Study on the Mechanism of the Wet Carbonation Reaction and Performance Characterization of Ammonium Chloride-Modified Steel Slag

Base-activated waste carbonation (BAWC) is a highly promising carbon sequestration strategy that utilizes alkaline solid waste to react with CO₂, converting it into stable mineral carbonates. This approach achieves dual objectives of carbon storage and resource utilization. This study proposes a wet carbonation process for steel slag modified with ammonium chloride, aiming to achieve effective CO₂ sequestration while promoting the resource recovery of steel slag, thereby mitigating greenhouse gas emissions. The study first investigates the modification effect of ammonium chloride solution on steel slag, demonstrating significant improvements in its physicochemical properties, particularly in terms of reactivity and surface structure. Subsequently, a wet carbonation process is employed, and the effects of temperature, stirring speed, carbonation time, and liquid-to-solid ratio on the carbonation reaction are systematically examined using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and other characterization techniques. The carbonation products and CO₂ sequestration efficiency of the modified steel slag under these four factors are analyzed. Experimental results indicate that the primary mineral components of the modified steel slag are Ca₂SiO₄, MgO, and CaO, confirming its potential as an industrial waste material with excellent CO₂ storage capacity. After carbonation, the main products are calcite-type calcium carbonate crystals and silica gel. Microstructural analysis reveals that the carbonated slag exhibits a denser and more compact structure, with reduced porosity and disordered aggregates of polyhedral crystals. Under optimized reaction conditions (60 °C, 30 min of CO₂ bubbling, liquid-to-solid ratio of 200 g/L, and stirring speed of 600 rpm), the modified steel slag achieves a maximum CO₂ sequestration efficiency of 32.2%, meaning that each kilogram of modified slag can mineralize and absorb 0.322 kg of CO₂. These findings demonstrate the significant potential of the wet carbonation process for both steel slag recycling and CO₂ capture.