Bentonite
(anionic smectite clay)
Bentonite is the name given to the anionic smectite clay material used to improve
retention and drainage. The composition of the particles can be described as
very thin plates caused by the salts in the clay. This gives a large surface
area for the particle to bond with other particles and cationic polymer.
The bentonite has two functions, primarily when
use either before or after a cationic polymer it serves as a drainage/
retention aid. When bentonite is used with cationic polymer it can be used to
control the level of pitch, tacky materials (commonly referred to as Anionic
trash).
Bentonite added down-stream to polymer improves
dewatering on the wire. Best achieved when high mass cationic polymer is used
has been added so that the stock furnish has a momentary net cationic charge.
If the stock has a high level of Anionic trash it makes sense to firstly treat
the stock with sufficient cationic polymer.
Bentonite works with the polymer to increase the dewatering capabilities of the
paper web, the two chemicals work in unison to achieve this. Bentonite works as
a drainage aid allowing the water to be removed more easily from the web. When
adjusting the chemicals the set points of both the polymer and the hydrocol
must be reduced or increased together, having a high polymer dosage and low
hydrocol dosage or vice versa for example can decrease the drainage on the
machine and cause poor formation.
Diluted Bentonite is added post
screen and works by reforming the fiber flocculation’s that have been broken down by shear forces going through the primary machine screen. Bentonite brings the
smaller flocs together for better formation on the fourdrinier.
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