Search

Increased generation of spent lithium-ion batteries (LIBs) has driven the exploration of new methods for reusing and/or recycling LiCoO₂ cathode materials. Herein, an electrochemical relithiation method was proposed to directly regenerate LiCoO₂ cathode materials using the waste LiₓCoO₂ electrode as a base. It was shown that Li⁺ was successfully inserted into the waste LiₓCoO₂ electrode, and this relithiation process became faster with either a higher Li₂SO₄ concentration or a higher cathodic current density. The XRD analysis confirmed that the peak positions of the relithiation products were consistently close to those of a standard LiCoO₂ material. The crystal structure of the relithiation products was restored with a post-annealing process. The activation energy for electrochemical relithiation (Eₐ) was estimated at 22 kJ mol–¹, and the constant of equilibrium constant k₀ was determined as 1.35 × 10–⁶ cm s–¹. The relithiation process was controlled by the charge transfer process when the Li₂SO₄ concentration was high (e.g., 1, 0.8, and 0.5M), and a lower concentration at 0.01–0.3 M led to a diffusion control pattern. The electrode made of the regenerated LiCoO₂ materials had a charge capacity of 136 mAh g–¹, close to that of the commercial LiCoO₂ electrode (140 mAh g–¹). A potential mechanism of electrochemical relithiation was proposed involving lithium defects, relithiation, and crystal regeneration.

While CIGS solar cell has been experiencing an expanded photovoltaic market and increasing research interest in cell design, its treatment after obsoletion remains an upcoming issue. The heavy metals involved, such as Cd, can threat the environment, while strategic resources, such as rare metals In and Ga, offer a great recycling oppotunity. However, due to its multimetal feature, traditional recycling methodology shows poor separation-extraction efficiency and additional environmental burdens with intense reagent consumption and waste generation. Here, we report a sequential electrodeposition method for pure metal recycling from this Cu-In-Cd-Ga quaternary system in a more environmentally friendly and efficient manner. Stability constant-corrected redox potential supplemented with metal electroreduction tests predicts well the potential window for sequential electrodeposition. Cu and In electrodeposition shows 100% separation with high Coulombic efficiency (>80%), whereas Ga electrodeposition presents slower kinetics and performs better at a pH of 2.5. Environmental impact assessment indicates that the proposed recycling route allows remarkable reduction of global warming and toxicity impacts compared with metal production from virgin mining and reference processes. We further unveiled the applicability of the electrodeposition technique in the context of anthropogenic mineral recycling, emphasizing resource sustainability and cleaner production.

Recycling resources from millions of tons of e-wastes are a global challenge. E-wastes is complex and contains both toxic organics and valuable metals. Therefore, the technologies for e-wastes recycling are totally different from those used for mineral separation. Current technologies for e-wastes tend to focus on recycling materials with high economic value and ignore components that cannot be recycled or have low reuse value. As a result, some secondary pollution problems inevitably occur due to the recycling process. Based on these problems, we summarize the universal characteristics of e-wastes and explore new approaches to achieve complete resource recycling of e-wastes with minimum secondary waste generation. A concept of element recycling is proposed to achieve complete resource recycling of e-wastes in the study. We can use the properties of the elements in different types of e-wastes to achieve e-wastes recycling, i.e., recycle of elements in e-wastes. Under the guidance of element recycling, various e-wastes types have common connections. If element recycling in e-wastes is realized, all components in e-wastes can be fully recycled without/with minimal production of secondary waste. The two case studies are discussed to clarify the concept and principle of element recycling. This study explores the recycling of e-wastes from a new perspective-element recycling in e-wastes. The concept of element recycling is significant for resource recycling from e-wastes.

Germanium, as scarce and strategic resource, is widely used in infrared devices, polymerization catalysts and optical fibers. Manufacturing scraps and coal fly ash are the main secondary germanium resources, where germanium exists as GeO2. Carbothermic reduction method is a promising technology for germanium recovery from such wastes and its feasibility has been confirmed recently. However, the kinetics and reaction mechanism of the recovery process remained unclear, which blocked deep insight into the process and further improvement of recovery technology. In this study, the kinetics of carbothermic reduction of GeO2 as well as reaction mechanism was studied in detail. A transformation of reaction path was confirmed: Path I: Reduction product GeO desorbed from reaction region at the first stage; Path II: Ge became the main reduction product and evaporate slowly at the second stage. The kinetic parameters of these two paths were calculated where the kinetic model corresponded to an autocatalytic model. Germanium monoxide (GeO) was the main recovered species accompanied with a small amount of Ge and GeO2 and an overall reduction scheme was also proposed. These results can provide theoretical basics and implications for germanium recovery from waste scraps through carbothermic reduction method.

Every year, billions of tons of lignite are burnt to generate electricity, meanwhile generating large amounts of coal fly ash (CFA) that is regarded as an industrial waste. During lignite combustion, arsenic and scarce metals are simultaneously volatilized in the form of oxide into CFA. This study proposed an effective vacuum distillation method to remove As and recover Ge and W from CFA. The feasibility of separating As and recycling Ge and W from CFA was verified by the theoretical analysis. The experimental result indicated that the removal ratio of As was 96 ± 1% and the contents of Ge and W reached 0.75 ± 0.023 and 0.24 ± 0.016 wt % in the residue, which were enriched 17.2 and 1.2 times, respectively, at a temperature of 550 °C, with 50 wt % sulfurizing agent added under pressure of 1 Pa and 240 min of heating. For the condensed product, chemical species As2S3 and As4S4 were detected by X-ray photoelectron spectroscopy analysis. For Ge and W in the residue, GeOx (x < 2), GeS, WOx (x < 3), and WS2 were the main chemical species. The potential mechanism involved in the release of arsenic from CFA, vacuum sulfurization, evaporation, and condensation was proposed. The kinetic analysis indicated that the apparent activation energy (Eα) was 31.24 kJ mol-1. Those results encourage further exploration of vacuum separation technology to environmentally friendly recycle CFA.

