2997
Novel bentonites for containment barrier applications
Bentonites novatrices pour des applications comme barriers de confinement
Bohnhoff G., Shackelford C.
Colorado State University, Fort Collins, Colorado, USA
Malusis M.
Bucknell University, Lewisburg, Pennsylvania, USA
Scalia J., Benson C., Edil T.
University of Wisconsin, Madison, Wisconsin, USA
Di Emidio G.
Ghent University, Zwijnaarde, Belgium
Katsumi T.
Kyoto University, Kyoto, Japan
Mazzieri F.
Universita` Politecnica delle Marche, Ancona, Italy
ABSTRACT: Sodium bentonite (Na-bentonite) commonly is used in geoenvironmental containment barriers to control liquid flow
and contaminant migration, but is known to be thermodynamically unstable in environments where multivalent cations are present.
As a result, a host of novel, chemically-modified bentonites designed for improved resilience have been developed. The objective of
this paper is to illustrate selected properties of some of these bentonites being considered for containment barrier applications. The
bentonites considered in this paper include Na-bentonite polymerized with acrylic acid (bentonite-polymer nanocomposite, or BPN),
Na-bentonite amended with sodium carboxymethyl cellulose (HYPER clay), and a propylene carbonate modified Na-bentonite
(multiswellable bentonite, or MSB). Engineering properties of the novel bentonites relevant to two specific types of barriers (i.e.,
cutoff walls and geosynthetic clay liners) are compared and contrasted with those of natural Na-bentonites. The results illustrate the
potential for improved hydraulic performance of barriers containing the novel bentonites. However, further research is needed
elucidate the mechanisms responsible for differences in behavior and performance among these bentonites.
RÉSUMÉ : La bentonite à base de sodium (bentonite-Na) est utilisée couramment comme barrière de confinement géo-
environmentale pour contrôler les flux de liquides et la migration de contaminants ; elle est cependant connue pour être instable
thermodynamiquement dans des environnements qui contiennent des cations multivalents. Pour palier cet inconvénient, diverses
bentonites novatrices modifiées chimiquement et conçues pour présenter une résistance améliorée aux écoulements ont été
développées. L’objectif de cet article est d’illustrer certaines propriétés techniques de quelques unes de ces bentonites étudiées leur
utilisation dans les barrières de confinement. Cet article présente les propriétés de la bentonite-Na polymérisée avec de l’acide
acrylique (« bentonite-polymer nanocomposite », ou BPN), de la bentonite-Na modifiée avec de la carboxymethylcellulose sodique
(ou « HYPER Clay ») et d’une bentonite-Na modifiée avec du carbonate de propylène (« multiswellable bentonite », ou MSB). On a
procédé à une analyse comparative des propriétés des bentonites novatrices correspondant à deux types spécifiques de barrières
(c.a.d., parois de séparation et revêtement par des géomembranes synthétiques) et celles des bentonites-Na naturelles. Les résultats
illustrent le potentiel d’amélioration de la performance hydraulique que présentent des barrières contenant les nouvelles bentonites.
Des recherches supplémentaires sont cependant nécessaires pour comprendre les mécanismes susceptibles d’expliquer les différences
de comportement et de performance entre ces bentonites.
KEYWORDS: Bentonite; Bentonite slurry; Cutoff wall; Geosynthetic clay liner; Hydraulic conductivity; Polymerized bentonite
1
INTRODUCTION
Bentonite is a natural clay composed primarily of the mineral
montmorillonite, a member of the smectite group of clay
minerals. Montmorillonite is characterized by large surface
area (100-800 m
2
/g), a net negative charge typically on the
order of 80 to 150 cmol
c
/kg, and exchangeable surface cations
(Grim 1968). These characteristics, in turn, impart a strong
affinity by bentonite for water, resulting in swelling, sealing,
and adhesive characteristics (Eisenhour and Brown 2009).
Bentonite commonly is used to control flow (seepage) and
contaminant transport in a variety of hydraulic containment
applications, such as soil-bentonite (SB) groundwater cutoff
walls, barriers for waste containment (e.g., landfills, wastewater
ponds, manure lagoons, nuclear storage, etc.), secondary
containment in petroleum tank farms, and seals in monitoring
and water supply wells. In all of these applications, sodium
bentonite (Na-bentonite) typically is used, meaning that sodium
(Na
+
) is the predominant cation on the exchange sites of the
individual bentonite particles. The preference for Na-bentonite
stems from desirable engineering properties, such as low
hydraulic conductivity to water,
k
w
(typically < 10
-10
m/s), and
the existence of semipermeable membrane behavior, the latter
giving rise to hyperfiltration, chemico-osmotic flow, and
reduced diffusion (Malusis et al. 2003). Unfortunately, Na-
bentonite is thermodynamically unstable in environments where
multivalent cations (e.g., Ca
2+
, Mg
2+
) are present, including
most naturally occurring pore waters as well as waste streams
containing heavy metals (e.g., landfill leachates, acid mine
drainage) or radionuclides. Under such conditions, multivalent
