Debromination Efficiency Research Articles

Mechanism of PGMs capture from spent automobile catalyst by copper from waste printed circuit boards with simultaneous pollutants transformation

The traditional pyrometallurgical recycling of nano-sized platinum group metals (PGMs) from spent automotive catalysts (SACs) is an energy-intensive process that requires the addition of large quantities of copper capture and slag-forming reagents. Similarly, pyro-recycling of valuable metals from waste printed circuit boards (WPCBs) is also an energy- and reagent-intensive process that and carries a risk of pollution emissions. Based on the complementarity of composition and similarity of recycling process, synergistic pyro-recycling of SACs and WPCBs allow copper in WPCBs to capture PGMs in SACs and oxides from two waste form slag jointly, which offers benefits of enhanced metal recovery, reduced reagent and energy consumption, and suppressed pollutant emissions. However, the mechanisms of PGMs capture and pollutant transformation in co-smelting remain unknown. Here, we investigated the sub-processes mechanisms of slag formation, brominates fixation, multi-metal distribution and kinetic settlement. Oxides in both wastes support SiO2-Al2O3-CaO slag formation with low melting point and viscosity, where CaO suppresses the emission of brominated pollutants. Copper (50–100 μm) from WPCBs facilitates nano-sized PGMs in SACs recovery through capture and settlement. The results of demonstration experiments indicated a recovery rate of 94.6 %, 96.8 %, 97.2 %, and 98.1 % for Cu, Pt, Pd, and Rh, respectively, with a debromination efficiency exceeding 98 %. The theoretical analysis provides support for the establishment of a synergistic pyro-recycling process for SACs and WPCBs and provides insights into the potential for a greener and more efficient co-recycling of multi urban mines.

Completely recyclable and reusable automatic phase-separable catalytic system for the reductive debromination of polybrominated diphenyl ethers

An automatic phase-separable catalytic system was developed for the reductive debromination of polybrominated diphenyl ethers (PBDEs) using thiol-modified Pd nanoparticles (thiol-Pd NPs) as the catalyst, H2 as the reducing agent, and n-butanol (oil phase) and water (water phase) as solvents. This system achieved efficient and complete debromination of various PBDEs with 1–10 bromine atoms and other bromo-organic pollutants at concentrations ranging from 15 to 1500 mg L−1. Typically, this system achieved a debromination efficiency of 100 % within 15 min for all the tested bromo-organic pollutants. Importantly, the debromination reaction was conducted in a microemulsion state under stirring; upon stopping the stirring, the microemulsion automatically separated into an upper oil phase, a down water phase, and a thiol-Pd NP self-assembled membrane phase at the oil/water interface. These three phases could be easily separated from each other, allowing for their reuse across multiple debromination cycles with good reusability. The thiol modifier enhanced the stability and reusability of Pd NPs and improved the adsorption of PBDEs, facilitating their reaction with atomic hydrogen (the dominant reactive species). This method successfully eliminated PBDEs in soils by integrating with a pre-extraction process.

Catalytic Pyrolysis of Waste-Printed Circuit Boards Using a Cu/Fe Bimetal Synergistic Effect to Enhance Debromination

Deep and efficient debromination is a critical step in achieving environmentally friendly recycling and ensuring the sustainability of waste-printed circuit boards (WPCBs) because of their high toxicity and carcinogenicity. To this end, this study used a copper–iron (Cu/Fe) bimetal as a debromination agent to remove bromides from WPCBs using in situ catalytic pyrolysis technology. The results show that the maximum debromination efficiency was 97.14% under the following conditions: a Cu mole ratio of 0.20 (Cu/Fe-0.20), a Cu/Fe-0.20 dosage of 0.4, a pyrolysis temperature of 600 °C, and a retention time of 10 min. The main bromine species in pyrolysis oil and gas were bromophenol, bromomethane, HBr, and Br2. The conversion of bromine species and the debromination of the Cu/Fe-0.20 bimetal were analyzed in real time using a thermogravimetry-coupled Fourier transform infrared and mass spectrometer (TG-FTIR-MS). Using the Cu/Fe bimetal synergistic effect, we determined that the debromination mechanism could be used for bromide conversion and fixing. The Cu in the Cu/Fe-0.20 transformed the organic Br (bromophenol and bromomethane) into inorganic Br (HBr and Br2) by providing empty orbitals for lone pairs of electrons. Then, the generated HBr and Br2 reacted with Fe in the Cu/Fe-0.20 and were fixed in pyrolysis residue. This study provides theoretical support and a practical method for WPCB deep debromination and recycling.