Background: Gastroesophageal varices is a serious complication of compensated advanced chronic liver disease (cACLD). Primary prophylaxis to reduce the risk of variceal hemorrhage is recommended if high-risk varices (HRV) are detected. We performed this study to compare the accuracy, patients’ satisfaction and safety of detection of HRV by detachable string magnetically controlled capsule endoscopy (DS-MCCE) with esophagogastroduodenoscopy (EGD) as the reference. Methods: We prospectively recruited participants with cACLD from 12 university hospitals (11 in China and one in the United Kingdom) between November 2018 and December 2019 (ClinicalTrials.gov, NCT03749954). All participants underwent DS-MCCE, followed by EGD within a week in a blinded fashion. Following endoscopy, and on the same day, participants were asked to fill in a satisfaction questionnaire regarding their experience. Findings: A total of 105 eligible participants were enrolled. With EGD as the reference standard, the concordance index, sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio, and negative likelihood ratio of DS-MCCE in diagnosis of HRV were 0•90 (95% confidence interval [CI]: 0•83–0•95), 92% (95% CI: 78–98%), 88% (95% CI: 78–95%), 80% (95% CI: 70–92%), 95% (95% CI: 90–100%), 7•91 (95% CI: 4•10–15•30), and 0•09 (95% CI: 0•03–0•30), respectively. The kappa score of 0•78 (95% CI: 0•65–0•90) suggested substantial agreement between DS-MCCE and EGD. Moreover, in participants undergoing EGD without sedation, the satisfaction of DS-MCCE was significantly better than that of EGD (p < 0•0001, d = 1•15 [95%CI: 0•88–1•42]). All participants confirmed the excretion of the capsule, and no adverse events occurred. Interpretation: DS-MCCE is an accurate alternative to EGD for detecting HRV in cACLD, which is safe and associated with better satisfaction. Funding: A full list of funding can be found in the Funding Support section.

With a huge amount of waste liquid crystal displays (LCDs) generated annually, their proper recycling raises continuous concern to realize pollution control (heavy metal and liquid crystal) and resource recovery (indium). However, due to their multi-metal feature, traditional hydrometallurgy lacks of sufficient selectivity, which makes the recycling route lengthy, costly, and generate more waste. Electrodeposition acts as a promising technique for selective metal extraction from multi-metal system due to its high selectivity and electron as clean reagent. To fully develop its application in metal recovery, stepwise Cu/MoO

Recycling activity for waste electrical and electronic equipment is always accompanied with leaching solution containing copper. Its selective extraction is of environmental and economic significance, and is beneficial for subsequent resource purification procedure. Compared with techniques such as chemical precipitation and solvent extraction, potentiostatic electrodeposition is outstanding with the advantage of high selectivity, electron as clean reagent, and minimal chemical usage. However, key factors affecting copper electrodeposition behavior as well as its kinetic process remain unclear, which blocks its further application. In this study, selective copper electrochemical extraction from multi-metal leaching solution of waste liquid crystal display panels is explored. Copper electrodeposition is analyzed from electrochemical and mass transport point of view, and the main results are summarized: (i) copper can be first electrodeposited due to its higher reduction potential compared with indium; (ii) applied potential and agitation are the most influential factors towards space-time yield and current efficiency; (iii) a semi-empirical kinetic model could quantitatively describe the influence of agitation and the time-current-concentration relationship. The model-predicted extraction rate agreed well with experimental data throughout electrodeposition; (iv) electrodeposition experiments show over 95% of copper can be selectively extracted as ultrafine copper powder (~150 nm) at 0.05 V (vs. SHE).

How to realize the high value-added utilization of scrap copper from e-waste is a meaningful topic. In the study, an Ohno Continuous Casting (OCC) process is an existing method you applied to purify the copper. Based on the model of diffusion-controlled grain growth kinetics, the redistribution of impurity of tin in the scrap copper were studied under the different continuous casting speed and mold temperature. On the centerline, macrosegregation in the axial direction of the tin was more obvious with the decrease of continuous casting speed. The small continuous casting rate was beneficial to the segregation and enrichment of tin. The axial segregation gradually decreased with the increase of the mold temperature. The flattening of the liquid–solid interface resulted in a weakening of the solute enrichment at the root of the interface with the increase of temperature. Morphology, electron backscattered diffraction (EBSD) analysis showed the structure of single crystal copper. The range of resistance of single crystal copper was from 5 × 10-6 to 3 × 10-5 Ω m. Obviously, the resistance of the single crystal copper was significantly smaller than that of ordinary copper wire (9.0 × 10-3 Ω m). This study provided a key theoretical and practical basis for the high value-added reuse of copper in e-waste.

