Thermochemical behaviour of several common salts blended with cement raw material

Abstract

Experiments were conducted to study the thermochemical behaviour of common chlorides, sulfates and alkali salts when blended with cement raw materials at high temperatures and the phenomena of element migration and the transformation of chlorine, sulfur, potassium and sodium in the process. There was little effect on the formation of clinker with the addition of 20% potassium chloride + sodium chloride and 10% calcium sulfate. Potassium chloride and sodium chloride were observed to melt at 800°C and completely volatilise at 1100°C, while calcium sulfate was not completely decomposed until 1450°C. The addition of 10% calcium chloride, 20% potassium carbonate + sodium carbonate or 20% potassium sulfate + sodium sulfate resulted in the appearance of the liquid phase of raw materials at 800°C. Potassium carbonate + sodium carbonate predominantly formed complex and stable potassium salts and sodium salts through reactions with the raw materials, significantly affecting the formation of C2S and C3S. Calcium chloride and potassium sulfate + sodium sulfate mainly produced liquid phases through melting. Calcium chloride completely volatilised after reaching 1250°C, and the molten calcium chloride inhibited the decomposition of calcium carbonate, thereby inhibiting the formation of C2S and C3S. Although the potassium sulfate and sodium sulfate melted, they only formed stable sulfate salts, without affecting the formation of C2S and C3S.