Predicting divalent metal sorption to hydrous Al, Fe, and Mn oxides

Area of Science:

• Environmental Chemistry
• Geochemistry
• Materials Science

Background:

• Intraparticle diffusion in amorphous oxides of aluminum, iron, and manganese influences contaminant mobility and bioavailability in soils and sediments.
• Sorption processes are often slow, necessitating predictive methods for thermodynamic and transport parameters.

Purpose of the Study:

• To develop predictive methods for assessing thermodynamic and transport parameters of metal cation sorption on amorphous oxides.
• To correlate metal cation properties with sorption behavior for environmental applications.

Main Methods:

• Adsorption enthalpies were analyzed to determine reaction type (physical adsorption with retained hydration).
• A correlation using hydrated radius and hydration number predicted enthalpy and affinity.
• Polanyi relation was used to evaluate activation energy for Ni and Ca.
• Site activation theory and a sinusoidal surface potential function predicted surface diffusivity.

Main Results:

• Adsorption of Zn, Cd, and Sr is a physical process driven by electrostatic attraction.
• Predicted enthalpies and affinities correlated well with metal cation properties.
• Activation energies for Ni and Ca were comparable across oxides.
• Metals from the same periodic group showed similar sorption complexes and Polanyi constants.
• Predicted sorption parameters matched experimental values within error margins.

Conclusions:

• A predictive model for metal cation sorption on amorphous oxides was successfully developed.
• The model relies on fundamental metal ion properties, offering a valuable tool for environmental studies.
• Findings contribute to understanding contaminant fate and transport in soil and sediment systems.