(630a) Kinetics of Cobalt Extraction by Supercritical Carbon Dioxide

This work employs classical kinetic models from leaching of metal to examine the experimental data from cobalt extraction by supercritical carbon dioxide.  Fourteen experiments of cobalt extraction by D2EHPA(Di-2-Ethyl Hexyl Phosphoric Acid) from a pilot SFE(supercritical fluid extraction) unit are examined.  The classical kinetics predicts that the extraction rate can be increased by increasing the concentration of D2EHPA.  However, it is found that the improvement of extraction is not linearly enhanced by increasing the concentration of D2EHPA in supercritical carbon dioxide.   This paper substracts the uptake time to reach the adsorption equilibrium from the experimental data to obtain a generalized extraction curve, which is derived from the classical kinetics.  This implies that adsorption kinetics confines the extraction, and the effect of increasing D2EHPA concentration on extraction is diminished.  The consideration of adsorption kinetics is also applied to reveal the reaction mechanism of the ion exchange between metal and acid D2EHPA.  It is found that cobalt prefers to react with the monomer of D2EHPA rather than the dimer, and the activation energy for the coordination reaction is estimated as 40.0 KJ/mol.  Although a generalized model has not yet been established in this paper, this work proposed a simple adjustment of the uptake time to explain the experimental results by classical kinetics model.  It can help to reveal the extraction mechanism and to understand the confinement of the metal extraction by supercritical carbon dioxide.