# Antimony Trioxide Extraction from E-Waste Brominated Flame-Retardant Laden Plastics by Simultaneous Liquid-Liquid Extraction and Leaching

Morvan Gaudin, Vincent Semetey, Frédéric Rousseau, Grégory Lefevre

► To cite this version:

Morvan Gaudin, Vincent Semetey, Frédéric Rousseau, Grégory Lefevre. Antimony Trioxide Extraction from E-Waste Brominated Flame-Retardant Laden Plastics by Simultaneous Liquid-Liquid Extraction and Leaching. ACS Sustainable Resource Management, 2025, 2 (3), pp.473-480. 10.1021/acssusres- mgt.4c00466. [https://doi.org/10.1021/acssusres- mgt.4c00466](https://doi.org/10.1021/acssusres- mgt.4c00466)

HAL Id: hal-05307882

https://hal.science/hal-05307882v1

Submitted on 10 Oct 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
Antimony trioxide extraction from e-waste brominated flame-retardant laden plastics by
simultaneous liquid-liquid extraction and leaching

Morvan Gaudin †, Vincent Semetey †, Frédéric Rousseau †, Grégory Lefevre †*

† Institut de Recherche de Chimie Paris, Chimie ParisTech, CNRS, PSL Research University, 11 rue

Pierre et Marie Curie, 75005 Paris Cedex 05, France

*gregory.lefevre@chimieparistech.psl.eu

Keywords: Sb₂O₃, recycling, hydrometallurgy, dissolution, WEEE

Abstract

A novel method for extracting antimony from electronic waste plastics has been investigated in this work. Antimony trioxide is initially incorporated into these plastics in synergy with brominated molecules hence their common name “brominated plastics”. This combination offers excellent flame-retardant properties. The mechanical recycling of brominated plastics is prohibited due to the hazardous nature of the molecules that are generated during the process. Therefore, this article explores the use of a plastic dissolution method combined with liquid-liquid interfacial leaching to remove antimony trioxide while recovering a plastic cleansed of this problematic additive. The primary investigative focus pertained to the refinement of the aqueous extractant solution, while the secondary focus centred on the selection of the dissolution solvent. The process demonstrates high efficiency in antimony extraction, achieving up to 98 mass% recovery, with minimal impact on the structural integrity of the ABS (Acrylonitrile Butadiene Styrene) plastic. By insolubilizing the plastic to recover it, it is also feasible to recover up to 98 mass% of the brominated molecules, thereby ensuring compliance with legal thresholds for the reuse of plastics. This methodology not only
addresses the challenge of safely recycling hazardous materials in electronic waste but also offers
insights for future enhancements in electronic waste management and antimony recycling.

30

31

# 1. Introduction

E-waste or Waste Electrical and Electronic Equipment (WEEE) is the fastest-growing household waste
category, reaching 4.7 million tons of e-waste collected in the EU, averaging 11 kg per inhabitant¹.

This waste comprises approximately 22,000 tonnes of brominated flame retardant (BFR) plastics
containing over 2,000 ppm of bromine predominantly as tetrabromobisphenol A (TBBPA).² Flame
retardants fall into three primary categories: 1 – metal hydroxides like Al(OH)₃, 2 – organohalogen
compounds, (mainly brominated combined with its synergist antimony trioxide (Sb₂O₃) in the form of
micrometric crystals), and 3 – organophosphorus compounds. Flame retardants are crucial for the
safety of plastics being used in construction materials, electronics, textiles, and coated products.³

Around 50 mass% of antimony consumed globally is in flame retardants, with 70 mass% being used in
plastics containing bromine for electrical and electronic equipment.⁴ Acrylonitrile Butadiene Styrene
(ABS) and high-impact polystyrene (HIPS) are prominent plastics under scrutiny. Depending on the
category, between 48% and 96% of the plastics found in WEEE are styrenics.⁵ Bromine and
antimony can account for 10 mass% and 6 mass% of the plastic waste mass, respectively ⁶,⁷.

Exceeding the European legal limit of 0.2 mass% Br renders the waste hazardous and prohibits
recycling.⁸ Thus, safe disposal requires high-temperature incineration, resulting in the loss of bromine
and antimony.

48

Extracting critical elements from electronic waste, such as antimony, is an essential environmental and
economic priority due to its depletion as a primary mining resource. The world relies heavily on
China, which mines 80% of primary antimony ore, making antimony a critical material in the
EU.⁹ Several methods have been proposed in the literature for antimony extraction, but they all result
in the destruction of the plastic matrix.¹⁰

54
In 2009, an approach involving oxidative combustion of antimony-rich halogenated waste was proposed. The study found that 64 mass% of the antimony remained in the residual bottom ash, while 36 mass% was released to the gas phase.¹¹ In a 2009 study, alkaline reforming of WEEE in supercritical water and NaOH was demonstrated to achieve the recovery of 97 mass% of bromine and 98 mass% of antimony.¹² A 2012 study demonstrated that the use of CaO and Ca(OH)₂ during pyrolysis effectively reduces bromine and antimony levels, resulting in significantly lower concentrations in the resulting oil.¹³ However, this method did not recover bromine or antimony. The research conducted in 2019 showed that leaching ABS with 12 mol.L⁻¹ HCl, 18 mol.L⁻¹ H₂SO₄, or aqua regia can extract up to 20 mass% of antimony oxide.¹⁴

