A novel management strategy for removal and degradation of polybrominated diphenyl ethers (PBDEs) in waste printed circuit boards

Mitigation of PBDE net discharge in hazardous waste thermal treatment system through reintroducion of sludge and fly ash into GASMILD operations

The presence of polybrominated diphenyl ethers (PBDEs) in consumer products, waste treatment processes, and treated ashes poses a significant environmental threat. Due to the lack of research on the removal of PBDEs during waste incineration, this study investigated the effectiveness of a Hazardous Waste Thermal Treatment System (HAWTTS) utilizing reburning of sludge and fly ash (SFA) with gasification-moderate or intense low-oxygen dilution (GASMILD) combustion for PBDE removal. The closed-loop treatment of sludge and ash within the HAWTTS provides a potential pathway for near-zero PBDE emissions. The GASMILD combustion addresses potential combustion issues associated with fly ash recirculation. The system achieved an impressive overall removal efficiency of 98.4% for PBDEs, with minimal stack emissions (2.45 ng/Nm³) and a negative net discharge rate (-1.02 μg/h). GASMILD combustion played a crucial role (92.7%-97.6% destruction) in addressing challenges associated with high-moisture feedstocks and SFA residues. Debromination of highly brominated PBDEs occurred within the incinerator, resulting in an increased proportion of lower brominated PBDEs in the bottom slag compared to the feedstock. Air Pollution Control Devices (APCDs) achieved a total PBDE removal efficiency of 74.4%. However, the hydrophobic nature of PBDEs limited removal efficiency in scrubbers (36.0%) and cyclonic demisters (37.86%). This study demonstrates that reintroducing SFA into the GASMILD combustion process offers an effective and environmentally sustainable strategy for reducing net PBDE levels in hazardous waste. This approach also provides additional benefits such as energy conservation, reduced carbon emissions, and lower operating costs associated with secondary treatment of thermally treated byproducts.

Occurrence and ecotoxicological impacts of polybrominated diphenyl ethers (PBDEs) in electronic waste (e-waste) in Africa: Options for sustainable and eco-friendly management strategies

Polybrominated diphenyl ethers (PBDEs) are persistent contaminants used as flame retardants in electronic products. PBDEs are contaminants of concern due to leaching and recalcitrance conferred by the stable and hydrophobic bromide residues. The near absence of legislatures and conscious initiatives to tackle the challenges of PBDEs in Africa has allowed for the indiscriminate use and consequent environmental degradation. Presently, the incidence, ecotoxicity, and remediation of PBDEs in Africa are poorly elucidated. Here, we present a position on the level of contamination, ecotoxicity, and management strategies for PBDEs with regard to Africa. Our review shows that Africa is inundated with PBDEs from the proliferation of e-waste due to factors like the increasing growth in the IT sector worsened by the procurement of second-hand gadgets. An evaluation of the fate of PBDEs in the African environment reveals that the environment is adequately contaminated, although reported in only a few countries like Nigeria and Ghana. Ultrasound-assisted extraction, microwave-assisted extraction, and Soxhlet extraction coupled with specific chromatographic techniques are used in the detection and quantification of PBDEs. Enormous exposure pathways in humans were highlighted with health implications. In terms of the removal of PBDEs, we found a gap in efforts in this direction, as not much success has been reported in Africa. However, we outline eco-friendly methods used elsewhere, including microbial degradation, zerovalent iron, supercritical fluid, and reduce, reuse, recycle, and recovery methods. The need for Africa to make and implement legislatures against PBDEs holds the key to reduced effect on the continent.

An alkali-enhanced subcritical water treatment strategy of short-chain chlorinated paraffins: Dechlorination and hydrocarbons recovery

As persistent organic pollutants, short-chain chlorinated paraffins (SCCPs) have attracted wide attention in the field of environmental health risk and hazardous waste management. Efficient dechlorination of high content of SCCPs in plastic waste is the committed step for its detoxification and safety treatment. In this study, a high-efficiency and low-temperature process for dechlorination and hydrocarbons recovery from typical SCCPs (52#SCCPs) by subcritical water (SubCW) with alkali enhancer was developed. The introduction of alkali enhancer in the SubCW process had significantly enhanced effect on the dechlorination of 52#SCCPs, and the order of the enhanced effect of alkali enhancer for the dechlorination was NaOH > Na2CO3 > NaHCO3 > NH3·H2O > KOH. The dechlorination behaviors of 52#SCCPs in the NaOH-enhanced SubCW process were studied systematically under different conditions including temperature, residence time, alkali concentration, and volume ratio. The results showed that high-efficiency dechlorination (100 %) of 52#SCCPs could be achieved by the NaOH-enhanced SubCW process at low temperature for a short time (250 °C, 5 min). All of the chlorine released from the molecular chain of 52#SCCPs was transferred to the aqueous phase in the form of inorganic chlorine. The continuous HCl elimination reaction was the primary dechlorination mechanism for 52#SCCPs in the NaOH-enhanced SubCW process. After the dechlorination of 52#SCCPs, high value-added hydrocarbons such as 2,4-hexadiyne (31.74 %) could be obtained. The alkali-enhanced SubCW process proposed in this study is believed to be an environmentally friendly and high-efficiency method for dechlorination/detoxification and resource recovery of SCCPs.

