A comparative study of the physicochemical properties of Mg-rich and Ca-rich quicklimes and their effect on reactivity

We studied the physicochemical properties of quicklimes derived from typical carbonate rocks, focusing on variations in chemical composition and their effects on reactivity. Samples were selected based upon their composition (two Mg-rich and two Ca-rich samples), freshness (scarce secondary alteration features), texture (two common Hellenic limestones and two marbles), and similarity to materials commonly used in industrial practice. We characterized the samples in detail by chemical analysis, X-ray diffraction, N 2 -BET, scanning electron microscopy, petrography, TG/DTA and EN 459-2 testing, and examined correlations between measured properties and reactivity. Surprisingly, specific surface area (SSA) is found not to be a determinant factor for reactivity. As expected, chemical composition has an important role in the sintering and slaking mechanisms. Impurities such as Fe 2 O 3 and K 2 O facilitate, while MgO inhibits, sintering. Mg-rich quicklime, with impurities in trace amounts, calcined at 1,200 °C, has SSA of 11.9 m 2 /g while Ca-rich quicklime, with considerable impurities, has SSA of 0.6 m 2 /g. Variations in the slaking behavior, monitored by reactivity tests, were identified and related to the properties of the quicklimes. The variations can be understood in the context of a proposed five-step slaking mechanism. Slaking curves are found to be insensitive to source-rock texture; they are similar for the two sets of Mg-rich and the two sets of Ca-rich quicklimes, respectively. MgO is found to improve hydration resistance of the material, leading to more complex slaking curves. A general firing scheme is proposed based on the investigated material properties.