate solution, such as 1M HNO₃, to remove excess middle lanthanide or rare earths including Ce from the La, Ce, and Tb containing LAP fraction; d4) Application of a plurality of tetra-alkyl ammonium ionic extractants to remove lighter lanthanides, such as La and Ce; d5) Application of a plurality of alkyl phosphate to remove Y or Eu from the YOX phosphor; d6) Reduction of Eu in alkyl acid in order to separate Gd.

These method steps provide a recovery of the REE content in e- waste at a commercially acceptable high level of purity and a comprehensive solution to the earlier mentioned problems faced by the rare earth recycling field.

With this process, the Y separation from the YOX fraction has been achieved in a single extraction stage up to 99% purity and compares favorably well compared to the requirement of 10- 20 stages in earlier inventions. Further, the application of transition metal reduction using Zn is a well-established method, but applied in our process for the first time to the Eu and Gd enriched solution emerging from the fluorescent powder e-waste. It is noteworthy that Eu and Gd are immediate neighboring elements in the lanthanide series and they are hence very difficult to separate from each other.

The major advantage of the step of a controlled dissolution of the YOX phosphor at different HC1 mineral acid solution

conditions, preferably in the range from 0.5 to 1 M HC1, being executed to remove heavier lanthanides or rare earths including Y consists in the meaning of this step as a preconcentration step in the processing of the YOX phosphor independently .

The controlled dissolution of the LAP phosphor containing fraction at different nitrate solution (0.5 to 1M HNCg) has the advantage that middle lanthanide or rare earths including Ce can be removed. This step also works as a preconcentration step, thus avoiding redox chemistry, oxalate precipitation and calcination .

The step of the application of a plurality of tetra-alkyl ammonium ionic extractants including A1336 can be executed to remove lighter lanthanides by liquid-liquid extraction. This step also provides a faster decontamination advantage of La and Ce without oxidation chemistry requirement.

Further, the step of the application of a plurality of alkyl phosphate, such as HDEHP in toluene, can be executed to remove Y or Eu from YOX phosphor by liquid-liquid extraction. This step has the advantage of a single stage Y purification and thus enriching the Eu concentrations.

Furthermore, a reduction of Eu in alkyl acid, such as acetic acid, can be executed in order to separate a Gd content and achieve the pure Eu and Gd. Thus, this goal can be achieved in one / single reduction stage without the need of sophisticated apparatus and a plurality of re-precipitations steps.

Preferred embodiments of the present invention are described hereinafter in more detail with reference to the attached drawing which depicts in:

Figure 1 schematically a sequential digestions scheme for the

FP e-waste to process the targeted pure REE containing phosphor products and their clear separation from HALO; Figure 2 schematically the REE recycling process for fluorescent powder e-wastes;

Figure 3 a graph on the optimized Eu enrichment by excess Y removal as function of extraction stages;

Figure 4 a chart on the Eu enrichment by La, Ce, Tb and

residual Y removal as function of extraction stages;

Figure 5 a chart on the REE concentrations with the Tb

purification process as function of extraction stages ;

Figure 6 a chart on the Eu content (% on REE basis only) under different extraction/process conditions; and

Figure 7 a chart on the Tb content (% on REE basis only) under different extraction/process conditions.

According to the present invention to accomplish the

hydrometallurgical operations on the e-waste streams it is first necessary to do the mechanical shredding or segregation in order to arrive at a separated fluorescent powder. The separated fluorescent powder is digested at different mineral acid conditions to find the best suitable sequential leaching conditions. The processes has been optimized for achieving the best possible leaching efficiency for different phosphors and/or for individual rare earth elements (see Figure 1, Table 1) . The separation of HALO and YOX could be achieved at ambient or room temperatures and in less processing time under the conditions described by the present invention. In the state of the art reports, the combined or total leaching makes the rare earth mixture too complex to resolve it in an

economical way due to the huge non rare earth impurities content. Also, in literature the problem of leaching of Tb from the LAP phosphor is reported.. The present process step can successfully overcome an Tb dissolution issue by using the present process conditions and slightly higher temperatures such as 60°C. This also allows a clear separation of the remaining fine glass fraction in a purity grade suitable for the cement or glass industry. The present digestion efficiency is based on the comparison with the experimental content analysis of rigorously digested fluorescent powder using a high pressure, high temperature microwave furnace.

