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The traditional hydrometallurgical process is the mainstream technology to recover precious metals from e-waste, which usually adopts strong acid/base and strong oxide with high environmental cost and energy consumption. In the present study, the selective extraction of precious metals was simulated and experimented with DMF as the solvent and Cl - ions provided by CaCl 2 and CuCl 2 (oxidizing agent). The leaching and precipitation rates of precious metals (Au, Ag, Pd) can reach more than 98% under optimization conditions. Kinetic data shows that the control model of the leaching process on precious metals was determined by linear fitting of the shrinkage model. The complex trace precious metals were extracted selectively using dimethylglyoxime and deionized water as precipitators by the leaching-precipitation-cycle method. Meanwhile, the waste liquid produced by this reaction process could be cyclically utilized. Furthermore, the leaching mechanism of precious metals was proposed. DMF could be complexed with the metals as well as coordination ions (Cl - ), which can reduce the redox potentials. Cu(II) could be easily reduced to Cu(I) in the DMF system due to the higher second ionization energy of copper, which is not influenced by the hydration effect, thus shifting the equilibrium to the metal leach side. Oppositely, the addition of water promoted the conversion of Cu(I) to Cu(II) since the higher hydration energy of Cu(II) compensates for the second ionization energy. This research opens up a new path of sustainable development and provides basic theory and practical experience for environmentally friendly recovery of precious metals from e-waste., Competing Interests: Declaration of Competing Interest 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., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