However, there are developed methods that preserve the plastic matrix. In 2016, researchers developed the Creasolv process which effectively removed 90 mass% of Sb₂O₃ and 98 mass% of BFR from plastics using a combination of centrifugation and heating.¹⁵ In 2008, a study explored liquid-liquid and liquid-solid extractions using ionic liquids, achieving 92.7 mass% extraction of bromine and 99.9 mass% extraction of antimony.¹⁶ However, the costs of ionic liquids and industrial centrifugation are high. In 2021, another dissolution precipitation method using supercritical CO₂ was developed for extracting brominated molecules, achieving a 43 mass% extraction yield.¹⁷ Thus, the dissolution-precipitation method has great potential for extracting antimony and bromine. In 2013, a study reported a 50 mass% recovery of antimony through a specific solvent-assisted leaching process that used tartaric acid as a complexing agent in association with nitric acid and using DMSO.¹⁸

The present study draws inspiration from the aforementioned article and undertakes an investigation into the impact of different solvents on the solvent-assisted lixiviation of antimony using immiscible solvent. The method combines dissolution-precipitation and extractive hydrometallurgy to Sb₂O₃ at room temperature using common reagents as chemical pathway instead of costly physical pathways (e.g., centrifugation) is explored. The focus is on ABS plastics, the primary thermoplastic in WEEE. The extraction involves three steps: polymer dissolution, antimony recovery through liquid/liquid extraction with an acidic solution, and selective polymer precipitation using a non-solvent. In this
article, the first two stages have been explored. Firstly, various combinations of acids and a
complexing agent are tested using the same solvent. A second part focuses on choosing the most
suitable solvents to make the Sb₂O₃ more accessible for the liquid-liquid extraction. A thorough
investigation was conducted into the sustainability of the solvents that had been selected. Our
approach was to proceed in this order to ensure first the optimal combination for extracting Sb₂O₃, and
then to improve the release from its polymer matrix. Thus, this work paves the way to a process able to
valorise brominated plastics by extracting antimony and reducing the bromine content below the legal
threshold which prevents their recycling.

## 2. Experimental Section

### 2.1. *Chemical compounds*

The plastic components employed in the protocol was a dismantled 5-mm thick ABS computer case, provided by the French eco-organisation Ecosystem. A sample is depicted in Figure 1. This waste is typical of the industrial sorting chains. Other compounds were also used to produce standardized samples with known antimony oxide and bromine compositions. Low filler commercial ABS Magnum 3453 Natural have been purchased from Resinex. Antimony trioxide (> 99.5%) was provided by Thermo Scientific and tetrabromobisphenol A (> 99%) by VWR. Purity of such tartaric acid powder was > 99.6%. All solvents and acids used in this work are standardized and come from well-known suppliers such as Sigma Aldrich, VWR or Carlo Erba.

### 2.2. *Analytical and characterisation techniques*

Plastic samples were analysed using a ThermoScientific Nicolet iS50 FT-IR spectrometer with an
attenuated total reflectance (ATR) accessory. Dissolved antimony has been quantified by Inductively
Coupled Plasma-Optical Emission Spectroscopy (ThermoScientific ICAP 6300 Duo ICP-OES) after
dilution and acidification with nitric acid. Solid samples were analysed with X-ray fluorescence
spectrometry (XRF) using a Malvern Epsilon 1 analyser. Molecular weights (MWs) and molecular
weight distributions (D) were determined using size exclusion chromatography (SEC), consisting in a
Waters 1515 isocratic high-performance liquid chromatography pump, two Styragel HR 5E columns,
and a refractive index (RI) detector. Gaz chromatography was performed with an Agilent 8860 GC coupled to an MSD 5977C with a column model HP 19091S-433. Details on analytical protocols with XRF, SEC and GC are given in SI.

## 2.3. Extraction protocol

Figure 1 shows the steps in the experimental protocol, especially those (circled in red) which have been refined in this work, and the analytic methods. During step A, plastic plates were cleaned with MilliQ water and soap, cut into 10 mm × 10 mm pieces (approximately 0.3 g each). One fragment was analysed using ATR-FTIR to identify the polymer and the main brominated molecule, XRF for the initial concentration of bromine and antimony, and SEC to identify the molecular weight of the polymer. At step B for solubilization, 1 g of WEEE pieces were placed in a 20 mL glass tube sealed with a hermetic polypropylene stopper. Each tube received 10 mL of solvent and was agitated on a linear shaker at 200 movements per minute for 3 hours. At step C, 10 mL of the extractant solution was added to each tube. Tubes were hermetically sealed and placed on the linear shaker at the same frequency for 3 hours. This extraction time was chosen to assume steady-state conditions, thus enabling a comparison of the other parameters. The room temperature was kept constant and controlled during steps B and C (20 °C). During step D, the mixture was transferred into 30 mL of diethylether as non-solvent, resulting in the formation of three phases: organic, aqueous, with a solid at the interface. The action of the non-solvent to reform the plastic is an essential step that has been studied extensively (19, 20, 21) and will not be discussed in detail in this article. Moreover, this non-solvent also acted as an extraction solvent for brominated molecules. It was refrigerated at 4 °C for 12 hours to aggregate plastic particles, facilitating retrieval with tweezers. The obtained fraction was rinsed with 10 mL of clean non-solvent, oven-dried above the boiling point of solvents for 24 hours to remove residual solvents. Aqueous and organic phases were separated with a funnel and stored. The organic phase was oven-dried above the boiling point of the solvents to obtain a solid residue.
<figure><img src="image_2.png" /><figcaption>Figure 1: Protocol for extracting antimony oxide from brominated plastic and pictures of the sample at different stages of the process.</figcaption></figure>

