Kinetics and equilibrium studies on the treatment of nitric acid with Mg-Al oxide obtained by thermal decomposition of NO_3--intercalated Mg-Al layered double hydroxide

摘要

Mg-Al oxide obtained by thermal decomposition of NO_3--intercalated Mg-Al layered double hydroxide (NO_3·Mg-Al LDH) was found to treat HNO_3, acting as both a neutralizer and fixative for NO_3- The degree of NO_3- removal increased with time, Mg-Al oxide quantity, and temperature. The NO_3- removal could be represented by a first-order reaction. The apparent activation energy was 52.9kJmol-1, confirming that NO_3- removal by Mg-Al oxide proceeded under chemical reaction control. Furthermore, the adsorption of NO_3- 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 NO_3- from HNO_3 by Mg-Al oxide proceeded spontaneously.