Mechanical recycling of waste electric and electronic equipment: a review

The production of electric and electronic equipment (EEE) is one of the fastest growing areas. This development has resulted in an increase of waste electric and electronic equipment (WEEE). In view of the environmental problems involved in the management of WEEE, many counties and organizations have drafted national legislation to improve the reuse, recycling and other forms of recovery of such wastes so as to reduce disposal. Recycling of WEEE is an important subject not only from the point of waste treatment but also from the recovery of valuable materials.WEEE is diverse and complex, in terms of materials and components makeup as well as the original equipment's manufacturing processes. Characterization of this waste stream is of paramount importance for developing a cost-effective and environmentally friendly recycling system. In this paper, the physical and particle properties of WEEE are presented. Selective disassembly, targeting on singling out hazardous and/or valuable components, is an indispensable process in the practice of recycling of WEEE. Disassembly process planning and innovation of disassembly facilities are most active research areas. Mechanical/physical processing, based on the characterization of WEEE, provides an alternative means of recovering valuable materials. Mechanical processes, such as screening, shape separation, magnetic separation, Eddy current separation, electrostatic separation, and jigging have been widely utilized in recycling industry. However, recycling of WEEE is only beginning.For maximum separation of materials, WEEE should be shredded to small, even fine particles, generally below 5 or 10mm. Therefore, a discussion of mechanical separation processes for fine particles is highlighted in this paper.Consumer electronic equipment (brown goods), such as television sets, video recorders, are most common. It is very costly to perform manual dismantling of those products, due to the fact that brown goods contain very low-grade precious metals and copper. It is expected that a mechanical recycling process will be developed for the upgrading of low metal content scraps.     

CFD models in the development of electrical waste recycling technologies

Nowadays electrical waste (EW) recycling has become a practical way to provide raw material for new devices. Computer parts such as memory, motherboard or other parts contain large amount of metals from which the recovery of precious metals and copper represents the highest economical potential. With a proper chemical treatment these metals can be efficiently extracted and separated from the actual waste. For this task a specially designed leaching reactor, equipped with a perforated rotating drum, was used. This work is aimed at investigating if computational fluid dynamics (CFD) tools can be efficiently applied to model the chemical reactor used to dissolve the metals from the EW. First a hybrid CFD-compartment approach was developed to describe the dissolution process in the leaching reactor while the CFD models were used to model the hydrodynamics of the process. Based on the detailed model containing momentum and component mass balance the developed simulator could be used to enhance the performance of the existing reactor system. For the modelling studies COMSOL Multiphysics was used as CFD software.     

Prospects for cleaning ash in the acidic effluent from bioleaching of sulfidic concentrates

Leaching of ashes in sulfuric acid (pH 1.0, liquid-to-solid (L/S) ratio 10:1, 25 degrees C) has been characterized with respect to the neutralizing capacity and the dissolution of dominant ions and trace elements. The conditions mimic the oxidation stage of a biohydrometallurgical process for base metal production from sulfidic mineral concentrates. Direct acid leaching of ash, integrated with this metallurgical process, offers a feasible route to the sustainable handling of metal-rich ashes. The treated ash will be deposited together with the inert mineral residue. Cd, Co, Cu, Ni and Zn are effectively leached and can be recovered utilizing existing hydrometallurgical technology, but the recovery of other readily dissolved metals, notably Mn, U and V, requires that additional steps are implemented. We make two recommendations for industrial processes. The first is to replace limestone with ash from biofuels, except peat, for pH control in biohydrometallurgical processing. This requires a modest increase of fresh alkali compared with limestone. The second is to implement sulfuric acid leaching of fly ash from the combustion of solid waste and other metal-rich fuels (used wood, tires), thereby avoiding costly ash-deposits. There is a significant economic incentive for these changes, since no costly ash-deposits and less limestone will be needed.     

