The key to designing Bentonite liners and vertical cut-off barriers lies in understanding clay chemistry.
Bentonite is a clay mineral made of hydrous aluminosilicate sheets or plates. Unsatisfied charges within its crystal structure resulting from the substitution of aluminium by magnesium atoms cause a net negative surface charge. To counteract this charge imbalance, bentonite has a strong affinity for cations and water molecules.
This attraction results in the formation of several diffuse layers of cations and water molecules that surround the clay crystal. These layers increase the effective size of the clay structure, giving Bentonite it’s well-known swelling properties when hydrated with water.
Bentonite properties are greatly influenced by the types of cations absorbed on the clay structure. These alter the water absorption, depending on their size and valence.
Sodium Bentonites have relatively more diffuse layers and therefore absorb much more water than Calcium Bentonites which have larger divalent calcium ions which are held more strongly to the clay and the net negative surface charges on each clay particle are lower, Calcium Bentonites, therefore, have smaller diffuse layers, absorb less water and do not swell as much as Sodium Bentonites.
Bentonite behavior in liners and cut-off trenches depends on the size of diffuse layers. Clay plate faces have a negative charge and the edges a positive charge. This results in a repulsion between the crystal faces and an attraction between the edges and the faces.
For Sodium Bentonite, the diffuse layer is large and its particles well dispersed, with little face to face contacts. However, when monovalent sodium ions are exchanged with multivalent ions from contaminated groundwater or waste leachate, the diffuse layer is reduced and repulsion between crystal faces lowered. High salt concentration in contaminants also alters the diffuse layer by changing the electrical potential between clay particles and the absorbed pore water.
At smaller interparticle spacings, attractive forces, are greater than repulsive forces and the clay particles flocculate giving an increase in permeability.
Highly concentrated organic compounds, high salt solutions, and low pH levels can cause a sudden and dramatic failure in bentonite liners.
Simply!! Sodium Bentonite powder coats all the particles and with the addition of water swells and fills the voids with a dense clay barrier.
Complete our Contact Form with your requirements and we will get back to you or call Bentonite SA today +27 72 341 2428 and find out if bentonite clay is right for you.