Enhanced deep dehalogenation of brominated DBPs on vitamin B12 composite electrodes by the synergistic effect of UV irradiation: Accelerated formation of Co-Br bonds and enhanced mediation by atomic H*

Complete dehalogenation of halogenated organic pollutants has attracted increasing attention, and electrocatalytic reduction processes are considered prospective technologies due to their high selectivity for carbon-halogen bonds. In this study, a vitamin B12 (VB12) composite electrode was prepared and applied to remove the refractory tribromoacetic acid (TBAA). The reduction process dominated by the VB12 composite electrode showed a degradation efficiency of 55.2 % for 200 μg/L TBAA within 60 min. Interestingly, UV irradiation considerably increased the efficiency of TBAA for dehalogenation on the VB12 composite electrode. The photoelectrochemical co-catalytic system of a VB12 composite electrode coupled with UV (LP UV 254 nm) could remove 92.2 % of TBAA in 20 min with a rate constant 12 times higher than the VB12-only electrolysis system. The in situ Raman characterization and cyclic voltammetry tests confirmed that the accelerated formation of Co-Br bonds and the enhanced atomic H* mediated ability were responsible for improving debromination efficiency. The degradation of TBAA mainly underwent chemical reactions of debromination and mineralization. Acetic acid, formic acid, formaldehyde, and Br- were the major transformation products of TBAA. Acidic conditions favoured TBAA removal in the UV synergistic VB12 electrolytic system, and excellent cycling stability of debromination was obtained in complex aqueous environments (actual bodies of water containing various inorganic and organic matter). This research provides an efficient dehalogenation technology for halogenated micropollutants and novel perspectives on the scientific design of photoelectrochemical dehalogenation processes.

Magnetically separable Pd-iron-oxides composites as highly efficient and recyclable catalysts for ultra-rapid degradation and debromination of polybrominated diphenyl ethers

When precious nano-metals are used as environmental catalysts, it is important to tune the particle sizes and the reusability of the nano-metals for achieving their highly efficient catalytic performance at a low cost. In the present work, magnetic iron oxides (FeOx-Y) nanoparticles were pre-prepared as supports of nano-metals, where Y represented the mole percentage of Fe(III) in the total iron (Y ≥ 50 %). FeOx-Y (support), PdCl42− (Pd source) and NaBH4 (reducing agent) were added into the organic pollutant solution containing 2,2′,4,4′-tetrabromodiphenyl ether (BDE47). After the NaBH4 was added, the followed reaction realized not only the rapid in-situ preparation of a Pd-loaded FeOx-Y composite catalyst (Pd-FeOx-Y), but also the ultra-fast and complete debromination of BDE47 within 30 s. Comparing the case without adding FeOx-Y, the debromination efficiency of BDE47 was much promoted in the presence of FeOx-Y. The support-induced enhancing effect on the catalytic ability of Pd nanoparticles was improved by increasing the Fe(III) content in the support, being attributed to the much more hydroxyl groups on the support surface. Considering both the catalytic and recovery abilities of Pd-FeOx-Y, Pd-FeOx-75 was the optimal choice because it could be magnetically recovered and re-used for multiple cycles with high catalytic activities. The presently developed “catalyst preparation-pollutant degradation” one-pot system could be applied to conduct complete debromination of all the PBDEs.

Enhancing Debromination Efficiency through Introducing Water Vapor Atmosphere to Overcome Limitations of Conventional Pyrolysis.

Bromine removal is significant in the recycling of waste printed circuit boards (WPCBs). This study found that the critical factors limiting the debromination efficiency of conventional pyrolysis are the formation of coke impeding mass transfer and conversion of bromine into less volatile species, such as coking-Br and copper bromide. According to frontier molecular orbital analysis and thermodynamic equilibrium analysis, C-O bonds of resin are sites prone to electrophilic reactions and copper bromide in residue may undergo hydrolysis; therefore, introducing H2O during pyrolysis was a feasible method for thorough debromination. Through pyrolysis in a water vapor atmosphere, the diffusion limitation of debromination was overcome, and resin was converted into light components; thereby, rapid and deep removal of bromine was achieved. The result indicated that 99.7% of bromine was removed, and the residue could be used as a clean secondary resource. According to life-cycle assessment, pyrolysis of WPCBs in water vapor could be expected to reduce 77 Kt of CO2 emission and increase financial benefits by 60 million dollars, annually.

Quantum chemical study on the catalytic debromination mechanism of brominated epoxy resins

The study employed Density Functional Theory (DFT) to investigate the catalytic debromination mechanism of brominated epoxy resins (BERs) by iron (Fe) and copper (Cu) catalysts. By introducing electric field (EF), intramolecular electron transfer and polarization effects on BERs debromination were explored and experimentally validated. Results indicated that the bond dissociation energy (BDE) of the C-Br bond was 312.27 kJ/mol without catalysis, while with Fe, Cu, and EF, it was 114.47 kJ/mol, 94.85 kJ/mol, and 292.59 kJ/mol, respectively, enhancing reactivity. EF parallel to the C-Br bond and oriented toward the C atom, altered electrostatic potential and dipole moment around C-Br bond, leading to 68.60% and 50.19% increment in electronic contribution difference and molecule polarity, respectively, thereby reducing the C-Br BDE. Fe and Cu facilitated electron transfers with BERs, inducing reactions between their negative electrostatic potentials and Br's positive potential, changing electron sharing, resulting in 19.87% and 12.11% increase in polarity, respectively, and further BDE reduction. Structural modifications by the EF and catalysts also intensified van der Waals forces with bromine atoms and decreased spatial hindrance, collectively making C-Br bond breakage easier. Experiments revealed the EF enhanced BERs' debromination efficiency but hindered Fe/Cu's catalysis at lower temperatures.

Heterogeneous catalytic reactions of in-situ generated bromide ions via hydrodehalogenation of tetrabromobisphenol A in advanced oxidation processes over palladium nanoparticles

Herein, we report a novel and efficient approach for degrading tetrabromobisphenol A (TBBPA) via catalytic hydrodehalogenation (HDH) and advanced oxidation processes (AOP). Using heterogeneous catalytic HDH of TBBPA over palladium nanoparticles (Pd NPs) achieves the in-situ generation of bromide ions (Br-), which effectively accelerate and reinforce the degradation of debromination intermediates during peroxymonosulfate-based AOP. The conversion of TBBPA to bisphenol A (BPA) by the HDH process reaches up to 99.9% debromination efficiency in 1 h under near-neutral condition, along with the removal of 99.4% BPA in 15 min during the AOP. Further studies show that free bromine and 1O2 produced by in-situ generated Br- reacting with peroxymonosulfate are the most effective reactive species for promoting the BPA degradation. Sustainability footprint analysis reveals considerable stability and high sustainable footprint of the integrated process during long-term operation. This work provides a promising strategy to elimination of bromine organic pollutants in water treatment.

Removal of disinfection byproducts through integrated adsorption and reductive degradation in a membrane-less electrochemical system

Proper control/removal of disinfection byproducts (DBPs) is important to drinking water safety and human health. In this study, a membrane-less electrochemical system was developed and investigated to remove DPBs through integrated adsorption and reduction by granular activated carbon (GAC)-based cathode. Representative DPBs including trihalomethanes and haloacetonitriles at drinking water concentrations were used for removal experiments. The proposed system achieved >70% removal of most DBPs in a batch mode. The comparison with control tests under either open circuit or hydrolysis demonstrated the advantages of electrochemical treatment, which not only realized higher DPBs removal but also extended GAC cathode lifetime. Such advantages were further demonstrated with continuous treatment. High dechlorination and debromination efficiencies were obtained in both batch (82.2 and 94.3%) and continuous (79.3 and 87.6%) reactors. DBPs removal was mainly contributed by the electrochemical reduction and adsorption by the GAC-based cathode, while anode showed little oxidizing effect on DBPs and halide ions. Dehalogenated products of chloroform and dichloroacetonitrile were identified with toxicity reduction. The energy consumption of the continuously operated system was estimated to be 0.28 to 0.16 kWh m−3. The proposed system has potential applications for wastewater reuse or further purification of drinking water.

Alkali-thermal activated persulfate treatment of tetrabromobisphenol A in soil: Parameter optimization, mechanism, degradation pathway and toxicity evaluation

The continued accumulation of halogenated organic pollutants in soil posed a potential threat to ecosystems and human health. In this study, tetrabromobisphenol A (TBBPA) was used as a typical representative of halogenated organic pollutants in soil, for alkali-thermal activated persulfate (PS) treatment. The results of response surface methodology (RSM) showed a optimal debromination efficiency of TBBPA was 88.99 % under the optimum reaction conditions. Quenching experiments and electron paramagnetic resonance (EPR) confirmed that SO4−•, HO•, O2−• and 1O2 existed simultaneously in the oxidation process. SO4−• played a major role in the initial stage of the reaction, and O2−• played a major role in the the last stage. Based on density functional theory (DFT) and intermediate products, two degradation pathways were proposed, including debromination reaction and β bond scission. Moreover, the basic physical and chemical properties of the soil were affected to a certain extent, while the soil surface structure, elements and functional group composition rarely changed. In addition, the T.E.S.T. analysis and biotoxicity tests proved that alkali-thermal activated PS can effectively reduce the toxicity of TBBPA-contaminated soil, which is conducive to the subsequent safe secondary utilization of soil.

The production of debrominated aromatics via the catalytic pyrolysis of flexible printed circuit boards

Pyrolysis is an environmental technology for the proper treatment of electronic waste (e-waste) for the production of fuel. However, the presence of brominated compounds in pyrolysis oil makes its commercialization difficult. In this study, various types of zeolites, HY (30), HZSM-5 (30), HZSM-5 (50), HZSM-5 (280), and basic metal oxides (MgO and CaO) were used for the pyrolysis of flexible printed circuit boards (FPCBs) for the first time to produce bromine-free oil. A higher production efficiency of debrominated aromatic hydrocarbons, primarily benzene, toluene, ethylbenzene, xylenes (BTEXs), and naphthalene with zeolites, was achieved over basic metal oxides. The use of HZSM-5 (HZ) (30) increased the amount of benzene (an area of 31.5 × 107) and toluene (an area of 17.6 × 107), and a high debromination efficiency was observed for basic metal oxides owing to the strong affinity of halides toward the Ca2+ and Mg2+ ions. Among the BTEXs, benzene (an area of 31.5 × 107) and toluene (an area of 17.6 × 107) were obtained as highly selective monoaromatics in the presence of the catalyst HZ (30). CaO and HZ (30) were effective for debromination and aromatic production, respectively. The in-situ CaO/ex-situ HZ (30) combination revealed ∼ 100% debromination efficiency; however, the total aromatic hydrocarbon production was higher on the in-situ HZ (30)/ex-situ CaO with ∼ 77.5% debromination efficiency. Meanwhile, the in-situ HZ (30)/ex-situ CaO configuration could achieve ∼ 100% debromination efficiency by increasing the amount of CaO to 7 times to feed.

A feasible approach for the treatment of waste computer casing plastic using subcritical to supercritical acetone: Statistical modelling and optimization

Electronic waste (e-waste) usage has increased tremendously with the rapid evolution of technologies. The accumulated e-waste has now emerged as one of the crucial concerns regarding environmental pollution and human health. Recycling e-waste is commonly focused on metal recovery; nevertheless, a significant fraction of plastics (20–30%) are in e-waste. There is an indispensable need to focus on e-waste plastic recycling in an effective way, which has been mostly overlooked to date. An environmentally safe and efficient study is conducted using subcritical to supercritical acetone (SCA) to degrade the real waste computer casing plastics (WCCP) in the central composite design (CCD) of response surface methodology (RSM) to achieve the maximum oil yield of the product. The experiment parameters were varied in the temperature span of 150–300 °C, residence time between 30 and 120 min, solid/liquid ratio between 0.02 and 0.05 (g/ml), and NaOH amount from 0 to 0.5 g. Adding NaOH into the acetone helps to achieve efficient degradation and debromination efficiency. The study emphasized the attributes of oils and solid products recovered from the SCA-treated WCCP. The characterization of feed and formed products is performed with different characterization techniques such as TGA, CHNS, ICP-MS, FTIR, GC-MS, Bomb calorimeter, XRF, and FESEM. The highest oil yield achieved is 87.89% from the SCA process at 300 °C, in 120min, 0.05 S/L ratio, and 0.5 g of NaOH. GC-MS results disclose that the liquid product (oil) comprises single- and duplicate-ringed aromatic and oxygen-containing compounds. Isophorone is the significant component of the liquid product obtained. Furthermore, SCA's possible polymer degradation mechanistic route, bromine distribution, economic feasibility, and environmental aspect were also explored. This present work represents an environmentally friendly and promising approach for recycling the plastic fraction of e-waste and recovering valuable chemicals from WCCP.

Integrated effect of bulk cations on nano-confined reactivity of clay-intercalated subnanoscale zero-valent iron in water-tetrahydrofuran mixtures

Smectite clay-intercalated subnanoscale zero-valent iron (CSZVI) exhibits superior reactivity toward contaminants due to the small iron clusters (∼0.5 nm) under nano-confinement, which however is significantly influenced by the solution chemistry e.g., various cations, of polluted soil and water. This work was undertaken to elucidate the mechanisms of solution chemistry effects on dehalogenation ability of CSZVI in water-tetrahydrofuran solution using decabromodiphenyl ether as a model contaminant. By combined spectroscopic characterization and molecular dynamics simulation, it was revealed that bulk cations, i.e., Na+, K+, Mg2+ and Ca2+ collectively affected the interlayer distance, water content and Brønsted acidity of CSZVI and thus its degradation efficiency. Although causing inter-particle aggregation, Mg2+ induced optimal nano-confined interlayers at concentration of 20 mM, exhibiting a superior debromination efficiency with rate constant 9.84 times larger than that by the common nano-sized ZVI. Conversely, K+ rendered the interlayers less reactive, but protected CSZVI from corrosion loss with higher electron utilization efficiency, which was 1.7 times higher than CSZVI in presence of Mg2+. The findings provide new strategies to manipulate the reactivity of nano-confined CSZVI for effective wastewater and contaminated soil remediation.

Rapid photocatalytic degradation of tetrabromobisphenol A using synergistic p-n/Z-scheme dual heterojunction of black phosphorus nanosheets/FeSe2/g-C3N4

Tetrabromobisphenol A (TBBPA), as a typical brominated flame retardant, has been confirmed to pose potential threats for human health and developed into a global pollutant. Graphitic carbon nitride (g-C3N4) is the most used catalyst for refractory organic pollutants removal, but the weak conductivity and quick recombination of photogenerated carries restrict its practical application. To improve the photocatalytic activity of pristine g-C3N4, a p-n/Z-scheme dual heterojunction photocatalyst (BFC) was designed and prepared by introducing black phosphorus nanosheets and FeSe2 into porous g-C3N4 (CN). Compared to traditional heterojunction catalysts, BFC not only can promote photogenerated carriers directed migration and effective separation, but also can retain higher redox potential for simultaneous generating O2− and OH, which are due to the synergistic effects of built-in electric field formation in p-n heterojunction and bandgap structure optimization by Z-scheme heterojunction. Above advantages promote BFC to achieve 100% TBBPA degradation efficiency in 40 min and 22.6% debromination efficiency in 60 min under visible light irradiation. The superfast reaction rate constant (0.143 min−1) is almost 10 times higher than that of pristine CN. This study proposes a facile design strategy to construct heterojunction photocatalysts and provides an alternative method to rapidly remove TBBPA in water.

Performance and mechanisms for tetrabromobisphenol A efficient degradation in a novel homogeneous advanced treatment based on S2O42− activated by Fe3+

Tetrabromobisphenol A (TBBPA), a representative brominated flame retardant (BFR), generally could be debrominated and degraded effectively in photolysis systems with the high energy consumption. In this study, the novel sulfate radical (SO4•-) generation resource of dithionite (S2O42−), activated by the common transition metal of Fe3+, has been applied for establishing an innovative homogeneous advance treatment system for BFR treatment in water. When coupling Fe3+ with S2O42−, TBBPA degradation efficiency could be remarkably improved from 38.7% to 93.8% with the debromination and mineralization efficiency of 83.9% and 18.5% in 60 min, respectively. The primary reactive species also have been identified as SO3•-, SO4•- and •OH responsible for TBBPA treatment and the contributions of SO4•- and •OH have been calculated as 43.8% and 28.4% for TBBPA degradation, respectively. In Fe3+/S2O42− system, TBBPA was effectively degraded in a wide initial pH range (3.0–9.0), whose activation energy was calculated as 32.01 kJ mol−1. Due to the only operation of reagents dosing, the energy consumption and cost could be decreasing significantly without any light energy input and reaction conditions (e.g., pH and dissolved oxygen) adjustment compared with the general photolysis process. Moreover, some possible degradation approaches of TBBPA also have been proposed via GC–MS including debromination, hydroxylation, methylation, and mineralization in Fe3+/S2O42− system. And these probable degradation pathways also have been confirmed with the decreased Gibbs free energy (ΔG) based on density functional theory (DFT). This study has revealed that it was promising of Fe3+/S2O42− system for BFRs degradation and detoxification efficiently through the simple operation and mild condtions.

Production of BTX via Catalytic Fast Pyrolysis of Printed Circuit Boards and Waste Tires Using Hierarchical ZSM-5 Zeolites and Biochar

The conversion of plastic wastes into benzene, toluene, and xylenes (BTX) is a promising strategy to achieve a circular economy and carbon neutrality. Here, the ex situ catalytic fast pyrolysis of epoxy-printed circuit boards (PCBs) and waste tires (WTs) was studied using hierarchical ZSM-5 zeolites and biochar (BC). The results show that the alkali–acid treatment created the micromesoporous structures of zeolites with higher specific surface area, and the hierarchical zeolites promote BTX formation. Particularly, the ZSM-5 treated with 0.2 M NaOH (2MZ) resulted in a BTX yield 15.6 times larger than that obtained without catalysts; correspondingly, the yields of phenolic and brominated compounds were reduced. The BC promoted the depolymerization of PCB pyrolyzates and provided a debromination efficiency of 96%. The combination of BC and 2MZ resulted in the highest BTX yield without producing brominated compounds. Sequential experiments indicated that, by effectively removing bromine, BC helped maintain the catalytic activity of 2MZ. Additionally, the catalytic fast copyrolysis of PCBs and WTs resulted in an increased BTX yield and mitigated catalytic deactivation simultaneously. The proposed advanced catalytic fast copyrolysis with BC and hierarchical zeolites is a promising strategy for the environmentally friendly upcycling of heteroatom-containing plastic wastes toward BTX production.

Mechanochemical debromination of waste printed circuit boards with marble sludge in a planetary ball milling process.

An effective management of waste printed circuit board (WCB) recycling presents significant advantages of an economic, social, and environmental nature. This is particularly the case when a suitable valorisation is made of the non-metallic parts of the WCBs, well known for their "hidden" toxicological risks. Such benefits motivate research on techniques that could contribute to mitigating their adverse socio-environmental impacts. In this work, waste printed circuit boards (WCBs) containing tetrabromobisphenol A (TBBPA) as a brominated flame retardant (BFR) underwent debromination using a mechanochemical treatment (MCT) and marble sludge, another recoverable waste, as well as pure CaO as additives. All runs in this work were performed at an intermediate rotation speed of 450rpm, using additive/WCB mass ratios (Rm) of 4:1 and 8:1, ball to powder ratios (BPR) of 20:1 and 50:1, treatment times from 2.5h to 10h, two WCB sizes (powder and 0.84mm) and marble sludge, from original to precalcined conditioning. Stainless steel jars and balls were used to verify the effect of each parameter on the system and to seek an optimum process. Complete debromination of 0.84mm WCBs was achieved at 450rpm, using a Rm of 8:1, a BPR of 50:1, a residence time of 10h (more than 95% in only 5h), and a precalcined marble sludge as additive. The results revealed that when using a Rm of 4:1 instead of 8:1, more waste could be effectively treated, per batch with a lesser need for additives, at the expense of a slightly lower level of debromination efficiency. In the same way, an appropriate apparent ball diameter (with respect to the volume of the used jar) should be carefully studied in relation to WCB size in order to achieve a beneficial total amount of energy transfer during milling.

