ES2662956A1 - PROCEDURE FOR THE RECOVERY OF METAL METAL TANK ELECTROLYTIC CONDENSERS (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Procedure for the recovery of tantalum metal from electrolytic capacitors. The object of the present invention is a method for the recovery of tantalum metal from electrolytic capacitors. The process includes several stages, mainly physical operations for the extraction of tantalum from the condensers, being especially important the grinding of the dark material comprising tantalum metal and MnO 2 and the reduction conditions of the latter compound for get the metal tantalum. These operations must not affect the existing tantalum or provide any metallic element to the reaction mixture. In this way it is ensured that tantalum remains as such and that it is not contaminated with any additional component. (Machine-translation by Google Translate, not legally binding)

Description

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PROCEDURE FOR THE RECOVERY OF METAL TANDAL OF ELECTROLYTIC CONDENSERS

DESCRIPTION

SECTOR AND OBJECT OF THE INVENTION

The process object of the present invention is framed in the sector of the recovery of valuable metals from waste electrical and electronic equipment, especially the tantalum of the capacitors.

The process includes several stages, the grinding of the dark material comprising tantalum metal and MnO2 being especially important and the conditions of reduction of the latter compound to obtain the tantalum metal.

STATE OF THE TECHNIQUE

Currently, 20 to 50 tons of waste electrical and electronic equipment in the world are discarded annually. Due to the importance and shortage of some of the metals and raw materials that contain this waste, its use is interesting. With this in mind, the European Commission (EC) published in 2011 [Document COM (2011) 25 final “Addressing the challenges of commodity and raw material markets”; 2/2/2011] a document in which a classification of fourteen materials appeared because of its particularly significant and critical situation, among which was the tancello. There are collection techniques and recycling technologies quite advanced for some applications of precious metals (Pt, Pd, Au, Ag) so that recycling percentages greater than 50% are achieved for these elements. For rare earths as well as for Ta, Ga and In the recycling percentage is less than 1%, despite being critical materials according to the EC.

Tantalum has an abundance of 0.0001% (1 ppm) in the earth's crust. Some of its physical properties are given in the following table:

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Table 1. Physical properties of Tantalum

Melting point (ºC)

2980

Boiling Point (ºC)

5534

Enthalpy of fusion (kJ / mol)

24.7

Vapor enthalpy (kJ / mol)

758.2

Enthalpy of atomization (kJ / mol)

782

Density, at 20ºC (g / cm3)

16.65

Electrical Resistivity (Ω · m)

~ 12.4

At high temperature it is attacked by O2 and by halogens; He is also able to

5 be combined with most nonmetals. It is passivated by an oxide coating, which gives it corrosion resistance. It is inert to non-oxidizing acids and molten alkalis attack it at elevated temperatures. Its maximum and most stable oxidation state is +5. In lower oxidation states it usually forms hexanuclare “clusters” with metal-metal bonds [Housecroft C. E., Sharpe A. G. Inorganic Chemistry; Pearson

10 Educación S.A., 2006. pp. 654-658].

Tantalum is found mainly in nature in an isomorphic series of minerals that contain tantalum, niobium, iron and manganese oxides, and especially in a mineral composed of colombite and tantalite, of a very dark black or brown color, 15 better known as coltan . Slag from tin metallurgy (Thailand, Malaysia, Brazil) is a non-primary source of Ta, previously concentrated pyrometallurgically to raise its Ta2O5 content. Another source of Ta is found in pegmatitic deposits (a type of igneous rock), both in opencast quarries in Australia, and underground in Canada, from which it is extracted by blasting and crushing.

20 and subsequently concentrated by gravity.

Similar atomic sizes of Nb and Ta due to the contraction of the lanthanides, make them together in nature forming the iron and manganese niobatotantalate (Fe, Mn) (Nb, Ta) 2O6. This compound is the constituent of coltan. Due to the current importance of tantalum in technology, methods have been developed to separate it from niobium. Currently, once Ta is separated from Nb, heptafluorotantalate, K2TaF7, is reduced with sodium. This method

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It was first used by Siemens & Halske AG in the early twentieth century, and has been improving over time. The reactor is introduced into an electric arc furnace and heated below 1000 ° C. It is necessary to control the temperature, diluent and agitation because the quality of tantalum depends on them. If the Ta is separated from the Nb in the form of Ta2O5, the oxide is reduced electrochemically, but sufficient quality is not achieved for some applications

[López-López G., López-López J., García-Yagües M. R; TANTALO: A strategic metal, Engineering and Chemical Technologies, Vol. 84, nº3, (2009), pp. 1-6].

