Department of Earth Sciences, University of Bristol
Aqueous and Environmental Geochemistry
Prof. D. M. Sherman

Ongoing Research Projects

A. Metal Complexation in Aqueous and Hydrothermal Solutions

Metal complexation in aqueous and hydrothermal solutions is a fundamental step in the formation of ore deposits and also controls the solubility and bioavailabily of heavy metals in groundwater. We are investigating metal coordination chemistry in aqueous solutions using ab initio and classical molecular dynamical simulations in addition to in situ EXAFS spectroscopy of hydrothermal solutions. First-principles simulations, however, allow us to explore the nature of aqueous fluids in regimes that are inaccessible to experiment. Moreover, atomistic simulations allows us to go beyond the classical Born theory of hydrothermal solutions that has dominated aqueous geochemistry for the past 40 years.

Current Support
  • Transport of lithophile elements in magmatic-hydrothermal fluidsFunded by the Natural Environment Research Council (NERC)
  • Indium: from source to sink Funded by the Natural Environment Research Council (NERC)

B. Sorption of Aqueous Ions by Mineral Surfaces

The solubility and bioavailability of heavy metals and nutrients in soil, groundwater and seawater is controlled by sorption of aqueous metals onto colloidal (nanocrystalline) oxides and clay minerals. Sorption reactions can occur by the formation of outer- or inner-sphere surface complexes, nanocrystalline surface precipitates or by incorporation into colloidal substrates via isomorphous solid solutions or ion exchange. We need to understand the mechanisms of these sorption reactions in order to understand their reversibility; we also need a molecular understanding before we can develop thermodynamic data to model element cycles in aqueous systems. Such data are especially needed for future applications of environmental geochemistry to risk assessment and remediation. We are determining the mechanism of ion sorption onto Fe-Mn oxides and clay minerals using EXAFS spectroscopy and first-principles calculations of the geometries and energetics of possible surface complexes. When we have a molecular understanding of the structural mechanism of sorption, we can fit our laboratory sorption experiments to a thermodynamic model stability constants that can be used in geochemical simulations. We are one of the few groups in the world that is solving these problems using both experiment and first-principles theory.

Previous Support
  • Geochemistry of arsenic at the mineral-water interface: a molecular understanding from quantum chemistry, X-ray spectroscopy and surface complexation modelling.Funded by Natural Environment Research Council (NERC)

  • Mineral-microbe controls on the fate and transport of depleted-uranium corrosion products in the soil environment. Funded by Natural Environment Research Council (NERC)

C. Electronic Structures of Minerals and Their Surfaces

The most important chemical processes that couple the lithosphere-hydrosphere with the biosphere are redox reactions. Most of these reactions occur at the surfaces of iron and manganese oxide and sulfide minerals. Some of these reactions are promoted by sunlight and control the bioavailability of trace nutrients in the photic zone. Extracellular electron transfer processes involving mineral substrates are believed to occur in the deep biosphere. In order to understand the redox chemistry of Fe-Mn oxides and sulfides, we need to understand their electronic structures.

We can probe the electronic structures of transition metal oxides and sulfides using density functional calculations and soft X-ray spectroscopy. Oxygen K-edge spectroscopy, in particular, offers a very direct way to probe electronic structure. Using both electron yield and fluorescence yield detection, we can compare the electronic structures of the bulk and surfaces of minerals. Oxygen K-edge spectroscopy also provides a sensitive probe of the oxidation of sulfide mineral surfaces. Our experiments on x-ray spectroscopy are primarily done at the Advanced Light Source (California).

Previous Support

  • Electronic structure and chemical reactivity of Fe-Mn (hydr)oxide minerals in aquatic environments Funded by Natural Environment Research Council (NERC)

EXAFS Spectroscopy

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