Potential Use of Surfactant-Modified Zeolite for Attenuation of Trace Elements in Fly Ash Leachate

Large volumes of fly ash and other coal combustion products (CCPs) are produced every year by coal-fired power plants. About 50% of the CCPs produced in the U.S. is buried in impoundment lagoons or dry landfills. Fly ash is generally enriched in several potentially hazardous trace elements, such as As, B, Cd, Co, Cr, Mo, Se, Sr, and V, which can leach from older, unlined disposal sites. Therefore, effective remediation of older CCPs disposal sites is needed to minimize any potential impact of leachate on the groundwater system. Fly ash samples collected from four power plants were used in this study. Sequential leaching with distilled and deionized water indicated a significant amount of leachable elements in these fly ash samples. For each ash sample, leachate was produced by shaking 30 g of ash in 450 ml of DDI water for 48 hours. The generated leachate solutions were separated from the ash and treated with surfactant-modified zeolite (SMZ). HDTMA-Br modified clinoptilolite was used at different percentages (1% to 20% of 2.67 g of ash) to treat 40 ml of ash leachate. Quantitative comparison of the elemental composition of SMZ-treated and untreated leachate indicated that SMZ is effective in decreasing the concentration of oxyanion and cationic trace elements associated with coal fly ash. In general, up to 30% of the As, Mo, and V; up to 80% of the Cr; and up to 20% of the Se and Sr were removed from the leachate after SMZ treatment. These results support potential use of SMZ in permeable reactive barriers to control the dispersion of heavy metals and metalloids from ash disposal sites. INTRODUCTION Worldwide, coal fired power plants produce hundreds of millions of tons of coal combustion products (CCPs) annually, including fly ash, bottom ash, boiler slag, flue gas desulfurization (FGD) materials, and different gasses. Fly ash, the most voluminous fraction of CCPs, is fine particulate matter collected thorough mechanical, electrostatic, and fabric filters from the flue gas produced by the combustion of pulverized coal in the boiler assembly. In 2007, 71.7 million metric tons of fly ash was produced by coal-fired power plants in the US, accounting for 57% of the total CCPs. Although the beneficial use of fly ash and other CCPs had slightly increased in recent years (44% or 31.6 Mt of fly ash was recycled and used in 2007), the majority of the fly ash is still being buried in impoundment lagoons or dry landfills, along with other unused CCPs. Fly ash contains numerous trace elements which can potentially pose health hazards in humans; therefore, development of feasible and effective techniques to control the dispersion of 2009 World of Coal Ash (WOCA) Conference May 4-7, 2009 in Lexington, KY, USA http://www.flyash.info/