Evaluation of the recycling potential of obsolete mobile phones through secondary material resources identification: A comprehensive characterization study

The growing concern over the management of e-wastes has generated an interest in the recovery of resources from these wastes under the concept of urban mining and circular economy. However, in the absence of accurate knowledge of the physico-chemical compositional structure of these wastes makes the recycling process difficult. Thus, the present study conducted a recycling-oriented characterization of waste mobile phones (WMPs) for the identification of secondary materials and estimated their recycling potential. The characterization was performed using ICP-OES and FTIR techniques after dismantling WMPs for the determination of elemental composition and the polymeric fractions respectively. Dismantling of the WMPs revealed that enclosures, batteries, display modules, and PCBs consist of 35.33 wt%, 28.9 wt%, 19.44 wt%, and 16.31 wt% respectively. Of these components, PCBs constitute the highest economic recovery potential with an estimated potential revenue generation of more than 50,000 US $ per ton of waste PCBs. Copper showed the highest recovery potential (234.39 tons/year) with an economic value of approximately 3317 US $/ton of WPCBs followed by Sn (27.37 tons/year) and Ni (24.64 tons/year). Among different precious metals, Au was found to have the highest percentage of economic value (76.22%) followed by Pd (8.16%) and Ag (3.13%). The display modules and enclosures were found to have relatively lower contributions than WPCBs in the overall recycling potential due to lower metal contents and mixed polymeric fractions. The findings in the study indicate that WMPs could serve as a promising new source for sustainable secondary mining of rare and valuable metals. Further, the study will help the policymakers in designing effective e-waste management strategies through the promotion of sustainable recovery of materials.

A novel conversion strategy for organic compounds in waste liquid crystal displays based on the near/supercritical methanol process

Waste liquid crystal displays (LCD) contain a large number of organic compounds such as cellulose triacetate (CTA), poly(vinyl alcohol) (PVA), triphenyl phosphate (TPP), and liquid crystal (LC). It is important to recover organic compounds from waste LCD due to their value and environmental toxicity. However, it is challenging to recover organic compounds from waste LCD because of the heterogeneous mixture of glass, organics and metals contained therein. In this study, an environment-friendly near/supercritical methanol (NSCM) process was developed as a closed cycle technology for the conversion of organic compounds from waste LCD. The acid-base catalytic activity and nonpolar property of the NSCM could efficiently promote the conversion of organic compounds from waste LCD. TPP could be extracted below 200 °C in the NSCM process. Below 250 °C, the conversion ratio of organic compounds from waste LCD ranged from 5 % to 68 % due to the extraction or decomposition of TPP, LC, and PVA. The main products obtained at 250 °C included long-chain alcohols and alkanes with a similar composition to industrial liquid paraffin, which could be widely used in other industrial processes. Under the optimal operation parameters (300 °C, 30 min, and 1:20 g/ml), the conversion ratio of organic compounds could reach 98 % due to the efficient decomposition of CTA. The main products obtained included ketones and esters chemicals, which could be further used as a chemical feedstock. No secondary pollutant was generated in the whole process. The low-boiling methanol could easily be recycled, which could make the NSCM a clean process for the production of high value-added organic products from waste LCD.

