Thermal Transformation of Waste Toner Powder into a Value-Added

Research Article Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX-XXX

pubs.acs.org/journal/ascecg

Thermal Transformation of Waste Toner Powder into a Value-Added Ferrous Resource Vaibhav Gaikwad,*,† Uttam Kumar,† Farshid Pahlevani,† Alvin Piadasa,‡ and Veena Sahajwalla† †

Centre for Sustainable Materials Research and Technology (SMaRT), School of Materials Science and Engineering, University of New South Wales, Gate 2, High Street, Sydney, NSW 2052, Australia ‡ TES AMM Australia Pty Ltd, 1 Marple Avenue, Villawood, NSW 2163, Australia S Supporting Information *

ABSTRACT: This paper describes the development of a thermal transformation process to recycle waste toner powder in a sustainable and environmentally friendly manner. The process leverages hightemperature reactions and the morphology and chemical composition of waste toner powder, mainly the iron oxide and carbon content, by utilizing the gases evolved during the thermal transformation as an in situ source of carbon to convert the waste toner powder into 98% pure iron. A temperature of 1550 °C was employed in the present study to ensure the complete transformation of waste toner powder to iron and also because of its practical relevance to operating conditions encountered in metal manufacturing and processing industries. The process delivers an iron recovery of 81.6%. X-ray diffraction, scanning electron microscopy−energy-dispersive spectroscopy, and inductively coupled plasma optical emission spectroscopy analyses were employed to confirm the composition of the metallic product. GC−MS analysis was utilized to monitor gaseous aromatic compounds during the thermal degradation studies of the waste toner powder, and none were detected above 1200 °C. In addition, this paper presents a comprehensive characterization of the waste toner powder and resultant products using various analytical techniques, a kinetic study of the thermal decomposition of waste toner powder, and a pelletization technique to overcome its material handling hazards. KEYWORDS: E-waste, Toner powder, Thermal transformation, Ferrous resource, High purity

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INTRODUCTION Electronic waste (e-waste), otherwise known as waste electrical and electronic equipment (WEEE), is recognized as one of the fastest growing wastes in the world. An estimated 47.8 million tons of it will be generated in 2017 with an annual growth rate of 4−5%.1 The e-waste terminology can broadly be used to describe all electronic and electrical equipment, including its parts, that has been discarded by its users as waste without the intention of reusing it.1 With rapidly changing technology, it is expected that the contents and type of equipment encountered in e-waste will also change. For example, the 2012 EU directive on e-waste provides six broad categories for classifying e-waste, in contrast to its earlier and more specific 10 classifications from previous directives.2,3 With 20 kg of e-waste generated per inhabitant, Australia is one of the highest per-capita e-waste creators in the world.1 The majority of e-waste management in Australia is done through the National Television and Computer Recycling Scheme (NTCRS), which was initiated in in 2011 and targets an 80% recycling rate of computers, computer-related products, and TVs by 2021−22.4 As per the government data, ∼121.8 kilotons of computers and televisions reached end of life in Australia in 2014−15, of which ∼35% was recycled through the NTCRS.5 However, the scheme does not focus on end-of-life toner cartridges and the residual toner powder contained © XXXX American Chemical Society

within, despite the fact that they are part of the e-waste landfilled or disposed in Australia and globally. It is estimated that 1.1 billion cartridges are sold annually and that more than 500 million of them end up in landfills across the world.6 This results in tremendous damage to the environment due to leaching of toxic chemicals, especially from the residual toner powder, into the soil and aquifer, uncontained release of gases such as methane and carbon dioxide, which are responsible for global warming, and loss of valuable resources, including metals and plastics. In addition, the residual toner powder is combustible and has a very fine particle size, which increases the risk of a dust explosion if it is airborne.7 An end-of-life toner cartridge can contain up to 8% by weight of residual toner powder.8 In view of the number of cartridges landfilled every year, this amounts to a significant quantity of toner powder that is being disposed in an unsafe and environment-damaging manner, which further amplifies the impact of the aforementioned hazards. Previously some research has been conducted on recycling and transforming waste toner powder into potentially useful products. Yordanova et al.9 explored the use of waste toners as Received: August 18, 2017 Revised: October 23, 2017 Published: October 25, 2017 A

