Copper solvent extraction by ultrasound-assisted emulsification

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.