Behavior of organic substances under conditions of evaporation of nitric-acid raffinates

Abstract

Nitric-acid raffinates produced during extractive reprocessing of spent nuclear fuel are ordinarily evaporated and nitric acid is recovered from the liquor vapors, obtained during evaporation, by rectification [1]. Raffinates can contain organic substances, which end up in them as a result of dissolution and removal of the extracting agent and technological additives (as complexing agents and reducing agents). Ordinarily, under conditions of evaporation of raffinates organic substances interact with nitric acid, and some of them are simultaneously distilled off with the liquor vapor, which could influence the technological regimes and the quality of the products of the evaporation and rectification operations. For this reason, it is of practical interest to investigate the behavior of organic substances under conditions of evaporation of raffinates. The results of such investigations reported in this paper supplement existing results (see, for example, [2-4]) or are published for the first time.We determined the kinetics of the interaction of organic substances with nitric acid in water solutions. The concentration regions studied are determined by technological necessity. The investigations were performed in a glass vessel with a reflux cooler and electrical heating of the walls. A vacuum system was connected to the cooler in order to maintain a prescribed boiling point of the solution and to a system of flasks filled with saturated NaCI solution for the purpose of measuring the volume of the gases released, with NaOH solutions for absorption of the acid gases (CO 2 and NO2), and with hydrogen peroxide for absorption of NO. The concentration of nitric acid was determined by alkalimetric titration and that of the organic substances was determined by the standard methods.Interaction of Lactic and Nitric Acids. The acid concentration was determined by potentiometric titration with an alkali in water medium [5] and in acetone [6]. It follows from Table I that the interaction of nitric and lactic acids is noticeable with an initial concentration of the former (X o) of 3.44 moles/liter. It intensifies with increasing X o and m o (it was determined that Mn 2 + and Fe 3 + also increase the interaction rate). The reaction terminates approximately after 4 h (X and m become constants). To identify the organic matter remaining after completion of the reaction, a portion of the solution was distilled off. This yielded condensates which were analyzed to determine the equilibrium distribution of organic material contained in them between the liquid and vapor (equilibrium was determined by the method of [7]). The composition of the condensates fell into the range X = 0.5-1.4 moles/liter and m = 0.2-0.3 moles/liter. At atmospheric pressure the distribution factor of the organic matter between the vapor and the liquid was equal to 0.6-1, which was close to the distribution factor of the acetic acid determined under the same conditions. The presence of traces of acetic acid in the condensates was confirmed by qualitative analysis...