Superfund Research Program
Oxidative Remediation of Superfund Contaminants
Final Progress Reports
Year: 2016 2010
The investigators aim to develop and test new approaches for oxidizing contaminants that are difficult to treat with existing technologies (e.g., PCBs, 1,4-dioxane, and perfluorinated compounds) and apply these approaches to make treatment systems more robust and efficient. Successful completion of the proposed research will result in new oxidative treatment systems that will substantially reduce the costs of remediating contaminants that are difficult to clean up.
What has been done so far
The investigators facilitate the reaction of iron with oxygen or hydrogen peroxide so that it produces large amounts of powerful oxidants, such as hydroxyl radicals, that are capable of degrading chemical contaminants. Due to their high surface area and reactivity, these reactions are especially fast on iron nanoparticles, raising the possibility of using iron nanoparticles for oxidative remediation of contaminants.
In the first phase of the research, the investigators demonstrated that, under conditions normally encountered in contaminated soil and groundwater, only a small fraction of the oxygen or hydrogen peroxide reacts with the iron-containing particles to produce hydroxyl radicals. The reaction pathway responsible for much of the loss of oxidant appeared to produce reactive species that were incapable of oxidizing most important organic contaminants encountered at Superfund sites.
To make more efficient use of the potential for iron-containing particles to facilitate oxidation of recalcitrant contaminants, their subsequent research has focused on ways of increasing the yield of hydroxyl radicals when oxygen or hydrogen peroxide reacts with iron. Research showed that using a heterogeneous catalyst in which the iron was associated with silica or aluminum oxide increased oxidant yields from hydrogen peroxide by almost two orders of magnitude at near-neutral pH values relative to hydrogen peroxide decomposition on iron oxides.
During the past year, they have shown that when iron is associated with aluminosilicate clay minerals, it exhibits high yields for oxidant production. They also observed that dissolved silica present in groundwater interacts with the surfaces of iron oxides to decrease their catalytic activity, prolonging the lifetime of hydrogen peroxide in the subsurface.
The results are significant to Superfund site chemical oxidation applications in which hydrogen peroxide is added to soil or groundwater to remediate recalcitrant organic contaminants. The research suggests that hydrogen peroxide addition is much more likely to succeed when the soil or aquifer contains iron in association with aluminosilicate clay minerals. Furthermore, it may be possible to manipulate the subsurface to remove iron oxides or increase the amount of iron associated with aluminosilicate clays as a means of improving the performance of these remediation systems.