Field of the invention

The present invention relates to an innovative hydrometallurgical method for the recycling and recovery of base metals such as copper (Cu), tin (Sn), lead (Pb) and nickel (Ni) and precious metals such as gold (Au) and silver (Ag) from electronic boards or printed circuits of electrical and electronic equipment, typically from electronic boards of personal computers and cellular phones (in particular smartphones).

Present state of the art

The electronic board (printed circuit board or PCB) or printed circuit is an important component of most electrical and electronic equipment (EEE).

The current innovations in the production of these devices have resulted in a significant reduction in the working life of devices and electronic boards (e.g. 2-3 years for cellular phones and 3-5 years for personal computers, etc.).

Consequently, most broken devices are no longer repaired and therefore regarded as waste which is then disposed of mainly in waste tips.

However, the discarding and disposal of said waste electronic boards in waste tips is discouraged also for environmental reasons, and various technologies for processing said boards have been tested in order to reduce the quantity of waste and recover their precious content.

Waste printed circuit boards (WPCB), which are made up of about 60 elements, have attracted a great deal of attention because of their recovery and recycling potential. This is due mainly to their content of precious metals (in particular gold, Au).

Hitherto numerous methods aimed at the recovery and recycling of base metals (i.e. Cu, Sn, Pb, Ni, zinc Zn, iron Fe and aluminium Al) and precious metals (i.e. gold Au and silver Ag) from electronic boards or printed circuits of electronic equipment are known and many form the subject of patent applications or patents.

The technologies for recycling base metals and precious metals known in the art consist of physical/mechanical and chemical procedures for recovery of said metals. With the physical/mechanical procedures, however, it is not possible to obtain complete separation of the valued metals in a single fraction and therefore these procedures are used mainly as a pre-treatment step in a chemical method (see Korean patent application KR 20030006792 A in this respect). Moreover, a physical/mechanical pre-treatment procedure may result in the diffusion, in the air, of small metal particles, especially where particles of gold are involved, these being particularly prone to this reaction.

The chemical procedures for the recovery and recycling of base metals consist in pyrometallurgical, hydrometallurgical or biometallurgical methods (see the patent applications CN 105420500 (A), CN 105297077 (A), CN 106500113 (A), CN 104775034 (A), CN 104328283 (A), EP 2984153 (A2), CN 103801554 (A), CN 103484680 (A), US 2012318681 (Al) and WO 2015052658 (Al)).

Compared to the pyrometallurgical and biometallurgical methods, hydrometallurgical methods have the advantage that the processing operations may be controlled more easily _> said methods also do not result in the emission of toxic fumes, require a smaller outlay and have a faster reaction time.

Pyrometallurgical methods, in particular, require temperatures close to 1200°C and are particularly costly and polluting.

US 2012318681 describes a mechanical/physical/thermal/wet method for the recovery of Cu, Au, Pb, palladium Pd, platinum Pt, Sn, Ag and other metals. Said method involves a first step where the boards are ground, then undergo physical separation by means of air classification and then the copper concentrate which also contains other elements (Sn, Pb, Au, Ag, Pd and Pt) undergoes a heat treatment. Then, by means of hydrometallurgical processes, the selective recovery of the elements is performed. Said method is particularly long and complex (it comprises at least eight steps) and, in order to recover the copper, it involves the use of a solution which contains sulphuric acid, sodium chloride and manganese dioxide (MnOa). As is known, manganese dioxide is self-heating and may catch fire and is harmful for operators and therefore should be avoided.

WO 2015052658 (Al) describes a hydrometallurgical method for the recovery of metals from electronic boards which comprises a leaching step in which the electronic board is immersed in a solution containing at least 20% by weight of nitric acid and with a solid/liquid ratio equal to or less than 1 and wherein leaching is performed optionally in the presence of a peroxide. Said method is intended mainly to recover Sn, Au, Pb, Ag, Fe and Cu.

In any case, said method envisages the use of nitric acid, which is very corrosive and very difficult to eliminate from the waste water which is produced at the end of the process. Moreover, it has been noted that even when using this method the yield levels for recovery of the metals, in particular Sn, Au, Pb, Ag and Cu, which are achieved, and likewise the quality of the metals, are not very high.

