By-product materials in cement clinker manufacturing

The use of Cl- and SO3-containing by-products from chemical industries for manufacturing Portland cement clinker using a wet process was examined. The chemical and mineralogical compositions of the by-products and raw materials were determined. Homogeneous raw mixes containing different concentrations of by-products (5-30%) were prepared and the influence of the by-products on all steps of burning the mixes in a kiln to form a cement clinker was investigated. It was shown that introducing Cl- and SO3-containing by-products to the raw mixes significantly changes all the cement clinker producing stages and changes the chemical and mineralogical compositions at all intermediate stages and in the finished products, forming new minerals containing Cl and SO3 [CaOx (SiO2)(y) CaCl2] or [CaOx (SiO2)(y) CaSO4] and increasing the amount of well-known intermediate minerals. The presence of the chlorides and sulfates in the cement clinker burning processes removes alkali from the raw mixes, turning them to volatile forms, accelerating the raw mineral decomposition processes and accelerating the formation processes of cement minerals (C2S, C(12)A(7), C(4)AF) and formation of chloride and sulfate cycles in the kiln, forming clinker liquids and decreasing the formation and growth of the main cement minerals (C(3)A, C3S). The cement clinker contains some quantity of minerals with Cl or SO3. Their presence in the final product decreases cement quality by reducing the amount of active CaO (C) and reducing the active CaO/SiO2 ratio. (C) 1999 Elsevier Science Ltd. All rights reserved.