Solvent extraction chemistry of acids is critically reviewed. The acids under consideration are strong mineral, carboxylic (acetic, lactic, citric, etc.) and amino acids. Extractants used are carbon-bonded, phosphorus-bonded oxygen-donors and aliphatic amines. Extractive transfer process obeys the Nernst mass action law. Expressions of equilibrium constants;and distribution ratios are presented. At low acid concentrations the experimental results, presented by authors, are in a good agreement with the calculated ones. The effects of different parameters of extractants, solvents (synergistic, modifiers, etc.), diluents (polar, nonpolar, electron-donating/accepting), pH, pKa, temperature, etc., are critically discussed.
The complicated behavior of extraction systems conflicts, in some cases, with the mass action law models, especially at increased acid concentrations. Some researchers describe over-stoichiometry through hydrogen bonding and aggregation.