Extractive removal of Cr(VI) from aqueous acidic media by aliquat 336/xylene system: Optimization and modelling of equilibrium

Abstract

The extractive removal of Cr (VI) from aqueous sulfate and nitrate solutions by Aliquat 336/xylene system has been studied at 298.2 K and 101.3 kPa. The extraction efficiency of Cr (VI) by Aliquat 336 follow the order H₂SO₄ > HNO₃. The carrier yields a maximum Cr (VI) removal efficiency fixed at the concentration ratio (Aliquat 336/Cr (VI) ≤ 0.5) for 0.1 mol/dm³ aqueous acidity. Separation profile of Cr (VI) is dependent equally strongly on the types and concentrations of the carrier, acid and the transferred Cr (VI) species. Distribution data have been subjected to formulation of an optimization structure for an effective Cr (VI) separation based on a derivative variation method. The method calls for the use the first order derivatives of the optimized quantity. 0.2 mol/dm³ Aliquat 336 concentration is optimal for achieving 99 and 80% Cr (VI) removal from aqueous sulfate and nitrate media, respectively. Re-extraction results indicate that Cr (VI) is stripped successfully from the organic phase by NaOH, NaCl and Na₂SO₄ solutions, yielding 88, 54.5 and 13.8% stripping degrees, respectively. Modelling efforts based on the LSER (linear solvation energy relation) and mass-action law principles have shown considerable success. The LSER-based solvation model using nine physical descriptors of components yielded a mean error of 10% and satisfies established limiting behaviour of the physical event.