ECO-FRIENDLY METHOD FOR RECYCLING ELECTRONIC WASTE

Field of the Invention

[0001] The present invention relates to the field of electronics, chemical engineering and environment, particularly to the field of electronic waste management and methods for recycling valuable metals.

[0002] The present invention relates to a method for recovering valuable metals contained in waste electronic material, particularly printed circuit boards, and more particularly, to a method for recovering gold fingers from waste printed circuit boards by separating several layers using an organic solution and then separating the gold fingers from the non-metallic and base metal components using a magnetic separation process.

Background of the Invention

[0003] Electronic waste is created when an electronic product is discarded after the end of its useful life. The rapid expansion of technology and the consumption driven society results in the creation of a very large amount of e-waste in every minute.

[0004] Electronic waste is considered the fastest-growing waste stream in the world with million tonnes of waste generated every year. Waste electrical and electronic equipment (WEEE) is generated globally, with an increasing annual growth rate ¹ .

[0005] Nowadays, the production of modern Electric and Electronic Equipment (EEE) requires the use of scarce and expensive resources, as it is the case of gold. According to industry information's, it is estimated that, currently, around 300 tons of Au are used in the production of new printed circuit boards (PCBs). Therefore, considering the high price of gold, the isolation of this raw material from obsoletes PCBs is a worldwide attractive business niche for the recycling companies. [0006] WEEE contain 3-5% of PCBs, which are the most valuable part of WEEE. PCBs are constituted by a heterogeneous mixture of metals, ceramic and plastics, such as fiber glass. Among these fractions, the driving force for recycling waste PCBs is the recovery of metals, particularly precious metals (PMs), such as gold.

[0007] Electronic scrap components contain potentially harmful materials such as lead, cadmium, beryllium, or brominated flame retardants (BFRs). Recycling and disposal of electronic waste may involve significant risk to health of workers and their communities.

[0008] Rapid changes in technology, changes in media (tapes, software, MP3, etc.), falling prices, and planned obsolescence have resulted in a fast-growing surplus of electronic waste around the globe.

[0009] Currently, in developed countries, the recovery of PMs from PCBs is mainly performed in the smelters via pyrometallurgy followed by hydrometallurgical refining but this technology presents important drawbacks, such as the loss of PMs, generation of hazardous emissions (namely dioxins plus flue dust containing metals) and is very energy intensive.

[0010] From the methods known from the state of the art to recycle electronic waste, the following were considered to be relevant to highlight the problem solved by the present invention.

[0011] Document JP2001064735A discloses a method that recovers gold and other PMs from waste PCBs of waste mobile phones. The invention in JP2001064735A relates to a method and a system for collecting gold and other PMs from a portable telephone set or the like. In JP2001064735A, the cut is referred to as "crushing", indicating that there is not a specific technique to cut the PCBs. Additionally, in JP2001064735A the separation of metals is obtained via a molten metals furnace, which operate at very high temperatures.

[0012] The method of crushing the waste material, namely PCB's, has several disadvantages, namely forming potentially harmful dusts, losing part of the valuable metals in the electronic waste material, namely gold and platinum and being environmentally unfriendly due to the high energy waste. [0013] Document WO 2010/055489 relates to a method for treating materials containing a mixture of plastic and metal materials in electronic waste. This method includes crushing the material (20 to 30 mm) to be treated following a pyrolysis (between 300 and 600 °C) of the crushed material. After the pyrolysis process, a first magnetic separation is performed to separate the ferrous metal fraction (iron and iron derivatives) from the non-ferrous material (aluminum and zinc). Subsequently, a second magnetic separation is performed to the non-ferrous fraction to separate the nonferrous metal fraction from the non-magnetic residue (copper, lead, tin, fiber glass and PMs, such as Au and Pt). This document suggests the recovery of the PMs, namely gold, contained in the non-magnetic fraction. It is described the use of sulphuric acid followed by electrowinning to recover copper. This document does not disclose any specific procedure or method to recover a valuable metal, namely gold, from the electronic waste.

