Heavy-metal extraction from PVC in a dissolution process

Abstract

The invention is directed to an extraction method for extracting a heavy metal from a heavy metal-containing polyvinyl chloride (PVC) based material. The method comprises a dissolution step of dissolving at least part of the heavy metal-containing polyvinyl chloride (PVC) based material in a solvent system. The method may further comprise a separation step, a treatment step and a recovery step. The method provides a simple and effective method and allows for an improved extraction efficiency.

Description

HEAVY-METAL EXTRACTION FROM PVC IN A DISSOLUTION PROCESS

[0001] The invention is directed to an extraction method for extracting a heavy metal from a heavy metal-containing polyvinyl chloride (PVC) based material.

[0002] It is essential to add stabilisers (commonly named stabiliser one-packs) to PVC during processing to avoid PVC degradation. PVC is thermally unstable because of the presence of defects; these defects that are e.g. tertiary chlorine or allylic chlorine atoms are initiation sites for degradation. In the past, heavy metal-based stabilisers, such as lead-based and / or cadmium-based stabilisers were added to PVC in Europe. Lead- or cadmium-based stabilisers were used to i.a. give thermal stability to the PVC and to protect PVC from photo-degradation. However, as is well known, heavy metals like cadmium and lead are toxic elements that may affect human health and environment. Following a voluntary commitment of the Vinyl industry, cadmium-based and lead-based stabilisers are no longer used by the PVC industry since 2001 and 2015 in Europe, respectively. These stabilisers are therefore not present in new articles. However, lead and cadmium can be present in post-consumer PVC recyclate coming from old PVC products.

[0003] Regulation (EU) 494 / 2011 sets the restrictions for cadmium content, being a maximum of 0.01 wt% (=100 ppm) cadmium in all plastic materials; with a derogation for recovered PVC used exclusively in rigid PVC applications where the maximum limit is set to 0.1 wt% (=1000 ppm). As the skilled person is aware, ppm herein corresponds to mg / kg.

[0004] Commission Regulation (EU) 2023 / 923 issued on 3 May 2023 restricts the lead content in PVC and its compounds to 0.1 wt% (=1000 ppm). This restriction includes a derogation until May 2033 for recycled PVC based on rigid formulations provided their lead content is below 1.5 wt% of the recovered rigid PVC. By way of derogation, this 0.1 wt% limit shall not apply to PVC articles containing recovered flexible PVC until May 2025. After these two deadlines (May 2025 and May 2033), both rigid and flexible recovered PVC will have to comply with the 0.1 wt% (=1000 ppm) lead threshold.

[0005] To comply with the regulations, the content of heavy metals, in particular lead, in Recycled PVC (R-PVC) based on post-consumer waste will have to be reduced in the coming years. It is desired to provide a method to reduce heavy metal content to guarantee R-PVC fulfills the regulations in place. Several of such attempts have been made.

[0006] One example is described in WO2006 / 05907. Herein, a process for the purification of PVC comprising e.g. lead is described. This process comprises dissolving PVC in a solvent and treating this solution with an additive that forms a complex with the lead.

[0007] Another example is provided in EP4067421. A halogenated polymer comprising one or more further components is dissolved to provide a continuous phase and a discontinuous phase. These phases are separated. An additive is added to the continuous phase, followed by evaporation of the solvent to provide a halogenated polymer product.

[0008] KR20230097852 discloses mixing PVC waste with a treatment agent. A removing agent may be added to the mixture, to remove one or more heavy metals.

[0009] EP4299271 details a purification method for purifying PVC comprising at least one heavy metal compound. The method includes dissolving PVC in 2-methyltetrahydrofuran in a stirred and heated reactor.

[0010] Disadvantageously, these processes do not allow for optimal extraction of heavy metals from a heavy metal-containing PVC based material, i.e. the extraction efficiency is limited. Other related methods are described in JP2009096869A, JP 4743794B2 and MASAMI TSUNEKAWA ET AL: "Removal of lead compounds from polyvinylchloride in electric wires and cables using cation-exchange resin",JOURNAL OF HAZARDOUS MATERIALS, ELSEVIER,AMSTERDAM, NL,vol. 191, no. 1,27 April 2011 (2011-04-27), pages 388-392,XP028225954,ISSN: 0304-3894, DOI: 10.1016 / J.JHAZMAT.2011.04.098 [retrieved on 2011-05-04].General Disclosure

[0011] It is therefore an objective of the present invention to provide a method that overcomes at least part of the above-mentioned drawbacks. In particular, the method according to the present invention provides a simple and effective method to extract a heavy metal from PVC based materials. The method according to the present invention allows for an improved extraction efficiency. In addition, the method may be suitably applied on larger (industrial) scale.

