JPS6225796B2 - - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for deinking waste paper pulp by hydrogen peroxide bleaching and flotation. PRIOR ART A conventional method for deinking colored or printed waste paper is carried out as follows. 1st stage Waste paper is turned into pulp using machines such as a disk integrator and a beater. 2nd step Add alkali hydroxide and detergent to the waste paper pulp. When deinking and bleaching are carried out at the same time, hydrogen peroxide or sodium peroxide is also added in addition to the above substances. In addition, sodium silicate is added as a PH buffer and a sequestering agent, and at a temperature around 40°C in the case of soaking, and in the case of bleaching.
Hold at a temperature of 60-70 ° C for several hours. This treatment liberates the carbon or colored pigments in the ink in the case of used printed paper, and in the case of paper colored or printed with pigments, the colored pigments separate from the hydrophobic groups of the detergent. They bond together and become covered with hydrophilic groups. Hydrogen peroxide or sodium peroxide acts to oxidatively decompose the ink binder and bleach the pulp. Third stage After completing the second stage, flotation is performed after lowering the pulp concentration to improve the fluidity of the pulp. The floatator sends fine air bubbles from below, and as these air bubbles rise, they take away carbon particles or colored pigment particles covered with hydrophilic groups and float to the water surface, forming a floss layer. The carbon or colored pigment is separated by scraping or pouring out to complete the decoloring process. However, since fine carbon particles or colored pigment particles are difficult to be entrained by air bubbles in this flotation treatment, such fine carbon particles or colored pigment particles tend to remain in the pulp. Therefore, some measure was needed to improve the deinking effect. One way to do this is to use an alkali metal salt of a higher fatty acid, ie, a so-called soap, as a detergent and use this product as a deinking agent. This method uses the soaking and bleaching treatment described above.
When the carbon particles or colored pigment particles are completely released into the pulp liquid, a water-soluble metal salt of divalent or higher valence is added to convert some or all of the higher fatty acid metal salts into insoluble metal soaps. At this time, the insoluble metal soap precipitates in the pulp liquid and becomes a floc, but at the same time, the fine carbon particles or colored pigment particles that have been bonded to the alkali metal salt of the higher fatty acid are also trapped in the floc. It is thought that the paper floats to the surface of the water along with the air bubbles produced by the flotation process, making it possible to remove fine carbon particles or colored pigment particles and improve the overall whiteness of the waste paper. Hydrochlorides and sulfates of magnesium, calcium, zinc, barium, aluminum, iron, etc. can be used as water-soluble metal salts with divalent or higher valences, and can make alkali metal salts of higher fatty acids water-insoluble. Anything can be used as long as it is. Calcium chloride was commonly used. However, in this case, there is a drawback that not only calcium ions as an insolubilizing agent but also chlorine ions are generated which react with the sodium ion of the soap and thereby generate a considerable amount of common salt, and there is a risk of corrosion of the equipment. Another problem was that, although the purpose was to improve the whiteness of waste paper, expensive calcium chloride had to be added as an insolubilizer after peroxide bleaching. (Objective of the Invention) In order to solve the problems of conventional peroxide bleaching and subsequent deinking treatment using sodium higher fatty acids and calcium chloride, the present inventors developed and used a new insolubilizing agent to replace calcium chloride. As a result of repeated research aimed at effectively utilizing bleaching aids and improving whiteness, the present invention was achieved. (Structure of the Invention) The present invention is a method for deinking waste paper pulp, characterized in that the following three steps are combined in the following order. 1st step (a) Hydrogen peroxide solution, (b) Sodium silicate, (c)
Sodium carbonate and (d) calcium hydroxide and/or calcium oxide are added and mixed to unbleached waste paper pulp to bleach the pulp. 2nd stage: A higher fatty acid alkali metal and calcium chloride are added and mixed to the mixture obtained in the 1st stage. Third stage The mixture obtained in the second stage is subjected to flotation. (Summary of the Effects of the Invention) In the first step of the present invention, sodium carbonate is reacted with calcium hydroxide and/or calcium oxide to form sodium hydroxide within the system. Calcium carbonate, which is produced by the above reaction, is fixed in the pulp as a filler and also contributes to opacity. Calcium carbonate that has not been fixed in the pulp can be removed using the normal flotation method, in which part or all of the alkali metal salts of higher fatty acids added immediately before flotation are changed into insoluble metal soaps, and no metal salts of higher fatty acids are added. It acts to remove fine particulate carbon or colored pigments that cannot be removed by other methods. (Soda Carbonate) Soda carbonate can be used in any form, but if it is a sulfite pulp mill in connection with the chemical recovery process in the pulp manufacturing process, for example, the Tampera method (Special Publication No. 10057
If the factory adopts the method (see US Pat. No. 3,508,863), sodium carbonate monohydrate extracted from the crystal separation step of the recovery step may be used. In addition, if the pulp mill has a kraft pulping process, an aqueous solution of smelt (green liquor) obtained by concentrating and burning black liquor.