Cleaning of waste smelter slags and recovery of valuable metals by pressure oxidative leaching

Huge quantities of slag, a waste solid product of pyrometallurgical operations by the metals industry are dumped continuously around the world, posing a potential environmental threat due to entrained values of base metals and sulfur. High temperature pressure oxidative acid leaching of nickel smelter slags was investigated as a process to facilitate slag cleaning and selective dissolution of base metals for economic recovery. Five key parameters, namely temperature, acid addition, oxygen overpressure, solids loading and particle size, were examined on the process performance. Base metal recoveries, acid and oxygen consumptions were accurately measured, and ferrous/ferric iron concentrations were also determined. A highly selective leaching of valuable metals with extractions of >99% for nickel and cobalt, >97% for copper, >91% for zinc and <2.2% for iron was successfully achieved for 20 wt.% acid addition and 25% solids loading at 200-300 kPa O(2) overpressure at 250 degrees C in 2h. The acid consumption was measured to be 38.5 kg H(2)SO(4)/t slag and the oxygen consumption was determined as 84 kg O(2)/t slag which is consistent with the estimated theoretical oxygen consumption. The as-produced residue containing less than 0.01% of base metals, hematite and virtually zero sulfidic sulfur seems to be suitable for safe disposal. The process seems to be able to claim economic recovery of base metals from slags and is reliable and feasible.     

Mechanochemical-Assisted Leaching of Lamp Phosphors: A Green Engineering Approach for Rare-Earth Recovery

Rare-earth elements (REEs) are essential metals for the design and development of sustainable energy applications. Recycling these elements from waste streams enriched in them is crucial for securing an independent future supply for sustainable applications. This study compares the mechanisms of mechanical activation prior to a hydrometallurgical acid-leaching process and a solvometallurgical mechanochemical leaching process for the recovery of REEs from green lamp phosphor, LaPO₄:Ce³⁺,Tb³⁺. After 60 min of processing time, the REE leaching rates showed a significant enhancement of 60% after cycled mechanical activation, and 98% after the combined mechanochemical leaching process. High-resolution transmission electron microscopy (HR-TEM) imaging disclosed the cause for the improved REE leaching rates: The improved leaching and leaching patterns could be attributed to changes in the crystal morphology from monocrystalline to polycrystalline. Reduction of the crystallite size to the nanoscale in a polycrystalline material creates irregular packing of chemical units, resulting in an increase in defect-rich grain boundaries in the crystals, which enhances the leaching process. A solvometallurgical method was developed to combine the mechanical activation and leaching process into a single step, which is beneficial for operational cost. This results in an efficient and simple process that provides an alternative and greener recycling route for lamp phosphor waste.     

多技术联用鉴别含铅固体废物

采用X射线荧光光谱、X射线衍射等技术,结合超景深显微镜、扫描电镜等设备,对某含铅样品进行化学成分、物相组成和微观形貌分析,判断是否为固体废物.结果表明:样品主成分为Pb3(CO3)2(OH)2,PbSO4和Na2SO4等,并且含有大量玻璃态的钠钙铝硅酸盐和呈球状、椭球状、串珠状的金属铅和铅铁氧化物.样品中的硫酸铅呈疏松...     

废弃氧化铟锡中铟的回收技术综述

废弃氧化铟锡(ITO)的回收利用对我国铟资源的可持续发展与环境保护具有重要意义。本文首先对废弃ITO的回收潜能进行了初步评估;进而系统概述了废弃ITO回收技术的研究进展,回收工艺主要包括湿法与火法,分析比较了现有回收技术的优缺点;在此基础上,指出了当前废弃ITO资源化处理过程中存在的主要问题及相应的解决对策;最后展望了废弃ITO资源化利用未来的研究趋势,开发高效、环境友好型回收工艺是今后重要的研究课题。     