Table 1 : Leaching efficiency of different REEs from the developed sequential digestion process as calculated from ICP- OES data

A preferred digestion process comprises the following steps: Initially, Hg removal is carried out by heat treatment at 400°C, as shown in Figure 2, to avoid the melting of glass and further inaccessibility of REEs due to vitrification. The digestion is performed to achieve distinct separation of different phosphors HALO, YOX, LAP and glass powder with optimized, unique sequential approach. To achieve the

effective leaching of LAP, HC1 is used for digestion with sequentially increasing concentration, preferably from 0.1 M to 10 M HC1, at room temperature and, finally, at an elevated temperature of 60°C, preferably for about one hour. These conditions are much milder when compared with earlier state of the art inventions (T=150°C for 4-6 hours) . In this carefully designed and optimized process, Tb was near quantitatively leached for the first time in the literature. One highlight of the process is the cost effective method to leach and purify the Tb metal, which is one of the most expensive rare earth elements. The cost effectiveness given by recycling (re-use) of the organic fluids and principally also the extractants used in the liquid -liquid extraction steps are further advantages. Moreover, also the digestion acid can be re-used several times with the sequential step within the pH-strength step it came from. The efficiency and cost

effectiveness of the present process was improved further by pre-washing the fluorescent powder prior to the digestion steps with water to remove soluble components and dirt, as well facilitating wetting effect, hereby lowering our demand of acid even more.

The literature methods for digestion of fluorescent powder are based on the use of other acids, such as HNCg or H₂SO₄, but not on sequential use of HC1 at increasing strength levels.

Moreover, state of the art processes require prolonged heating in oxidative conditions, hence, producing more corrosiveness. With H₂SO₄, it may also be accompanied by sulphate

precipitations. The higher corrosiveness not only increases the requirement for a special set up (special glassware, tubing, etc.), but also implies higher costs. However, the present process can operate even with plastic containers for separation of HALO and YOX fractions and HC1 is a cheaper option than HNO₃ or H₂SO₄.

At present, the three different extraction procedures were developed at the Paul Scherrer Institute, Villigen,

Switzerland, for purifying Y, Tb, and Eu, respectively. Gd was achieved in already 97% purity as a by-product with the Eu separation procedure and La and Ce of about 60 and 80%, respectively, as by-products with the Tb purification steps. The recycled products (Y, Eu, Tb, Gd, La, and Ce) had been achieved successfully along with promising process economics.

The process according to the example comprises the following steps depicted in Figure 2 : 1. Removal of the still remaining traces of non-RE impurities (Ca, Na, K, Mg, Ba, B and Mg) by washing out YOX solid

fraction with dilute HC1 medium. This also offers the

additional benefit of Y enrichment by 1.5 times than compared with the digested YOX that has been achieved in sequential digestion process.

2. Selective Y separation from Eu and Gd in pre-enriched YOX fraction using 0.5M Alkyl Phosphates, e.g. Bis-2-Ethylhexyl- hydrogen Phosphate (HDEHP) in toluene (Extracting organic phase) at 0.5M HC1 (loading) aqueous phase with 50gm/L YOXC1 loading (Y and Eu containing fraction arriving from sequential digestion process) . Use of single diluent medium and half amount of extractant is the key advantage of this process, whereas state of the art methods necessitate additional modifier chemicals to avoid gel or third phase formation. They also need much more liquid-liquid separation sequence steps of 10-20 stages. However, in our process, >99% pure Y was

achieved in a single stage in the strip solution (washing aqueous phase) of 2M HC1 and without any need of a phase modifier. Moreover, the acid used here is similar to the one used in the present digestion procedure.

3. Removal of excess Y to enrich Eu and Gd using the above mentioned system with several repeated extraction stages performed with the YOX chloride concentrate as aqueous feed solution. This has the advantage of using the same chloride matrix and avoids additional neutralization and oxalate precipitations in earlier methods mentioned in literature to change the medium.

4. This task was performed on the Y-enriched YOX fraction arriving from step 3. Removal of excess La and Ce impurity from enriched YOX nitrate using a nitrate derivative of Tetra- alkyl ammonium ionic extractant, e.g. Methyltrioctyl ammonium chloride (A1336) . A1336 was dissolved in 70:30

Toluene : Kerosene .