An efficient, microwave-assisted chemical recovery approach for epoxy resin and glass fiber from non-metallic components (NMC) in waste printed circuit boards (WPCBs) for resource reutilization was developed in this research. HNO 3 was selected as the chemical reagent because epoxy resin has low corrosion resistance to HNO 3 . The influence of reaction parameters such as reaction time, temperature, concentration of HNO 3 , liquid-solid ratio, and power of the microwave synthesizer on the separation efficiency of NMC (epoxy resin and glass fiber) and the reaction mechanism were investigated. The physical and chemical properties of NMC, reaction solvent, and decomposed products were analyzed using energy dispersive X-ray Spectroscopy (SEM-EDX) and Fourier transform infrared spectroscopy (FT-IR). The results showed that up to 88.42% of epoxy resin and glass fiber ((5 g) 10 mL/g) could be separated under the action of 300 W microwave power at 95 ℃ for 12 h and a HNO 3 concentration of 7 mol/L. During the reaction, C-N bonds formed by the crosslinking agent and the three-dimensional network structure of the thermosetting epoxy resin were destroyed. The carbon chain structure and chemical properties of epoxy resin did not change significantly and the functional groups of ethyl acetate maintained the chemical structure before and after the reaction. This uncomplicated and efficient inorganic acid chemical microwave-assisted process holds promise for use as a feasible recovery technology for epoxy resin and glass fibers in NMC. The proposed process is particularly appealing because of its high selectivity, considerable economic advantages, and environmental benefits., Competing Interests: Declaration of Competing Interest 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., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Non-metallic components (NMC) in waste printed circuit boards (WPCBs) are made of the thermosetting epoxy resin and glass fiber, which has been a research concern in the waste recycling area. The recycling of thermosetting epoxy resin is a serious challenge due to their permanent cross-linked structure. An efficient approach to chemical recycling of epoxy resin for resource reutilization was developed in this research. ZnCl 2 /CH 3 COOH aqueous solution was selected as catalysts system to decompose epoxy resin under a mild reaction condition. The influence of reaction parameters such as reaction temperature, time, liquid-solid ratio and ZnCl 2 amount on the decomposition efficiency of epoxy resin and reaction mechanism were investigated. The physical and chemical properties of NMC, reaction solvent and decomposed products were analyzed using scanning electron microscope(SEM), Fourier transform infrared spectroscopy (FT-IR) and Gas chromatography-mass spectrometry (GC-MS). Results showed that up to 81.85% of epoxy resin could be dissolved by using a temperature of 190 °C during 8 h with a mixture of acetic acid (15 wt%): ZnCl 2 (5 g) 20 mL/g. Incompletely coordinated zinc ions enables the cleavage of CN, CBr and CO bonds in the thermosetting brominated epoxy resin, which was mainly converted to phenol, 2-Bromophenol and 2, 4-Dibromophenol with high resource value. And the functional groups of ethyl acetate and acetic acid maintained chemical structure before and after reaction. This research provided a practical approach to the dissolution and reutilization of NMC in WPCBs., Competing Interests: Declaration of Competing Interest 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., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Recycling of plastics from e-waste can conserve resources, however, aging during the use of plastic products can cause the migration of heavy metals in additives. This study presents a methodology for evaluating the risks of heavy metals in waste plastic secondary products during long term use associated with heavy metal migration. The study processes were investigated by: (1) recycling waste plastics and producing secondary products; (2) thermal aging of secondary products; and (3) toxic leaching used to quantitatively analyse the dissolution of heavy metals. Combined with the changes in mechanical properties and microstructure, the effect of aging on the migration of heavy metals was observed. The results showed that the polymer appeared to delaminate, the adhesion of waste plastics to additives decreased, and the mechanical properties clearly decreased after the thermal aging experiment. Leaching experiments showed that the leached concentrations of Ni, Cu, Zn, Pb, and Sb in the three types waste plastic products increased over time. After 8 d of aging, the leached concentrations of Ni, Sb, and Pb exceeded the third, fourth, and third class of the groundwater quality standard, respectively. Specifically, the concentrations of Sb were 141, 289, and 21.1 times higher than the maximum permissible level. Therefore, management hierarchy and safe environmental recycling methods should be developed to reduce the risk of heavy metals in waste plastic secondary products., Competing Interests: Declaration of competing interest 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., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Recycling is the primary method to handle electronic waste plastics, however, little attention has been paid to the risk posed by heavy metal migration in waste plastic products. The effect of multistage recycling processes on heavy metal migration and the environmental risk posed by heavy metals during recycling processes were investigated by: (1) Recycling waste plastics and determining the heavy metal contents in secondary products; (2) Using toxic leaching experiments to assess environmental risks of heavy metal migration in secondary products; and (3) Evaluating the effect of recycling processes on the mechanical properties and microstructure of plastics. Results showed that the contents of some harmful heavy metals in processed products exceeded the Safety of Toys Standard. Toxic leaching tests showed that Ni, Cu, Zn, Pb, and Sb migrated outward during secondary products use. With increased recycling times, concentrations of migrated Ni, Cu, Zn, Pb, and Sb increased, and the leached concentrations exceeded the limits stipulated in the Groundwater Quality Standard. Increased recycling times also accelerated waste plastics aging and caused the deterioration of mechanical properties. Furthermore, adhesion between layers decreased, stratification and cracking in polymers appeared, and adhesion of waste plastics to additives decreased. Therefore, the environmental risks of waste plastic recycling should be carefully considered., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interests., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Polycyclic aromatic hydrocarbons (PAHs) are considered to be persistent organic pollutants, which pose a great threat to human health and the surrounding environment. In order to explore the influence of informal electronic waste (e-waste) dismantling activities on inhabitants who live nearby, soil samples were collected from informal e-waste dismantling areas in Xinqiao, China and analysed for 16 United States Environmental Protection Agency (USEPA) priority PAHs. Results indicated that the 16 USEPA priority PAHs were found at all seven sampling locations. Sampling location 3, which was only 10 m away from a residential area, had 1053.69 μg kg -1 of PAHs and seriously exceeded the standard value specified by the Netherlands. The total percents of 4-ring and 5-ring PAHs accounted for 61.74 and 71.70%, respectively, indicating that most of the detected PAHs belonged to high-ring PAHs. The informal e-waste dismantling activities are the major sources of soil PAHs in Xinqiao. Furthermore, the concentration of seven carcinogenic PAHs was 114.76 μg kg -1 and represented a potential health risk to humans. Thereinto, benzo[a]pyrene contributed the most, accounting for more than 50% in these locations. Our results may provide a reference about the influence of informal e-waste dismantling activities on the surrounding inhabitants and suggest that e-waste dismantling activities must be conducted in a formal enterprise which is far away from residential areas.