The largest reserves of coltan (80%) are found in Africa, especially in the area of the Democratic Republic of the Congo. Since the use of electronic devices was extended, tantalum extracted from other parts of the world such as Australia, Brazil or Thailand began to be scarce. Although these types of devices include small amounts of metal, they use more than 80% of the worldwide extraction of Ta.

Tantalum is used in the industry to build reaction vessels and heat exchangers to be placed in corrosive atmospheres, due to their chemical inertia. Also in biomedicine, for sutures, screws, wires, meshes, implants ... for being a biocompatible material. In the 1990s the demand for metal was increased due to its application in electronics, especially in solid tantalum capacitors, a use that 80% of the production is dedicated to, because it is possible to achieve greater capacities in smaller sizes.

The development of the electrical and electronic industry has led to an increase in the demand for tantalum, so it is interesting to recover them from the devices where they are once they have finished their useful life. These devices suppose between 20 and 50 tons of waste annually.

There are previous works that study the recovery of tantalum from capacitors. One of the methods consists of an oxidation with air with a subsequent magnetic separation and washing, to treat the obtained with HNO3 and then reduce it with Mg, to end up separating the Ta with an acid wash [Matsuoka R., Mineta K., Okabe TH Recycling process for tantalum and some other metal scraps; Metals & materials society The minerals. 2004. EPD Congress; Mineta K., Okabe T. H. Development of a recycling process for tantalum from capacitor scraps. Journal of Physics and Chemistry of Solids, Vol. 66, (2005), pp. 318-321]. It is possible to destroy the epoxy resin coating of the condenser with NaOH to recover the sintered Ta inside, as found by Katano S., Wajima T., Nakagome H. Recovery of tantalum sintered compact from used tantalum condenser using steam gasification with sodium hydroxide . APCBEE Procedia, Vol. 10, 2014, pp. 182-186.

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The object of the present invention is a simple procedure for the recovery of tantalum from the solid capacitors that contain it. For this purpose, it is set as objective not to carry out any chemical reaction with the tantalum that is already in the condensers as tantalum metal. This is the main difference with patents and publications of the state of the art that begin by oxidizing to tantalum (V), since then they must use very energetic and expensive reduction methods, either electrochemical or reduction with molten sodium, which make recycling significantly more expensive. .

Document JPS6475632A refers to a procedure for recovering Ta from electronic scrap with capacitors. The possibility of dissolving MnO2 efficiently by applying, among other means, H2O2 in acidic medium is mentioned in this process. The Ta resulting from separating the MnO2 is treated in order to purify it by conventional methods.

Document US2013336858A1 refers that the most applied recovery processes do not allow obtaining a Ta with sufficient purity to be used as raw material to, for example, manufacture new Ta condensers since impurities such as Si, Sb, Mn, Sn, Pb are carried away , Zn, Fe, Ni, Cu, Al which are present in the PCBs from which the capacitors containing Ta are extracted.

This publication refers to JP2010214352A in relation to previous concentration processes (grinding, sieving, magnetic separation, gravity separation and, again, another magnetic separation). Non-magnetic materials, where Ta remains, are then subjected to an acid treatment with concentrated HCl. In one of the alternatives, the addition of H2O2 to the acid treatment is contemplated, which leads to removing the Cu from the solid substrate in a slight but superior measure. This acid treatment that is subjected to the result of the stages of gravimetric and magnetic separation is not the last stage since it is followed by others where an alkaline attack, the roasting of the substrate and another alkaline attack are followed, all especially to strip of tungsten solid substrate.

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Wei Yuezhou; Sato Nobuaki; Takenaka Toshihide; Nanjo Michio Leaching reaction of manganese dioxide from tantalum capacitor scrap. A study on the recycling of high quality rare metal secondary resource; Shigen to sozai, Vol. 105, Nr. 2 (1989), 181-187 specifically refers to the use of H2O2 among other agents for the extraction of MnO2 from the substrate where Ta remains in capacitors from electronic scrap. Among the reducing agents applied are Na2SO3, H2O2, as well as FeSO4 in sulfuric acid medium. Therefore, H2O2, together with Na2SO3, was the most effective when extracting more than 90% of MnO2 after acting on the substrate for 24 hours at room temperature.

The document of Orlov V M .; Kiselev E.N. Leaching of manganese dioxide from porous bodies; Russian Journal of Applied Chemistry Vol. 85, Nr. 11 (2012), pp. 1699-1702, literally reveals the reduction of MnO2 with H2O2 in H2SO4 acid medium (also HCl). It is oriented to solid electrolyte capacitors, although it does not refer that the capacitors from which Ta is intended to be recovered are subjected to a previous operation of grinding and gravimetric and magnetic separations.

EXPLANATION OF THE INVENTION

Consistent with what is stated in the state of the art section, the approach is to develop a procedure that mainly includes physical operations for the extraction of the tantalum from the capacitors.