[0014] Document US 7867317 discloses a method for recovering valuable metals contained in waste PCBs. The method uses organic solvents for liberating metal and plastic laminated in waste PCBs and then separation and recovery of the liberated metal components using an electrostatic separation process. The process includes:

(a) heating and stirring the waste PCBs after putting them into an organic solvent.

(b) cleaning and optionally drying the metal and the plastic after separating the metal and the plastic by filtering them out.

(c) recovering the metal from a mixture of the metal and the plastic dried using an electrostatic separation process.

[0015] In document US7867317, the optimum condition was described as cutting the waste of PCBs in size of 7 mm, 5mm, and 3mm and the cut waste of PCBs put into a beaker of N,N-Dimethyl formamide (DMF) (solid/liquid ratio of 1:10). The temperature used during the process was 130° C and the stirring was performed for 1 hour at a revolution velocity of 900 rpm. Subsequently, the dried components pass through the electrostatic separation process, thereby obtaining the metal recovery rate of 99.99 %. The separation is performed by an electrostatic separation process allowing to separate only metals and non-metals, not specifying the amount of the gold recovered or even in what way they can separate the gold from other base-metals present in the metal fraction.

[0016] Unlike document JP2001064735A, the method of the present invention presents a different cut of the waste of PCBs focused on the connecting terminals containing the gold fingers from the PCBs that allows an increase in the amount of recovered gold. Additionally, the method of the present invention allows complete separation of gold fingers, copper laminates and plastic fraction through magnetic separation.

[0017] Unlike W02010/055489, the method of the present invention leads to a complete delamination of the several constituent layers of PCBs or other electronic waste allowing to obtain copper layers separated from the gold fingers and the plastic fraction.

[0018] The magnetic separation performed in the method of the present invention allows to easily separate the metallic fraction of the electronic waste, namely gold fingers, which contains the PM, namely gold, from the copper foils and the plastic fraction. In the present method, it was found that the gold fingers can be magnetized by an external magnetic field and, thus, being easily separated from the other components (copper layers and fiber glass) of the mixture.

[0019] In a surprising way, the method of the present invention performs a different cut of the waste of PCBs or other electronic waste. The cut of the present invention is focused on the connecting terminals containing the gold fingers from the electronic waste, particularly PCBs, allowing an increase in the amount of gold recovered. Secondly, the present method is performed in a low-pressure reactor. The increase of the pressure in the organic swelling process decreases the time of the complete delamination of the metal and plastic laminates in waste PCBs. In the present method, the complete separation of the copper laminates, the gold fingers and the plastic fraction occur preferably in 30-20 minutes, half the time reported in document US7867317 (1 h).

[0020] In an embodiment, the optimum conditions of the present invention were obtained using different organic solvents, preferably N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO) accompanied by a gold fingers recovery ratio of 98.3 and 97.1 % respectively, via this organic swelling pressure-assisted and magnetic separation process. Additionally, the method of the present invention regards the separation process of the obtained wet or dried metal and plastic fractions after the organic swelling. In the present method, the gold fingers can be easily separated and recovered from the copper laminates and the plastic fraction through a magnetic separation since they possess magnetic properties.

[0021] Documents CN1313208C, CN109609767A and CN101100706A are also outlined to enhanced the problem solved by the present invention.

[0022] The most critical step in recycling PCBs is to separate metallic components from the non-metallic components through removing or degrading the organic materials. Several recycling technologies using mechanical, chemical and thermal approaches have been searched for that purpose. Nowadays, the available technologies do not allow to recover gold fingers plus copper in an efficient and environmentally friendly manner and with a lower carbon footprint. Milling or pulverization are common methods for that, but they generate a large amount of dusts and there is also a high energy consumption and losses of PMs. Also, pyrometallurgical followed by hydrometallurgical refining processes, used in the smelters, present important drawbacks as for example loss of PMs, generation of hazardous and toxic emissions, like dioxins and furans substances, and high energy consumption ²

[0023] A friendly method for the complete delamination of waste PCBs consists in dissolving the brominated epoxy resin (BER) in an appropriate organic solvent ³ ' ^4,5 . This dissolution allows to destroy the reinforced multi-layered PCBs structure and, thus, the enveloped metals are liberated.

