Chloride adsorption on Fe- and Al-(hydr)oxide: estimation of Gibbs free energies

In this study, we used chemical quantum methods to analysis the adsorption of chloride on Al and Fe-(hydr)oxide clusters. Inner and outer sphere complexes were the generating complexes during the adsorption process on variably charged Al- and Fe-(hydr)oxide clusters. For the chloride adsorption on Al-(hydr)oxide, the outer sphere complexes—H-bonded—were favored for all clusters, while the adsorption modes as inner sphere complexes—BB or MM—were not favored. It was found, that the H-bonded complex on neutral clusters was the most thermodynamically favored with an adsorption energy of − 63.4 kJ/mol. For iron clusters, thermodynamic favorability was observed for both outer (− 70.5 kJ/mol) and inner monodentate (− 65.8 kJ/mol) sphere complexes. These theoretical results indicated that the thermodynamic favorability of chloride adsorption on Fe and Al-(hydr)oxide was directly related to positive surface charge. © 2018 Springer Science+Business Media, LLC, part of Springer Natur

Transport of dissolved Si from soil to river: a conceptual mechanistic model

This paper reviews the processes which determine the concentrations of dissolved silicon (DSi) in soil water and proposes a mechanistic model for understanding the transport of Si through a typical podzol soil to the river. DSi present in natural waters originates from the dissolution of mineral and amorphous Si sources in the soil. However, the DSi concentration in natural waters will be dependent on both dissolution and deposition/precipitation processes. The net DSi export is controlled by soil composition like (mineralogy and saturated porosity) as well as water composition (pH, concentrations of organic acids, CO2 and electrolytes). These state variables together with production, polymerization and adsorption equations constitute a mechanistic framework determining DSi concentrations. For a typical soil profile in a temperate climate, we discuss how the values of these key controls differ in each soil horizon and how it influences the DSi transport. Additionally, the impact of external forcings such as seasonal climatic variations and land use, is evaluated. This model is a first step to better understand Si transport processes in soils and should be further validated with field measurements