Copper recovery from waste printed circuit boards by the flotation-leaching process optimized using response surface methodology

Recycling of waste printed circuit boards (PCBs) receives increasing attention due to abundant metallic resources and significant environmental threats. This work proposes a process for copper recovery from PCBs by froth flotation and oxidation leaching. Copper grade is improved from 38.70% to 68.34% with the recovery of 88.76% by froth flotation, and froth flotation is significantly influenced by copper liberation and particles dispersion of PCB powders. Process variables of oxidation leaching are examined by response surface methodology (RSM). A reliable mathematical model is obtained to predict the response as a function of independent variables and their interactions. Oxidation leaching is remarkably influenced by experimental variables, and the interactions between sulfuric acid and hydrogen peroxide are significant. Optimum conditions are achieved as sulfuric acid 1.0 mol/L, hydrogen peroxide 17%, temperature 50°C, and time 234 minutes, and the maximum leaching ratio of Cu is up to 99.94%, indicating that oxidation leaching is an effective method for Cu recovery from PCBs.Implications: Recycling of waste printed circuit boards (PCBs) receives increasing attention due to abundant metallic resources and significant environmental threats. This work proposes a novel process for copper recovery from PCBs by froth flotation and oxidation leaching. Froth flotation is efficient to enrich copper in metal fractions. Process variables of oxidation leaching are examined by response surface methodology (RSM). A reliable mathematical model is obtained to predict the response as a function of independent variables and their interactions. The froth flotation-oxidation leaching process is practicable and effective for copper recovery from waste printed circuit boards. This study significantly contributes to recycling metal resources from waste PCBs. We believe that this work will attract a broad readership and lead others to follow our approach.

Evaluation of polybrominated diphenyl ether (PBDE) flame retardants from various materials in professional seating furnishing wastes from French flows

Polybrominated diphenyl ethers (PBDEs) are brominated flame retardants that are used in polymeric materials. Due to their adverse health effects, the use of recycled wastes has been forbidden if the total PBDE content exceeds 0.1% (w/w). The objective was to estimate the proportion of PBDEs in professional seating furnishing wastes to identify the materials in which the content of PBDEs (and particularly BDE-209) could exceed the limit to eliminate them from recycling. An analytical process (microwave extraction followed by purification and chromatographic analysis) was adapted to assess with a unique methodology the amounts of eight PBDEs in materials that result from various seating wastes, such as hard plastics, foams and accompanying textiles. X-ray fluorescence (XRF) was used to rapidly predict critical PBDE concentrations via Br. From 100 samples, the total PBDE content did not exceed the current tolerated threshold. The examined materials contained only trace levels of former PBDE formulations, and BDE-209 was identified at higher amounts, mainly in hard plastics, but these amounts were less than 312 mg kg^-1. Since XRF was not reliable for quantitative measurements and was not specific, no direct correlation could be identified between Br and PBDE levels. Br was strongly associated with As in all the materials, but the presence of PBDEs was not clearly associated with the presence of other metals that are used in flame retardants.

Microwave-assisted organic swelling promotes fast and efficient delamination of waste printed circuit boards

A large amount of waste printed circuit boards (WPCBs) that contain valuable metals, namely gold and copper, are produced annually. WPCBs are constituted by a multi-layer structure reinforced by a brominated epoxy resin (BER), which is very difficult to separate into the metallic and non-metallic components. The main aim of this work was to evaluate the ability of microwave for assisting in the delamination of WPCBs by organic swelling of the BER. Additionally, its performance was compared with other strategies (thermostatic and ultrasonic baths) previously described in the literature. Firstly, a library of solvents [dimethyl formamide (DMF), dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), cyclohexanone (CH), γ-butyrolactone (GBL), tetrahydrofurfuryl alcohol (TFA) and dimethyl malonate (DM)] was selected based on the calculation of Hansen solubility parameters plus others exclusion parameters and their performance to detach all components of WPCBs (25 mm²) was tested by microwave (200 °C for 10 min), thermostatic (153 °C for 10 min) and ultrasonic (60 °C for 25 h) baths. Microwave showed to be the most efficient approach and the delamination order for WPCBs was: NMP > DMSO >DMF > DMAc. Subsequent optimization of key parameters (dimensions of WPCBs and reaction time) were obtained: dimensions of 225 mm² using NMP (solid/liquid ratio of 300 g/L) at 200 °C with 2 cycles of 10 min. In conclusion, microwave-assisted swelling revealed to be more efficient and faster process to delaminate WPCBs into metallic and non-metallic components, which are important advantages when envisaging a future industrial waste management implementation.

