Direct aqueous carbonation of electric arc furnace slag: process optimisation through experimental design

At present, one of the strategies to reduce the embodied carbon of cement is to partly replace clinker with metallurgical slags. In this perspective, this study investigates the accelerated aqueous carbonation of electric arc furnace slag as possible treatment for its reuse in the cement industry. In view of developing a low-energy and industrially integrated process, mild carbonation conditions were selected: ambient pressure, low liquid-to-solid ratio, minimised temperature (between 20 °C and 60 °C) and short duration time (ranging from 20 to 60 min). To optimise the carbonation process, a design of experiments was developed. The Response Surface Methodology showed a non-representative trend along time. Therefore, a non-linear model was adopted for a better prediction of CO2 content above 50 min. The results were satisfactory with an optimum CO2 uptake of 7.7% and the carbonation degree obtained, 30.2%, was the highest registered in previous literature for open systems. Moreover, a literature analysis on previous aqueous and wet direct carbonation of Electric Arc Furnace slag was carried out using Principal Component analysis. This exploratory data analysis identified the most effective carbonation parameters based on the reactor type and suggested the investigation of further parameters such as liquid-to-solid ratio and CO2 flow rate and partial pressure, maintaining the perspective of a sustainable process.