## 2.4. Axe of investigation - phase 1: Sb₂O₃ extraction solution

Various combinations were tested (entries numbered from 1.1 to 1.7), including 1 mol.L⁻¹ nitric, 1 mol.L⁻¹ sulfuric acid, 1 mol.L⁻¹ hydrochloric acid, each with or without 1 mol.L⁻¹ tartaric acid, along with 1 mol.L⁻¹ tartaric acid without mineral acid. The experiments have been done in triplicate. Then, the ideal concentrations of nitric acid and tartaric acid were determined, varying nitric acid concentrations from 0 mol.L⁻¹ to 1 mol.L⁻¹ and tartaric acid from 0 mol.L⁻¹ to 1 mol.L⁻¹. Initially, dichloromethane is used as it is described by several sources as one of the best solvents for all types of ABS <sup>(22, 23)</sup>. The Sb₂O₃ in the aqueous samples was collected prior to the insolubilization step, while the plastic samples were collected after insolubilization.

## 2.5. Axe of investigation - phase 2: solvent
Different solvents are tested at this stage, (entries numbered from 2.1 to 2.16 in Table 1 - solvents are named from 1 to 16) each involved a 0.5 mol.L⁻¹ tartaric acid extractant solution (without mineral acids) for the aqueous phase. Various organic phases were explored. Two solvents from each major chemical family were tested. The representatives were chosen, whenever possible, for their low miscibility with water, to be compatible with liquid-liquid extraction²⁴. The selected group and their representatives include amines, ethers, aliphatic hydrocarbons, esters, halogenated solvents, alcohols, aromatics and ketones. Polar aprotic and acidic solvents were excluded due to their miscibility with water. Samples were collected before the insolubilization step. Sb₂O₃ concentration in the aqueous phase was measured *via* ICP-OES. Experiments were conducted in triplicate.

Experiment 3.0 was performed under the best extraction conditions, using *n*-butyl acetate as a solvent and tartaric acid 1 mol.L⁻¹.

<table><caption>Table 1: Summary of experiments conducted and characteristics of solvents.</caption><thead><tr><th rowspan="2">Sample number</th><th rowspan="2">Name</th><th rowspan="2">Chemical group</th><th colspan="3">Solvent</th><th colspan="2">Aqueous solution</th></tr><tr><th>Solubilization (MPA<sup>1/2</sup>)</th><th>Water solubility (w/w)*</th><th>Acid (1 mol.L<sup>-1</sup>)</th><th>Tartaric acid concentration</th></tr></thead><tbody><tr><td>1.1</td><td>Dichloromethane</td><td>Halogenated</td><td>Yes</td><td>20.2</td><td>0.24 %</td><td>Nitric Acid</td><td>none</td></tr><tr><td>1.2</td><td>Dichloromethane</td><td></td><td></td><td></td><td></td><td>Sulfuric acid</td><td>none</td></tr><tr><td>1.3</td><td>Dichloromethane</td><td></td><td></td><td></td><td></td><td>Hydrochloric acid</td><td>none</td></tr><tr><td>1.4</td><td>Dichloromethane</td><td></td><td></td><td></td><td></td><td>none</td><td>1 M</td></tr><tr><td>1.5</td><td>Dichloromethane</td><td></td><td></td><td></td><td></td><td>Nitric Acid</td><td>1 M</td></tr><tr><td>1.6</td><td>Dichloromethane</td><td></td><td></td><td></td><td></td><td>Sulfuric acid</td><td>1 M</td></tr><tr><td>1.7</td><td>Dichloromethane</td><td></td><td></td><td></td><td></td><td>Hydrochloric acid</td><td>1 M</td></tr><tr><td>2.1</td><td>Nitrobenzene #1</td><td>Amine</td><td>Yes</td><td>22.84</td><td>0 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.2</td><td>Aniline #2</td><td>Amine</td><td>Yes</td><td>23.73</td><td>5 %</td><td>none</td><td>0.5 M</td></tr></tbody></table>
<table><tr><td>2.3</td><td>Diethylether #3</td><td>Ethers</td><td>No</td><td>15.4</td><td>1.26 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.4</td><td>1,4-dioxane #4</td><td>Ethers</td><td>No</td><td>19.76</td><td>Miscible</td><td>none</td><td>0.5 M</td></tr><tr><td>2.5</td><td>Cyclohexane #5</td><td>Aliphatic hydrocarbons</td><td>No</td><td>16.8</td><td>0.01 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.6</td><td>Heptane #6</td><td>Aliphatic hydrocarbons</td><td>No</td><td>15.3</td><td>0.01 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.7</td><td>Isoamyl acetate #7</td><td>Esters</td><td>Yes</td><td>17.1</td><td>1.60 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.8</td><td>n-butyl acetate #8</td><td>Esters</td><td>Yes</td><td>17.4</td><td>1.20 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.9</td><td>Chloroform #9</td><td>Halogenated</td><td>Yes</td><td>18.7</td><td>0.06 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.10</td><td>Dichloromethane #10</td><td>Halogenated</td><td>Yes</td><td>20.2</td><td>0.24 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.11</td><td>Cyclohexanol #11</td><td>Alcohols</td><td>No</td><td>22.4</td><td>12 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.12</td><td>2-phenoxyethanol #12</td><td>Alcohols</td><td>Yes</td><td>23.53</td><td>low</td><td>none</td><td>0.5 M</td></tr><tr><td>2.13</td><td>Ethylbenzene #13</td><td>Aromatics</td><td>Yes</td><td>17.9</td><td>0 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.14</td><td>Toluene #14</td><td>Aromatics</td><td>Yes</td><td>18.2</td><td>0.03 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.15</td><td>Methyl isobutyl Ketone #15</td><td>Ketones</td><td>Yes</td><td>17</td><td>2 %</td><td>none</td><td>0.5 M</td></tr><tr><td>2.16</td><td>Cyclohexanone #16</td><td>Ketones</td><td>Yes</td><td>20.33</td><td>8.70 %</td><td>none</td><td>0.5 M</td></tr><tr><td>3.0</td><td>n-butyl acetate</td><td></td><td>Yes</td><td></td><td></td><td>none</td><td>1 M</td></tr></table>

* from references 22 and 24 (except for 2-phenoxyethanol: reference 28).

