title: Electrochemical analyses of redox-active iron minerals: a review of nonmediated and mediated approaches.
abstract: Redox-active minerals are ubiquitous in the environment and are involved in numerous electron transfer reactions that significantly affect biogeochemical processes and cycles as well as pollutant dynamics. As a consequence, research in different scientific disciplines is devoted to elucidating the redox properties and reactivities of minerals. This review focuses on the characterization of mineral redox properties using electrochemical approaches from an applied (bio)geochemical and environmental analytical chemistry perspective. Establishing redox equilibria between the minerals and working electrodes is a major challenge in electrochemical measurements, which we discuss in an overview of traditional electrochemical techniques. These issues can be overcome with mediated electrochemical analyses in which dissolved redox mediators are used to increase the rate of electron transfer and to facilitate redox equilibration between working electrodes and minerals in both amperometric and potentiometric measurements. Using experimental data on an iron-bearing clay mineral, we illustrate how mediated electrochemical analyses can be employed to derive important thermodynamic and kinetic data on electron transfer to and from structural iron. We summarize anticipated methodological advancements that will further contribute to advance an improved understanding of electron transfer to and from minerals in environmentally relevant redox processes.
authors: †Department of Environmental Systems Science, Institute of Biogeochemistry and Pollutant Dynamics, Environmental Chemistry, Swiss Federal Institute of Technology (ETH), Universitätstrasse 16, 8092 Zurich, Switzerland.
authors: Michael
authors: M
authors: Sander
authors: ‡Environmental Chemistry, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Ueberlandstrasse 133,8600 Duebendorf, Switzerland.
authors: Thomas B
authors: TB
authors: Hofstetter
authors: §Civil and Environmental Engineering, The Pennsylvania State University, 212 Sackett Building, University Park, Pennsylvania 16802-1408, United States.
authors: Christopher A
authors: CA
authors: Gorski
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D000077215:Clay; D055664:Electrochemical Techniques; D004566:Electrodes; D004583:Electrons; D007501:Iron / Q000737:chemistry*; D008903:Minerals / Q000032:analysis* / Q000737:chemistry; D010084:Oxidation-Reduction; D011199:Potentiometry
chemical_list: D000538:Aluminum Silicates; D008903:Minerals; D007501:Iron; D000077215:Clay