Evaluation of shredder residue as cement manufacturing feedstock

Abstract Metal recycling from automobiles, appliances and scrap steel occurs at over 200 dedicated metal shredding operations in the US. Shredder residue (SR) consists of glass, rubber, plastics, fibers, dirt, and fines that remain after ferrous and non-ferrous metals have been removed. Over 3 million tonnes of SR generated in the US each year are landfilled. The results of a previous end-of-life impact assessment showed that use of SR as a fuel supplement for cement manufacturing was environmentally beneficial to the current practice of landfilling and appears better in comparison to the other management methods studied. However, because many reuse and recycling options may not be cost effective, there is a need for further study. Simplistic methods to separate SR into energy and mineral rich streams may facilitate the use of a sizable fraction of SR. Due to the large scale of the cement industry in the US, a significant amount of SR is recoverable. The goal of this study was to identify the feedstock quality parameters needed to satisfy kiln operators and then to assess the mechanical means necessary to process SR into material acceptable as coal and mineral substitutes. Field tests were conducted to separate and beneficiate the coarse SR waste stream. Density separation techniques commonly used by shredders in the past were tested to separate rubber and plastics from non-combustibles and contaminants (e.g., PVC and copper wire). A fraction constituting about 30 wt% of the total SR had fuel characteristics mirroring those of coal. However, remaining levels of potentially problematic constituents (e.g., total chlorine and heavy metals) may limit use to a low relative addition rate at some kilns. An economic review of a full-scale separation system showed that processing SR appears to be economically marginal considering avoided landfilling costs alone. However, significant economic benefits would result from additional non-ferrous metals recovery (namely copper). The project results showed that commonly available separation systems should produce an acceptable fuel supplement; however, regulatory barriers which inhibit economically viable recycling may need to be addressed.