As seen in the preceding chapters, the amount of waste utilized and the extent of development and experience for a given application vary considerably. Of the wastes described, fly ash utilization has a long history for some applications. WEEE, on the other hand, is a relatively new waste. The techniques used to recover metal from electronic waste are similar to primary metal recovery and hence the application is well developed. In the metal processing sector, some wastes like slag from iron and steel production are almost fully utilized, while red mud applications are mainly reported in scientific literature.