THIRD-PHASE BEHAVIOR IN EXTRACTION OF OXALIC ACID WITH TRIOCTYLAMINE

The third-phase behavior in extraction oxalic acid by trioctylamine (TOA) was investigated through measuring the solubility of oxalic acid in organic solvent.The result showed that n-octanol affected the dissolution of oxalic acid in the organic solvent apparently, and the solubility of oxalic acid, the complex of oxalic acid with TOA in the organic solvent and the extractability of oxalic acid with TOA increased with n-octanol concentration in the organic solvent. An obvious shift of the solubility of oxalic acid appeared when the oxalic acid concentration was larger than the saturated concentration of oxalic acid for TOA, which depended on the formation of complex dimer. Comparatively, the solubility of oxalic acid in organic phase for the experiment of extraction equilibrium was more than that of the organic solvent without water, and the water in the organic solvent was good for the dissolution of oxalic acid. Meanwhile, mathematical models were established to describe the solubility of oxalic acid and the complex, and the model parameters were obtained by fitting the experimental data.