电子废弃物回收镓技术的研究进展

含镓电子废弃物通常可分为废弃电子产品及其生产过程中产生的含镓废料两类,由于伴生重金属、易燃有机物等有害物质而具有环境和资源的双重属性,其资源循环近年来受到广泛关注.镓在电子废弃物中主要以化合物形式赋存,具有伴生元素多、物理化学性质稳定等特征.本工作系统梳理了含镓电子废弃物回收处理现状,总结了湿法冶金、火法冶金及生物冶金...     

MOCVD生产废料中镓、铟提取工艺及其动力学研究

近年来，LED以其节能及环境友好等特性被广泛运用于各类照明领域。作为LED产品关键部件，采用金属有机气相沉积(MOCVD)生产外延片过程产生大量的生产废料。随着LED行业的快速发展，绿色、清洁回收MOCVD生产废料备受关注。本研究以硫酸为浸出剂，重点研究了MOCVD生产废料中Ga和In元素的浸出行为和浸出动力学。通过对浸出试剂种类、H2SO4浓度、固液比、浸出温度和浸出时间等参数的过程优化，在H2SO4浓度3 mol/L、固液比50 g/L、温度80℃、反应2 h的最佳工艺条件下，Ga和In的浸出率仅为67.50%和91.46%。动力学研究表明，在293.15~333.15 K温度范围内，Ga和In的浸出动力学符合收缩核模型，浸出过程受表面化学反应和外扩散混合控制。同时，XRD和SEM-EDS结果也印证了符合收缩核模型。在293.15~333.15 K温度范围内，Ga和In的浸出活化能分别为25.7和21.7 kJ/mol。基于对Ga和In浸出行为的动力学分析，提出并验证了MOCVD生产废料强化焙烧-浸出工艺的可行性。研究结果表明，强化焙烧-酸浸工艺可以使Ga和In的浸出率分别由67.50%和91.46%提升至88.27%和98.32%，并得到了氧化镓副产品。本研究结果有望为MOCVD生产废料的工业化资源循环提供基础数据支撑和新路径选择。     

Statistical Evaluation of Factors Affecting the Leaching Process of Waste Electrical and Electronic Equipment using Sodium Persulfate

Recycling of waste electrical and electronic equipment (WEEE) is important not only to reduce the amount of waste requiring treatment, but also to promote the recovery of valuable materials. Implementation of the European Directive on WEEE and recycling targets imposed in the European Union will require new processes to be developed and applied to recover metals from WEEE. This study aims to provide an alternative process for the dissolution of metals from WEEE which contains Cu and Zn based on our previous research. The effects of leaching parameters, such as temperature, Na₂S₂O₈ concentration, and leaching time, were separately investigated on leaching of copper, zinc, and brass (alloy composition ?35% zinc and 65% copper) in Na₂S₂O₈ solution (0.1, 0.2 and 0.3 M). Box–Behnken experimental design (BBD) method was used to determine the number and the condition of necessary leaching experiments. Statistical analysis of variance (ANOVA) was performed to see whether process parameters such as leaching time, temperature, and oxidant concentration are statistically significant or not on the leaching performance. Results show leaching time as the most influential factor in the dissolution process, for the first six models. Two extended models have been developed to optimize the parameters of the investigated process. In these models, we consider the metal composition as a model input next to the earlier investigated parameters. Optimal condition for maximum copper and zinc dissolution in Na₂S₂O₈ environment can be found for parameter values: temperature 45°C, oxidant concentration 0.1 M and leaching time 35 min.     

Preparation of Alkali‐Activated Slag‐Fly Ash‐Metakaolin Hydroceramics for Immobilizing Simulated Sodium‐Bearing Waste

