Effect of reductant on property and carbon dioxide sequestration for belite cement from phosphogypsum Auswirkungen von Reduktionsmitteln auf die Eigenschaften und die Kohlendioxidbindung von Belit-Zement aus Phosphorgips

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 °C for 2 hours 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 calcium sulfide (CaS) to calcium sulfate (CaSO₄) was 3, respectively. The Sulfur trioxide contents in the clinkers were 0.80 wt.-% 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 °C, 75 % relative humidity and 20 % carbon dioxide (CO₂) concentration. As the carbonation curing age increased, the compressive strengths of the samples gradually enhanced. When 10 wt.-% carbon was employed as the reductant, compressive strengths of the samples were 15.5 MPa, 15.6 MPa, and 15.6 MPa after carbonation curing at 3 day, 7 day and 28 day, respectively. When calcium sulfide was employed as the reductant, the compressive strengths of the samples were 19.8 MPa, 27.2 MPa, and 34.1 MPa after carbonation curing for 3 day, 7 day and 28 day, respectively. The carbon dioxide sequestration contents of the samples prepared with a 10 wt.-% carbon and calcium sulfide reductant, were 11.6 % and 9.2 % after carbonation curing for 28 days, 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 carbon dioxide in the atmosphere during curing process.