There exists therefore the need for a hydrometallurgical method for the recycling and recovery of base metals such as Cu, Sn, Pb and Ni and precious metals such as Au and Ag which overcomes the disadvantages and drawbacks of the methods according to the prior art.

Summary of the invention

A hydrometallurgical method for the recycling and recovery of base metals, such as Cu, Sn, Pb and Ni, and precious metals, such as Au and Ag, from a waste material comprising catalytic converter powder and/or electronic boards of electrical and electronic equipment, has been surprisingly discovered.

The hydrometallurgical method according to the present invention is very simple, does not require a large outlay and is able to achieve a high yield in terms of recovery of the said metals from the surface of the waste material.

The present invention therefore relates first and foremost to a hydrometallurgical method for the recycling and recovery of base metals and precious metals from a waste material comprising catalytic converter powder and/or electronic boards of electrical and electronic equipment, the hydrometallurgical method comprising the following stages:

I) Leaching the base metals and the precious metals from the surface of said waste material by means of immersion of the waste material, if necessary pre-treated, in an acid solution containing water, acetic acid, hydrochloric acid, hydrogen peroxide (H ₂ O-C ₂ H ₄ O ₂ -HCI- H ₂ O ₂ ) and subsequent removal of the waste material from the acid solution as defined above;

II-A) selective recovery of the precious metals silver (Ag) and gold (Au) from the acid aqueous solution obtained in stage I) in the case where said waste material comprises electronic boards of electronic equipment;

III) selective recovery of the base metals copper (Cu), tin (Sn), lead (Pb) and nickel (Ni) from the acid aqueous solution obtained from the stage II-A);

II-B) selective recovery of platinum (Pt) and palladium (Pd) from the aqueous acid solution obtained from stage I) in the case where said waste material comprises catalytic converters in powder form.

The dependent claims describe preferred embodiments of the invention, forming an integral part of the present description.

Brief description of the figures

The Figure shows a block diagram of the hydrometallurgical method according to the present invention.

In the case where the waste material comprises electronic boards of electrical and/or electronic equipment, stage (I) of leaching the waste material, stage II-A) of selectively recovering silver and gold, and finally stage (III) of selectively recovering copper, tin, lead and nickel are performed in sequence.

In the case where the waste material comprises catalytic converter powder, stage (I) of leaching the waste material, followed by stage II-B) for selectively recovering platinum and palladium, are performed in sequence. Detailed description of the invention

In accordance with the present invention the terms "printed circuit" and "electronic board" are used interchangeably.

The electronic board, in accordance with the present invention, may be the electronic board of a personal computer or a cellular phone, such as a smartphone.

Preferably the electronic board used in the hydrometallurgical method according to the present invention is a waste electronic board or a waste printed circuit of a personal computer or a cellular phone, such as a smartphone. In accordance with a particularly preferred aspect of the present invention the electronic board is a waste electronic board of a personal computer.

Said electronic board (or printed circuit), in order to undergo the leaching stage I), must not have electrolytic capacitors containing A1 (aluminium), heat dissipators, batteries, connection peripherals, plastic connectors, transistor-type components and steel components in general. Therefore, if the aforementioned components are present on the electronic board or printed circuit, the board or printed circuit may be pre-treated preferably manually so that said components are removed.

In the case where the waste material to be treated consists of catalytic converters, before subjecting them to the hydrometallurgical treatment grinding of the catalytic converters is performed: in this way the size suitable for the hydrometallurgical process is obtained.

Stage I) of leaching the base metals (Cu, Sn, Pb and Ni) and the precious metals (Au, Ag) from the surface of the waste material is performed by means of immersion of the waste material in an acid solution containing water, acetic acid, hydrochloric acid and hydrogen peroxide (H ₂ O-C ₂ H ₄ O2-HCI-H ₂ O ₂ ): this leaching stage I) is entirely innovative and may be performed in a single step.

