ARTICLE Examining fly ash as a sorbent for benzene, trichloroethylene, and ethylbenzene in cement-treated soils Craig B. Lake, Ghazal Arefi, and Pak K. Yuet Abstract: The objective of this study was to examine the potential for beneficial reuse of fly ash as a sorbent for benzene, trichloroethylene, and ethylbenzene in soils treated with cement (i.e., cement-based solidification/stabilization (S/S)). Batch testing was performed with soil–cement mixtures containing fly ash and compared with similar samples with humic acid as a source of organic carbon. The experimental batch test results were fit to the Freundlich sorption model assuming both linear and nonlinear behavior. It was found that the level of sorption is low for benzene and trichloroethylene, but relatively higher for ethylbenzene. Cement addition appeared to not only decrease sorption values obtained for fly ash, but also eliminate the nonlinear sorptive behavior, likely due to the blocking–coating of sorption sites. To demonstrate the practical application of the sorption observed, a hypothetical contaminated site is modeled with a one-dimensional contaminant transport program. It iss shown that the addition of fly ash can potentially reduce off-site migration of trichloroethylene (TCE), but is more effective at reducing ethylbenzene migration, for the time frames considered in the modeling. Key words: fly ash, cement, sorption, volatile organic compounds (VOCs), stabilization, solidification. Résumé : L’objectif de cette étude est d’évaluer le potentiel de réutilisation des cendres volantes en tant que sorbant pour le benzène, trichloréthylène et éthylbenzène dans des sols traités avec du ciment (solidification/stabilisation (S/S) avec du ciment). Des essais en batch ont été réalisés avec des mélanges sol–ciment contenant des cendres volantes, et par la suite ont été comparés a ` des échantillons similaires avec de l’acide humique comme source de carbone organique. Les résultats des essais en batch ont été associés au modèle de sorption de Freundlich en supposant un comportement linéaire et non-linéaire. Il a été observé que le niveau de sorption est faible pour le benzène et le trichloréthylène mais relativement élevé pour l’éthylbenzène. L’ajout de ciment semble diminuer les valeurs de sorption obtenues pour les cendres volantes et aussi éliminer le comportement en sorption non-linéaire, probablement en raison du blocage–enveloppement des sites de sorption. Pour démontrer l’application pratique de la sorption observée, un site contaminé hypothétique est modélisé avec un programme de transport de contami- nants en une dimension. Il est démontré que l’ajout de cendres volantes peut potentiellement réduire la migration hors du site de trichloréthylène (TCE), mais est plus efficace pour réduire la migration de l’éthylbenzène, pour les périodes de temps considérées dans la modélisation. [Traduit par la Rédaction] Mots-clés : cendres volantes, sorption, composés organiques volatils (COV), stabilisation, solidification. Introduction The use of cement or other binder materials to solidify and (or) stabilize contaminants present in soils has been used extensively in the USA and the UK as a source-control remediation technology for contaminated lands (e.g., Hills et al. 2010; Schifano et al. 2010). Traditionally, cement-based solidification/stabilization (S/S) treat- ment technology has been utilized for metal-contaminated sites (USEPA 2006), but is being used more frequently for sites contain- ing both inorganic and organic contaminants (Bates 2010). The inability of cement-based S/S treatment techniques to limit the contaminant migration of organic contaminants has received considerable attention in the literature (e.g., Bone et al. 2004; Paria and Yuet 2006). The most common method of improving the performance of cement-based S/S treatment systems with respect to organic contaminant transport is to add a source of organic carbon to the mixture (e.g., organoclays, fly ash, activated carbon, etc.). Various researchers (e.g., Côté et al. 1990) and consultants (e.g., Shaw Technology 2004) have reported on the use of fly ash in cement-based S/S mixtures, but few published studies have fo- cused on quantifying the sorption of fly ash in cement-based S/S mixtures. Leonard and Stegemann (2010) published work related to cement treatment of semi-volatile organics and reported sorp- tion coefficients based on leaching tests. This quantification of sorption is important in evaluating beneficial reuse qualities of fly ash in cement-based S/S mixtures. Because fly ash is a waste prod- uct, there are substantial cost savings to be made when replacing cement and (or) organic additives such as organoclays and activated carbon in cement-based S/S mixtures. However prior to substitution with fly ash, it should be demonstrated that the use of fly ash as an additive is beneficial not only from a cost perspective, but also from an organic contaminant attenuation perspective. The purpose of this paper is to examine the beneficial reuse of fly ash in cement-treated soils as a sorbent for three volatile or- ganic compounds (VOCs) — benzene, trichloroethylene (TCE), and ethylbenzene — using batch sorption testing. Soils consisting of mixtures of sand, kaolinite, and (or) humic acid were tested with and without cement – fly ash binders to (i) investigate the relation- ship between fly ash and cement in the VOC sorption process and (ii) quantify sorption of these VOCs to the various mixtures. To examine the potential engineering benefits of implementing fly ash into cement-treated soils for cement-based S/S treatment, a Received 28 May 2012. Accepted 3 December 2012. C.B. Lake. Department of Civil and Resource Engineering, Dalhousie University, 1360 Barrington Street, Building D, Room D215, Halifax, NS B3J 1Z1, Canada. G. Arefi. HEMMERA: Suite 250 – 1380 Burrard Street, Vancouver, BC V6Z 2H3, Canada. P.K. Yuet. 300 110th Ave NE, Bellevue, WA 98004, USA; formerly Dalhousie University, Halifax, NS, Canada. Corresponding author: Craig B. Lake (e-mail: craig.lake@dal.ca). 423 Can. Geotech. J. 50: 423–434 (2013) dx.doi.org/10.1139/cgj-2012-0198 Published at www.nrcresearchpress.com/cgj on 17 April 2013. Can. Geotech. J. Downloaded from www.nrcresearchpress.com by DALHOUSIE UNIVER on 03/11/15 For personal use only.