Kinetics and equilibrium studies on the treatment of nitric acid with Mg-Al oxide obtained by thermal decomposition of NO3--intercalated Mg-Al layered double hydroxide

Mg-Al oxide obtained by thermal decomposition of NO3--intercalated Mg-Al layered double hydroxide (NO3 center dot 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 52.9 kJ mo(-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 3.8 mmol g(-1) and 1.33, respectively. The Gibbs free energy change was -18 kJ mo(-1), confirming that the uptake of NO3- from HNO3 by Mg-Al oxide proceeded spontaneously. (C) 2011 Elsevier Inc. All rights reserved.