Clean energy technologies are emerging as a major contributor to the total energy supply. Some metals play irreplaceable roles in these technologies. The supply risk of metals used in clean energy technologies is gradually increasing. Hence, it is necessary to investigate the supply risks of these metals worldwide. In this study, a comprehensive assessment is conducted to quantify the supply risks of critical metals. The production of the metals is imbalanced worldwide. China, Russia, the United States, Canada, and Australia dominate the supply of these metals. China has the largest supply risk, and the main risk contribution is linked to mining governance and policy, which suggests that strengthening government regulations is necessary. The supply risks in the United States, Russia, and Canada are moderate, and most risks are associated with geologic availability and recycling restrictions. Al, Cu, Fe, Pb and Ag displayed high risks linked to geologic availability and recycling restrictions. Pd, B, Sb, W, Re, Ge and Ga exhibited high risks related to mining governance and policy and environmental sustainability. Difficult exploration processes and highly sensitivity market supplies increased the supply risk. This study provides an important reference for the strategic application of the metals in clean energy technologies in the future.

Electronic waste (e-waste), as hazardous waste, is a promising secondary resource of precious metals. The extraction of precious metals from e-waste has great environmental and economic benefits. Most of the existing methods have high energy consumption, environmental pollution or low recovery efficiencies. This study proposed the application of green electrodeposition technology to realize targeted recovery of Ag-Pd alloy from Ni, Cu, Ag, Pd, Bi polymetallic e-waste leaching solution. Linear sweep voltammetry was conducted to determine the feasibility of targeted extraction. The high purity of Ag-Pd alloy was realized by controlling the potential. The recovery efficiencies of Ag and Pd were 97.72% and 98.05% after 5 hours in 0.5 mol/L HNO3 with applied potential of 0.35 V. The results indicated the formation of monophase Ag-Pd alloy. Besides, the effect of acidity and potential on the particle size of alloy was analyzed. Chronoamperometric method was applied to study the electrodeposition mechanism. The Ag-Pd electrodeposition followed three-dimensional instantaneous nucleation and growth mechanism analyzed with Scharifker-Hills model, thus producing a solid solution. The nucleation site increased with the overpotential. This study provides a novel, efficient and green approach for the targeted recovery of Ag and Pd from the complex multi-metal system of e-waste.

Germanium, because of its unique performance, has been widely used in the manufacture of optical fiber. Recycling germanium is significant because of geographical scarcity and technical barriers. I...

Scattered metals play irreplaceable role in some clean energy technologies and advanced materials, and they will become much more important in the future. Global consumption of scattered metals has significantly grown in recent decades. However, at present, imbalances of exploitation, manufacturing and recycling of scattered metals are quite severe resulting in some uncertain supply risk. Hence, securing reliable, ordered and sustainable access to these scattered metals from minerals, functional products to wastes is necessary. This paper focuses on scattered metals in wastes and investigates minerals distribution, material flow, and current recycling technology of scattered metals from minerals to wastes. Especially, for the recycling technology, some representative methods including selective extraction, ion exchange and flotation, precipitation and vacuum metallurgical technology etc, the specific procedures, reagent, optimization and recycling situation of scattered metals were summarized in the review. Meantime, environmental and supply risk, and recycling challenges are expounded in detail. Although these technologies had obtained quite satisfactory results for recycling of a certain scattered metals in wastes, it is no deny that current technologies still have some challenges for further promotion. Overexploitation, disordered mining and the imbalance of the exploitation, production and recycling had also increased supply risk and environmental risk. For recycling technology, the shortages and defects of each technology are discussed from the perspective of technological promotion and environmental protection in the review. Furthermore, future replying strategies for scattered metals from wastes from the perspective of mining governance, environmental and supply sustainability, and technological improvement were proposed.

Recycling rare metal tantalum from waste tantalum capacitors (WTCs) is significant to alleviate the shortage of tantalum resource. However, environmental problems will be caused if the organic materials from WTCs are improperly disposed. This study presented a promising vacuum pyrolysis technology to recycle the organic materials from WTCs. The organics removal rate could reach 94.32 wt% according to TG results. The optimal parameters were determined as 425 °C, 50 Pa and 30 min on the basis of response surface methodology (RSM). The oil yield and residual rate was 18.09 wt% and 74.94 wt%, respectively. All pyrolysis products can be recycled through a reasonable route. Besides, to deeply understand the pyrolysis process, the pyrolysis mechanism was also proposed based on the product and free radical theory. This paper provides an efficient process for recycling the organic material from WTCs, which can facilitate the following tantalum recovery.

Precious metal (PM) retrievement from e-waste is of great significance for reducing virgin mining activity and promoting rare resource sustainability. However, current PM recycling methods rely mainly on caustic aqua regia or unstable sulfur-based ligand, which has caused severe environmental damage and process inefficiency. Here, we propose an environmentally friendly halide-regulated strategy, utilizing milder and renewable oxidant—cupric/ferric ion for facile PM dissolution. This is realized by the synergistic effect of enhanced oxidizing ability of Cu(II) and reduced oxidation potential of PM with halide addition. Electrochemical tests and leaching experiment results show that Cu(II)/Cu(I) redox potential experiences great change with bromide, increasing from 0.4 to 0.75 V. Fast corrosion feature was observed for Au in Cu(II)/Fe(III)-Br- and Pd in Cu(II)/Fe(III)-Cl-, and it can be accelerated by increasing oxidant and halide concentration. Our proposed strategy outperforms traditional methods with stable and fast dissolution, where 2.5 mol/L Br- is appropriate for Au dissolution. Moreover, selective dissolution of base metal, Pd/Ag, and Au can be achieved via ligand alteration and be further combined with electrodeposition technique for multi metal recovery and oxidant regeneration. This halide-regulated strategy can lead PM recycling from pollutive status towards environmentally friendly road.

