Effect of polyhydric phenols on the phase separation of an aqueous nonionic surfactant solution and the cloud-point extraction of antimony(V)

Abstract

The cloud-point extraction (CPE) of Sb(V) with pyrogallol (H3PG) was studied using Triton®X-100 as a nonionic surfactant in sulfuric acid solutions. The phase separation of a 2% (v/v) Triton X-100 solution was studied with respect to the following parameters: H3PG and sulfuric acid concentrations, temperature, and heating time. The cloud point of the surfactant solution increased with an increase in the sulfuric-acid concentration, while it decreased with an increase in the H3PG concentration. The volume of the surfactant-rich phase after heating also decreased with the increase in the H3PG concentration. Consequently, the dehydration of the extractive phase, or the aggregation of micelles effectively occurred in the presence of H3PG. On the basis of such phase separation behavior, the CPE of Sb(V) was investigated using 2% (v/v) Triton X-100. More than 92% of Sb(V) was extracted to the surfactant-rich phase with 0.15 mol L−1 H3PG in 0.9 mol L−1 sulfuric acid by heating for 60 min at 70°C; a concentration factor of 20 was achieved. The Sb(V) species extracted was investigated by ESI-MS, and was found to be an ion-association complex, (H3O · nTriton X-100) · Sb(HPG)3.