Construction Materials from Stainless Steel Slags: Technical Aspects, Environmental Benefits, and Economic Opportunities (original) (raw)

2015, Journal of Industrial Ecology

State-of-the-art technologies that implement the 'Industrial Ecology' concept only make it to the market if environmental gains and economic benefits are significant. Therefore, the paper investigates, in an interdisciplinary way, two innovative technologies that valorize Stainless Steel (SS) slags as block masonry (bricks): carbonation and thermo-alkali-activation. The technical, environmental and economic features of three SS bricks-solid bricks, perforated bricks and lightweight aerated blocksare compared to commercially available construction materials. Although the produced bricks meet industrial standards, technical challenges such as optimization of alkali addition and use of metal molds should be dealt with before upscaling to industrial production. A cradle-to-gate Life Cycle Analysis (LCA) that aggregates the results of the various impact categories shows that the environmental impact of solid and perforated SS bricks is lower than the impact of conventional clay-baked bricks thanks to the avoidance of additives for slag stabilization and energy consumption for sintering clay. The impact of aerated SS bricks was found to be similar to the commercially available aerated blocks. More specifically, the CO2 uptake from carbonation reduces the overall environmental impact whereas use of alkalis increases the impact. A SWOT analysis highlights the economic advantages of SS bricks originating from lower energy requirements, reduced dependence on primary resources and improved metal recovery from slag. However, in order to apply the innovative technologies at industrial scale, challenges related to processing conditions, feedstock variability and potential competition from existing brick suppliers have to be overcome. used as aggregates, mostly in road construction, kept in temporary storage or landfilled (Nielsen 2008). However, use as road aggregate is a low-value application for the slag. Moreover, borate additions increase the risk of leaching (Shen and Forssberg 2003), posing a further environmental and legal challenge for the use of this slag (JRC 2010). Use of SS slag as construction material not only avoids slag disposal, but also, to some extent, limits the utilization of virgin resources for the production of construction materials. Construction materials from the current raw material sources and processes account for a large portion of the global anthropogenic carbon dioxide (CO2) generation. For example, the production of ordinary Portland cement (OPC) contributes to about 5-8% of the total global CO2 emissions (van Deventer et al. 2010; The World Business Council for Sustainable Development,www.wbcsd.org.). As a result, the "Cement and Technology Roadmap 2009" has laid a task for a 50% reduction by 2050 of global CO2 emissions from cement production (WBCSD 2009). Also, yearly emissions of the ceramic industry are estimated at 400 Mtons of CO2 (IEA 2013). Considering this, the production of construction materials from alternative sources like SS slag is an ambitious and promising option. Recent technical research has developed construction materials in the form of masonry bricks from fine AOD and CtCs SS slag by applying two innovative processes (Salman et al 2014): 1) thermo-alkali-activationa process where the latent hydraulic (binding) property of the slag is activated by use of alkalis and high temperature and 2) carbonationa process where CO2 is used to bind the slag particles together by the formation of stable carbonates. Fig. 1 illustrates that, in line with the 'Industrial Ecology' paradigm, both technologies unlock slag properties in order to substitute energy and primary material consuming production processes (Graedel and Allenby 1995; Lifset and Graedel 2002).