The behavior of mercury in the soil with special emphasis on complexation and adsorption processes - A review of the literature

The behavior of Hg in the soil is mainly controlled by adsorption and desorption processes depending on complexation, the most important ligands in solution being OH^?, Cl^?, and organic anions. Since the solubility of HgCl₂ and Hg(OH)₂ is rather high, the affinity of Hg to these ligands leads to an increased mobility. This is especially true for HgCl₂, whereas the hydrolysis of Hg²⁺ may result in the specific adsorption of Hg on mineral colloids. The high affinity of Hg to S explains the strong binding of Hg to soil organic matter and also the stability of HgS. Further precipitation products than HgS are unlikely to occur, since the activity of Hg²⁺ remains too low to exceed the solubility product of any other defined Hg compound. It is mainly the physical fractioning of soil organic matter (dissolved vs adsorbed) that determines the behavior and distribution of Hg in soils.