Deinking
Sometimes the pulp must undergo
a "pulp laundering" operation called deinking
(de-inking) to remove printing ink and "stickies"
(sticky materials like glue residue and adhesives).
Papermakers often use a combination of two deinking
processes. Small particles of ink are rinsed from
the pulp with water in a process called washing. Larger
particles and stickies are removed with air bubbles
in another process called flotation.
During flotation deinking,
pulp is fed into a large vat called a flotation
cell, where air and soap-like chemicals call surfactants
are injected into the pulp. The surfactants cause
ink and stickies to loosen from the pulp and stick
to the air bubbles as they float to the top of the
mixture. The inky air bubbles create foam or froth
which is removed from the top, leaving the clean
pulp behind.
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