Sodium carbonate obtained by evaporating and concentrating and crystallizing and separating may be used. The addition rate of soda carbonate per pulp is approximately 1~
It may be 10%, but the preferred range is about 2-6%. (Calcium oxide and/or calcium hydroxide) Calcium hydroxide which reacts with soda carbonate to produce caustic soda in situ in the method of the present invention is contained in the pulp slurry as a calcium hydroxide slurry or as a powder of calcium hydroxide. may be added to. The calcium hydroxide to be added may be a powder rich in calcium carbonate in the center and calcium oxide in the surface layer. The addition rate of calcium oxide and/or calcium hydroxide to the pulp may be within the range of about 1 to 10%, and the preferred range is about 1 to 5%. Also, the addition rate of peroxide per pulp is
Approximately 0.5 to 10% in terms of hydrogen peroxide, preferably approximately
It is 0.5-5%. (Effects of the invention) The effects of the invention are as follows. (1) Chemical costs can be reduced because soda carbonate and calcium hydroxide and/or calcium oxide are used, which are cheaper than caustic soda. (2) By adjusting the amount of calcium hydroxide and/or calcium oxide added to soda carbonate, it is possible to freely adjust the amount of caustic soda generated. Depending on the situation, the amount of sodium silicate added can also be reduced. (3) Since caustic soda, which is a strong alkali, is not used, wastewater COD and BOD loads can be significantly reduced. As a result, the bleaching yield also improves. (4) Since a wide range of calcium salts are already present in the pulp system, the amount of expensive calcium chloride added can be reduced. (5) Since the amount of calcium chloride can be reduced, the amount of chlorine ions entering the system is reduced. Therefore, corrosion caused by common salt can also be reduced. (6) The deinked pulp obtained by the present invention has a higher deinking rate and whiteness than the deinked pulp obtained by the conventional method, if the same calcium chloride addition rate as the conventional method is used. . (Embodiments of the Invention) Next, embodiments of the method of the present invention will be explained with reference to the accompanying drawings (Fig. 1), and Examples and Comparative Examples will also be shown, which will make it easier to understand the present invention. It is intended to do so, and is not intended to limit the present invention. The unbleached pulp is introduced into a dehydrator 2 via an unbleached pulp transfer pipe 1. The waste water from the dehydrator passes through the drain pipe 3 and is either circulated to the previous process or subjected to appropriate treatment and then disposed of. The unbleached pulp from the dehydrator has a pulp consistency suitable for peroxide bleaching, i.e. 5-20
It is diluted in the high concentration mixer 5 with dilution water supplied by the dilution water inlet pipe 4 so as to be in weight percent. The calcium oxide and/or calcium hydroxide stored in the calcium oxide and/or hydroxide storage 6 is solid;
Alternatively, it is added as a slurry to the high concentration mixer 5, and then the soda carbonate stored in the soda carbonate storage tank 7 is also added. Further, the sodium silicate stored in the sodium silicate storage tank 8 is also added to the high concentration mixer and mixed well. The peroxide in the peroxide storage tank 9 and the surfactant in the surfactant tank 10 are then fed into a high concentration mixer, and after thorough mixing are fed into the bleaching tower 10. Bleaching of the pulp is completed by keeping it in a bleaching tower at a temperature of 50 to 70°C for 2 to 6 hours. In the bleached pulp described above, the ink has already been desorbed from the fibers. Next, the sodium oleate aqueous solution stored in the sodium oleate storage tank 13 is added to the bleached pulp in the high concentration mixer 12 and thoroughly mixed. When adding calcium chloride, add calcium chloride from the calcium chloride storage tank 14 to the high concentration mixer 1.