## 2.6. Modelling tools

### 2.6.1. Simulation of speciation within the aqueous systems

Medusa software²⁵ was used to simulate the speciation of Sb in the different systems. The software integrates chemical reactions, at 25 °C and 1 bar conditions, and the involved species' thermodynamic
properties. The Hydra Chemical Equilibrium Database has been completed with published data on antimony complexes.²⁶

## 2.6.2. Hildebrand solubility parameter (∂)

The Hildebrand solubility parameter (∂) was used in this study as a tool to understand the compatibility of materials. It quantifies the cohesive energy density of substances, i.e. the amount of energy required to completely remove a unit volume of molecules from their neighbours to infinite separation. ∂ is in MPa¹/².

$$ \partial = \sqrt{\frac{\Delta H_v - RT}{V_m}} \qquad (1) $$

Where ΔH_v is the heat of vaporization of a compound, R is the perfect gas constant, T is the temperature, and V_m is the molar volume in the condensed phase. The principle of 'like dissolves like' suggests that the closer the Hildebrand parameter of the solvent is to that of the polymer, the more it solubilises it. The ∂ values for the polymer fractions of ABS (polystyrene (PS), polyacrylonitrile (PAN), polybutadiene (PB)) and the solvents are obtained from literature.²³

# 3. Results and discussion

## 3.1. Identification of the plastic and the flame-retardant additive.

The materials coming from recycling chains have been characterized by infrared spectroscopy, following the approach from Diaz et al (²⁷). Commercial ABS from Resinex was compared with the end-of-life brominated plastics (spectra reported in Fig. SI1), and the WEEE plastic was identified as ABS with TBBPA as flame retardant. The chemical nature of the brominated molecule TBBPA, was confirmed by GC-MS analysis with a probability of 98.9 %. The content in antimony and bromine were 30,500 ppm (Sb) and 90,500 ppm (Br).
## 3.2. Phase 1: Setting the extraction solution.

During this phase, the results from experiments 1.1 to 1.7 were performed. The yield is calculated as the ratio between the quantity of Sb₂O₃ (in grams) extracted and the quantity of Sb₂O₃ initially present in the plastic (in grams). The plastic was solvated by dichloromethane in this part of the study focused on the most efficient extraction solution with the same solvent used. Figure 2 shows that the use of molar HNO₃ or H₂SO₄ allowed only 10 mass% of Sb₂O₃ to be extracted from the plastic and 7 mass% with HCl.
<figure><img src="image_3.png" /><figcaption>(B)</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>(C)</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>(D)</figcaption></figure>

<figure><img src="image_6.png" /></figure>
Figure 2: (A) Sb₂O₃ extraction yield for ABS WEEE using dichloromethane and various acidic extraction solutions (with number of the corresponding experiment) in modelling Sb₂O₃ speciation (14 mM) as a function of pH: (B) in water, (C) in presence of tartaric acid (tartrate) 1 mol.L⁻¹ or (D) hydrochloric acid 1 mol.L⁻¹.

The experimental extraction yields results were consistent with the modelling with Medusa/Hydra software (Fig. 2B-D) when the mineral acid chosen is nitric acid or sulfuric acid, showing a low solubility at low pH (Fig. 2B). It is not consistent for experiments using HCl where the presence of chloride ions is expected to increase the solubility due to the formation of SbCl₄⁻ complex at sufficiently low pH (Fig. 2D), perhaps because this species reacts in presence of water, forming insoluble oxy-chlorides not referenced in the software database. Figure 2B shows that the tartaric species make Sb(III) soluble even at neutral pH, what is consistent with the measurements. Indeed, using a 1 mol.L⁻¹ tartaric acid solution, it was observed that the system extracted 88 mass% of Sb₂O₃ (Fig. 2) from the plastic without the presence of a mineral acid (the pH value was measured at 1.65). Using a solution of tartaric acid with nitric acid or hydrochloric acid resulted in slightly higher extraction rates, while H₂SO₄ led to a slightly lower yield. Although HCl may enhance yields, its use is expensive due to steel corrosion and is not favoured.

From these first results, additional experimentations have been made to identify the impact of the concentrations of the optimum mixture, tartaric acid with nitric acid (Fig. 3A-B). Thus, tartaric acid concentration of 0.1 mol.L⁻¹ alone can extract 90 mass% of the antimony oxide without the need for nitric acid. Yields reached a plateau for tartaric acid concentrations above 0.1 mol.L⁻¹ and up to 0.1 mol.L⁻¹ nitric acid. Above this HNO₃ concentration, yields decrease can be attributed to the partial oxidation of Sb₂O₃ to Sb₂O₅ by HNO₃. Sb₂O₅ remains as a solid under acidic conditions, and Sb(V) is not complexed by tartaric acid (see speciation of Sb(V) in Fig. SI2).²¹
<figure><img src="image_7.png" /><figcaption>Figure 3: Extraction efficiency of Sb<sub>2</sub>O<sub>3</sub> extraction from a solvated WEEE ABS by varying (A) the concentrations of nitric and (B) tartaric acid and corresponding pH, and (C) Comparison of complexation kinetics of antimony oxide by 1 mol.L<sup>-1</sup> tartaric acid with Sb<sub>2</sub>O<sub>3</sub> powder (grey) and Sb<sub>2</sub>O<sub>3</sub> within a WEEE ABS (black)</figcaption></figure>

