A new facile process to remove Br− from waste printed circuit boards smelting ash: Thermodynamic analysis and process parameter optimization

Journal Pre-proof A new facile process to remove Br- from waste printed circuit boards smelting ash: thermodynamic analysis and process parameter optimization

Gongqi Liu, Yufeng Wu, Bin Li, De’an Pan, Feihua Yang, Junqing Pan, Yishu Wang, Na Cheng PII:

S0959-6526(20)30223-7

DOI:

https://doi.org/10.1016/j.jclepro.2020.120176

Reference:

JCLP 120176

To appear in:

Journal of Cleaner Production

Received Date:

27 September 2019

Accepted Date:

16 January 2020

Please cite this article as: Gongqi Liu, Yufeng Wu, Bin Li, De’an Pan, Feihua Yang, Junqing Pan, Yishu Wang, Na Cheng, A new facile process to remove Br- from waste printed circuit boards smelting ash: thermodynamic analysis and process parameter optimization, Journal of Cleaner Production (2020), https://doi.org/10.1016/j.jclepro.2020.120176

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.

Journal Pre-proof A new facile process to remove Br- from waste printed circuit boards smelting ash: thermodynamic analysis and process parameter optimization Gongqi Liua, Yufeng Wua, Bin Lia, De’an Pana*, Feihua Yangb, Junqing Panc, Yishu Wanga, Na Chengd aCollege

of Materials Science and Engineering, Beijing University of Technology,

Beijing 100124, P. R. China bSolid

Waste Reuse for Building Materials State Key Laboratory, Beijing Building

Materials Academy of Science Research, Beijing 100038, P. R. China cState

Key Laboratory of Chemical Resource Engineering, Beijing University of

Chemical Technology, Beijing 100029, P. R. China dShenyang

Zhongke Ecological Environmental Assessment Co. Ltd, Shenyang

110014, P. R. China *Corresponding author.
E-mail addresses: [email protected]

Funding: This work was supported by the National Key Research and Development Program of China (No. 2018YFC1903104, 2018YFC1903603).

Nomenclature WEEE PCBs WPCBs-SA RSM SR CCD ANOVA XRF XRD SEM EDS XPS R2adj 3-D

Waste electrical and electronic equipment Printed circuit boards Waste printed circuit boards smelting ash Response surface methodology Sulfation roasting The central composite design The analysis of variance X-ray fluorescence X-ray diffraction Scanning Electron Microscopy Energy Dispersive Spectrometer X-ray photoelectron spectroscopy Adjusted R2 Three-dimensional

Journal Pre-proof Graphical Abstract

A new facile process for recover bromine: Debrominated diagram of WPCBs-SA using the SR process

Journal Pre-proof A new facile process to remove Br- from waste printed circuit boards smelting ash: thermodynamic analysis and process parameter optimization Gongqi Liua, Yufeng Wua, Bin Lia, De’an Pana*, Feihua Yangb, Junqing Panc, Yishu Wanga, Na Chengd aCollege

of Materials Science and Engineering, Beijing University of Technology,

Beijing 100124, P. R. China bSolid

Waste Reuse for Building Materials State Key Laboratory, Beijing Building

Materials Academy of Science Research, Beijing 100038, P. R. China cState

Key Laboratory of Chemical Resource Engineering, Beijing University of

Chemical Technology, Beijing 100029, P. R. China dShenyang

Zhongke Ecological Environmental Assessment Co. Ltd, Shenyang

110014, P. R. China *Corresponding author.
E-mail addresses: [email protected]

Abstract： Waste printed circuit boards smelting ash (WPCBs-SA) is generated by the smelting process of waste printed circuit boards (WPCBs), which contains valuable metals, such as copper (Cu), zinc (Zn), and sliver (Ag), and a large amount of harmful bromide (Br-). In this work, a facile sulfation roasting (SR) proposed for the removal of Br- from WPCBs-SA with high efficiency. The thermodynamic analysis is systemically investigated, and the results demonstrate that Br- in WPCBs-SA is converted into HBr or Br2 comfortably below 564.8 K during the SR process. The influences of essential variables such as the ratio of sulfuric acid into smelting ash, roasting temperature and time are systematically investigated, and the variables are also optimized via response surface methodology (RSM). Under the optimized experimental conditions, the Br- removal efficiency reached up to 98.97%, and the values of the three variables were 0.8 g/g, 590.04 K and 123.25 min, respectively. The proposed RSM model equation shows a good correlation with the experimental data, with a correlation coefficient (R2) of 96.05%. This work will be a new method to enrich the harmful elements of WPCBs-SA and reduce the potential environmental pollution of related hazardous wastes. Keywords： Waste printed circuit boards smelting ash (WPCBs-SA); Sulfation roasting (SR); Thermodynamic; Debromination process; Response surface methodology (RSM); Optimization

Journal Pre-proof 1. Introduction Recently, with the rapid development of the electronic information industry, electronic product manufacturing has been dramatically accelerated by the continuous demands of technological innovation and an expanded market (Ismail and Hanafiah, 2019). The rapid growth of waste electrical and electronic equipment (WEEE) has generated a large amount of electronic waste (Isildar et al., 2019; Lee et al., 2007). According to statistics, approximately 96,000 tons of electronic waste will be produced per day worldwide, leading to an annual WEEE output as high as 30-50 million tons (Herat, 2008; Ni et al., 2012), with a growth rate of 2.5-8% per year (Zhang and Xu, 2016). Such a large amount of e-waste is considered a considerable threat to the global ecological environment and has become a new environmental problem that plagues global sustainable development (Alassali et al., 2019; Guo et al., 2014). At present, the relevant policies are improving (Gu et al., 2020; Zhou et al., 2020). As an important component of electrical and electronic products, printed circuit boards (PCBs) with complex components mainly comprise electronic components, glass fiber-reinforced epoxy resin and copper foil laminate (Park and Kim, 2019; Li et al., 2007; Yang et al., 2019). The content of precious metals such as gold (Au), sliver (Ag) and palladium (Pd) is much higher than that in original mineral deposits with great expected recycling value (Ghodrat et al., 2016; Ghosh et al., 2015; Li et al., 2008). PCBs also contain heavy metals, brominated flame retardants and other harmful substances, which could bring a challenge to the recycling process (Buekens and Yang, 2014; Diaz et al., 2016). Landfill, incineration, thermal degradation and other traditional recycling methods have caused severe damage to the ecosystem (Gao and Xu, 2019), and the main harms are shown in Table 1 (Duan et al., 2016; Soler et al., 2017; Zhou et al., 2013). Table 1 Main pollutants produced in the smelting incineration process of PCBs Pollutants

Compositions

Characteristics

Acidic gases Incomplete combustion products Organic pollutants with aromatic rings

HBr,Br2,HCl,NOx,SOx CO, carbon black, hydrocarbon

Corrosive Gas, solid

Brominated dioxins (PBDD/FS), Polybrominated biphenyls (PBBS), Bromobenzene series, bromophenol (PBPh), polycyclic aromatic hydrocarbons (PAHs), etc. Brominated hydrocarbons, aliphatic hydrocarbon antimony (Sb), copper (Cu), lead (Pb), zinc (Zn), tin (Sn), Au, Ag, etc

Many homologs, different toxicity, difficult to detect and degrade

Fat chain pollutant Smelting ash

organic

Gas Small, difficult to dispose

Smelting and incineration technology are widely used in the treatment of e-waste due to its suitability to burn low-grade fuels and effectively capture SOx, HCl and other poisonous gases (Hay and Rankin, 1994; Kim et al., 2015). However, because the

Journal Pre-proof manufacturing process of PCBs is generally added with a brominated epoxy resin having a fire-proof function, the concentration of bromine could be up to 15%, causing a large amount of volatile HBr gas to be generated during the smelting and incineration processes (Chien et al., 2000; Jin et al., 2011; Xiao et al., 2017). These volatile HBr could react with the other heavy metals (such as Cu, Pb, Zn, Sn, etc.) to convert into inorganic bromide, which is concentrated in the waste printed circuit boards smelting ash (WPCBs-SA) (Blazsó et al., 2002; Ortuño et al., 2014). At the same time, during the smelting process of the WPCB, some Au, Ag, and Pd are adsorbed together by these heavy metals into the WPCBs-SA. Therefore, WPCBs-SA has its excellent resource value with potential environmental risks (Pérez-Moreno et al., 2018; Wang et al., 2017). In recent years, many studies have been conducted to comprehensively utilize copper smelting ash and other nonferrous metal smelting intermediates, such as Electric-arc furnace dust (Walburga Keglevich De Buzin et al., 2017), copper smelting slag (Guo et al., 2018; Guo et al., 2018; Sarfo et al., 2017), lead-acid batteries (Pan et al., 2012; Pan et al., 2016), and copper anode slime (Ding et al., 2017), especially the extraction of valuable elements such as Cu, Pb, Zn, arsenic (As), selenium (Se), tellurium (Te) and Ag (Khalid et al., 2019; Qiang et al., 2014). They were involved in pyrometallurgical (Chairaksa et al., 2015; Lin et al., 2017) and hydrometallurgical processes (Miki et al., 2016; Tsakiridis et al., 2010). Sabzezari and Koleini (2019) reported a microwave-leaching method, applicable to the recovery of Cu and Zn from a copper smelter dust. The effect of different parameters and their interactions were studied using a central composite design (CCD) to find an optimum condition. Liu et al. (2018) suggested oxidation leaching with controlled potential technology for the extraction of Cu, As and Fe from copper smelting dust. Zhang et al. (2019) worked on the hydrometallurgical processing that involved a two-stage acid-leaching process, after alkali leaching of arsenic from copper smelting hazardous dust. There are some interesting methods for selective leaching of Zn by hydrothermal reduction (Zhang et al., 2019), leaching of Pb and Cu by citric acid (Gargul and Bukowska, 2019), arsenic removal by NaOH-H2O2 leaching (Gu et al., 2019) and solidification/stabilization of heavy metals (Pb, Zn, Cu and Cr) (Xia et al., 2019). However, studies on WPCBs-SA have rarely been reported so far. Unfortunately, the existing valuable metal recycling process cannot meet the comprehensive recycling requirements of WPCBs-SA. The high content of Br is difficultly recovery from WPCBs-SA, leading to serious environmental pollution. Therefore, it is very necessary to remove Br from WPCBs-SA by pretreatment before recovering valuable metals. Sulfation roasting(SR) is a widely applicable, economical and efficient recovery method, which is often used to treat refractory minerals or secondary resources (Lin et al., 2019). Optimization using response surface methodology (RSM) is one of the best multivariate techniques for metallurgical processes because it demonstrates suitable precise results and determines the interactions between effective parameters (Gasemloo et al., 2019; Gong et al., 2015; Yuan et al., 2019). The process optimization of SR for the Br- removal from WPCBs-SA has not been reported in the literature. Hence, a new facile method of sulfation roasting was applied to convert inorganic bromide from WPCBs-SA with high efficiency, and the thermodynamic analysis and

Journal Pre-proof RSM were used to verify and optimize the optimum conditions of Br- removal efficiency. This work will be a new method to enrich the harmful elements of WPCBsSA and reduce the potential environmental pollution of related hazardous wastes.

2. Materials and methods 2.1 Materials and apparatus The WPCBs-SA used in this study was collected from CECEP (SHANTOU) Recycling Resources Technology Co., Ltd. of China, as shown in Fig 1. The pretreatment was carried out before the experiment, and WPCBs-SA was continuously ball milled for 6 hours (particle size <0.178 mm) using a spherical ball mill (QM-3SP2; Nanjing University Instrument Factory, China). Next, it was dried in a vacuumed oven at 105℃ for 12 h. The content of each element was taken as the average of three measurements using ICP-OES (Optima8000; Perkin Elmer Co., Ltd, Japan), but the content of Br in the sample was titrated by the iodometric method (Li et al., 2014), as shown in Table 2. The powder composition was analyzed by XRF (Magix-PW2403; PANalytical Co., Ltd, Netherlands). The mineralogical analysis of the sample was carried out by XRD (Rigaku diffractometer [D/max 2500] using Cu Kα radiation) analysis before and after roasting. The morphology of the sample was examined by SEM using an EDS system (Nova Nano200; FEI Co., Ltd, America). The valence states of the main elements in WPCs-SA were determined by XPS (ESCALab220i-XL electron spectrometer; Thermo Fisher Scientific Company, America). All chemical reagents, including sulfuric acid (H2SO4) and sodium hydroxide (NaOH) were analytical grade with the purities of ≥99.9%, and only tap water (filtered water) was used as the leaching agent. Table 2 Chemical composition of WPCBs-SA (Wt, %) Br

Cu

Zn

O

Pb

Cl

Sn

Cd

Sb

24.9 0

18.7 9

13.5 5

12.5 0

8.6 0

6.2 0

2.7 6

0.5 3

0.4 9

A g 0. 3

As

Au *

Other s

0.00 3

29

11.37

*：g/t, Br was titrated by iodometric method and the other elements were tested by ICP-OES (Firstly dissolved by aqua regia (V(HNO3)/V(HCl)=3/1), then denitrificated and diluted with 5% nitric acid).

Fig. 1 Raw material of WPCBs-SA ((a) Appearance, (b)SEM, (c) EDS, (d) XRD, (e) Br, (f)

Journal Pre-proof Cu, (g) Zn, (h) Cl, (i) Sn, (j) Pb.)

2.2 Experimental methods The SR experiments were carried under a laboratory scale of 50 g. WPCBs-SA was mixed and stirred with sulfuric acid at a controlled acid: material ratio (g/g), and then the mixture was placed in a ceramic crucible overnight to undergo the full-aging process. When the temperature reached a set value, the mixture was heated in a tubular furnace and maintained at a controlled temperature. After various durations, the roasted samples were cooled down to room temperature. The generated flue gas was treated with excess 20% concentration NaOH solution to enrich of bromide salt during the roasting process. The integrated procedure of this study is shown in Fig. 2. If the roasted sample was sticky with high acidity, the excess sulfuric acid was removed with 10% NaOH solution, followed by adjusting the pH value to neutral and drying in a vacuumed oven at 378.15 K for 12 h. After ball grinding (particle size <0.178 mm), a part of the dried roasted samples was titrated using the iodometric method. Data from all experiments were averaged over three times, and relative standard deviations were found to be within ±0.5%. The removal efficiency of Br- was estimated by Eq. (1): α=

（

𝑾𝟐 ∙ 𝑿𝟐

𝟏 ― 𝑾𝟏 ∙ 𝑿𝟏

） × 𝟏𝟎𝟎%

（𝟏）

Where 𝑊1 is the initial mass of raw material, 𝑊2 is the mass of the roasted sample, and 𝑋1 and 𝑋2 are the elemental contents in the raw material and roasted sample, respectively.

Fig. 2 Debrominated diagram of WPCBs-SA using the SR process

2.3 Experimental design The experimental domain of single-factor experiments was defined considering the operational limits of the instrument and the results of thermodynamic analysis. All the independent parameters in the SR process were chosen as variables: acid: material ratio (0.6-1.5 g/g), roasting temperature (400-600 K) and roasting time (30-150 min). RSM was chosen to optimize the roasting process and analyze the interaction between the experimental parameters (Singh et al., 2010). Consideration of the obtained results in single-factor experiments, the experimental domain of the central composite design (CCD) was defined (Ahmad et al., 2019). The acid: material ratio (A=0.6-1.0 g/g), roasting temperature (B=553-593 K) and roasting time (C=90-150 min) were used as the independent variables, and their factors and levels are shown in Table 3. DesignExpert 8.0 software was used for experiments of CCD (Ahmad et al., 2018). As shown

Journal Pre-proof in Table 4, only 20 experiments comprising 6 replicates, 6 axial points and 8 factorial points at the central points were needed to obtain the conclusions using Eq (2) (Kılıç et al., 2014; Moghaddam et al., 2010; Ooi et al., 2018). All the experiments were performed in triplicate. N = 2𝑛 + 2n + n𝑐 = 23 + (2 × 3) + 6 = 20 (2) In Eq. (2), N represents the number of experiments, n is the number of factors, and nc represents the number of repetitions of the center point. Table 3 Independent variables and levels. Variables

Code

Acid: material ratio Roasting temperature Roasting time

A B C

Unit g/g K min

Real values of code level -1

0

1

0.6 553 90

0.8 573 120

1.0 593 150

Table 4 Experimental design and results. Run

A

B

C

Comment

Responses (% Br-removal efficiency)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

1 0 0 1 1 0 1 1 -1 0 -1 0 0 0 0 -1 0 -1 0 -1

-1 0 -1 0 1 0 -1 1 1 0 -1 0 0 0 0 1 0 -1 1 0

1 1 0 0 -1 0 -1 1 -1 -1 -1 0 0 0 0 1 0 1 0 0

Full factorial Axial Axial Axial Full factorial Center Full factorial Full factorial Full factorial Axial Full factorial Center Center Center Center Full factorial Center Full factorial Axial Axial

97.01 98.80 97.49 96.10 97.88 98.78 96.19 97.98 98.04 97.07 96.90 98.77 98.78 98.79 98.77 97.39 98.78 97.59 98.81 96.89

A second-order model, as shown in Eq. (3), in the form of a quadratic polynomial equation, was given to evaluate the response variables and their interaction (Mohammed et al., 2017). 𝑛

𝑛

𝑛

𝑛

𝛾 = 𝛽𝑜 + ∑𝑖 = 1𝛽𝑖𝜒𝑖 + ∑𝑖 = 1𝛽𝑖𝑖𝜒2𝑖 + ∑𝑖 = 1∑𝑗 > 1𝛽𝑖𝑗𝜒𝑖𝜒𝑗

(3)

Journal Pre-proof In Eq. (3), response γ (%) is the Br- removal efficiency. βo represents a constant coefficient, and βi, βij and βii represent the coefficients of the linear, interaction and quadratic terms, respectively. The coded values of the independent variables are denoted by χi and χj, respectively. The analysis of variance (ANOVA) was used to completely analyze the results of the experiment. ANOVA of the SR for Br- removal was performed using Design-Expert program 8.0 software. The results of ANOVA can provide some important coefficients to estimate which factors are important model terms (Javed et al., 2018). The 3-D curves and contour plots of the response surfaces were also developed using Design-Expert software (Watson et al., 2016). The interactive effects of the independent variables were evaluated using these figures.

3. Results and discussion 3.1 Material characterization The chemical composition of the sample is shown in Table 2. WPCBs-SA contains many potentially toxic elements (PTEs), including 18.79% Cu, 13.55% Zn, 8.60% Pb, 2.76% Sn, 0.53% Cd, and 0.48% Ni, and some toxic elements that are 24.90% Br, 6.20% Cl and 0.003% As. The precious metals including 0.3% Ag and 30 g/t Au were also found in this sample. The phase of each element in WPCBs-SA was determined by Xray diffraction (XRD) analyses, and the results are shown in Fig. 1(d). The results indicated that the used WPCBs-SA mainly comprised CuBr, PbBr/Cl, ZnO and SnO2. Scanning electron microscopy (SEM) analysis of the raw materials is shown in Fig. 1(b). The morphology of the ash was found to be irregular. Energy-dispersive spectrometer (EDS) analysis was utilized on the block as shown in Fig. 1(c) and Fig.1(e)-(j). Its main components wereCu, Br, Zn and Sn, which were also consistent with the XRF and XRD results. X-ray photoelectron spectroscopy (XPS) was applied to confirm the valence states of main elements in WPCBs-SA. Fig. 3(a) shows the overview XPS spectra of the coexistence of Br, Cu and Pb with other minor elements in WPCBs-SA. Fig. 3(b) shows the detailed XPS spectra of Br 3d after peak separation. Both peaks at 68.74 and 69.67 eV correspond to Br-. As shown in Fig. 3(c), two strong peaks appear at 932.87 and 952.74 eV, which are attributed to Cu+ (Huang et al., 2014). The peaks at 138.78 and 143.54 eV belong to Pb 4f of Pb2+ in Fig. 3(d). The XPS results are consistent with those of CuBr and PbBr2 in XRD. The presence of bromide is not conducive to the recovery of valuable metals, making the experimental environment harsh. Under the normal conditions, Br- in WPCBs-SA is hardly soluble in acid or alkali solution. Through the above analysis, this study attempts to pretreat WPCBs-SA via SR, which converts Br- into volatile substances of Br- and achieves the complete separation of bromine with other valuable components. It will facilitate the subsequent recovery of valuable metals in WPCBsSA.

Journal Pre-proof

Fig. 3 (a) XPS survey spectra, (b) Br 3d, (c) Cu 2p, and (d) Pb 4f spectrum of WPCBs-SA

3.2 Thermodynamic analysis of the debrominated process The SR of WPCBs-SA is a complex system with multiple phases and multireactions. The reactions in the system are complex physical and chemical reactions under constant temperature and constant pressure conditions (Long et al., 2014; Tang et al., 2018). To simplify complex metallurgical processes and present an accurate reaction mechanism as clearly as possible, CuBr, PbBr2 and PbCl2 represent compounds of bromine in the WPCBs-SA. Table 5 shows the reactions that may occur in the roasting process and the calculation formulas of Gibbs free energy for each chemical reaction obtained according to Eq (4), under one atmosphere pressure (Li et al., 2017; Radi et al., 2019; Ye et al., 2015). The relationship between the free energy of the chemical reactions and temperature is shown in Fig. 4. ∆𝐺𝜃𝑇 = ∆𝐻𝜃𝑇-T∆𝑆𝜃𝑇

（4）

Table 5 The ∆𝑮𝜽𝑻-T of main chemical reactions during SR Reaction

∆𝐺𝜃𝑇-T（kJ/mol）

2CuBr+3H2SO4=2CuSO4+2HBr+SO2+2H2O PbBr2+H2SO4=PbSO4+2HBr(g) PbCl2+H2SO4 =PbSO4+2HCl(g) 2HBr + H2SO4 = Br2+ SO2+ 2H2O Sn(SO4)2+4HBr=SnBr4+2H2SO4 SnBr4+2H2O =SnO2 +4HBr(g) 4HBr+O2=2H2O+2Br2(g) 2H2SO4=2SO2+2H2O+O2(g) H2SO4=SO3+H2O

∆𝐺𝜃𝑇 = 258.07-0.58T ∆𝐺𝜃𝑇 = 97.65-0.33T ∆𝐺𝜃𝑇 = 70.50-0.23T ∆𝐺𝜃𝑇 = 137.15-0.32T ∆𝐺𝜃𝑇=-167.95+0.22T ∆𝐺𝜃𝑇 = 72.01-0.06T ∆𝐺𝜃𝑇=-276.44+0.13T ∆𝐺𝜃𝑇 = 55.07-0.76T ∆𝐺𝜃𝑇=176.42-0.29T

Eqs （5） （6） （7） （8） （9） （10） （11） （12） （13）

Journal Pre-proof H2SO4(l)= H2SO4(g) SO2+Br2+H2O=2HBr(g)+SO3(g)

∆𝐺𝜃𝑇=73.43-0.13T ∆𝐺𝜃𝑇=39.27+0.03T

（14） （15）

Fig. 4 ∆𝑮𝜽𝑻 - T diagrams of Eqs（5）-（15）

As shown in Fig. 4(a), the reaction in Eq (7) could occur spontaneously when the temperature was maintained between 300 K and 1000 K and ∆𝐺𝜃𝑇 was less than 0. Thus, PbCl2 can easily react with concentrated H2SO4 to yield PbSO4. Additionally, the free energies of Eqs (5) and (6) decreased with the increase in temperature. The reaction temperatures of ∆𝐺𝜃𝑇 = 0 for PbBr2 and CuBr reacted with H2SO4 were 430.15 K and 446.2 K, respectively, indicating that these reactions can occur spontaneously at low temperature, and bromine can be converted into volatile HBr. It was also found that, at 432.84 K, Eq (8) began to proceed, and the reaction between volatile HBr and H2SO4 was accelerated to further generate bromine gas and sulfur dioxide gas. The analysis showed that it is not possible to treat the tail gas only with water because, as shown in Fig. 4 (d) and Eq (15), within the roasting temperature range, the Gibbs free energy of the SO2 and Br2 reaction was greater than zero; thus, it cannot be carried out spontaneously. Moreover, with the increase in temperature, the Gibbs free energy became increasingly larger. As shown in Eq (11) of Fig. 4(b), the HBr generated in the roasting process can be rapidly oxidized by oxygen in the air to form Br2 because all the ∆𝐺𝜃𝑇 values were below 0.0 when the reaction temperature was maintained between 300 K and 1000 K. At the same time, Sn(SO4)2 generated in the roasting process reacted with HBr to generate SnBr4 at a temperature lower than 700 K because ∆𝐺𝜃𝑇 < 0 in Eq (9) at the reaction temperature less than 750 K. SnBr4 had good chemical stability because ∆𝐺𝜃𝑇 < 0 in Eq (10) is in the roasting temperature range. The decomposition reaction of H2SO4 was also investigated as Eqs (12) - (14) in Fig. 4(c). It was shown that the temperatures of the release of SO2 and SO3 from H2SO4 should be higher than 720 K and 611 K, respectively. Additionally, the sulfuric acid volatilization temperature should be higher than 564.8 K. Thus, most of the

Journal Pre-proof decomposition of sulfuric acid will be SO2 in the low-temperature roasting process. Thermodynamic analysis of the above roasting process showed that Br in the WPCBs-SA can be converted into volatile HBr or Br2 rapidly and completely under the condition that the temperature was less than 564.8 K. SO2, SO3 and H2SO4 gases will not be produced by the decomposition of sulfuric acid in the roasting process. Therefore, SR is an effective method to achieve Br- removal of WPCBs-SA. 3.3 Effects of the parameters 3.3.1 Effect of the roasting temperature To study the influence of different roasting temperatures on the Br- removal efficiency, five different roasting temperatures were set under the condition of an acid: material ratio of 1:1 (g/g) and a roasting time of 120 min. According to the previous thermodynamic analysis results, the temperature range of the SR was set at 400-600 K.

Fig. 5 Removal efficiency of bromine in the roasting process. ((a) Acid: material ratio of 1:1 (g/g) and roasting time of 120 min, (b) Roasting temperature of 550K and time of 120 min, (c) Acid: material ratio of 0.8 (g/g) and roasting temperature of 550 K.)

Fig. 5(a) shows that the Br- removal efficiency was 6.7% after 120 min, under a lower roasting temperature of 450 K. The main reason was that, when the roasting temperature was 450 K, PbBr2 and CuBr in WPCBs-SA could react with sulfuric acid slowly. At this time, the mixture of concentrated sulfuric acid and WPCBs-SA was viscous, hindering bromine to volatilize and leading to a low bromine removal rate. With the increase in calcination temperature, the removal rate of bromine increased sharply. At 500 K, the Br- removal efficiency increased to 77.1%, and it reached a maximum of 98.71% by 550 K. With the further increase in the calcination temperature, the rate of debromination increased slowly. Under the condition of 600 K, the Brremoval efficiency was not increased; it was maintained at 98.75%. The high roasting temperature is beneficial for the decomposition of PbBr2 and CuBr in WPCBs-SA. When the roasting temperature reaches at the boiling point of sulfuric acid at 600 K, the accelerated volatilization of sulfuric acid will hinder the evaporation of bromine

Journal Pre-proof vapor, resulting in lower Br removal efficiency. As comprehensive consideration of the amount of residual sulfuric acid in the roasting sand, the suitable temperature was set at 550 K. 3.3.2 Effect of acid: material ratios After the roasting temperature was determined, the ratios of the acid: material in the Br- removal efficiency were further investigated (the ratios were 0.6:1, 0.8:1,1:1, 1.2:1, and 1.5:1 (g/g)) at 550 K for 120 min. Fig. 5 (b) shows that the Br- removal efficiency was higher under the roasting conditions of a lower acid: material ratio. When the ratio range was set at 0.6-1, the Brremoval efficiency was maintained between 98.44% and 98.78%; with the increase in the ratio (to 1.2), the Br- removal efficiency tended to decrease slowly (down to 96.3%). When the ratio was further increased to 1.5, the Br- removal efficiency rapidly dropped to approximately 74%, mainly determined by the stoichiometric ratio of PbBr2 and CuBr with sulfuric acid. Under the condition of 0.6-1.0, gases such as HBr and Br2 volatilize more fully. When the acid ratio was continuously increased, the excessive sulfuric acid could not be completely volatilized and remained in the calcined sand, hindering the volatilization of bromine, resulting in a low Br- removal efficiency. So, the best ratio should be chosen at approximately 0.8 g/g for the highest Br- removal efficiency. 3.3.3 Effect of the roasting time After determining the roasting temperature of 550 K and the acid: material ratio of 0.8 g/g, the effect of the roasting time (30-150 min) on the Br- removal efficiency was investigated. As shown in Fig. 5(c), the roasting test results revealed that the removal rate of Br increased with the increase in roasting time. The roasting time was extended from 30 min to 150 min, and the removal rate of bromine was rapidly increased from 68.8% to 98.7%, indicating that PbBr2, CuBr and sulfuric acid reacted more fully with the higher Br- removal efficiency within this temperature range. With the extension of the reaction time, the removal effect of bromine tended to be stable and gradually stabilized at approximately 98.7%, mainly because bromide was completely converted into volatile hydrogen bromide or bromine gas during this period. So, the optimal roasting time is approximately 120 min. The roasted sample (at 550 K, acid: material ratio of 0.8 g/g and a roasting time of 120 min) was neutralized by 10% NaOH solution. The XRD test results (Fig. 6(a)) after drying showed that the presence of bromine and its compounds were not detected compared with the raw materials. The results of SEM showed that (Fig. 6(b)) small particles could be observed on the surface of the calcined products under 10,000 times magnification in a scanning electron microscope. We conducted an EDS analysis on the particulate matter and found that bromine and its compounds were not found at the 1# position in Fig. 6(c), but only a small amount of bromine existed at the 2# position in Fig. 6(d). The reason for the analysis may be that the calcination process was in a ceramic crucible with a certain depth and without stirring in the roasting process. Thus, the reaction was not complete, resulting in a small amount of bromine and its compounds at the bottom of the crucible being surrounded by other major elements and

Journal Pre-proof not being sufficiently volatile. However, the content of Br in roasted samples was much lower than that in WPCBs-SA (24.9%), and further roasting can completely remove it, which was also consistent with the test results.

Fig. 6 XRD and SEM-EDS of the roasted sample

3.4 Response analysis and interpretation 3.4.1 Statistical analysis and model fitting According to the CCD of experiments, all 20 experiments were conducted, as shown in Table 4. The efficiency of Br- removal was found to range from 96.1 % to 98.79 % in response to the variation. Table 6 shows the ANOVA of the response surface quadratic model for Br- removal by the SR process. Table 6 Analysis of variance(ANOVA) for Br removal. Source Model A:Acid: material ratio B:Roasting temperature C:Roasting time AB AC BC A2

Sum of Squares

Degree of freedom(DF)

Mean Square

F-Value

Prob > F

Remarks

15.76

9

1.75

27.04

< 0.0001

significant

0.35

1

0.35

5.41

0.0423

2.48

1

2.48

38.28

0.0001

1.10

1

1.10

16.92

0.0021

0.37 0.10 0.53 9.78

1 1 1 1

0.37 0.10 0.53 9.78

5.71 1.49 8.19 150.95

0.0380 0.2496 0.0169 < 0.0001

Journal Pre-proof B2 C2 Residual Lack of Fit Pure Error Cor Total

0.82 1.43 0.65 0.65 0.000283 16.41

1 1 10 5 5 19

0.82 1.43 0.06 0.13 0.000057

12.67 22.03

0.0052 0.0009

2285.69

< 0.0001

significant

R2=0.9605;R2adj=0.9250

As shown in Table 6, the proposed model was significant because its F-value is 27.04. The values of “Prob>F” used to check the significance of the corresponding coefficient was less than 0.0001, which indicates that the proposed model is of great significance for Br- removal. The linear, interaction, and quadratic terms were A, B, C, AB, BC, A2, B2, and C2, and their Prob > F values of 0.0433, 0.0001, 0.0021, 0.0380, 0.0169, <0.0001, <0.0052, and 0.0009, respectively. In other words, the linearity, quadratic and interaction terms of these factors were significant regarding the Brremoval efficiency. Among the linear terms, roasting temperature (B) had a more significant effect on the Br- removal efficiency than the roasting time (C) and acid: material ratio (A) due to the high F-value (38.28). The order of the significant influence on the response value of Br- removal efficiency was as follows: B > C> A. Comparing the linear terms, the effect of the interaction between the acid: material ratio and roasting temperature (AB) and between the roasting temperature and roasting time (BC) also affected the Brremoval efficiency significantly. Moreover, the quadratic term of the acid: material ratio (A2) has a larger effect on the Br- removal efficiency due to the high F-value (150.95) than the roasting temperature (B2) and roasting time (C2). Therefore, the final equation, including the most important coding factors, is shown as Eq (16). Y=98.78-0.16A+0.43B+0.28C+0.22AB-0.26BC-0.82A2-0.24B2-0.31C2 (16) Lack of fit was important relative to the pure error because its F-value is 1185.69. The values of R2 and R2adj (adjusted R2) were 0.9605 and 0.9250, respectively. The R2 and R2adj values were sufficiently high and comparable. Thus, the experimental data has a good correlation with the given quadratic response surface model (Javed et al., 2018; Tyagi and Kumari, 2018). 3.4.2 Model validation Some significant diagnostic plots were used to evaluate if the experimental data of the SR process are suitable for the given quadratic response surface model (Yuan et al., 2019), and the results were shown in Fig. 7. In Fig. 7(a), the normally distributed error terms are independent of each other since these points are roughly distributed around the line (Mohammed et al., 2017). As shown in Fig. 7(b) and (c), the points are randomly distributed between -3.0 and +3.0 and around zero. This indicated that the RSM of quadratic accurately established the relationship between Br- removal efficiency and the main variables of the SR process (Yuan et al., 2019). The relationship between the actual and predicted values of the Brremoval efficiency is shown in Fig 7(d). The linearly distributed points indicated that the actual value could be successfully predicted by the developed model (Nazari et al., 2014).

Journal Pre-proof Three-dimensional (3-D) response plots show the results of interactions between the various variables regarding the Br- removal efficiency. The shape of the response surface plots and the projection contour map of the fitted model can effectively characterize the significance of the effectiveness of variables (Kılıç et al., 2014). In Fig 8, one factor at the central level was held constant, while the other two were varied within the experimental ranges.

Fig.7 Diagnostic plots of the quadratic RSM model

Fig. 8(a) clearly shows that, when the roasting temperature increased from 553 to 593 K, the Br- removal efficiency significantly increased. With increasing the acid: material ratio from 0.6 to 1.0 g/g, a decrease in the Br- removal efficiency was obtained. As shown in Fig. 8(a), contour plots of the roasting temperature and acid: material ratio effect indicate similar results to those of the 3-D surface plot. This phenomenon is consistent with the results of Fig 5. The maximum Br- removal efficiency can be obtained with a roasting temperature of 563-593 K and an acid: material ratio of 0.7– 0.9 g/g. Comparing the effects of roasting time and acid: material ratio on the Brremoval efficiency, it can be seen in Fig. 8(b) that Br- removal efficiency raised with increasing the roasting time up to 150 min. Both the contour and surface plots in Fig. 8(b) showed that increasing the acid: material ratio from 0.6 to 1.0 g/g results in a decrease in the Br- removal efficiency. Similarly, Fig. 8(c) shows that the increase of roasting time and temperature could improve the Br- removal efficiency. As shown in Fig. 8(c), the maximum Br- removal efficiency region that could be obtained at the estimated conditions: 573-593 K and 90-150 min. Therefore, the results indicate that the acid: material ratio, roasting temperature and time had a significant influence on the Br- removal efficiency.

Journal Pre-proof

Fig.8 3-D response plots shown the results of interactions between the various variables. ((a) the roasting temperature and acid: material ratio, (b) the roasting time and acid: material ratio, (c) the roasting time and temperature.)

3.4.3 Optimization of the roasting process for Br- removal The ultimate goal of RSM is to obtain the optimal results of independent variables in the SR process for Br- removal using the developed model. In the optimization process, the target value for the response (Br- removal efficiency) was selected to the desired goal of 100%. The variables of the acid: material ratio, roasting temperature and time were chosen to be within the range using Design Expert 8.0 software (Öelmez, 2009), and the results are shown in Fig 9. The optimum conditions for the acid: material ratio, roasting temperature and time were as followed: 0.8 g/g, 590.04 K and 123.25 min, respectively. The maximum removal efficiency of Br- was 98.97% under the optimum conditions, and the predicted values were consistent with the results of singlefactor experiments.

Journal Pre-proof

Fig 9 Optimized ramps show the optimized values of various variables for the maximum Brremoval efficiency

4 Conclusion In the present study, the acid: material ratio, roasting time and temperature and other effects of essential variables on the Br- removal efficiency were systematically studied on the SR process from WPCBs-SA. The thermodynamic analysis results demonstrated that SR is an effective method for Br- removal, and Br in WPCBs-SA was converted into HBr or Br2 below 564.8 K. The results of the present study indicated that RSM is a suitable method for the optimizing the conditions of SR process for Br- removal. Under the optimized experimental conditions, the Br- removal efficiency was up to 98.97% and values of the variables were 0.8 g/g, 590.04 K and 123.25 min, respectively. The proposed RSM model equation has a good correlation with the experimental data, with a correlation coefficient (R2) of 96.05%. The produced SO2 and HCl/Br2 flue gas in the process of SR was absorbed by 20% NaOH solution, and the bromide and sulfate was obtained from the alkali solution by treatment. Therefore, the process embodies the principle of clean production. This work will be a new method to enrich the harmful elements of WPCBs-SA and reduce the potential environmental pollution of related hazardous wastes. Explaining the debrominated mechanism requires more in-depth research in the field of the kinetics of the sulfation roasting process, which is the subject of another manuscript we are working on.

Acknowledgment This work was supported by the National Key Research and Development Program of China (No. 2018YFC1903104, 2018YFC1903603).

Journal Pre-proof References Ahmad, F., Anwar, S., Firdous, S., Dachuan, Y., Iqbal, S., 2018, Biodegradation of bispyribac sodium by a novel bacterial consortium BDAM: Optimization of degradation conditions using response surface methodology. J. Hazard. Mater 349, 272-281. Ahmad, F., Ashraf, N., Zhou, R., Chen, J.J., Liu, Y., Zeng, X., Zhao, F., Yin, D., 2019, Optimization for silver remediation from aqueous solution by novel bacterial isolates using response surface methodology: Recovery and characterization of biogenic AgNPs. J. Hazard. Mater 380. Alassali, A., Abis, M., Fiore, S., Kuchta, K., 2019, Classification of plastic waste originated from waste electric and electronic equipment based on the concentration of antimony. J. Hazard. Mater 380. Blazsó, M., Czégény, Z., Csoma, C., 2002, Pyrolysis and debromination of flame retarded polymers of electronic scrap studied by analytical pyrolysis. J. Anal. Appl. Pyrol 64, 249-261. Buekens, A., Yang, J., 2014, Recycling of WEEE plastics: a review. J. Mater. Cycles Waste 16, 415434. Chairaksa, F.R., Inoue, Y., Umeda, N., Itoh, S., Nagasaka, T., 2015, New pyrometallurgical process of EAF dust treatment with CaO addition. Int. J. Min. Met. Mater 22, 788-797. Chien, Y.C., Wang, H.P., Lin, K.S., Huang, Y.J., Yang, Y.W., 2000, Fate of bromine in pyrolysis of printed circuit board wastes. Chemosphere 40, 383-387. Diaz, L.A., Lister, T.E., Parkman, J.A., Clark, G.G., 2016, Comprehensive process for the recovery of value and critical materials from electronic waste. J. Clean. Prod 125, 236-244. Ding, Y., Zhang, S., Liu, B., Li, B., 2017, Integrated process for recycling copper anode slime from electronic waste smelting. J. Clean. Prod 165, 48-56. Duan, H., Hu, J., Yuan, W., Wang, Y., Yu, D., Song, Q., Li, J., 2016, Characterizing the environmental implications of the recycling of non-metallic fractions from waste printed circuit boards. J. Clean. Prod 137, 546-554. Gao, R., Xu, Z., 2019, Pyrolysis and utilization of nonmetal materials in waste printed circuit boards: Debromination pyrolysis, temperature-controlled condensation, and synthesis of oil-based resin. J. Hazard. Mater 364, 1-10. Gargul, K., Boryczko, B., Bukowska, A., Jarosz, P., Malecki, S., 2019, Leaching of lead and copper from flash smelting slag by citric acid. Arch. Civ. Mech. Eng 19, 648-656. Gasemloo, S., Khosravi, M., Sohrabi, M.R., Dastmalchi, S., Gharbani, P., 2019, Response surface methodology (RSM) modeling to improve removal of Cr (VI) ions from tannery wastewater using sulfated carboxymethyl cellulose nanofilter. J. Clean. Prod 208, 736-742. Ghodrat, M., Rhamdhani, M.A., Brooks, G., Masood, S., Corder, G., 2016, Techno economic analysis of electronic waste processing through black copper smelting route. J. Clean. Prod 126, 178-190. Ghosh, B., Ghosh, M.K., Parhi, P., Mukherjee, P.S., Mishra, B.K., 2015, Waste Printed Circuit Boards recycling: an extensive assessment of current status. J. Clean. Prod 94, 5-19. Gong, Y., Wang, S., Xu, H., Guo, Y., Tang, X., 2015, Partial oxidation of landfill leachate in supercritical water: Optimization by response surface methodology. Waste Manage 43, 343-352. Gu, K., Li, W., Han, J., Liu, W., Qin, W., Cai, L., 2019, Arsenic removal from lead-zinc smelter ash by NaOH-H2O2 leaching. Sep Purif. Technol 209, 128-135. Gu, Y., Wu, Y., Liu, J., Xu, M., Zuo, T., 2020. Ecological Civilization and Government Administrative System Reform in China. Resour. Conserv. Recy 155. Guo, X., Qin, F.G.F., Yang, X., Jiang, R., 2014, Study on low-temperature pyrolysis of large-size printed

Journal Pre-proof circuit boards. J. Anal. Appl. Pyrol 105, 151-156. Guo, Z., Pan, J., Zhu, D., Zhang, F., 2018, Green and efficient utilization of waste ferric-oxide desulfurizer to clean waste copper slag by the smelting reduction-sulfurizing process. J. Clean. Prod 199, 891-899. Guo, Z., Zhu, D., Pan, J., Zhang, F., 2018, Innovative methodology for comprehensive and harmless utilization of waste copper slag via selective reduction-magnetic separation process. J. Clean. Prod 187, 910-922. Hay, S.M., Rankin, W.J., 1994, Recovery of iron and zinc from blast furnace and basic oxygen furnace dusts: A thermodynamic evaluation. Miner Eng 7, 985-1001. Herat, S., 2008, Environmental impacts and use of brominated flame retardants in electrical and electronic equipment. Environmentalist 28, 348-357. Huang, H., Hua, L., Wang, A., Zhong, S., Fang, K., Feng, J., 2014, Green synthesis of peptide-templated fluorescent copper nanoclusters for temperature sensing and cellular imaging. Analyst 139, 6536-6541. Isildar, A., van Hullebusch, E.D., Lenz, M., Du Laing, G., Marra, A., Cesaro, A., Panda, S., Akcil, A., Kucuker, M.A., Kuchta, K., 2019, Biotechnological strategies for the recovery of valuable and critical raw materials from waste electrical and electronic equipment (WEEE) – A review. J. Hazard. Mater 362, 467-481. Ismail, H., Hanafiah, M.M., 2019, An overview of LCA application in WEEE management: Current practices, progress and challenges. J. Clean. Prod 232, 79-93. Javed, U., Farooq, R., Shehzad, F., Khan, Z., 2018, Optimization of HNO3 leaching of copper from old AMD Athlon processors using response surface methodology. J. Environ. Manage 211, 22-27. Jin, Y., Tao, L., Chi, Y., Yan, J., 2011, Conversion of bromine during thermal decomposition of printed circuit boards at high temperature. J. Hazard. Mater 186, 707-712. Khalid, M.K., Hamuyuni, J., Agarwal, V., Pihlasalo, J., Haapalainen, M., Lundstrom, M., 2019, Sulfuric acid leaching for capturing value from copper rich converter slag. J. Clean. Prod 215, 1005-1013. Kılıç, M., Pütün, E., Pütün, A.E., 2014, Optimization of Euphorbia rigida fast pyrolysis conditions by using response surface methodology. J. Anal. Appl. Pyrol 110, 163-171. Kim, Y., Han, T.U., Watanabe, C., Teramae, N., Park, Y., Kim, S., Hwang, B., 2015, Analytical pyrolysis of waste paper laminated phenolic-printed circuit board (PLP-PCB). J. Anal. Appl. Pyrol 115, 87-95. Lee, J., Song, H.T., Yoo, J., 2007, Present status of the recycling of waste electrical and electronic equipment in Korea. Resour. Conserv. Recy 50, 380-397. Li, G., Sun, P., Yu, L., 2014, Test Method for Bromide Ion in Liquid Waste Containing Bromine. Sd. Chem. Indu 43, 76-77. Li, J., Lu, H., Guo, J., Xu, Z., Zhou, Y., 2007, Recycle technology for recovering resources and products from waste printed circuit boards. Environ. Sci. Technol 41, 1995-2000. Li, J., Lu, H., Liu, S., Xu, Z., 2008, Optimizing the operating parameters of corona electrostatic separation for recycling waste scraped printed circuit boards by computer simulation of electric field. J. Hazard. Mater 153, 269-275. Li, Y., Chen, Y., Tang, C., Yang, S., He, J., Tang, M., 2017, Co-treatment of waste smelting slags and gypsum wastes via reductive-sulfurizing smelting for valuable metals recovery. J. Hazard. Mater 322, 402-412. Lin, J., Liu, C., Cao, H., Chen, R., Yang, Y., Li, L., Sun, Z., 2019, Environmentally benign process for selective recovery of valuable metals from spent lithium-ion batteries by using conventional sulfation roasting. Green. Chem, 21,5904-5913.

Journal Pre-proof Lin, X., Peng, Z., Yan, J., Li, Z., Hwang, J., Zhang, Y., Li, G., Jiang, T., 2017, Pyrometallurgical recycling of electric arc furnace dust. J. Clean. Prod 149, 1079-1100. Liu, W., Fu, X., Yang, T., Zhang, D., Chen, L., 2018, Oxidation leaching of copper smelting dust by controlling potential. T. Nonferr. Metal. Soc 28, 1854-1861. Long, Y., Li, J., Timmer, D.H., Jones, R.E., Gonzalez, M.A., 2014, Modeling and optimization of the molten salt cleaning process. J. Clean. Prod 68, 243-251. Miki, T., Chairaksa, F.R., Maruyama, K., Nagasaka, T., 2016, Hydrometallurgical extraction of zinc from CaO treated EAF dust in ammonium chloride solution. J. Hazard. Mater 302, 90-96. Moghaddam, S.S., Moghaddam, M.R.A., Arami, M., 2010, Coagulation/flocculation process for dye removal using sludge from water treatment plant: Optimization through response surface methodology. J. Hazard. Mater 175, 651-657. Mohammed, I.Y., Abakr, Y.A., Yusup, S., Kazi, F.K., 2017, Valorization of Napier grass via intermediate pyrolysis: Optimization using response surface methodology and pyrolysis products characterization. J. Clean. Prod 142, 1848-1866. Nazari, E., Rashchi, F., Saba, M., Mirazimi, S.M.J., 2014, Simultaneous recovery of vanadium and nickel from power plant fly-ash: Optimization of parameters using response surface methodology. Waste Manage 34, 2687-2696. Ni, M., Xiao, H., Chi, Y., Yan, J., Buekens, A., Jin, Y., Lu, S., 2012, Combustion and inorganic bromine emission of waste printed circuit boards in a high temperature furnace. Waste Manage 32, 568-574. Öelmez, T., 2009, The optimization of Cr(VI) reduction and removal by electrocoagulation using response surface methodology. J. Hazard. Mater 162, 1371-1378. Ooi, T.Y., Yong, E.L., Din, M.F.M., Rezania, S., Arninudin, E., Chelliapan, S., Rahman, A.A., Park, J., 2018, Optimization of aluminium recovery from water treatment sludge using Response Surface Methodology. J. Environ. Manage 228, 13-19. Ortuño, N., Conesa, J.A., Moltó, J., Font, R., 2014, Pollutant emissions during pyrolysis and combustion of waste printed circuit boards, before and after metal removal. Sci. Total. Environ 499, 27-35. Pan, J., Zhang, C., Sun, Y., Wang, Z., Yang, Y., 2012, A new process of lead recovery from waste leadacid batteries by electrolysis of alkaline lead oxide solution. Electrochem. Commun 19, 70-72. Pan, J., Zhang, X., Sun, Y., Song, S., Li, W., Wan, P., 2016, Preparation of High Purity Lead Oxide from Spent Lead Acid Batteries via Desulfurization and Recrystallization in Sodium Hydroxide. Indu. Eng. Chem Res 7, 2059-2068. Park, H.S., Kim, Y.J., 2019, A novel process of extracting precious metals from waste printed circuit boards: Utilization of gold concentrate as a fluxing material. J. Hazard. Mater 365, 659-664. Pérez-Moreno, M.S.M., Gázquez, M.J., Ruiz-Oria, I., Ríos, G., Bolívar, J.P., 2018, Diagnose for valorisation of reprocessed slag cleaning furnace flue dust from copper smelting. J. Clean. Prod 194, 383-395. Qiang, L., Pinto, I.S.S., Zhao, Y., 2014, Sequential stepwise recovery of selected metals from flue dusts of secondary copper smelting. J. Clean. Prod 84, 663-670. Radi, S., El Abiad, C., Moura, N.M.M., Faustino, M.A.F., Neves, M.G.P.M., 2019, New hybrid adsorbent based on porphyrin functionalized silica for heavy metals removal: Synthesis, characterization, isotherms, kinetics and thermodynamics studies. J. Hazard. Mater 370, 80-90. Sabzezari, B., Koleini, S.M.J., Ghassa, S., Shahbazi, B., Chelgani, S.C., 2019, Microwave-Leaching of Copper Smelting Dust for Cu and Zn Extraction. Materals 12. Sarfo, P., Das, A., Wyss, G., Young, C., 2017, Recovery of metal values from copper slag and reuse of

