Phosphates - the building blocks of vertebrate skeletal materials - have the fascinating ability to accommodate a vast range of elements in their crystalline lattice. We are investigating the growth kinetics and mechanisms of these phases to improve technologies for nutrient recovery from municipal and distributed wastewater streams and for heavy metal remediation in contaminated soils and sediments.
(left) SEM image of synthetic hydroxyapatite crystals.
(right) AFM image of uranium phosphate nanocrystals decorating the surface of a Caulobacter crescentus bacterium.
Clay minerals are essential components of soil due to their nanoparticulate nature, their very high surface area, and in some cases their structural charge. These properties enable clay to immobilize or adsorb nutrients and contaminants from the aqueous phase and can provide a useful catalytic substrate.
We are using classical molecular dynamics simulations (MD) to investigate the adsorption of the Cs-137 radionuclide to surface and interlayer sites of the clay mineral illite. These simulations could provide information on the mechanisms by which illite strongly retains Cs deep within the clay interlayer structure, giving us insights into the transport of Cs in contaminated soil.
Clay minerals are essential components of soils and geologic reservoir rocks due to their impact on bulk mechanical properties and permeability as well as their incredible capacity to adsorb ions and organic species.
We are using a variety of simulation techniques including classical and ab initio molecular simulations as well as coarse-grained MD and kinetic Monte Carlo simulations to investigate the kinetics and thermodynamics of ion exchange and radiocesium adsorption to exterior and interlayer surfaces of clay minerals. These simulations provide information on the mechanisms by which illite clay strongly retains Cs over long timescales, giving us insights into the transport of Cs through engineered barriers for nuclear waste disposal and in contaminated soils such as those in the vicinity of the Fukushima nuclear disaster. More fundamentally, our findings elucidate the key role of chemical-mechanical coupling in facilitating ion exchange in clay interlayers, which bear the majority of potential exchange capacity.
Four layer nanoparticle of K-illite in aqueous solution (water molecules not shown).
Carbonate minerals are widely studied to investigate the basic mechanisms of crystal growth. Moreover, the isotopic and trace element compositions of these phases are widely used to reconstruct paleoenvironment. Growth rate affects the partitioning of isotopes and trace elements into minerals, but the mechanisms controlling the rate dependence of isotope fractionation and impurity uptake are not well understood.
We investigate the interfacial processes governing carbonate mineral growth and recrystallization in soils and marine carbonate sediments, emphasizing the interplay between impurity uptake, thermodynamic stability and growth kinetics, with the goal of one day being able to control crystal growth from complex fluids.
(left) Schematic of the custom double-titration chemostat apparatus used to perform crystal growth experiments under fixed chemical conditions, including solution saturation state, pH, and temperature.
(right) Electron probe image of magnesian calcite overgrowth material precipitated over pure calcite seed crystals to investigate Mg partitioning and its influence on the stable isotope composition of calcite.