EP4669781A1 - METHOD FOR RECOVERING TANTALUM AND DERIVATIVES THEREOF - Google Patents

METHOD FOR RECOVERING TANTALUM AND DERIVATIVES THEREOF

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Publication number
EP4669781A1
EP4669781A1 EP24711626.2A EP24711626A EP4669781A1 EP 4669781 A1 EP4669781 A1 EP 4669781A1 EP 24711626 A EP24711626 A EP 24711626A EP 4669781 A1 EP4669781 A1 EP 4669781A1
Authority
EP
European Patent Office
Prior art keywords
tantalum
ranging
treatment
grinding
fraction
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP24711626.2A
Other languages
German (de)
French (fr)
Inventor
Matteo GIARDINO
Camila MORI DE OLIVEIRA
Davide Luca Janner
Paola MARINI
Marco ACTIS GRANDE
Rossana BELLOPEDE
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Politecnico di Torino
Original Assignee
Politecnico di Torino
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Politecnico di Torino filed Critical Politecnico di Torino
Publication of EP4669781A1 publication Critical patent/EP4669781A1/en
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/005—Separation by a physical processing technique only, e.g. by mechanical breaking
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B11/00—Obtaining noble metals
    • C22B11/04—Obtaining noble metals by wet processes
    • C22B11/042—Recovery of noble metals from waste materials
    • C22B11/046—Recovery of noble metals from waste materials from manufactured products, e.g. from printed circuit boards, from photographic films, paper or baths
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
    • C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
    • C22B3/08—Sulfuric acid, other sulfurated acids or salts thereof
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
    • C22B3/16—Extraction of metal compounds from ores or concentrates by wet processes by leaching in organic solutions
    • C22B3/1608—Leaching with acyclic or carbocyclic agents
    • C22B3/1616—Leaching with acyclic or carbocyclic agents of a single type
    • C22B3/165—Leaching with acyclic or carbocyclic agents of a single type with organic acids
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/22—Treatment or purification of solutions, e.g. obtained by leaching by physical processes, e.g. by filtration, by magnetic means, or by thermal decomposition
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/44—Treatment or purification of solutions, e.g. obtained by leaching by chemical processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B34/00—Obtaining refractory metals
    • C22B34/20—Obtaining niobium, tantalum or vanadium
    • C22B34/24—Obtaining niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B47/00—Obtaining manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/006—Wet processes
    • C22B7/007—Wet processes by acid leaching
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the present invention relates to a cheap, sustainable process for recovering tantalum and derivatives thereof from waste or spent electronic components.
  • Tantalum is a metal considered to be a “critical raw material”, because it is mainly mined in countries with unstable geopolitical situations, such as Nigeria, the Congo and Brazil.
  • Tantalum is widely used in specific capacitors, namely electrolytic capacitors, wherein the tantalum acts as an anode, covered with a layer of oxide that acts as a dielectric, surrounded by a conductive cathode.
  • tantalum enables the production of a very thin dielectric layer. This means a greater capacity value per volume, and consequently a reduction in the size of the final capacitor with no loss of capacity. Tantalum capacitors are also preferable to other types due to their greater stability and longer working life.
  • Tantalum capacitors are also widely used in the corresponding surface-mount formats because they are much cheaper than the equivalent aluminium electrolytic capacitors and can better withstand the soldering process.
  • tantalum capacitors generates a significant amount of waste materials and non-conforming parts, and a recovery and recycling strategy is definitely necessary, to provide an economic return and reduce their environmental impact.
  • tantalum recovery processes use heat treatments that are expensive in terms of both energy and cost, such as pyrolysis, roasting treatments to achieve oxidation, and more generally, heat treatments at temperatures which may exceed 450°C, sometimes reaching alkaline calcination temperatures equal to or greater than 700°C, for long periods, which may even exceed 24 h.
  • the known approaches focus on dissolving tantalum rather than eliminating other elements (such as, for example, metal oxides or pure metals of the other components of the electronic device) for the purpose of tantalum recovery.
  • the present invention solves the problems of the known methods and meets the above- mentioned criteria of cheapness and low environmental impact due to a sequence of grinding, sieving, magnetic and electrostatic separation steps, associated with chemical treatments of the separated conductive material under mild conditions.
  • “Pyrolysis step” means a step wherein the polymer (electrical insulator) is degraded to carbon (electrical conductor). Said step, if present, can also worsen the yield of the electrostatic separation step.
  • a method for recovering tantalum from waste materials containing spent or recovered tantalum capacitors which comprises:
  • the invention relates to a method for recovering tantalum from waste materials containing spent or recovered tantalum capacitors, comprising: a) grinding said waste materials containing tantalum; b) sieving the waste material with a sieve ranging from 0.05 mm to 0.2 mm; c) magnetic separation of the oversize fraction obtained from step b), thus obtaining a magnetic fraction and a non-magnetic fraction; d) grinding the non-magnetic fraction obtained from step c), and further sieving with a sieve ranging from 0.18 mm to 0.45 mm; e) electrostatic separation of the undersize fraction obtained from the further sieving of step d), and of the undersize fraction obtained from the sieving of step b), thus obtaining an electrically conductive fraction and a non-electrically conductive fraction; f) treating the electrically conductive fraction obtained in step e), containing Ta/Ta2Os, MnCh and Ag, with L-ascorbic acid in an acid environment to remove manganese dioxide
  • a further aspect of the present invention is a concentrated solid residue consisting of tantalum metal and optionally tantalum pentoxide Ta2Os obtainable by the process described above.