For the objective of evaluating the contamination degree of heavy metals and analysing its variation trend in soil at a waste electrical and electronic equipment processing area in Shanghai, China, evaluation methods, which include single factor index method, geo-accumulation index method, comprehensive pollution index method, and potential ecological risk index method, were adopted in this study. The results revealed that the soil at a waste electrical and electronic equipment processing area was polluted by arsenic, cadmium, copper, lead, zinc, and chromium. It also demonstrated that the concentrations of heavy metals were increased over time. Exceptionally, the average value of the metalloid (arsenic) was 73.31 mg kg -1 in 2014, while it was 58.31 mg kg -1 in the first half of 2015, and it was 2.93 times and 2.33 times higher than that of the Chinese Environmental Quality Standard for Soil in 2014 and the first half of 2015, respectively. The sequences of the contamination degree of heavy metals in 2014 and the first half of 2015 were cadmium > lead > copper > chromium > zinc and cadmium > lead > chromium > zinc > copper. From the analysis of the potential ecological risk index method, arsenic and cadmium had higher ecological risk than other heavy metals. The integrated ecological risk index of heavy metals (cadmium, copper, lead, zinc, and chromium) and metalloid (arsenic) was 394.10 in 2014, while it was 656.16 in the first half of 2015, thus documenting a strong ecological risk.

This research focused on the application of the hydrothermal sulphidisation method to separate lead from scrap cathode ray tube funnel glass. Prior to hydrothermal treatment, the cathode ray tube funnel glass was pretreated by mechanical activation. Under hydrothermal conditions, hydroxyl ions (OH(-)) were generated through an ion exchange reaction between metal ions in mechanically activated funnel glass and water, to accelerate sulphur disproportionation; no additional alkaline compound was needed. Lead contained in funnel glass was converted to lead sulphide with high efficiency. Temperature had a significant effect on the sulphidisation rate of lead in funnel glass, which increased from 25% to 90% as the temperature increased from 100 °C to 300 °C. A sulphidisation rate of 100% was achieved at a duration of 8 h at 300 °C. This process of mechanical activation and hydrothermal sulphidisation is efficient and promising for the treatment of leaded glass., (© The Author(s) 2015.)

The effect of calcium-based addition on the brominate flux during printed circuit board (PCB) pyrolysis was investigated. It was found that bromine (Br) can be effectively fixed in solid phase during PCB pyrolysis by adding calcium-based waste materials. Phenol and 4-ethylphenol are the major products of pyrolysis. When the two kinds of red mud were used as additive, their content was 85.25 and 84.81%, respectively, which was higher than others. The 2-bromophenol and 2-bromo-4-methyl-benzene are the main Br-containing pyrolysis volatiles. After adding calcium-based additive, these two volatiles were apparently reduced and only small amounts of 2-bromo-4-methyl-benzene were detected in the products, namely 0.71 and 0.86%, respectively for the two kinds of red mud. Hence, no matter from the perspective of product use or simple Br-fixing, the bromine in the three-phase products can be effectively regulated and controlled by adding calcium-based waste residue during PCB pyrolysis. Finally, the Br-fixing mechanism was analysed. As a result, when calcium-based waste materials were added to the PCB pyrolysis it made bromine fix easily in the resident yielding a byproduct that can be further used.