DOI: 10.1021/acssuschemeng.7b02875 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering fillers and colorants in synthetic rubber manufacturing. Ruan and co-workers proposed various production line systems to separate toner powder from cartridges in an environmentally friendly manner and recently utilized vacuum gasification condensation to convert waste toner powder into synthetic oils, gases, nano-Fe3O4, and nano-SiO2.8,10−13 Li et al.14 investigated the heat treatment of waste toner powder and its utilization as an anode in Li ion batteries. Waste toner powder is also being used as an ingredient in TonerPave, an asphalt product for making roads developed by an Australian company.15 However, despite such developments, the amount of toner waste being generated and landfilled continues to increase. This necessitates the development of an alternative and novel approach that can, in addition to the existing technologies, tackle the environmental problems caused by waste toner powder. In this paper, we propose a thermal transformation process that utilizes the carbon from waste toner powder as a reductant to transform the toner powder into 98% pure iron. The process takes advantage of the morphology of the iron oxide particles and polymeric resins within the waste toner powder. The development of the process was undertaken with consideration given to potential industrial applications, utilizing a temperature of 1550 °C. It is thus well-aligned to large and small metallurgical industries, including iron and steel making, which usually use temperatures in the range of 1500−1600 °C for their standard operations and hence would not require additional energy costs or inputs to reach the thermal transformation conditions employed in this study. In addition, such high temperatures preclude the formation of potentially toxic compounds such as dioxins. The waste toner powder utilized in the present study was provided by TES-AMM Australia Pty Ltd., one of Australia’s leading providers of endto-end information technology life cycle solutions. In the following sections of the paper, we provide an exhaustive characterization of the waste toner powder using various analytical techniques, a detailed kinetic study of its thermal decomposition, a pelletization technique, the thermal transformation process for waste toner powder, and a detailed analysis of the solid and gaseous products from the process.

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during the TGA experiments were qualitatively monitored using a combination of an FTIR spectrometer (PerkinElmer Spectrum 100) and a gas chromatograph−mass spectrometer (PerkinElmer, Clarus 580/SQ 8S with an Elite-5MS column), which were coupled to the TGA instrument. Inductively coupled plasma optical emission spectrometry (ICP-OES) (PerkinElmer Optima 7300DV) was utilized to analyze the elemental composition of the metallic residue obtained afte thermal transformation experiments of waste toner powder. The ΔG° values for the reactions in the proposed mechanism were calculated using the thermodynamic modeling software FactSage version 7.1. Pellet Making. Pelletization of the toner powder was performed using a cylindrical die with an adjustable piston and heated platen press (Carver model 2697). Toner powder (0.6 g) was introduced in the die and loaded onto a heated platen press for pelletization. The platen temperature was maintained at 185 °C, and a pressure of 30 bar was applied on the die for 32 min. The die was then taken out of the press and dismantled after cooling, and the toner pellet was removed. The weight of the resultant pellet was ∼0.5 g, and its diameter and thickness were 20 and 3 mm, respectively. Thermal Transformation Experiments. A schematic representation of the setup for the thermal transformation experiments is provided in Figure 1. The toner pellet was introduced in a horizontal

Figure 1. Schematic representation of the horizontal tube furnace. furnace atop an alumina crucible that was placed on a graphite rod. The rod was held in the cold zone for 5 min to avoid thermal shock and then pushed into the hot zone at 1550 °C and held there for 15 min. The furnace was continuously purged with argon at a flow rate of 1 L min −1. The off gases from the furnace were analyzed using an online IR spectrometer (ABB, AO 2000 series) capable of quantitatively monitoring CO, CO2, and CH4. A CCD camera was utilized for real-time visual observation of the toner pellet during thermal transformation experiments. After thermal transformation, the metallic droplets deposited on the crucible were collected for further analyses.

