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 Publication: PULP & PAPER MAGAZINE RECYCLING UPDATEFlotation deinking flexo-printed newsWastepaper with water-based ink is relatively easy to deink by the washing deinking method due to the small ink particle size. In contrast, water-based printed newspapers and magazines have presented an insurmountable challenge when deinking is attempted using the increasingly popular flotation deinking process. A "universal collector," which can handle all of the varieties of water-based, oil-based, and solvent-based ink, has been developed by Sun Chemical and Rheox, Inc., a subsidiary of NL Industries, a specialty chemical manufacturer. The success of this collector was explained at the Wastepaper IV Conference and Exhibition in Chicago by Bob Horocek, eastern regional manager of Lion Industries, and is described as follows. HOW COLLECTORS WORK. Chemical collectors are mixed with pulp and dispersed air to enhance differences in surface properties of the ink and pulp fiber. The particles to be removed from the pulp have to be made hydrophobic (water-hating) to enable effective attachment to the air bubbles and effective removal of the inks. The flotation collector molecules selectively adsorb--i.e., attach themselves through their functional groups--onto the surface of the particles and render them hydrophobic. The collector has to be specific enough not to adsorb on the surface of the material which is to stay in the pulp; otherwise, the separation will never be complete. By the same token, the collector has to have high affinity to all the materials to be removed from the pulp. The new collector, called Lionsorb, marketed by Lion Industries, functions by converting both the oil- and water-based inks to a hydrophobic form. High ink-removal efficiency by flotation during trials attests to the attraction of Lionsorb to both types of inks. The low paper fiber loss during flotation attests to the collector's lack of affinity toward woodfiber. COMMERCIAL TRIAL. A system trial was run in a 30 ton/day continuous commercial-scale process. A wastepaper mixture containing 30% flexo newsprint (San Francisco Examiner), 40% mixed offset newsprint, and 30% mixed magazines was pulped in 1,400-lb batches in a high-consistency batch pulper. In addition to standard screening and cleaning operations, the process consisted of flotation cells followed by a disc washer, belt press, disperser, post-dispersion flotation, and additional thickening. All equipment was operated at typical conditions and consistencies, e.g. 1% consistency for flotation, and thickening to 5% by the washer and 35% by the belt press prior to mechanical dispersion. TRIAL RESULTS. Buchner funnel filtrate of the mixed wastepaper pulper without Lionsorb addition was very black and contained high concentrations of free flexo ink that passed through the filter paper. Buchner filtrate of the wastepaper pulped with Lionsorb addition was clear, indicating that the flexo ink had been successfully removed. It was no longer in the water phase and could not follow the water during filtration. Buchner filtrate from pulp after flotation was even a bit clearer due to the absence of flexo ink in the pulp. Brightness results at various points in the continuous, commercial-scale trial were measured using standard Tappi brightness pads. Brightness after flotation was approximately 50 throughout the trial, representing a brightness increase of 8 to as much as 17 points. This kind of increase would be reasonable with a conventional newsprint furnish, but is particularly impressive given the 30% flexo content. A synthetic surfactant, used in flotation and combination flotation/washing systems, was also added prior to post-dispersion flotation to promote flotation efficiency of the larger offset newsprint and magazine ink particles. An additional brightness jump of about 4 points was seen in post-dispersion flotation from removal of these and remaining tiny oil-based and flexo ink particles. In addition to these brightness increases, efficient ink removal also enabled efficient bleaching. There was a significant increase, about 5 points, due to fiber brightening from peroxide addition in the dispersion stage. An additional 3-point increase was gained from hydrosulfite bleaching at the end of the system, for a final pulp brightness of 63.5. Primary flotation rejects were very concentrated, confirming the high removal efficiency of both inks and coating particles. By comparison, rejects from post-dispersion flotation cells were relatively light, consistent with the very high removal efficiency and concentrated rejects in the primary cells. The washer effluent recycled for dilution in the system was clean throughout the trial, and filtrate turbidity remained consistently low. Effluent clarity of the washer following post-flotation was higher than that following initial flotation, underscoring the degree of ink removal by the system. There was no indication of brightness or quality deterioration from ink buildup in the system, and since no effluent clarification was performed, the process relied totally on flotation for ink removal. One of the major process benefits of this new technology is that flotation ink-removal effectiveness is sufficient for a process having only flotation equipment for ink removal. The thickener or washer effluent stream is clean enough to be recycled for dilution in the process without clarification. --Andy Harrison_
  
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