Strategies For Aluminum Recycling: Insights From Material System Optimization

level, the primary decisions for a remelter involve composing alloy batches by carefully selecting and mixing various amounts of scrap and primary materials. Sorting provides added flexibility as well as complexity to these decisions by affording the secondary processor the opportunity to upgrade the materials which they have at hand. With sorting, the set of operational decisions include what raw materials to use, which to sort and how much of sorted and unsorted materials should be allocated towards which product. In practice, sorting may not occur at the remelting facility, but rather at the scrap supplier. Furthermore, sorting technologies might be developed in-house in which case it can be interpreted as incurring fixed costs, amortized over the useful life of the sorter. From an analytical perspective, the methods and results presented here are equally applicable to these arrangements. A remelter will need to decide whether to rent the service from a third-party, buy it or to develop sorting capabilities in-house. If the latter route is taken, how much should be spent? For a scrap supplier, it is critical to identify those markets for whom sorting provides added value and which technologies are able to deliver that most effectively. Both parties will need to know which scraps to sort if sorting is deemed appropriate. 6.3.1 Single-Stage Sorting and Mixing Model The model presented below is an extension of one developed to examine strategic raw material allocation decisions (Cosquer and Kirchain 2003). The model developed here assumes that sorting occurs as a single stage 1-to-j stream operation. There is no theoretical limit onj. In a physical sense, this means that for any scrap stream entering the sorter, j possible output streams can be modeled where the characteristics of the j