Kinetic modeling of chromium(III) extraction with aliquat 336 from alkaline aqueous solutions containing chlorides

The effects of time, composition and history of preparation of the aqueous phase on the liquidliquid extraction of chromium(III) with Aliquat 336 from the aqueous alkaline solutions containing chlorides were studied. At time far from the equilibrium the yield and initial rate of the chromium(III) extraction depend on NaOH concentration, ionic strength of the aqueous phase and the way of its preparation. At the constant composition of the feed solution, rate of the Cr(III) extraction in approach to the equilibrium is higher when chromium(III) is extracted from the alkaline aqueous phase freshly prepared by direct dissolution of a weighted sample of CrCl3 than from that obtained by dilution of aged stock solution of CrCl3. Kinetic analysis by the mathematical models showed that within the whole period of time needed to reach the equilibrium, the rate of the Cr(III) extraction is limited by the second-, and third-order chemical reaction towards Cr(III), irrespective of composition and preparation history of the aqueous phase. The three-dimensional diffusion and chemical reaction at phase boundary substrateproduct (the contracting volume) models have a significant effect on the chromium(III) extraction within the initial extent of the process.