Effect of NaCl on hydraulic properties of bentonite and bentonite–palygorskite mixture J. Frankovska ´ 1 , S. Andrejkovic ˇova ´ 2 and I. Janotka 3 1 Slovak University of Technology, Faculty of Civil Engineering, Radlinskeho 11, 813 68 Bratislava, Slovakia, Telephone: +421 2 59274624, Telefax: +421 2 52925642, E-mail: jana.frankovska@stuba.sk 2 Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dubravska cesta 9, 845 36, Bratislava, Slovakia, Telephone: +421 2 59410484, Telefax: +421 2 59410444, E-mail: Slavka.Andrejkovicova@savba.sk 3 Building Testing and Research Institute, Studena 3, 821 04 Bratislava, Slovakia, Telephone: +421 2 49228251, Telefax: +421 2 49228258, E-mail: Janotka@tsus.sk; Institute of Construction and Architecture, Slovak Academy of Sciences, Dubravska cesta 9, 845 03 Bratislava, Slovakia, Telephone: +421 2 59410484, Telefax: +421 2 59410444, E-mail: Ivan.Janotka@savba.sk Received 11 February 2009, revised 10 February 2010, accepted 2 June 2010 ABSTRACT: Sodium bentonite (Na-bentonite) is used as a sealing component in geosynthetic clay liners (GCL). Na-bentonite is very sensitive to chlorides, and flocculation occurs when it is exposed to saline environments. The purpose of this work is to investigate the properties of Na- bentonite and bentonite–palygorskite filler material for GCL in saline solutions in the range between 0.5% and 10% (0.09 and 1.8 M) NaCl concentration. The investigation has been carried out to evaluate and study the chemical and geotechnical properties of Na-bentonite and bentonite– palygorskite mixture. The observations suggest that the resistance of Na-bentonite to chlorides is increased by adding 40% palygorskite. The bentonite–palygorskite mixture is characterised by high liquid and plastic limits, and also by high water adsorption and free swell in water, crude oil and petrol. Hydraulic conductivity was determined for water and for 10% NaCl (1.80 M) solution. The results show that Na-bentonite palygorskite mixture serves as an effective absorber of both water and saline solutions up to a concentration of 10% (1.80 M) of NaCl without increasing the hydraulic conductivity. KEYWORDS: Geosynthetics, Geosynthetic clay liners, Bentonite, Palygorskite, Geotechnical properties, Chemical properties REFERENCE: Frankovska ´, J., Andrejkovic ˇova ´, S. & and Janotka, I. (2010). Effect of NaCl on hydraulic properties of bentonite and bentonite–palygorskite mixture. Geosynthetics International, 17, No. 4, 250–259. [doi: 10.1680/gein.2010.17.4.250] 1. INTRODUCTION Palygorskite has some particularly desirable sorption, colloidal-rheological and catalytic properties, in compari- son with other clay minerals (Jones and Gala ´n 1988). This clay is characterized by high viscosity, a high surface area, a moderate layer charge, and a large number of silanol groups on its surface as a result of its inverted structure and fibrous morphology (A ´ lvarez-Ayuso and Garcı ´a- Sa ´nchez 2007). Fuller information on the physico- chemical properties of palygorskite is provided by Neaman and Singer (2004). Based on these properties, the industrial applications of palygorskite are numerous, such as drilling mud, agricultural carriers, industrial floor absorbents, cat box absorbents, catalyst supports, gelling agents in paints, adhesives and cosmetics, and reinforcing filler in rubbers and plastics (Murray 2000a, 2000b), although those related to environmental protection are much more scarce. Bentonite is clay composed mainly of montmorillonite, the most common mineral of the smectite group. It may contain kaolinite, feldspars, micas, cristoballite and quartz (Parkes 1982). The properties of bentonite include the ability to form thixotropic gels with water, the ability to adsorb large amounts of water, and a high cation exchange capacity. In contact with water, bentonites swell and reduce the pore spaces, resulting in very low per- meability (Egloffstein 1996). Von Maubeuge and Ehren- berg (1996), among others, report on experience gained with the use of needle-punched geosynthetic clay liners (GCLs) consisting of two geotextiles with an encapsu- lated layer of bentonite. With respect to their particular Geosynthetics International, 2010, 17, No. 4 250 1072-6349 # 2010 Thomas Telford Ltd