Innovative method for removing bromine in waste printed circuit boards: Ultrafine milling and porous media loaded debromination agent

Resin is the main harmful substance in waste printed circuit boards (WPCBs) due to the presence of harmful bromine. In this study, the methods of ultrafine milling of resin and loading debromination agent on porous gasification slag were proposed to improve the debromination effect. The morphology, composition and phase of the gasification slag and resin were analyzed by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The results show that the residual carbon in the gasification slag has porous structure, which contributes to the loading of debromination agent. The specific surface area and porosity of gasification slag before and after acid treatment were analyzed by BET. Using the porous properties of gasification slag, different debromination agents were attached to prepare efficient debromination agents, which were adopted for thermal debromination of resin in WPCBs. Subsequently, ICP-MS was used to determine the content of bromine in pyrolysis residue. The results show that when FeCl2/FeCl3 was used as the debromination agent, the debromination efficiency was only 67.19% and 58.29%, while using gasification slag-FeCl2/FeCl3 composite, the debromination efficiency can be increased to 81.63% and 76.25%. Therefore, the cooperative treatment can realize the resource utilization of the two wastes.

Debromination and Reusable Glass Fiber Recovery from Large Waste Circuit Board Pieces in Subcritical Water Treatment.

The great economic, social, and environmental interest that favors an effective management of the recycling of waste printed circuit boards (WCBs) encourages research on the improvement of processes capable of mitigating their harmful effects. In this work, the debromination of large WCBs was first performed through a hydrothermal process employing potassium carbonate as an additive. A total of 32 runs were carried out at 225 °C, various CO32–/Br– anionic ratios of 1:1, 2:1, 4:1, and 6:1, treatment times from 30 to 360 min, proportion of submerged WCBs in the liquid of 100, 50, and 25% that corresponded with the use of three WCB sizes of 20 mm × 16.5 mm, 20 mm × 33 mm, and 80 mm × 33 mm, respectively, and solid/liquid ratios of 1:2 and 1:1 g/mL without other metallic catalysts. A debromination efficiency of 50 wt % was reached at only 225 °C (limited by mechanical reasons) and 360 min, using a CO32–/Br– anionic ratio of 4:1 and a solid/liquid ratio of 1:2 for a large WCB with only 25% of its volume submerged in the liquid. This means conservation of water and energy compared to previous studies. A muffle furnace was used later to thermally treat a total of 101 debrominated samples, at constant temperature or following a temperature scaling program. An estimated decrease in resistance to rupture of glass fibers of only around 50% was accomplished by following a temperature scaling program up to 475 °C, obtaining clean glass fibers of large size. The simple techniques proposed to obtain reusable glass fibers from WCBs as large as the size of the reactor allows (as it might be in their original size) could significantly improve interest in the industry.

Nano Pd doped Ni foam electrode stimulated electrochemical reduction of tetrabromobisphenol A: Optimization strategies and function mechanism

Tetrabromobisphenol A (TBBPA), a hazardous and persistent flame retardant, has been widely detected in the natural aquatic system. The acceleration of reductive debromination (rate-limiting process) is vital during the decomposition and detoxification of TBBPA. This study achieved superior TBBPA electrochemical reductive debromination performance by nano Pd doped Ni foam electrode (4.8 times higher than Ni foam electrode). The optimal TBBPA reductive debromination performance was obtained under −1.2 V of cathode potential, 1.2 wt% of Pd loading, 10 mg L−1 of TBBPA and 100 mM of Na2SO4 as the electrolyte solution. UPLC-QTOF-MS verified that Br atoms in TBBPA were removed sequentially to form bisphenol A as the major product. Most TBBPA was reductively debrominated by atomic H* through indirect hydrodebromination, evidenced by the atomic H* quenching test. The higher solution conductivity and appropriate TBBPA concentration would contribute to the debromination efficiency. Excessive H2 generation whether by over negative potential or H atom richness electrolyte largely disturbed the reaction process and restricted the debromination. The improved generation of reductant (H*)adsPd was the most significant, while excessive Pd loading would make aggregation and limit the debromination efficiency. The study confirmed the optimization strategies of conditions for Pd/Ni foam electrode and revealed the related function mechanism for stimulating TBBPA electrochemical reduction, giving suggestions for the efficient removal of TBBPA in the aquatic environment.