  • the invention also relates to the use of said concentrated solid residue consisting of tantalum metal and optionally tantalum pentoxide (Ta2Os), having a concentration obtainable by the process described above, in electronic and/or biomedical field, preferably for applications selected from manufacture of electrolytic capacitors, heat exchangers, multidielectric optical filters, anti -reflective coatings, biomedical applications such as suture threads, bone plates and screws, more preferably for electrolytic capacitors.
  • Ta2Os tantalum pentoxide
  • Figure 1 shows the process chart according to the invention, as used in Example 1.
  • Figure 2 shows the SEMZEDX (Scanning Electron Microscopy / Energy Dispersive Spectroscopy) analysis of the product obtained according to Example 1.
  • Figure 3 shows the XRD (X-Ray Diffraction) analysis of the product obtained according to Example 1. Detailed description of the invention
  • the proposed process is significantly cheaper and more advantageous in terms of energy because it does not use any high-temperature steps (e.g. in high-temperature ovens), vacuum treatments or treatments in particular atmospheres.
  • the proposed process enables Cu and Fe/Ni electrodes to be separated and recovered with no need for aggressive chemical treatments.
  • the proposed process also offers the further advantage of producing low-hazard waste which is easily disposable at low cost.
  • the first grinding step preferably comprises cryo-milling of waste material containing tantalum.
  • the cryo-milling is conducted at a temperature ranging from -200°C to -40°C, more preferably at a temperature of -196°C.
  • cryo-milling is performed by immersing the tantalum-containing material in liquid nitrogen (N2) or another cryogenic fluid at temperatures below -40°C, for a time ranging from 5 to 30 minutes, more preferably for a time of 15 minutes, to embrittle the more ductile materials and facilitate their grinding so as to obtain a better degree of separation.
  • N2 liquid nitrogen
  • the tantalum-containing material preferably has a particle size ranging from 0.05 mm to 2 mm, preferably from 0.1 mm to 1 mm.
  • Cryo-milling has the effect of making the more ductile components of the tantalum- containing material more fragile, so as to obtain a particle size preferably in the range described above, thereby increasing the separation efficiency, and consequently the tantalum recovery.
  • cryo-milling can be conveniently performed in various types of mill, such as a ball mill.
  • the process according to the invention comprises multiple grinding and sieving steps.
  • Step b) of first sieving of the ground material obtained from step a), is advantageously performed with a sieve having holes of a diameter ranging from 0.05 mm to 0.3 mm, preferably from 0.1 mm to 0.2 mm, and more preferably being 0.18 mm.
  • Said step can be followed by a second grinding step at a temperature ranging from 15 to 40°C, and by a second sieving as described above.
  • the magnetic separation (step c) is conducted on the ground, sieved material retained by the sieve (oversize), preferably using neodymium magnets, CoAlNi alloy magnets or electromagnetic separators to remove the Fe/Ni alloy ferromagnetic terminals efficiently.
  • step c) is followed by a step d) of third grinding and sieving with a sieve having holes of a diameter ranging from 0.18 mm to 0.450 mm, preferably from 0.320 to 0.400 mm, and more preferably being 0.350 mm, wherein the material having a diameter smaller than the diameter of the holes (undersize) is sent to the next step e) of electrostatic separation, while the material having a diameter larger than the diameter of the holes, mainly containing copper (Cu) electrodes, is separated.
  • step d) of third grinding and sieving with a sieve having holes of a diameter ranging from 0.18 mm to 0.450 mm, preferably from 0.320 to 0.400 mm, and more preferably being 0.350 mm wherein the material having a diameter smaller than the diameter of the holes (undersize) is sent to the next step e) of electrostatic separation, while the material having a diameter larger than the diameter of the holes, mainly containing copper (Cu) electrodes, is separated.
  • Cu copper
  • Step d) of grinding of the non-magnetic fraction which is performed after magnetic separation c) and before sieving, increases the degree of release of the various constituents after removal of the (ductile) ferromagnetic material, thus increasing the efficacy of grinding.
  • the process according to the invention therefore enables the material of the copper (Cu) electrodes to be removed by sieving alone, with no need for them to be dissolved by acid attack, thus reducing the use of aggressive chemical agents.
  • Said sieving step with a sieve having holes of a diameter larger than the hole diameter of the sieve used in the previous sieving, enables the copper electrodes to be removed without eliminating the tantalum anodes, which are thus sent, with the rest of the undersize material from sieving step b), for electrostatic separation in step e).
  • Step e) of electrostatic separation a well-known physical separation technique used to separate particles on the basis of their different electrical conductivities, is performed in an electrostatic separator.
  • the material is processed at least twice, preferably twice, in said electrostatic separator, and two fractions are identified and separated.
