EP4259408A1

EP4259408A1 - Plastics and glass recovery from end-of-life photovoltaic panels

Info

Publication number: EP4259408A1
Application number: EP21835837.2A
Authority: EP
Inventors: Luigi Toro; Pietro ALTIMARI; Ludovica Maria BALDASSARI; Emanuela Moscardini; Francesca Pagnanelli
Original assignee: Eco Recycling Srl
Current assignee: Eco Recycling Srl
Priority date: 2020-12-09
Filing date: 2021-12-07
Publication date: 2023-10-18
Also published as: IT202000030176A1; WO2022123444A1

Abstract

The invention relates to a process for the treatment of photovoltaic panels at the end of their life and has the aim of recovering plastics and especially high-purity glass, to put them back on the market as secondary raw materials. The process involves a mechanical treatment of grinding and physical detachment of the adhesives from the other components (glass and other plastics) and further chemical treatments of the plastics and of the fine glass fraction for the recovery of metals in order to obtain an enhanced solid residue. The process allows to reach and exceed the minimum material recovery target set by the European directive 2012/19/EU and equal to 85% by weight.

Description

Plastics and glass recovery from end-of-life photovoltaic panels

Technical field

The present invention refers to the recovery of plastics and glass from photovoltaic panels at the end of their life. The invention also includes the recovery of the metals present in said panels.

Prior art

Solar panels pose an environmental problem as, when their useful life is over, they become a form of hazardous waste. The recycling of solar panels has gradually become an important environmental issue not only for the metals they contain, largely made up of heavy metals (lead, tin and cadmium) but also because the incorrect treatment of these waste involves a large production of waste whose destiny is to landfill.

Therefore, the recovery of solar panels can reduce energy waste and environmental pollution and also the recycling of the materials thus recovered can effectively reduce production costs.

There are various types of photovoltaic panels, but generally their structure can be schematized as a sandwich system (figure 1 ) which coomprises glass, adhesives (typically EVA), photovoltaic cell, anti- reflective layer in precious plastics (for instance fluoride, typically Tedlar®), junction boxes, aluminum frame, the latter two components that are previously separated before the recovery treatments of metals, glass and plastics.

Currently the recovery processes are particularly focused on the enhancement of the metals of the solar cells and little has been done on the recovery of the glassy part, which instead constitutes about 70% of the panel and which is often recovered with ineffective techniques or remains as a degraded part in metal recovery processes and is disposed of as waste. Instead, it should be emphasized that the glass used in solar panels is a material with a high added value. In fact, according to current prices, cement glass has a value close to € O/ton, common recycling glass has a value of approximately € 52/ton (Recycling - secondary material price indicator, Eurostat, Source: Statistics Explained (htl s:Z/eo,eurQpa^eu/eurQS at/sta istjCsexpfeined/) - 21/10/2020) while solar glass for panels has an economically high value that exceeds> 100 €/ton (recycled crushed glass, Alibaba). In fact, only the latter type of glass can be used for glass containers in the food or cosmetic industry or to create new solar panels.

Among the techniques for recovering solar panels known to date, which also deal with the recovery of the glassy parts, many can be mentioned.

Some techniques involve processing the entire panel without first carrying out specific mechanical pre-treatments and these processes are highly disadvantageous above all because they involve a considerable waste of reagents and reduced efficiency since the solvent/panel contact surface is not maximized, thus preventing detachment of the glue from the glass. The immersion of the entire panel (or in any case after disassembling the frame) does not allow the optimal separation of the components and therefore implies their reuse as materials with low added value (for instance the cement market). If mechanical pre-treatments are carried out, a suitable particle size separation of the fractions aimed to the downstream recovery processes is not carried out.

Other techniques involve a strong comminution of the panel which involves its pulverization: this glass powder is excluded from applications with high added value (such as technical glasses used in the food or cosmetic field).

In the known art it is sometimes suggested to detach the plastics from the glass, which is carried out with solvents (alcohols) used for the purpose of dissolving the plastics, but it is not detailed how the plastics detached from the glass must subsequently be separated from each other. Neither the separation and recovery efficiencies nor the purities of the plastics separated from each other are described. Not separating the plastics from each other means not recovering the precious plastic, typically fluorinated (for instance Tedlar®) which could instead be reintroduced directly into the production cycles as a secondary raw material (SRM) on the market. The incorrect separation of the adhesive plastics from the fluorinated compounds causes the recovery of a contaminated and practically unusable fluorinated plastic.

In some cases the solvent consists of gas in supercritical conditions (for instance CO2 fed between 50 and 500 bar). These technologies pose disadvantages both from an economic point of view, implying high costs, and safety, associated with the use of a gas under pressure. Consequently, even industrial plants that use these processes will have a high cost of construction (they must be designed to withstand pressure) and maintenance.

In general, the use of drastic operating conditions in terms of reagents used, process operating parameters (temperatures and reaction times) entail economic burdens associated with high operating costs in relation to the quality and quantity of products obtained.

There are types of treatment that employ:

• Lamination or laser rays, techniques that are very expensive in themselves and sometimes not easily applicable on an industrial scale: in fact, glass is a very wearing material and easily ruins the blades (expensive maintenance of the machine used). They also generate a loss of non-recoverable glass powder.

• Thermal treatments, in which a high temperature degradation takes place which leads to the obtainment of dirty and opaque glass and does not allow the recovery of plastics such as fluorinated ones (compounds with high added value), thus involving an energy consumption and a high cost, attributed to the smoke abatement treatment.