If a chemical operation is proposed, it should not affect the existing tantalum nor should it provide any additional metallic element to the reaction mixture. This ensures that the tantalum remains as such and that it is not impurified with any additional metallic element.

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Therefore, the object of the present invention is a process for the recovery of tantalum metal from electrolytic capacitors from electronic scrap comprising the following steps: -controlled breaking of the capacitors into parts with a size between 0.5 and 1 cm - gravity separation of the coating surrounding the tantalum electrode - magnetic separation of the metal terminals of the capacitors containing at least Cu and Ni - isolation of the dark material obtained after the previous stages and comprising tantalum metal and MnO2 characterized because the separation of the metal tantalum from the MnO2 includes: - crushing the dark material to a size between 0.1 and 0.5 mm - reduction of the MnO2 by treatment with a reducing agent comprising citric acid at a temperature between 20 ºC and 60 ºC for a period of time between 90 min and 24 h -filtration of the product obtained in the previous stage -washing with an aqueous solution of the solid resulting from the previous stage to remove the manganese citrate-drying of the solid obtained after the washing step at a temperature between 60 ° C and 200 ° C which contains tantalum metal with at minus 99.5% purity.

In a preferred embodiment of the process object of the invention, the capacitors have rectangular prism geometry with volumes between 24 and 240 mm 3, the controlled rupture thereof being performed by crushing. Alternatively, the capacitors may have other geometries, particularly ellipsoidal.

The gravity separation stage is carried out by floating in water, leaving the internal part of the condensers containing the metal tantalum below. The coating material can be of various types, particularly flame retardant or ceramic epoxy resin.

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The magnetic separation stage is performed by applying a magnetic field with a flow density between 0.1 and 0.25 T

Optionally, the magnetic terminals of the capacitors may contain other metals selected from Ag, Pb, Sn or Zn or mixtures and combinations thereof. For an optimal result of the process of the invention, the dark material separated in the previous steps must be crushed to a size of 0.2 mm and the subsequent reduction of the MnO2 of the dark material with the reducing agent comprising citric acid must be carried out in agent proportion reducer / dark material comprised between 0.4 gr and 20 gr of reducing agent per gram of dark material.

The reducing agent may additionally comprise oxalic acid.

The aqueous solution used for washing the resulting solid after the reduction stage comprises HCl in a proportion between 3% and 33% by weight of HCl in water and the solid drying stage, once washed, is carried out. at any temperature between 60ºC and 200ºC. Tests have been carried out at 75 ° C and in some games with H2O2 dried at 140 ° C ..

DETAILED DESCRIPTION AND MODE OF EMBODIMENT OF THE INVENTION

The first operation of the process of the invention is the rupture of the tantalum electrolytic capacitors of type SMD (Surface Mounting Device), which have sizes of 8x 4.5x 4 cm or smaller which is carried out by crushing until sizes between 0, 5 and 1 cm. In this way, its three components are well separated: a flame retardant epoxy resin coating that surrounds a black sintered Ta electrode, from which two metal terminals come out.

The metal terminal parts are separated from the mixture by means of a 010.25 T magnet containing metals such as Cu, Ni and varying amounts of Ag so that they can be incorporated into a recycling process for these metals.

From the resulting mixture, the pieces of epoxy resin can be separated from the rest of the inner part by flotation in water. The difference in densities of this part (less than water) from the majority of which Ta (metal density 16.65) contains allows almost complete separation.

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The dark colored internal part has to be crushed to a size between 0.1-0.5 mm

5 (150-35 mesh) preferably 0.2mm (70 mesh). This part consists of tantalum and manganese (MnO2) in an average analysis of approximately 74% of Ta and the rest 26% MnO2, in addition to small amounts of other elements.

10 Table 1. Crush result

FRACTION

SEPARATION % (BY WEIGHT) IN CONDENSERS % BY WEIGHT (determined by XRF)

Terminals

Magnet 6% 52.11 ± 0.11% Cu 15.41 ± 0.01% Sn 10.46 ± 0.06% Ni 8.66 ± 0.05% Ag 8.01 ± 0.09% Zn 5.35 ± 0 , 06% Pb

External part

Flotation (above) 53.7% -

Inner part

Flotation (below) 40.3% 83.76% ± 0.21% Ta 16.24% ± 0.21% Mn

To obtain the metal Ta, a reduction of manganese is carried out for which the following reducers have been tested:

15 Table 2. Reducers used to reduce Mn (IV)

REDUCER / MEDIUM

TERMS REACTION

Glucose (C6H12O6) (H +)

Ambient temperature -1day Do not

60ºC -1 day

Do not

Citric acid (C6H8O7) (H +)

