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.
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•Current recovery technologies for metals in WEEE are summarized and reviewed.•Defects and shortages of existing technologies are analyzed in detail.•Suggestions for technology promotion and environmental protection are presented.
•The status recycling methods for the precious metal recovery from the waste print circuit board are reviewed.•The effects of environment by the improper recover methods are analyzed.•The bottlenecks ...in precious metals recycling system are proposed.•Addressing future metal recycling challenges and recommendations are presented.
Nowadays, rapid economic growth, continuous technological innovation and the improvement of living standards have result in large amounts of waste electric and electronic equipment (WEEE). Amongst all these WEEE, waste printed circuit boards (WPCBs) are considered as the most valuable components due to precious metals contained. Previous studies found that the presence of precious metals are richer in WPCBs than in typical metal mines, which are driven recycling precious metals from WPCBs to a profitable business without proper pollution controls in developing countries. However, recovering precious metals from WPCBs is a challenge because WPCBs are both valuable and harmful simultaneously, which are caused by their complex materials makeup. Hence, the proper technologies to recycle metals from WPCBs without negative effects to the environment and human health are urgent and essential. In this article, the current metals recycling technologies from WPCBs are reviewed. Then, an integrated technological route, including metals enrichment and precious metals recovery, is proposed. Finally, in order to promote the development of metals (precious metals) recovery from WPCBs, some improvements and recommendations in techniques and the future trend are also put forward.
This paper focuses on current progress of supercritical fluid (SCF) technology for e-waste treatment through reviewing characteristics and challenges of existing technologies. With the high-speed ...development of science and technology, electronic and electric equipment continually upgrades and updates, which bring a series of problems on dealing with the e-waste. The most serious problem is that the harmless disposal of halogen flame retardants and refractory polymers in e-waste is difficult. In recent years, the recycling technologies for e-waste has entered a new stage through tireless efforts of the researchers. Compared with the common recycling technologies like pyrolysis and acid leaching, SCF technologies have great advantages in the field of environment, without air or water pollution risks. Supercritical fluids such as supercritical water and supercritical carbon dioxide are sustainable green solvents as well as highly promising reaction mediums. The principles, operation procedures and optimized parameters of SCF treatment are discussed and summarized in this paper. Furthermore, SCF technologies applied in the field of e-waste recycling have also achieved satisfactory results. Significant progress has been made in the detoxification of e-waste and removal of refractory polymers by SCF technologies. The dechlorination efficiency and debromination efficiency has been reported to be over 90%. The base metals, the precious metals, and other inorganic materials were all reported to be recovered from e-waste by SCF technologies with a recovery rate of more than 93%. Common challenges in SCF process like corrosion and salt precipitation also came up with some propose solutions. Hence, the application of SCF technology in e-waste treatment demonstrates green reaction and resource recovery with significant economy and environment perspectives.
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•Current supercritical fluid technology for e-waste treatment are reviewed in detail.•Principles, advantages and disadvantages of SCF technology are investigated.•Challenges and proposed solutions are discussed.•New approaches and future perspectives are proposed.
Lithium is a rare metal because of geographical scarcity and technical barrier. Recycling lithium resource from spent lithium ion batteries (LIBs) is significant for lithium deficiency and ...environmental protection. A novel approach for recycling lithium element as Li2CO3 from spent LIBs is proposed. First, the electrode materials preobtained by mechanical separation are pyrolyzed under enclosed vacuum condition. During this process the Li is released as Li2CO3 from the crystal structure of lithium transition metal oxides due to the collapse of the oxygen framework. An optimal Li recovery rate of 81.90% is achieved at 973 K for 30 min with a solid-to-liquid ratio of 25 g L–1, and the purity rate of Li2CO3 is 99.7%. The collapsed mechanism is then presented to explain the release of lithium element during the vacuum pyrolysis. Three types of spent LIBs including LiMn2O4, LiCoO2, and LiCo x Mn y Ni z O2 are processed to prove the validity of in situ recycling Li2CO3 from spent LIBs under enclosed vacuum condition. Finally, an economic assessment is taken to prove that this recycling process is positive.
•NMFs from WEEE were treated by incineration or land filling in the past.•Environmental risks such as heavy metals and BFRs will be the major problems during the NMFs recycling processes.•Methods and ...technologies of recycling the two types of NMFs from WEEE, plastics, glasses are reviewed.•More environmental impact assessment should be carried out to evaluate the environmental risks of the recycling products.
The world’s waste electrical and electronic equipment (WEEE) consumption has increased incredibly in recent decades, which have drawn much attention from the public. However, the major economic driving force for recycling of WEEE is the value of the metallic fractions (MFs). The non-metallic fractions (NMFs), which take up a large proportion of E-wastes, were treated by incineration or landfill in the past. NMFs from WEEE contain heavy metals, brominated flame retardant (BFRs) and other toxic and hazardous substances. Combustion as well as landfill may cause serious environmental problems. Therefore, research on resource reutilization and safe disposal of the NMFs from WEEE has a great significance from the viewpoint of environmental protection. Among the enormous variety of NMFs from WEEE, some of them are quite easy to recycle while others are difficult, such as plastics, glass and NMFs from waste printed circuit boards (WPCBs). In this paper, we mainly focus on the intractable NMFs from WEEE. Methods and technologies of recycling the two types of NMFs from WEEE, plastics, glass are reviewed in this paper. For WEEE plastics, the pyrolysis technology has the lowest energy consumption and the pyrolysis oil could be obtained, but the containing of BFRs makes the pyrolysis recycling process problematic. Supercritical fluids (SCF) and gasification technology have a potentially smaller environmental impact than pyrolysis process, but the energy consumption is higher. With regard to WEEE glass, lead removing is requisite before the reutilization of the cathode ray tube (CRT) funnel glass, and the recycling of liquid crystal display (LCD) glass is economically viable for the containing of precious metals (indium and tin). However, the environmental assessment of the recycling process is essential and important before the industrialized production stage. For example, noise and dust should be evaluated during the glass cutting process. This study could contribute significantly to understanding the recycling methods of NMFs from WEEE and serve as guidance for the future technology research and development.
