Deinking

Biermann, C. J. (1996). Handbook of Pulping and Papermaking, 2nd ed. Academic San Diego, California. 

Darmstadt, W. J., and Tomlinson, G. H. (1960). Magnesia Base Pulping and Recovery, Presented before the Acid Pulp Session of TAPPI, February, 23. The Babcock Wilcox Company Bulletin BR-751. 

Tatsumi, K., Murayama, K., and Terashima, N. (1987). TAPPI International Oxygen Delignification Conference Proceedings, TAPPI Press, Atlanta, p. 99. 

The Institute of Paper Chemistry (1960). Project 2184, Progress Report 2, Use of Magox in Magnesium-Base Sulfite Pulping. 

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Newsprint wash deinking mili Office paper deinking mili Newsprint/magazine deinking mill Tissue mill Old corrugated container mill... 

Low consistency pulping (3—6% soflds) is common in newsprint and many tissue mills. Medium (6—12%) and high consistency pulping (12—18% sohds) is common in mills deinking office papers. Pulping temperature is typically 40—55°C, the pH is usually 9.0—10.5, and process time ranges from 4 to 60 minutes. 

Ink particle redeposition on cellulose fibers can reduce deinked paper brightness. Should larger ink particles redeposit on fibers, visible ink specks may result. Sodium siUcate is often added to the pulper to act as a dispersant and reduce this redeposition (6,14). Up to 5% based on dry paper weight may... 

The optimum surfactant hydrophi1ic 1ipophi1ic balance (HLB) for wash deinking is dependent on ink composition. Surfactants with a HLB of about 14.5 provide the highest deinked newsprint brightness (24). The optimum deinking surfactant HLB for ledger inks is 13—14, whereas that for toner inks is 10-11 (25). 

Typical papers processed using wash deinking are 100% old newspaper and sorted office paper from which toner ink-printed paper has been removed. The effluent from washers is heavily laden with ink, mineral coating and filler particles, and small cellulose fibers. As a result, it can be difficult to clarify. 

Flotation. Flotation (qv) is used alone or in combination with washing and cleaning to deink office paper and mixtures of old newsprint and old magazines (26). An effective flotation process must fulfill four functions. (/) The process must efficiently entrain air. Air bubble diameter is about 1000 p.m. Typically air bubbles occupy 25—60% of the flotation cell volume. Increa sing the airRquid ratio in the flotation cell is said to improve ink removal efficiency (27). (2) Ink must attach to air bubbles. This is primarily a function of surfactant chemistry. Air bubbles must have sufficient residence time in the cell for ink attachment to occur. (3) There must be minimal trapping of cellulose fibers in the froth layer. This depends on both cell design and surfactant chemistry. (4) The froth layer must be separated from the pulp slurry before too many air bubbles coUapse and return ink particles to the pulp slurry. 

Mechanical Gleaning. A cleaner is a hydrocyclone device utilizing fluid pressure to create rotational fluid motion (20). Pulp is introduced tangentially near the top of the cleaner. Contaminants denser than water such as chemically treated toner inks and sand migrate toward the outer wall of the cleaner and exit in a separate (reject) stream. For most forward cleaners, optimal ink removal efficiency is obtained at a pulp consistency of 0.2—0.3%. Most forward cleaners deinking efficiency declines at pulp feed consistencies greater than 0.4%. However, a cleaner said to be efficient at 1.2% pulp consistency has been reported (39). 

Cleaners are most efficient on relatively large particles, 80—300 pm in diameter (see Fig. 1). Flat toner ink particles can fragment during processing, therefore it is probably best to locate mechanical cleaners early in the sequence of office paper deinking unit operations (40). 

Inorganic chemicals may also be used. Beatonite may be used as a flocculant ia combination with polymer treatmeat. Alum, oace a common coagulant, is less used because its concentration can build up ia recycle water. Alum oftea biads ink to fibers and iacreases the difficulty of deinking. Removal of the very small flexographic ink particles ia process water is difficult. Ultrafiltratioa (qv) has beea proposed for removing these very small dispersed ink particles (53). 

THE APPLICATION OF DIALDEHYDE CHEMISTRY FOR CONTROL OF CATALASE IN THE DEINKING PROCESSES... 

The deinking process (DIP) can be compared with a giant washing machine, that removes the printing ink off the fibre, two major types exist ... 

Wash deinking often used for flexo-printed waste and in older tissue mills, large water consumption. Flotation deinking for oil-based printings such as offset and rotogravure, technology from the mining industry. 

Figure 2 Schematic draw on a two loop flotation deinking process...

Pulp mills. These separate the fibers of wood or other materials, such as rags, Enters, waste-paper, and straw, in order to create pulp. Mills may use chemical, semichemical, or mechanical processes, and may create coproducts such as turpentine and tall oil. Most pulp mills bleach the pulp they produce, and, when wastepaper is converted into secondary fiber, it is deinked. The output of some pulp mills is not used to make paper, but to produce cellulose acetate or to be dissolved and regenerated in the form of viscose fibers or cellophane. 

Pulp production from recovered paper or paperboard without deinking processes to produce tissue, paperboard, molded products, and construction papers... 

Contaminant removal processes depend on the type and source of secondary fiber to be pulped. Mill paper waste can be easily repulped with minimal contaminant removal. Recycled postconsumer newspaper, on the other hand, may require extensive contaminant removal, including deinking, prior to reuse. Secondary fiber is typically used in lower-quality applications such as multiply paper-board or corrugating paper. 

Deinked secondary fibers are usually bleached in a bleach tower, but may be bleached during the repulping process. Bleach chemicals may be added directly into the pulper. The following are examples of chemicals used to bleach deinked secondary fibers hypochlorite [HCIO, NaOCl, Ca(OCl)2], hydrogen peroxide (H202), and hydrosulphite (NaHS03). 

Generation of clarified water for deinking plants (air flotation). 

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