• Electrical treatments, in which the recovery degree of the components is not specified and the connected electrical consumption is high, therefore difficult to apply on an industrial scale. Patent EP 2997169 deals with the recovery of solar panels at the end of their life, but is focused on the recovery of metals and does not provide useful lessons with regard to the recovery of glass and plastics. In fact, in the patent it is suggested to carry out a first shredding and a subsequent grinding to maximize the obtainment of fine materials, obtaining three fractions of ground glass (coarse fraction 0.5 cm-1 mm, intermediate fraction 0.1 -1 mm, fine fraction <0.1 mm):

• The grinding operation is therefore shifted towards the production of small pieces, since two sequential grindings are made, the second being considered fundamental. Therefore the glass fraction recovered in greater quantity has a small size, between 0.1 -1 mm or less;

• The fine fraction of the ground glass (<0.1 mm) is chemically treated to recover the metals and the residue eventually transferred to the cement factories;

• The intermediate fraction (0.1 -1 mm) is considered to be made up of clean, directly reusable glass; however it contains impurities (plastics and metals) and is difficult to market due to the size as it is too fine. It is therefore not usable as solar glass and is also given to cement factories, although lately even this use is no longer suitable due to the presence of contaminating residual metals;

• The coarse fraction is treated with solvents that could dissolve the plastics (cyclohexane/acetone mixtures) but the operating conditions described for the subsequent separation of the detached components do not allow to obtain a clean glass. In addition, the high temperatures (80-100°C) involve considerable evaporation and require a strong condensation for the recovery of the vapors (with economic burden), not to mention that the mixture used is highly volatile and with a wide range of explosiveness;

• As there is no refining stage for the separation of metal contacts, the glass fraction recovered will be contaminated by these metal filaments. • As an alternative to the solvent process, a heat treatment of the coarse fraction is proposed, which however has the disadvantage of opacifying the glass and burning the fluorinated compounds which are toxic.

The process identified in the aforementioned patent leads to a recovery of the small size glass and is contaminated by plastic and metals due to an unsuitable separation of the detached components through a dry screening. Currently, such contaminated glass is only partially used in the cement industry market, and only provided that the concentration of metals and other contaminants such as plastics is not too high.

Considering the need for recovery imposed by the European directive 2012/19/EU equal to 85% by weight, there is the need to enhance all the components of the panels and obtain recycled glass that is enhanced and not disposed of in a cement factory.

Patent US10618268 describes a method for recycling the various components of photovoltaic panels by mechanical crushing to obtain three dimensional fractions, followed by washing. The washing is performed separately for the three fractions and is carried out in tanks with the use of a water-based fluid containing surfactants and organic solvents designed to separate light particles from larger and heavier particles, such as glass fragments. At the end of the washing the separation can be carried out by filtration. However, the fine fraction will be dispersed in the liquid medium and will make separation more difficult, even contaminating the coarser products.

From the patent it appears that the plastics/adhesives remain solubilized in the complex washing mixture, leading to an overall final fouling of the separated products, which will necessarily undergo further washing/purification stages.

Furthermore, the use of the surfactant component has numerous other disadvantages, in addition to that of dirtying the products being treated and creating foams on which the finer granulometry products adhere. In fact, the surfactant, by its nature, facilitates the miscibility of all liquids, including the solvents present in the washing mixture, therefore it hinders the recovery and separation of the individual fluids, which cannot therefore be reused. This involves wastewater waste that must be properly disposed of or makes the recycling of liquid components extremely complex, preventing closed-cycle operations.

From the known art, therefore, there is no efficient recovery of either the glass or the fluorinated compounds. In fact, if the three phases are not separated effectively: glass/adhesive plastics/other plastics (for instance fluorinated), contaminated products that cannot be reused are inevitably obtained.

It should be emphasized that, for silicon-based panels, about 70% of the panels consist of flat solar glass, a particularly pure and highly expensive product, which in the processes of the known art is degraded and mostly disposed of in cement factories. Fluorinated plastics are also products of high added value that are not enhanced in the known art.

The need is therefore felt to develop a process that allows to maximize the recovery of a glass that maintains its high added value, which can be reused in sectors where it can be used as an SRM and not as a waste material.

To date, to the knowledge of the inventors, there are no known techniques for recovering the glass of the panels, such as to maintain the characteristics of flat glass with high transparency and suitable grain size (> 1 mm).

The need is also felt to achieve an efficient recovery of plastics, especially fluorinated ones.

Finally, the need is felt to operate the aforementioned recoveries with a treatment that has a minimal environmental impact, creating a process that works mainly in a closed cycle with the minimization of the waste produced.

If not specifically excluded in the detailed description that follows, what is described in this chapter is to be considered as an integral part of the detailed description of the invention. of the invention

An object of the present invention is therefore to enhance the glassy material of the photovoltaic panels at the end of their life in order to recover clean glass with the same characteristics as the original glass.

Another object of the invention is to maximize the amount of glass to be reused as a secondary raw material and minimize the amount of glass powder (size <1 mm) by reducing the amount to less than 10% by weight of the initial panel.

Still another object is to enhance the plastics, separating the various types from each other so as to recover those of interest such as fluorinated ones, such as Tedlar®.

Still further object is that of recovering the metals adhered to the adhesive plastics, and that of recovering also these plastics, which constitute the least exploitable part of the panels and which can be reused in the mixes for bitumen.

An additional object is to treat the residual glass powder, which is sent to the chemical recovery of the metals and which, when cleaned of them, can then be sent to the cement factories without load of polluting metals.

These and other objects, advantages and features of the present invention will be described more fully in a detailed description of the preferred embodiments which follows, furthermore the claims describe preferred variants of the invention, forming an integral part of the present description.

