On the Possibility of Predicting the Extraction of Dicarboxylic Acids with Tributylphosphate Dissolved in a Diluent

The extraction of dicarboxylic acids (itaconic, maleic, malic, oxalic, tartaric, and succinic acid) from aqueous solutions with tributylphosphate dissolved in dodecane was studied at different volume phase ratios. The concentration of the acids was varied in a broad range. The experimental data were interpreted by the chemical interaction mechanism. Considering the mass action law, two complexes (one molecule of dicarboxylic acid interacting with one or two molecules of extractant) were assumed to exist in the organic phase, and the corresponding extraction constants were evaluated. It was shown that the number of interacting molecules of the extractant and hence the overall extraction constant strongly depend on the composition of the extraction system. The prediction of acid extraction was possible only for a limited range of acid concentrations. The experimental results revealed that the concentration of the interaction product in the aqueous phase cannot be neglected.