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Pond Liners and Sealants
Guest article by Charles R. Landis, Ph.D., Bentonite Performance
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The little known, but widely used
industrial mineral called "Wyoming" bentonite can create
a natural "hydraulic barrier" in a wide range of
industrial, commercial and consumer applications. From
industrial effluent lagoons to stormwater retention basins to animal feedlot
settling ponds to decorative water features around your home,
bentonite-based, hydraulic barriers offer the opportunity for one
to easily construct a pond or lagoon.
What is Bentonite?
is an industrial mineral, rich in a clay mineral called
montmorillonite. Bentonites used for hydraulic barriers in
North America are produced from the naturally occurring sodium
bentonites mined in the state of Wyoming. These bentonites
have a unique cation chemistry. The cations that balance
electrostatic charge in the clay structure are
"exchangeable" cations and consist of sodium (Na+),
calcium (Ca++), and Mg (++) cations. The largest deposits of
commercial sodium bentonite are found in Wyoming, Montana and
South Dakota. Over the years, these special bentonites have become
famous and commonly referred to as "Wyoming" bentonite.
The combination of the relative
purity, its unusual geochemistry and structure is why
"Wyoming" bentonite is used as a sealant. Purity is
defined by the amount of sodium montmorillonite as compared to the
other minerals present in the bentonite. A typical
"Wyoming" bentonite contains ~90% montmorillonite while
other bentonites produced around the world have only 70-80%
The montmorillonite structure
contributes to the usefulness of bentonite. Montmorillonite is a
layered aluminum and silicate mineral, which is thought to occur
as very small, two dimensional mineral form called a
"platelet". The thickness of this basic building
block is approximately 1.0 - 1.5 nanometers, or about 50,000 times
thinner than a human hair. These montmorillonite platelets
have aspect ratios of 500:1 to over 1000:1 (width x height) which
in turn creates a very high surface area per unit volume.
These platelets physically occur in nanometer-scale stacks or
"Wyoming" Bentonite as a Pond or
principal function of bentonite for earthen ponds and lagoons is
as a hydraulic barrier. It is the hydration properties of
"Wyoming" bentonite that provide its unique sealing or
barrier qualities. Due to its sodium content, it is
different from calcium and sodium-activated bentonites because of
its ability to swell 1000% of its natural volume when introduced
to water. It is this swelling property that allows bentonite
when hydrated to fill "sandy" soils and
"self-heal" if breached. This self-healing
property is a unique and distinguishing feature
"Wyoming" bentonites when compared to conventional
synthetic or polymer membrane liners.
Bentonite hydration is an area of
ongoing research and the "swelling" phenomenon not
completely understood. Visually, hydrated bentonite appears
as pasty or tacky gel with the consistency of butter. Upon
hydration, bentonite in a geosynthetic clay liner (GCL) or amended
soil, swells to form a layer or liner of low-permeability.
GCL and Amended Soil Liners
There two general types of
bentonite products are used for liner markets. Bentonite is
utilized in industrial markets in the form of geosynthetic clay
liner (GCL) or as a compacted, amended bentonite/soil mixture.
Geosynthetic clay liners are used
in a range of applications from livestock pond liners to landfill
liners. Liners are composites of geotextile fabric and
bentonite. The GC liners sandwich low-permeability bentonite
between two layers of high-quality geotextile fabric(s).
These liners have become a favored option in the industry due to
their long-term containment capability, chemical resistance,
environmental compatibility and ease of installation.
A compacted clay liner can either
be in the form of an bentonite/soil mixture with the disturbed
soil or as a discreet layer of bentonite. For the
bentonite/soil amended liners, the granular or powdered bentonite
is mixed with the disturbed soils or earthen materials at ratios
of 3:1 to 5:1 (soil/clay) depending on the texture of the
soil. After a uniform mixture is achieved, the mixture is
compacted. For the discreet compacted clay liner, 4-8 inches
of the product is compacted over the area of the pond prior to
Bentonite for Decorative Water
new market for bentonite-based products is emerging in North
America, the "decorative water features" market. A
"decorative water feature" is any manmade stream,
fountain, waterfall, or other manmade water feature that contains
water for landscape purposes. These consumer-oriented
markets also require convenience, performance and safety.
Customers ask the same questions,
"how do I prevent seepage?" and "how is bentonite
used as a decorative pond liner?". Bentonite
Performance Minerals produces a special bentonite product called
Enviro-Seal™ HG is that can be used to control seepage. With
a minimum application rate of 5 to 6 lbs per square foot spread
over the pond area for sealing, the bentonite is tilled into the
soil to a depth of 4 to 6 inches prior to compaction. Once
it is compacted, the pond may be further decorated with sands,
gravels or stones.
Bentonite for Water
Clarification and Phosphorus Removal
Bentonite Performance Minerals also
offers a new generation bentonite products called BaraClear™, a
time-released, water clarification product for the water treatment
market. It is available in form of a tablet or
briquette. The primary use of BaraClear™ is for organic and
inorganic contaminate removal, including phosphorus. It is an
efficient way to clarify natural and industrial waters and remove
phosphorus, a key contaminant in many natural water systems.
About our Author:
Dr. Charles R. Landis, Ph.D.
New Business and Technology Director
Bentonite Performance Minerals
410 17th Street, Suite 405
Denver, CO 80202
more information: Any questions you might have about the use of any
of Bentonite Performance Minerals' products, please feel free to
Ms. Juli Johnson
Bentonite Performance Minerals
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