Despite the improvement of the extraction solution, a quantitative extraction yields of 100 mass% were not achieved. Therefore, a comparison of the complexation kinetics of pure Sb<sub>2</sub>O<sub>3</sub> powder and Sb<sub>2</sub>O<sub>3</sub> in plastic has been carried out (Fig. 3C). This highlights that the transfer of antimony oxide into
the aqueous phase from the polymer matrix is a slow process under ambient temperature (25 °C). The kinetics within the plastic approach a yield value of 85 mass% to 90 mass%, while it approaches 100 mass% for Sb₂O₃ alone. This suggests that the plastic is only partially solvated by dichloromethane, leading to the retention of approximately 10 mass% of the Sb₂O₃ inside the polymer. This would mean that dichloromethane would only be able to partially, though almost completely, dissolve this ABS. It is therefore necessary to find a solvent that makes the polymer completely soluble to release the Sb₂O₃ crystals trapped in the mesh of the polymer chains. To prevent organobromine degradation in the presence of H₂SO₄ and HNO₃ (Zhong *et al.* 2014 (²⁸)), only 0.5 mol.L⁻¹ tartaric acid was used in phase 2.

### 3.3. Phase 2: Influence of the solvent.

The previous section demonstrated that Sb₂O₃ should be completely dissolved in aqueous solution containing tartaric acid. However, this does not match to the experimental results, presumably due to the partial solubilisation of the polymer by dichloromethane. Thus, the ability of the solvent to open the plastic matrix and release all the antimony oxide crystals has been studied. Molecules from specific chemical families were chosen based on their low water solubility (see Table 1) (²⁴,²⁹). This ensures two distinct liquid-liquid extraction phases and minimises the impact of water on the solvent properties. Typically, water is a non-solvent for most plastics including ABS. The extraction yields of Sb₂O₃ after liquid-liquid extraction for each solvent (reference numbers are given in Table 1) are presented in Figure 4A. Halogenated solvents, esters, ketones, and molecules containing aromatic rings such as 2-phenoxyethanol (#12), aniline (#2), nitrobenzene (#1), toluene (#14), ethylbenzene (#13) allow maximum Sb₂O₃ extraction, while others like heptane (#6), cyclohexane (#5), or cyclohexanol (#11) do not. It is worth noting that 1,4-dioxane (#4) is a special case as it is completely miscible with water, making it a poor ABS solvent. It can be concluded that short-chain esters (#7 and #8) and halogenated molecules, particularly chloroform (#9) and methyl isobutyl ketone (#15), are effective solvents for plastics as they facilitate the release and extraction of antimony oxide from plastics to the aqueous phase. Peng *et al.* (2010)²³ consider chloroform and dichloromethane to be
effective solvents, in agreement with our results, but also toluene, albeit one that yields a lower
extraction rate. Thus, the conventional binary understanding of solubility in ABS should be revised,
suggesting an alternative approach that recognises a continuous spectrum of solubility values.
Antimony trioxide could be used as a tracer to assess the real solubility of the polymer, in a better way
than usual visual inspection.

<figure><img src="image_8.png" /><figcaption>Figure 4: (A) Extraction yield of Sb<sub>2</sub>O<sub>3</sub> as a function of the solvent used for liquid-liquid extraction (aqueous solution = 0.5 mol.L<sup>-1</sup> tartaric acid) depending on their chemical group. A table of results can be found in SI (Table S11). (B) Extraction yield of Sb<sub>2</sub>O<sub>3</sub> as a function of the solvents used for liquid-liquid extraction (aqueous solution = 0.5 mol.L<sup>-1</sup> tartaric acid) and the Hildebrand parameters of these solvents</figcaption></figure>
To explain these results, the Hildebrand solubility parameters of each solvent and ABS fraction were examined. ABS is a terpolymer composed of PS ($\partial_{PS} = 18.78 \text{ MPa}^{1/2}$), PAN ($\partial_{PAN} = 27 \text{ MPa}^{1/2}$) and PB ($\partial_{PB} = 16.6 \text{ MPa}^{1/2}$). Each component has significantly different Hildebrand solubility parameter, particularly polyacrylonitrile. Therefore, it is unlikely that a single solvent will solubilise all ABS fractions simultaneously. This prompts consideration of the fraction that provides maximum Sb$_2$O$_3$ extraction. Figure 4B displays the coordinates for each solvent, with each polymer fractions $\partial$ represented by coloured lines.

The Hildebrand parameter is indicative of the energy required to separate a molecular unit from its neighbours. Applied to extractability of antimony, the simplicity of Hildebrand parameters lies in the comparison of two figures to obtain information on the solubility of the polymer. Upon the dissolution of the lattice, the release of antimony oxide crystals is initiated, resulting in their mobility within the organic phase, to the aqueous phase and form complexes. The data for ethylbenzene (#13), toluene (#14), chloroform (#9), dichloromethane (#10) and cyclohexanone (#16) appear to form a Gaussian curve centred around the PS value. In fact, Burke in 1984 ($^{30}$) represented the decrease in solubility as a function of distance from the Hildebrand parameter of the polymer using a Gaussian function, and Figure 4B shows that most solvents follow a Gaussian distribution around the Hildebrand parameter. For solvents located between the Hildebrand parameters of PB and PS, the extraction is maximal, indicating that these solvents are the most effective in dissolving the polymers. Chloroform (#9), the most effective solvent (97 mass%), theoretically solubilises PS completely, as do isoamyl acetate (#7), n-butyl acetate (#8) and MIBK (#15). This suggests that, to extract antimony oxide from the plastic, solvents must be within this value range as a priority. On the contrary, it appears that solubilisation of PB alone has not the same impact. Indeed, when the Hildebrand parameter of a solvent is lower than that of PB, only a minimal amount of Sb$_2$O$_3$ is extracted. This phenomenon has been observed in the case of diethylether (#3), cyclohexane (#5) and heptane (#6).

