Use of aqueous two-phase systems formed by Triton X and choline chloride for extraction of organic and inorganic arsenic

Abstract

The use of aqueous two-phase systems (ATPSs) for the extraction/speciation of arsenic has received attention in recent years. However, only ATPSs formed by polymer and salt have been used, hindering a global understanding of the mechanism of partitioning of the metalloid and limiting the development of strategies for arsenic speciation in these systems. Therefore, it is important to study the partitioning of different arsenic species in new and more environmentally friendly ATPSs, such as those formed by ionic liquids based on the choline cation. In this work, ATPSs formed by Triton X nonionic surfactant, choline chloride ionic liquid, and water were used to study the partitioning of three arsenic species (As(III), As(V), and dimethylarsinic acid (DMA)), in the absence and presence of the extracting agent ammonium pyrrolidine dithiocarbamate (APDC). Evaluation was made of the effects of the parameters extraction time, pH, tie-line length, extractant concentration, and nature of the surfactant on the distribution of the arsenic species in the ATPS. In the absence of the extracting agent, all the arsenic species were mainly transferred to the choline chloride-rich phase, with maximum extraction percentages of 69.02, 92.99, and 90.05% for As(III), As(V), and DMA, respectively. In the presence of APDC, the As(V) and DMA species mainly remained in the choline chloride-rich phase, while the As(III) was transferred to the surfactant-rich phase, with the best removal to this phase achieved using the ATPS formed by TX-165 + choline chloride + water, at pH 1.00 and with an APDC:arsenic molar ratio of 25. Compared to ATPSs formed by polymer and salt, the ATPSs formed by Triton X and choline chloride required up to nineteen times smaller amounts of APDC for quantitative extraction of As(III) to the phase low in electrolyte. Thus, the results demonstrated the excellent potential of the Triton X + choline chloride + water systems for the extraction, preconcentration, and speciation of arsenic, with the advantage that the components used to form the ATPSs make the technique more environmentally friendly.