Superfund Research Program
Mechanisms of Hg Adsorption and Metals Exposure from Mixed Pollutant Streams
Project Leader: Robert H. Hurt
Grant Number: P42ES013660
Funding Period: 2005-2009
Project Summary (2005-2009)
Among the scientific issues surrounding mercury management, the nature of mercury interactions with carbon sorbent surfaces is one of the most complex and arguably the most relevant to a broad range of remediation technologies. Dr. Hurt hypothesizes that Hg/C interactions are highly dependent on the presence of specific carbon surface sites and secondary components in vapor and aqueous mixtures and that optimal capture requires sorbent surface chemistries tailored for specific waste streams. The goal of this project is to understand Hg/C heterogeneous chemistry on a site-by-site basis to guide the surface engineering of carbon sorbents for mixed waste applications. Project investigators are also interested in the interactions between ultrafine carbon and other transition metals, as these interactions determine toxicity in realistic, complex co-exposure scenarios.
Specifically, Dr. Hurt's team is
- Measuring mercury vapor adsorption kinetics and capacities on new molecularly engineered carbon nanomaterials recently synthesized at Brown University. These new materials have highly ordered, all-edge or all-basal surfaces, which allow a unique investigation of the separate contributions of graphene planes and edge sites for the elucidation of mechanism.
- Preparing and characterizing carbon/metal composite nanomaterials for toxicological testing. These composite materials serve as model systems for studying co-exposure to ultrafine carbon and transition metals.
- Measuring transient desorption behavior and oxidation state changes to provide information on the chemical form and binding energies of adsorbed or imbedded metals.
- Extending the test matrix of (1,2,3) to include other binary and ternary mixtures incorporating common secondary components in pollutant streams.
- Carrying out aqueous phase Hg adsorption experiments as a function of pH and chloride concentration on the same set of new surface-engineered carbon nanoforms.
- Preparing to use the results from (1)-(5) to propose a comprehensive mechanism for metal/C interactions and to develop guidelines for tailoring sorbent surface chemistry for specific target waste streams.
- Working with SBRP partners to identify case studies involving Hg or metal/particulate-containing mixed waste streams and characterize their wash and thermal desorption effluents.
The resulting information will be used to identify capture options using the mixture/sorbent mapping rules discovered in (1)-(6) and the most promising sorbent formulations will be further tested and evaluated for commercial potential.
Relevance To The Superfund Program
Mercury is one of the nation's highest-priority pollutants because it causes neurological effects at low doses during prenatal development. Mercury is present in soils and sediments typically in combination with other heavy metals and organics and its thermal desorption leads to complex off-gas streams from which capture must occur. Other transition metals (Fe, Ni, Cr) also pose health risks, which depend on their form and association with secondary components in the environment.
Significance Of The Research
This research project will identify the carbon surface properties ultimately responsible for effective Hg capture leading to the development of optimal nanostructured and surface engineered sorbents tailored for mixed wastes streams of varying composition. It will also document the synergistic health effects of metal and ultrafine particulate consistent with the Brown SBRP theme of complex exposures.