Unveiling the cooperation effects of fluorine and copper on tricalcium silicate (C3S) during cement kiln co-processing hazardous wastes containing Cu

Abstract

Fluorine (F) from fluorite mineralizer and copper (Cu) would be introduced together into raw meals during cement kiln co-processing hazardous wastes containing Cu, unfortunately the cooperation effects of fluorine and copper on the properties of cement clinker are still vague, it directly restricts the resource utilization of these wastes in the cement industry. Therefore, the cooperation effects of fluorine (CaF2) and copper (CuO) on the formation and properties of tricalcium silicate (C3S) were unveiled. The results indicated that a small cooperation addition of CuO could reduce distinctly f-CaO content of C3S doped with CaF2, and its burnability would be promoted notably, the immobilization of fluorine and copper in doped C3S also were promoted. Compared with C3S doped with CaF2, a cooperation addition of CuO and CaF2 further improved the formation of C3S grains and increased the structural symmetry of C3S crystal. The cooperation effects triggered the diffraction peaks for C3S polymorphisms to shift right, and induced the visible defects on the surface of C3S grains. In the current incorporation amounts of CaF2 and CuO into C3S, F- and Cu2+ would dissolve in its structure possibly by the replacement of O2– and Ca2+ respectively. CaF2 addition accelerated the initial hydration, but postponed the later hydration of C3S. The initial hydration was further accelerated by a cooperation addition of CuO, and its effects would be quite different if changing cooperation amounts of CaF2, accelerating or decelerating the hydration process of doped C3S relied on the cooperation amounts of CaF2 and CuO. The findings in this work would be expected to provide a promising solution to reduce the large energy consumption and CO2 emission in cement industry.