Journal Pre-proof residual secondary slag. Waste Manage 70, 272-281. Singh, R., Chadetrik, R., Kumar, R., Bishnoi, K., Bhatia, D., Kumar, A., Bishnoi, N.R., Singh, N., 2010, Biosorption optimization of lead(II), cadmium(II) and copper(II) using response surface methodology and applicability in isotherms and thermodynamics modeling. J. Hazard. Mater 174, 623-634. Soler, A., Conesa, J.A., Ortuño, N., 2017, Emissions of brominated compounds and polycyclic aromatic hydrocarbons during pyrolysis of E-waste debrominated in subcritical water. Chemosphere 186, 167-176. Tang, L., Tang, C., Xiao, J., Zeng, P., Tang, M., 2018, A cleaner process for valuable metals recovery from hydrometallurgical zinc residue. J. Clean. Prod 201, 764-773. Tsakiridis, P.E., Oustadakis, P., Katsiapi, A., Agatzini-Leonardou, S., 2010, Hydrometallurgical process for zinc recovery from electric arc furnace dust (EAFD). Part II: Downstream processing and zinc recovery by electrowinning. J. Hazard. Mater 179, 8-14. Tyagi, M., Rana, A., Kumari, S., Jagadevan, S., 2018, Adsorptive removal of cyanide from coke oven wastewater onto zero-valent iron: Optimization through response surface methodology, isotherm and kinetic studies. J. Clean. Prod 178, 398-407. Walburga Keglevich De Buzin, P.J., Heck, N.C., Faria Vilela, A.C., 2017, EAF dust: An overview on the influences of physical, chemical and mineral features in its recycling and waste incorporation routes. J. Mater. Res. Technol 6, 194-202. Wang, F., Zhao, Y., Zhang, T., Zhang, G., Yang, X., He, Y., Wang, L., Duan, C., 2017, Metals recovery from dust derived from recycling line of waste printed circuit boards. J. Clean. Prod 165, 452-457. Watson, M.A., Tubić, A., Agbaba, J., Nikić, J., Maletić, S., Jazic, J.M., Dalmacija, B., 2016, Response surface methodology investigation into the interactions between arsenic and humic acid in water during the coagulation process. J. Hazard. Mater 312, 150-158. Xia, M., Muhammad, F., Zeng, L., Li, S., Huang, X., Jiao, B., Shiau, Y., Li, D., 2019, Solidification/stabilization of lead-zinc smelting slag in composite based geopolymer. J. Clean. Prod 209, 1206-1215. Xiao, H., Zhou, Z., Zhou, H., Liu, Q., Ren, W., Lin, H., Zhu, H., He, C., Tian, K., 2017, Conversion of HBr to Br 2 in the flue gas from the combustion of waste printed circuit boards in post-combustion area. J. Clean. Prod 161, 239-244. Yang, J., Feng, J., Li, W., Chen, X., Liu, X., Ruan, J., Qiu, R., Xiong, Y., Tian, S., 2019, A resourceutilization way of the waste printed circuit boards to prepare silicon carbide nanoparticles and their photocatalytic application. J. Hazard. Mater 373, 640-648. Ye, L., Tang, C., Chen, Y., Yang, S., Yang, J., Zhang, W., 2015, One-step extraction of antimony from low-grade stibnite in Sodium Carbonate – Sodium Chloride binary molten salt. J. Clean. Prod 93, 134139. Yuan, Y., Zhang, Y., Liu, T., Hu, P., Zheng, Q., 2019, Optimization of microwave roasting-acid leaching process for vanadium extraction from shale via response surface methodology. J. Clean. Prod 234, 494502. Zhang, D., Ling, H., Yang, T., Liu, W., Chen, L., 2019, Selective leaching of zinc from electric arc furnace dust by a hydrothermal reduction method in a sodium hydroxide system. J. Clean. Prod 224, 536544. Zhang, L., Xu, Z., 2016, A review of current progress of recycling technologies for metals from waste electrical and electronic equipment. J. Clean. Prod 127, 19-36. Zhang, Y., Jin, B., Huang, Y., Song, Q., Wang, C., 2019, Two-stage leaching of zinc and copper from arsenic-rich copper smelting hazardous dusts after alkali leaching of arsenic. Sep. Purif. Technol 220,

Journal Pre-proof 250-258. Zhou, G., Gu, Y., Wu, Y., Gong, Y., Mu, X., Han, H., Chang, T., 2020. A Systematic Review of the Deposit-Refund System for Beverage Packaging: Operating Mode, Key Parameter and Development Trend. J. Clean. Prod 251, 119660. Zhou, X., Guo, J., Lin, K., Huang, K., Deng, J., 2013, Leaching characteristics of heavy metals and brominated flame retardants from waste printed circuit boards. J. Hazard. Mater 246-247, 96-102.

Journal Pre-proof Author Contribution Statement According to the author's contribution in the manuscript, the correct sequence of coauthors is Gongqi Liu, Yufeng Wu, Bin Li, De’an Pan*, Feihua Yang, Junqing Pan, Yishu Wang and Na Cheng. Detailed instructions are as follows: Gongqi Liu: Methodology, Designed and carried out experiments, Writing- Original draft preparation; Yufeng Wu: Conceptualization, Writing- Reviewing and Editing; Bin Li: Validation, Data Curation; De’an Pan: Supervision, Project administration, Funding acquisition; Feihua Yang: Resources; Junqing Pan: Visualization, Writing- Reviewing and Editing; Yishu Wang: Formal analysis; Na Cheng: Formal analysis

Journal Pre-proof

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Journal Pre-proof Highlights 

Sulfation roasting is used to enhance the debromination rate from WPCBs-SA.



Thermodynamic analysis and RSM were applied to verify and optimize the process.



The three independent variables modelled shows various interaction effects.



The RSM model equation has an excellent correlation with the experimental data.