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THE USE OF SULPHATE WASTE FOR MODIFYING CEMENT CLINKERS

Yury Krivoborodov

Abstract

In cement production waste of various industries (metallurgical, chemical, etc.) is widely used. This contributes to the improvement of environmental protection and intensification of the clinker firing process, as well as improving the quality of clinker by modifying clinker minerals. Due to the large variety of wastes, the decision to use them effectively in the production of Portland cement clinker should be based on the results of scientific research both in the laboratory and in the industrial environment.The presence of trace impurities (titanium, zinc, sulfur, chromium, manganese, etc.) in many wastes of nonferrous metallurgy and chemistry plants predetermined the need to study their role in the burning processes of the raw mix and the formation of clinker phases. The research of many scientists is devoted to this problem. In the study of V. V. Timashev and his students, as well as I. Maki, F. Taylor and others, special attention was paid to the modification of clinker minerals as a way to increase the hydration activity of clinker. The most common modifying materials are wastes containing sulphates and magnesium oxide. It was found that magnesium oxide stabilizes the M3-form C3S, and sulfate ions stabilize the M1-form. This contributes to the strength of the modified clinker cement. However, the problem of using these wastes remains very important. At a number of plants, the use of sulfate waste leads to a deterioration of the clinker firing process, the appearance of rings in the furnace, an increase in clinker dusting, and a decrease in the hydration activity of cement. The aim of our work was to study the anomalous effect of sulfate waste on the phase composition of Portland cement clinker. This is especially important for cement plants using limestone with a high content of magnesium oxide. The effect of SO3 and MgO separately and at their joint presence in the raw mixture was studied. It is established that sulphates and magnesium oxide influence on the process of clinker formation, the phase composition of clinker and, accordingly, the properties of cements. The degree of their influence is manifested due to the formation of metastable compounds and alloys at the stage of solid-phase sintering, changes in the composition and properties of the main clinker melt, the formation of liquation zones of the melt, changes in the crystallization rate of the clinker phases, the formation of solid solutions. It was established the optimum content of magnesium oxide and the ratio of MgO/SO3 in the raw mixture, which ensures the normal firing of clinker. The strength of cement based on modified clinker is significantly increased.

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DOI resolver: doi.org/10.5593/sgem2019/6.2/s26.039

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