EXPERIMENTAL SECTION

Characterization. The as-received waste toner powder sample was analyzed using various analytical techniques. Attenuated total reflectance Fourier Transform infrared (ATR-FTIR) spectroscopy (PerkinElmer Spectrum 100) was utilized to determine the types of polymers present in the toner powder. X-ray diffraction (XRD) on a PANalytical Empyrean Bragg−Brentano geometry X-ray diffractometer with a Co source (Co Kα = 1.79 Å) was used to identify different metallic oxides and crystalline components in the toner powder and the resultant products. Phase identification was performed using X’pert High Score software. Elemental analysis of the toner powder was performed using X-ray fluorescence (XRF) spectroscopy (PHILIPS PW2400) and ultimate analysis (LECO TruSpec CNS). Proximate analysis was performed to determine the moisture content, volatile matter, and fixed carbon. Scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS) (Hitachi S3400) was used to study the morphology and elemental composition of the waste toner powder as well as the products after heat treatment. Thermogravimetric analysis (TGA) (PerkinElmer STA 8000) was performed to study the thermal degradation behavior of the waste toner powder and determine kinetic parameters such as the activation energy from the resultant data. TGA experiments were performed at two different heating rates (10 and 20 °C min−1) in a nitrogen atmosphere from ambient temperature to 1250 °C. The gases evolved

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RESULTS AND DISCUSSION Characterization. Elemental Composition. The chemical composition of the waste toner powder is provided in Table 1. As is evident, the waste toner powder is an excellent source of carbon and hydrogen, which can be converted to gases such as CO and CH4 under reaction conditions employed in the Table 1. Ultimate and Proximate Analyses of Waste Toner Powder Ultimate Analysis

B

carbon

hydrogen

44.7%

4.43%

nitrogen

total sulfur

oxygen (by difference)

0.42% 0.21 Proximate Analysis

8.34

inherent moisture

ash

volatile matter

fixed carbon

0.4%

41.5%

58.0%

0.1%


Research Article

ACS Sustainable Chemistry & Engineering

peaks in the vicinity of 2900 cm−1 can be attributed to the aliphatic C−H stretching vibrations from the CH2 groups.16,17 The presence of acrylic resins such as poly(methyl methacrylate) (PMMA) is suggested by the peaks at ∼2960, 1720, 1452, and 1184 cm−1. The peaks around ∼2960−2920 cm−1 can be attributed to C−H stretching vibrations from the CH3 and CH2 groups, and the peak at 1720 cm−1 is due to the CO (carbonyl) stretch.18 The peak at 1452 cm−1 may be due to the C−H bending vibration of a CH3 group.19,20 The C−O− C stretching vibration is exhibited in the peak at ∼1184 cm−1.16,20,21 In addition, the peaks at 1509 and 830 cm−1 are suggestive of the presence of a bisphenol A-based polymer, such as polyester.22 On the basis of the FTIR analysis, the polymeric component of the waste toner powder sample is predominantly a PS−PMMA-type copolymer along with some bisphenol A-based polyester resin. X-ray Diffraction Analyses. The X-ray diffractogram in Figure 3 clearly indicates magnetite (Fe3O4) to be the

present study. In addition, the results also indicate that the toner does not contain any fixed carbon and that almost all of the carbon content is volatile. XRF analysis was performed on the ash obtained from waste toner powder, and results indicate a high iron oxide content (see Table 2). Since the ash content is 41.5%, the total Table 2. XRF Analysis (Major Oxides in Waste Toner Powder Ash) compound

value (%)

SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O TiO2 Mn3O4 P2O5 SO3 SrO BaO ZnO

2.92 0.41 82.4 0.24 1.34 0.19 0.04 0.64 11.0 0.03 0.41 0.96 0.12 0.08

concentration of iron oxide in the waste toner powder is 34.1%. It should be noted that although the iron content is expressed as Fe2O3, the form of iron oxide present in the waste toner powder is magnetite (Fe3O4), which is evident in the results of XRD analysis. ATR-FTIR Analyses. Since the toner powder studied in the present investigation is a mixture of different types of toners, unequivocal identification of the polymeric components is difficult. However, by means of FTIR spectroscopy it is possible to identify various functional groups present in the toner powder, which can help in determining the types of polymers present in the sample. Figure 2 depicts the ATR-FTIR

Figure 3. X-ray diffractogram of the waste toner powder before thermal transformation.