  • a first conductive fraction for example having electrical resistivity ranging from 1 10" 9 Qm to 1 • 10' 5 Qm measured by impedance spectroscopy, namely the fraction containing Ta, also contains an amount of MnCh (originating from the electrolyte of the tantalum capacitors) and Ag and is therefore sent to the next step of the process according to the invention.
  • the first conductive fraction undergoes a tantalum concentration step by selective elimination of manganese dioxide and silver.
  • manganese dioxide is eliminated in step f) by treatment with L-ascorbic acid (CeH ⁇ Oe) in the presence of acids such as sulphuric acid (H2SO4), hydrochloric acid (HC1), citric acid (GHxO?) and mixtures thereof, at a pH ranging from 0 to 4, preferably from 0.5 to 2, and more preferably being 1.
  • acids such as sulphuric acid (H2SO4), hydrochloric acid (HC1), citric acid (GHxO?) and mixtures thereof, at a pH ranging from 0 to 4, preferably from 0.5 to 2, and more preferably being 1.
  • the L-ascorbic acid is typically used at a concentration ranging from 0.1 M to 2.0 M, preferably of 0.4 M, while the sulphuric acid concentration can range from 0.001 M to 2.0 M, preferably of 0.5 M.
  • the treatment with L-ascorbic acid and H2SO4 is performed at a temperature ranging from 15 to 40°C under stirring at a speed typically ranging from 10 to 400 rpm, preferably from 20 to 200, and more preferably of 40 or 200 rpm.
  • Step f) involves the reduction of Mn(IV) to Mn 2+ ion and the consequent oxidation of L-ascorbic acid to dehydroascorbic acid according to the following equation:
  • the conductive fraction without manganese oxide obtained from step f) is filtered and sent to a second step g) for removal of metallic silver by treatment with a compound selected from ammonium thiosulphate ((NH4)2S2C>2) or sodium thiosulphate (Na2S2C>2), optionally combined with copper sulphate (CuSCL) or glycine combined with hydrogen peroxide in a basic environment.
  • a compound selected from ammonium thiosulphate ((NH4)2S2C>2) or sodium thiosulphate (Na2S2C>2) optionally combined with copper sulphate (CuSCL) or glycine combined with hydrogen peroxide in a basic environment.
  • said step g) is performed under stirring at a speed ranging from 10 to 400 rpm, preferably from 20 to 200, and more preferably of 40 or 200 rpm.
  • step g) is performed in ammonium thiosulphate and copper sulphate (Q1SO4), said step is preferably conducted at a temperature ranging from 90°C to 20°C, preferably from 50 to 70°C, and more preferably of 60°C, in an environment alkalinised with NaOH, at a pH ranging from 9 to 12, preferably at pH 11.
  • the ammonium thiosulphate is at a concentration ranging from 0.1 M to 2.0 M, even more preferably is 0.5 M, and the copper sulphate is at a concentration ranging from 0.01 M to 0.5 M, even more preferably of 0.05 M.
  • step g) is performed by treatment with glycine and hydrogen peroxide (H2O2)
  • said step is conducted at a temperature ranging from 20 to 85°C, preferably 50 to 70°C, and more preferably of 60°C, in an environmentalkalinised with NaOH, at a pH ranging from 9 to 12, preferably at pH 11.
  • the glycine is used at a concentration ranging from 0.03 M to 3 M, preferably 0.1 M to 1.0 M, and more preferably is 0.3 M
  • the hydrogen peroxide is at a concentration ranging from 0.1% to 5% m/m, and even more preferably is 1% m/m.
  • Glycine treatment step g) involves complexation of silver by glycine, with oxidation of hydrogen peroxide with emission of water:
  • a reagent containing thiosulphate ions such as ammonium thiosulphate
  • glycine and hydrogen peroxide can be combined with the use of glycine and hydrogen peroxide.
  • step g) is preferably conducted in ammonium thiosulphate and copper sulphate (CUSO4) or step g) is preferably conducted by treatment with glycine and hydrogen peroxide (H2O2)
  • the method according to the invention allows to avoid removal of metallic silver (Ag) by treatment with nitric acid, and is therefore a more environment-friendly solution.
  • Filtration of the concentrated solid residue obtained from the preceding step provides a final concentrated solid residue consisting of tantalum metal and tantalum pentoxide, having a concentration of carbon residues, MnCh and metallic silver (Ag) not exceeding 4%.
  • step f), step g) or both can be performed in the presence of a surfactant. Said addition guarantees better wettability of the electrically conductive fraction obtained in step e), thus preventing agglomeration.
  • the final concentrate can be optionally subjected to treatments designed to reduce tantalum pentoxide to tantalum metal; for example it can undergo a heat treatment in a reducing atmosphere, such as a hydrogen-based atmosphere or a carbon monoxide-based atmosphere, or undergo a magnesio-thermic reduction treatment.
  • a reducing atmosphere such as a hydrogen-based atmosphere or a carbon monoxide-based atmosphere
  • the powders of the final concentrate can be further completely oxidised to Ta2Os by heat treatment and consolidated by applying rapid sintering techniques with FAST (Field Assisted Sintering Techniques) or SPS (Spark Plasma Sintering) techniques to obtain density values of the finished product equal to or higher than 95%.
