Innovative Hydroxide Slurry Processing System Reclaims Mercury From Groundwater

Frederick K. (Rick) Marotte, P.E. DEE, presented at the Water Environment Federation Conference in Chicago in October, 2002

ABSTRACT
Olin Corporation operates a large groundwater pump and treatment system as part of the remedial action program at its McIntosh, Alabama plant. As a result of historical releases at this plant, some of the groundwater became contaminated with salt brine, mercury, various organic compounds, and acid. Because of the groundwater's low pH, aluminum and iron have been extracted from native soil and are dissolved in the groundwater. To allow removal of the mercury from the groundwater without generating aluminum and ferric hydroxide sludge, an innovative slurry treatment system was developed. The first step in the process is to acidify the slurry to re-dissolve the aluminum and iron. The acidified solution can then be treated in activated carbon without the aluminum or iron precipitating and fouling the system. Mercury is concentrated in the activated carbon and can be ultimately reclaimed by retorting the spent carbon. The mercury-free solution is neutralized and discharged. Aluminum and iron are re-precipitated in this step but is discharged within the existing NPDES permit limits. The treatment system has been in operation since May 2001. The avoidance of sludge dewatering and disposal costs has offset the additional cost of the slurry processing facilities. This approach shows promise in eliminating aluminum and iron fouling in other groundwater treatment systems.

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