M.A. Reuter

Informal electronic waste recycling: A sector review with special focus on China

Informal recycling is a new and expanding low cost recycling practice in managing Waste Electrical and Electronic Equipment (WEEE or e-waste). It occurs in many developing countries, including China, where current gaps in environmental management, high demand for second-hand electronic appliances and the norm of selling e-waste to individual collectors encourage the growth of a strong informal recycling sector. This paper gathers information on informal e-waste management, takes a look at its particular manifestations in China and identifies some of the main difficulties of the current Chinese approach. Informal e-waste recycling is not only associated with serious environmental and health impacts, but also the supply deficiency of formal recyclers and the safety problems of remanufactured electronic products. Experiences already show that simply prohibiting or competing with the informal collectors and informal recyclers is not an effective solution. New formal e-waste recycling systems should take existing informal sectors into account, and more policies need to be made to improve recycling rates, working conditions and the efficiency of involved informal players. A key issue for Chinas e-waste management is how to set up incentives for informal recyclers so as to reduce improper recycling activities and to divert more e-waste flow into the formal recycling sector.

Process Knowledge, System Dynamics, and Metal Ecology

A key principle in industrial ecology is the cyclic use of materials, a characteristic of natural ecosystems but a challenge in economic systems. Indeed, in society, metal retention, that is, the ongoing use or ready availability of metal in the economy between the life-cycle stages of resource extraction and final disposal back into the lithosphere, is finite because of the limited grade of secondary (recycled) metals. Currently, the utility of metals is maintained through the addition of high primary (virgin) metals, bringing the concentration of the recycled metals to desired levels. This mixing with high-grade primary metals keeps these recycled metals in the cycle. Long term, this practice of dilution of the undesired substances prevents a closure of the material cycles, whereas recovery without dilution reduces the quality (or quantity) of recycled metals. Metals participate in a system of linked cycles and thus cannot be produced or recovered independently from one another. The metal wheel is introduced in this article as a concise but powerful instrument for the communication of available process knowledge in process metallurgy, the science and technology of producing metals from natural ores and societal raw materials, residues, and end-of-life products. It summarizes the chemical and physical linkages between metals found in ores and the set of metallurgical processes that has been developed to accommodate these linkages. A dynamic mass-flow model is introduced to characterize the global metal cycles. The model facilitates the visualization of the evolution of their structure and technological content. To illustrate the interdependency of metal cycles using the metal wheel and the dynamic model, the transition to lead-free solder is evaluated. Neglect of metal-cycle linkages and dynamics in policy formulation may lead to a shortage of lead substitutes. In case of an extended ban on lead, both the availability and recovery of a range of metals will be affected.

The time-varying factors influencing the recycling rate of products

In Europe targets have been laid down by EU legislation for the recycling rate of end-of-life vehicles to be achieved within the nearby future. It is illustrated in this paper that the definition of the recycling rate and the realisation of the imposed targets are very much dependent on different parameters such as the changing lifetime of the product and product design. It may seem obvious that the recycling rate is determined by various time-varying factors, however, this paper endeavours to describe and quantify the role of these factors on the recycling rate over time by the use of a dynamic systems model. This model permits the prediction of the recycling rate as a function of the numerous presented parameters, changing design scenarios etc. In addition, different definitions of the recycling rate will be presented and discussed. This will lead to a better understanding of the parameters affecting the recycling system and a more precise understanding of the recycling targets and their realisation as imposed by EU legislation. This paper focuses on cars, but the discussion and the definitions derived are equally valid for any end-of-life product.

