ES2662956B1 - PROCEDURE FOR THE RECOVERY OF METAL TANK OF ELECTROLYTIC CONDENSERS - Google Patents

Description

p r o c e d e n t o f t o f th e r e c tio n t t t t

c o n d a n d o r e r e s

d e s c r ip c io n

s e c t o r y o b t in in v e n c tio n

The process object of the present invention is part of the field of recovery of valuable metals from waste electrical and electronic equipment, more especially tantalum condensers.

The process includes several steps, being particularly important the grinding of the dark material comprising tantalum metal and Mn02 and the conditions of reduction of the latter compound to obtain the metal tantalum.

e s ta d o d the tea c n ic a

Currently, between 20 and 50 tons of waste electrical and electronic equipment are discarded in the world every year. Due to the importance and scarcity of some of the metals and raw materials that contain this waste, its use is interesting. Taking this into account, the European Commission (EC) published in 2011 [Document COM (2011) 25 final "Addressing the challenges of commodity and commodity markets"; 2/2/2011] a document in which there was a classification of fourteen materials because their situation was especially significant and critical, among which was the tango.

There are collection techniques and quite advanced recycling technologies for some precious metals applications (Pt, Pd, A ^u , Ag) so recycling percentages higher than 50% are obtained for these elements. For rare earths as well as for Ta, Ga and ln the percentage of recycling 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:

Table 1. Physical properties of Tantalum

At high temperature it is attacked by 02 and by the halogens; It is also able to combine with most non-metals. It is passivated by an oxide coating, which gives it resistance to corrosion. E ^s inert to acids I ^I I ^I nonoxidizing and molten alkali attack at elevated temperatures. S ^or maximum and more stable oxidation state is 5. In lower oxidation states tends to form "clusters" hexanuclares with metal-metal bonds [Housecroft CE, Sharpe AG Inorganic Chemistry; Pearson Education SA, 2006. pp.654-658].

Tantalum is found mainly in nature in an isomorphic series of minerals containing oxides of tantalum, niobium, iron and manganese, and especially in a mineral composed of colombite and tantalite, black or very dark brown, better known as coltan. The tin metallurgy slag (Thailand, Malaysia, Brazil) is a non-primary source of Ta, previously concentrated pyrometallurgically to raise ^its Ta205 content. Another source of Ta is found in pegmatitic deposits (a type of igneous rock), both in open-pit quarries in Australia, and underground in Canada, from which it is extracted by blasting and crushing and then concentrated by gravity.

The similar atomic sizes of Nb and Ta due to the contraction of the lanthanides cause them to be together in nature forming the iron and manganese niobatotantalate (Fe, Mn) (Nb, Ta) 206. This compound is the constituent of coltan. Due to the current importance of tantalizing it in technology, methods have to be developed to separate it from niobium. Currently, once Ta is separated from Nb, the heptafluorotantalate, K2TaF7, is reduced with sodium. This method It was first used by Siemens & Halske AG in the early twentieth century, and has been improving over time. The reactor is introduced in an electric arc furnace and heated below 1000oC. It is necessary to control the temperature, the diluent and the agitation because the quality of the tantalum depends on them. If the Ta is separated from the Nb in the form of Ta205, the oxide is reduced electrochemically, but sufficient quality is not achieved for some applications

[López-López G., López-López J., García-Yagües M. R; TÁNTALO: A strategic metal, Engineering and Chemical Technologies, VoI.84, n03, (2009), pp. 1-6].

The largest reserves of coltan (80%) are found in Africa, especially in the Democratic Republic of the Congo area. Since I ^use electronic devices ^will spread, tantalum extracted from other parts of the world like Australia, Brazil and Thailand began to dwindle. Although this type of device includes small amounts of metal, they use more than 80% of the global extraction of Ta.

Tantalum is used in the industry to build reaction vessels and heat exchangers that are going 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 nineties the demand for metal was increased due to ^its application in electronics, especially in solid capacitors of tantalum, which is used for 80% of production, 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 ^their useful life is over. These devices account for between 20 and 50 tons of waste annually.