With a huge amount of waste liquid crystal displays (LCDs) generated annually, their proper recycling raises continuous concern to realize pollution control (heavy metal and liquid crystal) and resource recovery (indium). However, due to their multi-metal feature, traditional hydrometallurgy lacks of sufficient selectivity, which makes the recycling route lengthy, costly, and generate more waste. Electrodeposition acts as a promising technique for selective metal extraction from multi-metal system due to its high selectivity and electron as clean reagent. To fully develop its application in metal recovery, stepwise Cu/MoO2 and In electrodeposition from In-Cu-Mo-Fe waste LCD leachate is explored in depth. Electrochemical behavior analysis shows Cu and MoO2 can be first electrodeposited for their higher electroreduction potential. Cl- plays a key role in accelerating indium electroreduction kinetics, which largely shortens the extraction time without the sacrifice of current efficiency. This accelerating effect is attributed to the increased concentration of electroactive species or collision frequency. Under optimized condition, 99.41% of indium (> 99% purity) can be electrodeposited within 13 h with high current efficiency. This study provides a cleaner approach for waste LCDs recycling and gives implications for the potential application of electrochemical technique in e-waste recycling.

The fundamental mechanisms underlying the influence of nuclear wastes on concrete properties remain poorly understood, especially at the molecular level. Herein, caesium ions (Cs+) are introduced into calcium silicate hydrates (CSH) to investigate its effect using molecular dynamics simulation. Structurally, a swelling phenomenon is observed, attributed to the CSH interlayer expansion as Cs+ occupies larger space than Ca2+. The diffusion of interlayer water, Ca2+ and Cs+, following an order of water > Cs+ > Ca2+, is accelerated with increasing Cs+ content, owing to three mechanisms: expanded interlayer space, weakened interfacial interaction, and loss of chemical bond stability. Mechanically, the Young's modulus and strength of CSH are degraded by Cs+ due to two mechanisms: (1) the load transfer ability of interlayer water and Ca2+ is weakened; (2) the load transfer provided by Cs+ is very weak. Additionally, a "hydrolytic weakening" mechanism is proposed to explain the mechanical degradation with increasing water content. This study also provides guidance for studying the influence of other wastes (like heavy metal ions) in concrete.

The contradiction of energy, resource, and environment from waste LCD panels is prominent because they contain both harmful liquid crystals and the valuable resource indium. However, traditional whole crush technology is difficult to realize sustainable recycling of waste LCD panels due to a challenge from the low concentrations of liquid crystals and indium. Secondary pollution inevitably occurred in recycling process. In this work, a stripping product enriched in liquid crystals and indium was first gained by a mechanical stripping separation. Then, liquid crystals were reused as carbon source in pyrolysis process to form carbon fiber in control. Carbon fiber clusters can form well under the optimal condition of 500 °C, with 30% molecular sieve (particle size < 0.3 mm) and pyrolysis time of 15 min. The pyrolysis mechanism of liquid crystals and the formation mechanism of carbon fiber were discussed. Finally, vacuum in situ reduction of indium oxide from stripping product with the prepared carbon fiber c...

The contradiction of energy, resource and environment from waste liquid crystal display (LCD) panels is becoming more and more prominent because it contain both harmful liquid crystals and valuable metal indium. However, scarce researches have considered how to separate liquid crystals and recycle indium from waste LCD panels by an environment-friendly process. In this work, an integrated technological process to recycle energy and valuable resource from LCD panels is proposed. Firstly, a stripping product enriched liquid crystals and indium is gained by a mechanical stripping separation. Then, based on a series of pyrolysis separation, vacuum chlorinated separation and substitution reaction, concentration of indium is increased to 36 wt % in final product from 0.02 wt % in waste LCD panels. Several highlights were summarized as follows: (i) Feasibility, principle and reaction mechanism was studied to understand this integrated process. (ii) For pyrolysis process, separation rate of liquid crystals approached 82.06% under optimized parameters by response surface methodology. For vacuum chlorinated process, recovery rate of indium can reach 97.16%. This technological process is quite significant in accordance with the “Reduce, Reuse and Recycle Principle” for solid waste and further provides a new opportunity for sustainable development of LCD markets.

In the past, most of technologies adopted whole crush for waste LCD panels to treat liquid crystals and indium but had low recovery due to its low concentration. In this work, a mechanical stripping process was proposed firstly to gain stripping product enriched liquid crystals and indium. Liquid crystals are enriched from 0.3 wt% in waste LCD panels to 53 wt% in the stripping product. Likewise, indium is enriched from 0.02 wt% to 7.95 wt%. Liquid crystals in stripping product should be removed in advance since it is disadvantage for indium recovery. This study can successfully remove liquid crystals by pyrolysis process. The results were summarized as follows: (i) Liquid crystals in waste LCD panels were mainly TFT type liquid crystals by thermal gravimetric analysis and chromatograph-mass spectroscopy. (ii) Liquid crystals can be well separated under optimized condition of 873 K, 40 min and 2 L/min N2 flow rate. Oil and gas produced in pyrolysis process can be reused as energy and fuel. (iii) Pilot scale experiments were utilized to assess the actual effect of pyrolysis separation; decomposition rate of liquid crystals can reach 80%. It gives some valuable information for industrial separation of liquid crystals and provides a necessary preparation for further recovery of indium.