Waste printed circuit boards (WPCBs), which have lots of highly valuable components and toxic substances, are important subjects for disposal of waste electric and electronic equipment (WEEE). Nowadays material recycling and components reusing are still the main disposal methods of WPCBs. Increased crushing-sorting separation technology to extract valuable metals from WPCBs usually produce large amounts of resin powder which result in seriously secondary pollution. The study aims to the disassembly acceleration and separation of components without damage on WPCBs. The components reuse-oriented disassembly technology is studied, in which the key technologies of leaching and sealing-off. Fluoboric acid/ Hydrogen peroxide leaching system is discussed in detailed including solution concentration, reaction time and metal leaching rate. The experiments realize the dismantling of WPCBs by selectively dissolve solder and offer a new way to recycle valuable materials from WPCBs and prevent the environmental pollution effectively. [ABSTRACT FROM AUTHOR]

In the past few decades, cathode ray tube (CRT) is widely equipped in TV and computer devices as an important part of monitors. However, in recent years, due to the rapid development of monitor technology, CRT is replaced by liquid crystal display (LCD) gradually. Therefore, amounts of waste CRT is increasing sharply around the world. CRT consists of leaded glass which belongs to hazardous waste. Lead is one kind of metal, which is harmful to human health. So the disposal and treatment of leaded glass have become one of the hotspots and difficulties in the disposal field of e-waste. Due to the stability of lead wrapped in glass matrix, the lead separation from glass is hard. At present, there is no effective way to deal with leaded glass. However, a variety of new methods have been studied in laboratory, and good effects have been gained. Several advanced methods such as high temperature separation and pretreatment +hydrometallurgical leaching are introduced in this paper. [ABSTRACT FROM AUTHOR]

To improve the copper bioleaching efficiency from waste printed circuit board (WPCB) by Acidithiobacillus ferrooxidans ( A. ferrooxidans ), a novel simplified material (nitrogen-doped carbon nanotubes (NCNTs) modified electrode) was used in this paper. Experiments mainly including the exploration of NCNTs optimal concentration and recycling effect of NCNTs modified electrode were investigated. The variations of pH, ORP, Fe 2+ concentration and Cu 2+ concentration were studied in detail, and the mechanism of the modified electrode was also analyzed in this study. Conclusions were obtained that the optimal experimental conditions were: bacteria inoculation 10%, initial pH 2.0, WPCB powder 1 g, solid/liquid (w/v) ratio 1/50, temperature 28 °C, rotational speed 125 r/min and modified electrode 2.5 mg/cm 2 . The copper bioleaching rate reached 99% after 9 days reaction, and it was 20% higher than that of the group which was only added A. ferrooxidans. With the analysis of XRD, the precipitate formed (NH 4 )Fe 3 (SO 4 ) 2 (OH) 6 at the end of the reaction, and the modified electrode didn’t affect the formation of the yellow precipitate. Meanwhile, the modified electrode could be recycled, and the positive effect wasn’t weakened obviously on these processes. The results may provide a reference for enhancing the copper bioleaching efficiency from WPCBs and expand the application of NCNTs in hydrometallurgy field. [ABSTRACT FROM AUTHOR]

Traditional mechanical pretreatment and hydrometallurgy is the mainstream technology to recycle gold from waste printed circuit boards (PCBs). However, this method is cumbersome and often employs toxic/harsh chemicals. In the present study, gold was easily recycled from PCBs gold-plated layer of waste mobile phones (WMPs) in DMF-CuCl 2 -CaCl 2 (DMF: dimethyl formamide) system what we call "mild aqua regia" without pretreatments or enrichment process, and the reaction system could be cyclic utilized. In such reaction system, gold could be recycled through leaching, precipitation and filtration. The reaction parameter optimization and reaction mechanisms were studied. Under the optimized conditions, the gold leaching rate and precipitation rate could reach over 99%. DMF plays a significant role in the leaching system. As a typical polar aprotic solvent, DMF cannot solvate Cl−. Thus, "Cl−" exists in a "naked state", and it can easily react with Au. Besides, Au (III) could generate a complex through the complexation with DMF which could result in the redox potentials reduce and move the equilibrium to the Au leaching side. In summary, this study provided a fundamental basis as well as practical guidance for recovering precious metals from waste electrical and electronic equipment in an efficient manner. Image 1 [ABSTRACT FROM AUTHOR]