Sorption of silver(I) onto the surface of pure and natural quartz sands

Abstract

Silver is a heavy metal which is present at different oxidation states in the environment and which can be released into aquatic systems from agricultural activities or industries (mines, metallurgy, pharmaceutical and electronic activities, electrochemistry, photography, nuclear industry and power plants, etc). The aim of this work was to understand the Ag(I) sorption at low concentrations in aquatic systems, specially natural porous media such as soils, sediments and ground waters. Kinetic and thermodynamic experiments were performed in batch reactors at room temperature in the dark. A pure silica sand and a natural aquifer quartz sand were used. Silver concentration and pH (2, 4, 6 and 8) play an important role, while the ionic strength (NaNO 3 ) does not affect neither sorption kinetics nor sorption thermodynamics. For each point, more than four days were necessary to observe equilibrium state. Ag sorption rate law does not appear to be simple, with a change in the reaction order depending on experimental conditions. Sorption isotherms were modelled with Langmuir type relationship for a Ag-range concentration from nanomolar to millimolar. In both kinetic and thermodynamic experiments, one to three sites were necessary to take into account the surface heterogeneity of the natural quartz sand depending on experimental conditions.