Lu Zhan

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.

Novel recycle technology for recovering rare metals (Ga, In) from waste light-emitting diodes.

This work develops a novel process of recycling rare metals (Ga, In) from waste light-emitting diodes using the combination of pyrolysis, physical disaggregation methods and vacuum metallurgy separation. Firstly, the pure chips containing InGaN/GaN are adopted to study the vacuum separation behavior of rare metals, which aims to provide the theoretical foundation for recycling gallium and indium from waste light-emitting diodes. In order to extract the rare-metal-rich particles from waste light-emitting diodes, pyrolysis and physical disaggregation methods (crushing, screening, grinding and secondly screening) are studied respectively, and the operating parameters are optimized. With low boiling points and high saturation vapor pressures under vacuum, gallium and indium are separated from rare-metal-rich particles by the process of evaporation and condensation. By reference to the separating parameters of pure chips, gallium and indium in waste light-emitting diodes are recycled with the recovery efficiencies of 93.48% and 95.67% under the conditions as follows: heating temperature of 1373 K, vacuum pressure of 0.01-0.1 Pa, and holding time of 60 min. There are no secondary hazardous materials generated in the whole processes. This work provides an efficient and environmentally friendly process for recycling rare metals from waste light-emitting diodes.

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.

Products derived from waste plastics (PC, HIPS, ABS, PP and PA6) via hydrothermal treatment: Characterization and potential applications

In this study, hydrothermal method was applied for the treatment of five typical waste plastics (PC, HIPS, ABS, PP and PA6). The hydrothermal products of oils and solid residues were analyzed for the product slate and combustion behaviors. Some predominant chemical feedstock were detected in the oils, such as phenolic compounds and bisphenol A (BPA) in PC oils, single-ringed aromatic compounds and diphenyl-sketetons compounds in HIPS and ABS oils, alkanes in PP oils, and caprolactam (CPL) in PA6 oils. The hydrothermal solid residues were subjected to DSC analysis. Except the solid residues of PA6, all the solid residues had enormous improvement on the enthalpy of combustion. The solid residues of PC had the maximum promotion up to 576.03% compared to the raw material. The hydrothermal treatment significantly improved the energy density and facilitated effective combustion. Meanwhile, the glass fiber was recovered from the PA6 plastics. In addition, the combustion behaviors of the uplifting residues were investigated to provide the theoretical foundation for further study of combustion optimization. All the results indicated that the oils of waste plastics after hydrothermal treatment could be used as chemical feedstock; the solid residues of waste plastics after hydrothermal treatment could be used as potentially clean and efficient solid fuels. The hydrothermal treatment for various waste plastics was verified as a novel waste-to-energy technique.

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.