The radioactive sodium‐bearing waste (SBW), which is mainly generated from spent nuclear fuel reprocessing activities, requires to be stabilized into a solid form for geological disposal. In this study, the alkali‐activated slag–fly ash–metakaolin hydroceramic (ASFMH) waste form for solidifying simulated SBW (S‐SBW) was prepared by hydrothermal process. The mineralogy, morphology, composition, compressive strength, and chemical durability of ASFMH waste form were investigated. It is shown that crystalline analcime phase was formed in the hydration products of ASFMH waste form after alkaline activation and hydrothermal process. The introducing of S‐SBW not only contributed to forming crystalline zeolite phase but also reduced the temperature and time for forming zeolite phase. Importantly, the cations including simulated radionuclides Sr²⁺ and Cs⁺ in S‐SBW could be immobilized as cationic components in the channels or voids of zeolitic structure during the formation of analcime phase. Moreover, when the loading content of S‐SBW in ASFMH waste form was 37.5 wt%, ASFMH waste form still exhibited superior mechanical strength, which was higher than 24 MPa. The product consistency test leaching results showed that ASFMH waste form possessed superior chemical durability after leaching test carried out for 7 d. It is suggested that ASFMH waste form is a promising candidate for application in immobilizing SBW.     

Extraction of potash values from pyrophyllite mine waste

A waste sample generated during the mining of pyrophyllite ore is characterized for the extraction of potash values. Mineral liberation analysis (MLA) reveals that the waste material consists of muscovite, K-Feldspar (orthoclase), and pyrophyllite as the major mineral phases. The sample contains 49.5% SiO_2, 23.9% Al₂O_3, 1.8% Fe₂O₃, and 9.8% K₂O as its prime constituents. An effort has been made for the extraction of potash value by physical and chemical beneficiation techniques. Beneficiation studies using magnetic separation, froth flotation, and even chemical leaching with inorganic acids could not extract any appreciable potash values. Finally, a roast leach method using calcium chloride followed by leaching in water has been employed. The process variables such as calcium chloride dosage, roasting time, and temperature are optimized using L9 Taguchi statistical design. It has been possible to achieve about 85% potash values at 900°C, 45 minutes of roasting time and calcium chloride dosage of 75% with respect to the ore. The change in mineral phases in the feed, roast, and leached residue has been characterized by X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), which shows the phase conversion into wollastonite and halite potassian.     

Composition and Recyclability Analysis of Poly(Vinyl Chloride) Recovered from Computer Power Cables and Commercial Wires

The product‐based recycling of the electrical and electronic devices and their by‐products are limited due to their complex characteristics and dissimilar material characteristics. However, such recycling procedures give clear ideas about the composition and possible recycling options of the materials present in them. Consequently, the present study deals with isolation and recycling of the major polymeric fraction present in the waste computer power supply cables (CPS) and electrical power supply (EPS) wires isolated from the household items. The composition analysis of CPS and EPS indicates that the poly(vinyl chloride) (PVC) is the major polymeric fraction along with minor content of polyethylene (PE) and polycarbonate (PC). Further, this research compares the mechanical recyclability of the PVC recovered from the CPS and EPS. Among the PVC's analyzed, PVC isolated from the EPS has been indicated superior mechanical properties. Similarly, thermal degradation analysis (TGA) indicated higher thermal stability for the PVC isolated from EPS. Besides, the flammability of the PVC specimens was studied and concluded with the possible mechanism occurring during combustion. Moreover, this study points out that PVC recovered from EPS and CPS can be mechanically recycled for the elimination of the waste. J. VINYL ADDIT. TECHNOL., 26:213–223, 2020. © 2019 Society of Plastics Engineers     

SHS/QP Synthesis and Characterization of Ce‐Bearing Zirconolite‐Rich Waste Forms Using MoO3 as the Oxidant

In this study, zirconolite (CaZrTi₂O₇)/Mo composite was rapidly synthesized by self‐propagating high‐temperature plus quick pressing (SHS/QP) technique using MoO₃ as the oxidant. As the surrogate of tetravalent actinide nuclides, up to 50 at.% CeO₂ (about 17.5 wt% of the raw material) was introduced to substitute the Zr site of zirconolite. Perovskite (CaTiO₃) and rutile TiO₂ were inevitably produced after the incorporation of CeO₂. The raw CeO₂ was partially reduced to trivalent state, which promotes the substitution of Ce into the Ca sites of perovskite and zirconolite. The aqueous durability of Ce‐bearing waste form was investigated with normalized leaching rates (42 d) of Ce in moderate value of about 10^?2 g m^?2 d^?1.     

