Effects of Calcium Sulfate and Stannous Sulfate on Cement Properties and Dissolution of Hexavalent Chromium

Cr(III) (trivalent chromium) is converted to Cr(VI) (hexavalent chromium) during the production of clinker. Calcium sulfate in cement will increase the dissolution concentration of Cr(VI) in cement paste. Stannous sulfate (SnSO4) as a common hexavalent chromium reducing agent was added to adjust the setting time and reduce the content of Cr(VI) in cement paste. In this study, stannous sulfate (SnSO4), a common hexavalent chromium reducing agent, was added to adjust the setting time and reduce the content of hexavalent chromium in the cement paste. When calcium sulfate and stannous sulfate were added to the clinker, the cement hydration performance and the content of Cr(VI) were studied through experiments such as setting time, compressive strength, x-ray diffraction, Fourier infrared spectroscopy, thermogravimetry, and generalized acid neutralization. The results showed that when a certain amount of SnSO4 (25%) was substituted for gypsum, it not only could regulate the setting time of the cement paste, but also could promote the formation of hydrated calcium silicate (C─S─H) in cement hydration and increase the compressive strength. Stannous sulfate could reduce the concentration of Cr(VI) in the cement paste, and the unreduced Cr(VI) was immobilized in the ettringite. The aforementioned studies demonstrated that SnSO4 substitution for gypsum can be used in cement production engineering, which can not only reduce the content of Cr(VI), but also promote the performance of cement.