Minerals constitute a significant fraction of soils, typically making up ~45% by volume. Beyond their structural role, they also regulate soil chemistry, influencing nutrient cycling, pollutant dynamics, and microbial activity. Many soil minerals contain redox-active transition metals (e.g., iron and manganese), enabling them to function as both electron donors and acceptors in biogeochemical processes. These redox interactions play an important role in contaminant transformation, nutrient cycling, and the stabilization of soil organic matter. Understanding the environmental factors and processes governing these reactions at the mineral-water interface is essential for predicting and managing soil geochemistry in both natural and anthropogenic environments.
The overarching goal of this project is to identify the key mineral parameters that control the reactivity of redox-active soil minerals in response to changing environmental conditions. To achieve this, the study will focus on manganese and iron oxides, as well as smectite clay minerals, which represent a significant fraction of redox-active minerals found in soils.
The project is divided into two main parts. The first part focuses on characterizing mineral reactivity using a combination of experimental approaches, including mediated electrochemical analysis and UV-Vis spectroscopy. These techniques will be used to quantify the reactivity of minerals toward electron shuttles—redox-active compounds that mediate electron transfer between minerals and microbes—as a function of Eh (redox potential) and pH. Additionally, physical characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and surface area analysis will be employed to assess mineral crystallinity, surface properties, and morphological changes that may influence variations in mineral reactivity.
The second part of the project will focus on developing a predictive framework for mineral reactivity based on the redox properties determined from the experiments. This framework will define mineral reactivity as a function of reaction free energy (ΔGᵣ), providing a robust thermodynamic basis for understanding redox transformations in soils. Ultimately, this framework may offer insights into how mineral reactivity evolves under changing environmental conditions driven by periodic fluctuations in redox potential, pH, and other geochemical factors.
People: Vineeth Pothanamkandathil