CO 2 sequestration utilizing basic-oxygen furnace slag: Controlling factors, reaction mechanisms and V–Cr concerns Tung-Hsin Su 1 , Huai-Jen Yang 1, ⁎ , Yen-Hong Shau 2 , Eiichi Takazawa 3 , Yu-Chen Lee 4 1. Department of Earth Sciences, National Cheng-Kung University, Tainan 70101, Taiwan 2. Department of Marine Biotechnology and Resources, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan 3. Department of Geology, Niigata University, 8050, Ikarashi 2-no-cho, Nishi-ku, Niigata 950-2181, Japan 4. China Steel Corporation, 1, Chung-Kang Rd., Kaohsiung 81233, Taiwan ARTICLE INFO ABSTRACT Article history: Received 10 February 2015 Revised 23 June 2015 Accepted 25 June 2015 Available online 5 September 2015 Basic-oxygen furnace slag (BOF-slag) contains >35% CaO, a potential component for CO 2 sequestration. In this study, slag–water–CO 2 reaction experiments were conducted with the longest reaction duration extending to 96 hr under high CO 2 pressures of 100–300 kg/cm 2 to optimize BOF-slag carbonation conditions, to address carbonation mechanisms, and to evaluate the extents of V and Cr release from slag carbonation. The slag carbonation degree generally reached the maximum values after 24 hr slag–water–CO 2 reaction and was controlled by slag particle size and reaction temperature. The maximum carbonation degree of 71% was produced from the experiment using fine slag of ≤ 0.5 mm under 100°C and a CO 2 pressure of 250 kg/cm 2 with a water/slag ratio of 5. Vanadium release from the slag to water was significantly enhanced (generally >2 orders) by slag carbonation. In contrast, slag carbonation did not promote chromium release until the reaction duration exceeded 24 hr. However, the water chromium content was generally at least an order lower than the vanadium concentration, which decreased when the reaction duration exceeded 24 hr. Therefore, long reaction durations of 48–96 hr are proposed to reduce environmental impacts while keeping high carbonation degrees. Mineral textures and water compositions indicated that Mg-wüstite, in addition to CaO-containing minerals, can also be carbonated. Consequently, the conventional expression that only considered carbonation of the CaO-containing minerals undervalued the CO 2 sequestration capability of the BOF-slag by ~20%. Therefore, the BOF-slag is a better CO 2 storage medium than that previously recognized. © 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. Keywords: Mineral CO 2 sequestration BOF-slag Carbonation Introduction Continuously increasing CO 2 emission from combusting fossil fuels for decades has been considered as the major cause for global warming (Hansen et al., 1981; Mann et al., 1998; Smith et al, 2013). Among the technologies for mitigating the increase in atmospheric CO 2 concentration, mineral sequestration is distinct from others for its advantage of long-term stability (e.g., IPCC, 2005; Oelkers et al., 2008). The basic concept of mineral sequestration is to incorporate CO 2 into minerals through JOURNAL OF ENVIRONMENTAL SCIENCES 41 (2016) 99 – 111 ⁎ Corresponding author. E-mail: hjyang@mail.ncku.edu.tw (Huai-Jen Yang). http://dx.doi.org/10.1016/j.jes.2015.06.012 1001-0742 © 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. Available online at www.sciencedirect.com ScienceDirect www.elsevier.com/locate/jes