[0024] One of the main advantages of this method is that the BER does not decompose and does not produce toxic gases. However, the most critical point (yet to be solved) corresponds to the subsequent efficient separation of the various metallic elements (gold fingers and copper laminates) from the non-metallic fraction (glass fiber), which is crucial if the desirable aim is to recycle selectively all valuable components, in particular gold.

[0025] These facts are outlined to enhance the problem solved by the present invention. General Description of the Invention

[0026] The present invention discloses a new method for recovering valuable metals, particularly gold, from PCBs or other electronic wastes, by separating several polymeric layers using organic solvents and separating the non-metallic and other base metal components from gold fingers using magnetic separation with sieving.

[0027] In an embodiment, the choice of the waste PCBs was targeted at random access memories (RAMs), graphics and soundboards, and ethernet boards of WEEE due to the high concentration of gold on their composition.

[0028] The new methodology developed by the inventors is addressed to fill the need for a more efficient and environmental-friendly process for recycling valuable metals from electronic waste, in particular for recycling gold, copper and glass fibers from waste PCBs.

[0029] End-life PCBs may contain up to 60 different chemical elements and have a metal content as high as 40% by weight. PCB is a thin board made of epoxy resin and glass fiber, which is coated with a layer of thin copper laminate. The metals in PCB substrate are in the forms of copper laminates (10-27% of PCB mass) and the coatings [tin, nickel, gold, silver, etc.] on the surface of copper layers, pins and holes that increase conductivity and oxidation resistance. The levels of PMs vary considerable depending on the age of the device. The basic structure of the PCBs is the copper layer, glass fiber- reinforced epoxy resin and several metallic materials.

[0030] In a particular embodiment, the present work relates to a new method for recovering valuable metals, particularly gold from PCBs, by separating several non- metallic layers using an organic solution and separating non-metallic components and copper laminates from gold fingers using magnetic separation with sieving.

[0031] In an embodiment, the choice of the waste PCBs is targeted at random access memories (RAMs), graphics and sound boards, and ethernet boards from personal computers and laptops due to the high concentration of gold on their composition ⁶ . The person skilled in the art will acknowledge the existence of other targets as for example processors for laptops, desktops, cell phones, servers, discs and the like. The scope of the present invention is not limited to the components herein described. [0032] In an embodiment, the method for liberating and recovering gold from wastes

PCBs includes, as shown in Figure 1: a) cutting the connecting terminals containing gold fingers from the PCBs using a mechanical process (for example a guillotine or a rotary knife), b) optionally placing the cut PCBs connected terminals in an overnight process with stirring in an appropriate organic solvent, c) performing an organic swelling in a low-pressure reactor with heating and stirring and finally, d) using magnetic separation process followed by sieving to recover the gold fingers from a mixture of the copper laminates and the NMF, optionally dried previously.

[0033] In optimum conditions, the global yield recovery of gold fingers ranged from 97.1 to 98.3 %.

[0034] Other important additional advantages of this process when compared with the main current technologies, is based on the simplicity, rapidity and environmentally friendly character of the developed method to isolate valuable metals from electronic waste. Additionally, it does not require sophisticated equipment as for example complex air extraction systems.

[0035] Furthermore, the combination of the physical and chemical processes proposed in this invention leads to an easy scale-up technology for industrial application.

[0036] Taking this into account, the new method of the present invention allows separating the non-metallic and the two main metallic components (gold fingers and copper laminate) from the waste PCBs by separating the several laminated layers via simple use of organic solvents and obtaining a high gold recovery ratio, via this organic swelling pressure-assisted and magnetic separation process.

[0037] The method of the present invention has the advantages to provide a smart process that can minimize the generation of wastes, namely, dusts and wastewaters containing metals, energy consumption and equipment space. Furthermore, other important additional advantages of the present method, when compared with the main current technologies, is based on the simplicity, time and environmentally friendly character of the process developed to recover gold with high yield from the wastes PCBs.

