Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Bentonite Clay

Last updated: April 5, 2018

What Does Bentonite Clay Mean?

Bentonite clay is a clay which is an absorbent aluminum phyllosilicate consisting mostly of montmorillonite. The main uses of bentonite clays are for drilling mud, and as a binder, purifier, absorbent and groundwater barrier.

Bentonite clay is a chemically inert, non-corrosive, natural clay. It is the most economical and efficient desiccant bag-filling material. It is also used as a backfill material for cathodic protection.

There are different types of bentonite, each named after the respective dominant element, such as potassium (K), sodium (Na), calcium (Ca) and aluminum (Al). For industrial purposes, two main classes of bentonite exist: sodium and calcium bentonite.


Corrosionpedia Explains Bentonite Clay

Bentonite clay is composed dominantly of smectite clay minerals that give the clay its ability to swell when in contact with free water. Many of the bentonite clays are formed in the hydrothermal alteration of glassy, igneous material of volcanic origin. It is composed of the mineral montmorillontite, a hydrous aluminum silicate.

The adsorption capacity of bentonite is considerable, even at low humidity levels, and increases with increasing relative humidity. The adsorption capacity of bentonite is greater than silica gel in packaging conditions below 30% relative humidity (RH), usually the case for most packaging applications.

Bentonite is used in various backfill materials for cathodic protection. It is an important component in chemical backfill. Bentonite has all the qualities of the ideal backfill for ground rods. It is easy to prepare, non-corrosive and highly conductive. When mixed with water, it absorbs up to 13 times its dry volume.

Bentonite absorbs whatever moisture is present into its structure and it maintains its consistency. In direct sunlight the top few inches become hard and seal itself off, but the rest of the bentonite stays moist and conductive.

Bentonite has a resistivity of 2.5 ohms-M at 300% moisture. This low resistance is a result of the electrolyte formed when water is added. The water held in the bentonite clay allows the minerals in the clay (soda, potash, lime, magnesia and other material salts) to ionize. The result is a strong electrolyte with a pH as high as 10.


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