For both the waste treatment of large quantities of blast furnace (BF) slag and carbon dioxide (CO2) that are discharged in ironworks, mineral carbonation by BF slag was proposed in this decade. However, it has not been widely used due to its high energy consumption and low production efficiency. In this study, a microwave roasting method was employed to mineralize CO2 with BF slag, and the process parameters for the sulfation and energy consumption were investigated. A mixture of BF slag and recyclable ammonium sulfate [(NH4)2SO4] (mass ratio, 1 : 2) was roasted in a microwave tube furnace, and then leached with distilled water at a solid : liquid ratio of 1 : 3 (g mL-1). Under the optimized experiment conditions (T = 340 °C, holding time = 2 min), the best sulfation ratios of calcium (Ca), magnesium (Mg), aluminum (Al), and titanium (Ti) were 93.3%, 98.3%, 97.5%, and 80.4%, respectively. Compared with traditional roasting, the production efficiency of this process was more than 10 times higher, and the energy consumption for mineralizing 1 kg of CO2 could be reduced by 40.2% after simulation with Aspen Plus v8.8. Moreover, 236.1 kg of CO2 could be mineralized by one ton of BF slag, and a series of by-products with economic value could also be obtained. The proposed process offers an energy-efficient method with high productivity and good economy for industrial waste treatment and CO2 storage.