XPS Investigation of Surface Passivation during Fe(II)-activated Recrystallization of Al-, Cr-, and Sn-substituted Goethite and Hematite
EMSL Project ID
46196
Abstract
Microbially-mediated iron redox cycling results in secondary abiotic reactions between aqueous Fe(II) and solid Fe(III) oxide minerals. These reactions induce iron oxide minerals such as goethite and hematite to recrystallize through coupled oxidative adsorption of Fe(II) and reductive dissolution of Fe(III) at spatially-separated surface sites, with electrons conducting across the surface or through the bulk structure. We have recently shown that this recrystallization causes the repartitioning of elements like Ni and Zn between the aqueous solution, mineral surface, and mineral bulk structure, with adsorbed elements incorporating in regions of oxidative overgrowth and incorporated elements being released back into solution in regions of reductive dissolution. This previously unknown element cycling may substantially affect contaminant fate and micronutrient availability. We are currently investigating how insoluble elements such as Al, Cr, and Sn that commonly substitute in natural iron oxides affect the release of soluble metals like Ni and Zn. Kinetic batch studies show that these insoluble elements inhibit metal release. We hypothesize that during recrystallization the insoluble elements buildup on the mineral surface, causing passivation and inhibiting further recrystallization. We propose to conduct X-ray photoelectron spectroscopy (XPS) measurements at EMSL to test this hypothesis of insoluble element buildup and passivation as the mechanism causing metal release inhibition. Ni- or Zn- substituted iron oxides codoped with Al, Cr, or Sn will be reacted with solutions containing aqueous Fe(II). The solid phase will then be analyzed by XPS to determine the surface composition; Fe(II)-free control samples will also be examined. The proposed XPS measurements will determine if common iron oxide impurities that are insoluble at environmentally-relevant pH values repartition from the mineral structure to the surface during biogeochemical processes that cause mineral recrystallization. The expected results will provide insight into the mechanism behind trace element and contaminant release from iron oxide minerals during Fe(II)-Fe(III) ETAE and identify how coincorporation of insoluble substituents inhibits release. This work may identify mechanisms through which iron oxide dopants can inhibit electron transfer reactions involved in microbe-mineral reactions and contaminant reduction. In addition, the proposed research will advance EMSL's mission and further its science themes of Geochemistry/Biogeochemistry and Subsurface Science and Science of Interfacial Phenomena and the Biogeochemistry Grand Challenge by exploring novel molecular-scale processes that affect contaminant fate during biogeochemical iron cycling and the energetics of microbial metabolic processes involving iron oxide minerals as substrates.
Project Details
Project type
Exploratory Research
Start Date
2012-01-17
End Date
2013-02-12
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Frierdich AJ, M Scherer, JE Bachman, MH Engelhard, and JG Catalano. 2012. "Inhibition of trace element release during Fe(II)-activated recrystallization of Al-, Cr-, and Sn-substituted goethite and hematite." Critical Reviews in Environmental Science and Technology.