Utilization of sepiolite materials as a bottom liner material in solid waste landﬁlls Yucel Guney a , Bora Cetin b,⇑ , Ahmet H. Aydilek c , Burak F. Tanyu d , Savas Koparal a a Department of Civil Engineering, 2 Eylul Campus, Anadolu University, Eskisehir 26480, Turkey b Department of Civil and Environmental Engineering, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA c Department of Civil and Environmental Engineering, University of Maryland, College Park, MD 20742, USA d Department of Civil and Environmental Engineering, George Mason University, Fairfax, VA 22030, USA article info Article history: Received 13 November 2012 Accepted 9 October 2013 Available online 9 November 2013 Keywords: Landﬁlls Solid wastes Bottom liner Sepiolite Zeolite Adsorption Heavy metals abstract Landﬁll bottom liners are generally constructed with natural clay soils due to their high strength and low hydraulic conductivity characteristics. However, in recent years it is increasingly difﬁcult to ﬁnd locally available clay soils that satisfy the required engineering properties. Fine grained soils such as sepiolite and zeolite may be used as alternative materials in the constructions of landﬁll bottom liners. A study was conducted to investigate the feasibility of using natural clay rich in kaolinite, sepiolite, zeolite, and their mixtures as a bottom liner material. Unconﬁned compression tests, swell tests, hydraulic conductivity tests, batch and column adsorption tests were performed on each type of soil and sepio- lite–zeolite mixtures. The results of the current study indicate that sepiolite is the dominant material that affects both the geomechanical and geoenvironmental properties of these alternative liners. An increase in sepiolite content in the sepiolite–zeolite mixtures increased the strength, swelling potential and metal adsorption capacities of the soil mixtures. Moreover, hydraulic conductivity of the mixtures decreased signiﬁcantly with the addition of sepiolite. The utilization of sepiolite–zeolite materials as a bottom liner material allowed for thinner liners with some reduction in construction costs compared to use of a kaolinite-rich clay. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Compacted clay liners located below the municipal solid waste are one of the most important parts of the landﬁlls. The primary duty of these liners, sometimes referred to as bottom liners, is acting as a hydraulic barrier to prevent leaching of inorganic and organic pollutants (which is leaching from municipal solid waste in the landﬁlls) into the groundwater or surface water. Hydraulic conductivity and strength of a typical liner material used in the landﬁll should not be less than 1  10 9 m/s and 200 kPa respec- tively (Daniel and Benson, 1990; Guney et al., 2008; Osunibu and Nwaiwu, 2006; Kang and Shackelford, 2010; Fransisca and Glatstein, 2010). Liners are usually constructed with locally avail- able clay soils due to their high unconﬁned compressive strength and low hydraulic conductivities (Kayabali, 1997). However, in re- cent years it has become harder to ﬁnd locally available natural soil that satisﬁes the engineering properties mentioned above. There- fore, researchers seek alternative materials that may be used as a liner in municipal waste landﬁlls. Recent studies have proposed replacing natural clay soils with soil-like geomaterials such as sand–bentonite mixtures, foundry sand, ﬂy ash, wood ash, and ﬂy ash amended tire rubber (Kenney et al., 1992; Pandian et al., 1996; Palmer et al., 2000; Abichou et al., 2004; Akgun, 2010). Constructing liners with such alternative materials can provide signiﬁcant money savings since most of these alternative materials can be obtained at a marginal cost (Cetin et al., 2010). Even though these materials generally satisﬁed the engineering properties that are needed to be used in liner constructions, issues pertinent to their mechanical and environmental suitability have been re- ported. For instance, Edil et al. (1992) and Palmer et al. (2000) sug- gested that utilization of ﬂy ashes in liner construction is feasible. However, compaction process of ﬂy ashes in the ﬁeld can be difﬁ- cult and may yield higher hydraulic conductivity and lower stiff- ness (Palmer et al., 2000). In addition, ﬂy ash itself contains a high amount of heavy metals which poses an additional environ- mental concern (Goswami and Mahanta, 2007; Morar et al., 2012; Cetin et al., 2012). Sand–bentonite mixtures and foundry sand provided reasonable stiffness and hydraulic conductivity val- ues with pure deoinized water inﬂuent solutions. However, the hydraulic conductivity of these soils increased signiﬁcantly when chemical inﬂuent solutions were used (Abichou et al., 2004). 0956-053X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.wasman.2013.10.008 ⇑ Corresponding author. Tel.: +1 336 686 1361; fax: +1 605 394 5171. E-mail addresses: yguney64@gmail.com (Y. Guney), bora.cetin@sdsmt.edu (B. Cetin), aydilek@umd.edu (A.H. Aydilek), btanyu@gmu.edu (B.F. Tanyu), askopara@ anadolu.edu.tr (S. Koparal). Waste Management 34 (2014) 112–124 Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman