Energy consumption in the production of calcined kaolinitic clays for use as supplementary cementitious materials

Calculation of energy consumption is crucial for the evaluation of the economic viability and environmental impact of thermal processes involved in cement production. As calcined clays become more widely accepted as supplementary cementitious material (SCM) around the world, it becomes very important to reliably predict the energy requirements for the industrial calcination of clays. In this study, a simple mathematical model is developed to estimate the calcination energy required for the conversion of kaolinite into metakaolin considering the drying and dehydroxylation process. The model was developed using seven natural clays with varying chemical compositions and a wide range of kaolinite contents (73–25%). The two key input parameters, namely, moisture content and kaolinite content, were found to be sufficient for obtaining a reasonable prediction of the energy demand (R2 = 0.97). In addition, the study found that the associated minerals also have a slight influence on the calcination energy, with iron-rich clays exhibiting relatively lower energy demand compared to quartz-rich clays. The model was validated with 22 other clay samples and the results indicate that good estimates of energy requirements for the calcination process can be made and that the model can be used satisfactorily for the design of clay calcination processes.