dominant crystalline phase in the toner powder. The magnetite was found to have a cubic crystal structure, with the prominent characteristic peaks at 2θ = 35.1° (220), 41.4° (311), 50.5° (400), 67.3° (511), and 74.1° (440). The broad peak ranging from 2θ = 18° to 27°, which is superimposed with two sharp peaks from Fe3O4, is representative of the amorphous components of the toner powder (i.e., the polymeric resins). SEM-EDS Analyses. SEM micrographs for the waste toner powder are shown in Figure 4. It is mainly composed of spherical particles with diameters of ∼5−10 μm. These are essentially resin particles that may be encapsulating other components of the toner powder, including pigments such as magnetite and manganese oxide. The toner powder can thus be considered to comprise numerous iron−carbon composite micropellets with a core−shell structure. The core is composed of iron oxide, which is encapsulated with a carbon-rich shell of polymers such as PS−PMMA. Toners synthesized using the chemical route usually have such structures.23,24 Hence, the SEM-EDS mapping of the toner powder predominantly shows carbon and some clusters of Fe3O4 particles not encapsulated by the resins. In addition, they also contain SiO2, which is added as charge control agent to prevent aggregation of the particles. Some SiO2 might also be found on the surface of these resin particles.

Figure 2. ATR-FTIR spectrum of the waste toner powder.

spectrum of the waste toner powder. The peaks at 698 and 757 cm−1 along with those at 1609, ∼2900, and 3025−3060 cm−1 are indicative of the presence of polystyrene (PS). More specifically, the peaks at 698 and 757 cm−1 can be attributed to the aromatic ring bending and C−H out-of-plane bending vibrations, respectively. Aromatic CC stretching vibrations are manifested in the 1609 cm−1 peak and the aromatic C−H stretching vibrations in the peaks at 3025−3060 cm−1. The C


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Figure 4. (a) SEM and (b) SEM-EDS micrographs of the waste toner powder before thermal transformation.

Figure 5. (a) SEM and (b) SEM-EDS micrographs of a toner pellet cross section before thermal transformation.

After pelletization, the resins are melted, and the magnetite particles encapsulated within them are clearly visible in the SEM-EDS micrographs depicted in Figure 5. As the magnetite particles are no longer coated with resins, they tend to aggregate and form clusters with a larger particle size. As can be seen, even after melting there is close proximity and good binding between the magnetite particles and the carbon (from resins), which can be an important contributing factor for achieving complete reduction of Fe3O4 to Fe. Kinetics of Waste Toner Powder Thermal Degradation and Analyses of the Resultant Gases. The kinetic parameters of toner thermal degradation were obtained using the Coats−Redfern (CR) method, which can be represented by the following equations:25,26 ⎛ AR ⎞ ⎡ ln(1 − α) ⎤ E ln⎢ − ⎟− a, ⎥ = ln⎜ 2 ⎣ ⎦ T ⎝ βEa ⎠ RT

Figure 6 displays the TGA and differential thermogravimetric analysis (DTG) plots for the toner at a heating rate of 10 °C

n=1

⎡ 1 − (1 − α)1 − n ⎤ ⎛ AR ⎞ E ln⎢ ⎥ = ln⎜ ⎟− a, 2 ⎣ T (1 − n) ⎦ ⎝ βEa ⎠ RT

(1) Figure 6. TGA curve and Gaussian fit of the DTG curve for the toner powder obtained at a heating rate of 10 °C min−1.

n≠1 (2)

min−1. The plot indicates the occurrence of two distinct degradation steps. The first degradation occurs in the temperature range of 330−440 °C with a DTG peak at 408 °C, and the second degradation occurs in the range of 820−950 °C with a DTG peak at 910 °C. Also, it can be seen that toner

where T is the temperature (in K), α is the degree of conversion of the material at time t, n is the reaction order, A is the Arrhenius pre-exponential factor (in s−1), R is the universal gas constant (8.314 J K−1 mol−1), β is the heating rate (in K min−1) and Ea is the activation energy (in kJ mol−1).27 D


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ACS Sustainable Chemistry & Engineering loses around 60 wt % of its original weight when the temperature reaches 1000 °C. The TGA data thus obtained were used to produce CR plots (Figure S1) in order to understand the kinetics associated with the degradation of toner. Kinetic parameters such as activation energy (Ea), preexponential factor (A), and reaction order (n) were obtained by analyzing the fitting data from CR plots. The fitting data from the plots and the calculated kinetic parameters for the first and second degradation steps are listed in Table 3. The kinetic Table 3. Fitting Data and Kinetic Parameters for Toner Thermal Degradation from Coats−Redfern Plots n≠1

n=1 parameter slope intercept adjusted R2 n Ea (kJ mol−1) ln A (min−1)

10 °C min

−1

−12705.19 4.979 0.9995 1 105.63 16.73

20 °C min

−1

−12076.46 3.711 0.9991 1 100.40 16.10

10 °C min

−1

−14115.00 7.2 0.9982 1.5 117.35 19.06

20 °C min−1 −12643.00 4.606 0.9984 1.3 105.11 17.05

Figure 7. 3D projection of the FTIR spectrum of gases formed during thermal degradation of the toner in TGA experiments.