In the case of treatment of electronic boards of computers or smartphones, the leaching stage I) according to the present invention may be carried out on all the electronic boards (or printed circuits) of computers or smartphones, without having to shred them, and allows selectively Au, Ag, Cu, Sn, Pb and Ni to be recovered in their metallic or complex form.

An acid solution containing water, acetic acid, hydrochloric acid and hydrogen peroxide (H2O-C2H4O2-HCI-H2O2) in accordance with stage I) of the present method typically contains:

2-5 M, preferably 3 - 4.5 M, hydrochloric acid

2-6 M, preferably 2-3 M, acetic acid;

1-4 M, preferably 1-2 M, hydrogen peroxide.

By way of example of the leaching procedure for electronic boards the following may be used: HC1 (4.20 M), C2H4O2 (2.51 M) and H2O2 (1.47 M). For the leaching of catalytic converter powder, 100 g of material in powder form is immersed in 1 litre of solution of HC1 (3-5 M), C2H4O2 (1-2 M) and H ₂ 0 ₂ (1-2 M).

The concentration of the electronic boards used in stage I) in the acid aqueous solution (H2O-C2H4O2-HCI-H2O2) is equal to about 10- 50% (w/w), preferably about 25-35% w/w, preferably about 30% w/w.

In the case of treatment of catalytic converters, the concentration of the catalytic converter powders in the acid aqueous solution (H2O-C2H4O2-HCI-H2O2) is equal to 10% w/v.

Stage I) according to the method of the present invention, involving leaching in an acid solution, may be typically performed at room temperature and at atmospheric pressure.

Moreover, stage I) of leaching in an acid solution may be performed in a time interval of 1-8 hours, preferably 2-4 hours, with or without stirring, preferably with stirring.

In the case of waste material consisting of electronic boards, once leaching has been completed, the electronic boards may be removed from the acid solution and, if necessary, immersed in washing water.

In the water used for washing the boards, the integrated chips, the multilayer capacitors and the Ta (tantalum) capacitors) are separated from the surface of the electronic board.

In the case of waste material consisting of catalytic converter powder, once leaching has been completed, the catalytic converter residue must be separated from the solution by means of filtration and then washed with water. Stage II-A) of the present invention relates to the selective recovery of the precious metals silver (Ag) and gold (Au) from the acid aqueous solution obtained from stage I) in the case where said waste material comprises electronic boards of electrical equipment.

With reference to stage II-A) of the method according to the invention, in order to recover selectively the silver (Ag), the acid aqueous solution obtained from stage I) may be cooled to a temperature of between about 0°C and about 10°C, preferably to about 4°C, until a precipitate of silver chloride (AgCl) is obtained.

The precipitate of AgCl may be separated by means of methods known in the art, for example by means of filtration of the suspension, typically using a Buchner filter. Generally, AgCl is obtained with a yield of 70% and purity greater than 50%.

As regards the selective recovery of Au (stage II-A), the acid aqueous solution resulting from stage I) is subjected to the following treatments:

a) extraction using methyl isobutyl ketone (MIBK) and then the resultant organic solution comprising MIBK is subject to stripping/precipitation of Au using an oxalic acid solution;

b) treatment with ascorbic acid in order to reduce the gold to its metallic form.

For extraction in accordance with the method a), the ratio (v/v) of aqueous solution to methyl isobutyl ketone is between 2:1 and 5:1 and preferably 20 ml of MIBK per 100 ml of aqueous solution are used, the aqueous solution/MIBK ratio being therefore 5:1.

The step of extracting the acid aqueous phase using the same 20 ml of MIBK is repeated at least twice, preferably three the resultant organic solution with MIBK thus obtained is then separated from the aqueous solution, which is then sent to stage III) of the method according to the invention.

The gold is stripped and precipitated as metallic gold (Au°) from the resultant organic solution with MIBK by means of addition of a solution of oxalic acid which typically has a concentration of 5-10% (w/v), preferably 5% (w/v). Typically a (volume) ratio of oxalic acid solution and organic solution equal to 1:1 v/v is used. Preferably 20 ml of oxalic acid for every 20 ml of organic solution with MIBK are used.

