Realising the CO2 sequestration potential
of steel and iron making slags

Abstract

Climate change is now recognised as being a serious threat to the current structures of
advanced human societies, however, technological innovations can help remove CO2 from
the atmosphere and one such innovation which shows promise is carbon capture and storage
(CCS). Metallurgical slag products have been shown to readily carbonate thereby creating an
uncharacterised carbon sink. This sink could help the UK attain its net CO2 targets and
reducing the net amount of carbon emitted by the industrial blast and basic-oxygen furnaces.
This thesis argues that metallurgical slag products provide an economic way of sequestering
significant amounts of CO2 and provides data to show that approximately 6,434 to 10,127
tonnes of CO2 was being passively sequestered at the Lafarge-Tarmac Redcar site by the
volume of slag products located there in 2015. This thesis also reports results of experimental
studies that aim to actively react metallurgical slag with CO2 under pressure conditions of 10
bar or 100 bar CO2 pressure, temperatures of 25 ˚C or 125 ˚C as well as under differing water
availabilities. Further experiments investigated the effect upon the material carbonation due
to the pre-treatment of samples with 1M HCl or 1M NaOH. A field trial investigating the
potential to carbonate metallurgical slag samples under environmental pressures and
temperatures using a gas line delivering 2 dm3 min-1 CO2 was also undertaken. This thesis also
shows the economics of combining the net-CO2 uptake with different energy sources used to
power and recommends that further reduction in net-CO2 emissions can be achieved by
switching to ‘green’ energy sources. Comparing the %-metal-cation content of each material,
conversion of 0.55% to 1.76% was achieved by steel slags and 0.3% to 4.89% for blast furnace
slags. Further work needs to focus on the mineralogy of the samples and the carbonate
mineral growth processes in order to create the optimum conditions needed to realise further
untapped carbonation potential.