The analysis presented above is challenged by three solvents: nitrobenzene (#1), aniline (#2) and 2-phenoxyethanol (#12) but Hildebrand parameters are most appropriate for non-polar or weak hydrogen bonding molecules, so they are not analysed using this model. Another discrepancy is found with
ethylbenzene (#13) and toluene (#14) whose Hildebrand parameters are between those of PB and PS. Their extraction results are lower than expected because SAN and PB nodules require solvents with very different polarities, making apolar (as #13 and #14) or highly polar solvents less effective. It can be assumed that an ideal solvent would have Hildebrand parameters within the range of PB and PS, and sufficiently polar to facilitate the solubilisation of the PAN fraction. PB seems less accessible since it is within the SAN matrix and requires the solubilisation of at least one of the other two fractions. The concept of polarity is not incorporated within the Hildebrand parameter, contrary to Hansen's solubility parameters. Pallab *et al.* (2023) used them for ABS and brominated molecules to identify the most effective solvents for the separation of the latter, but no studies have been published using this methodology for antimony trioxide separation.³¹

Taking into account the hazardousness in the selection of solvents was done following the methodology by Prat *et al.* (2016)³². The results are reported in Table SI2, showing that chloroform leads to the best yield but is problematic. Conversely, n-butyl acetate, a recommended solvent for use, has a lower yet satisfactory yield (89 mass%).

### 3.4. Analysis of plastic properties before and after Sb extraction

An analysis was conducted on the WEEE samples before and after extraction by *n*-butyl acetate and tartaric acid 1 M, followed by plastic precipitation in diethylether. Figure SI3 shows the FTIR analysis of brominated ABS after extraction. The characteristic peaks of TBBPA have been significantly reduced, while the peaks of ABS remain present. This suggests that the chemical structure of ABS has not been altered by this protocol. To supports this hypothesis, the values of MW, Mn, and the polymer's polydispersity, found in Table 2, have not changed before and after insolubilization. The limitation of this method is that it quantifies the chain length of the SAN only, but not the polybutadiene fraction, since the eluent (DMF) does not solubilise polybutadiene. The extraction process removed 98.4 mass% of antimony and 97.8 mass% of bromine. The remaining Br concentration is lower than the legal threshold, allowing the mechanical recycling of this plastic.
<table><caption>Table 2. Properties of the plastic after the diethyl ether insolubilization step by steric exclusion chromatography and X-ray fluorescence for the best Sb extraction conditions (solvent: n-butyl acetate; extractant: tartaric acid = 1 M)</caption><thead><tr><th rowspan="2">Analytical method</th><th colspan="4">SEC</th><th colspan="2">XRF</th></tr><tr><th>Retention time (min)</th><th>Mn (g.mol<sup>-1</sup>)</th><th>MW (g.mol<sup>-1</sup>)</th><th>Polydispersity</th><th>Sb (ppm)</th><th>Br (ppm)</th></tr></thead><tbody><tr><td>Plastic before extraction</td><td>16.874</td><td>159,897</td><td>281,616</td><td>1.76</td><td>30,500</td><td>90,500</td></tr><tr><td>Plastic after extraction</td><td>16.883</td><td>155,494</td><td>285,773</td><td>1.83</td><td>&lt;500</td><td>1980</td></tr><tr><td>Variations (abs)</td><td>0.009</td><td>4,403</td><td>4,157</td><td>0.07</td><td>30,000</td><td>89,320</td></tr><tr><td>Extraction yield (%)</td><td></td><td></td><td></td><td></td><td>98.4 %</td><td>97.8 %</td></tr></tbody></table>

In the context of this interfacial leaching extraction method, the extraction yields of Sb and Br are equivalent to the publication by Schlummer *et al.*¹⁵. However, it should be noted that centrifugation was not employed in our study, and the extraction was conducted at room temperature (rather than at 80°C) to obtain equivalent results.

## 4. Conclusion

This study successfully demonstrates a novel solvation-based extraction method paired with chemical extraction using a complexing agent for antimony from brominated ABS plastics, offering an alternative to traditional centrifugation-filtration methods. The operating mechanisms of the process described in this article have been detailed in Figure 5. Thermoplastics are made up of networks of macromolecules that are entangled but not linked together. The solvent opens the polymer network, allowing the release of antimony oxide crystals in stage B. Antimony oxide can flow into the aqueous phase, where it is transformed into antimony tartrate, a charged molecule with no affinity for the organic phase. Then a poor solvent for the plastic is added in step D, which is a good solvent for the brominated molecule, enabling the latter to be recovered from the solution and the plastic to be recovered as a solid.
<figure><img src="image_9.png" /><figcaption>Figure 5: Conceptual stage of antimony oxide extraction</figcaption></figure>

The method achieves over 98 mass% extraction efficiency for antimony, emphasizing the importance of solvent selection aligned with the Hildebrand parameter, between the value of PB and PS fraction, and sufficiently polar to solubilize PAN. It has been shown that an extracting solution composed of a common weak acid, tartaric acid, without mineral acid allows very good extraction yields of antimony trioxide at room temperature.