Resource recycling of millions of solid wastes is a world’s problems. Because element is the basic unit of all wastes, the essence of wastes recycling is to realize cycle of elements in wastes. In this paper, a new concept of element cycle in wastes is proposed. Under guidance of element cycle, various wastes have common connection point. The concept is clarified by a case of C, H, Cl and In element cycle from waste PVC plastic and LCD panels. In this paper, a vacuum pyrolysis of waste PVC was proposed to recycle indium in LCD and synchronously prepare carbon coating. Cl in PVC combined with In in LCD was mainly regenerated in the form of InCl3. Meantime, C and H in PVC were reused to prepare carbon coating and energy products, such as pyrolysis oil and gas. The recycling system means to change two kinds of wastes into resources by their own element characteristics. Under optimized conditions, recovery rate of indium exceeded 98 %. Meantime, with increasing temperature, microstructure of carbon coating is...

The coordinated treatment for two kinds of waste is an effective way to save energy and improve the recovery efficiency of resource. In worldwide, more than half of palladium is used to produce catalysts in automobile. However, with the increasing consumption of palladium, the scarcity of palladium resource is becoming prominent. This paper proposed an integrated process based on capture of copper scrap and electrodeposition process to recycle palladium in spent catalysis from automobile. The technological process mainly consisted of two procedures: capture of copper scrap with the purposes of enriching palladium and electrodeposition process with the purposes of separating and purifying palladium. Several highlights were summarized as follows: (i) a capture mechanism of palladium by copper scrap was studied by the calculation of surface thermodynamics and first principles. (ii) Optimum designs, parameter and product analysis were developed to guide industrial recycling. The appropriate parameters for capture of copper scrap are the melting temperature reached 1400 °C, adding 20% dosage of copper scrap and 2 of mass ratio of SiO2/Al2O3 and for the electrodeposition process, nearly 100% of palladium was deposited on the cathode under 0.1 M concentration of HNO3, −0.042 V of electrodeposition potential and 25 °C reaction temperature with 9 h. (iii) This process overcame the shortages of traditional process and showed its efficiency and environmental performance. This study is significant for high-efficient, low-cost and environment-friendly recycling of valuable resource in spent catalysis from automobile.

The fundamental mechanisms under concrete creep are far from being fully understood, especially at the molecular level. Hereby, a calcium-silicate-hydrate (C-S-H) molecular model is developed to explain, for the first time, the creep characteristics at various stress states, temperature levels and water contents, which are not accessible experimentally. Rather tensile and compressive loadings, C-S-H only creeps under shear loadings originating from the sliding of the calcium silicate layers over each other as the interlayer component (water and ions) acts as a lubricator. A heterogeneous creep characteristic is observed. Elevated temperature reduces the interlayer lubricator viscosity and weakens the interfacial adhesion between the layers and the interlayer lubricator, which accelerates C-S-H creep. The removal of interlayer water enhances the creep resistance, resulting from the reduced interlayer space and enhanced interfacial adhesion. The atomic-level mechanisms explain the inter-CSH-particle behaviours at the microscale, which bridges the gap between atomistic simulation and microcosmic phenomenon.

Electronic waste, as hazardous waste, contains a large amount of metals, which is of great recovery value. However, they are difficult to separate due to wide variety and complex distribution. Most of current recycling methods are environmentally-unfriendly or complicated. In this study, a simple, efficient and green approach for metals separation from Ni-Cu-Ag-Pd-Bi-Sn multi-metal system of e-waste was proposed combining mild leaching and stepwise potential-controlled electrodeposition. The leaching efficiencies of Ni, Ag, Pd, Cu and Bi were 99.16%, 99.09%, 94.91%, 99.61% and 23.76% with 1 mol/L HNO3 at 80 °C. The leaching process was analyzed. It showed that the existence of Ag-Pd continuous solid solution in the alloy lowered the oxidation potential of Pd, which facilitated its leaching. Sn precipitated as SnO2. Then Ag-Pd alloy and Cu-Bi alloy were separately extracted from the leaching solution by stepwise electrodeposition. 97.72% of Ag and 98.05% of Pd were recycled after 5 h with potential of 0.35 V. The recovery efficiencies of Cu and Bi were 97.87% and 97.33% after 7 h with potential of 0.05 V. The EDS results showed high purity property of Ag-Pd and Cu-Bi alloy. This process can achieve cleaner and efficient extraction of metals from multi-metal system in e-waste.

Recycling waste multilayer ceramic capacitors (MLCCs) has attracted much attention owing to its rich metal resource and environment pollution. Existing recycling processes have deficiencies in environmental protection, efficiency and metal purity. Capture technology is promising with advantages of efficient enrichment and less pollution, which was applied to recycle metals in this study. In order to study the mechanism for it, the behavior of enrichment and migration of metals in the recovery of waste MLCCs by eutectic capture of copper was discussed. The recovery rates of Ag, Pd and Bi were 87.53%, 100% and 100%, respectively. Alloy (Cu–Ag–Pd–Bi–Pb) and recyclable slag were obtained. There were three phases of Ag, Cu–Pd and Bi–Pb with the analysis of morphology and composition for the alloy. Then the capture mechanism was revealed. The slag and metal separated due to differences in chemical bonds, surface energy, density and viscosity. The interaction of metals was analyzed through phase diagrams and density functional theory. Pd tended to enter Cu phase. Ag and Cu existed as two phases. Bi and Pb neither entered Ag nor Cu phase based on phase diagrams and formation energy. This study provides a theoretical basis for the application of capture technology in metal enrichment.