  • FAST Field Assisted Sintering Techniques
  • SPS Spark Plasma Sintering
  • the process according to the invention allows 60% of the tantalum contained in the treated waste to be recovered.
  • the resulting product has a purity of up to 96% or more.
  • a further aspect of the invention is the concentrated solid residue consisting of tantalum metal and optionally tantalum pentoxide, at a concentration of at least 96%, obtainable from the process described above.
  • the invention also relates to the use of said solid residue obtainable from the process described above in the electronic field, for example for the manufacture of electrolytic capacitors, heat exchangers, multidielectric optical filters and antireflective coatings, and for biomedical applications such as suture threads, bone plates and screws.
  • tantalum capacitors purchased new and selected to obtain a batch as similar as possible to a waste batch, namely having either manganese oxide (MnCh) or a conductive polymer such as poly(3,4- ethylenedi oxy thiophene) (PEDOT) or poly(3,4-ethylenedioxythiophene):poly(styrene- sulphonate (PEDOTS:PSS) as electrolyte.
  • MnCh manganese oxide
  • PEDOT poly(3,4- ethylenedi oxy thiophene)
  • PES poly(styrene- sulphonate
  • the process according to the invention proceeded as follows: a) immersion of the sample for 15 minutes in liquid nitrogen at -196°C and subsequent grinding treatment for 60s at 30Hz in a zirconia ball mill; b) sieving of the material obtained in step a) with a UNI sieve having 0.18 mm holes; c) grinding for 30s at 30Hz of the undersize material obtained from step b) in a zirconia ball mill; d) sieving of the material obtained from step a) with a UNI sieve having 0.18 mm holes; e) magnetic separation with neodymium magnets of the oversize fraction obtained from step d), thus obtaining a magnetic fraction and a non-magnetic fraction; f) grinding of the magnetic fraction obtained from step e) for 30s at 30Hz in a zirconia ball mill; g) electrostatic separation at 25kV of the undersize fraction obtained from the further sieving of step d), and
  • Said treatment was conducted for 3 h at room temperature (20°C), under magnetic stirring at 200 rpm; i) filtration and drying of the solid material remaining after the treatment of step h); j) removal of silver (Ag) by treatment with an 0.3M aqueous solution of glycine and hydrogen peroxide 1% by mass, basified to pH 11 with NaOH. Said treatment was conducted for 12 h at 60°C, under magnetic stirring at 200 rpm. k) filtration and drying of the solid material remaining after the treatment of step k). 3.4 g of concentrated solid tantalum residue, containing tantalum metal and tantalum pentoxide (Ta2Os), was thus obtained.
  • SEM/EDX analysis (shown in Figure 2) of the product obtained according to Example 1 shows its chemical composition and demonstrates that 96% of said solid consisted of metallic tantalum/tantalum pentoxide, while 4% consisted of metallic silver (Ag) and carbon residues.
  • XRD analysis shown in Figure 3 of the product obtained according to Example 1 shows its chemical composition and demonstrates that 96% of said solid consisted of metallic tantalum/tantalum pentoxide, while 4% consisted of metallic silver (Ag) and carbon residues.

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Abstract

The present invention relates to a process for recovery of tantalum and derivatives thereof from electronic waste, such as capacitors. The process according to the invention is cheap and advantageous in both energy and environmental terms.

Description

PROCESS FOR RECOVERY OF TANTALUM AND DERIVATIVES THEREOF
Technical field of invention
The present invention relates to a cheap, sustainable process for recovering tantalum and derivatives thereof from waste or spent electronic components.
State of the art
Tantalum is a metal considered to be a “critical raw material”, because it is mainly mined in countries with unstable geopolitical situations, such as Nigeria, the Congo and Brazil.
Its extraction process is currently very expensive, because tantalum is often present in the form of ore containing niobium, and the separation of said two metals requires highly sophisticated, energy-intensive treatments.
Tantalum is widely used in specific capacitors, namely electrolytic capacitors, wherein the tantalum acts as an anode, covered with a layer of oxide that acts as a dielectric, surrounded by a conductive cathode.
The use of tantalum enables the production of a very thin dielectric layer. This means a greater capacity value per volume, and consequently a reduction in the size of the final capacitor with no loss of capacity. Tantalum capacitors are also preferable to other types due to their greater stability and longer working life.
Tantalum capacitors are also widely used in the corresponding surface-mount formats because they are much cheaper than the equivalent aluminium electrolytic capacitors and can better withstand the soldering process.
However, the manufacturing process of tantalum capacitors generates a significant amount of waste materials and non-conforming parts, and a recovery and recycling strategy is definitely necessary, to provide an economic return and reduce their environmental impact.
The existing technologies are currently based on hydrometallurgical leaching treatments that use very strong, harmful acids, such as the combination of hydrofluoric, hydrochloric, sulphuric and nitric acid.
