Effect of reductant on property and CO 2 sequestration for belite cement from phosphogypsum

Abstract Gypsum can be decomposed at low-temperature by adding reductant, which is beneficial to obtain cement. The effects of different reductant on the phases of belite cement raw meals were studied by calcining at 1300℃ for 2h and using phosphogypsum as raw materials. Diffraction peaks of calcium sulfate were not observed in the samples when 10 wt% activated carbon was added and the molar ratio of CaS to CaSO4 was 3, respectively. The Sulfur trioxide contents of in the clinkers were 0.80 and 0.64 wt%, respectively. The effect of carbonation curing on the cement properties was also studied. Carbonation curing can promote cement hydration and increase strength at 20 ℃, 75 % relative humidity and 20% CO2 concentration. As the carbonation curing age increased, the compressive strengths of the samples gradually enhanced. When 10 wt% carbon was employed as the reducing agent, compressive strengths of the samples were 15.5, 15.6, and 15.6 MPa after carbonation curing at 3, 7 and 28 d, respectively. When CaS was employed as the reducing agent, the compressive strengths of the samples were 19.8, 27.2, and 34.1 MPa after carbonation curing for 3, 7 and 28 d, respectively. The carbon dioxide sequestration contents of the samples prepared with a 10 wt% carbon and CaS reductant, were 11.6% and 9.2% after carbonation curing for 28 d, respectively. These findings demonstrate the potential to use phosphogypsum with various reductants to enhance the quality of belite cement and at the same time consume more CO2 in the atmosphere during curing process.