Fundamental study on reactive components and leaching kinetics of ceramic waste for geopolymer production

This research identifies and systematically evaluates the reactivity of crystal and amorphous phases of five typical ceramic waste powders (CWP) based on selective chemical dissolution and quantitative X-ray powder diffractometry. The alkali-activity classification of mineral components of ceramic waste is identified. Four principal components are amorphous phase (glass mainly composed of Si and Al), reactive crystals mica, partially reactive feldspars, and inert crystals quartz and mullite. Their leaching kinetics of ceramic wastes in NaOH solution are studied. For geopolymer production, the amorphous phase is the main reactant phase. The average activation energy for the leaching of Si and Al is 103.49 and 90.01 kJ/mol, respectively. Based on the reaction kinetics, a rapid evaluation of the ceramic waste-alkali reactivity is proposed given individual leaching ratio of Si and Al. Besides, another simple assessment method based on the geometrical specific surface area (SSA) is provided for rough assessment of activity at room temperature. There is a good correlation between the order of reactivity ranking and the compressive strength of alkali-activated paste containing CWP. The reactivity evaluation methods are of great value to the application of CWP in production practice.