[0012] The present inventors surprisingly found that this objective is achieved by an extraction method comprising dissolving at least part of a heavy metal-containing PVC based material in a solvent system. The present inventors found that it may be particularly advantageous to treat the resulting solution, in particular the depleted PVC based fraction (vide infra), with an ionic exchange resin, as this advantageously allows for even more selective and effective extraction of heavy metals, in particular lead. This is especially for certain solvent systems.

[0013] Thus, the present invention is directed to an extraction method for extracting a heavy metal from a heavy metal-containing polyvinyl chloride (PVC) based material (herein also referred to as heavy metal containing material or heavy metal-containing PVC material). The extraction method can be applied for a method for producing a heavy metal depleted PVC based material.

[0014] According to an aspect of the invention, there is provided an extraction method for extracting a heavy metal from a heavy metal-containing polyvinyl chloride (PVC) based material, wherein said method comprises: a dissolution step comprising dissolving at least part of said heavy metal-containing PVC based material in a solvent system comprising a major solvent and a reaction agent, to obtain a depleted PVC material fraction and a heavy metal-rich fraction.

[0015] In the previous method, the reaction agent may be selected from the group consisting of an acid or a salt containing a sulfonate group or moiety and / or having an ability to form complexes with lead and / or cadmium compounds.

[0016] In the previous method, the reaction agent may be selected from the group consisting of nitric acid, sulfuric acid, citric acid, ethylenediaminetetraacetic acid (EDTA), methane sulfonic acid (MSA), and p-toluene sulfonic acid (PTSA).

[0017] In the previous methods, the method may further comprise a treatment step comprising treating said depleted PVC based material fraction with an ion exchange resin.

[0018] In the previous methods, the method may further comprise the treatment step for the solvent system.

[0019] In the previous methods, the heavy metal may be lead or cadmium.

[0020] In the previous methods, the major solvent may be selected from the group consisting of methyl ethyl ketone (MEK), 2-methyltetrahydrofuran (meTHF), tetrahydrofuran (THF), cyclohexanone and / or dimethyl carbonate.

[0021] In the previous methods, the solvent system may comprise at most 5 vol% of said reaction agent, preferably at most 4 vol%, more preferably at most 3 vol%, even more preferably at most 1 vol%, even more preferably at most 0.6 vol%, most preferably at most 0.3 vol% based on the total volume of the solvent system.

[0022] In the previous methods, the solvent system may comprise at least 0.1 vol% of said reaction agent.

[0023] In the previous methods, the dissolution step may be performed under an inert atmosphere and / or at a temperature in the range of 50 - 150 °C, preferably 60 - 120 °C, more preferably in the range of 60 - 110 °C, such as around 80 °C or around 100 °C and / or performed for a duration of at most 4 hours, preferably at most 3 hours, such as around 2 hours and / or at a pressure of at least 1 bar, preferably at least 1.5 bar, more preferably at least 3 bar such as 5 bar.

[0024] In the previous methods, the heavy metal-rich fraction may comprise heavy-metal aggregates, preferably heavy-metal aggregates having a median particle size (d50) between 0.01 - 500 μm, preferably between 0.1 - 50 μm, more preferably between 0.3 - 13 μm, even more preferably between 1 - 10 μm.

[0025] In the previous methods, the ionic exchange resin may be a cationic exchange resin, more preferably a cationic exchange resin comprising a sulfonic acid moiety.

[0026] In the previous methods, the method may further comprise a separation step comprising separating the depleted PVC based material fraction and the heavy metal-rich fraction, preferably wherein said separation step comprises centrifugation and / or sedimentation.

[0027] In the previous methods, the separation step may comprise disk-stack centrifugation.

[0028] In the previous methods, the method further may comprise a recovery step to obtain a depleted PVC based material from said depleted PVC based material fraction, preferably wherein said recovery step comprises evaporation and / or flocculation.

[0029] In the previous methods, the heavy metal-containing PVC based material may have a lead content above 1000 ppm, preferably above 4000 ppm, more preferably in the range of 6000 - 10000 ppm.

[0030] In the previous methods, the heavy metal-containing PVC based material may comprise post-consumer PVC.

[0031] In the previous methods, the heavy metal-containing PVC based material may comprise rigid PVC and / or plasticized PVC.

[0032] A heavy metal depleted PVC based material obtainable by any of the previous methods.

[0033] According to another aspect of the invention, there is provided a method for producing a heavy metal depleted PVC based material, comprising:a dissolution step comprising dissolving at least part of said heavy metal-containing PVC based material in a solvent system comprising a major solvent and an reaction agent, to obtain a depleted PVC material fraction and a heavy metal-rich fraction.

