Eric Forssberg

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 equipments 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.

An overview of recovery of metals from slags.

Various slags are produced as by-products in metallurgical processes or as residues in incineration processes. According to the origins and the characteristics, the main slags can be classified into three categories, namely ferrous slag, non-ferrous slag and incineration slag. This paper analysed and summarised the generation, characteristics and application of various slags, and discussed the potential effects of the slags on the environment. On this basis, a review of a number of methods for recovery of metals from the slags was made. It can be seen that a large amount of slags is produced each year. They usually contain a quantity of valuable metals except for blast furnace slag and they are actually a secondary resource of metals. By applying mineral processing technologies, such as crushing, grinding, magnetic separation, eddy current separation, flotation and so on, leaching or roasting, it is possible to recover metals such as Fe, Cr, Cu, Al, Pb, Zn, Co, Ni, Nb, Ta, Au, and Ag etc. from the slags. Recovery of metals from the slags and utilisation of the slags are important not only for saving metal resources, but also for protecting the environment.

A review of plastics waste recycling and the flotation of plastics

This paper summarizes the importance of plastic waste recycling and plastic waste separation. Based on an analysis of the physical and chemical characteristics of plastics and plastic waste, the potentials and limitations of several technological processes are discussed. In addition, a review of the surface chemical aspects of plastic flotation is presented. It can be concluded that the flotation of plastics is a fairly flexible technique and could prove to be a useful process for the separation of mixtures of several different types of plastics. However, more research and development effort is required before this technology can be introduced to industry.

Mechanical separation-oriented characterization of electronic scrap

Abstract The ever-increasing amount of electronic scrap and the steadily-decreasing contents of the precious metals used in electronics, as well as the ever-growing environmental awareness, challenges such conventional precious-metal-oriented recycling techniques as pyrometallurgy. Separation and beneficiation of various materials encountered in electronic scrap might provide a correct solution ahead. In this context, mechanical separation-oriented characterization of electronic scrap was conducted in an attempt to evaluate the amenability of mechanical separation processes. Liberation degrees of various metals from the non-metals, which are crucial for mechanical separation, were analyzed by means of a grain counting approach. It is found that the metallic particles below 2 mm achieve almost complete liberation. Particle shapes were also quantified through an image processing system. The results obtained show that the shapes of the particles, as a result of shredding, turn out to be heterogeneous, thereby complicating mechanical separation processes. In addition, separability of various materials was ascertained by a sink–float analysis. It has been shown that density-based separation techniques shall be viable in separating metals from plastics, light plastics (ABS, PS and PVC, etc.) from glass fiber reinforced resins and aluminum from heavy metals. Specifically, a high quality copper concentrate can be expected by density-based separation techniques. Moreover, FT-IR spectra of plastics pieces from the light fractions after the sink–float testing show that PC scrap primarily contains ABS, PS and PVC plastics with the density range of +1.0–1.5 g/cm 3 , whereas PCB scrap mainly contains glass fiber reinforced epoxy resins plastics with the density range of +1.5–2.0 g/cm 3 .

Froth stability, particle entrainment and drainage in flotation — A review

Abstract The froth and its stability, the entrainment and the drainage of particles in flotation were long before recognised as important factors which affect recovery and grade. A too stable froth is difficult to handle but, on the other hand, an unstable froth is least desirable. Therefore, a froth of correct stability is of utmost importance. However, the question is whether this phenomenon is related to the frothing properties of a frother or to the physical, chemical and geometrical conditions of a system! The entrainment and drainage of particles in flotation are concerned with the pulp/froth phases. The present paper deals with the current aspects on froth stability, particle entrainment and drainage, based on a detailed literature review.

Prediction of product size distributions for a stirred ball mill

Simulation of the ultra-fine grinding process is a formidable task, attended to by many researchers using models from conventional ball mill grinding. It has been realised that the first-order breakage hypothesis is not valid in fine grinding and that the process mechanism differs substantially from that for ball mills. In this paper, the difference between ball mill grinding and stirred ball milling is discussed. A size-energy model is proposed for simulation of stirred ball milling. The product size distributions below 10 μm from a stirred ball mill were simulated by the model satisfactorily. The model is simple and has only two parameters. The model was tested under different milling conditions for a stirred ball mill.

Intelligent Liberation and classification of electronic scrap

Abstract Mechanical recycling of electronic scrap oriented towards overall materials recovery from obsolete electronics is being implemented worldwide. The main reason is that the amount of electronic scrap is increasing and that the content of the precious metals present is decreasing. In this context, an effective liberation of various materials like metals and plastics is a crucial step towards mechanical separation. In addition, classification of electronic scrap is also important to be able to provide an appropriate feed material for the subsequent separation process. In the present study, liberation and its impact on the separation of personal computer (PC) scrap and printed circuit board (PCB) scrap has been investigated in detail. A special equipment functioning as a shape separator and an aspirator was used for the classification of electronic scrap.

Physicochemical and mineralogical properties of stainless steel slags oriented to metal recovery

In the present paper, physicochemical and mineralogical properties of stainless steel slags oriented to metal recovery were studied by using various methods. The tests were conducted on two types o ...

Selective flotation separation of plastics by chemical conditioning with methyl cellulose

The floatability of seven plastics (POM, PVC, PET, PMMA, PC, PS and ABS) in the presence of methyl cellulose (MC) and separation of plastics mixtures were investigated in this paper. It was found that the seven plastics can be separated into three groups by using the wetting agent MC. Group one includes POM and PVC. They are depressed at very low MC concentrations. Group two, including PET, PMMA and PC, has an intermediate floatability. Group three (ABS and PS) has a high floatability. They are almost not depressed within the given MC concentration range. In order to understand the mechanism of selective flotation of plastics and the chemical conditioning process, surface chemical factors, such as wettability of plastics and surface tension of flotation medium, and gravity factors, such as particle density and shape, were studied. It was found that the depressing effect of MC on plastics is ascribed mainly to its adsorption on the plastics surfaces. The MC molecules absorbed on plastics expose some of their polar groups oriented towards the aqueous phase, hence making the plastics surfaces hydrophilic. In addition, flotation selectivity for the plastics is dominated not only by wettability of plastics, but also by particle size, density and shape.

Selective flotation separation of plastics by particle control

In this paper, the characteristics of plastics particles in the cutting products and flotation behaviours of plastics were studied. On this basis, the relation of floatability of plastics with surface chemical related factor and gravity factors was derived and discussed. From the results, it was shown that plastics flotation is dominated not only by surface chemical factors, but also significantly by gravity factors. It is suggested that plastics flotation is a combination of froth flotation and gravity separation. According to this relation, the idea of particle control was first applied for the separation of plastics mixture. From the separation results, it can be seen that this method can greatly increase the separation efficiency for flotation separation of plastics mixture.