废旧家用电器塑料资源化利用及发展趋势

塑料是家用电器中广泛使用的原材料,如何高效高值地回收利用废旧家用电器塑料是至关重要的问题。各种塑料依据其性能优势在家电产品中得到广泛应用,并呈现轻量、健康和环保的发展趋势。通过对我国废塑料再生行业的政策和标准进行梳理和分析,综述了废塑料回收利用现状。最后,提出了发展建议：在生产者责任延伸制度的推动下,废旧家用电器塑料行业可采用智能化高效分选设备与复合处理工艺提升资源化利用价值;开展再生塑料行业的相关标准化工作;构建与完善再生材料的应用市场;加强生态设计提升原生塑料的可再生利用性。     

Electrolytic recovery of zinc from zinc ash using a catalytic anode

The process of galvanisation of steel generates zinc ash as the waste product, thus creating pollution problems. The recovery of zinc metal from zinc ash, with a zinc content of about 76% by leaching and electrowinning has been studied. The presence of chloride has been identified as the major problem area. A catalytic anode based on iridium dioxide (IrO₂) was used as the anode material to overcome this problem. Catalyst loading was kept at an economically acceptable level. The catalyst's stability, energy consumption and efficiency of zinc recovery are discussed. The service life of the IrO₂ active coating has been established by an accelerated polarisation test. The zinc deposit recovered from the zinc ash has been examined by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Copyright © 2004 Society of Chemical Industry     

Zinc(II)‐triflate as catalyst precursor for ring‐closing depolymerization of end‐of‐life polytetrahydrofuran to produce tetrahydrofuran

The recycling of polymers continues to be an important subject for a greener and sustainable society. Especially, the deconstruction of end‐of‐life polymers to monomers creates a feedstock for new high‐quality polymeric materials and contributes to conserve resources and allow an efficient waste‐managing system. In this study, zinc(II)‐triflate as catalyst precursor has been examined in detail In the ring‐closing depolymerization of end‐of‐life polytetrahydrofuran (PolyTHF) to generate tetrahydrofuran (THF). Noteworthy, the produced THF can be a suitable starting material for new polymeric materials. With the cheap and abundant Zn(OTf)₂ (1.0 mol %) as precatalyst excellent yields (up to 95%) were feasible for the depolymerization of PolyTHF at 180°C within 30 min. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39791.     

硫脲法浸出废弃电脑线路板中金的研究

废弃电脑线路板是一种典型的电子废弃物,其中含有丰富的贵金属资源,而金的回收是废弃电脑线路板资源化研究的热点。研究了用硫脲浸出废弃电脑线路板中的金,考察了硫脲质量浓度、反应时间、反应温度、三价铁离子质量分数、溶液pH对金浸出率的影响。结果表明,在硫脲质量浓度为12 g/L、反应时间为60 min、反应温度为30 ℃、三价铁离子质量分数为0.45%、溶液pH为1.5条件下,金的浸出率达到90.93%。硫脲法浸金因具有浸出速率快、浸出时无毒、对环境污染小、试剂易再生、干扰离子少等优点而具有广泛的应用前景。     

Valorization of waste thermoset material as a filler in thermoplastic: Mechanical properties of phenolic molding compound waste‐filled PP composites

As most thermoset material, phenolic molding compound (PMC) wastes are an environmental problem. Very few recycling solutions have been proposed so far for this type of material. A mechanical recycling method to valorize these materials is proposed in this work. It relies on the use of phenolic waste as filler in thermoplastic. Such phenolic filler can increase mechanical properties (tensile, flexural) of the matrix, and be used in substitution of traditional particulate fillers such as calcium carbonate or talc. In this study, several morphological parameters influencing the final mechanical properties of a PMC‐filled polypropylene (PP) micro‐composite are studied, such as filler loading rate, particles size distribution of the filler, and interfacial adhesion between the filler and the matrix. Some structural parameters are also studied and linked with mechanical properties, such as dispersion of the filler and crystallinity of the matrix. Finally, the properties of PMC‐filled PP are compared with CaCO₃‐ and talc‐filled PP. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45849.     

Biomass tar recycling and destruction in a CFB gasifier

Conversion of biomass into producer gas by thermal gasification broadens the scope of biomass applications. Usually, tar has to be removed from the producer gas. Tar recycling within the gasification process may solve the associated waste problem and increase the system efficiency, provided tar is broken down under gasification conditions. We present results of tar recycling experiments at a Circulating Fluidised Bed gasifier. At 830 °C, from each of 15 main tar compounds 70-80% are broken down. Continuous recycling of tar would increase the tar content in raw producer gas by 50% at most and save about 3% fuel input.     