Again, the enriched YOX nitrate was dissolved in HNCg 50gm/L and extracted using A1336 in controlled and H⁺ competing conditions. This helped faster removal of La and Ce in several repeated stages. Strip solution used was 0.001M HNCg . Such rapid decontamination of La and Ce made it possible to obtain Tb in desired purity as clear advantage over state of the art methods. The precipitation methods generally used in the literature to remove Ce are not sufficient enough to achieve >99% purity of Tb from complex e-waste solutions. Also, the advantage is that the process does not need the use of

ammonium nitrate or change of phase to sulphate medium. The present faster decontamination approach and removal of La and Ce (lighter REEs) was important to get the targeted higher purity .

5. Thereafter, this enriched YOX fraction still contains remaining Tb impurity. To remove this, YOX was converted from nitrate to sulphate again via hydroxide. It was dissolved in a 1.5M H₂SO₄ solution (loading aqueous phase) with 50gm/L concentration. Extracting organic phase used here was 1M Alkyl phosphate e.g. HDEHP in toluene and strip solution was 2.5M H₂SO₄. This helped the removal of still remaining Tb and Y in several repeated stages to arrive at a 60:40 Eu : Gd (molar) composition similar to mining compositions. This was

inseparable using extractive methods. It is noteworthy that earlier inventions have not focused on the Gd separation, although it is present in FP waste in substantial amounts (close to 3%) and it has good commercial value.

6. This inseparable Eu and Gd mixture was subjected to

optimized and unique reduction conditions in Alkyl Acid referring to acetic or other analogs of acetic acid medium at dilute acid pH conditions. The Eu/Gd mixture was dissolved in alkyl acid, e.g., acetic acid solution and was purged with 4% Hydrogen in Argon. The reduction was carried out using Zn metal powder. The reduced Eu was precipitated using 1M H₂SO₄ and was washed with 0.001M H₂SO₄ three times to remove adsorbed Gd impurity. This resulted in 99% Eu and 97% Gd purity in respective precipitate and supernatant fractions (see Table 2) in single reduction cycle. The conventional Eu reduction method in Zn chloride medium was not found suitable. The Zn reduction method applied here is well established in the literature, however, its application to such difficult REE mixture of Eu and Gd arriving from e-waste is being proposed and applied successfully for the first time here. As the Eu and Gd are immediate neighbors in lanthanide series of the periodic table, their separation is very difficult. This method has an advantage that, with fine Zn powder, the higher surface area gives efficient reduction reaction and it doesn't need sophisticated equipment to process. The acetic acid used here is being employed for the first time to recover pure rare earths from FP e-waste as a cheaper option, whereas the use of HC1 showed very poor results and likely needed multiple reduction and precipitation cycles. Therefore, the alternative and suitable method applicable in e-waste containing complex solutions has been established with our process. .

7. LAP fraction of green phosphor was processed independently for the recovery of La, Ce and Tb rare earth metals. The LAP in chloride emanating from acid digestion was converted to nitrate (via hydroxide) . This avoids the use of oxalate precipitation and cost intensive calcination (at T=1000°C) used in earlier reports. This solution feedstock was taken to extraction cycles with Tetra-alkyl ammonium ionic extractant, e.g., A1336, in 70:30 Toluene : Kerosene volume mixture as extractant organic solution. This method is cheaper and efficient, because the use of additional phase modifier is avoided. The feed with Tb containing LAP fraction was

maintained at nitrate conditions to selectively remove lighter lanthanides or rare earths e.g. La and Ce .

8. Most of the lighter lanthanides, e.g. La and Ce, were removed from this pre-concentrated LAP phosphor fraction within several hydrometallurgical extraction stages (with stripping using 0.001M HNCg) . The La and Ce purity achieved during the process was 79 and 59%, respectively.

9. The subsequently further concentrated Y impurity was removed using 1M alkyl phosphate extractant, e.g., HDEHP in Toluene as extractant organic solution with 1.5M HSO solution (initial metal loading aqueous phase) with 50 gm/L

concentration. The strip solution was 2.5M H₂SO₄. After several stages, the extraction gave 99% pure Tb as a product. The use of the same organic extractants and acidities is the key feature of this invention and this facilitates the recycling of used acids and organic fraction within the process, keeping the cost down for highly conservative field of waste

recycling .