[0034] Fig.1 shows that the lead extraction efficiency is dropping below 98% when the reaction agent is below 0.1 vol% in the solvent system.Description of Embodiment

[0035] The heavy metal-containing material generally comprises a PVC matrix. The heavy metal-containing material may be based on or may be a plasticized and / or rigid PVC formulation (herein also referred to as flexible or rigid PVC, respectively). These terms are known in the art. Generally, plasticized PVC is used to refer to PVC formulations that contain plasticizers, while rigid PVC has little to no plasticizers. It may be appreciated that the present invention may be suitably applied to both flexible and rigid PVC.

[0036] Due to the use of cadmium- and / or lead-based stabilisers, the heavy metal typically comprises lead and / or cadmium, preferably lead. The heavy metal-containing material typically has a lead content above 1000 ppm, such that it is required by the issued regulation that the lead content is reduced. Typically, the heavy metal-containing material has a lead content above 4000 ppm or 5000 ppm, such in the range of 6000 - 10000 ppm. Additionally, or alternatively, the heavy metal-containing material typically has a cadmium content below 1000 ppm, for instance below 200 ppm, such that it is not required by the issued regulation that the cadmium content is reduced. Nonetheless, it may be appreciated that the method may suitably be employed to extract cadmium. Accordingly, the method may be employed if needed to reduce the cadmium content.

[0037] As the use of cadmium-based stabilisers has been phased out over 20 years ago, the most prominent stabilisers found in heavy metal-containing PVC-based material comprises lead. Accordingly, it is most preferred that the heavy metal comprises or even is lead. The heavy metal-containing PVC-based material is therefore preferably a lead-containing PVC-based material (herein also referred to as lead-containing material).

[0038] It may be appreciated that generally the heavy metal-containing material comprises post-consumer PVC, for instance post-consumer PVC waste. The heavy metal-containing material may further comprise a variety of stabilizers, such as e.g. Ca / Zn, Ba / Zn, lubricants such as oxidized polyethylene, stearic acid, fillers such as calcium carbonate, plasticizers such as phthalates, trimellitates and / or pigments. The composition of the heavy metal-containing PVC material typically depends on the type of waste, for instance pipe or (window) profile waste, but could also comprise more difficult to treat waste such as composite, tarpaulin, cable, flooring, slush moulding, etc., that are known to the person skilled in the art.

[0039] The heavy metal-containing material may be provided in any size and any form, such as powder, pellets, chips and / or flakes. Generally the smaller the size, the faster the dissolution process. However, for the sake of energy and costs, it may be preferred to keep the median particle size (d50) above 100 μm, such as at least 250 μm. Such sizes may be obtained by pretreating the heavy metal-containing PVC based material. The pretreatment may comprises reducing the size of the heavy metal-containing material, such as by grinding, pulverizing, cutting and / or crushing.

[0040] The method comprises a dissolution step comprising dissolving at least part of the heavy metal-containing PVC based material in a solvent system. The solvent system may be solvent system (a), solvent system (b), and / or solvent system (c). Unless specifically indicated otherwise, the term 'solvent system' as used herein refers to solvent system (a), solvent system (b) and / or solvent system (c).

[0041] Dissolution of the heavy-metal containing material generally makes the access to the PVC additives (such as the heavy metals) easier. The amount of dissolved heavy metal-containing material may depend on the composition. For instance, plasticized and rigid PVC may comprise non-soluble additives, such as fillers, pigments and metals. Furthermore, plasticized PVC typically comprises up to 60 wt% plasticizers, based on the total weight of the plasticized PVC, which may be miscible with the solvent system. Accordingly, generally at least 40 wt% of the heavy metal-containing PVC based material is dissolved in the solvent system, based on the total weight of the heavy metal-containing material. Nonetheless, it may be appreciated that typically at least 90 wt%, more preferably at least 95 wt%, more preferably at least 99 wt% of the PVC (e.g. the PVC polymer chains or PVC matrix) present in the heavy metal-containing material is dissolved in the solvent system, based on the total weight of PVC present in the heavy metal-containing material.

[0042] Accordingly, at least part of the heavy metal-containing PVC based material may be dissolved in solvent system (a) (i.e. comprising the major solvent, preferably without a reaction agent), solvent system (b) (i.e. comprising the major solvent and a first reaction agent) and / or in solvent system (c) (i.e. comprising the major solvent and a second reaction agent). In other words, the solvent system may thus comprises a major solvent (solvent system (a)), the major solvent and a first reaction agent (solvent system (b)) and / or the major solvent and a second reaction agent (solvent system (c)). Preferably, at least part of the heavy metal-containing PVC based material may be dissolved in solvent system (a), solvent system (b) or in solvent system (c). Unless specifically indicated otherwise, the term 'reaction agent' as used herein refers to the first and / or second reaction agent.