Ambient temperature -1day Do not

60ºC -1 hour 30

Yes

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minutes

Oxalic Acid (H2C2O4)

Temperature -1day ambient Do not

(H +)

60ºC -1 minutes hour 30 Yes

Methanol (CH3OH) (H +)

Temperature -1 day ambient Do not

2-phenylacetone (C6H5COCH2C6H5) (H +)

Temperature -1 day ambient Do not

Hydrogen peroxide (H2O2) (H +)

Temperature -1 hour ambient Yes

The best results are obtained with citric acid in which the reduction takes place without the addition of additional acid of any kind, whereby the method is mild and only with organic additives whose reaction products are CO2 and H2O and whose excess if

5 you want to remove, it can be done by heating. The use of hydrogen peroxide requires the addition of an acid such as sulfuric acid, which is a source of possible impurities and inconveniences if it is desired to take advantage of the manganese (II) salts that are formed as a byproduct.

10 Once the reduction is done, it is filtered and the resulting solid is washed in water to remove the solution containing manganese citrate (II).

The reduction with oxalate progresses properly but manganese (II) oxalate is formed which is insoluble in the medium and is difficult to remove by washing and

15 decanting in water

Example

The starting sample contains 83.76% of Ta and 16.24% of Mn according to the X-ray fluorescence analysis (XRF).

A dispersion of 0.9932 g of powdered sample (containing 0.2552 g MnO2; 2.94 mmol MnO2) in 10 ml of distilled water is treated with citric acid (1.1304 g; 5.88 mmol), following the following reaction:

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9 MnO2 + C6H8O7 + 18 H + • 9 Mn2 + + 13 H2O + 6 CO2

The mixture is allowed to stir at 60 ° C for one hour and 30 minutes. After this time, a transparent solution of greenish color and a black solid is observed. It was filtered by gravity in a conical funnel with double filter paper and the precipitate was washed

5 with 10 ml of a solution of HCl in H2O 1:10 and then with distilled water until the waters were colorless. The solid is then dried in the oven at 75 ° C on a filter paper, collecting 0.72 g of black solid. This result is equivalent to 2.9 grams of tantalum being recovered from 10 grams of starting capacitors.

10 XRF (Wirec): 99.83 ± 0.08% Ta; 0.17 ± 0.06% Mn.

Claims (7)

image 1 1.-Procedure for the recovery of metal tantalum from electrolytic capacitors from electronic scrap comprising the following stages: -controlled breaking of the capacitors into parts with a size between 0.5 and 1 cm -separation by separation of the surrounding coating to the tantalum electrode-magnetic separation of the metal terminals of the capacitors containing at least Cu and Ni -isolation of the dark material obtained after the previous stages and comprising tantalum metal and MnO2 characterized in that the separation of the metal tantalum from the MnO2 comprises in turn: crushing the dark material to a size between 0.1 and 0.5 mm -reduction of the MnO2 by treatment with a reducing agent comprising citric acid at a temperature between 20 ° C and 60 ° C for a period of time between 90 min and 24 h -filtration of the product obtained in the previous stage -washing with a an aqueous solution of the solid resulting from the previous stage to remove the manganese citrate-drying of the solid obtained after the washing step at a temperature between 60 ° C and 200 ° C which contains tantalum metal with at least 99.5% purity. 2. Method according to claim 1, wherein the capacitors have rectangular prism geometry with volumes between 24 and 240 mm3, the controlled rupture thereof being performed by crushing. 3. Method according to claims 1 or 2, wherein the gravity separation step is carried out by means of water flotation, the internal part of the condensers containing the metal tantalum being below. 4. Method according to any one of claims 1 to 3, wherein the magnetic separation is performed by applying a magnetic field with a flow density between 0.1 and 0.25 T 12 image2 5. Method according to claim 4, wherein the magnetic terminals of the capacitors additionally contain other metals selected from Ag, Pb, Sn or Zn or mixtures and combinations thereof. 6. Method according to any one of claims 1 to 5, where the grinding of the dark material is carried out to a size of 0.2 mm. 7. Process according to any one of claims 1 to 6, wherein the reduction of MnO2 with the reducing agent comprising citric acid is carried out in proportion 10 reducing agent / dark material comprised between 0.4 gr and 20 gr of reducing agent per gram of dark material. 8. Method according to claim 7, wherein the reducing agent further comprises oxalic acid. Method according to any one of claims 1 to 8, wherein the aqueous solution that is used for washing the resulting solid after the reduction step comprises HCl in a proportion between 3% and 33% by weight of HCl in water Method according to any one of claims 1 to 9, wherein the step of drying the solid, once washed, is carried out at a temperature between 60 ° C and 200 ° C. 13