Development and characterization of polymer inclusion membranes for the separation and speciation of inorganic As species

This study involves the preparation and optimization of polymer inclusion membranes (PIMs) based on the polymer cellulose triacetate and the extractant (carrier) Aliquat 336 (a mixture of quaternary ammonium chlorides) for the transport of inorganic As species (arsenite and arsenate) from their aqueous solutions. The influence of the composition of the membranes on its extraction and transport properties was investigated. Better membrane performance was obtained when the membranes did not contain plasticizer and the concentration of the extractant was high. Under these conditions arsenate (As(V)) could be quantitatively separated from As(III) within 5 h even in the presence of common anions (i.e. chloride, phosphate, nitrate, sulfate and carbonate) often encountered in natural waters and industrial and domestic wastewaters. Electrical impedance spectroscopy measurements allowed the determination of the dielectric constant and conductivity values of the PIMs of interest. These results suggested that the extracted As(V) species was HAsO42− which was further transported across the membrane by a hopping mechanism, counter currently to the transport of the chloride anions present at a high concentration in the stripping solution. The overall performance of the proposed PIM in terms of stability, selectivity and permeability compared favorably to those of an Aliquat 336 based supported liquid membrane and a commercial multi-valent anion exchange membrane.