Use of LCA for the environmental evaluation of the recycling of galvanized steel

Abstract

Life Cycle Assessment has been used to compare the environmental performance of landfilling of the zinc used for galvanizing steel with recycling by a number processes. Hypothetical process routes were composed involving three different EAF dust treatment processes, Waelz kiln, DC-furnace, and EZINEX, as well as scrap dezincing. The study shows that recycling of zinc used for galvanizing steel clearly has environmental benefits in that it saves zinc resources. However, zinc recovery does not necessarily decrease the potential impact on global warming and acidification. The magnitude of these two impact categories is tightly correlated with the amount and type of primary energy consumed in a process. Due to the high electricity consumption in the dezincing process, this route has the highest impact on Global Warming Potential as well as Acidification Potential. The major part of the energy requirement for the production of zinc from primary and secondary sources is consumed in the reduction of ZnO to Zn. The consequence is that the theoretically possible saving in primary energy by recycling zinc-containing materials is relatively small. The impact categories land use and waste generation are not considered in this study, but most likely the evaluation of such impacts would further increase the potential environmental impact of the landfill alternative. The results also show that the location of an electricity-intensive process highly affects the potential environmental impact. Comparing process and material alternatives in LCA studies where branch average data is used is therefore considerably more complex than when LCA is used within a company.