Waste multilayer ceramic capacitors (MLCCs) are important secondary resource containing silver and palladium. Current methods of directly recovering precious metals from waste MLCCs have certain deficiencies in terms of environmental protection, recovery efficiency and purity. Capture technology has advantages of high enrichment efficiency and less pollution. Nickel can be used as the capture agent. Therefore, this study proposed a novel approach to recycle silver and palladium from waste nickel-rich MLCCs by in-situ nickel capture technology without adding additional capture agent. SiO2 and Al2O3 were selected as the slag former. Silver and palladium were enriched in the alloy and separated from the slag. The recovery rates of silver and palladium were 98.31% and 98.62% under the optimal conditions. Through the microstructure and component analysis of the alloy, nickel and silver formed two phases and palladium existed in silver phase. Furthermore, the capture mechanism was proposed as the separation process of metals and slag, and alloy formation process. Recycling of slag can be achieved by crystallization. This study proposed a green and efficient process to recycle silver and palladium in waste nickel-rich MLCCs and provided a theoretical basis for capture technology to recycle waste MLCCs.

With the rapid decrease of high-quality coal reserves, utilization of lignite is already a trend in worldwide. Unlike anthracite, lignite often contains special elements Ge, W, As. When these incineration ashes are reused, some resuspended fine particles will inevitably escape into the air, thereby affecting the surrounding environment. The study aims to understand the rule of element distribution of fine particles incineration ash from lignite to avoid the potential risks in future recycling and reuse process of ashes. Hence, we systematically investigated the morphology, element distribution, and chemical species of heavy metals in fine and ultrafine particles. For bottom ash, the large spherical and blocky particles with Dp 10–4.7 were observed in fine particles. The morphology of particles changed to irregular agglomerate particles with Dp 4.7–0.4. The average relative percentage of C, O, Si, and Al in bulk was significantly higher than fine particles, but the heavy metals did not present the rule of enrichment. The residue fraction (F4) of heavy metals were the predominant fraction. For fly ash, some spherical particles of Dp1.1–0.7 and Dp 0.7–0.4 were agglomerated with irregular ultrafine particles. The concentrations of Na, Ge, W, As, Cr, Cd, Pb increased with the decrease of particle sizes. Ca, Al, Mg etc. were acid extractable fraction (F1), and Fe, Pb, As, W, Ni had more proportion of reducible fraction (F2) and oxidizable fraction (F3). A formation of fine particles ashes and release mechanism of heavy metals in incineration process was proposed. Consequently, this study is quite significant for understand rule of element distribution from lignite and future risk prevention from of fine particles.

Cobalt is an increasingly important strategic metal with the emerging of clean energy technologies. China is a resource scarcity country but the world’s largest cobalt consumer. It is of great strategic significance to study the application and current status of cobalt resources for the sustainable development of China’s economy. The objective of this study is to quantitatively investigate the status of cobalt flows from raw materials to waste management in mainland China in 2015 by using material flows analysis (MFA), and to identify the material efficiency and supply security strategy for sustainable use of cobalt. The results show that China’s overall supply of raw materials, chemical production and product manufacture of cobalt in 2015 were 66.5 kt, 62.9 kt and 45.4 kt, respectively. China’s cobalt is highly reliant on imports with a dependency of over 80%. Cobalt outflows were mainly from exports of cobalt chemicals and end-use products. At the end-use product stage, batteries consume the most cobalt, followed by superalloys, cemented carbides and magnets. The emerging of the electric vehicle industry seems to increase the burden of cobalt supply, but also represents huge opportunities for cobalt recycling as a secondary resource. Future efforts on improving material efficiency and ensuring supply security should focus on reducing losses at the beneficiation process by technology upgrades, improving the cobalt recycling rate by integrating cobalt resources into China’s circular economy and environment policy, and establishing national cobalt collection system. This study can provide guidance for future decision-making around the clean production and rational utilization of cobalt resources.

The development of the recycling technologies for waste electrical and electronic equipment (WEEE) has entered a new stage. The WEEE disposing technologies have evolved from simple disassembly, classification and sorting to high value-added utilization technologies. In the past decade, some modified and novel technologies have been developed to recover metals from WEEE. This paper focuses on the recycling of metals from WEEE. The recycling principle, separating process, and optimized operating parameters of existing technologies are summarized and discussed in detail. Based on traditional recycling technologies of WEEE, pyrometallurgical technology and some mild extracting reagent, such as chloride medium, ammonia–ammonium and non-cyanide lixiviants can effectively recycle metals. Compared with the conventional acid and cyanide leaching, they have vast improvements in aspect of environmental protection. More than 98% of Cu and 70% of Au can be extracted. In addition, electrochemical technology, supercritical technology, vacuum metallurgical technology, etc. are also applied to recycle WEEE. The recovery rate of Cu and Pb under optimum conditions is around 84.2% and 89.4% respectively in supercritical water oxidation (SCWO) combined with electrokinetic (EK) technology. Vacuum technology has good environmental performance due to its avoiding discharge of waste water. Other new technologies such as ultrasound technology, mechanochemical technology, and molten salt oxidation technology have also been tried to recycle metals from WEEE. Regrettably, although many endeavors to develop recycling technologies have been attempted, these technologies are still relatively single and limited because WEEE is a complex system. Hence, the shortages and defects of each technology are discussed from the perspective of technological promotion and environmental protection. Furthermore, the outlook about the further development of recycling technologies for metals from WEEE is presented.