CO2 can be identified from its characteristic peaks at 2250− 2400 cm−1. The presence of aromatic species is also possible, as indicated by the peaks observed in the region near 1500 and 1600 cm−1. In addition, the peaks in the region from 700 to 900 cm−1 can be mainly attributed to monosubstituted aromatic compounds. However, as the temperature increases, CO2 tends to be the only dominant gas observed in the spectrum. This observation is similar to some of our previous research work involving high-temperature polymer pyrolysis.31 The gas chromatography−mass spectrometry (GC−MS) results obtained at 408 and 1200 °C (see Figure 8) are in

parameters thus obtained can provide a lot of useful information leading to an understanding of the reaction mechanism. For example, the activation energy can be regarded as the energy threshold that must be overcome to initiate a reaction, and the pre-exponential factor A represents the frequency of molecular collisions.28 As shown in Table 3, the activation energy values for the first degradation step are just over 100 kJ mol−1, and those for the second step are in the range of 20−60 kJ mol−1. The Ea values at a heating rate of 20 °C min−1 are slightly less than that for 10 °C min−1. The pre-exponential factor also has smaller values at the higher heating rate compared with the values at the lower heating rate. The decrease in activation energy with an increase in heating rate has been observed by several other researchers as well. Ko et al.29 reported this behavior for polyethylene terephthalate (PET) and macadamia nut shell. Polystyrene, polyethylene, polypropylene, and acrylonitrile−butadiene− styrene plastics demonstrated the same trends in activation energy values with increasing heating rate in a study conducted by Encinar and González.30 To some extent, the activation energy is affected by the heat transfer limitations within a sample with a change in heating rate. This decrease in the values of Ea and A with increasing heating rate can also be explained by the fact that increased heat input causes rapid volatilization of the degradation products away from the residues, resulting in a decrease in the number of molecular collisions within the solid state.29,30 Furthermore, the reaction order (n) decreased from 1.5 at a heating rate of 10 °C min−1 to 1.3 at a heating rate of 20 °C min−1. The decreased values of n and Ea at higher heating rates indicate a less complex reaction mechanism and faster thermal degradation, respectively.29 Figure 7 depicts a three-dimensional (3D) FTIR spectrum of the gaseous products formed during thermal degradation of the toner in TGA experiments. On the basis of the spectrum, it can be said that the types of gases evolved during the decomposition change with temperature. At 408 °C, the temperature at which maximum degradation of toner occurs, the spectrum indicates the presence of various gases. The peaks in the region between 2900 and 3200 cm−1 can be attributed to a stretching vibration from sp3 C−H bonds, indicating the presence of species such as CH4 and C2H6. The presence of

Figure 8. GC−MS chromatograms of gases formed during thermal degradation of the toner in TGA experiments.

agreement with the FTIR analysis for gaseous products. Aromatic compounds such as toluene, ethylbenzene, styrene, phenol, methylbenzene, and allylphenol were detected during the analysis performed at 408 °C. The GC−MS results also support the ATR-FTIR analysis of the toner powder, since the aforementioned compounds are well-known thermal degradation products of the other resins found in the waste toner powder.32,33 At 1200 °C, no aromatic compounds were detected, as is clearly indicated in GC−MS chromatogram for that temperature. The peak at 2.49 min is crossed-out in both chromatograms because it is an attribute of the GC column material and not due to any product. E


Research Article

ACS Sustainable Chemistry & Engineering Thermal Transformation of Waste Toner Powder. The decomposition of polymers from the toner powder, including PS−PMMA and bisphenol A-based resins, under the temperature conditions investigated in the present study results in the formation of gases such as CO, CO2, and CH4 (see Figure 9).34

CO2 + H 2 → CO + H 2O ΔG° = 27.6 − 0.026T kJ mol−1

(R7)

Mn3O4 + CO → 3MnO + CO2 ΔG° = 82 − 0.095T kJ mol−1

(R8)

2MnO + SiO2 → Mn2SiO4 ΔG° = −170 + 0.062T kJ mol−1

(R9)

The 0.501 g pellet used in the present study yielded 0.101 g of metallic product, which was subjected to ICP-OES, XRD, and SEM-EDS analyses. The ICP-OES results (see Table 4) Table 4. ICP-OES Analysis of the Metallic Product

Figure 9. Gas evolution during thermal transformation of waste toner powder at 1550 °C.

