Pilot Deinking Treatment of Mixed Office Waste Using a Standpipe Flotation Facility

Abstract

Mixed office waste (MOW) is one of the least effectively recycled items among recyclable paper products due to difficulty in deinking laser-printed and xerographic paper, and the mixing of white and colored sheets. We combined the effects of centri-cleaning, and macro- and micro-air bubble flotation (DAF) capabilities and built a pilot-scale standpipe-type treatment unit to conduct deinking tests. Wastepaper was first deinked in our lab using a blender for disintegration and then bubble aeration for flotation in beakers. The results indicated that without treatment, hand sheets of recycled MOW had a speck area of ca. 4000mm^2 m^(-2), while with the addition of only commonly used deinking chemicals, the ink speck could be reduced to less than 760mm^2 m^(-2); the best result achieved was a 93% overall removal rate. In the preliminary pilot-scale deinking test, the deinking chemicals were added during repulping of the MOW wastepaper. After consistency adjustment, the ensuing flotation deinking was carried out using a standpipe unit. The results after a hydraulic retention time equivalent to 3 recirculations reduced the ink speck area from 2377mm^2 m^(-2)to＜79mm^2 m^(-2) with the best result being 28mm^2 m^(-2); an overall removal rate of 98.8% was achieved. In the formal test series, the MOW was first disintegrated using a high-consistency pulper at 2 levelseach of consistency, temperature, NaOH, and surfactant dosages. Then after dilution, each treated batch was deinked in the standpipe flotation unit using the optimal pulp flow and aeration rates for a treatment time equivalent to 3 recirculations. Handsheets from untreated wastepaper contained ca.10,800mm^2 m^(-2) ink specks, and after flotation treatment, the speck count was markedly reduced, with the best result of only 252 mm^2 m^(-2) which equals an overall deinking efficiency of 97.7%. The temperature and consistency during repulping were shown to be the most influential operational parameters. Practical application of this deinking technology to the production line appeared very promising.