During the process of treating and recycling Municipal Solid Waste Incinerators (MSWIs) fly ash, polychlorinated dibenzo-p-dioxins (PCDD/Fs) and polychlorinated dibenzofurans (dl-PCBs) in fly ash may potentially mobilize in the atmosphere and be widely distributed in the environment because of the inevitable re-suspension. Thus, this work presents the distributions of PCDD/Fs and dl-PCBs in inhalable coarse particles (Dp10-2.5 (particle diameter in μm)), fine particles (Dp

Recycling palladium from waste multilayer ceramic capacitors (MLCCs) has attracted much attention recently. The existing recycling methods have many shortcomings including pollution, low purity and recovery rate of palladium. This study proposed to separate and purify palladium from waste MLCCs by electrodeposition technology efficiently based on the difference in reduction potentials of metal ions in HNO3 solution. The electrochemical behavior of palladium at titanium electrode was studied, which showed higher concentration of HNO3 decreased the peak current of palladium and the corresponding potential shifted negatively. Besides, a mathematical model was established to describe the electrodeposition process at different agitation speeds. The diffusion coefficient and thickness of diffusion region were calculated. Furthermore, the optimal conditions for electrodeposition were determined as applied potential of −0.25 V, agitation speed of 240 rpm and HNO3 concentration of 0.5 M, under which high-purity palladium (>99%) was recovered with the recovery rate of 99.02%. The morphology analysis showed the electrodeposited palladium was nanoparticles. Finally, an efficient process combining enrichment and electrodeposition for recycling waste MLCCs was proposed in an environmentally friendly way. The results of this study can provide reliable information for efficient recycling of palladium resource from waste MLCCs.

Recycling waste multilayer ceramic capacitors (MLCCs) is significant for environmental protection and resource recovery, which contain rich precious metals including palladium and silver. The existing recycling methods have many shortcomings such as environmental pollution, low recovery efficiency and low purity of precious metals. In view of the special structure of MLCCs and low content of precious metals per unit mass, a novel approach of enrichment for recovering palladium and silver from waste MLCCs by eutectic capture process of copper was proposed, in which process precious metals were separated and enriched for subsequent recovery. The recovery rates of palladium and silver reached 100 % and 87.53 %, respectively under the optimal condition. And the enrichment multiples of palladium and silver were 13.16 and 7.37. The Cu-Pd-Ag alloy was formed in the capture process, of which palladium and copper formed Cu-Pd solid solution, while silver was a separate phase through the analysis of SEM-EDS, XPS and XRD. Besides, the molten residue can be reused to prepare glass-ceramics. Finally, the mechanism was analyzed through thermodynamics, which was divided into two processes: migration of precious metals and alloy formation. This study provides a highly efficient and environmentally friendly method for recycling precious metals from waste MLCCs.

Proper treatment of mining wastewaters is critically important to minimize contamination by heavy metals contained in those wastewaters. Herein, a bioelectrochemically-assisted electrodeposition (BES-EDP) system was developed and investigated for selective removal and recovery of Pb and Zn from a mimicked smelting wastewater. It was observed that those two metals were reduced at different cathodic potentials and electrodeposition time. At a cathodic potential of −0.75 V vs. Ag/AgCl, 98.5 ± 1.4 % of Pb was recovered after 10 h of reaction while there was little Zn deposition. Increasing the cathodic potential to −1.2 V could achieve 98.7 ± 0.7 % of Zn with the electrodeposition time of 6 h. The composition of the deposits confirmed the results from solution analysis and metal oxides were also formed during metal reduction. The diffusion impedance was much higher than the charge transfer resistance, suggesting that the diffusion process was a rate limiting step for electrodeposition. The diffusion process was verified by chronoamperometry with a good fit in Cottrell equation. The electrodeposition equilibrium constant k0 was determined as 3.76 cm s−1. Those results have demonstrated the feasibility of using bioelectricity to assist with selective metal recovery and warrant further investigation of technologies for sustainable management of mining wastewaters.

Since indium (In) was the most valuable resource in waste liquid crystal panels (LCDs), most researches only focused on preliminary recovery of In, while those coexisting metal elements (Cu, Sn, Al) raised little concern. This could lead to waste of resources, potential risk of heavy metal pollution, and also complexation of following In purification procedures. Besides, current hydrometallurgy processes for In purification are complicated, consume more reagents and generate more wastewater. Therefore, this research applied simple acid leaching and two-step electrodeposition for In-Sn and In-Cu-Al separation with minimum waste generation and input. Considering the special doping structure of indium-tin oxide (ITO), feasibility for concurrent In leaching and Sn precipitation was explored based on the unique Sn species’ dissolution and precipitation behavior during acid leaching. Since the behavior of Sn was more sensitive to acidity and temperature, 97.07% of Sn removal and 99.25% of In recovery could be achieved using 1 mol/L H2SO4 at 70 ℃ for 1 h. A specific kinetic model depicting In leaching in thin ITO film situation was developed referring to avrami equation. Then, the application of two-step electrodeposition enabled 95.32% extraction of Cu and deposition of In with a purity over 99 wt% at respective potential.

