Development of a Dynamic Substance Flow Model of Zinc in Japan

In this paper, a dynamic substance flow model of zinc in Japan was conducted. Currently, approximately 60% of zinc in Japan is used for galvanized steel (galvanized sheet and other galvanized products), followed by brass. In other words, zinc has many linkages to other substances. A dynamic model was used to look at these linkages of zinc to other substances in the production stage through other stages. In addition, dissipated zinc used in galvanized sheets and other galvanized products during the use stage was taken into account, using the results of previous atmospheric-exposure tests. Most discarded zinc is recovered as steel scrap or copper-alloy scrap. When used steel is remelted in an electric arc furnace (EAF), zinc is vaporized and collected as EAF dust. Therefore, this steel-associated zinc reenters the zinc cycle. By comparison, when zinc is used in copper alloys, zinc is not recycled and ends its life in the copper cycle. The mass balance of zinc as derived by our substance flow analysis was verified by comparing estimated values of the model with statistics and other estimates on zinc recovery. Using this model, zinc stocks in Japan was estimated to total approximately 3 300 kt at 2005 (26 kg/cap), or enough for around seven years. The amount of unrecovered zinc in 2005 was estimated at around 182 kt. Of this zinc loss, 73% went unrecovered in the steel cycle, e.g. it dissipated into the environment as sacrificial materials, or was in steel that was not collected for recycling.