Recycling of distributed aluminium turning scrap

Abstract The relationship between scrap type and its recoverable metal content can play a crucial role in industrial recycling processes. In this paper, the recyclability of different aluminium turnings has been experimentally studied. Various categories of scrap were melted at 800 °C to recover aluminium metal with the protective salt flux of NaCl–KCl–Na 3 AlF 6 under nitrogen atmosphere. In order to understand the melting behaviour, thermo-gravimetric analysis was applied to investigate the weight loss during the melting process. It is shown that the difficulty of recycling the selected aluminium scrap depends on scrap type, scrap size distribution, contaminant, and the ratio of surface area to body volume. Lower distribution mean value, more non-metallic contaminates (oil, plastics), smaller size and higher ratio of surface area to body volume generally led to a lower metal yield. The effect of cryolite addition on the metal yield was also studied, especially for the scrap with higher ratio of surface area to body volume. It was shown that the accumulation of the metal beads was improved with higher amount of cryolite addition. A simple statistical approach is presented to correlate metal yield to scrap properties for inclusion in process optimisation and control models.

Life cycle impact assessment of the average passenger vehicle in the Netherlands

Goal, Scope and BackgroundIn this article, the Life Cycle Impact Assessment of the average passenger vehicle of the Netherlands is performed, with emphasis on the current dismantling and recycling practice in this country. From calculations on recovery rates of the several material streams from ELY (End-of-Live Vehicle) recycling, it seems that attaining the European ELV legislation recycling targets (Directive 2000/53/EC 2000) is very difficult, even for countries with advanced collection and recycling infrastructures such as the Netherlands. An LCA of the current average passenger vehicle of the Netherlands, including a detailed modelling of the recovery and recycling should form a sound basis for comparison with alternative automotive life cycle designs and legislation efforts.Model and System DefinitionAn average passenger vehicle is defined, having average weight and material composition. A cradle to grave approach is taken, including all relevant upstream processes for the production of materials and fuels, and the return of the recycled materials to the material cycles in the EOL (End-of-Life) phase. A particularity of this model is the detailed description of the Dutch collection and recycling infrastructure, with current data for the shredding, separation and metallurgical recycling processes (ARN 2000, Barkhof 1998, Chapman 1983, Püchert et al.1994, Worrel et al. 1992).Results and DiscussionAccording to the Eco-indicator 99 (EI99) (Ministerie van V.R.O.M 1999), the largest environmental impact of the passenger vehicle’s life cycle occurs in the use phase — over 90% —, due to the combustion and depletion of fossil fuels. This is in agreement of previous studies (Kasai 2000, Kanesaki 2000). Also in the other life cycle phases, the use of fossil fuels is the dominant impact, even for the production phase. Resource depletion due to the use of the materials employed in the vehicle causes a comparatively lower environmental impact, namely due to the high recovery rate and efficiency of the metallurgical recycling, that balances for about 30% the total impacts of the materials production and use. NOx emission was one of the smallest emissions to air in quantity, but was responsible for 36% of the impact of the life cycle, while CO2 was the largest emission to air but caused only 6% of the environmental impact.Conclusion and RecommendationAlthough there is a growing awareness and concern on increasing the recyclability of vehicles, the use phase still has the largest environmental impact of the vehicle’s life cycle. A life cycle assessment can be a sound basis to evaluate and compare design alternatives to increase the sustainability of passenger vehicles. The ASR (Automotive shredder residue) is currently the greatest concern with regard to the recovery targets. It is a large amount of materials (about 32 wt.%), difficult and costly to recycle, and thermal recovery is limited to a maximum of 15wt.% in 1015 by the European ELV legislation. Joint efforts from the automotive industry and legislative institutions are required to find a sensible solution. LCA can be a useful tool to support legislative decisions, as purely weight-based recovery definitions are not adequate to evaluate the sustainability of the automobile life cycle.

Dynamic modelling and optimisation of the resource cycle of passenger vehicles

This paper discusses a dynamic optimisation model for the recycling of cars. Various case studies will illustrate the application of the model to the recycling of aluminium cast and wrought, steel, copper, remainder, which includes the organic fraction. The scope of the dynamic model covers the complete path of product design and manufacturing, the use-phase, mechanical recycling and metal recovery back to the product. The optimisation model determines the recovery rate and covers in detail the processing of the end-of-life vehicle, starting from dismantling, shredding, and various separation steps, including the metal production once again.