Work is in progress to improve the use of Hansen parameters to predict the solubility of ABS, thus providing a generalist model for solubilization to choose suitable solvents for the complete extraction of antimony trioxide. It would allow the use of more sustainable solvents. Step D of this process, the insolubilization, deserves also to be continued to understand the extraction of TBBPA and other brominated molecules from ABS.

Future research should focus on other materials such as HIPS as well as other ABS since every WEEE has its own ABS composition. These findings hold promise for improving electronic waste management strategies.

### 5. Supporting Information
Supporting information consists of one file. Characterization techniques are detailed, along with the ATR-FTIR spectrum of WEEE plastic and brominated ABS, before and after the extraction step. The numerical values of Figure 4A are given in a table. The modelling of Sb₂O₅ solubility as a function of pH is shown. The scores and rankings of the solvents utilised in terms of safety, health and environment are listed.

## 6. Funding and Acknowledgements

This research was supported by the French eco-organization Ecosystem.

## 7. References

(1) Waste statistics - electrical and electronic equipment. https://ec.europa.eu/eurostat/statistics-explained/index.php?title=Waste_statistics_-_electrical_and_electronicEquipment (accessed 2024-09-23).

(2) Hennebert, P.; Filella, M. WEEE Plastic Sorting for Bromine Essential to Enforce EU Regulation. Waste Management 2018, 71, 390–399. https://doi.org/10.1016/j.wasman.2017.09.031.

(3) de Wit, C. A. An overview of brominated flame retardants in the environment q. 2002.

(4) Buekens, A.; Yang, J. Recycling of WEEE Plastics: A Review. J Mater Cycles Waste Manag 2014, 16 (3), 415–434. https://doi.org/10.1007/s10163-014-0241-2.

(5) Martinho, G.; Pires, A.; Saraiva, L.; Ribeiro, R. Composition of Plastics from Waste Electrical and Electronic Equipment (WEEE) by Direct Sampling. Waste Management 2012, 32 (6), 1213–1217. https://doi.org/10.1016/j.wasman.2012.02.010.

(6) Turner, A.; Filella, M. Field-Portable-XRF Reveals the Ubiquity of Antimony in Plastic Consumer Products. Science of The Total Environment 2017, 584–585, 982–989. https://doi.org/10.1016/j.scitotenv.2017.01.149.

(7) Turner, A.; Filella, M. Bromine in Plastic Consumer Products – Evidence for the Widespread Recycling of Electronic Waste. Science of The Total Environment 2017, 601–602, 374–379. https://doi.org/10.1016/j.scitotenv.2017.05.173.

(8) Directive 2011/65/EU of the european parliamant and the council of 8 June 2011 on the restriction of the use of certain hazardous substances in electrical and electronic equipment. https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX%3A32011L0065 (accessed 2024-09-23).

(9) Henckens, M. L. C. M.; Driessen, P. P. J.; Worrell, E. How Can We Adapt to Geological Scarcity of Antimony? Investigation of Antimony's Substitutability and of Other Measures to Achieve a Sustainable Use. Resources, Conservation and Recycling 2016, 108, 54–62. https://doi.org/10.1016/j.resconrec.2016.01.012.
412 (10) Smith, R. Regulation (EC) No 883/2004 of the European Parliament and of the Council of 29 April 2004. In *Core EU Legislation*; Macmillan Education UK: London, 2015; pp 288–318. https://doi.org/10.1007/978-1-137-54482-7_27.

414 (11) Klein, J.; Dorge, S.; Trouvé, G.; Venditti, D.; Durécu, S. Behaviour of Antimony during Thermal Treatment of Sb-Rich Halogenated Waste. *Journal of Hazardous Materials* **2009**, *166* (2–3), 585–593. https://doi.org/10.1016/j.jhazmat.2008.12.006.

417 (12) Onwudili, J. A.; Williams, P. T. Degradation of Brominated Flame-Retarded Plastics (Br-ABS and Br-HIPS) in Supercritical Water. *The Journal of Supercritical Fluids* **2009**, *49* (3), 356–368. https://doi.org/10.1016/j.supflu.2009.03.006.

419 (13) Jung, S.-H.; Kim, S.-J.; Kim, J.-S. Thermal Degradation of Acrylonitrile-Butadiene-Styrene (ABS) Containing Flame Retardants Using a Fluidized Bed Reactor: The Effects of Ca-Based Additives on Halogen Removal. *Fuel Processing Technology* **2012**, *96*, 265–270. https://doi.org/10.1016/j.fuproc.2011.12.039.

422 (14) Alassali, A.; Abis, M.; Fiore, S.; Kuchta, K. Classification of Plastic Waste Originated from Waste Electric and Electronic Equipment Based on the Concentration of Antimony. *Journal of Hazardous Materials* **2019**, *380*, 120874. https://doi.org/10.1016/j.jhazmat.2019.120874.

425 (15) Schlummer, M.; Wolff, F.; Maurer, A. Recovery of PC/ABS from WEEE Plastic Shred by the CreaSolv ® Process. In *2016 Electronics Goes Green 2016+ (EGG)*; IEEE: Berlin, 2016; pp 1–6. https://doi.org/10.1109/EGG.2016.7829841.

427 (16) Lateef, H.; Grimes, S. M.; Morton, R.; Mehta, L. Extraction of Components of Composite Materials: Ionic Liquids in the Extraction of Flame Retardants from Plastics. *J of Chemical Tech & Biotech* **2008**, *83* (4), 541–545. https://doi.org/10.1002/jctb.1829.

430 (17) Gripon, L.; Belyamani, I.; Legros, B.; Seaudeau-Pirouley, K.; Lafranche, E.; Cauret, L. Brominated Flame Retardants Extraction from Waste Electrical and Electronic Equipment-Derived ABS Using Supercritical Carbon Dioxide. *Waste Management* **2021**, *131*, 313–322. https://doi.org/10.1016/j.wasman.2021.06.020.

433 (18) Tostar, S.; Stenvall, E.; Boldizar, A.; Foreman, M. R. St. J. Antimony Leaching in Plastics from Waste Electrical and Electronic Equipment (WEEE) with Various Acids and Gamma Irradiation. *Waste Management* **2013**, *33* (6), 1478–1482. https://doi.org/10.1016/j.wasman.2013.03.002.

436 (19) Altwaiq, A. M.; Wolf, M.; Van Eldik, R. Extraction of Brominated Flame Retardants from Polymeric Waste Material Using Different Solvents and Supercritical Carbon Dioxide. *Analytica Chimica Acta* **2003**, *491* (1), 111–123. https://doi.org/10.1016/S0003-2670(03)00785-2.

439 (20) Schlummer, M.; Brandl, F.; Mäurer, A.; van Eldik, R. Analysis of Flame Retardant Additives in Polymer Fractions of Waste of Electric and Electronic Equipment (WEEE) by Means of HPLC-UV/MS and GPC-HPLC-UV. *Journal of Chromatography A* **2005**, *1064* (1), 39–51. https://doi.org/10.1016/j.chroma.2004.12.016.

442 (21) Anderson, L.; Yu, E.; Chen, W.-T. Chemical Recycling of Mixed Plastics in Electronic Waste Using Solvent-Based Processing. *Processes* **2021**, *10* (1), 66. https://doi.org/10.3390/pr10010066.

444 (22) Deng, W.; Long, M.; Zhou, Q.; Wen, N.; Deng, W. One-Step Preparation of Superhydrophobic Acrylonitrile-Butadiene-Styrene Copolymer Coating for Ultrafast Separation of Water-in-Oil Emulsions. *Journal of Colloid and Interface*
446 *Science* **2018**, *511*, 21–26. https://doi.org/10.1016/j.jcis.2017.09.070.

447 (23) Peng, P.; Shi, B.; Jia, L.; Li, B. Relationship between Hansen Solubility Parameters of ABS and Its Homopolymer

448 Components of PAN, PB, and PS. *Journal of Macromolecular Science, Part B* **2010**, *49* (5), 864–869.

449 https://doi.org/10.1080/00222341003603693.

450 (24) Smallwood, I. M. *Handbook of Organic Solvent Properties*; Arnold; Halsted Press: London: New York, 1996.

451 (25) PUIGDOMENECH, I. HYDRA (hydrochemical equilibrium-constant database) and MEDUSA (make equilibrium

452 diagrams using sophisticated algorithms) programs. *Royal Institute of Technology, Sweden*. KTH.

453 https://www.kth.se/che/medusa/downloads-1.386254 (accessed 2024-06-18).

454 (26) Filella, M.; May, P. M. Critical Appraisal of Available Thermodynamic Data for the Complexation of

455 Antimony(Ii) and Antimony(v) by Low Molecular Mass Organic Ligands. *J. Environ. Monit.* **2005**, *7* (12), 1226.

456 https://doi.org/10.1039/b511453e.

457 (27) Díaz, E.; Alonso, R.; Valenciano, R.; de Arenaza, I. M. Determinación de retardantes de llama bromados en

458 plásticos de equipos eléctricos y electrónicos.

459 (28) Zhong, Y.; Li, D.; Mao, Z.; Huang, W.; Peng, P.; Chen, P.; Mei, J. Kinetics of Tetrabromobisphenol A (TBBPA)

460 Reactions with H2SO4, HNO3 and HCl: Implication for Hydrometallurgy of Electronic Wastes. *Journal of Hazardous

461 Materials* **2014**, *270*, 196–201. https://doi.org/10.1016/j.jhazmat.2014.01.032.

462 (29) Stenutz, R. *Tableaux pour la chimie organique*. http://www.stenutz.eu/chem/ (accessed 2024-07-17).

463 (30) Burke, J. Burke, John. Part 2. Hildebrand Solubility Parameter. Solubility Parameters: Theory and Application;

464 *The Book and Paper Group of the American Institute for Conservation: Washington, DC, USA 1984*.

465 (31) Das, P.; Zeng, Q.; Leybros, A.; Gabriel, J.-C. P.; Yong Tay, C.; Lee, J.-M. Enhanced Extraction of Brominated

466 Flame Retardants from E-Waste Plastics. *Chemical Engineering Journal* **2023**, *469*, 144126.

467 https://doi.org/10.1016/j.cej.2023.144126.

468 (32) Prat, D.; Wells, A.; Hayler, J.; Sneddon, H.; McElroy, C. R.; Abou-Shehada, S.; Dunn, P. J. CHEM21 Selection

469 Guide of Classical- and Less Classical-Solvents. *Green Chem.* **2016**, *18* (1), 288–296. https://doi.org/10.1039/C5GC01008J.

470
<figure><img src="image_10.png" /></figure>

472

473

474

475 Synopsis

476

477

Flame-retardant plastics can be recycled by the extraction of antimony using a polymer solvent combined with liquid-liquid interfacial leaching.

478

479

480

481

482