A novel approach to accelerate carbon dioxide sequestration of ladle furnace slag using sodium bicarbonate solution

The annual output of ladle furnace (LF) slag exceeds 20 million tons. The slag pulverises easily and contains heavy metals, leading to severe environmental pollution during stacking. However, slag is suitable as a material for carbon dioxide sequestration owing to its high calcium oxide content. This study focuses on exploring a new scheme because the direct carbonation method requires strict operating conditions and the indirect carbonation method hinders the materialisation of ladle furnace slag. In this new scheme, a sodium bicarbonate solution acts as the treatment solution for the carbonate LF slag, and the treated solution regenerates by injecting carbon dioxide. The experimental results show that the sodium bicarbonate concentration, stirring speed, and liquid-to-solid ratio have minor effects on the CO2 uptake percentage. With increasing reaction time, the CO2 uptake percentage increases during the first 120 min and then remains constant. The rise in temperature has a negative impact on the CO2 uptake percentage. However, decreasing the particle size of the LF slag greatly improves the CO2 uptake. CO2 injection at a flow rate of 1 L/min for 100 min decreased the pH of the treated solution to 8.9, achieving regeneration of the treated solution. Thermodynamic analysis indicates that for the reactions between sodium bicarbonate solution and minerals, calcium oxide and calcium aluminate have a significant thermodynamic driving force, indicating that slag with high basicity and CaO-Al2O3 base slag is more suited for sequestering CO2. The study provides a novel method for CO2 sequestration and ladle furnace slag stabilization.