Physico-Chemical Study of the Possibility of Utilization of Coal Ash by Processing as Secondary Raw Materials to Obtain a Composite Cement Clinker

Abstract

A significant amount of energy waste has accumulated in the world, in particular, large-tonnage fine ash from central heating stations (coal ash), which can negatively affect the natural environment and the health of the population. However, at the same time, due to its chemical composition, this waste can be disposed of by complex processing as a secondary mineral component, thus reducing the anthropogenic load on the natural environment. This article presents a physico-chemical study of coal ash for its further use as a secondary mineral component, in particular, a component of a raw mixture with limestone to produce a composite Portland cement clinker. Coal ash and limestone were subjected to granulometric, chemical, differential thermal, scanning electron microscopy, elemental chemical and X-ray structural analyses, as well as modeling to assess the possibility of optimizing the raw material and mineralogical composition of the composite Portland cement clinker. During the research, the chemical and elemental compositions of the coal ash and limestone were determined and SEM images of the coal ash were obtained; it was found that 68.04% of the coal ash was represented by the fraction with granules <0.16 mm. Using X-ray diffraction analysis, the main limestone minerals were identified, which were represented by calcite and silica. Based on the results of mathematical modeling of the utilization of coal ash from a thermal power plant by processing with limestone, a two-component raw material mixture containing 23.66% fly ash and 76.34% limestone was optimized and the optimal mineralogical composition of the composite Portland cement clinker was determined. Utilization of coal ash by processing as a secondary raw material can be carried out at almost any ash storage facility anywhere in the world, taking into account the chemical composition of the processed ash. It was found that the replacement of natural raw materials with man-made raw materials in the form of coal ash contributed to a reduction in fuel consumption for firing (kg of conventional fuel) by 13.76% and a decrease in the thermal effect of clinker formation by 5.063%.