Selenite and Selenate Speciation in Natural Waters: Interaction with Divalent Metal Ions

Abstract

Selenium is a trace element of environmental relevance. Studies on its solution chemistry are scarce and were mostly carried out under experimental conditions of little relevance to environmental research. Thus, we have performed new studies of selenium speciation in solutions of low ionic strength, in contrast to those prevailing in the literature data. In this work, potentiometric titrations (at 20.0 °C, and I=0.15 mol⋅L−1 NaClO4) were carried out for systems containing Se(VI) or Se(IV) oxyanions and divalent metal ions (Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg, and Pb). Ion pairs such as [M(SeO4)] and [M(HSeO4)2], or [M(HSeO3)]+ and [M(SeO3)], exist in solutions. The data reported here provide the basis for determining selenium speciation in natural aquatic systems, on which the bioavailability and toxicity of this element depends.