Insights into Coproduction of Silica Gel via Desulfurization of Steel Slag and Silica Gel Adsorption Performance

Steel slag is a calcium-containing alkaline industrial solid waste that can replace limestone for flue gas desulfurization. It can remove SO₂ and coproduce silica gel while avoiding CO₂ emission from limestone in the desulfurization process. In this study, steel slag with a D ₅₀ of 3.15 μm was used to remove SO₂. At room temperature, with a solid-liquid ratio of 1:10, a stirring speed of 800 rpm, and the mixed gas introduced at a flow rate of 0.8 mL/min, 1 ton of steel slag could remove 406.7 kg of SO₂, a SO₂ removal efficiency typical of existing calcium-rich desulfurizers. As limestone desulfurization can release CO₂, when limestone desulfurization was replaced with steel slag of equal desulfurization ratio, CO₂ emissions could be reduced by 279.6 kg and limestone could be reduced by 635.5 kg. The yield of silica gel was 5.1%. Silica gel pore structure parameters were close to those of commercially available B silica gel. Products after desulfurization were mainly CaSO₄ ·2H₂O, CaSO₄ ·0.5H₂O, CaSO₃ ·0.5H₂O, and silica gel. With a silica gel dosage of 30 mg, a temperature of 20 °C, a pH value of 6.00, a stirring time of 0.5 h, and a methylene blue concentration of 0.020 mg/mL, the removal ratio of methylene blue adsorbed by silica gel was 98.4%.