Carbon Sequestration in Steel and Cement Industries using Indirect Mineral Carbonation (IMC) Process (Flexible Funding 2024)

Dr Nejat Rahmanian, University of Bradford, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “Carbon Sequestration in Steel and Cement Industries using Indirect Mineral Carbonation (IMC) Process”.

Introduction

The steel and cement sectors are among the largest industrial contributors to global carbon dioxide (CO₂) emissions, responsible for approximately 7% and 6.5% of total emissions respectively. Current estimates indicate that steel production releases between 1.8 and 2.2 tonnes of CO₂ per tonne of steel, depending on the production technology employed, while cement production emits approximately 0.9 to 1 tonne of CO₂ per tonne of cement. To meet global climate goals, carbon emissions from steel, cement, and concrete must be reduced by over 90% by 2050.

Figure 1 Infographic shows the contribution of the steel and cement sector to CO2 emission (Source Industrial Deep Decarbonization, shorturl.at/tR9SD)

This UKCCSRC-funded project explored a practical route to CO₂ capture and utilisation by converting industrial by-products, i.e. steelmaking slag and cement kiln dust and finally its sequestration and conversion to calcium carbonate. The approach is rooted in indirect aqueous mineral carbonation, with a focus on using commonly available chemicals, minimal energy input, and lab-scale process simplification.

The overall aim was to recover calcium from waste streams using controlled leaching and subsequently convert it into a stable mineral form by reacting it with captured CO₂.

Figure 2: Overall view of CO2 capture and storage in the steel industry

Methodologies

To achieve the aim of the project, the study investigated a novel Indirect Mineral Carbonation (IMC) pathway for CO₂ sequestration, leveraging industrial alkaline wastes from steel and cement plants. The methodology was strategically designed as an integrated four-stage framework: (i) sample characterisation, (ii) acid leaching and process optimisation, (iii) impurity removal and CO₂ capture, and (iv) product synthesis and characterisation. Together, these stages ensured a robust evaluation of technical feasibility to support the project’s four core objectives and deliver reliable data for process feasibility and optimisation.

Calcium extraction from a range of waste materials was investigated. These included BOF slag, blast furnace slag, and ladle slag using different acids under various operating conditions. The experimental design employed a full factorial approach to determine the influence of acid type, leaching temperature, reaction time, and solid-to-liquid ratio on calcium extraction efficiency and selectivity. Following the leaching stage, a pH swing method was applied to selectively precipitate major impurities such as Fe, Al, and Mg, thereby improving the quality of the calcium-enriched filtrate for subsequent carbonation. The purified solution was then carbonated using sodium carbonate, generated in a preceding CO₂ scrubbing step, to precipitate high-purity calcium carbonate under the ambient conditions.

Overall Conclusion and Looking Forward

This study demonstrated a four-stage indirect mineral carbonation process for the valorization of calcium-bearing industrial wastes from steel and cement industries successfully, albeit with the limited time and budget, specifically basic oxygen furnace (BOF) slag for CO₂ capture and permanent storage as solid calcium carbonate (CaCO₃).

The successful indirect mineralization of CO₂ from captured gas via the carbonation process using real industrial waste under low-energy conditions demonstrates the potential of this pathway as a carbon management strategy. By coupling resource recovery with CO₂ utilization, the process delivers dual environmental benefits—reduction in emissions and valorization of waste.

These findings establish a basis for future research aimed at process optimisation, including improving carbonation kinetics, enhancing material conversion efficiency, and evaluating scale-up potential. Further investigation into system integration and lifecycle assessment is also recommended.

Acknowledgment

The PI would like to thank UKCCSRC/EPSRC for providing this funding opportunity. The author welcomes potential industrial collaborators interested in continuing this research project and invites them to get in touch via email.

Read more on Nejat’s Flexible Funding 2024 project page.