电子废弃物资源化处理现状

伴随着信息技术的高速发展,电子废弃物的种类和总量日益增多,它具有数量多、危害大、潜在价值高、回收利用困难等特点。本文中分析了火法处理、湿法处理、机械处理、热裂解等电子废弃物资源化处理技术,并指出了不同技术的优缺点,重点介绍了机械处理、湿法处理及热裂解处理方法工艺特点,同时对最新研究进展作了简要评述和展望。     

从蓄电池中回收铅的技术进展

废铅蓄电池是再生铅的主要原料，其中的铅除金属外还含有不同数量的PbO、PbO2和PbSO4，因此其再生过程较为复杂，目前国内外主要采用火法和湿法回收铅。本文详细阐述火法和湿法回收铅的原理和工艺流程。     

Hydrometallurgical processing of carbon steel EAF dust

In this study, the hydrometallurgical processing of electric arc furnace (EAF) steelmaking dust is investigated on a laboratory scale under normal temperature and pressure conditions. The behaviour of zinc and iron under the influence of sulphuric acid as the leaching agent is discussed. The dependence between the temperature and acid concentration is investigated. The main aim is the transfer of zinc into the solution while iron ought to remain as a solid residue. The hydrometallurgical recovery of zinc from EAF dust is feasible with relatively high recovery yield, while iron mostly remains in the solid phase. It results from the use of sulphuric acid in low concentration. This way, it is possible to set up the conditions for the EAF dust leaching, adjusting sulphuric acid concentration in order to achieve an optimum zinc yield to the solution without iron dissolution. However, the problem is that the chemical and mineralogical composition of each steelmaking dust is individual.     

废脱硝催化剂钒、钨的浸出-搅拌对浸出率的影响

实现废脱硝催化剂高效综合再利用具有重大的社会和经济效益。本文采用NaOH浸出废脱硝催化剂中钒钨离子并考察其浸出影响因素,对比研究了搅拌和不搅拌作用下废脱硝催化剂中的钨离子浸出动力学。结果表明,提高浸出温度和NaOH浓度均有利于钒、钨的浸出;在搅拌条件下(350 r/min),液固比3.5∶1,浸出温度160℃,NaOH浓度40%,浸出时间3.5 h,钒、钨浸出率均达到100%。动力学研究结果钨离子浸出过程属于固膜扩散控制,搅拌条件下钨浸出表观活化能为29.28 kJ/mol,而不搅拌时,其表观活化能仅为1.26 kJ/mol,搅拌强化可增加扩散速率,减小扩散阻力,强化钒钨的浸出。     

Automobile shredded residue valorisation by hydrometallurgical metal recovery

The aim of this work was developing a hydrometallurgical process to recover metals from automobile shredded residue (or car fluff). Automobile shredded residue (ASR) was characterised by particle size distribution, total metal content and metal speciation in order to guide the choice of target metals and the operating conditions of leaching. Characterisation results showed that Fe is the most abundant metal in the waste, while Zn was the second abundant metal in the fraction with diameter lower than 500 μm. Sequential extractions denoted that Zn was easily extractable by weak acid attack, while Fe and Al required a strong acid attack to be removed. In order to recover zinc from <500 μm fraction leaching tests were operated using acetic acid, sulphuric acid and sodium hydroxide at different concentrations. Sulphuric acid determined the highest zinc extraction yield, while acetic acid determined the highest zinc extractive selectivity. Sodium hydroxide promoted an intermediate situation between sulphuric and acetic acid. Zn recovery by electro winning using acetic leach liquor determined 95% of Zn electro deposition yield in 1h, while using sulphuric leach liquor 40% yield in 1h and 50% yield in 2h were obtained. Simulation results showed that the sulphuric leaching process was more attractive than acetic leaching process.     

