Effect of PIM composition on As(III) extraction using a dithiophosphinc acid derivative as a carrier

Arsenic pollution is one of the most significant environmental problems. Arsenic can be found in the environment in different forms and the inorganic ones, such as arsenate and arsenite, are considered particularly dangerous. As(III), especially, shows an accentuated toxicity due to its high affinity towards the sulfhydryl groups of biomolecules. In light of this, techniques able to extract this pollutant are required. Polymer Inclusion Membranes (PIMs) containing the carrier Aliquat 336 have shown to effectively remove As(V) from natural waters. However, to our knowledge, no studies were performed on PIMs able to extract As(III). Thus, in the present study, we have prepared and characterized PIMs based both on the polymers cellulose triacetate (CTA) and poly(vinylchloride) (PVC) and the carrier bis(2,4,4-trimethylpentyl) dithiophosphinc acid (Cyanex 301) for the extraction of As(III) in different aqueous media. The effect of PIM composition was tested using PIMs prepared with the two polymers and with different carrier content. Moreover, these membranes were investigated for two different media: NaCl and HCl. A quantitative extraction was achieved using a PIM made of 50% CTA and 50% Cyanex 301 and using an acid solution of As. However, this PIM was not effective for the extraction of As(III) in 0.1M NaCl solution since a precipitate appeared in the solution after five minutes. This fact was not observed when using a PIM made of PVC, which allowed the extraction of As(III) in both media even though the efficiency in HCl was much lower than in the case of PIM made of CTA. It is worth mentioning that a lower content of carrier (30%) resulted in a null extraction of As. In conclusion, a PIM made of CTA and Cyanex 301 allowed the quantitative extraction of As(III). Unlike As (V), for which previous studies showed that the membrane composition does not affect its extraction, the choice of the polymer and the amount of carrier is a crucial aspect in the case of As(III). An excellent performance is obtained in HCl medium when CTA is employed, but the use of this polymer is limited by the pH, since in neutral condition a precipitate appears. From this point of view, a PIM constituted by 50% of PVC as polymer and 50% of Cyanex 301 as carrier seems to represent a promising alternative.