Mixed office waste containing xerographic ink is becoming an important
source of recycled fiber. This research examined the use of ultrasoun
d to break down xerographic ink particles prior to removal by conventi
onal flotation. The raw material was standard xerographic sheets print
ed with common toners (styrene-butadiene and styrene-acrylate). Prelim
inary tests were carried out with a 500-W piezoelectric transducer cap
able of batch processing. Results from these tests provided a base for
subsequent tests with an ultrasonic whistle suitable for continuous,
flow-through operation. Both systems reduced xerographic particles to
sizes suitable for removal by flotation. Performance of the continuous
system was strongly affected by treatment pH, the number of treatment
cycles, and pulp consistency. Response-surface methodology was employ
ed to determine the best operating conditions for the ultrasonic whist
le. Results for the continuous, flow-through ultrasound system suggest
that scale-up experiments should be pursued.