[0043] The major solvent typically allows for good and sufficient dissolution of the heavy-metal containing material. Suitable major solvents are known in the art. Preferably, the major solvent is selected from the group consisting of methyl ethyl ketone (MEK), 2-methyltetrahydrofuran (meTHF), tetrahydrofuran (THF), cyclohexanone and / or dimethyl carbonate. Typically, these solvents allow to provide a 5 - 15% solution, typically 5 - 10%. It was found that particularly good results were obtained for a solvent system comprising MEK as major solvent. In addition, MEK is typically preferred due to its low costs and low toxicity.

[0044] The reaction agent advantageously allows for good extraction of the heavy-metal, in particular the lead-based stabilisers. An acid may react with a lead-based stabiliser through a salt metathesis reaction type, and thereby forming a lead salt. It was found that not all acids are particularly suitable, for instance hydrochloric acid and acetic acid do not tend to improve the heavy metal extraction. The reaction agent is selected from the group consisting of an acid or a salt containing a sulfonate group or moiety and / or having an ability to form complexes with lead and / or cadmium compounds. The sulfonate group or moiety is represented by a formula R-SO3-,where R is an organic group such as aliphatic or aryl group. The reaction agent is typically seleted from the group consisting of methane sulfonic acid (MSA), p-toluene sulfonic acid (PTSA), nitric acid, sulfuric acid, citric acid and / or ethylenediaminetetraacetic acid (EDTA). Particularly suitable and particularly preferred reaction agents are MSA and / or PTSA, due to low volatility, strong acidity and low toxicity. Additionally, it was surprisingly found that the use of MSA and / or PTSA results in a low residual heavy metal content and a high efficiency, even with mild separation conditions for the separation step (vide infra). Accordingly, the first reaction agent is selected from the group consisting of MSA and / or PTSA. In particular MSA beneficially reacts with lead due to its high acid strength. Moreover, MSA is considered a green acid, has a low volatility and low toxicity. Accordingly, MSA is most preferred as first reaction agent. The second reaction agent is selected from the group consisting of nitric acid, sulfuric acid, citric acid and / or ethylenediaminetetraacetic acid (EDTA).

[0045] Typically, the solvent system comprises at most 5 vol% of the reaction agent, preferably at most 4 vol%, more preferably at most 3 vol%, even more preferably at most 1 vol%, even more preferably at most 0.6 vol%, most preferably at most 0.3 vol%, based on the total volume of the solvent system. Typically, the solvent system comprises at least 0.1 vol% of the reaction agent. As may be appreciated, this may be applicable on solvent system (b) and / or (c) independently. It is particularly preferred that in case MSA is used as the reaction agent, that at most 0.3 vol% MSA is used in the solvent system. For PTSA, nitric acid, sulfuric acid, citric acid and / or EDTA 0.6 - 3 vol% is typically considered sufficient.

[0046] To allow for good dissolution of the heavy metal-containing material, the dissolution step is preferably performed at a temperature in the range of 50 - 150 °C, preferably 60 - 120 °C, more preferably in the range of 60 - 110 °C, such as around 80 °C or around 100 °C. Additionally, or alternatively, the dissolution step is typically performed for a duration of at most 4 hours, preferably at most 3 hours, such as around 2 hours. Additionally or alternatively, a pressure of at least 1 bar, preferably at least 1.5 bar, more preferably at least 3 bar, such as 5 bar is applied during the dissolution step. In order to avoid the risk of explosion and / or degradation of the solvent system, it may be preferred that the dissolution step is performed under an inert atmosphere, such as argon or nitrogen. It may be appreciated that the best results may be obtained for MEK as a major solvent, at approximately 100 °C, under a pressure of roughly 5 bar and under a nitrogen atmosphere.

[0047] The dissolution step typically results in a depleted PVC based material fraction (herein also referred to as depleted material fraction or depleted PVC material fraction) and a heavy metal-rich fraction. The depleted PVC based material fraction may be a solution comprising the depleted PVC based material (herein also referred to as the depleted material or depleted PVC based material) and the solvent system. The heavy metal-rich fraction is typically a solid fraction comprising the heavy metal. Nonetheless, it may be appreciated that some heavy metal may remain in the depleted PVC based material fraction. As the heavy-metal is typically lead, the heavy metal containing PVC based material is typically a lead-containing PVC based material, the depleted PVC based material fraction is typically a lead-depleted PVC based material fraction, the depleted PVC based material is typically a lead-depleted PVC based material and the heavy metal-rich fraction is typically a lead-rich fraction.

