Kinetics and equilibrium studies on the treatment of nitric acid with Mg–Al oxide obtained by thermal decomposition of [formula omitted]-intercalated Mg–Al layered double hydroxide

Abstract

Mg–Al oxide obtained by thermal decomposition of NO3--intercalated Mg–Al layered double hydroxide (NO3·Mg–Al LDH) was found to treat HNO3, acting as both a neutralizer and fixative for NO3-. The degree of NO3- removal increased with time, Mg–Al oxide quantity, and temperature. The NO3- removal could be represented by a first-order reaction. The apparent activation energy was 52.9kJmol−1, confirming that NO3- removal by Mg–Al oxide proceeded under chemical reaction control. Furthermore, the adsorption of NO3- on Mg–Al oxide could be expressed by a Langmuir-type adsorption isotherm. The maximum adsorption amount and equilibrium adsorption constant were 3.8mmolg−1 and 1.33, respectively. The Gibbs free energy change was −18kJmol−1, confirming that the uptake of NO3- from HNO3 by Mg–Al oxide proceeded spontaneously.