[0038] The technical feature of cutting the connecting terminals containing valuable metals from electronic waste using a mechanical process, for example a guillotine, a rotary knife or a grinder is of extreme relevance. The specific cut (Figures 2 and 3) of the connecting terminals containing valuable metals from the electronic waste allows the pre-concentration of the gold from the overall amount of electronic waste and benefits the separation and recovery in the subsequent steps. A different cut of the electronic waste, such as PCBs waste, focused on the connecting terminals containing the gold fingers from the waste allows an increase in the amount of recovered gold or other valuable metal.

[0039] The optional technical feature consists in placing the cut PCBs or other electronic waste connected terminals in a pre-swelling process with stirring in an appropriate organic solvent. The specific cut performed in the electronic waste is an important aspect of the present invention since it provides a high contact surface with the organic solvent during the subsequent swelling step in the low-pressure reactor, allowing the effective separation between the gold fingers or other valuable metal layers from the copper laminates and plastics fraction under mild conditions, preferably in less than one hour, more preferably in less than 45 minutes, even more preferably in less than 30 minutes, and most preferably in 20 minutes.

[0040] The technical feature of performing an organic swelling in a low-pressure reactor with stirring is of the utmost importance. The swelling step using organic solvents for promoting the separation of the metallic and non-metallic parts of the electronic waste belongs to the state of the art, but the optimized conditions of the present invention, namely the duration of the swelling step and the dimensions of the cut pieces provide an unexpected result. The method of the present invention is performed in a low- pressure reactor and it achieves complete separation in half the time of the usual processes known from the state of the art.

[0041] The technical feature of isolating gold fingers from a mixture of the copper foils and the fiber glass using a magnetic separation process with sieving is also very relevant. The separation process proposed for gold fingers recovery from the non-metal and other base-metal components after organic swelling using magnetic separation with sieving is novel and inventive and provides an efficient, clean and easy way to separate the gold layers from the mixture containing copper and plastic layers.

[0042] For "low-pressure reactor" it shall be understood as a sealed vessel (reactor) in which the process of the present invention is performed under enough pressure to promote the technical effect of complete delamination of the waste PCBs. In a particular embodiment of the present invention, with no limitation of the scope of the same, for "low-pressure reactor" it shall be understood that a reactor performing the process of the present invention under a pressure from 1 to 10 atm is covered. Nevertheless, this parameter shall be interpreted in the broadest manner in the sense that the pressure depends on the volume of the sealed vessel (reactor), the volume of the solvent and temperature, the type of solvent itself and all these factors combined.

[0043] For "mechanical process" it shall be understood any mechanical process suitable for performing the cut of electronic waste, preferably PCB's.

[0044] For "pre-swelling" it shall be understood any type of swelling performed before the swelling step of the process of the present invention.

[0045] For "metal components" it shall be understood the metallic fraction of the electronic waste.

[0046] For "organic solvent" it shall be understood any carbon-based substance capable of dissolving or dispersing one or more other substances. By "organic solvent" it shall also be understood the mixture of two or more organic solvents as well as the mixture of different functional groups in the same molecule of organic solvent.

[0047] For "polymeric components" it should be understood any plastic, resin and fiber glass components.

[0048] For "non-metallic fraction" it should be understood any non-metallic components, such as fiber glass and polymeric components. Detailed Description of Figures

[0049] Figure 1. is a flow diagram of the overall procedure for recovering gold fingers (plus copper layers and other non-metallic fraction) from the waste PCBs according to the present invention.

[0050] Figure 2. Connector's terminals containing gold fingers before treatment (A); approximate length (B) and width (C) of connector's terminals containing gold fingers before treatment.

[0051] Figure 3. Schematic drawing of a cut and its average length (15 mm), average width (0.2-7.0 mm) and its average height (4 mm).

[0052] Figure 4. Separated components obtained after the swelling of the waste PCBs constituted by glass fibers, gold fingers and copper laminates using NMP as solvent. The experimental conditions were solid/liquid ratio of 1:10, waste PCB area/size of 60 mm ² /15x4 mm, at 150 °C for 30 min with pressure, without overnight and velocity of 1000 rpm.

Detailed Description of the Invention

[0053] After cutting the connecting terminals from the waste PCBs into an appropriate size using a cutting tool, such as a grinder, a knife rotary or a guillotine, the cut pieces are putted into an appropriate organic solvent listed below and then optionally stirred (pre-swelling process), which will help the liberation of the metallic and non-metallic components from the waste PCBs in the subsequent swelling process. In the specific case of the results presented herein, the cut waste of PCBs is preferably put into the organic solvent (in a solid/liquid ratio of 1:10 g/mL or preferentially 1:5 g/mL) for an optional period of 17 hours with a stirring of 600 rpm.

[0054] The mixture resultant from the optional pre-swelling (pre-swollen cut waste of PCBs together with the organic solvent) or the cut waste of PCBs (in a solid/liquid ratio of 1:10 g/mL or preferentially 1:5 g/mL) is preferably put into a low-pressure reactor using stirring to efficiently cause the dissolution of the BER using one or a mixture of organic solvents. The solvents can be chosen among others: amides [such as dimethylformamide (DMF), dimethylacetamide (DMA), hexamethylphosphoramide (HMPA)], ketones [such as, methylethylketone (MEK), cyclohexanone, cyclopentanone, acetone], lactones [such as y-butyrolactone, y-caprolactone, y-valerolactone, s- caprolactone], sulfoxides [such as, dimethyl sulfoxide (DMSO), diethyl sulfoxide], lactamas [such as N-methylpyrrolidone (NMP), N-ethylpyrrolidone, N- propylpyrrolidone, N-buthylpyrrolidone], carboxylic acids [such as acetic acid], sulfonic acids [such as methanesulfonic acid], alcohols [such as, tetra hydrofurfuryl alcohol (TFA), propan-2-ol, butan-l-ol, ethanol], esters [such as, dimethyl malonate, ethyl acetate, butyl acetate, terc-butyl acetate, methyl ethanesulfonate], aromatics solvents [such as, phenol, benzene, m-cresol, N,N-difluorobenzene], amines [such as, pyridine, N,N'- diethyl-l,2-ethanediamine, 4-methylpyridine, 3-methyl-l-hexanamine] , nitrile [such as, acetonitrile, decane nitrile], ethers [such as dioxane, tetrahydrofuran (THF)] and ionic liquids [such as l-n-butyl-3-methylimidazolium chloride, l-ethyl-3-methylimizadolium tetrafluoroborate]. Additionally, not excluding solvents with mixtures of functional groups, such as diacetone alcohol, ethyl acetoacetate, ethyl pyruvate.

[0055] The stirring is preferentially but not restricted performed at a rotation rate ranging from 600 to 1000 rpm at a temperature range between 60 °C to 250 °C, depending on the boiling point (Bp) of the solvent, with pressure during a sufficient period of time, in the specific case of the results presented, 30 minutes were used to efficiently cause the optimum dissolution of the BER using the organic solvent and, consequently, the liberation of the non-metallic and metallic layers.

[0056] After swelling is performed, it is preferable to recover the metallic and non- metallic fractions, along with collecting the organic solvent via solid-liquid separation step. After the solid-liquid separation, the solid fraction containing the metallic and non- metallic components recovered are subject to an optional drying step, and then the gold laminates are separated from the copper foils and the non-metallic fraction using magnetic separation process with sieving. The separation process is carried out using magnetic separation.

[0057] In an embodiment, the sieving process allows separating the large fibers using sieves preferably from 0.707 to 2mm, remaining the recovered gold fingers separated.

[0058] In an embodiment, for the remaining components (fiberglass, copper and other base metals), the copper and other base metals are separated from the non-metallic fraction recovered using an established process, such as electrostatic separation. In a preferred embodiment, the used organic solvent is recycled by evaporation.

EXAMPLES

Example 1 - Delamination of the multi-layered structure of waste PCBs

[0059] Table 1 summarizes the gold fingers recovery yield results achieved according to the present method, after organic swelling with each described solvent followed by magnetic separation.