Inevitable human exposure to emissions of polybrominated diphenyl ethers: A perspective on potential health risks

Polybrominated diphenyl ethers (PBDEs) serve as flame retardants in many household materials such as electrical and electronic devices, furniture, textiles, plastics, and baby products. Though the use of PBDEs like penta-, octa- and deca-BDE greatly reduces the fire damage, indoor pollution by these toxic emissions is ever-growing. In fact, a boom in the global market projections of PBDEs threatens human health security. Therefore, efforts are made to minimize PBDEs pollution in USA and Europe by encouraging voluntary phasing out of the production or imposing compelled regulations through Stockholm Convention, but >500 kilotons of PBDEs still exist globally. Both 'environmental persistence' and 'bioaccumulation tendencies' are the hallmarks of PBDE toxicities; however, both these issues concerning household emissions of PBDEs have been least addressed theoretically or practically. Critical physiological functions, lipophilicity and toxicity, trophic transfer and tissue specificities are of utmost importance in the benefit/risk assessments of PBDEs. Since indoor debromination of deca-BDE often yields many products, a better understanding on their sorption propensity, environmental fate and human toxicities is critical in taking rigorous measures on the ever-growing global deca-BDE market. The data available in the literature on human toxicities of PBDEs have been validated following meta-analysis. In this direction, the intent of the present review was to provide a critical evaluation of the key aspects like compositional patterns/isomer ratios of PBDEs implicated in bioaccumulation, indoor PBDE emissions versus human exposure, secured technologies to deal with the toxic emissions, and human toxicity of PBDEs in relation to the number of bromine atoms. Finally, an emphasis has been made on the knowledge gaps and future research directions related to endurable flame retardants which could fit well into the benefit/risk strategy.

DEHP degradation and dechlorination of polyvinyl chloride waste in subcritical water with alkali and ethanol: A comparative study

In this study, subcritical water-NaOH (CW-NaOH) and subcritical water-C₂H₅OH (CW-C₂H₅OH) processes were developed for diethylhexyl phthalate (DEHP) degradation and dechlorination of polyvinyl chloride (PVC) waste. The introduction of NaOH or C₂H₅OH in subcritical water had a noticeable influence on the mechanism of DEHP degradation and dechlorination. For both CW-NaOH and CW-C₂H₅OH treatments, the increase in temperature could increase dechlorination efficiency (DE) of PVC. The DE of CW-NaOH is much higher than that of CW-C₂H₅OH under the same conditions. The DE of CW-NaOH could exceed 95% at 300 °C. Hydroxyl nucleophilic substitution was the main dechlorination mechanism in CW-NaOH, while nucleophilic substitution and direct dehydrochlorination were equally important in CW-C₂H₅OH. In CW-NaOH treatment, 2-ethyl-1-hexanol, benzaldehyde, and toluene were obtained by hydrolysis and reduction reactions of DEHP. Acetophenone was produced by the further cyclization, dehydrogenation and rearrangement reactions of 2-ethyl-1-hexanol. Transesterification was the main degradation pathway of DEHP in CW-C₂H₅OH at 300 °C. The cyclization and dehydration of 2-ethyl-1-hexanol resulted in producing a high level of ethyl-cyclohexane and 1-ethyl-cyclohexene in CW-C₂H₅OH at 350 °C. Furthermore, high concentration of ethyl palmitate and ethyl stearate could be prepared in CW-C₂H₅OH system by the strong reactivity of C₂H₅OH with the lubricants in PVC.

Efficient low-temperature debromination and high selectivity products recovery from brominated epoxy resin waste by subcritical water-urea treatment

In this study, a subcritical water-urea (SubCW-urea) process was developed for the treatment of brominated epoxy resin powder (BRP) waste. The SubCW-urea process had two significant advantages: efficient low-temperature debromination and highly selective products recovery. The NH₃ and CO₂ released from urea in the SubCW medium had a prominent enhancement effect on the decomposition and debromination of BRP waste when the SubCW temperature was below 300 °C. The debromination efficiency of SubCW-urea treatment was significantly enhanced in comparison with that of SubCW-NH₃ and single SubCW treatments. The debromination efficiency of BRP could reach 38.21%, 85.3%, and 99.92% at 200 °C, 250 °C, and 300 °C, respectively. The debromination rate constant of BRP in SubCW-urea, SubCW-NH₃, and single SubCW system was 0.1363, 0.1254, and 0.0146 min^-1, respectively. No brominated chemical compound could be detected in the oil phase products when the treatment temperature was higher than 250 °C. The decomposition products of BRP waste could be easily regulated by controlling the treatment temperature of SubCW-urea. 2-bromo-phenol with the purity of 72.5% could be selectively prepared from BRP by SubCW-urea process at 200 °C. The purity of the recovered phenol could reach as high as 81.5% at 250 °C. The selectivity of the products decreased greatly at 300 °C due to the secondary reactions. The SubCW-urea process has an application prospect in the safe treatment of BRP waste with the aim of high-efficiency debromination and high selectivity products recovery at low temperature.

