Zhenming Xu

Separating and recovering Pb from copper-rich particles of crushed waste printed circuit boards by evaporation and condensation.

Waste printed circuit boards (WPCBs) are treated by crushing and electrostatic separation to obtain the copper-rich particles. However, the copper-rich particles contain a certain content of solder, which may cause Pb contamination if improperly treated. The separation behaviors of Pb from single solder and solder mixed with Cu particles under vacuum are studied in this work. Due to the presence of Cu particles in the copper-rich particles, it becomes much easier to separate Pb from mixed particles than from single solder. On the basis of the experiments, the rules and phenomena different from previous studies are concluded, including the multilayer evaporation effect, the formation of Cu-Sn intermetallic compound and so on. Mechanisms of these phenomena are also explored. Pb is separated and recovered from copper-rich particles of crushed WPCBs at 1123 K for 90 min under 0.1-1 Pa. The metals including Cu, Pb, Sn in WPCBs are all efficiently recovered. This work enriches separating rules for recovering Pb by evaporation and condensation, and also points out an efficient and promising method for recovering toxic heavy metals from WPCBs.

The status and development of treatment techniques of typical waste electrical and electronic equipment in China: A review

A large quantity of waste electrical and electronic equipment (WEEE) is being generated because technical innovation promotes the unceasing renewal of products. China’s household appliances and electronic products have entered the peak of obsolescence. Due to lack of technology and equipment, recycling of WEEE is causing serious environment pollution. In order to achieve the harmless disposal and resource utilization of WEEE, researchers have performed large quantities of work, and some demonstration projects have been built recently. In this paper, the treatment techniques of typical WEEE components, including printed circuit boards, refrigerator cabinets, toner cartridges, cathode ray tubes, liquid crystal display panels, batteries (Ni–Cd and Li-ion), hard disk drives, and wires are reviewed. An integrated recycling system with environmentally friendly and highly efficient techniques for processing WEEE is proposed. The orientation of further development for WEEE recycling is also proposed.

Environmental friendly crush-magnetic separation technology for recycling metal-plated plastics from end-of-life vehicles.

Metal-plated plastics (MPP), which are important from the standpoint of aesthetics or even performance, are increasingly employed in a wide variety of situations in the automotive industry. Serious environmental problems will be caused if they are not treated appropriately. Therefore, recycling of MPP is an important subject not only for resource recycling but also for environmental protection. This work represents a novel attempt to deal with the MPP. A self-designed hammer crusher was used to liberate coatings from the plastic substrate. The size distribution of particles was analyzed and described by the Rosin-Rammler function model. The optimum retaining time of materials in the crusher is 3 min. By this time, the liberation rate of the materials can reach 87.3%. When the density of the suspension is 31,250 g/m(3), the performance of liberation is the best. Two-step magnetic separation was adopted to avoid excessive crushing and to guarantee the quality of products. Concerning both the separation efficiency and grade of products, the optimum rotational speed of the magnetic separator is 50-70 rpm. On the basis of the above studies about the liberating and separating behavior of the materials, a continuous recycling system (the technology of crush-magnetic separation) is developed. This recycling system provides a feasible method for recycling MPP efficiently, economically, and environmentally.

Electrostatic Separation for Recycling Conductors, Semiconductors, and Nonconductors from Electronic Waste

Electrostatic separation has been widely used to separate conductors and nonconductors for recycling e-waste. However, the components of e-waste are complex, which can be classified as conductors, semiconductors, and nonconductors according to their conducting properties. In this work, we made a novel attempt to recover the mixtures containing conductors (copper), semiconductors (extrinsic silicon), and nonconductors (woven glass reinforced resin) by electrostatic separation. The results of binary mixtures separation show that the separation of conductor and nonconductor, semiconductor and nonconductor need a higher voltage level while the separation of conductor and semiconductor needs a higher roll speed. Furthermore, the semiconductor separation efficiency is more sensitive to the high voltage level and the roll speed than the conductor separation efficiency. An integrated process was proposed for the multiple mixtures separation. The separation efficiency of conductors and semiconductors can reach 82.5% and 88%, respectively. This study contributes to the efficient recycling of valuable resources from e-waste.

Management strategies on the industrialization road of state-of- the-art technologies for e-waste recycling: the case study of electrostatic separation—a review

Electronic waste (e-waste) management is pressing as global production has increased significantly in the past few years and is rising continuously at a fast rate. Many countries are facing hazardous e-waste mountains, most of which are disposed of by backyard recyclers, creating serious threats to public health and ecosystems. Industrialization of state-of-the-art recycling technologies is imperative to enhance the comprehensive utilization of resources and to protect the environment. This article aims to provide an overview of management strategies solving the crucial problems during the process of industrialization. A typical case study of electrostatic separation for recycling waste printed circuit boards was discussed in terms of parameters optimization, materials flow control, noise assessment, risk assessment, economic evaluation and social benefits analysis. The comprehensive view provided by the review could be helpful to the progress of the e-waste recycling industry.