Add to 4. Next, in order to improve the fluidity of the pulp, water is introduced into the high concentration mixer 1 from the dilution water introduction pipe 15.
The mixture thus obtained is sent to a floatator 16 for flotation to separate carbon or colored pigments. Sulfite water is supplied from the sulfite water storage tank 18 to the deinked pulp obtained by the above operation to decompose unreacted peroxides, thereby completing the method of the present invention. Comparative example 1 Pre-disintegrated and dehydrated waste paper pulp 50
g into a polyethylene bag, and the pulp density is 10.
The pulp was diluted with clear water to % by weight, preheated in a 70°C hot bath, the following substances were added, stirred thoroughly, and stored for 2 hours to bleach the pulp. The addition ratio of each substance is % by weight based on the bone dry pulp. Caustic soda (deinking agent) 1.1g Sodium silicate 1.4% Surfactant 0.05% Hydrogen peroxide (bleaching agent) 2% The pH at the beginning of the above bleaching process is 11.1, but the pH after bleaching is 9.5. Ta. 0.4% by weight of sodium oleate and calcium chloride as flotation aids are added to the thus bleached pulp as shown in Table 1 below, and after thorough stirring, the pulp is diluted to a pulp concentration of 1.0% by weight. Floatation was performed using a test floatator (Kyokuto Shinko Co., Ltd.). After flotation, sulfite water was added to the pulp to adjust the pH to 5.5. The deinking rate of the deinked pulp thus obtained was as shown in Table 1 below. However, the deinking rate is the whiteness increase rate when a large amount of aluminum sulfate is added before and after flotation to fix all free ink carbon to the pulp, and the pulp whiteness is measured. The sheet for measuring whiteness was prepared by the Tappi standard method. Example 1 A bleaching process was carried out in the same manner as in Comparative Example 1, except that the following substances were used instead of caustic soda and sodium silicate. However, the pH is 11.0 at the beginning of bleaching.
~11.5, and 9.8 to 10.1 after bleaching. Anhydrous sodium carbonate 1.2 to 1.5% by weight Calcium hydroxide 1.4 to 1.8% by weight After completion of bleaching, anhydrous calcium chloride and sodium oleate were added as shown in Table 1 below, and flotation was then carried out in the same manner as in Comparative Example 1. Summer. The resulting deinking rates are shown in Table 1. 【table】

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of a preferred embodiment of the method of the present invention, and the reference numerals in the figure indicate the following. 1...Unbleached pulp transfer pipe, 2...Dehydrator, 3...
... Drain pipe, 4 ... Dilution water introduction pipe, 5 ... High concentration mixer, 6 ... Calcium oxide and/or calcium hydroxide storage tank, 7 ... Sodium carbonate storage tank, 8 ... Sodium silicate storage tank, 9 ... Peroxide storage tank, 10... Surface active storage tank, 11... Bleaching tank, 12... High concentration mixer, 13... Sodium oleate storage tank, 14... Calcium chloride storage tank, 15... Dilution water introduction pipe, 16... ...Floatator, 17...Reaction tank, 18...Sulfite water storage tank.

Claims (1)

[Claims] 1. In the first step, (a) hydrogen peroxide, (b) sodium silicate, (c) sodium carbonate, and (d) calcium hydroxide and/or calcium oxide are added to and mixed with unbleached waste paper pulp to prepare the pulp. bleach and second
The step is to add and mix alkali metal salts of higher fatty acids and calcium chloride to the mixture obtained in the first step, and the third step is to apply the mixture obtained in the second step to flotation. Deinking method.