Phosphate-background electrolyte interaction affecting the transport of mercury through a Brazilian Oxisol

Elemental mercury has been extensively used for gold recovery. Although the solubility and mobility of elemental mercury is low, this metal can undergo many transformations, leading to mercury contamination in humans. The complexity of Hg chemistry in the environment reflects the various possible oxidation states, species and complexes with different physico-chemical properties. The interaction of Hg(II) in the terrestrial system, as well as in the aquatic environment, is of importance to understand the mercury cycle. This article reports data on the transport of Hg complexes through an Oxisol soil. Results show that the interaction of Hg(II) at the soil–solution interface, which can affect Hg mobility and bioavailability, depends strongly on the complex formed, due to the type of ligand in solution. The presence of the chloride anion increases the mobility of Hg(II) through the soil, due to a relative lower affinity of mercury chloride at the oxide surface. In the absence of chloride, Hg(II) forms strong complexes with the surface and its adsorption behaviour is in agreement with the adsorption of other hydrolysable cations. The presence of the phosphate anion at the oxide surface has practically no effect on Hg(II) mobility in the presence of chloride. However, when the chloride ligand is absent, the presence of phosphate enhances the retention of Hg(II), decreasing its mobility through the soil column.