Decomposition of Potent Greenhouse Gas Sulfur Hexafluoride (SF₆) by Kirschsteinite-dominant Stainless Steel Slag

In this investigation, kirschsteinite-dominant stainless steel slag (SSS) has been found to decompose sulfur hexafluoride (SF₆) with the activity higher than pure metal oxides, such as Fe₂O₃ and CaO. SSS is mainly made up of CaO·FeO·SiO₂(CFS)/MgO·FeO·MnO­(RO) phase conglomeration. The SF₆ decomposition reaction with SSS at 500–700 °C generated solid MF₂/MF₃ and gaseous SiF₄, SO₂/SO₃ as well as HF. When 10 wt % of SSS was replaced by Fe₂O₃ or CaO, the SF₆ decomposition amount decreased from 21.0 to 15.2 or 15.0 mg/g at 600 °C. The advantage of SSS over Fe₂O₃ or CaO in the SF₆ decomposition is related to its own special microstructure and composition. The dispersion of each oxide component in SSS reduces the sintering of freshly formed MF₂/MF₃, which is severe in the case of pure metal oxides and inhibits the continuous reaction of inner components. Moreover, SiO₂ in SSS reacts with SF₆ and evolves as gaseous SiF₄, which leaves SSS with voids and consequently exposes inner oxides for further reactions. In addition, we have found that oxygen significantly inhibited the SF₆ decomposition with SSS while H₂O did not, which could be explained in terms of reaction pathways. This research thus demonstrates that waste material SSS could be potentially an effective removal reagent of greenhouse gas SF₆.