Other known tantalum recovery processes use heat treatments that are expensive in terms of both energy and cost, such as pyrolysis, roasting treatments to achieve oxidation, and more generally, heat treatments at temperatures which may exceed 450°C, sometimes reaching alkaline calcination temperatures equal to or greater than 700°C, for long periods, which may even exceed 24 h.
Moreover, the known approaches focus on dissolving tantalum rather than eliminating other elements (such as, for example, metal oxides or pure metals of the other components of the electronic device) for the purpose of tantalum recovery.
Further approaches are known, such as Piotrowicz A. et al. “Dissolution of manganese (IV) oxide from tantalum capacitor scrap by organic acids”, Acta Innovations, no. 32, 2019, pages 63-77, WO 2018/046786 Al, E.A. Oraby et al. “The leaching of gold, silver and their alloys in alkaline glycine-peroxide solutions and their adsorption on carbon”, Hydrometallurgy, col.152, 2015, pages 199-203, Petter P.M.H. et al. “Evaluation of gold and silver leaching from printed circuit board of cellphones”, Waste Management, vol. 34, no. 2, 2013, pages 475-482, and Wei Yuezhou et al. “Leaching reaction of manganese dioxide from tantalum capacitor scrap”, Shigen to sogai - Journal of the Mining and Materials Processing Institute of Japan, vol. 105, no. 2, 1989, pages 181-187; however, they do not achieve sufficient, selective physical separation of tantalum from the electrodes, for example from the copper electrodes of recycled tantalum capacitors.
In view of the above, there is still a need for a method for recovering tantalum from waste materials or spent capacitors which is at the same time cheap, fast, with low environmental impact, and allows simultaneous removal of metal or metal oxide residues.
DESCRIPTION OF THE INVENTION
The present invention solves the problems of the known methods and meets the above- mentioned criteria of cheapness and low environmental impact due to a sequence of grinding, sieving, magnetic and electrostatic separation steps, associated with chemical treatments of the separated conductive material under mild conditions.
Moreover, as the method according to the invention does not involve pyrolysis steps, it avoids high energy use and high operating costs, together with the production of possibly harmful waste substances due to the degradation of the polymers contained in waste materials containing spent tantalum capacitors. “Pyrolysis step” means a step wherein the polymer (electrical insulator) is degraded to carbon (electrical conductor). Said step, if present, can also worsen the yield of the electrostatic separation step.
More generally, a method for recovering tantalum from waste materials containing spent or recovered tantalum capacitors is disclosed, which comprises:
1) grinding said waste materials;
2) separating from the grinded materials of a magnetic fraction and a conductive fraction;
3) removal of manganese dioxide from the conductive fraction by treatment with ascorbic acid in an acid environment, and subsequent removal of silver by treatment with thiosulphate in the presence of copper, or with glycine and hydrogen peroxide in a basic environment.
In a first aspect, the invention relates to a method for recovering tantalum from waste materials containing spent or recovered tantalum capacitors, comprising: a) grinding said waste materials containing tantalum; b) sieving the waste material with a sieve ranging from 0.05 mm to 0.2 mm; c) magnetic separation of the oversize fraction obtained from step b), thus obtaining a magnetic fraction and a non-magnetic fraction; d) grinding the non-magnetic fraction obtained from step c), and further sieving with a sieve ranging from 0.18 mm to 0.45 mm; e) electrostatic separation of the undersize fraction obtained from the further sieving of step d), and of the undersize fraction obtained from the sieving of step b), thus obtaining an electrically conductive fraction and a non-electrically conductive fraction; f) treating the electrically conductive fraction obtained in step e), containing Ta/Ta2Os, MnCh and Ag, with L-ascorbic acid in an acid environment to remove manganese dioxide; g) treatment of the solid residue filtered out from step f) with thiosulphate, preferably sodium thiosulphate or ammonium thiosulphate, optionally in the presence of copper ions, or with glycine and hydrogen peroxide for the removal of silver in basic environment; h) filtration and drying of the residue consisting essentially of Ta and Ta2Os.
A further aspect of the present invention is a concentrated solid residue consisting of tantalum metal and optionally tantalum pentoxide Ta2Os obtainable by the process described above.
The invention also relates to the use of said concentrated solid residue consisting of tantalum metal and optionally tantalum pentoxide (Ta2Os), having a concentration obtainable by the process described above, in electronic and/or biomedical field, preferably for applications selected from manufacture of electrolytic capacitors, heat exchangers, multidielectric optical filters, anti -reflective coatings, biomedical applications such as suture threads, bone plates and screws, more preferably for electrolytic capacitors.
BRIEF DESCRIPTION OF FIGURES
Figure 1 shows the process chart according to the invention, as used in Example 1.
Figure 2 shows the SEMZEDX (Scanning Electron Microscopy / Energy Dispersive Spectroscopy) analysis of the product obtained according to Example 1.
Figure 3 shows the XRD (X-Ray Diffraction) analysis of the product obtained according to Example 1. Detailed description of the invention
The selection of the process parameters (pH, temperature, reagents and their concentration, and treatment time), as described below, allowed to maximise the tantalum recovery yield (also in the form of tantalum pentoxide) and to minimise the costs of the manganese oxide (MnCh) and metallic silver (Ag) chemical treatment (leaching) step.
