Trace Metal Interactions with Fly Ash in Combustion Flue Gas

Stanford University, Stanford CA

Investigators

Abstract

Arsenic, mercury, and selenium exist as trace metals (TMs) in minerals and organic matter in coal and may be emitted to the environment during coal conversion processes. The ultimate goals of the proposed research efforts are to understand heterogeneous TM speciation on mineral surfaces in contact with flue gases as a function of the size and chemical phase of the fly ash particles, with broader impacts toward understanding their life cycle throughout the environment in addition to their potential toxicity. Foundational knowledge from catalysis, geochemistry, surface chemistry, and fuel combustion science will be compiled, applied, and advanced in the proposed work. The synergistic coupling of geological and fuel chemistry perspectives can be highlighted by considering the commonalities and differences of the TMs-interface systems relevant to both ground water and fuel exhaust systems. Geochemical studies of well-characterized single crystal surfaces of metal oxides will provide the required framework for understanding fuel combustion particle-bound TM emissions. In addition, the integration of experimental and theoretical approaches to the interaction of TMs with fly ash particles under a broad range of relevant conditions will result in new information on sequestration mechanisms and stability of reaction products. Intellectual Merit will be achieved since the proposed investigations will be the first of their kind focusing on high-level fly ash characterization and testing closely coupled with theoretical models to determine heterogeneous TM reactivity in simulated combustion flue gas. Additionally, the PIs are using a novel self-designed experimental technique based on mass spectrometry to directly speciate the various forms of TM in flue gas. In this way, both redox and sorption activity of the fly ash particles will be determined. The Broader Impacts of the proposed efforts are evident through the use of software packages based upon results of this work by major utility companies and technology developers worldwide to determine the most effective strategies of minimizing the release of toxic TMs into the atmosphere. Additionally, the PIs have direct links to industry through collaborations, which will facilitate summer internships for students involved in the research. Results of the proposed work will also provide indication of the TM life cycle once these species enter the environment.