Manganese recovery from secondary resources: a green process for carbothermal reduction and leaching of manganese bearing hazardous waste

During the hydrometallurgical extraction of zinc by electrowinning process, a hazardous solid waste called anode mud is generated. It contains large quantity of manganese oxides (55-80%) and lead dioxide (6-16%). Due to the presence of a large quantity of lead, the anode mud waste is considered hazardous and has to be disposed of in secure landfills, which is costly, wastes available manganese and valuable land resources. For recovery of manganese content of anode mud, a process comprising of carbothermal treatment using low density oil (LDO) followed by sulphuric acid leaching is developed.     

Processing of low grade tungsten ore concentrates by hydrometallurgical route with particular reference to India

Tungsten, because of its high strength and high melting point occupies a prime position amongst metals. With depletion of high grade resources considerable R and D work is still being carried out in tungsten producing countries around the world for the processing of low grade and secondary resources. The paper gives a brief review of the hydrometallurgical processes developed to recover tungsten from low grade concentrates. The R and D work carried out on purification and recovery of tungsten as tungstic oxide/ammonium paratungstate (APT) from a number of off-grade products such as table concentrate (WO₃=66%, SiO₂=2·2%, S=1·8%), middlings (18–20% WO₃, and 28–30% S) and jig concentrate (4·6% WO₃) are discussed in this paper. It has been found that more than 75% of silica and 90% of sulphur could be removed from the table concentrate by curing with hydrofluoric acid and subsequent roasting of the desilicated product at 650°C. In the case of middlings, it was possible to recover over 90% of tungsten as tungstic oxide by an oxidative roast followed by pressure leaching with soda. A detailed study on the low grade jig concentrate to recover tungsten as APT, showed that over 90% extraction was possible by adopting the pressure leaching-solvent extraction route. Effect of parameters such as soda concentration, time, temperature and pressure during leaching; as well as extraction and stripping behaviour of tungsten from leach solution at different pH and aqueous to organic ratio during solvent extraction with Alamine-336, were studied and a flow-sheet was developed for processing of jig concentrate analysing 4·6% WO₃.     

Alchemy‐Inspired Green Paper for Spontaneous Recovery of Noble Metals

Recycling of noble metal from waste materials, namely from electronic wastes (e‐waste), spent catalyst, and industrial wastewater, is attracting growing attention due to the scarcity, economic importance, and criticality of those noble metals. Traditional techniques reported to date require toxic reagent and strict extraction conditions, which deeply hinders the development of precious metal recovery in complex environments. Here, an approach is proposed that uses flexible metallic transition metal dichalcogenide (TMD) paper, which provides abundant active sites for spontaneous adsorption and reduction of noble metal ions, as an Alchemy‐inspired template to recover noble metal in an efficient and green way without the aid of reductant and heating. The metallic TMD (MoS₂, WS₂) paper is shown to rapidly extract five noble metal ions (Au, Pd, Pt, Ag, and Ru) from complex samples containing various interferents. This unique property endows the metallic TMD paper with gifted ability in extracting gold from e‐waste, and recovering platinum group metals (palladium and platinum) from spent catalysts, which provides a blueprint for the design of next‐generation green platforms for noble metal regeneration.     

WEEE recovery strategies and the WEEE treatment status in China

The electric and electronic equipment has been developed, applied, and consumed world wide at a very high speed. Subsequently, the ever-increasing amount of waste electric and electronic equipment (WEEE) has become a common problem facing the world. In view of the deleterious effects of WEEE on the environment and the valuable materials that can be reused in them, legislations in many countries have focused their attention on the management of WEEE, and new techniques have been developed for the recovery of WEEE. In China, rapid economic growth, coupled with urbanization and growing demand for consumer goods, has increased the consumption of EEE in large quantity, thus made the WEEE manifold rapidly, posing a severe threat to the environment and the sustainable economic growth as well. This article reviewed the implementation of strategies of WEEE treatment and the recovery technologies of WEEE. It presented the current status of WEEE and corresponding responses adopted so far in China. The concept and implementation of scientific development is critical to the sector of electronics, one of the important industrial sectors in China's economy. To achieve this objective, it is significant to recycle WEEE sufficiently to comply with regulations regarding WEEE management, and to implement green design and cleaner production concepts within the electronics industry to comply with the upcoming EU and China legislation in a proactive manner.     