Potential utilization of oil sludge incineration bottom ash for glass-ceramics: Crystallization kinetics,properties and toxicological evaluation

The bottom ash (OIBA) generated from the incineration of hazardous oil sludge is classified as a hazardous waste. In this work, the OIBA was applied as raw material to prepare SiO₂-Al₂O₃-CaO system glass-ceramics by melt-sintering with the addition of waste glass wool (GW). The effects of basicity (CaO/SiO₂ ratio, 0.52-1.05) and sintering temperature (900–1050 °C) on the crystallization kinetics, properties, microstructure, leaching concentrations of heavy metals and potential toxicity of glass-ceramics were investigated. The results showed that the crystallization pattern was two-dimensional crystallization, and with the decrease of basicity, the main crystalline phase evolved from gehlenite to diopside. And the glass-ceramics with basicity of 0.88 and sintering temperature of 950 °C exhibited the best comprehensive properties, including density (2.72 g/cm³), water absorption (0.06%), compressive strength (452.45 MPa) and chemical corrosion resistance. In addition, the reduction of heavy metal leaching concentration indicates that produced glass-ceramics showed excellent solidification effect on heavy metals, the low toxicity of glass-ceramics leaching solution to the wheat seeds and Artemia suggests the environmental protection characteristics of OIBA-based glass-ceramics. These findings proved that the glass-ceramics produced by OIBA and GW could be a promising method to dispose hazardous waste with preparing high value-added construction materials.     

Investigations on the self‐ignition of deposits containing combustibles

Self‐ignition of deposited combustibles is a possible reason for excessive fires occurring on deposits for recycling materials or on waste dumps. Two series of experiments were performed to assess the hazard of self‐ignition: hot storage tests with different homogeneous mixtures of combustible material and inert material and tests with pockets of combustible material embedded in inert matter. In the first test series considerable exothermicity (ΔT>60K) was observed for mass fractions of combustible material as low as 2.5%. In the second series it could be shown that the heat transfer from a pocket of burning material through the inert matter can ignite a second pocket of combustible matter. Based on the experimental data, numerical simulations were performed to predict self‐ignition on real‐scale waste deposits. For a deposit of specific size and shape, the influence of the ambient temperature on the occurrence of self‐ignition has been investigated. Copyright © 2008 John Wiley & Sons, Ltd.     

Designing oligomeric ethylene terephtalate building blocks by chemical recycling of polyethylene terephtalate

The intelligent recycling of plastics waste is a major concern. Because of the widespread use of polyethylene terephtalate, considerable amounts of PET waste are generated that are ideally re‐introduced into the material cycle by generating second generation products without loss of materials performance. Chemical recycling methods are often expensive and entail environmentally hazardous by‐products. Established mechanical methods generally provide materials of reduced quality, leading to products of lower quality. These drawbacks can be avoided by the development of new recycling methods that provide materials of high quality in every step of the production cycle. In the present work, oligomeric ethylene terephthalate with defined degrees of polymerization and defined molecular weight is produced by melt‐mixing PET with different quantities of adipic acid as an alternative pathway of recycling PET with respect to conventional methods, offering ecofriendly and economical aspects. Additionally, block‐copolyesters of defined block length are designed from the oligomeric products. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39786.     

Photo‐curing behaviors of bio‐based isosorbide dimethacrylate by irradiation of light‐emitting diodes and the physical properties of its photo‐cured materials