Brief description of the Figures

The objects and advantages of the present invention will become clear from the following detailed description of an example of its embodiment (and its variants) and from the attached drawings given purely by way of non-limiting explanation, in which:

Figure 1 , schematically illustrates a polycrystalline silicon solar panel: A) frame of aluminum or aluminum alloys; B) tempered glass; C) glue layer (for instance based on EVA (ethylene/vinyl-acetate copolymer); D) metallic element (or solar cell) based on Silicon with metals such as cadmium, selenium, tellurium, gallium, molybdenum, indium, silver, zinc etc. E) Backboard based on fluorinated polymers, for instance Tedlar®; F) Junction Box which includes diodes, cables and connectors;

Figure 2, is a block diagram of the process;

Figure 3, is a scheme of a reactor for sink and float separation with turbulent movement of the fluid in the liquid bulk,

FIGURES 4A and 4B, respectively show the results of the sink and float separation process carried out with an unsatisfactory (4A) and satisfactory (4B) medium according to the invention. As can be seen in the first figure, the separation of the detached components with the previous treatment is not effective due to the unsuitability of the density of the medium used. Instead, the means chosen by the invention is the most effective because it allows an optimal separation of the components, as can be seen in the figure, which are positioned in different points of the vehicle;

FIGURE 5 shows clean glass particles following the treatment object of the invention;

FIGURE 6 shows EVA particles recovered following the treatment object of the present invention;

FIGURE 7 shows clean TEDLAR® particles separated with the treatment object of the invention.

Detailed description

The present invention relates to a process for the treatment of all types of mono, poly-crystalline and amorphous silicon-based photovoltaic panels and of the latest generation thin-film panels (such as the so-called CIGS (copper-based , indium, gallium, selenium) and those in kesterite which do not have the silicon cell), which can be treated together or, preferably, separately.

The main objective of the invention is to recover the plastics of different nature that make up the panel and the high-purity glass, thus preserving their added value, in order to be able to put them back on the market as secondary raw materials (SRM).

The process involves a mechanical treatment of grinding and physical detachment of the adhesives from the other components (glass and other plastics) and further chemical treatments of the plastics and of the fine glass fraction for the recovery of metals in order to obtain a enhanced solid residue.

The adhesive plastics have strong adhesive characteristics and are used in the preparation of the photovoltaic module to encapsulate the metal cell and adhere to the transparent glass, favoring the sandwich structure typical of the panels, these plastics will hereinafter also be referred to generically, but not limitedly, with the term "adhesives". The plastics that are used in the other layers of the panel, such as for instance in the anti- reflective layer, do not have adhesive characteristics and are often high- quality plastics such as fluorinated ones, these plastics will hereinafter also be referred to generically, but not limitedly, with the terms "heavy plastics", “adhesive plastics" or simply "plastics ".

The process according to the invention comprises the following stages to operate on the panel, once the frame (typically aluminum or its alloys) and the electrical connections (usually junction boxes) have been eliminated:

(i) Mechanical grinding and screening treatments consisting of dimensional reduction operations and particle size separations aimed at separating two streams sent to subsequent specific treatments, typically two fractions will be produced, a coarse fraction (> 1 mm, preferably 1 -20 mm) and a fine fraction (<1 mm), processed as described below;

(ii) Physical treatments with solvent to be carried out on the coarse fraction, which are also effective on this size and which comprise the contact of the coarse fraction with a solvent to allow detachment, but not solubilization, of the glue from the glass and other plastics included those fluorinated; (iii) Densimetric separation treatments of the "sink and float" type following treatments with solvent to allow the separation in liquid medium immiscible with the solvent, of the detached components and the recovery of glass, metal contacts, plastics, for instance fluorinated and plastic glue;

(iv) Chemical treatments for the recovery of metals both adhered to the glue part and to the fine fraction.

The process allows to reach and exceed the minimum material recovery target set by the European directive 2012/19/EU and equal to 85% by weight.

More in detail, the operations include the following stages:

(i) Grinding to obtain the two fractions (fine and coarse) by means of a grinding device o the fine fraction will then be subjected to hydrometallurgical treatment for the recovery of the metals while the glass residue (now cleaned of the metals) will be sent for disposal, for instance in a cement factory; o the coarse fraction is treated separately in the next stage;

The mechanical grinding treatment is aimed at the production of only two fractions in which the finer dimensional fraction is minimized. The latter is also separated from the main coarse fraction before entering the subsequent wet process stages, with the advantage of avoiding product contamination. This is advantageous in view of recovering clean glass of a coarse size with a high added value that allows it to be reused.

(ii) The coarse fraction is treated in a reactor (typically a reactor at atmospheric pressure and low temperature, in the range T (ambient)-80°C, preferably 25-70°C, more preferably 55-65°C) with a solvent or mixture of solvents that does not solubilize plastics (the solvent will typically be an aprotic apolar solvent, such as cyclohexane, kerosene or light hydrocarbons such as hexane) in order to allow the detachment of the various components (glass, metal contacts, adhesive plastics/glues with adhered portions of metallic solar cell, other plastics, including for instance fluorinated ones); the skilled in the art will be able to find the appropriate conditions to have an efficient separation in order to have the greatest possible separation between the various elements (glass and plastics) bearing in mind that the treatment will be a physical separation treatment and will not lead to the solubilization of the plastics (in particular the adhesive plastics will only be swollen by the solvent), thanks to the chosen solvent or at most the plastics, in particular the adhesive plastics will be dissolved only in traces. Advantageously, agitation will be maintained inside the reactor through external recirculation of liquid and not through mechanical means such as blades or rotors in order not to shatter the glass. The recirculation will be such as to maintain an expanded bed condition within the liquid bulk in order to favor glass/plastic contact and allow the latter to remain suspended in the liquid medium. The solvent leaving the reactor, before being recirculated in the reactor, can be subjected to filtration in order to intercept the adhesive plastics with adherent metal cell fractions possibly entrained, which will then go to hydrometallurgical recovery. The solvent and the conditions chosen for this stage are also effective on a coarse size which allows to separate a coarse glass which maintains its added value in its subsequent re-uses. The absence of compounds such as surfactants and the choice of using a solvent or mixture of apolar aprotic solvents makes their substantial recovery possible and therefore allows to work in a closed cycle, an aspect that would be impossible if a mixture of numerous complex components were used including surfactants. Closed-cycle processing therefore involves a lower consumption of reagents and lower production of wastewater with advantages both in economic and environmental terms in full compliance with the principles of the green economy;