Metals are vital raw materials for industrial production and are consuming rapidly as the development of the world. People are always enthusiasm about searching new metal resource even if the results ...are more and more disappointed. Thus, return of consumed metals is crucial for substantial development of the world. E-waste was rapidly generated together with the innovation of electronic industry. E-waste is called urban mine and metals accounted for above 70wt%. Recover e-waste is significant for returning metals. However, because of employing crude recovery technology, serious environmental pollution had been generated in the places of recovering e-waste. Environment-friendly and efficient technology has been the pressing demand in the return of metals from e-waste. This paper reported how to construct environment-friendly return road of metals from e-waste. The road was advised to be constructed by physical technologies of crushing, magnetic separation, eddy current separation, corona electrostatic separation, vacuum metallurgy separation and et al. For improving the efficient of the return road, the finished and future works of each technology were presented and proposed. For improving the added value of the recovered metals, further processing was planned in the return road. Additionally, some efforts on environmental friendly construction of the return road were presented. At last, three constructed return roads of metals (above 88wt% metals were recovered) from e-waste were reported. We expect this paper can contribute to the treatment of e-waste and the development of cyclic economy.
Many countries have gained benefits through the solar cells industry due to its high efficiency and nonpolluting power generation associated with solar energy. Accordingly, the market of solar cell ...modules is expanding rapidly in recent decade. However, how to environmentally friendly and effectively recycle waste solar cell modules is seldom concerned. Based on nitrogen pyrolysis and vacuum decomposition, this work can successfully recycle useful organic components, glass, and gallium from solar cell modules. The results were summarized as follows: (i) nitrogen pyrolysis process can effectively decompose plastic. Organic conversion rate approached 100% in the condition of 773 K, 30 min, and 0.5 L/min N2 flow rate. But, it should be noted that pyrolysis temperature should not exceed 773 K, and harmful products would be increased with the increasing of temperature, such as benzene and its derivatives by GC-MS measurement; (ii) separation principle, products analysis, and optimization of vacuum decomposition were discussed. Gallium can be well recycled under temperature of 1123 K, system pressure of 1 Pa and reaction time of 40 min. This technology is quite significant in accordance with the “Reduce, Reuse, and Recycle Principle” for solid waste, and provides an opportunity for sustainable development of photovoltaic industry.
Over the past 30 years, China has been suffering from negative environmental impacts from distempered waste electrical and electronic equipments (WEEE) recycling activities. For the purpose of ...environmental protection and resource reusing, China made a great effort to improve WEEE recycling. This article reviews progresses of three major fields in the development of China’s WEEE recycling industry: legal system, formal recycling system, and advanced integrated process. Related laws concerning electronic waste (e-waste) management and renewable resource recycling are analyzed from aspects of improvements and loopholes. The outcomes and challenges for existing formal recycling systems are also discussed. The advantage and deficiency related to advanced integrated recycling processes for typical e-wastes are evaluated respectively. Finally, in order to achieve high disposal rates of WEEE, high-quantify separation of different materials in WEEE and high added value final products produced by separated materials from WEEE, an idea of integrated WEEE recycling system is proposed to point future development of WEEE recycling industry.
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) <0. Then, palladium atom replaced the copper atom in the Cu crystal to form the Cu–Pd alloy when the values of ΔH and Ecoh<0.
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•Pd in the spent catalyst was captured by eutectic Cu with recovery rate of 97%.•The carrier in spent catalyst with certain additives can be fused into glass phase.•A thermodynamic mechanism of the capture process of Cu for Pd was proposed.•No waste residue and wastewater are produced in whole capture process.
In recent era, more and more electric and electronic equipment wastes (e-wastes) are generated that contain both toxic and valuable materials in them. Most studies focus on the extraction of valuable ...metals like Au, Ag from e-wastes. However, the recycling of metals such as Pb, Cd, Zn, and organics has not attracted enough attentions. Vacuum metallurgy separation (VMS) processes can reduce pollution significantly using vacuum technique. It can effectively recycle heavy metals and organics from e-wastes in an environmentally friendly way, which is beneficial for both preventing the heavy metal contaminations and the sustainable development of resources. VMS can be classified into several methods, such as vacuum evaporation, vacuum carbon reduction and vacuum pyrolysis. This paper respectively reviews the state-of-art of these methods applied to recycling heavy metals and organics from several kinds of e-wastes. The method principle, equipment used, separating process, optimized operating parameters and recycling mechanism of each case are illustrated in details. The perspectives on the further development of e-wastes recycling by VMS are also presented.