The technology described herein thus enables the recycling of electronic waste through green techniques, and the recovery of “critical raw materials^
The proposed process is significantly cheaper and more advantageous in terms of energy because it does not use any high-temperature steps (e.g. in high-temperature ovens), vacuum treatments or treatments in particular atmospheres.
The absence of pyrolysis steps also avoids the production of toxic or pollutant gaseous species.
Moreover, by using combinations of grinding, sieving and magnetic separation, the proposed process enables Cu and Fe/Ni electrodes to be separated and recovered with no need for aggressive chemical treatments.
The proposed process also offers the further advantage of producing low-hazard waste which is easily disposable at low cost.
The first grinding step preferably comprises cryo-milling of waste material containing tantalum. Typically, the cryo-milling is conducted at a temperature ranging from -200°C to -40°C, more preferably at a temperature of -196°C.
Advantageously, cryo-milling is performed by immersing the tantalum-containing material in liquid nitrogen (N2) or another cryogenic fluid at temperatures below -40°C, for a time ranging from 5 to 30 minutes, more preferably for a time of 15 minutes, to embrittle the more ductile materials and facilitate their grinding so as to obtain a better degree of separation.
After the first grinding, the tantalum-containing material preferably has a particle size ranging from 0.05 mm to 2 mm, preferably from 0.1 mm to 1 mm.
Cryo-milling has the effect of making the more ductile components of the tantalum- containing material more fragile, so as to obtain a particle size preferably in the range described above, thereby increasing the separation efficiency, and consequently the tantalum recovery.
The cryo-milling can be conveniently performed in various types of mill, such as a ball mill.
In an advantageous, preferred embodiment, the process according to the invention comprises multiple grinding and sieving steps.
Step b) of first sieving of the ground material obtained from step a), is advantageously performed with a sieve having holes of a diameter ranging from 0.05 mm to 0.3 mm, preferably from 0.1 mm to 0.2 mm, and more preferably being 0.18 mm.
Said step can be followed by a second grinding step at a temperature ranging from 15 to 40°C, and by a second sieving as described above.
The magnetic separation (step c) is conducted on the ground, sieved material retained by the sieve (oversize), preferably using neodymium magnets, CoAlNi alloy magnets or electromagnetic separators to remove the Fe/Ni alloy ferromagnetic terminals efficiently.
Said step c) is followed by a step d) of third grinding and sieving with a sieve having holes of a diameter ranging from 0.18 mm to 0.450 mm, preferably from 0.320 to 0.400 mm, and more preferably being 0.350 mm, wherein the material having a diameter smaller than the diameter of the holes (undersize) is sent to the next step e) of electrostatic separation, while the material having a diameter larger than the diameter of the holes, mainly containing copper (Cu) electrodes, is separated.
Step d) of grinding of the non-magnetic fraction, which is performed after magnetic separation c) and before sieving, increases the degree of release of the various constituents after removal of the (ductile) ferromagnetic material, thus increasing the efficacy of grinding.
The process according to the invention therefore enables the material of the copper (Cu) electrodes to be removed by sieving alone, with no need for them to be dissolved by acid attack, thus reducing the use of aggressive chemical agents. Said sieving step, with a sieve having holes of a diameter larger than the hole diameter of the sieve used in the previous sieving, enables the copper electrodes to be removed without eliminating the tantalum anodes, which are thus sent, with the rest of the undersize material from sieving step b), for electrostatic separation in step e).
Step e) of electrostatic separation, a well-known physical separation technique used to separate particles on the basis of their different electrical conductivities, is performed in an electrostatic separator.
More preferably, in said step e) the material is processed at least twice, preferably twice, in said electrostatic separator, and two fractions are identified and separated.
A first conductive fraction, for example having electrical resistivity ranging from 1 10" 9 Qm to 1 • 10'5 Qm measured by impedance spectroscopy, namely the fraction containing Ta, also contains an amount of MnCh (originating from the electrolyte of the tantalum capacitors) and Ag and is therefore sent to the next step of the process according to the invention.
A second non-conductive fraction, having electrical resistivity higher than 1 • 105 Qm measured by impedance spectroscopy, namely the fraction containing impurities such as polymers, SiCh and finer carbon particles, Ta20s and MnCh, is not further treated.
The first conductive fraction undergoes a tantalum concentration step by selective elimination of manganese dioxide and silver.
According to the invention, manganese dioxide is eliminated in step f) by treatment with L-ascorbic acid (CeH^Oe) in the presence of acids such as sulphuric acid (H2SO4), hydrochloric acid (HC1), citric acid (GHxO?) and mixtures thereof, at a pH ranging from 0 to 4, preferably from 0.5 to 2, and more preferably being 1.
The L-ascorbic acid is typically used at a concentration ranging from 0.1 M to 2.0 M, preferably of 0.4 M, while the sulphuric acid concentration can range from 0.001 M to 2.0 M, preferably of 0.5 M.
The treatment with L-ascorbic acid and H2SO4 is performed at a temperature ranging from 15 to 40°C under stirring at a speed typically ranging from 10 to 400 rpm, preferably from 20 to 200, and more preferably of 40 or 200 rpm.