(iii) The solvent is then removed to separate the liquid from the solids (for instance by drainage) while avoiding drying the solids; this operation must be quick to prevent the solids from reattaching to each other. The collected solvent, before being reused in the next treatment cycle, can be subjected to a rectification, to maintain its purity adequate. The process fluids, solvent and aqueous medium, do not come into contact with each other since two operations are foreseen in series and distinct from each other. Furthermore, since the two fluids are immiscible, any small contaminations do not compromise the purification of the process liquids which therefore remain easily separable thanks also to the non-use of components such as surfactants;

(iv) In the reactor from which the solvent has been drained, water or other non-solubilizing liquid is quickly added (preferably from below) to allow the separation of the various components. The water or other liquid that is not miscible with the solvent of stage (iii) has the function of behaving as a dense medium and allowing a sink and float separation such as the adhesive plastics, swollen and impregnated with solvent, will tend to float, separating from the glass, metal contacts and other heavier plastics, which instead will remain on the bottom. The separation therefore exploits the difference in density of the components that are distributed in the dense medium. In particular, the choice of the specific medium of the invention allows the stratification of the light components on the free surface and the deposition of glass and heavy plastics on the bottom of the reactor (exactly at the two ends of the dense medium). Their subsequent recollection is therefore easy and efficient. Furthermore, the chosen medium (water or other aqueous-based liquid that does not solubilize plastics and immiscible with the apolar aprotic solvent or solvents) has a very low impact from both an environmental and an economic point of view. In a simplified embodiment (illustrated in Figure 3) the plastics swollen with solvent are removed by skimming. The washing is carried out avoiding mechanical handling and moving the fluid by forced external circulation of the liquid, capable of maintaining a suitable turbulence in the liquid bulk (possibly assisted by the injection of nitrogen or inert gas). Once the washing and removal phase of the floating plastics is complete, the glass with the metal contacts and the heavy plastics, for instance fluorinated, remains as the bottom body, which is easily discharged after draining the water. The final product is wet only by water and not by the solvent: therefore no further washing of the products will be necessary.

(v) The heavy plastic, for instance fluorinated, recovered with the glass (but now detached from it) is separated for instance by means of separation by blowing air or by screening, due to the difference in density on one side and the different particle size on the other.

The treatment of the fraction separated with the sink and float and consisting of the adhesive plastics (type EVA) and the metals contained in the photovoltaic cell can be done by hydrometallurgical methods (with quantitative recovery of the adhesive that is reused as bitumen) or by thermal methods.

The solvents that can be used in stage (ii) are selected from: cyclohexane, specific aprotic apolar type solvent, kerosene or light hydrocarbons with a solid/liquid ratio (S/L) in the range from 1 :1 to 1 :8 (preferably 1 :4 ).

In relation to the procedure of stage (iii), also called sink and float procedure, it is good to specify that the liquid to be used must have an intermediate density between the plastics and the glass. Preferably, the liquid is water which allows to proceed according to a densimetric separation and provides significant simplifications to the total process, making it also advantageous from an environmental point of view as it is an easy to find component and does not involve any environmental impact related to its production.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The main objective of the present invention is to separate glass from plastics and plastics of different types (glue such as EVA or Duroplast (thermosetting composite plastic, similar to Formica and Bakelite htps fluorinated Tedlar® type, polyvinylidene fluoride (PVDF), polyethylene terephthalate (PET), polymers based on PEDOT (poly(3,4-ethylenedioxythiophene)- polystyrene), and similar plastics, with each other through the procedure described below. The process of the invention, illustrated in the block diagram of Figure 2, comprises the stages detailed below in a cooperative relationship.

The aluminum frames are removed using a robotic/automated system that uses specific tools even when hot. The operation is optimized to minimize the production of glass dust and separate the uncontaminated aluminum frame from the other panel components and directly marketable to the aluminum market as SRM. During the dismantling stage of the frames, the junction boxes are also removed.

GRINDING

The frameless panel is suitably ground with a suitable and specific system, such as single-shaft grinder with anti-abrasive plates or similar, such as the GR280 grinder from CAMEC (htt s://camec.net/divisioni/divisione- capable of minimizing the minute fraction to the advantage of the production of a coarse-sized fraction and equipped with a 20 mm control grid. The shredded product is then screened using a 1 mm sieve to separate two particle size fractions:

• A coarse fraction (1 -20 mm) consisting of glass flakes + glue (EVA type) with the photovoltaic cell attached + heavy plastics, for instance fluorinated (Tedlar type) and metal contacts;

• A fine fraction (<1 mm) consisting of a concentrate of metals and residues of glass dust and traces of plastics.

The metal contacts (tin, lead, aluminum and other filaments) released during grinding are preliminarily separated from the coarse fraction by means of an optical system or the like.