[0048] The method preferably further comprises a separation step comprising separating the depleted PVC material fraction and the heavy metal-rich fraction. The separation may be performed by any suitable means known in the art. Preferably, the separation step comprises centrifugation and / or sedimentation. Centrifugation typically allows for a faster separation, which is therefore preferred. Due to the relatively small size and softness of the heavy metal aggregates it is preferred that the separation step comprises disk-stack centrifugation. It may be appreciated that the separation step may be preceded by a pre-separation step. This may allow to extract additives with a large size in the pre-separation step (such as titanium- and / or calcium-based additives), the separation step may allow for the separation of the heavy-metal rich fraction that tends to have smaller sizes.

[0049] It was surprisingly found that there is a strong dependency between the centrifugation conditions and the residual heavy metal content. It is therefore preferred that centrifugation is at g-forces between 1000 - 3000 g for approximately 5 - 80 minutes, such as 30 minutes.

[0050] It may be appreciated that the heavy metal may be present as aggregates or fine particles. Accordingly, the heavy metal-rich fraction may comprise heavy metal aggregates. Depending on the reaction agent, the aggregates may be smaller or larger. Typically, the more favorable the reaction between the reaction agent and the heavy metal, the higher the conversion resulting in the formation of more Pb-complexes. Generally, it was observed that the more favorable the reaction, the larger the heavy metal aggregates. For instance, MSA results in enlargement of lead-based stabilisers. Typically, the heavy metal aggregates, such as lead aggregates, have a median particle size (d50) between 0.01 - 500 μm, preferably between 0.1 - 50 μm, preferably between 0.3 - 13 μm, more preferably between 1 - 10 μm, such as less than 5 μm. This may specifically the case when the heavy metal is lead and / or cadmium and the major solvent comprises, preferably, MEK. It may be appreciated that, in case the aggregates are very small, it may be cumbersome and complex to separate these heavy metal particles from the depleted PVC based material fraction, for instance due to clogging of a filter.

[0051] In view thereof, it may be preferred to increase the particle size. This may be achieved by adding a flocculant and / or a small amount of water, such as between 3- 5 vol% water, to the solvent system. As may be appreciated, this is typically not required when solvent system (b) is employed, i.e. when the solvent system comprises the first reaction agent (i.e.. PTSA and / or MSA), as the first reaction agents already allow for enlarged aggregates. Moreover, any optionally formed lead salts due to the reaction of PTSA and / or MSA with a lead-based stabiliser may dissolve in water.

[0052] For solvent system (a) and / or for solvent system (c), the method further comprises a treatment step comprising treating the depleted PVC based material fraction with an ion exchange resin (herein also referred to as resin). It may be preferred to employ this treatment step as well, when solvent system (b) is employed, to even further increase the extraction efficiency. The treatment step is typically performed after the separation step.

[0053] The ion exchange resin advantageously allows for extracting further heavy metals that may still be present in the depleted PVC based material fraction. Without wishing to be bound by theory, several lead-based stabilisers (e.g. tribasic lead sulfate (3PbO. PbSO4・.H2O)) adhere to the ion exchange resin.

[0054] Advantageously, the use of the ion exchange resin further improves the efficiency of the method according to the present invention, in particular for solvent systems (a) and / or (c). Additionally, the ion exchange resin allows for mild separation, in particular centrifugation, conditions for the preceding separation step. For instance, it may already be sufficient to apply a g-force of 1500 g for 5 minutes.

[0055] The ionic exchange resin preferably exhibits strong acidic properties, similar to MSA and / or PTSA. Accordingly, the ion exchange resin is preferably a cationic exchange resin. Typically, sulfuric acids tend to react very good with lead and thus with lead-stabilisers. Therefore, the ion exchange resin is more preferably a cationic exchange resin comprising a sulfonic acid moiety. Preferably, the ion exchange resin in a cationic exchange resin comprising porous (e.g. polystyrene) beads with sulfonic acid moieties. A suitable example includes Amberlyst (Registered Trademark) 15. The ion-exchange resin, in particular the ion-exchange resin beads, may be separated after the treatment step. This may be achieved by any means known in the art, such as filtration and / or sieving.