Step f) involves the reduction of Mn(IV) to Mn2+ ion and the consequent oxidation of L-ascorbic acid to dehydroascorbic acid according to the following equation:
The conductive fraction without manganese oxide obtained from step f) is filtered and sent to a second step g) for removal of metallic silver by treatment with a compound selected from ammonium thiosulphate ((NH4)2S2C>2) or sodium thiosulphate (Na2S2C>2), optionally combined with copper sulphate (CuSCL) or glycine combined with hydrogen peroxide in a basic environment.
Advantageously, said step g) is performed under stirring at a speed ranging from 10 to 400 rpm, preferably from 20 to 200, and more preferably of 40 or 200 rpm.
When step g) is performed in ammonium thiosulphate and copper sulphate (Q1SO4), said step is preferably conducted at a temperature ranging from 90°C to 20°C, preferably from 50 to 70°C, and more preferably of 60°C, in an environment alkalinised with NaOH, at a pH ranging from 9 to 12, preferably at pH 11.
More preferably, in said embodiment, the ammonium thiosulphate is at a concentration ranging from 0.1 M to 2.0 M, even more preferably is 0.5 M, and the copper sulphate is at a concentration ranging from 0.01 M to 0.5 M, even more preferably of 0.05 M.
When step g) is performed by treatment with glycine and hydrogen peroxide (H2O2), said step is conducted at a temperature ranging from 20 to 85°C, preferably 50 to 70°C, and more preferably of 60°C, in an environmentalkalinised with NaOH, at a pH ranging from 9 to 12, preferably at pH 11. The glycine is used at a concentration ranging from 0.03 M to 3 M, preferably 0.1 M to 1.0 M, and more preferably is 0.3 M, and the hydrogen peroxide is at a concentration ranging from 0.1% to 5% m/m, and even more preferably is 1% m/m.
Glycine treatment step g) involves complexation of silver by glycine, with oxidation of hydrogen peroxide with emission of water:
Advantageously, the use of a reagent containing thiosulphate ions, such as ammonium thiosulphate, can be combined with the use of glycine and hydrogen peroxide.
Thus, in both cases, whether step g) is preferably conducted in ammonium thiosulphate and copper sulphate (CUSO4) or step g) is preferably conducted by treatment with glycine and hydrogen peroxide (H2O2), the method according to the invention allows to avoid removal of metallic silver (Ag) by treatment with nitric acid, and is therefore a more environment-friendly solution.
Filtration of the concentrated solid residue obtained from the preceding step provides a final concentrated solid residue consisting of tantalum metal and tantalum pentoxide, having a concentration of carbon residues, MnCh and metallic silver (Ag) not exceeding 4%.
In one embodiment, step f), step g) or both can be performed in the presence of a surfactant. Said addition guarantees better wettability of the electrically conductive fraction obtained in step e), thus preventing agglomeration.
The final concentrate, if desired, can be optionally subjected to treatments designed to reduce tantalum pentoxide to tantalum metal; for example it can undergo a heat treatment in a reducing atmosphere, such as a hydrogen-based atmosphere or a carbon monoxide-based atmosphere, or undergo a magnesio-thermic reduction treatment.
The powders of the final concentrate can be further completely oxidised to Ta2Os by heat treatment and consolidated by applying rapid sintering techniques with FAST (Field Assisted Sintering Techniques) or SPS (Spark Plasma Sintering) techniques to obtain density values of the finished product equal to or higher than 95%.
The process according to the invention allows 60% of the tantalum contained in the treated waste to be recovered. The resulting product has a purity of up to 96% or more.
A further aspect of the invention is the concentrated solid residue consisting of tantalum metal and optionally tantalum pentoxide, at a concentration of at least 96%, obtainable from the process described above.
The invention also relates to the use of said solid residue obtainable from the process described above in the electronic field, for example for the manufacture of electrolytic capacitors, heat exchangers, multidielectric optical filters and antireflective coatings, and for biomedical applications such as suture threads, bone plates and screws.
The examples below further illustrate the invention.
Experimental part
The entire process has been laboratory tested. An amount equal to 24.3 g of tantalum capacitors, purchased new and selected to obtain a batch as similar as possible to a waste batch, namely having either manganese oxide (MnCh) or a conductive polymer such as poly(3,4- ethylenedi oxy thiophene) (PEDOT) or poly(3,4-ethylenedioxythiophene):poly(styrene- sulphonate (PEDOTS:PSS) as electrolyte.
