Coal fly ash interaction with environmental fluids: Geochemical and strontium isotope results from combined column and batch leaching experiments Tonya M. Brubaker a , Brian W. Stewart a,⇑ , Rosemary C. Capo a , Karl T. Schroeder b , Elizabeth C. Chapman a , Lev J. Spivak-Birndorf a , Dorothy J. Vesper c , Carol R. Cardone b , Paul C. Rohar b a Department of Geology & Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260, USA b National Energy Technology Laboratory, U.S. Department of Energy, 626 Cochrans Mill Rd., Pittsburgh, PA 15236, USA c Department of Geology & Geography, West Virginia University, Morgantown, WV 26506, USA article info Article history: Available online 8 September 2012 abstract The major element and Sr isotope systematics and geochemistry of coal fly ash and its interactions with environmental waters were investigated using laboratory flow-through column leaching experiments (sodium carbonate, acetic acid, nitric acid) and sequential batch leaching experiments (water, acetic acid, hydrochloric acid). Column leaching of Class F fly ash samples shows rapid release of most major ele- ments early in the leaching procedure, suggesting an association of these elements with soluble and surface bound phases. Delayed release of certain elements (e.g., Al, Fe, Si) signals gradual dissolution of more resistant silicate or glass phases as leaching continues. Strontium isotope results from both column and batch leaching experiments show a marked increase in 87 Sr/ 86 Sr ratio with continued leaching, yield- ing a total range of values from 0.7107 to 0.7138. For comparison, the isotopic composition of fluid output from a fly ash impoundment in West Virginia falls in a narrow range around 0.7124. The experimental data suggest the presence of a more resistant, highly radiogenic silicate phase that survives the combus- tion process and is leached after the more soluble minerals are removed. Strontium isotopic homogeni- zation of minerals in coal does not always occur during the combustion process, despite the high temperatures encountered in the boiler. Early-released Sr tends to be isotopically uniform; thus the Sr isotopic composition of fly ash could be distinguishable from other sources and is a useful tool for quan- tifying the possible contribution of fly ash leaching to the total dissolved load in natural surface and ground waters. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Coal combustion generates more than 50% of the electricity used in the USA and about 40% of that used worldwide, and results in by-products including fly ash, bottom ash, boiler slag, fluidized bed combustion ash and other solid fine particles (Asokan et al., 2005; Kim and Hesbach, 2009; Vejahati et al., 2010); collectively, these are referred to as coal utilization by-products (CUB). During the combustion process, fly ash is carried out of the boiler by ex- haust gases, and then most of it is collected and transported to market or to a landfill (Yeheyis et al., 2008). Improvements in the efficiency of fly ash collection (from 90% in older installations to better than 99% in modern emission-controlled facilities; Depoi et al., 2008), as well as increased coal combustion in emerging markets have resulted in greater use of CUB in bricks, cement, con- crete, wallboard, mining materials, adhesives, paint, and as a soil amendment and wood substitute (Feeley et al., 2004; Yeheyis et al., 2008). Coal utilization by-products have also been used as coal mine grouting material that takes advantage of the alkalin- ity-generating capacity of fly ash to neutralize acid mine drainage (AMD) (Dutta et al., 2009; Hamel et al., 2010). Fly ash, which comprises 80% of coal-fired power plant com- bustion residue (Dutta et al., 2009), can also contain significant quantities of potentially leachable toxic elements such as As (2– 440 ppm), Hg (0.01–12 ppm) and Se (0.2–130 ppm), as well as other trace elements of environmental concern such as B, Cr, Pb, Ni, Sr, V and Zn (Eary et al., 1990; Querol et al., 1995). Although the majority (89%) of Hg is released to the environment as vapor in stack emissions (Bignoli, 1989), >90% of most elements present in coal are not released in stack gases (Vejahati et al., 2010). There- fore, the trace elements that were present in both the mineral mat- ter and the organic component of coal become concentrated in fly ash, and are possibly made bioavailable through phase transforma- tions during combustion (Huffman and Huggins, 1986). Leaching of these elements, including Sr, in disposal ponds can have deleteri- ous effects on wildlife (Rowe et al., 2002; Bryan et al., 2012). High concentrations of toxic elements can limit use of fly ash as a 0883-2927/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apgeochem.2012.09.001 ⇑ Corresponding author. Tel.: +1 412 624 8883; fax: +1 412 624 3914. E-mail address: bstewart@pitt.edu (B.W. Stewart). Applied Geochemistry 32 (2013) 184–194 Contents lists available at SciVerse ScienceDirect Applied Geochemistry journal homepage: www.elsevier.com/locate/apgeochem