Leaching kinetics and reactivity regulation of red mud in an NaOH solution

Abstract

Red mud is an alkaline silico-aluminous solid waste with application potential in alkali-activated slag cement, determined by the leaching activity of Si, Al, and Ca ions in an alkaline solution. This study investigated the reactivity and leaching kinetics of silica and alumina in red mud in an NaOH solution. The leaching kinetics of Si and Al ions were investigated through inductively coupled plasma emission spectroscopy, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared absorption spectroscopy. Leached Si and Al primarily contributed to N-(C)-A-S-H formation. Diffusion across the product layer governed the leaching process of red mud in the NaOH solution. The activation energies for Si and Al leaching were 16.368 and 23.037 kJ/mol, respectively. Adding slag powder activated the chemical bonds between Si-O and Al-O, increasing the leaching activity of the red mud. This study clarified the interrelationships between the physicochemical properties, leaching behaviour, and reactivity of red mud.