[0056] In order to activate the ion exchange resin, in particular on a laboratory scale, it may be required to contact the ion exchange resin with a strong acid, such as hydrochloric acid (e.g. a 1M HCl solution). Typically, 100 ml resin may be activated in 1L of 1M HCl solution. Activation may accordingly be achieved by submerging the resin in an acidic solution for a certain time period, such as at least 30 minutes, preferably at least 45 minutes, such as approximately 60 minutes, optionally with stirring. This is followed by filtering the solution and rinsing the resin with e.g. distilled water. The remaining water is preferably removed to minimize the disadvantageous effect of water on the PVC solubility in the solvent system. Accordingly, the resin is preferably washed with the major solvent, such as MEK. In order not to affect the performance of the resin, it may be preferred that the major solvent used for washing has a conductivity below 4 μS / cm, preferably below 2 μS / cm. It may be needed to employ several washing cycles to obtain a conductivity below this threshold.

[0057] It was found that, particularly for laboratory experiments, the depleted PVC based material fraction (solution) is preferably treated by the ion exchange resin, generally fresh or regenerated resin, by bringing the ion exchange resin in contact with the depleted PVC based material in a vessel, typically in a volume ratio of resin to depleted PVC based material fraction in the range of 1:10 to 10:1, preferably 1:5 to 5:1, such as 3:2.

[0058] The mixture is typically kept for a certain period of time while agitating to ensure a good contact with the resin (typically in a roller bench), to allow for the heavy metal to be extracted by and / or adhere to the ion exchange resin. This may for instance be between 1 - 30 minutes, such as between 5 - 20 minutes, or approximately 15 minutes. The resin may afterwards be removed by any suitable means, such as by sieving, this is particularly useful if the ion exchange resin is an ion exchange resin bead.

[0059] The resins may be dried for storage or disposal. Alternatively or additionally, the resins may be rinsed with a major solvent to be reused. After rinsing with a major solvent, the resins may again be subjected to the activation procedure as detailed herein above. It may be appreciated that this is typically valid on a laboratory scale. However, valuable information may be retrieved for upscaling therefrom.

[0060] The method may further comprise a recovery step to obtain a depleted PVC based material from the depleted PVC based material fraction. The recovery step is preferably after separation step and / or preferably after the treatment step. The depleted PVC based material may be recovered by any suitable means known in the art. Examples include flocculation and / or evaporation. Flocculation may be achieved by addition of a non-solvent, such as methanol. The addition of the non-solvent allows for precipitation of the depleted PVC based material, which may accordingly be easily recovered by filtration. Alternatively, or additionally, the recovery step may comprise evaporation. Evaporation may be achieved by drying to air for e.g. 2-3 days or by placing it at elevated temperatures, optionally under vacuum, for e.g. 60 minutes at 50 °C. Optionally, the depleted PVC based material may further be dried, such as by air or under controlled environment (such as in a desiccator).

[0061] The depleted material generally has a lead content below 1000 ppm. Advantageously, this meets the REACH regulation set by the European union, wherein lead is identified on the candidate list as a substance of very high concern for authorization and therefore should be below 1000 ppm. Additionally, or alternatively, the depleted material may have a reduced cadmium content compared to the starting material, i.e. the heavy metal containing PVC based material. Advantageously, this not only already typically meets Regulation (EU) 494 / 2011, but may also allow for meeting any future regulations in which the cadmium content needs to be further reduced. Preferably, the depleted PVC based material is a lead-depleted PVC based material which has a lead content below 1000 ppm.

[0062] The method according to the present invention may allow for extraction efficiencies of at least 80%, such as at least 90% or even above 95%, such as above 98% or above 99%, such as 99.8%.

[0063] The invention is further directed to a heavy metal depleted PVC-based material obtainable by the method, in particular a lead depleted PVC-based material obtainable by the method. Preferably, the heavy metal depleted PVC-based material has a lead content below 1000 ppm. The heavy metal depleted PVC-based material typically comprises 50 - 100 ppm, such as at least 100 ppm sulfur. In cases where solvent system (b) is employed, the heavy metal depleted PVC-based material typically comprises at least 5000 ppm, preferably at least 7000 ppm, more preferably in the range of 5000 - 80000 ppm sulfur.

[0064] For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. 　　The present invention may further be illustrated by the following non-limiting examples. 　　In the examples, the lead and cadmium extraction efficiencies have calculated in the following way: Example 1

[0065] Solvent system without reaction agent and without an ion exchange resin treatment (comparative example) 　　PVC micronized powder based material comprising post-consumer PVC with lead content of 7300 ppm and a cadmium content of 170 ppm was used in these experiments. 2.3 g of post-consumer PVC were placed in a flask with a stirring rod. 97 mL of MEK was added to the flask. The mixture was warmed up to 80-85oC and stirred until all PVC was dissolved. Subsequently, the solution was allowed to cool to room temperature and was centrifugated for 5 minutes at a relative centrifugation force of 1740 g. Heavy metal depleted PVC was recovered by evaporation of the solvent by drying to air for 2-3 days. The residual lead and cadmium content measured by ICP-OES (Shimadzu 9820) were 1898 mg / kg and 108 mg / kg, respectively, resulting in an extraction efficiency of 74.0% for lead and of 36.5% for cadmium.Example 2

