Reactive Scrubbing for Mercury Removal and Stabilization

The release of mercury into the environment via combustion processes has become an issue of concern for the United States and the entire world. Major sources of mercury either are regulated or are under review to develop regulations to reduce emissions. ADA Technologies, Inc., successfully demonstrated the performance of a novel reactive scrubbing technology for the removal of vapor-phase mercury from incinerator exhaust gas streams. The technology has two major features. First, it is very efficient in the capture of mercury. Second, the final reaction product is granular solid mercuric sulfide, which is a compact, concentrated form of mercury that is stable under all environmental conditions. The final reaction product can be handled as nonhazardous waste because it easily passes the U.S. Environmental Protection Agency’s Toxicity Characteristic Leaching Procedure (TCLP) test for mercury leaching. In Phase I laboratory-scale tests, more than 99 percent of the vapor-phase mercury was captured in the scrubber and was successfully converted to a stable mercuric sulfide compound in the secondary waste treatment process. TCLP tests that were run on the treated waste showed mercury leachate levels well below the 200 ppb standard of the protocol. An economic model of the scrubber process was created and used to evaluate the cost of reactive scrubbing applied to an existing hazardous waste incinerator. The model predicted a cost savings for the reactive scrubbing technology of more than 28 percent when compared to the current technology of activated carbon injection. The Phase II research project will be directed at refining this process by identifying the most cost-effective technologies for specific functions, including the separation of reaction product solids and treatment of the gas stream with the scrubbing liquid. The secondary treatment process—to generate the concentrated mercuric sulfide final reaction product—also will be optimized in a series of laboratory tests. These improvements will be incorporated into a portable pilot-scale reactive scrubber system to be demonstrated on slipstreams of exhaust gas from operating incinerators in the Phase II option task. ADA Technologies partnered with Aketon Technologies, a subsidiary of CH2M HILL, to commercialize the reactive scrubbing technology. Aketon Technologies will participate in the design of the portable pilot-scale system in Phase II and has the expertise and market presence to deliver scrubber systems to customers. ADA Technologies will provide technical support to this partnership to optimize the operation of the reactive scrubbing technology for a range of applications.