The selective recovery of the gold may be performed at a temperature of between about 80° and about 100°C, preferably between about 85°C and about 90°C for a time period in the range of about 2-8 hours, preferably in the range of about 3-5 hours.

The solid precipitate of metallic gold (Au°) may be separated by means of methods known to the person skilled in the art, for example by means of filtration of the suspension, typically by means of filtration using a Biichner filter. Said precipitate of metallic Au may be further washed with water, preferably distilled water. The gold is obtained with a yield greater than 90% and purity of 50%.

Then, the selective recovery of the gold is completed using ascorbic acid in a concentration of between 0.005 - 0.05 M with stirring for 1 hour at room temperature. The precipitate is separated from the solution by means of filtration and then washed with water. The recovery of the Au is 100% and the purity of the precipitate is equal to 1%.

In stage III) of the method according to the present invention, Cu is recovered selectively from the aqueous solution obtained in stage II-A) by means of case hardening with metallic Sn. In this connection, for the case hardening step a quantity of metallic Sn equal to about 80% of the stoichiometric quantity of metallic Sn required by the reaction is added, depending on the quantity of Cu present in the solution.

Typically, 2-3 g of metallic Sn for every 100 ml of aqueous solution obtained in stage II-A) are added. In any case, depending on the quantity of Cu present in the aqueous solution, the quantity of metallic Sn added may vary typically between about 1 g and about 5 g for every 100 ml. v

The case hardening reaction for selective recovery of Cu may be performed for a time interval of between about 1 and 8 hours, preferably about 1-2 hours, preferably while stirring, more preferably at a stirring speed of about 200-400 rpm. At the end of the reaction the precipitate of metallic Cu is separated by means of methods known to the person skilled in the art, typically by means of filtration of the suspension, for example using a Biichner filter and if necessary washed with water (preferably distilled water). The copper is recovered with a 98% yield and 97% purity.

Sn, Ni and Pb may be recovered from the acid aqueous solution obtained from stage II-A) rich in SnCh, by means of co-precipitation in the presence of oxalic acid.

For the co-precipitation, the oxalic acid may be added to the solution in a stoichiometric reaction quantity, or less than 20% of the stoichiometric quantity, considering the quantity of Sn present in the solution.

Typically 2g of oxalic acid for every 100 ml of solution obtained are used. In any case, the quantity of oxalic acid may vary depending on the quantity of Sn present in the solution.

In this connection, for every 100 ml of solution, 1 g to 10 g of oxalic acid, preferably 2-4 g of oxalic acid for every 100 ml of solution, and more preferably 2 g of oxalic acid for every 100 ml of solution obtained from stage II-A), may be added. Said step may be performed while stirring, typically at a speed of 200-400 rpm, typically at room temperature and at atmospheric pressure.

This reaction may take place in a ti e interval of between 1 and 8 hours, preferably in a time interval of 1-2 hours. Once the reaction has been completed, the precipitates are typically separated by means of filtration of the suspension using a Biichner filter and preferably washed with water, more preferably with distilled water.

Co-precipitates of Sn, Pb, Ni in the form of oxalates with a yield of 70-80% and a purity of 99% are obtained. Said percentages are expressed as w/w.

Stage II-B) of the present invention relates to the selective recovery of platinum and palladium from the aqueous acid solution obtained from stage I) in the case where said waste material comprises catalytic converters in powder form.

Palladium and platinum are recovered from the acid aqueous solution obtained from stage I) by means of case hardening using metallic iron in powder form. In this connection, the process is performed using metallic Fe in a concentration of 1-10 g/1 for a time period of 2-4 hours, preferably with a stirring speed of 200-300 rpm. Once the reaction has been completed, the solid precipitate is recovered from the solution by means of filtration and then washed with water. The recovery obtained for the Pd and Pt is 100% and 60%, respectively, with a precious metal content of 59%.

The following examples illustrate in a non-limiting manner the hydrometallurgical method according to the present invention.

