The possibility of using a mathematical model based on consecutive first-order reactions to describe the Cr(III) ions pertraction in DCSLM system

Application of Response Surface Methodology (RSM) for the Optimization of Chromium(III) Synergistic Extraction by Supported Liquid Membrane

In this paper, the response surface methodology (RSM) was proposed for studying the synergistic extraction of chromium(III) ions by double-carrier supported liquid membrane (DCSLM) with organophosphorus carriers (D2EHPA/Cyanex272). At first, the optimization method of "one-factor-at-a-time" was adopted for determination of the best conditions for Cr(III) extraction by SLM with only one carrier (D2EHPA). The optimum/threshold D2EHPA concentration in the membrane phase increased linearly with initial concentration of Cr(III) ions in the feed phase. After the addition the second carrier (Cyanex272), the synergistic effect was observed. The largest percentage of extraction and the shorter time was obtained. The optimization of the synergistic extraction in DCSLM system by RSM using Box-Behnken design (BBD) for three variables (concentration and proportions of the carriers, initial concentration of Cr(III), and time of the process) was studied. The statistical model was verified with the analysis of variance (ANOVA) for the response surface quadratic model. The reduced quadratic model showed that the predicted values were in agreement with those obtained experimentally, as well as the fact that the concentrations and proportions of the carriers had a significant influence on the response. The developed model was considered to be verified and can be used to predict the optimal condition for the chromium ions extraction.

Transport of chromium(III) from mixtures of chromium ions by CTA- and PVC-based inclusion membranes

The author analysed the stability of cellulose triacetate (CTA)- and poly(vinyl chloride) (PVC)-based polymer inclusion membranes (PIMs) containing bis(2-ethylhexyl) phosphoric acid (D2EHPA) as a carrier for chromium(III) separation from mixtures of Cr(III)/Cr(VI) ions. He also studied the influence of carrier (D2EHPA) concentration in PVC- and CTA-based PIMs on chromium(III) ion transport, at different initial concentrations of the Cr(III) ions. Based on the results, the optimum range of carrier concentration in both membranes guaranteeing the fastest process was found. Moreover, PIMs with D2EHPA as the carrier worked as selective barriers for Cr(VI) ions. However, in the case of CTA/PIM, the increase in Cr(VI) concentration above 0.005 mol/dm³ negatively influenced Cr(III) transport, which was caused by the degradation of the polymer matrix. The PVC/PIM was not influenced by the Cr(VI) ions, thus PVC was definitely a better polymer for the synthesis of PIM for the separation of Cr(III/VI) ions. It was also demonstrated that both membranes were not stable over a long process time. The results reported in this study suggest that the factor that determines the stability of PIMs with D2EHPA is the presence of water in the membrane and the formation of unstable micellar structures.