There are previous works that study the tantalum recovery of capacitors. One of ^the methods consists of an oxidation with air with a subsequent magnetic separation and washing, to treat the obtained with HN03 and then reduce it with Mg, to finish separating the Ta with an acid wash [Matsuoka R., Mineta K., Okabe TH Recycling pmcess for tantalum and some other metal scraps; Metals & materials society The minerals. 2004. EPD Congress; Mineta K., Okabe TH Development of a recycler pmcess for tantalum from capacitor scraps. Journal of Physics and Chemistry of Solids, VoI. 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 Proceia, VoI. 10, 2014, pp. 182-186.

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

Document JPS6475632A refers to a procedure to recover electronic scrap Ta with capacitors. The possibility of dissolving Mn02 in an efficient manner is mentioned in this process by the application, among other means, of H2O2 in an acid medium. The result of separating the Mn02 is treated in order to purify it by conventional methods.

Document US2013336858A1 states that the most applied recovery processes do not allow to obtain a Ta with sufficient purity to be used as a raw material to, for example, manufacture new Ta capacitors as impurities are dragged as Si, Sb, Mn, Sn, Pb , Zn, Fe, Ni, C ^u , To which are present in the PCB ^s where ^the capacitors containing Ta are extracted.

This publication refers to the JP2010214352A in relation to the previous concentration processes (grinding, sieving, magnetic separation, gravity separation and, again, another magnetic separation). T ^he nonmagnetic materials, which remains Ta, are then subjected to an acid treatment with concentrated HCl. In one of the alternatives, the addition of H202 to the treatment is contemplated acid that is mentioned that leads to remove in a slight but superior measure the Cu of the solid substrate. This acid treatment to which it is submitted to the result of the gravimetric and magnetic separation stages 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 carried out, especially to strip of tungsten the solid substrate.

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, VoI.105, Nr.2 (1989), 181-187 specifically refers to the use of H2O2 among other agents for the extraction of Mn02 from the substrate where Ta remains in capacitors from electronic scrap. Among ^the reducing agents applied are Na2S03, H202, as well as FeS04 in sulfuric acid medium. For this reason, H202, together with Na2S03, was the most effective when extracting more than 90% of Mn02 after acting on the substrate for 24 hours at room temperature.

Orlov V M's paper; Kiselev EN Leaching of manganese dioxide from porous bodies; Russian Journal of Applied Chemistry V ^or I. 85, Nr.11 (2012), ^pp. 1699-1702, literally reveals the reduction of Mn02 with H2O2 in H2S04 acid medium (also HCl). It is oriented to the solid electrolyte capacitors, although it does not mention that the capacitors of which the Ta is intended to be recovered are subjected to a previous operation of grinding and gravimetric and magnetic separations.

e x p l ic ation of in v e n c io n

In coherence with what is stated in the section on the state of the art, the approach is to develop a procedure that mainly includes physical operations for the extraction of tantalum from ^the condensers.

If any chemical operation is proposed, it should not affect the existing tantalum nor should it contribute any additional metal elements to the reaction mixture. In this way it is ensured that tantalum remains as such and that it is not contaminated with any additional metallic element.

It is therefore the object of the present invention a method for the recovery of tantalum metal electrolytic capacitors from electronic scrap comprising the following steps:

- controlled breaking of the capacitors in parts with a size between 0.5 and 1 cm

- separation by gravity of the coating surrounding the tantalum electrode

- Magnetic separation of metallic terminals from capacitors containing at least C ^u and Ni

- isolation of the dark material obtained after the previous steps and comprising tantalum metal and Mn02

characterized in that the separation of the metal tantalum from the Mn02 comprises in turn: - grinding the dark material to a size comprised between 0.1 and 0.5 mm

- reduction of Mn02 by treatment with a reducing agent comprising citric acid at a temperature comprised between 200C and 600C for a period of time comprised 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 step to remove manganese citrate

- drying the solid obtained after the washing step at a temperature between 60 ^o C and 200 ^c which contains tantalum metal with at least 99.5% purity.

In a preferred embodiment of the process object of the invention, the capacitors have rectangular prism geometry with volumes comprised between 24 and 240 mm3, the controlled breaking thereof being carried out by crushing.

Alternatively, the capacitors may have other geometries, particularly ellipsoidal.