Highly pure Tb in >99% purity is achieved in 15-18 stages. Tb has higher commercial value and its digestion and separation is very difficult. It is noteworthy that, in the literature,

Tb purification needs rigorous precipitation and ion exchange methods. The early sorting of different fractions of phosphors by our sequential digestion method allows to enrich the Tb containing LAP fraction and the latter fraction needs less decontamination steps with respect to the lighter lanthanides, such as La and Ce . Both benefits make our invented process very efficient.

Table 2 : Eu purity confirmation using ICP-MS

Table 3: Optimization of LAP phosphor (calculated from ICP-OES data)

Table 4 : LAP fraction composition after digestion with

Chloride mineral acid and analyzed with ICP-OES (BDL = below detection limits)

The present invention therefore discloses totally innovative and an exclusive approach to extract pure Y, Eu, Tb, Gd, La, and Ce fractions using an efficient and optimized

hydrometallurgical process with fluorescent powder from shredded electronic (lamp) waste. The approach also claims the environment friendly and safe treatment of the toxic Hg content in this waste. The cost effective recycling process for Y, Tb and Eu rare earths with commercial acceptable purities has been developed with a minimum of chemical operations. The fluorescent powder waste has been successfully exploited as the potentials secondary resource. The process takes care of the waste and resource management of the major segment of municipal e-waste stream. The test was performed on fluorescent powder waste from lamp recycling. However, also other (e-waste resides can be processed with this methodology to obtain pure rare earths fractions after certain

optimizations to recover pure REE metal fractions.

Claims

Patent Claim

1. A method for recovering individual rare earth metal content in electronic waste, comprising the steps including but not limited to mechanical shredding, mercury removal, sequential acid digestion, liquid-liquid extraction and with wet

chemistry mentioned here in, comprising the steps of:

a) mechanical shredding or segregating of the electronic waste in order to arrive at a separated fluorescent powder;

b) thermal removal of Hg at temperatures below glass melting and and capturing evolved Hg using carbon filters under inert conditions ;

c) digesting the separated fluorescent powder at different mineral acid conditions using HC1 acid in order to separate different phosphors, preferably HALO, YOX, at room temperature and LAP, BAM and glass powder at temperatures above room temperatures in a plurality steps thereby choosing the mineral acid condition stepwise in order to avoid a combined digestion of different phosphors, such as HALO and YOX;

d) treating the different phosphors according to one or more hydrometallurgical steps independently for the individually targeted rare earth enrichment, such as hydroxide washing and nitrate conversion of phosphors (YOX, LAP and BAM) thereby avoiding additional oxalate precipitations and calcination steps .

2. The method according to claim 1, wherein a controlled dissolution of the YOX phosphor at different HC1 mineral acid solution conditions, preferably in the range from 0.5 to 1 M HC1, is executed to remove heavier lanthanides or rare earths including Y as a preconcentration step in the processing of the YOX phosphor independently.

3. The method according to claim 1 or 2, wherein a controlled dissolution of the LAP phosphor containing fraction at

different nitrate solution (1M HNO₃₎ is executed to remove excess middle lanthanide or rare earths including Ce as a preconcentration step, thus avoiding redox chemistry, oxalate precipitation and calcination.

4. The method according to any of the preceding claims, wherein an application of a plurality of tetra-alkyl ammonium ionic extractants including A1336 is executed to remove lighter lanthanides by liquid-liquid extraction giving faster decontamination advantage of La and Ce without oxidation chemistry requirement.

5. The method according to any of the preceding claims, wherein an application of a plurality of alkyl phosphate, such as HDEHP in toluene, is executed to remove Y or Eu from YOX phosphor by liquid-liquid extraction having the advantage of single stage Y purification and thus enriching the Eu

concentrations .

6. The method according to any of the preceding claims, wherein a reduction of Eu in alkyl acid, such as acetic acid, is executed in order to separate Gd content and achieve the pure Eu and Gd in one / single reduction stage without the need of sophisticated apparatus and number of re

precipitations .