Utilising steel production waste material for low pressure and passive carbon sequestration

Abstract

In 2019, the UK steel industry produced 12 million tonnes of CO2 equivalent greenhouse gas emissions, including indirect emissions from power production, which equated to 11.5% of the UK industrial emissions and 2.7% of the country’s
entire greenhouse gas emissions for that year (UK Steel, 2020). Therefore, lowcost strategies to reduce these emissions are needed for the UK to meet its commitments to a “net zero” by 2050. One of the major waste products produced by steel manufacture is steel slag, an alkaline waste material that is predominantly composed of Ca and Mg, both of which are suitable for the formation of carbonate minerals (CaCO3 and MgCO3). This process of carbonate mineral formation sequesters atmospheric CO2 as a stable mineral resource; therefore, it is possible for the CO2 emissions produced from the manufacture of steel to be sequestered using one of the other waste materials produced by the same process. Laboratory-based carbon sequestration experiments utilising the Port Talbot BOS steel slag were found to successfully sequester CO2 at ambient conditions through the formation of calcium carbonate (CaCO3). The steel slag reacts rapidly upon its introduction into the aqueous solution, with the calcium oxide (CaO) present in the steel slag quickly converting to calcium hydroxide (CaOH), and then into calcium (Ca2+) ions and hydroxide (OH-) ions. The introduction of CO2 into the reactor system generates carbonic acid (CO3 2-) within the aqueous solution and the release of H+ions, allowing for the formation of CaCO3 and its subsequent precipitation out of solution as it reaches saturation. A number of potentially economically useful elements were also liberated from the steel slag material during the carbon sequestration experiments, with the most abundant of these being; Si, V, Sr, B, Ba, Ti, Al, and Zn. Unfortunately, however, the low concentrations of these elements makes them unsuitable for exploitation at this scale, however a number of them do pose a potential environmental risk at the concentrations measured and recovery of them from any wastewater may be necessary. In addition, it was found that the legacy steel slag at the Port Talbot site shows evidence of passive carbon sequestration over time through the same process described above. Unfortunately, the results from the site were inconsistent, primarily attributed to the working nature of the site which makes it difficult to accurately determine the age of a particular steel slag sample, therefore, a more extensive investigation is required to clarify the extent of passive carbon sequestration occurring at the Port Talbot site.

Date of Award	2023
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Andy Mitchell (Supervisor) & Bill Perkins (Supervisor)