Président du jury Segers, Luc
Promoteur Delplancke, Jean-Luc ;Delplancke, Marie-Paule
Publication Non publié, 2010-03-25
Résumé : | The goal of this research is to improve an extractive metallurgy process based on solvent extraction. This process should fit the exploitation of small local copper-rich deposits. In these conditions, the plant has to be as compact as possible in order to be easily transported from one location to a subsequent one. Improved extraction kinetics could ensure a high throughput of the plant despite its compactness. In addition, the extraction reagent should not be damaging for the environnement. On this basis, we propose to use ultrasound-assisted solvent extraction. The main idea is to increase the extraction kinetics by forming an emulsion in place of a dispersion thanks to the intense cavitation produced by ultrasound. The benefit of this method is to improve the copper extraction kinetics by increasing the interfacial surface area and decreasing the width of the diffusion layer. We studied the implementation of an highly branched decanoic acid (known as Versatic- 10®acid) as a copper extraction reagent dispersed in kerosene. Emulsification is monitored through the Sauter diameter of the organic phase droplets in aqueous phase. This diameter is measured during pulsed and continuous ultrasound irradiation via a static light scattering technique. The phenomenon of emulsification of our system by ultrasound is effective, and the emulsification process carried out in the pulsed ultrasound mode is at least as efficient as the emulsification obtained under continuous mode. No improvement of emulsification is observed beyond a threshold time of the ultrasound impulse. This may be attributed to a competition between disruption and coalescence. The use of mechanical stirring combined with pulsed ultrasound allows to control the droplet size distribution. In presence of ultrasound, the extraction kinetics of Versatic-10 acid is multiplied by a factor ten, and therefore reached a value similar to the kinetics observed without ultrasound with an industrial extractant such as LIX-860I®(Cognis). Extraction kinetics measurements are carried out by monitoring the copper ion concentration in the aqueous phase with an electrochemical cell. We conclude that ultrasound-assisted emulsification can be implemented under certain conditions. Emulsification is a first step, and the following destabilization step has to be studied. The device using ultrasound-assisted emulsification should be followed by an efficient settling-coalescing device. A possible solution would be to promote emulsion destabilization by increasing the ionic strength with an addition of MgSO4, a salt that is not extracted by the extraction reagent in the considered range of pH. |