Conversion of magnesium fluoride to magnesium hydroxide

The conversion of magnesium fluoride to magnesium hydroxide was studied as part of a process to bleed magnesium from zinc sulphate electrolyte. Most electrolytic zinc plants have to deal with accumulating magnesium in their process liquors as the natural magnesium bleed usually does not balance input from concentrates. The most common forced magnesium bleed produces large amounts of waste gypsum and could potentially be environmentally unfriendly. An alternative process was suggested and discussed, which involves magnesium fluoride precipitation from zinc electrolyte. The magnesium fluoride is converted to magnesium hydroxide in order to produce a saleable product. Regeneration of chemicals from the resulting sodium fluoride solution can be accomplished by means of an electro-dialysis process. Previous experiments indicated a relatively high residual fluoride content in the conversion product, which might limit the application possibilities of the magnesium hydroxide. From the experiments described in this paper it followed that it is not possible to reduce the residual fluoride content of the magnesium hydroxide product to 1273 K. Thus a saleable product could be obtained.

The application of neural nets in the metallurgical industry

Abstract Although the potential of new techniques for the construction of accurate plant models, such as those based on connectionist methods, is generally acknowledged, little on their practical application can be found in the chemical and metallurgical engineering literature. In this paper the use of neural nets to model gold losses on a reduction plant and the consumption of an additive on a leach plant, as well as the pyrometallurgical processing of zinc and aluminium is discussed. The gold and leach plant models performed better than the multilinear regression models used on the plants, even where relatively few data were available. The neural networks used to model the recovery of lead and zinc from industrial flue dusts, process synthesis of zinc recovery plants and the processing of secondary aluminium in a rotary salt flux furnace produced realistic results that could be used by plant personnel to optimize their operations.

The flotation behaviour of chromite with respect to the beneficiation of UG2 ore

Abstract The UG2 reef of the Bushveld Igneous Complex in South Africa is a valuable source of platinum group metals (PGMs) that is beneficiated by flotation. Chromite is one of the main gangue consituents of UG2 ore and it is essential that the amount of chromite reporting to the concentrate during flotation be minimised since it is detrimental to the subsequent smelting operations. It is generally considered that chromite is naturally hydrophilic and only reports to the concentrate by entrainment. However, it is possible that, under certain conditions, the chromite can be activated by the typical reagent suite used in the flotation of UG2 ore, rendering it hydrophobic and amenable to true flotation. The aim of this work was to investigate the effect of copper sulphate and the collectors, sodium isobutyl xanthate and dithiophosphate on the flotability of chromite in a microflotation cell. The effect of copper sulphate on the zeta potential of chromite was also determined. It was found that collectors alone have an insignificant effect on the flotation of chromite whereas, in the presence of copper sulphate recoveries of above 60% were observed in mildly acid to mildly alkaline solutions decreasing 20% at a pH value of 10. The extent of activation depended on the copper sulphate dosage. Zeta potential measurements showed that, above pH 4 copper species were adsorbed on the chromite and between pH 5 and 9 the adsorption lead to charge reversal of the chromite particles to positive values. The speciation programme, MINTEQA2, was used to predict the copper species present over the pH range used. It was postulated that the activation is due to the adsorption of copper hydroxide species at the chromite surface, which then act as sites for collector adsorption.

The use of linear programming in the optimal design of flotation circuits incorporating regrind mills

Abstract Two linear models, the second being a subset of the first, are proposed for the simulation of flotation plants by use of linear programming. The first linear model produces the circuit structure, as well as the optimal flow rates of the valuable element between any number of flotation banks incorporating any number of recycle mills. An optimal grade for the valuable element in the concentrate is given by the second model. Operating conditions in the flotation banks and recycle mills are included as bounds in these models, permitting their possible application in expert systems. The simulated circuit structure, concentrate grade and recoveries closely resemble those of similar industrial flotation plants. The only data required by the simulation models are the feed rates of the species of an element, and their separation factors which are estimated from a multiparameter flotation model.