Leaching Behavior of Coal Combustion Products and the Environmental Implication in Road Construction
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Matching Research Agency
Electric Power Research Institute
Two graduate students will be involved in this research. One student will focus on the batch and column studies for various samples under various conditions (different pH, ammonia content, carbon content, etc.). Generalized leaching curves and leaching models for raw ash will be developed based on the coal or ash types. The other student will focus on the mechanistic studies, and develop predictive models to quantify the leachability of major oxyanionic elements as functions of pH, ash type, ash composition, ammonia, activated carbon, presence of other trace elements, etc. under controlled conditions.
The overall objective of this project is to help the construction industry and the energy industry in selecting the appropriate types of fly ashes for road construction and other beneficial use applications. Specifically, this research will: (1) generalize the leaching behavior of major oxyanionic elements for various fly ashes (generated from different coal sources and/or different power generation process -- NOx and mercury control); (2) understand the leaching mechanisms of oxyanionic elements for different ashes (as effects of pH, ash type, ash composition, ammonia, activated carbon, presence of other trace elements, etc.; and (3) quantify the leaching behavior of oxyanionic metals under various leaching conditions.
The use of coal fly ash in road base and sub-base applications can provide better properties and performance, and is superior to it being otherwise disposed and becoming a possible environmental liability. Understanding the metal leaching behavior for various fly ashes can help the construction industry and the energy industry in selecting the environmentally benign fly ash for road construction and for other beneficial use applications, and determining the long term environmental impact of fly ash during road construction. Coal fly ash contains many regulated cationic and oxyanionic elements such as antimony, arsenic, barium, boron, cadmium, chromium, cupper, lead, mercury, molybdenum, nickel, and selenium. Due to the implantation of several new air emission control regulations, future fly ash may contain elevated concentrations of volatile trace elements especially oxyanionic elements. Since oxyanionic elements have greater mobility in the environment, being less studied previously, and are generally more toxic than cationic elements, understanding the leaching behavior of oxyanionic elements from fly ash is significant in determining the potential environmental impact of fly ash during disposal or beneficial use, selecting the appropriate fly ash for road construction, and developing methods to control the leaching of oxyanionic elements. This research becomes more urgent due to the implementation of more stringent arsenic standards in drinking water that will become effective in January 2006. This research will focus on the leaching behavior of 6 major oxyanionic elements, antimony, arsenic, boron, chromium, molybdenum, and selenium, for various fly ashes under different management scenarios, using both batch and column experiments. Mathematical models will be developed to quantify the leaching behavior of these elements. Speciation of these oxyanionic elements will be determined using the most advanced Perkin-Elmer HPLC-ICP-MS system available at UMR.
The metal leaching behavior information for various coal fly ashes will help the construction industry in determining the types of fly ash that yield the minimum environmental impact for road construction. It will also help the energy industry in determining the potential environmental impact of the fly ash during disposal and other beneficial use applications.
Relationship to other Research/Projects
Dr. Wang's recent projects focus on the leachability of cationic and anionic trace elements including mercury, arsenic, selenium, lead, copper, nickel, cobalt, etc., from selected fly ashes. He developed various models to quantify the leaching of these elements from fly ash as effects of pH and ammonia concentrations. In addition, the Environmental Research Center (ERC) for emerging contaminants is equipment with the most advanced HPLC-ICP-MS system for oxyanionic metal determination and speciation analyses. Dr. Wang's experience and the available facility provide Dr. Wang with a unique capability for this proposed project.
Technology Transfer Activities
In addition to presentations at various conferences such as TRB conference and World of Coal Ash conference, journal publications, and reports, the PI will also conduct a workshop at the conclusion of this project, to disseminate the research findings of this project.
Transportation Research Board Keywords
Soil stabilization, fly ash, leaching, heavy metals