Mercury Immobilization by Subsurface Reactive Barriers

Abstract

Mercury contamination is becoming a prevalent problem for environmental engineers. Chlor-alkali plants and coal fire power plants are the main contributors to the spread of this neurotoxin into the environment. Mercury is a unique contaminant because it is volatile at room temperature; it dissolves in water, and is a groundwater and soil contaminant. Conventional means of clean up will spread the contamination further, therefore immobilization of this contaminant in place is an important means by which to prevent mercury contamination of land and aquifers. In this thesis, mercury immobilization was evaluated using an iron sulfide (FeS (s)) barrier as well as sulfide injections. An FeS (s) barrier was used because previous research has shown that the Fe2+ in this mineral will readily exchange with Hg2+ to form HgS (s), the least soluble mercury species. Sulfide injections were considered to determine if a HgS monolayer could form around elemental mercury (Hg0) beads reducing the availability of the mercury to interact with the surrounding groundwater. Column experiments were conducted to determine the performance of these immobilization methods under flowing conditions. The column tests revealed that FeS (s) is a good barrier for mercury removal under flowing conditions. The FeS (s) significantly adsorbed mercury from flowing groundwater conditions. Additionally, the column tests also showed that sulfide injections may be an effective means to contain mercury contamination and prevent contact between groundwater and Hg0.