Separating Criterion of Pb, Cd, Bi and Zn from Metallic Particles of Crushed Electronic Wastes by Vacuum Evaporation

The crushing process is usually adopted during the treatment of electronic wastes. Mixed metallic particles can be obtained after several kinds of separation methods. Most of the metals exist as elementary substances and their vapor pressure is quite different. For the metals with high vapor pressure, vacuum metallurgy separation is used to separate these metals. However, the vacuum evaporation rule of metallic particles is different from the traditional theory. Satisfactory parameters for separating these metallic particles could not be obtained merely according to the boiling point difference between metals. In this paper, the evaporation kinetics and mechanism of single metallic particles (Pb, Zn, Cd, and Bi) are investigated first. Then the criterion of separating these metals from each other is obtained. Under the instruction of separation criterion, different kinds of mixed metallic particles are successfully separated with the separation efficiency of the target metal more than 90 wt%. This study provides theoretical foundations for separating the heavy metals with high vapor pressure from e-wastes.

Disposal of waste computer hard disk drive: data destruction and resources recycling.

An increasing quantity of discarded computers is accompanied by a sharp increase in the number of hard disk drives to be eliminated. A waste hard disk drive is a special form of waste electrical and electronic equipment because it holds large amounts of information that is closely connected with its user. Therefore, the treatment of waste hard disk drives is an urgent issue in terms of data security, environmental protection and sustainable development. In the present study the degaussing method was adopted to destroy the residual data on the waste hard disk drives and the housing of the disks was used as an example to explore the coating removal process, which is the most important pretreatment for aluminium alloy recycling. The key operation points of the degaussing determined were: (1) keep the platter plate parallel with the magnetic field direction; and (2) the enlargement of magnetic field intensity B and action time t can lead to a significant upgrade in the degaussing effect. The coating removal experiment indicated that heating the waste hard disk drives housing at a temperature of 400 °C for 24 min was the optimum condition. A novel integrated technique for the treatment of waste hard disk drives is proposed herein. This technique offers the possibility of destroying residual data, recycling the recovered resources and disposing of the disks in an environmentally friendly manner.

Real-time monitoring system for improving corona electrostatic separation in the process of recovering waste printed circuit boards

Although corona electrostatic separation is successfully used in recycling waste printed circuit boards in industrial applications, there are problems that cannot be resolved completely, such as nonmetal particle aggregation and spark discharge. Both of these problems damage the process of separation and are not easy to identify during the process of separation in industrial applications. This paper provides a systematic study on a real-time monitoring system. Weight monitoring systems were established to continuously monitor the separation process. A Virtual Instrumentation program written by LabVIEW was utilized to sample and analyse the mass increment of the middling product. It includes four modules: historical data storage, steady-state analysis, data computing and alarm. Three kinds of operating conditions were used to verify the applicability of the monitoring system. It was found that the system achieved the goal of monitoring during the separation process and realized the function of real-time analysis of the received data. The system also gave comprehensible feedback on the accidents of material blockages in the feed inlet and high-voltage spark discharge. With the warning function of the alarm system, the whole monitoring system could save the human cost and help the new technology to be more easily applied in industry.

Assessment of heavy metals exposure, noise and thermal safety in the ambiance of a vacuum metallurgy separation system for recycling heavy metals from crushed e-wastes

Vacuum metallurgy separation (VMS) is a technically feasible method to recover Pb, Cd and other heavy metals from crushed e-wastes. To further determine the environmental impacts and safety of this method, heavy metals exposure, noise and thermal safety in the ambiance of a vacuum metallurgy separation system are evaluated in this article. The mass concentrations of total suspended particulate (TSP) and PM10 are 0.1503 and 0.0973 mg m−3 near the facilities. The concentrations of Pb, Cd and Sn in TSP samples are 0.0104, 0.1283 and 0.0961 μg m−3, respectively. Health risk assessments show that the hazard index of Pb is 3.25 × 10−1 and that of Cd is 1.09 × 10−1. Carcinogenic risk of Cd through inhalation is 1.08 × 10−5. The values of the hazard index and risk indicate that Pb and Cd will not cause non-cancerous effects or carcinogenic risk on workers. The noise sources are mainly the mechanical vacuum pump and the water cooling pump. Both of them have the noise levels below 80 dB (A). The thermal safety assessment shows that the temperatures of the vacuum metallurgy separation system surface are all below 303 K after adopting the circulated water cooling and heat insulation measures. This study provides the environmental information of the vacuum metallurgy separation system, which is of assistance to promote the industrialisation of vacuum metallurgy separation for recovering heavy metals from e-wastes.

Vacuum Separation Behavior of Pb from Copper-Rich Particles of Crushed E-Wastes

Due to lack of proper treatment methods, Pb pollution caused by improper treatment of electronic wastes (e-waste) has been attracting increasing attention. This paper investigates the separation behavior of Pb in the presence of Cu and other metallic particles (Cd, Bi, and Zn), in order to separate and recover various metals effectively from the copper-rich particles of crushed e-wastes. Vacuum metallurgy separation method is adopted to separate and recover Pb from the copper-rich particles of crushed e-wastes. Due to the variety and complexity of metals in copper-rich particles, this paper studies the effects of Cu, Cd, Bi, and Zn on vacuum separating and recycling of Pb. It is found that Cu particles have both a positive dispersing and a negative blocking effect on Pb evaporation. Cd can be evaporated preferentially, and then Pb can be subsequently separated for their huge vapor pressure gap. The formation of Pb-Bi alloy with a low vapor pressure makes the separation of Pb more difficult. As a result of different condensation characteristics, Pb and Zn can be evaporated together from Cu particles, and then be respectively condensed on different positions as pure Pb and Zn.