Effect of ferrous sulfate replacing gypsum on properties and reducing Cr(VI) of cement paste

Abstract

Ferrous sulfate has a negative effect on the properties of cement when reducing chromium (VI) in cement. Ferrous sulfate was used to replace gypsum in cement because of its similarity to gypsum. The effect of ferrous sulfate on cement properties and reducing chromium (VI) was characterized by setting time, compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM), the leaching of chromium (VI). Ferrous sulfate can adjust the setting time of cement paste, and the compressive strength was the highest when the amount of substitution is 25%. Furthermore, the content of portlandite in hydration products were reduced. The reduction efficiency of chromium (VI) was 88.11%, 98.00%, 98.91% and 98.57% respectively when the replacement amount of ferrous sulfate is 25%, 50%, 75% and 100%, the chromium (VI) was reduced to chromium (III) to form Cr3+-ettringite. Ferrous sulfate replacement gypsum can not only solve the negative effect of gypsum on chromium (VI) immobilization, but also further reduce the leaching amount of chromium (VI).