Materials and methods
Example 1 Treatment of waste containing tantalum by the process according to the invention
Starting with a mass of 24.3 g of waste tantalum capacitors, the process according to the invention proceeded as follows: a) immersion of the sample for 15 minutes in liquid nitrogen at -196°C and subsequent grinding treatment for 60s at 30Hz in a zirconia ball mill; b) sieving of the material obtained in step a) with a UNI sieve having 0.18 mm holes; c) grinding for 30s at 30Hz of the undersize material obtained from step b) in a zirconia ball mill; d) sieving of the material obtained from step a) with a UNI sieve having 0.18 mm holes; e) magnetic separation with neodymium magnets of the oversize fraction obtained from step d), thus obtaining a magnetic fraction and a non-magnetic fraction; f) grinding of the magnetic fraction obtained from step e) for 30s at 30Hz in a zirconia ball mill; g) electrostatic separation at 25kV of the undersize fraction obtained from the further sieving of step d), and of the undersize fraction obtained from the sieving of step b), thus obtaining an electrically conductive fraction and a non-electrically conductive fraction; h) removal of manganese dioxide (MnCh) from the non-electrically conductive fraction obtained from step g) by treatment in an aqueous solution of 0.4M L-ascorbic acid acidified to pH 1 with sulphuric acid. Said treatment was conducted for 3 h at room temperature (20°C), under magnetic stirring at 200 rpm; i) filtration and drying of the solid material remaining after the treatment of step h); j) removal of silver (Ag) by treatment with an 0.3M aqueous solution of glycine and hydrogen peroxide 1% by mass, basified to pH 11 with NaOH. Said treatment was conducted for 12 h at 60°C, under magnetic stirring at 200 rpm. k) filtration and drying of the solid material remaining after the treatment of step k). 3.4 g of concentrated solid tantalum residue, containing tantalum metal and tantalum pentoxide (Ta2Os), was thus obtained.
Example 2 SEM/EDX analysis of concentrated solid tantalum residue obtained by the process according to the invention
SEM/EDX analysis (shown in Figure 2) of the product obtained according to Example 1 shows its chemical composition and demonstrates that 96% of said solid consisted of metallic tantalum/tantalum pentoxide, while 4% consisted of metallic silver (Ag) and carbon residues.
Example 3 XRD analysis of concentrated solid tantalum residue obtained by the process according to the invention
XRD analysis (shown in Figure 3) of the product obtained according to Example 1 shows its chemical composition and demonstrates that 96% of said solid consisted of metallic tantalum/tantalum pentoxide, while 4% consisted of metallic silver (Ag) and carbon residues.

Claims

1. A method for recovering tantalum from waste materials containing spent or recovered tantalum capacitors comprising: a) grinding treatment of said waste materials comprising tantalum; b) sieving the waste materials with a sieve ranging from 0.05 mm to 0.2 mm; c) magnetic separation of the oversize fraction obtained from step b), thus obtaining a magnetic fraction and a non-magnetic fraction; d) grinding of the non-magnetic fraction obtained from step c), and further sieving with a sieve ranging from 0.18 mm to 0.45 mm; e) electrostatic separation of the undersize fraction obtained from the further sieving of step d) and the undersize fraction obtained from the sieving of step b), thus obtaining an electrically conductive fraction and a non-electrically conductive fraction; f) treatment of the electrically conductive fraction obtained from step e), containing Ta/Ta2Os, MnCh and Ag with ascorbic acid in an acid environment to remove manganese dioxide; g) treatment of the solid residue filtered out from step f) with thiosulphate, preferably sodium thiosulphate or ammonium thiosulphate, optionally in the presence of copper ions, or with glycine and hydrogen peroxide for the removal of silver in a basic environment; h) filtration and drying of the residue consisting essentially of Ta and Ta2Os.
2. The method according to claim 1, wherein said grinding step takes place at cryogenic temperatures, preferably at a temperature ranging from -200°C to -40°C.
3. The method according to claim 2, wherein said grinding step is performed by immersing the tantalum comprising material in liquid nitrogen (N2) at temperatures below -40°C for a time ranging from 5 to 30 minutes.
4. The method according to any one of claims 1-3, wherein said material comprising tantalum has, after grinding, a particle size ranging from 0.05 mm to 2 mm.
5. The method according to any one of claims 1-3, wherein step f) is conducted in L- ascorbic acid ranging from 0.1 M to 2.0 M and sulphuric acid or hydrochloric acid ranging from 0.001 M to 2.0M.
6. The method according to any one of claims 1-5, wherein step g) is conducted by treatment with ammonium thiosulphate at a concentration ranging from 0.1 M to 2 M in combination with copper sulphate at a concentration ranging from 0.01 M to 0.5 M.
7. The method according to any one of claims 1-5, wherein step g) is carried out by treatment with glycine at a concentration ranging from 0.03 M to 3 M and hydrogen peroxide H2O2 at a concentration ranging from 0.1% to 5% m/m, in a basic environment at a pH ranging from 9 to 12.
8. A concentrated solid residue consisting of tantalum metal and optionally tantalum pentoxide (Ta2Os), at a concentration of at least 96%, obtainable by the method according to any one of claims 1-7.
9. Use of the concentrated solid residue of claim 8 in electronic field, for the production of electrolytic capacitors, multi-dielectric optical filters, anti -reflective coatings or heat exchangers, or for biomedical applications.
EP24711626.2A 2023-02-21 2024-02-20 METHOD FOR RECOVERING TANTALUM AND DERIVATIVES THEREOF Pending EP4669781A1 (en)

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PCT/IB2024/051592 WO2024176097A1 (en) 2023-02-21 2024-02-20 Process for recovery of tantalum and derivatives thereof

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