Preparation of high surface area CaCO3 for SO2 removal by absorption of CO2 in aqueous suspensions of Ca(OH)2

High surface area and porous CaCO3 particles were produced by absorption of CO2 in aqueous suspensions of Ca(OH)2 with the addition of a suitable additive at 27 °C and 1 bar. The CaCO3 surface area was determined mainly by the shape and size of the constituting primary particles. In the absence of any additive, the CaCO3 surface area varied with the initial Ca(OH)2 concentration and reached a highest value (19.6 m2/g) at 2.4 wt.% Ca(OH)2. The CaCO3 surface area was affected little by the CO2 flow rate (1.0–3.5 L/min) and decreased with increasing solution temperature (27–45 °C). The CaCO3 surface area was affected markedly by the kind of additive, the amount of additive, and when to add the additive. The optimal conditions for maximizing the CaCO3 surface area were identified for each additive. Among the six additives tested (Dispex A40, Dispex N40, sodium bis (2-ethylhexyl) sulfosuccinate, Disponer 926, ammonium stearate, and stearic acid sodium), Dispex A40 and N40 were more effective. An effective additive in raising the CaCO3 surface area and pore volume was to enhance the formation of fine CaCO3 primary particles and the loose aggregation of them. High surface area CaCO3 was obtained when an effective additive was added after bubbling CO2 into the Ca(OH)2 suspension. The CaCO3 with the highest surface area (57 m2/g) was obtained by adding 0.25 wt.% Dispex A40 to a 2.4 wt.% Ca(OH)2 suspension when the solution pH dropped to 6.5–6.2. The high surface area CaCO3 was highly reactive toward SO2, and the reactivity increased with increasing surface area in general. A conversion of 0.87 was achieved when the CaCO3 with the highest surface area was sulfated at 950 °C and 4000 ppm SO2 for 1 min.