Selective transport of Cadmium by PVC/Aliquat 336 polymer inclusion membranes (PIMs): the role of membrane composition and solution chemistry

This study investigated the extraction and stripping performance of PIMs consisting of PVC and Aliquat 336. Extraction and stripping of three representative heavy metals - namely $Cd^{2+}$, $Cu^{2+}$, and $Zn^{2+}$ - by the synthesized membranes were evaluated as a function of sodium chloride concentration and under different stripping solutions (0.01 M $HNO_3$, Milli-Q water, 0.01 M HCl and 0.01 M NaOH), respectively. Results reported here indicate that the formation of negatively charged metal chloride complex species was responsible for the extraction of the target metal to PIMs. Experimental results and thermodynamic modeling of the speciation of chloro metal complexes further confirm that the extraction selectivity between $Cd^{2+}$, $Cu^{2+}$ and $Zn^{2+}$ can be controlled by regulating the chloride concentration of the feed solution. An acidic solution without any chloride was the most effective stripping solution, followed by Milli-Q water, and a diluted hydrochloric acid solution. On the other hand, the stripping of metals from PIMs did not occur when a basic stripping solution was used.