PHYSICAL TREATMENT Only the so cleaned \coarse fraction is sent to the physical treatment which consists of a wet treatment with a specific apolar aprotic solvent such as cyclohexane or kerosene or light hydrocarbons for the detachment of the glue (for instance EVA) from the glass. An S/L ratio is used in the range from 1 :1 to 1 :8 (preferably 1 :4) at a temperature between the Tambient - 80°C (preferably 65°C) and for an overall duration of the process comprised in the range 0.5-4 hours (preferably 2 hours). Agitation is maintained with forced external recirculation of liquid.

SINK AND FLOAT SEPARATION

A "sink and float" separation is then carried out in an appropriate liquid/thick medium which will have a density in the range 2-0.7 g/cm³ measured under standard conditions (for instance water or other nonsolubilizing liquid as mentioned above), or between that of the glass and the suspended polymeric elements. The treatment will be carried out at a temperature comprised in the range Tambient - 70°C (preferably 35°C) for the separation of two fractions: 1 ) glass with metal contacts and heavy plastic (for instance fluorinated such as Tedlar®) and 2) adhesive plastic (for instance EVA) with the photovoltaic cell attached. In this stage, a flow of inert gas (such as nitrogen) in the liquid medium with a quantity between 10-50 nitrogen vol./reactor vol. can be used at a pressure between 1.1 -5 bar to assist the separation or preferably an external forced circulation of the dense medium will be implemented to minimize the use of inert gas.

The subsequent separation of the glass from the fluorinated compound can be achieved with air blow or zig zag separators. The subsequent separation of the metal contacts from the glass can be achieved with an optical system.

CHEMICAL TREATMENT OF THE FINE FRACTION

The fine fraction is fed to a chemical treatment of the hydrometallurgical type for the recovery of the metals concentrated therein.

The sequential chemical washing for the recovery of metals and silicon can take place in one of the following ways: • Basic leaching at pH 12-14, particularly advantageous for silicon- based panels, using NaOH (0.5 M), for the selective extraction of Al and Zn. This operation is carried out at 80°C for 5h. Subsequently the lye is filtered thus obtaining a solid cake and a leach liquor:

• The leach liquor undergoes a precipitation process with H2SO4 which allows the recovery of Al and Zn in the form of hydroxides.

• The solid cake undergoes acid leaching with H2SO4 (2.5 M) for the removal of Fe and thus leading to obtaining a solid residue consisting of TiC and Ag, clean minute glass and traces of glue (for instance EVA). This operation is carried out at 40°C for 5 h. This solid fraction is treated with HNO3 (25% w) for the solubilization of residual silver and zinc, at a temperature in the range 40-80°C (preferably 60°C), for a duration of 2-4 h with a liquid/solid (L/S) ratio of 3 to 5 (preferably 4.6). HCI is then added to precipitate the silver in the chloride form. The precipitate is washed until any impurities (zinc, iron) are eliminated and then chemically reduced with caustic soda and dextrose. The silver is then washed with demineralized water and finally placed in an oven at about 300°C for a few hours after adding sodium bicarbonate. Finally it is melted in a well-type oven. The solid residue can be reused in cement factories.

• Simultaneous extraction of Zn, Al, Fe with acid leaching at pH <5 (from 2 to 5), typically with H2SO4 5M and 5% H2O2, 30-80°C, 2h, solid/liquid (S/L) = 1 :1 - 1 :2 obtaining the simultaneous extraction of Al, Fe, Zn and a solid residue (containing glass, Si, Ag, Ti dioxide) separated by filter press or centrifuge.

• The leach liquor is subjected to successive alkalinization stages and sequential precipitation of Al, Fe and Zn which are precipitated as hydroxides by adding alkaline agents at pH = 6-8. The solids are separated with a filter press or centrifuge.

The leach liquor after filtration contains mainly Zn and is subjected to recovery by precipitation as hydroxide, carried out by adding alkaline agents at pH 10-11 , or electrochemically, possible only after the previous purification operations.

Metallic Zn is produced by electrodeposition at T=20-40°C, pH = 4-6 and moderate agitation on aluminum cathodes and lead-antimony alloy anodes. In potentiostatic conditions 4V or 200 A/m² in 1 -2 days. Pneumatic agitation of the cell and continuous recirculation of the electrolytic solution. The Zn produced has> 98% purity.

• The residual solid containing glass, Si, Ag, TiO2 and traces of glue (for instance EVA) can be reused in the production of Si, Ag and Ti. This solid fraction is treated with HNO3 (25% w) for the solubilization of silver and residual zinc, at a temperature in the range 40-80°C (preferably 60°C), for 2-4 h with a liquid/solid (L/S) ratio of 3 to 5 (preferably 4.6). HCI is then added to precipitate silver in the form of chloride. The precipitate is washed until any impurities (zinc, iron) are eliminated and then chemically reduced with caustic soda and dextrose. The silver is then washed with demineralized water and finally placed in an oven at about 300°C for a few hours after adding sodium bicarbonate. Finally it is melted in a well-type oven. The solid residue can be reused in cement factories.

• Acid leaching, using H2SO4 (2M) and hydrogen peroxide, particularly advantageous for CIGS panels. This operation is carried out at 60°C for 5h. Subsequently the lye is filtered thus obtaining a solid cake and a leach liquor. • The leach liquor undergoes a precipitation process with NaOH which thus allows the recovery of a concentrate of the metals of interest (such as copper, indium, gallium, selenium) at pH = 9.

• The solid cake is made up of a residue of SiO2, glass and traces of glue (for instance EVA).

