Enhanced Recovery Process of Calcium Oxide and Metals from Steelmaking Slag with Net Carbon Sequestration

The iron and steel making (ISM) industry is one of the largest CO₂ emitters in the world. Despite a sustained global research effort, utilization of best available technologies will not result in CO₂ reductions for the industry that are sufficient to meet the Paris Climate Agreement. One area of the ISM process that still contains a large untapped potential for CO₂ reduction is the recycling of slag. Currently ∼46% of ISM slag in Japan is used as an additive in cement production, reducing CO₂ emissions. However, substantial grinding of slag is necessary prior to usage, which reduces the net CO₂ offset of this process. We propose an alteration to current cooling methods in order to reduce the grinding energy of slag. Additionally, this new method recovers more low entropy metallic species than current processes. Molten slag is poured into shallow trays and allowed to settle in order to increase the separation of accidentally entrained metals from the calcium silicate melt. Upon reaching the solidification temperature the slag is cooled rapidly enough to induce the amorphous structure necessary to use slag as a cement additive. After solidification, the slag is quenched from high temperature in an ambient temperature water bath to create fractures throughout the slag due to high thermal stresses. These fractures reduce the subsequent grinding energy and liberate disparate species. This method results in a potential reduction of CO₂ emissions for the Japanese ISM industry of ∼12.4 Mt/year; an increase of 3.0 and 2.1 times that of water-based and air-based cooling methods that include heat recovery, respectively. The process is validated by simulation and experimental results.