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What is Bentonite?

Bentonite Sealant

Sealant Systems

Methods

Products:

Canapell
animal feed binder

Geoplug
granular sealant

Canagel
drilling mud

Coregel
high viscosity drill mud

Canafloc
flocculant aid

Ezetrowel
stucco and mortar

Canabond
foundry sand binder

Bentonite as a Sealant

Bentonite is a commercially available clay consisting mainly of the clay mineral Montmorillonite and occurs in two main forms in nature; namely a sodium variety and a calcium variety. The two varieties differ mainly in that sodium bentonite is known to swell to several times its original volume when contacted by water. Calcium bentonite on the other hand swells to a much lesser degree. 

Bentonite is noted for its affinity for water and for tremendous swelling properties. It can be described as a bundled plate structure, the surface of which is populated by sodium ions. The addition of water causes the sodium ion to hydrate, generating a negative charge on the bentonite plate. Since like electric charges repel each other the platelets are moved apart causing a phenomena called "swelling". The rate of swelling depends upon the fineness, grade and how the bentonite is handled. All grades expand very slowly when water is poured on them, much faster when they are poured into water. Fine powdered bentonite grades absorb water slowly; intermediate and specially sized bentonite absorbs water more rapidly. 

Bentonite absorbs nearly five times its weight of water and at full saturation it occupies a volume of 12 to 15 times its dry bulk weight. On drying it shrinks to its original volume. Swelling is reversible - it can be (wetted), swelled and (dried), shrunk an infinite number of times if the water used is fairly pure. This swelling is important, since the entire swollen mass - that is clay and water -
behave as if they were clay. 

Natural clays are generally combinations of different types of clays in varying quantities. However, most clays contain substantial
non clay portions consisting of sand and silt. In such cases, the value of the native clay as a sealant is diminished in direct
relationship to the amount of non clay material present. In addition, the non clay (usually sand) can occur as "stingers"; that is
continuous veins running through the clay bed and providing pathways for the seepage of water or leachate into the ground water
table. 

Bentonite however, can be used in a practical fashion when mixed with soils because: 

     1. The product is shipped dry and applied as a dry granulated material and hence is easily handled; and 
     2. only a small amount of bentonite is required in order to effect a high quality seal. As indicated earlier, bentonite can swell  to ten times its original volume; thus the addition of 2% bentonite to the system will after swelling, behave like 20% native clay. 

Bentonite in contact with water remains flexible at all times. It never becomes rigid, sets or cures. It has existed underground in its present mineral form for many thousands of years. Therefore, by retaining an axle grease type consistency, it is not subject to tearing, ripping, cracking or any problems to which more rigid systems are susceptible. The flexible expanding and self sealing
properties of bentonite are important advantages when used for water impedance purposes. As a result, small ground movements that would break up concrete or synthetic liners will have minimal effect on the bentonite seal. Bentonite can also take a great deal of abuse from the handling without any substantial deterioration in its effectiveness. If a large hole appears in the seal, that will not self heal, but again Bentonite versatility can be used effectively. The scattering of dry bentonite over the surface of the water impoundment in question will frequently allow the hole to be sealed effectively by the swollen bentonite settling through the water and entering the unsealed area. 

Clearly, this can be a hit and miss approach if you don't know where the seepage area is. But since the water seepage is moving toward the leaking area it will carry the bentonite with it. Pinpointing the exact spot of the problem is not necessary, but of course it is more economical if the general area seepage is known. 

The bentonite can be scattered dry over the surface from a boat or blown by a gunite compressed air system over the surface of the water. In addition, a bentonite slurry can be pumped into the system either at the influent or over the surface of the water. 

Bentonite can be admixed with soils with a high seepage, or permeability rate and thereby lowers the permeability, or seepage rate in direct proportion to the amount and type of bentonite added and the uniformity of blending. 

 How bentonite works:

 Water cannot go through a grain of sand but by taking circuitous can easily find its way through the air voids in the soil. Beach sand containing 30% or more air spaces allows water to leak readily. 

  The same soil can be made impermeable with the BENTONITE. When trapped within the voids, BENTONITE   swells in contact with water. While the swelling of the BENTONITE is restricted by the sand and gravel grains, the  BENTONITE expands to fill the voids and forms a tough, leathery mineral mastic through which water cannot  readily move. 

     A 2 to 3 inch seal of BENTONITE and soil is as impermeable as a 12 to 18 inch layer of packed native clay.

In the past native clays of variable quality have been assumed to be as effective means of containing the water from ground infiltration. However there are several problems: 

     1. The variable quality of the natural clay. 
     2. The possibility of degradation of the natural clay by the components in the leachate. 
     3. Very large amounts of native clay are required, since a clay content of at least 30% is usually necessary to effect a seal. 
     4. Since clays are very difficult materials to handle, it is usually impossible to effect a good mix. 

ccp@canadianclay.com

P.O. Box 70
Wilcox, Saskatchewan S0G 5E0
Phone: (306)732-2085
Fax: (306)732-2100
Hours: 8:00 a.m. to 4:30 p.m.