[0066] Solvent system without reaction agent but with an ion exchange resin treatment (comparative example) 　　PVC micronized powder based material comprising post-consumer PVC with lead content 7300 ppm and a cadmium content of 170 ppm was used in these experiments. 2.3 g of post-consumer PVC were placed in a flask with a stirring rod. 97 mL of MEK was added to the flask. The mixture was warmed up to 80-85oC and stirred until all PVC was dissolved. Subsequently, the solution was allowed to cool to room temperature and was centrifugated for 5 minutes at a relative centrifugation force of 1740 g. Then the supernatant from centrifugation was treated by a cationic exchange resin (here Amberlyst(Registered Trademark)15 a cross-linked polystyrene-based ion exchange resin with sulfonic acid groups) in a volume ratio 3:2 resin / solution for 15 min under agitation (e.g. in laboratory scale in a roller bench) to promote the contact between the solution and the resin. Next, the resin beads were separated from the solution by filtration. Heavy metal depleted PVC was recovered by evaporation of the solvent by drying to air for 2-3 days. The residual lead and cadmium content measured by ICP-OES were 52 mg / kg and 30 mg / kg, respectively, resulting in an extraction efficiency of 99.3% for lead and of 82.3% for cadmium.Example 3

[0067] MSA used as reaction agent 　　PVC micronized powder based material comprising post-consumer PVC with lead content between 6000 and 7300 ppm and cadmium content between 170 and 400 ppm as well as artificial PVC samples with an initial lead content between 18000 and 19000 mg / kg were used in these experiments. 2.3 g of post-consumer PVC or, for the artificial samples, 2.3 g of processed PVC strips cut in pieces (from 0.5 x 0.5 up to 2 x 2 cm) were placed in a flask with a stirring rod. 97 mL of MEK and 0.6 ml of Methane Sulfonic Acid (MSA) were added to the flask. The mixture was warmed up to 80-85oC and stirred until all PVC was dissolved. Subsequently, the solution was allowed to cool to room temperature and was centrifugated for 30 minutes at a relative centrifugation force of 2315 g. Heavy metal depleted PVC was recovered by evaporation of the solvent by drying to air for 2-3 days. The residual lead content measured by ICP-OES was 12 mg / kg and 30 mg / kg for the post-consumer samples and for the artificial samples, respectively, resulting in an extraction efficiency of 99.8%. The residual cadmium content measured in the post-consumer samples was below 2 mg / kg, resulting in an extraction efficiency of 99.3%.Example 4

[0068] MSA used as reaction agent: cut of point of 0.1 vol% 　　Artificial PVC samples comparable to typical window profile formulations with an initial lead content of 17600 mg / kg were used in this experiment. 2.3 g of processed PVC strips cut in pieces (from 0.5 x 0.5 up to 2 x 2 cm) were placed in a flask with a stirring rod. 97 mL of MEK and Methane Sulfonic Acid (MSA) content varying from 0.6 ml to 0.01 ml were added to the flask. The procedure described in example 3 was used; except that various amount of MSA were dosed. The results obtained are plotted in Table 1 where we can see that the residual lead content is significantly higher when the reaction agent content (here MSA) is lower than 0.1 vol%. Figure 1 also illustrates that the lead extraction efficiency is dropping (below 98%) when the MSA content in the solvent system is below 0.1 vol%. Effect of the MSA content on the residual lead content (WP profile formulation with initial lead content of 17600 mg / kg). Test conditions are provided in [Example 3]Example 5

[0069] PTSA used as reaction agent 　　Artificial PVC samples comparable to typical window profile formulations with an initial lead content between 18000 and 19000 mg / kg were used in this experiment. The procedure described in example 3 was used; except that 1.6 g of PTSA (p-Toluene Sulfonic Acid) was used instead of the MSA. In this example, the residual content measured was 30 mg / kg, resulting in an extraction efficiency above 99.8%.Example 6

[0070] Citric acid used as reaction agent with ion exchange resin treatment 　　The same samples as in example 5 were used and placed in an flask with a stirring rod. 97 mL of MEK and 1.5 g citric acid were added to the flask. The mixture was warmed up to 80-85 °C and stirred until all PVC was dissolved. Subsequently, the solution was allowed to cool to room temperature and was centrifugated for 30 minutes at a relative centrifugation force of 2315 g. 　　The supernatant from centrifugation was brought in contact with a cationic exchange resin (here Amberlyst(Registered Trademark)15 a cross-linked polystyrene-based ion exchange resin with sulfonic acid groups) in a volume ratio 3:2 resin / solution for 15 min under agitation (e.g. in laboratory scale in a roller bench) to promote the contact between the solution and the resin. Next, the resin beads were separated from the solution by filtration. Heavy metal depleted PVC was recovered by evaporation of the solvent by drying to air for 2-3 days. The residual lead content measured was 40 mg / kg, resulting in an extraction efficiency of 99.8%.