• Acid leaching using H2SO4 (2-4M) and hydrogen peroxide particularly advantageous for kesterite panels and subsequent solid-liquid separation obtaining:

• Leach liquor containing the target metals to be sent to subsequent precipitation stages for the recovery of Fe as oxide, subsequent recovery of a metal concentrate in the form of hydroxides or sulphides such as Cu, Zn, Sn and subsequent recovery of Se and Mo.

• Solid residue consisting of insoluble polymers (Duroplast, PET) and contaminating metals, such as Ag and traces of Mo.

Patent EP 2997169 deals with the recovery of metals from solar panels at the end of their life. Unlike the proposed processes, this patent operates a sequential alkaline leaching by using soda at a high concentration (10M) to recover Al and Zn.

Furthermore, it is not detailed how the solid residue after filtration containing glass, Si, Ag, TiC is treated to recover the metals selectively.

TREATMENT OF THE ADHESIVE FRACTION + ADHERED CELL

The recovery of metals from the adhesive fraction + adhered cell, fraction separated after treatment with solvent and sink and float, can take place in the following ways:

- Chemically by means of leaching processes (the residual glue will be separated from the metals dissolved in the leaching solutions by means of filtration and may eventually be reintroduced into the bitumen market), or - By thermal means, which results in the production of heat for the combustion of the glue and the separation of the metallic powder as ground ash.

In both cases, the fraction consisting of glue impregnated with solvent adhered to the photovoltaic cell will first be dried to remove and recover the solvent that impregnates the glue.

In the first case, a leaching is carried out directly in the same ways as already described in the treatment of the fine fraction. The metals are recovered from the lye while the residual solid, sufficiently decontaminated by the metals, consisting of the glue granules (for instance EVA) is recovered and can be reused for instance in the bitumen market.

In the second case an incineration of the glue with the adhered cell is carried out between 500 and 700°C for 2-5 hours, preferably 650°C for 4 hours. The glue, burning, develops heat, while the bottom ashes are recovered and leached with nitric acid 1 .5 M, 60°C for 2 hours, using 30 ml per gram of ash or with a treatment described for the fine fraction.

The advantages of the invention are the following:

• The process works mainly in a closed cycle with the minimization of the waste produced. The solvent can be reused after refining. The quantities of reagents used are minimized and can be reused for a defined number of cycles. This is favored by the non-miscibility of the process liquids (solvents and aqueous phase) and their not expected mixing during the process.

• The solvent chosen for the separation is effective even on a coarse size. This is advantageous in view of recovering coarsesized glass with high added value.

• The grinding is targeted and designed in a specific way: it is aimed at producing a particle size fraction shifted towards high (not fine) sizes to obtain a product (glass) with high added value (without compromising the qualities of a flat and transparent material) and with a size such as to be reused in sectors such as glassworks for the food and cosmetic industry for which it is resalable at a higher value than e.g. to cement factories (for which a fine size is sufficient). The 1 mm granulometric fraction satisfies the requests of the end-users of the recovered product. Controlled grinding also allows the metal fraction to be concentrated in a specific dimensional range (0-1 mm) and therefore avoids chemical treating of other portions of the panel in which these metals are not present for the recovery of target metals (with an unavoidable dilution effect of metals in the sample leading to lower recovery efficiency).

• The removal of the fines from the crushed material fed to the separation processes (solvent and sink and float) avoids the contamination of the latter with respect to the products.

• Cutting the particle size fraction to 1 mm allows to reach a recycling percentage of the whole initial panel above 85% by weight, in line with the targets set by the European directive, which can reach 89% by weight or more.

The main advantage of the invention is the separation of four distinct and uncontaminated streams: glass, metal contacts, glue (for instance EVA) and plastic (for instance fluorinated such as Tedlar®). The proposed separation makes it possible to recover these fractions while preserving their added value so that they can be reintroduced directly into the market as SRM. In fact, they are recovered with the following degrees of purity: glass >99%, glue (EVA type) >95%, plastic (for instance fluorinated type Tedlar®) >95%, metal contacts >99%. The reference target for recovered glass is, for instance, that of glass factories where flat glass with high added value is used. This purity level is also achieved through the use of refining stages, such as the separation of metal contacts from glass by means of an optical separator.

The solvents to be used, object of the invention, are of the apolar aprotic non-carcinogenic type, kerosene and light hydrocarbons. Among these, the use of solvents with reduced volatility (for instance less than acetone) will be preferred. For instance, cyclohexane will be preferred which, in addition to not being carcinogenic, is 100% recyclable, an aspect that constitutes an additional added value: its recovery and re-use in the closed-cycle process avoids its disposal with minimization of the environmental impact. Mechanical agitation is completely eliminated both in the solvent treatment and during the "sink and float" separation: the separation is more efficient by fluid dynamics (through an external forced circulation of liquid that is reintroduced into the reactor) which favors solvent/panel flakes contact. Furthermore, the mechanical stirring system constitutes an obstacle to the correct fluid dynamics of the system and causes (even if weak) an unavoidable breakage of the glass. The process conditions are not difficult for the separation of the glass from the glue (for instance EVA) and from the polymer (for instance fluorinated Tedlar type) and gases (such as CO2) are not used in supercritical conditions. Working with gas in supercritical conditions implies very high operating pressures: this involves the creation of a complex compression and expansion system (with obvious economic burden). The proposed solvent treatment and sink and float separation temperatures are such that they do not involve an economic burden for a possible industrial application of the process (a heating boiler and a simple vapor condensation system would be sufficient). The times are such as to allow numerous processing cycles per day to maximize the processed panels and the recovered product.

