LAUSR

This study reveals ion exchange kinetics in hydrated calcium-alumino layered double hydroxides of the alumino-ferrite monosubstituent (AFm) subgroup. By careful analysis of solution phase (ion) concentrations and the solid phases, the rate of exchange of NO3– for Cl– ions from the interlayer positions is studied across a range of temperature, solution compositions, and solution conditions (i.e., static and convectively mixed). Ion exchange kinetics conform to an exponential first-order reaction that follows an Arrhenius formalism. The activation energy of ion exchange is 38.2 ± 4.6 kJ/mol for exchange occurring in the thermodynamically preferred (i.e., NO3– for Cl– ion exchange) direction and it is 1.8 times greater for the inverse less-preferred pathway. For ion exchange occurring in the favored direction NO3-AFm converts to Cl-AFm; whereas in the disfavored (less-favored) direction, the compositional change occurs in two steps with the formation of a Cl–NO3–AFm solid solution as an intermediate step; be...