Originally, industrial production relied on a linear material flow. Raw materials were mined and upgraded, premixes produced for the manufacture of components and equipment which were then utilized and eventually dumped into landfills after their useful life had elapsed. As the proportion of synthetic products in the total production volume increased, landfilling became ever more of a problem. The consequences of this disposal practice became unforeseeable. The price of landfilling rose dramatically. The resulting bottlenecks called for a fundamental change in our attitude towards disposal. Both industrial producers and consumers have since been looking for new concepts and solutions. As compared to the linear material flow, a cyclical concept offers the advantage of avoiding waste or at least postponing landfilling to a later date. Recycling of materials and products into the production processes soon became a commonly used phrase. Recycling can start in a production process itself or during or after the product's life. Thus, the maintenance of goods can be viewed as product recycling. Therefore the return of defective or partly renewed products should have the highest rank among the recycling priorities. Here, the product undergoes no changes in its form. If, on the other hand, the product is disassembled or decomposed into its basic components or substances, this is referred to as a resource recycling. Ideally, these materials or substances should be sorted and returned to the production route. A flow diagram of this cyclical material flow concept is shown in Figure 1.
From the point of view of quality assurance, recycling of used materials into production poses its own special problems. The used material originates from different material streams varying in their impurity content and age. They bear the traces of their former service life. Their original properties have suffered, changed or disappeared altogether. Another important factor to be considered is the material damage resulting from the stresses to which the materials were exposed during their former service life. The impact of such damage is not known and cannot be predicted without comprehensive testing. Processing of recycled materials involves unknown risks. This applies to post-use of metal, plastics just as well as to minerals and textiles. When it comes to supply, recyclers face a problem of finding reliable sources of used materials, and organizing their collection and transportation.
Supply may be a subject ofconsiderable seasonal fluctuations as it is for example the case of used batteries. Continuous operation of the recycling process therefore requires that a large volume of used materials are held in stock. Collection often requires the sophisticated organization and transportation, frequently not possible without the use of special means of transport. Thus logistics alone may jeopardize the profitability of a recycling process. This cost factor increases with decreasing value of the post-used materials to be collected and transported.
From the point of view of quality assurance, pure post-use material streams rank highest on the value ladder while mixed or contaminated materials are grouped into an inferior category.1
Metallgesellschaft AG as a process and raw material-oriented technology and services group has a long and successful track record in recycling of post-use metals. Ever since recycling of post-consumer goods and durables gained a foothold in industry, polymers recycling has been attracting growing attention. The first commercial-scale plastics recycling plants are currently in the planning phase. Several pilot plants are already in operation. BSB RECYCLING GmbH in Braubach, a subsidiary of Metallgesellschaft AG operates a secondary lead smelter for lead recovery from post-use lead-acid batteries.7 They process some 60,000 tons of batteries per annum which accounts for about half of the used battery volume to be disposed in the western states of the Federal Republic of Germany. BSB started to segregate the polypropylene from the battery casings and route it to a separate recycling process as far back as in 1984. For the recycling process, a quality assurance system geared to the specific requirements of the application has been developed and implemented.3
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