Impact of calorific value on thermal activation and desilication performance of high-alumina coal gangue

Abstract

Coal gangue is a major industrial solid waste generated from coal mining and processing, and amorphous silica removal is the key to its high-value utilization. To optimize thermal activation-desilication process of coal gangue, this study investigated the effect of inherent calorific value on the desilication performance of calcined clinker via comparative analysis of non-calorific gangue, controlled-calorific coal-gangue mixtures, and industrial coal gangue. Under standard conditions, non-calorific gangue achieved a desilication efficiency of 76.93% with a leached residue alumina-to-silica ratio (A/S) of 3.521. For controlled-calorific-value coal-gangue mixtures with calorific values spanning 287-3002 kcal/kg, residue A/S decreased from 3.45 to 2.25, showing a strong negative correlation between calorific value and A/S; the actual industrial coal gangue exhibited an identical variation trend. Coal gangue with high calorific value promotes mullite formation via the reaction of amorphous silica and alumina during thermal activation, thereby reducing alkaline-soluble amorphous silica content and impairing desilication performance. Controlling coal gangue calorific value below 784 kcal/kg achieves a balance between energy conservation and desilication efficiency. This study confirms calorific value as a critical factor, providing technical guidance for industrial coal gangue resource utilization via thermal activation and alkaline desilication.