Transfer mechanisms of contaminants in cement-based stabilized/solidified wastes

Stabilization/solidification (S/S) processes are routinely used for the final treatment of hazardous wastes prior to land disposal. Cement-based binder systems with partial replacement of cement by pulverized fuel ash (PFA) are common. In order to predict the long-term leaching characteristics of S/S wastes, it is important to understand the leaching mechanism. This paper presents experimental results from a study that has investigated the leaching behaviour of contaminants from cement-based S/S waste forms. A novel radial leach test (RLT) has been used to study the migration of heavy metals. The results show that contaminants migrate from the inner core of the S/S waste during leaching to the sample surface and accumulate near the edge of the S/S waste. The degree of accumulation is related to the contaminant species and the Ca(OH)2 content.     

超声波在回收氧化锆氧传感器中铂族贵金属的应用

主要介绍了利用超声波回收氧化锆氧传感器中铂族贵金属的方法。此方法具有简单高效,无毒无害的特点。铂族贵金属在氧化锆氧传感器中作为活性电极被大量应用,由于铂族贵金属资源稀缺和价格昂贵,从废弃的氧化锆氧传感器元件中回收铂族贵金属在经济和环保方面具有十分重要的意义。     

Assessment of removal of components containing hazardous substances from small WEEE in Austria

Minimum treatment requirements for waste electrical and electronic equipment (WEEE) established by Directive 2002/96/EC provide for the removal of specific components containing hazardous substances. To date, no comparative analysis of removal rates has been undertaken. The present paper examines the state of de-pollution of sWEEE in Austrian treatment plants. The mass of selected components removed and the corresponding mass of hazardous substances is compared to estimated values for sWEEE input material. The results obtained reveal that components are only partly removed, featuring a high variation between components and plants assessed. The overall rate of removal ranged from 72% of the estimated value for batteries to 21% of the estimated value for liquid crystal panels. This implies the forwarding of substantial quantities of hazardous substances to mechanical treatment processes, particularly relevant in terms of dispersion of pollutants. Furthermore, easily releasable pollutants, such as Hg from LCD-backlights, Cd from batteries or highly contaminated dust in general, pose substantial health risks for plant workers. Low removal rates of printed circuit boards, batteries and toner cartridges also lead to a reduction in quantities of valuable recyclable materials (precious metals, plastics).     

Galvanic sludge metals recovery by pyrometallurgical and hydrometallurgical treatment

This paper reports a study, on laboratory scale, of sulphating roasting to perform a treatment for a selective recovery of valuable metals from galvanic sludge. The target metals were copper, zinc and nickel and the sulphating agent used was pyrite, from coal wastes. The particularity of this treatment is the use of two hazardous wastes as raw material. They are generated in large quantities at coal extraction sites (coal wastes) and at plating shops (galvanic sludge). The wastes were characterized by X-ray fluorescence (XRF), particle size distribution and water contents. The chemical characterization showed sludges with high copper concentration, with more than 14% (dry base). In the roasting step, the galvanic sludge was mixed with pyritic waste and the parameters evaluated were galvanic sludge/pyrite ratio, roasting temperature and roasting time. After roasting, the product of reaction was leached with water in room temperature for 15 min. Considering that other studies have already demonstrated that the pyrometallurgical step determines the process efficiency, this paper only reports the influence of pyrometallurgical parameters. Hydrometallurgical processes will be better evaluated in further studies. The conditions that best reflect a compromise between the valuable metal recover and the economical viability of the process were achieved for 1:0.4 galvanic sludge/pyrite ratio, 90 min of roasting time and 550 degrees C of roasting temperature. These conditions lead to a recovery of 60% zinc, 43% nickel and 50% copper.