Dependence of Extraction Equilibrium on Apparent Basicity of Extractant

The extraction method based on reversible chemical complexation is highly effective and selective for separating polar organic solutes from dilute solutions. In this paper, trioctylamine (TOA) in 1-octanol, trialkyl phosphine oxide (TRPO), and tri-butyl-phosphate (TBP) in kerosene were selected as typical extractants. The apparent basicity of these extractants to HCl was measured. Dependences of the extraction equilibrium behavior on the apparent basicity of the extractant were investigated. Results showed that the apparent basicity of the extractant depended on extractant type and concentration. A new mathematic model was proposed, which can predict the extraction equilibrium of Lewis acid including the association driving force ((delta)pKa) and the hydrophobicity of the complex. The apparent extraction equilibrium constant for various extractant systems can be predicted well by using different coefficients in the equation. The correlative equation can be used as the basic style to correlate other extraction equilibria.