Bio‐based isosorbide (1,4:3,6‐dianhydroglucitol), which was obtained from biomass‐derived carbohydrates, has recently attracted much attention as an alternative to bisphenol A (BPA) because of its rigidity and transparency. BPA is still widely used for a variety of chemical applications even though it is known to be an endocrine‐disrupting chemical. BPA is a key precursor to most photo‐curable materials ranging from encapsulants of electronic devices to dental sealants. In this study, photo‐curable isosorbide dimethacrylate (ISDM) was synthesized from bio‐based isosorbide as a substitute for BPA, and the photo‐curing behaviors of ISDM by irradiation with light‐emitting diode (LED) light were investigated. The photo‐curing conversion and rates of ISDM formation were determined based on the change in the peak corresponding to the double bond within the methacrylate groups using attenuated total reflectance Fourier transform infrared (ATR–FTIR) spectroscopy. The effects of initiators and the wavelength of LED light on the photo‐curing conversion and rates of ISDM formation were examined, and a comparative study was carried out with 2,2‐bis[4(2‐hydroxy‐3‐methacryloyloxy‐propyloxy)phenylpropane] (Bis‐GMA), which is a photo‐curing material bearing a BPA moiety. In addition, the mechanical properties, such as surface hardness, adhesion strength, and transparency, after photo‐curing of ISDM were evaluated. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42726.     

Fabrication and application of porous materials made from coal gangue: A review

Coal gangue (CG), which is mainly generated during coal excavation, mining, and coal washing, is an industrial solid waste that is recognized as an environmental pollutant. The ever-increasing amount of CG produced is a serious threat to the ecological environment and property safety, especially in China, which is the largest coal producer and consumer in the world. Considerable studies have investigated means for utilizing CG worldwide. This review summarizes and discusses various porous inorganic materials made from CG, including cement-based porous materials, porous bricks, porous ceramics (cordierite and mullite) and glasses, porous geopolymers, zeolites, aerogels, and porous carbon materials. Different preparation processes and performances of each type of porous inorganic materials were reviewed. Porous CG-based materials can be used as promising adsorbents for the removal of various pollutants and have good potential for use in construction industry as well as catalyst material applications. Besides, porous materials obtained from CG have also been tested as slow-release fertilizers after the absorption of phosphate, as electrode materials, and as oil-in-water separation agents. The systematic summary of porous materials based on CG aims at promoting high-value-added applications for this waste. Future research directions for the use of CG as a raw material are also presented.     

Recycling of PET waste using 3‐amino‐1‐propanol by conventional or microwave irradiation and synthesis of bis‐oxazin there from

There is a growing interest in recycling of post‐consumer poly(ethylene terephthalate) (PET) waste for both environmental and economic reasons. PET in the form of disposable soft drink bottle waste was subjected to depolymerization via aminolysis using excess of 3‐amino‐1‐propanol under soxhlet by conventional heating as well as microwave irradiation using catalyst sodium acetate or potassium sulfate. The product obtained was characterized after purification by using melting point, IR spectroscopy, nuclear magnetic resonance, and differential scanning calorimeter and was found to be bis‐(3‐hydroxy propyl) terephthalamide (BHPTA). The BHPTA thus obtained was subjected to cyclization reaction using thionyl chloride to obtain bis‐oxazin under conditions of ambient temperature. Bis‐oxazin has applications in polymer synthesis as a chain extender or a cross linking agent. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Catalytic conversion of waste plastics: focus on waste PVC

Effective waste management must address waste reduction, reuse, recovery/recycling and, as the least progressive option, waste treatment. The increase in plastic waste production is a serious environmental issue. Plastics consumption continues to grow and while plastic recycling has seen a significant increase since the early 1990s, consumption still far exceeds recycling. Waste plastic can, however, serve as a potential resource and, with the correct treatment, can be reused or serve as hydrocarbon raw material or as a fuel. PVC, highly versatile with many applications, is non‐biodegradable and has a high Cl content (56% of the total weight). Waste PVC incineration is highly energy demanding and can result in the formation of toxic chloro‐emissions with adverse ecological, environmental and public health impacts. The Cl component must be removed from any waste PVC derived gas or oil before it can be used. An overview of the existing waste plastic treatment technologies is provided with an analysis of the available literature on thermal and catalytic PVC degradation. Thermal degradation results in random scissioning of the polymer chains generating products with varying molecular weights and uncontrolled Cl content. There is a dearth of literature dealing with the catalytic dechlorination of PVC. A case study is presented to illustrate the role heterogeneous catalysis can play in PVC waste treatment. The efficacy of Pd/Al₂O₃ to promote PVC dechlorination is demonstrated, where a significant decrease (by up to a factor of 560) in the liquid fraction Cl content is recorded in addition to differences (relative to thermal degradation) in the gas phase product, i.e. higher C₁? C₄ content with preferential alkane formation. Copyright © 2007 Society of Chemical Industry