BACKGROUND: Lactic acid is a versatile commodity chemical with a variety of applications. Synthesis of lactic acid either through fermentation of carbohydrates or through chemical synthesis is state of the art. Separation from dilute aqueous solution is complex and accounts for the major part of production costs. Reactive extraction based on reversible adduct formation is a promising alternative for the separation of lactic acid. RESULTS: Extraction was carried out with the organophosphorus solvents tri-n-butyl phosphate, tri-n-octylphosphine oxide and Cyanex 923. Shellsol T was used as diluent. Partition coefficients increase with increasing extractant content and decreasing temperature. Cyanex 923 has several advantages compared with tri-n-butyl phosphate and tri-n-octylphosphine oxide with respect to lactic acid distribution and hydrodynamic properties. Liquid-liquid phase equilibria for lactic acid extraction with Cyanex 923 were modeled. Selectivity of lactic acid extraction with respect to glycolic acid and formic acid was discussed. CONCLUSION: The organophosphorus extractant Cyanex 923 was found to be an appropriate solvent for lactic acid extraction from aqueous solutions. Experimental data and model data based on the Law of Mass Action showed good agreement. Lactic acid extraction from multi-acid solution showed good selectivity compared with glycolic acid. Lactic acid selectivity is low with respect to formic acid. (c) 2012 Society of Chemical Industry