Production of Portland cement clinker from spent chamotte refractory lining

Introduction. The cement industry is a major source of CO2 emissions, which highlights the need to implement circular economy principles, particularly the utilization of large-tonnage industrial wastes. Spent chamotte lining (SCL) from aluminum electrolyzers represents a significant environmental challenge – a Class IV hazardous refractory material containing fluorides and alkalis. The aim of this study was a comprehensive experimental assessment of the feasibility of technological integration of two types of waste – leached SCL and amorphous microsilica (MS) – into Portland cement clinker production as a replacement for traditional clayey raw material. Methods. The materials used included limestone, leached SCL, amorphous MS, and an iron-containing corrective sand. The raw mix composition was calculated and optimized using the Pearson's envelope method and solving a system of material balance equations with target values for the lime saturation factor (LSF = 0.90) and the silica ratio (SR = 2.3). Results and Discussion. Laboratory firing of pressed raw mix briquettes was conducted in a muffle furnace following a regime simulating the industrial cycle. The kinetics of decarbonation and phase formation were studied using Thermogravimetric Analysis methods with specifications. The phase composition of the clinker was determined by X-ray Diffraction Analysis, and its microstructure was examined using Scanning Electron Microscopy. The physico-mechanical properties of the obtained cement were tested according to standard methods. Conclusions. It was established that the introduction of a composite SCL+MS component (up to 14.5 % of the raw mix by mass) reduces the decarbonation temperature and the onset of alite (C3S) synthesis by 20–30 °C due to the combined effect of the high dispersity of MS and the residual mineralizing action of fluorides. The experimental clinker-based cement meets the requirements of PC 300 grade, demonstrating a 28-day compressive strength of 29.6 MPa, which is statistically indistinguishable from the control (29.8 MPa). Other critical parameters were evaluated for application which are: the equivalent alkali content (Na2Oₑq.) in SCL should not exceed 2.0–2.5 %, and its proportion in the raw mix can be 8–12 %. The results confirm the technical feasibility of utilizing hazardous waste to produce competitive cement with potential reductions in firing energy consumption.