(R1)

Once formed, methane decomposes to carbon and hydrogen at 1550 °C: CH4 → C(s) + 2H 2 ΔG° = 92.8 − 0.111T kJ mol−1

(R2)

There are several iron oxide reduction reactions: Fe3O4 + CO → 3FeO + CO2 (g) ΔG° = 26.5 − 0.03T kJ mol−1

(R3)

FeO + C(s) → Fe(l) + CO(g) ΔG° = 157 − 0.154T kJ mol−1

(R4)

FeO + CO(g) → Fe(l) + CO2 ΔG° = −4.56 + 0.014T kJ mol−1

(R5)

In addition, some side reactions occur at these temperatures: CO2 (g) + C(s) → 2CO(g) ΔG° = 161 − 0.168T kJ mol−1

wt %

Fe Mn Si S

97.73 0.0859 0.0884 0.1266

indicate 97.73 wt % of the metallic product to be iron, and therefore, the amount of iron recovered was 0.098 g. On the basis of the chemical analysis (XRF) presented in the earlier section of the paper, the toner powder contains 23.9 wt % metallic iron, and hence, the 0.501 g pellet should ideally yield ∼0.12 g of metallic iron. As mentioned earlier, 0.098 g of metallic iron was produced from a 0.501 g pellet, and hence, the iron recovery of the thermal transformation process is 81.6%. Experiments were repeated thrice to confirm the percentage recovery of iron, and the results were found to be within ±2% of each other. Photographic images of the toner pellet undergoing the thermal transformation at different stages of the process are provided in Figure S2. At the temperature investigated in the present study, it is possible that some solid carbon generated through reaction R2, might dissolve in the liquid iron during the thermal transformation process. In order to evaluate any potential carbon pickup, the metallic product was subjected to elemental analysis using a LECO instrument. Uniformity and reproducibility were ensured by analyzing the collective metallic product from four thermal transformation runs performed under identical experimental conditions. The carbon pickup was found to be 0.02%. The low carbon pickup was expected, as the toner did not inherently contain any fixed carbon. Moreover, the ICP analyses indicated ∼0.13% sulfur pickup by the metallic product, which would limit or retard the dissolution of carbon in iron.38,39 The X-ray diffractogram (Figure 10a) exhibits characteristic peaks of Fe with 2θ = 52.2° (110), 77.2° (200), 99.5° (211), and 123.8° (220) and no peaks from either FeO or Fe3O4, indicating complete reduction of Fe3O4 to metallic iron. Small peaks from Mn2SiO4 are visible in the diffractogram between 2θ = 36.6 and 50.9. Furthermore, the SEM-EDS micrograph of the metallic product obtained from thermal treatment of toner powder (Figure 10b) also shows Fe to be the predominant constituent, in agreement with XRD and ICP results. Overall, the thermal transformation process demonstrates that waste toner powder can be converted to a valuable ferrous resource, i.e., 98% pure iron, and provides an alternative and sustainable avenue for its recycling. The process does not

It was found that CO was the dominant gaseous product, followed by CH4 and CO2. The resultant gases and proximity of iron oxide and carbon in the toner powder play an important role in reduction of the iron oxide.35,36 It is-well established that above 570 °C, Fe3O4 reduction occurs in stages: Fe3O4 → FeO → Fe. During thermal treatment of the toner powder, several reactions occur simultaneously. A qualitative reaction mechanism for transformation of inherent iron oxide in the toner powder to metallic iron is postulated below.36,37 The reaction begins with thermal degradation of the polymers in the toner powder: polymers → CH4 , CO, CO2

element (majors)

