Ultrasonic Power to Enhance Limestone Dissolution in the Wet Flue Gas Desulfurization Process. Modeling and Results from Stepwise Titration Experiments

The goal of this work is to assess the application of ultrasonic power to the reactive dissolution of limestone particles in an acidic environment; this would represent a novel method for improving wet Flue Gas Desulfurization industrial systems. In this study a stepwise titration method is utilized; experiments were done by using different particle size distributions with and without the application of ultrasound. The use of ultrasonic power sensibly affected the reaction rate of limestone and its dissolution; a major difference could be observed when samples from the Wolica region in Poland were studied. In this case, the overall dissolution rate was found to increase by more than 70%. The reactive dissolution of limestone does not follow the same mathematical model when sonication is in effect; in this case, an extra Ultrasonic Enhancement Constant was introduced. It was demonstrated that the dissolution is proportional to an Effective Reaction Surface and, therefore, surface interactions should also be taken into consideration. For this purpose, a study is presented here on the Z-potential and electrophoretic mobility of limestone samples measured in aqueous dispersions by means of Laser Doppler Micro-Electrophoresis.

A method for phenomenological and chemical kinetics study of autocatalytic reactive dissolution by optical microscopy. The case of uranium dioxide dissolution in nitric acid media

Dissolution is a milestone of the head-end of hydrometallurgical processes, as the stabilization rates of the chemical elements determine the process performance and hold-up. This study aims at better understanding the chemical and physico-chemical phenomena of uranium dioxide dissolution reactions in nitric acid media in the Purex process, which separates the reusable materials and the final wastes of the spent nuclear fuels. It has been documented that the attack of sintering-manufactured uranium dioxide solids occurs through preferential attack sites, which leads to the development of cracks in the solids. Optical microscopy observations show that in some cases, the development of these cracks leads to the solid cleavage. It is shown here that the dissolution of the detached fragments is much slower than the process of the complete cleavage of the solid, and occurs with no disturbing phenomena, like gas bubbling. This fact has motivated the measurement of dissolution kinetics using optical microscopy and image processing. By further discriminating between external resistance and chemical reaction, the “true” chemical kinetics of the reaction have been measured, and the highly autocatalytic nature of the reaction confirmed. Based on these results, the constants of the chemical reactions kinetic laws have also been evaluated.