A novel safety treatment strategy of DEHP-rich flexible polyvinyl chloride waste through low-temperature critical aqueous ammonia treatment

Flexible polyvinyl chloride (f-PVC) contains high content of plasticizers and chlorine. Improper treatment of waste f-PVC can easily lead to resource wasting and bring environmental risks. In this work, a novel strategy for resource recycling and dechlorination of waste f-PVC containing high content of di-(2-ethylhexyl) phthalate (DEHP) was developed by using low-temperature critical aqueous ammonia (LCA) process. The LCA treatment of waste DEHP-rich f-PVC (WDP) was performed at the temperature range of 200-400 °C with the ammonia concentration of 1%-5%. The results indicated that the LCA temperature had a significant effect on the chemical composition of decomposition products. High concentration of 2-ethyl-1-hexanol (86.12%), which is an important chemical feedstock and is derived from the decomposition of DEHP, could be obtained from WDP by the LCA process at 250 °C, and the concentration of 2-ethyl-1-hexanol decreased markedly with increasing the temperature. Benzaldehyde and acetophenone were generated when the temperature increased to 300 °C, and their concentrations increased with the rise of temperature. The increase of the ammonia concentration and the temperature could enhance the dechlorination efficiency of WDP. The dechlorination could reach 98.7% at 300 °C. This result showed that the LCA process was a promising and high-efficiency strategy for the sustainable management of WDP.

Physico-chemical Characterization of Hydrochloric Acid-treated Kaolin Clay: An Industry Approach as a Potential Catalyst

AIMS AND OBJECTIVE

This study explains the FT-IR, XRD, XRF, SEM/EDX, TGA, and DSC/DTA characterization of commercially available kaolin clay. The objective of this paper is to explore the prominent utilization of kandites clay and useful chemical aspects for the modification of kaolin clay minerals.

MATERIALS AND METHODS

The untreated kaolin sample has been procured in this experimental work from AksharChem, Gujrat, India. The kaolin clay was treated with 4M hydrochloric acid. FT-IR, XRD, XRF, SEM/EDX, TGA, and DSC/DTA characterization methods have been used.

RESULTS

Loss on ignition was found at 10.89%. The fingerprint region of the acid-treated sample has broad and more bending vibrations than untreated samples. The high weight percentage of Ti and CaCO3 were spotted in the scanning electron micrograph by both atomic % and weight %. The FT-IR revealed the functional group of Al-O, A1-OH, and Si-O.

CONCLUSION

The morphology indicates that the presences of large particles are in the form of agglomerates. It was found that impurity like scandium vanished and manganese traced by the same atomic % 0.01 of zinc which had no presence after acid treatment. Thermogravimetric analysis indicates the sharp increments in heat flow in-between temperatures 0°C to 200°C and consequently increments in between 500°C to 550°C, a suitable range for the pyrolysis. Low amount of alumina and high amount of silica has been found out. TGA and DTA analysis satisfy the waste plastic valorization temperature ranges.

Swelling-enhanced catalytic degradation of brominated epoxy resin in waste printed circuit boards by subcritical acetic acid under mild conditions

Waste printed circuit boards (WPCBs) contain a large amount of brominated epoxy resins (BERs), which may cause environmental problems. However, BERs degradation under mild conditions is challenging due to the good thermal and chemical stabilities of BERs. This study proposes a mild and efficient method that uses subcritical acetic acid (220 °C-260 °C, 2.6-3.6 MPa) to decompose BERs. BERs swell quickly at 200 °C and are thoroughly decomposed into bisphenol A and phenol at 220 °C when the acetic acid mass concentration and holding time are fixed at 49.90% and 1 h, respectively. Experimental results show that subcritical acetic acid has excellent swelling and catalytic degradation effects on BERs. The quick swelling of BERs allows the free migration of the catalyst in the epoxy network and thus significantly enhances the catalytic degradation effect. Therefore, BERs can be thoroughly decomposed by subcritical acetic acid under mild conditions. Temperature and acetic acid concentration are the major parameters that control the resin degradation rate. Bromine-free oil phase products are obtained at ≥240 °C. The possible decomposition pathway of BERs in subcritical acetic acid is also investigated. Most of the bromine is transformed into HBr and enriched in the aqueous phase. In conclusion, the proposed mild method could be used as a novel practical and industrial procedure for the degradation and debromination of BERs.

Preparation of Cu2O@TiOF2/TiO2and its photocatalytic degradation of tetracycline hydrochloride wastewater

Cu₂O@TiOF₂/TiO₂composites with large surfaces were prepared by a hydrothermal method and exhibited excellent activity under simulated solar light, showing high efficiency for tetracycline hydrochloride photocatalytic degradation, and reusability.