• The solvent treatment temperature is optimized to minimize operating times without however causing excessive solvent evaporation: a temperature that is too high, due to the volatility of the solvents, in fact, would lead to a loss which would lead to the need to use recovery which entails an increase from an economic point of view.

• A "sink and float" separation of the wet detached components is carried out, which allows the optimal recovery of uncontaminated fractions. This separation also allows the different types of plastics to be optimally separated from each other.

• There are different types of densimetric separation, the one proposed in the present invention (sink and float) has the advantage of using the most readily available and undoubtedly applicable medium in an industrial plant, namely water. This stream can also be reused in a closed cycle after purification in specific filtration systems since the solvent does not solubilize the components and any residual plastics or glass powder can be separated by standard filtration operations.

• With reference to the recovery of metals from a specific fraction (fine fraction) and from the glue (for instance EVA) separated from the glass and from the other polymer (for instance fluorinated such as Tedlar), the application advantage, which represents a chemical improvement of the process, is to feed to the chemical treatment only the fraction of interest, wherein are concentrated metals more easily recoverable through hydrometallurgical processes. Before eventually feeding the entire panel to the chemical stage, in fact, a mechanical concentration is achieved (thanks to the optimization of the specific grinding and screening stage) which results in a much smaller quantity of sample to be treated.

• The thermal alternative is proposed only for the glue + photovoltaic cell fraction (12-18% of the coarse fraction) previously separated from the other components (such as fluorinated plastics, metal contacts and glass), thus avoiding the risk of obtaining a product (glass) that has become opaque and which loses its properties of transparent and reusable glass in the food and cosmetic sector.

• For the recovery of metals, reagents that are not particularly toxic or burdensome from an environmental, economic and safety point of view are used (no high pressure and non-explosive, risks otherwise associated for instance with hydrogen treatment). Hydrogen peroxide is used as a reducing agent where required (easily available, not used under pressure). The leaching of the metals of interest is followed by separation and recovery treatments such as precipitation.

The whole process, from the robotic/automated dismantling to the final chemical treatment, aims to maximize the recovery of material by recovering pure components that can be placed directly on the market as SRM.

EXAMPLES

Examples are presented below to illustrate the invention that are not to be considered limitative of its scope.

The conditions used for the experimentation shown in Figure 4A, which did not allow the separation of the components, involved the use of a pentane-water and surfactant mixture with a density of 0.69 g/cm³ at room temperature. The treatment that allowed an optimal separation of the components during the sink and float stage, as can be seen in figure 4B, used water at 35°C with a density of 0.993 g/cm³.

Claims

24 CLAIMS

1. A process for the treatment of photovoltaic panels at the end of their life, said panels comprising one or more junction boxes and an aluminum or aluminum alloy frame that encloses overlapping layers of: glass, adhesive plastics, heavy plastics with anti-reflective characteristics and elements of photovoltaic cells and metal contacts, said process comprising the following stages, to be carried out on said panels without the frame and junction boxes:

(i) Grinding and screening to obtain two fractions, a coarse fraction with particle size >1 mm, preferably 1 -20 mm, and a fine fraction with particle size <1 mm;

(ii) Physical treatment to be carried out in a reactor on the coarse fraction, comprising contacting said coarse fraction with an apolar aprotic liquid solvent in which the plastics are substantially insolubilized or are only in traces, to separate the coarse fraction into its fundamental components which comprise: glass, heavy plastics, adhesive plastics with adhering portions of the elements of photovoltaic cells and metal contacts, said physical treatment being followed by the drainage of the solvent;

(iii) Sink and float densimetric separation carried out by contacting the coarse fraction separated in its detached basic components deriving from stage (ii) with a non-solubilizing liquid, immiscible with the non-polar aprotic liquid solvent of stage (ii), with a density in the range 2-0.7 g/cm³, preferably 0.9-1 .1 g/cm³;

(iv) Recovery of the glass, of the plastics detached from the glass, of the metal contacts and of the metals contained in the portions of photovoltaic cells adhered to the adhesive plastics and optionally on the fine fraction by means of chemical and/or thermal treatments.

2. The process according to claim 1 wherein the fine fraction is subjected to hydrometallurgical treatment for the recovery of the metals and the glass residue, cleaned of the metals, is sent for disposal.

3. The process according to any one of claims 1 -2 wherein the treatment of stage (ii) is carried out at atmospheric pressure and temperature in the range T(ambient)-80°C, preferably 25-70°C, more preferably 55-65°C, with a solvent or mixture of solvents of apolar aprotic nature, used with a solid/liquid ratio in the range from 1 :1 to 1 :8, preferably 1 :4, for an overall process duration in the range of 0.5-4 hours, preferably 2 hours, to obtain the detachment of the various components: glass, metal contacts, adhesive plastics with attached portions of photovoltaic cells, heavy plastics, such as fluorinated ones.

4. The process according to any one of claims 1 -3 wherein stage (ii) is carried out under agitation by external solvent recirculation under expanded bed conditions to favor the detachment of the glass from the plastics and allow the latter to remain suspended in the solvent possibly by blowing in nitrogen or inert gas to maintain turbulent conditions in the reactor.

5. The process according to any one of claims 1 -4 wherein stages (ii) and (iii) are carried out in the same reactor, eliminating the solvent by drainage at the end of the conduction of stage (ii) and adding the non-solubilizing liquid to start the conduction of stage (iii).

6. The process according to any one of claims 1 -5 wherein the nonsolubilizing liquid of stage (iii) is water, and the treatment is carried out at a temperature comprised in the range T(ambient)-70°C, preferably 35°C for the separation of two fractions: 1 ) glass with heavy plastics and metal contacts and 2) adhesive plastics with adherent portions of the photovoltaic cell.

