Selective transport of platinum(IV) and palladium(II) through hybrid and activated composite membranes containing Aliquat 336

Regarding supported liquid membrane (SLM), the mutual solubility of both the organic and aqueous phases has an influence on its stability. Investigation into causes of mutual solubility is very important to prevent instability of the system. This work focuses on the influence of water pH as regards the solubility and stability of SLM. For the organic phase, ionic-liquid extractant viz. Aliquat 336, combining with various organic solvents, was used. As for the aqueous phase, acidic, neutral and basic water was prepared. The solubility of the liquid-liquid ternary systems (adjusted pH water + Aliquat 336 + organic solvents) was carried out at T = 303.2 K and atmospheric pressure. Tie-line data of the ternary systems were also determined. Good correlation of tie-line data from the NRTL model and experiments was confirmed and validated by the root-mean square deviation values which were <2%. For SLM stability, response surface methodology combined with Box-Behnken design was applied to obtain optimal conditions for platinum extraction and stripping. The stability of the system was observed under the different feed pH and optimal conditions.

The separation of platinum (IV) from wastewater across hollow fiber supported liquid membrane was successful in reaching 96% extraction and 88% stripping using 10% (v/v) trioctylmethyl-ammonium chloride (Aliquat 336) as the extractant. The mass transfer resistances were (1/k_a) 3.297 × 10⁴ s/cm, (1/k_m) 0.164 × 10⁴ s/cm, (1/k_o) 3.404 × 10⁴ s/cm and (1/K) 6.865 × 10⁴ s/cm. The system was governed by the mass transfer resistance from the liquid-membrane. Response surface methodology was used to qualify and estimate the influence of operating conditions. Predicted model with experimental data were in good agreement at a standard deviation of 1%.

The objective of this study was the development and optimization of a method for the liquid–liquid extraction and recovery of Uranium (VI) traces (0.10 mg/L). A comparison was made of three different extracting agents at 0.10 mol/L: tri-n-butyl phosphate, methyltrioctylammonium chloride, and bis(2-ethylhexyl) phosphoric acid. As the optimized chemical conditions of the liquid–liquid systems are very important for the future applications for the extraction, recovery and pre-concentration of Uranium (VI) traces, whether in bulk liquid membranes or in supported liquid membranes systems, a response surface methodology was adopted. A Doehlert design is used to obtain a quadratic function relationship between the percentage of recovery of uranyl ion and the amount of bis(2-ethylhexyl) phosphoric acid in kerosene, as extracting agent (0.001–0.050 mol/L) and that of phosphoric (0.192–0.718 mol/L) and citric (0.206–0.698 mol/L) acids, mixed as recovery agents. From the results, the most important effects on the recovery are the concentration of bis(2-ethylhexyl) phosphoric acid in the organic phase and the concentration of phosphoric acid in the stripping solution, while the concentration of citric acid only favors the extraction of Uranium (VI) when the other compounds are at opposite levels of concentration. From the mathematical model, optimal conditions for the back-extraction of Uranium (VI) were found with predicted recoveries of 99%, which were later corroborated experimentally.

Supported liquid membranes (SLMs) have demonstrated all along the years every high selectivity in facilitated transport of metal ions, however, they have some well known limitations, such as the gradual loss of the organic phase to the aqueous solutions. This paper describes two different types of novel membranes developed for the general purpose of separating and concentrating metal ions of interest in order to improve SLM physical and chemical characteristics. Both hybrid (organic—inorganic) membranes and activated composite membranes have been tested for the selective transport of Zn/Cd and Pt/Pd mixtures. For this purpose, different carriers have been used: 2-ethylhexyldithiophosphoric acid and 2-ethylhexylphosphoric acid for the separation of Zn and Cd whereas Aliquat 336 for Pt/Pd mixtures. The choice of these metal couples is related to environmental detoxification and catalyst recovery, respectively.