EXAMPLES

Example 1 (treatment of boards)

100 g of waste electronic boards, from which A1 electrolytic capacitors, heat dissipators, batteries, connection peripherals, plastic connectors, transistor-type components and steel components in general were manually removed, were immersed in 332 ml of an acid aqueous solution containing 116 ml of HCL (4.2 M), 48 ml of C2H4O2 (2.51 M) and 50 ml of H2O2 (1.47 M). The leaching reaction was carried out at room temperature and at atmospheric pressure and lasted about 3 hours. At the end of the reaction the waste electronic boards were removed and washed in water. In the washing water, the integrated chips, the multilayer capacitors and the Ta (tantalum) capacitors were separated from the surface of the electronic board.

The acid aqueous solution obtained from the leaching stage I) was subjected to recovery of the silver as AgCl by means of precipitation from the acid aqueous solution by means of cooling to a temperature of about 4°C. Said precipitate was separated by means of filtration using a Buchner filter.

The AgCl precipitate was obtained with a yield of 70% and a purity greater than 50%. The aqueous solution thus obtained, following separation of the AgCl precipitate, was subjected to extraction with methyl isobutyl ketone (MIBK), using 20 ml of MIBK for every 100 ml of aqueous solution. The extraction was carried 3 times using the same 20 ml of MIBK. Once the operation had been completed, the resultant organic solution of MIBK was subjected to stripping/precipitation/ reduction of its Au content using oxalic acid.

For this treatment, a volume of 20 ml of oxalic acid in a concentration of 5% (w/v) was added to the organic solution with resultant MIBK. After 3.5 hours of continuous stirring at a temperature of 90°C and subsequent cooling of the organic solution to room temperature, the precipitate of metallic gold (Au°) was recovered by means of filtration. A precipitate with a purity of 50% and a total recovery of 90% was obtained.

A treatment with ascorbic acid in a concentration of 5g/l resulted in the recovery of all the Au from the solution: the treatment was carried out at room temperature with stirring for 1 hour at 250 rpm. After separation of the metallic Au precipitate from the solution by means of filtration and subsequent washing with water, a product with 1% purity was obtained. Thereafter every 100 ml of aqueous solution resulting after extraction with MIBK were treated with 2.9 g of metallic Sn. The treatment was carried out while stirring (at 300 rpm) for 2 hours and then the precipitate of metallic Cu was separated from the aqueous solution by means of filtration. A total recovery of Cu greater than 90% with 97% purity was obtained.

2 g of oxalic acid were added in the aqueous solution after recovery of Cu and stirring was performed at 200 rpm at room temperature for 1 hour. With this process the co-precipitation of Sn, Ni and Pb as oxalates was obtained. The recovery of Pb and Ni was greater than 70% and 80% for Sn and the purity of the co-precipitates was 99%. Moreover, the recovery of metallic Sn from the solution obtained after the recovery of Cu was performed using metallic zinc in powder form. The reducing agent was added to the solution in an amount greater than 100% with respect to the stoichiometric quantity. The reaction time was 1 hour. The operation was carried out at room temperature with continuous stirring at a speed of 250 rpm.

Once the reaction had been completed, the metallic Sn precipitate was recovered from the solution by means of filtration and washing with water. At the end of the test a recovery yield of 90% with a purity of 95% was obtained. Example 2 (treatment of catalytic converters)

The catalytic converters were ground using a planetary mill to a size smaller than 0.5 mm. 10 g of powder obtained were added in an acid aqueous solution comprising HC1 (5 M), H2O2 (1 M), C2H4O2 (1 M) and H2O.

The treatment was carried out for 3 hours at a stirring speed of 250 rpm at room temperature. The solid residue was then separated from the solution by means of filtration and washed with 30 ml of H ₂ 0. The recovery of Pd and Pt was equal to 100% and 90%, respectively.

Thereafter, in order to obtain the recovery of Pd and Pt from the solution, 7.5 g/1 of metallic Fe in powder form were immersed in the solution. After 2 hours stirring at a speed of 250 rpm at room temperature, the co-precipitate of Pd and Pt was separated from the solution by means of filtration and then washed with water. The recovery efficiency was 100% for Pd and 70% for Pt. The co-precipitate had a content of 12.4% palladium and 47% platinum.

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