Estimation of potential of steel scrap as secondary resource of alloy elements using dynamic input-output model based material flow analysis

Nickel (Ni) and chromium (Cr) are regarded as strategic metals and mainly used for production of alloy steels especially stainless steel. For sustainable steel production and strategic use of alloy elements, recycling of steel... [ view full abstract ]

Nickel (Ni) and chromium (Cr) are regarded as strategic metals and mainly used for production of alloy steels especially stainless steel. For sustainable steel production and strategic use of alloy elements, recycling of steel scrap has important roles. In current recycling system, steel scrap is mainly used as iron source only with consideration for tramp elements such as copper and tin. When alloy steel scrap was treated not as a secondary resource for alloy steel, but as for ordinary steel, alloy elements would be regarded just as impurities. As a result, almost all of the alloy elements except Ni were dissipated into slag, gas phase or left as impurities in metal phase of carbon steels. This open-loop recycling of steel could result in quality loss and/or material loss of Ni, Cr and other alloy elements. To avoid these losses, new recycling system with consideration for composition of steel scrap is needed. Material flow analyses (MFAs) indicate important and fruitful information about structural problem of recycling. Therefore, in this study, dynamical material flow analysis of alloy element especially Ni, Cr associated with steel materials by using MaTrace model (Dynamic Waste Input-Output MFA model) was conducted to evaluate the amount of dissipation of Cr and Ni, and the possibility to reduce the amount of input of primary resources of Ni and Cr for steel industry by implementation of innovative technology. MaTrace model is IO-based Markov chain model with end of life and lifetime distribution. This model can analyze inter-industrial and comprehensive material flow about multi material by combining MFA and waste input output analysis. And also, this model can track and visualize the changing location of the material across final products and losses through consumption and recycling process. WIO table is based on Japanese IO for 2005. To trace the flow of alloy elements, sectors of ferrous materials, crude steel and steel scrap in WIO were subdivided into 33, 53, 10 sectors, respectively. If we focus on passenger car, only 10% of initial input of Ni and Cr is still used in products as alloy elements at 100 years after initial production. They mainly dissipate into refinery loss in case of Cr, unrecovered scrap in case of Ni or carbon steel as impurities in case of both elements. By scenario analysis considering implementation of scrap sorting, reduction of dissipation of Ni and Cr is estimated at few percentages. And also, inputs of Ni and Cr from scrap to alloy steel production are estimated at 44kt and 6.6kt, respectively.