The separation stage by gravity is carried out by flotation in water, leaving the internal part of the condensers contained in the tantalum metal below. The coating material may be of various types, particularly of fire retardant ^or ceramic epoxy resin.

The magnetic separation stage is carried out 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 method of the invention, the dark material separated in the previous steps must be ground to a size of 0.2 mm and the subsequent reduction of the Mn02 of the dark material with the reducing agent comprising citric acid should be carried out in an agent proportion reducer / dark material comprised between 0.4 gr and 20 g of reducing agent per gram of dark material.

The reducing agent may additionally comprise oxalic acid.

The aqueous solution used for the washing of the resulting solid after the reduction step comprises HCl in the proportion comprised between 3% and 33% by weight of HCl in water and the solid drying step, once washed, is carried out at any temperature between 60oC and 200oC. Tests were carried out at 75qC and in some batches with H2O2 it was dried at 140oc ..

d e s c r ip c io n d a t a n d a y m o d o de r e a l io n s

The first operation of the process of the invention is the breaking of the SMD (Surface Mounting Device) type tantalum electrolytic capacitors, which have sizes of 8x 4.5x4 cm or smaller, which is done by crushing to achieve sizes comprised 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 emerge.

The metal terminal parts are separated from the mixture by means of a 01.25 T magnet that contains metals such as C ^u , Ni and variable quantities 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 internal part by flotation in water. The density difference of this part (smaller than water), of which Ta contains most (metal density 16.65) allows almost complete separation.

The dark colored inner part has to be crushed to a size between 0.1-0.5 mm (150-35 mesh) preferably 0.2mm (70 mesh).

This part is constituted by tantalum and manganese (Mn02) in an average analysis of approximately 74% of Ta and the rest 26% Mn02, in addition to small amounts of other elements.

Table 1. Result of crushing

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

Table 2. Reducers used to reduce Mn (IV)

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 smooth and only with organic additives whose reaction products are C02 and H20 and whose excess if you want to eliminate, 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 drawbacks if it is desired to take advantage of the manganese salts (II) formed as a by-product.

Once the reduction is carried out, it is filtered and the resulting solid is washed in water to eliminate the solution containing manganese citrate (II).

The reduction with oxalate progresses adequately but manganese oxalate (ll) is formed which is insoluble in the medium and difficult to remove by washing and decanting in water

Example

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

A dispersion of 0.9932 g of powder sample (containing 0.2552 g Mn02, 2.94 mmol Mn02) in 10 ml of distilled water is treated with citric acid (1.1304 g, 5.88 mmol), following the following reaction:

9 Mn02 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 with 10 ml of a HCl solution in H20 1:10 and then with distilled water until the water was 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 the fact that 2.9 grams of tantalum have been recovered from 10 grams of starting capacitors.

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

Claims (10)

1. - Procedure for the recovery of tantalum metal electrolytic capacitors from electronic scrap comprising the following stages: - controlled breaking of the capacitors in parts with a size between 0.5 and 1 cm - separation by gravity of the coating surrounding the tantalum electrode - Magnetic separation of the metallic 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 MnO2 by treatment with a reducing agent comprising citric acid at a temperature comprised between 20 ° C and 60 ° C for a period of time comprised 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 step to remove 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, controlled breaking thereof by crushing. 3. Method according to claim 1 or 2, wherein the step of gravity separation is performed by flotation in water leaving the internal part of the condensers containing the metal tantalum below. 4. - Method according to any one of claims 1 to 3, wherein the magnetic separation is performed by applying a magnetic field with flow density between 0.1 and 0.25 T 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. Process according to any one of claims 1 to 5, wherein the grinding of the dark material is carried out up 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 the proportion reducing agent / dark material comprised between 0.4 g and 20 g of reducing agent per gram. of dark material. 8. Process according to claim 7, wherein the reducing agent further comprises oxalic acid. 9. Process according to any one of claims 1 to 8, wherein the aqueous solution used for the washing of the resulting solid after the reduction step comprises HCl in a proportion comprised between 3% and 33% by weight of HCl in Water. 10. Process according to any one of claims 1 to 9, wherein the step of drying the solid, once washed, is carried out at a temperature comprised between 60 ° C and 200 ° C.