7. The process according to any one of claims 1 -6 wherein the aprotic nonpolar solvent liquid of stage (ii) is selected from light hydrocarbons, such as hexane and cyclohexane and kerosene.

8. The process according to any one of claims 1 -7 wherein in stage (iii) the adhesive plastics and the heavy plastics are separated from the glass by densimetric separation and from the non-solubilizing liquid the swollen and adhesive plastics impregnated of solvent are recovered, separated from each other, lighter than glass, metal contacts and heavy plastics, which are deposited on the bottom of the reactor.

9. The process according to any one of claims 1 -8 wherein in stage (iii) the sink and float treatment is carried out avoiding the mechanical movement and operating a movement of the fluid through forced circulation of liquid outside the reactor and possibly, to maintain a suitable turbulence in the reactor, nitrogen or inert gas is blown.

10. The process according to any one of claims 1 -9 wherein at the outlet of stage (iii) the following are recovered: adhesive plastics adherent to the photovoltaic cell, which are removed from the reactor by skimming and a bottom body comprising glass, heavy plastics, e.g. fluorinated, and metal contacts; said bottom body being recovered after draining the nonsolubilizing liquid; said adhesive plastics being sent to the recovery of the metals contained in the residues of photovoltaic cells adhered to them.

11. The process according to any one of claims 1 -10 wherein the heavy plastics and the metal contacts, both detached from the glass, are separated from each other respectively by screening, by density or by optical separation means.

12. The process according to any one of claims 1 -11 wherein the recovery of the adhesive plastics in stage (iv) is carried out with chemical treatments with quantitative recovery of said adhesive plastics and their reuse as bitumen or thermally.

13. The process according to any one of claims 1 -12 wherein the adhesive plastic is EthyleneVinylAcetate or Duroplast and the heavy plastic is a plastic chosen from fluorinated plastics, for instance Tedlar®, PolyVinyldenFluoride, PolyethyleneTerephthalate, PEDOT.

14. The process according to any one of claims 1 -13 wherein the fine fraction is fed to a chemical treatment of the hydrometallurgical type for the recovery of the metals contained therein, said treatment being chosen from:

• Basic leaching at pH 12-14 for the selective extraction of Al and Zn, from which lye, after filtration, a solid cake and a leach liquor 27 are obtained; Al and Zn are recovered from the leach liquor in the form of hydroxides by precipitation with H2SO4, while the solid cake undergoes acid leaching with H2SO4 for the removal of Fe; the solid remaining from acid leaching comprises TiC and Ag, clean minute glass and traces of adhesive plastic; this solid fraction is treated with HNO3 for the solubilization of residual silver and zinc and finally HCI is added to precipitate the silver in the form of chloride; the AgCI precipitate is washed until any impurities are eliminated, chemically reduced with caustic soda and dextrose, treated at high temperatures by calcination to obtain pure silver that can be used as such, while the solid residue is disposed of in cement factories;

• Acid leaching at pH <5 typically using H2SO4 and H2O2, to obtain a leach liquor containing Al, Fe, Zn and a first solid cake containing glass, Si, Ag, TiO2 and traces of adhesive plastics, separated by filter press or centrifuge; the leach liquor is then subjected to successive stages of alkalinization and sequential precipitation of Al, Fe which are precipitated as hydroxides by adding alkaline agents at pH = 6-8, obtaining a second leach liquor and a second solid cake separated with a filter press or centrifuge; the second leach liquor mainly contains Zn which is recovered by precipitation as hydroxide by adding alkaline agents at pH 10-11 , or electrochemically; the first solid cake containing glass, Si, Ag, TiO2 and traces of adhesive plastics is treated with HNO3 to dissolve residual silver and zinc, then HCI is added to precipitate the silver in the form of chloride; the precipitate is washed until any impurities (zinc, iron) are eliminated and then chemically reduced with caustic soda and dextrose to obtain pure silver that can be used as such, while the solid residue is disposed of in cement factories;

• Acid leaching, using H2SO4 and H2O2; in this way a leach liquor is obtained containing the metals of interest such as copper, indium, gallium, selenium, which undergoes a precipitation process with NaOH at pH = 9; the solid cake resulting from the precipitation, 28 consisting of a residue of SiO2, glass and traces of glue, is disposed of in cement factories;

• Acid leaching using H2SO4 and H2O2 and subsequent solid-liquid separation obtaining a leach liquor containing the target metals to be sent to subsequent precipitation stages for the recovery of Fe in the form of oxide, subsequent recovery of a metal concentrate in the form of hydroxides or sulphides such as Cu, Zn, Sn and subsequent recovery of Se and Mo; the solid residue consisting of insoluble polymers and contaminating metals such as Ag and traces of Mo is treated with HNO3 for the solubilization of silver and molybdenum which are subsequently recovered.

15. The process according to any one of claims 1 -13 and 14 wherein the fraction consisting of adhesive plastic and adherent cell is fed to a treatment chosen from:

- Heat treatment at 650°C, the bottom ash being recovered and leached with nitric acid or being treated with a treatment described for the fine fraction in claim 14;

- Hydrometallurgical chemical treatment for the recovery of the metals of the adherent cell fractions, by means of leaching processes as described in the treatment of the fine fraction according to claim 14, the metals being recovered from the lye while the residual solid, sufficiently decontaminated from the metals and consisting of adhesive plastic granules, is recovered and reused in the bitumen market; said treatments being carried out on the previously dried fraction to remove and recover the solvent which impregnates it.