Table 1. Gold fingers recovery yield at the end of the proposed method with various organic solvents studied. All experiments were performed using stirring ranging from 600 to 1000 rpm velocity with pressure for 30 minutes for a solid/liquid ratio of 1:10 g/mL (* solid/liquid ratio of 1:5 g/mL). The present results have shown that high yield recoveries of the gold fingers and complete delamination was achieved with the DMSO and NMP solvents (Figure 4), NMP being a more appropriate solvent than DMSO. This can be due to the physical, chemical and structural properties of the NMP, although both being aprotic polar solvents.

Example 2

[0060] The connecting terminals from the waste PCBs are cut in a size area of 60 mm ² (15x4 mm) using a guillotine, 3g of the cut waste of PCBs is put into 30 mL of NMP (solid/liquid ratio 1:10 g/mL) into a low-pressure reactor made of stainless steel using two magnetic helical stirrers. The temperature is kept at 180 ² C and the resultant pressure achieved was about 3 atm. The stirring is performed for 30 minutes at a revolution velocity of 600 rpm. After the stirring finished, the swollen residue is separated from the organic solution via the filtering process and then dried. Subsequently, the dried residue is put into a flask under a stir plate for the separation process. The separation process is carried out using a magnetic stirrer at a revolution velocity of 600 rpm for 30 minutes. The gold fingers attracted to the magnet are then recovered. Additionally, to increase the recovery rate of the gold fingers, they are passed in a sieve with 2 mm and successively to another one of 0.707 mm. At the end of this method, the gold fingers are recovered with a rate of 98.3 % plus a mixture of fiber glass and copper layers.

Example 3

The connecting terminals from the waste PCBs are cut in a size area of 60 mm ² (15x4 mm) using a guillotine, 3g of the cut waste of PCBs is put into a goblet containing 30 mL of DMSO (solid/liquid ratio 1:10 g/mL) and, then, stirred at a rotation of 600 rpm for 17 hours (pre-swelling). After the pre-swelling, the content of the goblet is transferred into a low-pressure reactor made of stainless steel using two magnetic helical stirrers. The temperature is remained at 180 °C and the resultant pressure achieved was about 3 atm. The stirring is performed for 30 minutes at a revolution velocity of 900 rpm. After that, the swollen residue is separated from the organic solution via a solid-liquid separation and the solid is dried at a temperature of 80 °C in a vacuum oven. Subsequently, the dried residue is put into a flask under a stir plate for the separation process. The separation process is carried out using a magnetic stirrer at a revolution velocity of 600 rpm for 30 minutes. The gold fingers are attracted to the magnet and, thus, recovered from the remaining mixture. Additionally, to increase the recovery rate of the gold fingers, the dried residue is passed to a sieve with 2 mm and successively to another one of 0.707 mm. At the end of this method, the gold fingers are recovered with a rate of 97.1% plus a mixture of fiber glass and copper layers.

[0061] It is an object of the present invention to apply the process of the present invention at an industrial level, being within the scope of the present disclosure sieves with diameters other than the aforementioned, in particular from 0.5 to 5 mm.

[0062] Scaling the process of the present invention to an industrial level shall require the necessary adaptations, which a skilled person in the art should be aware of, without requiring the use of inventive skills.

[0063] Concerning magnetic separation of the gold fingers from the fiber glass and the copper laminates is easily achieved using a novel method based on magnetic separation with sieving. This is possible due to the presence of nickel in the composition of the gold fingers, which presents magnetic properties and can be attracted to a magnet and be easily separated from the mixture of fiber glass and copper laminates, as it is shown in Figure 4.

[0064] In an embodiment, the present disclosure describes a new process to recycle valuable metals, particularly gold fingers from waste electronic material, particularly PCBs. For this purpose, the combination of a swelling step of the cut connecting terminals containing gold from the waste PCBs, performed in a closed reactor, followed by the magnetic separation with sieving of the swollen mixture provides a rapid, efficient clean and easy way to separate the gold fingers from the other components (without dust formation). Subsequently, copper laminates can be recovered from the non- metallic fraction by applying an electrostatic separation process of the remaining mixture. [0065] As will be clear to one skilled in the art, the present invention should not be limited to the embodiments described herein, and a number of changes are possible which remain within the scope of the present invention.

[0066] Of course, the preferred embodiments shown above are combinable, in the different possible forms, being herein avoided the repetition all such combinations.

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