Pilot Deinking Treatment of MOW Using a Stand Pipe Flotation Facility

Mixed office waste (MOW) is one of the least effectively recycled items among the recyclable paper products due to difficulty in deinking laser and xerographic printed paper, and mixing of white and colored sheets. We combined the effects of centri-cleaning, macro- and micro-air bubbles flotation (DAF) capabilities and built a pilot scale stand pipe type treatment unit to conduct deinking tests. Wastepaper was first deinked in our lab using a blender for disintegration and then bubbler aeration for flotation in beakers. The results indicated that without treatment handsheets of recycled MOW had speck area of ca. 4000 mm2 m-2, with addition of only commonly used deinking chemicals, the ink speck could be reduced to less than 760 mm2/m2; the best result achieved being a 93% overall removal rate. In the preliminary pilot scale deinking test, the deinking chemicals were added during repulping of MOW wastepaper. After consistency adjustment, ensuing flotation deinking was carried out using the stand pipe unit. The results after hydraulic retention time equivalent to 3 recirculations reduced ink specks area from 2377 mm2 m-2 to less than 79 mm2 m-2, with the best being 28 mm2 m-2; achieving a overall removal rate of 98.8%. In the formal test series, MOW was first disintegrated using a high-consistency pulper at 2 levels each of consistency, temperature, NaOH and surfactant dosages. Then after dilution, each treated batch was deinked by the stand pipe flotation unit using the optimal pulp flow and aeration rate for a treatment time equivalent to 3 recirculations. Handsheet from untreated wastepaper contained ca.10800 mm2 m-2 ink specks, after the flotation treatment the speck counts reduced markedly, with the best result having only 252 mm2 m-2 which equals to a ovrerall deinking efficiency of 97.7%, and the temperature and consistency during repulping were shown to be the most influential operational parameters. Practical application of the deinking technology in production line appeared very promising.