(R6) F


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Figure 10. (a) X-ray diffractogram and (b) SEM-EDS micrograph of the metallic product (Fe) obtained after thermal transformation of the waste toner powder. (2) European Union. Directive 2012/19/EU of the European Parliament and of the Council of 4 July 2012 on waste electrical and electronic equipment (WEEE), 2012. http://eur-lex.europa.eu/ legal-content/EN/TXT/?uri=celex%3A32012L0019 (accessed July 9, 2017). (3) Widmer, R.; Oswald-Krapf, H.; Sinha-Khetriwal, D.; Schnellmann, M.; Böni, H. Global perspectives on e-waste. Environ. Impact Assess. Rev. 2005, 25 (5), 436−458. (4) Australian Government, Department of the Environment. The National Television and Computer Recycling SchemeOperational Review (November 2014). https://www.environment.gov.au/system/ files/pages/1de81785-ce48-4671-8182-9f1d9490b5ce/files/ operational-review-national-television-and-computer-recycling-scheme. pdf (accessed July 9, 2017). (5) Australian Government, Department of the environment. National Television and Computer Recycling Scheme Outcomes 2014−15 (October 2016). https://www.environment.gov.au/system/ files/resources/894d9750-8d95-432a-9c21-69e0df51b703/files/ national-television-and-computer-recycling-scheme-outcomes-201415.pdf (accessed July 9, 2017). (6) European Toner and Inkjet Remanufacturers Association. Remanufacturing cartridges is environmental-friendly. http://www. etira.org/environment/ (accessed July 9, 2017). (7) Koseki, H. Study and Countermeasure of Hazard of Dust Explosion of Various Toner Cartridges. Procedia Eng. 2014, 84, 273− 279. (8) Ruan, J.; Li, J.; Xu, Z. An environmental friendly recovery production line of waste toner cartridges. J. Hazard. Mater. 2011, 185 (2), 696−702. (9) Yordanova, D.; Angelova, S.; Dombalov, I. Utilisation Options for Waste Toner Powder. J. Environ. Sci. 2014, 3, 140−144. (10) Ruan, J.; Xu, Z. A new model of repulsive force in eddy current separation for recovering waste toner cartridges. J. Hazard. Mater. 2011, 192 (1), 307−313. (11) Ruan, J.; Li, J.; Xu, Z. Improvements of the Recovery Line of Waste Toner Cartridges on Environmental and Safety Performances. Environ. Sci. Technol. 2013, 47 (12), 6457−6462. (12) Ruan, J.; Xu, Z. Approaches To Improve Separation Efficiency of Eddy Current Separation for Recovering Aluminum from Waste Toner Cartridges. Environ. Sci. Technol. 2012, 46 (11), 6214−6221. (13) Ruan, J.; Dong, L.; Huang, J.; Huang, Z.; Huang, K.; Dong, H.; Zhang, T.; Qiu, R. Vacuum-Gasification-Condensation of Waste Toner To Produce Industrial Chemicals and Nanomaterials. ACS Sustainable Chem. Eng. 2017, 5 (6), 4923−4929. (14) Li, Y.; Mao, J.; Xie, H.; Li, J. Heat-treatment recycling of waste toner and its applications in lithium ion batteries. J. Mater. Cycles Waste Manage. 2017, DOI: 10.1007/s10163-017-0599-z. (15) TonerPave. https://tonerpave.com.au/ (accessed July 9, 2017).

require any added source of carbon to reduce the inherent iron oxide and effectively utilizes the resins within the toner powder as the reductant. Furthermore, the temperature of 1550 °C ensured complete conversion of iron oxide to iron, as confirmed by the results of XRD, SEM-EDS, and ICP-OES analyses. GC−MS analyses of the gases evolved during the thermal degradation studies of waste toner powder indicated that no aromatic compounds were detected at temperatures above 1200 °C.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b02875. Procedure for obtaining Coats−Redfern plots and kinetic parameters and photographic images of the waste toner pellet undergoing thermal transformation at different stages of the process (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Vaibhav Gaikwad: 0000-0002-4325-7610 Farshid Pahlevani: 0000-0002-0833-3227 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported under the Australian Research Council’s Industrial Transformation Research Hub funding scheme (Project IH130200025). The authors acknowledge the staff within the Mark Wainwright Analytical Centre at the University of New South Wales for their help with the XRF and ICP-OES experiments. V.G. acknowledges support from UNSW Sydney and Australia India Institute for the New Generation Network (NGN) fellowship.

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REFERENCES

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Thermal Transformation of Waste Toner Powder into a Value-Added

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