Claims

1. Extraction method for extracting a heavy metal from a heavy metal-containing polyvinyl chloride (PVC) based material, wherein said method comprises: 　　a dissolution step comprising dissolving at least part of said heavy metal-containing PVC based material in a solvent system comprising a major solvent and a reaction agent, to obtain a depleted PVC material fraction and a heavy metal-rich fraction.

2. Method according to claim 1, wherein the reaction agent is selected from the group consisting of an acid or a salt containing a sulfonate group or moiety and / or having an ability to form complexes with lead and / or cadmium compounds.

3. Method according to claim 1, wherein the reaction agent is selected from the group consisting of nitric acid, sulfuric acid, citric acid, ethylenediaminetetraacetic acid (EDTA), methane sulfonic acid (MSA), and p-toluene sulfonic acid (PTSA).

4. Method according to any of previous claims, wherein the method further comprises a treatment step comprising treating said depleted PVC based material fraction with an ion exchange resin.

5. Method according to claim 4, wherein the method further comprises the treatment step for the solvent system.

6. Method according to any of the previous claims, wherein the heavy metal is lead or cadmium.

7. Method according to any of the previous claims, wherein said major solvent is selected from the group consisting of methyl ethyl ketone (MEK), 2-methyltetrahydrofuran (meTHF), tetrahydrofuran (THF), cyclohexanone and / or dimethyl carbonate.

8. Method according to any of the previous claims, wherein the solvent system comprises at most 5 vol% of said reaction agent, preferably at most 4 vol%, more preferably at most 3 vol%, even more preferably at most 1 vol%, even more preferably at most 0.6 vol%, most preferably at most 0.3 vol% based on the total volume of the solvent system.

9. Method according to any of the previous claims, wherein the solvent system comprises at least 0.1 vol% of said reaction agent.

10. Method according to any of the previous claims, wherein said dissolution step is performed under an inert atmosphere and / or at a temperature in the range of 50 - 150 °C, preferably 60 - 120 °C, more preferably in the range of 60 - 110 °C, such as around 80 °Cor around 100 °Cand / or performed for a duration of at most 4 hours, preferably at most 3 hours, such as around 2 hours and / or at a pressure of at least 1 bar, preferably at least 1.5 bar, more preferably at least 3 bar such as 5 bar.

11. Method according to any of the previous claims, wherein said heavy metal-rich fraction comprises heavy-metal aggregates, preferably heavy-metal aggregates having a median particle size (d50) between 0.01 - 500 μm, preferably between 0.1 - 50 μm, more preferably between 0.3 - 13 μm, even more preferably between 1 - 10 μm.

12. Method according to any of the previous claims, wherein said ionic exchange resin is a cationic exchange resin, more preferably a cationic exchange resin comprising a sulfonic acid moiety.

13. Method according to any of the previous claims, wherein said method further comprises a separation step comprising separating the depleted PVC based material fraction and the heavy metal-rich fraction, preferably wherein said separation step comprises centrifugation and / or sedimentation.

14. Method according to the previous claim, wherein said separation step comprises disk-stack centrifugation.

15. Method according to any of the previous claims, wherein said method further comprises a recovery step to obtain a depleted PVC based material from said depleted PVC based material fraction, preferably wherein said recovery step comprises evaporation and / or flocculation.

16. Method according to any of the previous claims, wherein the heavy metal-containing PVC based material has a lead content above 1000 ppm, preferably above 4000 ppm, more preferably in the range of 6000 - 10000 ppm.

17. Method according to any of the previous claims, wherein said heavy metal-containing PVC based material comprises post-consumer PVC.

18. Method according to any of the previous claims, wherein the heavy metal-containing PVC based material comprises rigid PVC and / or plasticized PVC.

19. A heavy metal depleted PVC based material obtainable by the method according to any of the previous claims.

20. Method for producing a heavy metal depleted PVC based material, comprising: 　　a dissolution step comprising dissolving at least part of said heavy metal-containing PVC based material in a solvent system comprising a major solvent and an reaction agent, to obtain a depleted PVC material fraction and a heavy metal-rich fraction.

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