Aqueous Geochemistry Research

Surface Properties of Nanoparticles

Many of the physical and chemical properties of nanoparticles differ from the corresponding macroscopic particles. We are, therefore, investigating nanoscale size effects on the surface properties of titanium dioxide.

HR-TEM image of 3nm Anatase

Metal Adsorption Studies

Metal contamination is a major concern in many surface environments and industrial environments, for example stream contamination following mining operations. To accurate propose remediation plans an understanding of metal adsorption and desoption on mineral surfaces is essential.

Monovalent to trivalent metal ion adsorption and anion adsorption to metal-oxides is being been studied.

Tetradentate binding on rutile [110] surface

Surface charging of metal-oxides to high temperatures

Understanding the interfacial properties of metal–oxides in contact with hydrothermal solutions is critically needed in a wide range of applications, such as understanding mineral synthesis, radionuclide transport in nuclear power plants and storage facilities, and in many industrial and technical applications.

Interface studies of rutile and zirconium dioxide have been completed to 300°C.

SEM image of rutile with the [110] face predominating

Surface Complexation Modeling

The interfacial region between a mineral surface and solution is a complex domain termed the electrical double layer (EDL). This interfacial region profoundly influences a myriad of natural, industrial and technical processes.  Surface complexation modeling is employed to achieve a conceptual understanding of the EDL from the atomic to macroscopic scale.

Basic Stern Model of the EDL

Iron–Sulfate Complexation

Iron contaminated pond with pH < 2, Anaconda, MT. (Sand hill cranes on the banks)

The oxidation of metal sulfide minerals is known to generate acid rock drainage solutions, which comprise low pH, and high sulfate and iron concentrations.  These solutions are extremely detrimental to the environment. The ability to model iron-sulfate chemistry in these highly contaminated systems would greatly improve efforts to remediate environmentally sensitive environments.

Therefore, experiments are being conducted to determine association constants for iron-sulfate complexes.

Jarosite

SEM image of synthetic jarosite before (left)

and after (right) dissolution experiments

Jarosite is a common mineral in acidic sulfate-rich environments formed by the oxidation of sulfide minerals. Moreover, the Mars Exploration Rover Opportunity identified jarosite at the Meridiani Planum landing site in 2004. Despite jarosite being a common mineral and of interest to geologists, geochemists, mineralogists and metallurgists, the conditions under which it forms and remains stable are inadequately constrained.

Solubility studies aim to better determine dissolution kinetics and equilibria of jarosite.

Environmental Geochemistry

Perchlorate

Natural perchlorate was first identified in the Chilean nitrates from the Atacama Dersert, Chile, more than 100 years ago.  With advances in analytical capabilities prechlorate appears more widely spread throughout the environment.  The occurrence and distribution of perchlorate is of significant environmental and health concern.

Perchlorate has principally been identified in desert environments, therefore, studies are being undertaken to investigate the existence of any possible associations between perchlorate and evaporative salts. 

Evaporative Salts

Metal Distribution at the Anaconda Superfund Site, Montana

Nine decades of smelting operations at the Anaconda Smelter site, in southwestern Montana, has contaminated the local and surrounding soils (700 km²), groundwater, and the Clark Fork River; resulting in the area being designated an EPA Superfund Complex.

Metal association studies are utilized to determine the mobility and bioavailability of the contaminants in soils at the site.

Acid pond, pH < 2

Anaconda Smelter