Lithification of Slag-dominated Artificial Ground Through Atmospheric CO2 Drawdown

Legacy deposits of by-product slag from iron and steel making create significant volumes of artificial ground around the world. Composed mainly of calcium-silicate mineral phases, experimental studies have shown the potential of slag for capturing atmospheric CO2 by mineralisation (e.g. Huijgen et al. 2005). Renforth (2019) calculated that steel slag could capture ~370-400 kg CO2 per tonne of slag, depending on the type of slag. ~0.5 Gt of steelmaking slag is produced every year (USGS 2018) and this could potentially reach ~2 Gt yr-1 by the end of the century (Renforth 2019). In addition to new slag, there is an estimated 160 million m3 of legacy slag in the UK alone (Riley et al. 2020), stockpiled or dumped from historical steelmaking. Artificial ground poses challenges around ground stability but slag-dominated artificial ground also offers opportunities for atmospheric CO2 drawdown. In this contribution, we document the lithification of legacy slag deposits – conversion of loose gravelly slag material into a rock-like mass through cementation of calcite via drawdown of atmospheric CO2. Parts of slag heaps at our case study sites (Glengarnock and Warton, UK) have a lithified nature: gravel-to-cobble sized lumps of slag are visible but have been cemented together with a mineral cement, with an appearance not unlike a natural breccia rock. We present field, X-Ray Diffraction and δ13C data from these case study sites to document the lithification of slag-dominated artificial ground through mineralisation of atmospheric CO2 as a cementing phase; we present scanning electron microscope data to show the microstructural evolution of this lithification. This understanding has implications for artificial ground stabilisation and how atmospheric CO2 drawdown can be harnessed in this process