In recent years, the demand for cobalt is increasing dramatically because of its critical role in clean energy technologies globally. China has been a leading consumer and refiner of cobalt, and meanwhile is a scarce country of cobalt resources. Its growing domestic demand may impose significant pressure on sustainable development of cobalt resources and make it potentially vulnerable to supply shortages. Aiming at identifying the potential opportunities for improving cobalt resource efficiency and supply security, dynamic stocks and flows analysis was applied to track and quantify the anthropogenic cobalt cycles in mainland China such as its production, use, and trade over the years 1994–2016. The analysis results showed that the production, trade and consumption of cobalt resources in mainland China grew significantly in the past two decades. China has been a net importer of cobalt raw materials but a net exporter of cobalt chemicals and final cobalt-containing products, indicating that China is bearing increasing environmental burden of processing cobalt product for other economies. The in-use stock of cobalt has reached over 140,000 t by 2016, of which the cobalt contained in in-use batteries accounted for approximately 77%. The recycling rate of end-of-life (Eol) products kept at a very low level, less than 20% in the past decades. The cumulative domestic demand of cobalt is projected to exceed China's reserve base by around 2022 based on scenario analysis. Furthermore, some recommendations were proposed for the sustainable development of China's cobalt resource, including the improvement of national cobalt reserve system, development of diversified resource supply channel and the establishment of a recycling system and associated regulations for cobalt-containing obsolete products.

Integrated circuits (IC), a kind of widely used electronic component, is paid great attention to recover valuable materials and remove hazardous materials after being discarded. However, refractory epoxy resin as packaging material is tightly covered on waste IC. It is difficult to remove epoxy resin and recover metals environmentally friendly by traditional methods. In this study, decomposition of epoxy resin from waste IC in supercritical water (SCW) was investigated. The epoxy resin could be efficiently decomposed under SCW condition. High temperature and long operation time of SCW treatment was positive for decomposition efficiency. The main decomposition intermediates and products were phenol and its derivatives. The decomposition mechanism of epoxy resin in supercritical water belongs to complex free radical reaction. Seven proposed pathways for the formation of key intermediates were investigated, with the kinetic and thermodynamic parameters obtained by density functional theory calculations. The analyzation provided assistance in the optimization of SCW treatment. Epoxy resin conversion rate could reach 95.51% under the condition of 500 ℃, 23 MPa and 90 min, then metals could be easily separated and recovered from solid residue. Thus, SCW treatment presents an efficient and green process for the recycle of waste IC.

In worldwide, more than half of palladium is used to produce exhaust catalysts in the automotive industry. However, the recycling of palladium is a great challenge due to its low content and chemical inertness. A novel approach for recovery of palladium in spent catalyst material from automobile by a capture process of eutectic copper was proposed. In the capture process, copper is used as capture agent. The palladium is concentrated and entered the alloy phase under a certain temperature. Because the different density of the smelting slag and alloy, they are layered to realize the separation of the metals. The results were summarized as follows: (i) palladium in the spent catalyst material was captured by copper with 97% of recovery rate of Pd under optimal condition; (ii) the palladium atoms replaced to copper in Cu crystal to form Cu–Pd alloy by analysis of EDS, XPS and first principles calculation; (iii) the carrier of cordierite from spent catalyst material achieved glass transition and prepared the glass ceramics after the capture; (iv) a thermodynamic mechanism of the capture process of copper was proposed. Firstly, under molten state of the copper phase and the slag phase, palladium can be transferred from the slag phase to the copper phase when ΔEsurface = 2πrΔS1 (σpalladium-copper-σpalladium-slag-σslag-copper cosα)

During the pretreatment and recycling processes, the re-suspended dust from municipal solid waste incinerator (MSWI) fly ash might pose a significant health risk to onsite workers due to its toxic heavy metal content. In this work, the morphological and mineralogical characteristics of fly ash in different particle sizes are presented. The concentrations of seven trace elements (Zn, Pb, Cu, Cd, Cr, Fe and Mn) in these samples were determined. The results show that volatile metals, such as Zn, Pb, Cu and Cd, were easily concentrated in the fine particles, especially in Dp2.5-1 and Dp1, with soluble and exchangeable substances as the main chemical species. The health risk assessment illustrated that the cumulative hazard indexes for non-carcinogenic metals in Dp10-5, Dp5-2.5, Dp2.5-1, and Dp1 were 1.69, 1.41, 1.78 and 2.64, respectively, which were higher than the acceptable threshold values (1.0). The cumulative carcinogenic risk was also higher than the threshold value (10−6). For the onsite workers, the relatively apparent non-carcinogenic and carcinogenic effects were from Pb and Cr, respectively. The above findings suggest that fine-grained fly ash contained a considerable amount of heavy metals and exhibited a great health risk.

Recycling of waste liquid crystal display (LCD) panels is an urgent task with the rapid expanding LCD market. However, as important composition of LCD panels, the treatment of liquid crystal is seldom concerned for its low concentration. In present study, a stripping product enriched liquid crystal and indium is gained by mechanical stripping process, in which liquid crystal is enriched from 0.3wt.% to 53wt.% and indium is enriched from 0.02wt.% to 7.95wt.%. For the stripping product, liquid crystal should be removed before indium recovery because (a) liquid crystal will hinder indium recycling; (b) liquid crystal is hazardous waste. Hence, an effective and green approach by vacuum pyrolysis is proposed to treat liquid crystal in the stripping product. The results are summarized as: (i) From the perspective of apparent activation energy, the advantages of vacuum pyrolysis is expounded according to kinetic analysis. (ii) 89.10wt.% of liquid crystal is converted and the content of indium in residue reaches 14.18wt.% under 773K, 15min and system pressure of 20Pa. This study provides reliable information for further industrial application and an essential pretreatment for the next step of indium recycling.