HETEROGENEOUS CATALYTIC DENITRATION OF NITRIC-ACID SOLUTIONS

The Pt-catalyzed interaction between formic and nitric acids has been studied in the presence of 1% Pt/SiO2. Kinetic and stoichiometric meas urements were carried out under the following conditions: [HNO3](0) = 0.7-8 M; [HCOOH](0) = 0.55-4.5 M; T = 55-85 degrees C; liquid-to-solid ratio S/L = 0.1-0.02 g/ml. It was shown that in the presence of plati num catalyst the interaction between HCOOH and HNO3 starts with confid ence at 60-80 degrees C without any induction period. Complex nature o f the interaction between HCOOH and HNO3 in the presence of platinum c atalyst is revealed. It was found that the reactions of heterogeneous catalytic reduction of nitric acid and homogeneous autocatalytic denit ration proceed simultaneously. A contribution of each process depends on the acidity and the total nitrate concentration in the solution. Th e order of the reaction with respect to [HCOOH] is 1. The order of the reaction with respect to (HNO3) is 0 under the conditions when an aut ocatalytic accumulation of HNO2 does not take place. It was found that the catalytic interaction between HCOOH and HNO3 takes place in the p resence of antinitrite agents as urea and hydrazine, though the rate o f this process is not high. At the same time, the reaction of HCOOH ca talytic decomposition does not proceed in non-nitrate media (under the conditions of the experiments). A method of the catalytic denitration was proposed for the reprocessing of aqueous radioactive waste.