JPH05171582A - Regeneration of waste paper - Google Patents

Abstract

PURPOSE:To recover high-quality fibers from waste paper without degrading the fiber. CONSTITUTION:The pH of seawater is lowered with a specific acid and then increased with an alkaline agent and the formed precipitate (a) is removed. The treated seawater is concentrated and cooled and the formed precipitate is removed to obtain an aqueous solution (b) having high pH. Finely cut paper is put into the aqueous solution (b) having high pH to effect the defibration of the paper. The product is deinked by conventional method to obtain a pulp raw material. The process can be performed without using heating process and the amount of water can be reduced to suppress the environmental pollution caused by waste liquid. A high-quality fiber is produced because there is no destruction of the fiber in itself.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to newspaper, cardboard,
The present invention relates to a method of recycling used paper such as OA paper and milk carton.

[0002]

2. Description of the Related Art In recent years, the amount of waste paper discharged from OA equipment has increased, and on the other hand, the reusability of waste paper has become more important due to the absolute shortage of domestic supply of wood, which is a raw material for pulp.
Conventionally, the used paper is recycled by first disintegrating the used paper with a pulper, a digester, a kneader, etc., and removing the mixed polyester, adhesive tape and other foreign substances, and further dispersing it from the paper fiber in water to remove the ink. It is deinked by rotation method or washing method and used as pulp material.

In such a used paper recycling process, an aqueous sodium hydroxide solution and a surfactant are used to defibrate and deink the used paper while heating and defibrating and deinking.

[0004]

However, since such a conventional method uses a high-concentration aqueous sodium hydroxide solution and undergoes a heating step, the fibers of the paper are easily damaged and the recycled paper is used. The quality of I was forced to decline. Further, a large amount of water is required to wash away the sodium hydroxide aqueous solution, and the waste liquid discharged in the regeneration process is one of the causes of environmental pollution.

An object of the present invention is to provide a used paper recycling method which solves the above problems of the used paper recycling method and can obtain recycled paper of high quality. Another object of the present invention is to provide a used paper recycling method that does not require a heating step and can be washed with a relatively small amount of water. Another object of the present invention is to provide a method for recycling used paper that allows recycling of waste liquid in the recycling process and does not pose a problem of environmental pollution.

[0006]

In order to achieve such an object, in the method for recycling used paper of the present invention, seawater is adjusted to a low pH with a strong acid containing a sulfate ion, and then a strong alkali agent is added to increase the pH. , The seawater after removing the first precipitate formed at that time was further concentrated, and the waste paper was dissolved in a high-pH aqueous solution containing a salt obtained from the residual liquid from which the second precipitate formed by cooling was removed. After that, it is decolorized and the pulp raw material is taken out, and preferably the high pH aqueous solution further contains a mixture of the first precipitate obtained from the seawater and dilute lime.

[0007] Here, the salt obtained from seawater refers to JP-A-2
No. 221107, the salt obtained by the “separation method of seawater”, wherein seawater is adjusted to a low pH with a strong acid containing a sulfate ion, and then a strong alkaline agent is added to increase the pH.
The first precipitate (a) formed at that time is removed, and the seawater after the first precipitate (a) is removed is further concentrated, and the second precipitate formed by quenching is removed from the residual liquid (b). The seawater after the removal of the second precipitate exhibits a high alkalinity of about pH 14 or higher, and can be used as it is as a high pH aqueous solution. Alternatively, water may be removed from the seawater (b) to recover the salt (c), and the salt (c) may be appropriately dissolved in water before use. The pH of the high pH aqueous solution is preferably 12 or more,
It is preferably 13 or more, and more preferably about 14.

Further, a mixture of the first precipitate (a) obtained when seawater is treated with an acid and alkali and dilute lime may be added to the high pH aqueous solution used in the used paper recycling method of the present invention. .. A decolorizing effect can be obtained by adding this mixture. The mixing ratio of the precipitate (a) and the dilute lime can be appropriately selected, but is usually 3: 7 to.
It is in the range of 7: 3, preferably 4: 6 to 6: 4. In addition, the mixture of the precipitate (a) and dilute lime is dissolved in the diluted residual seawater (b), or dissolved in water together with the salt (c) obtained from the seawater (b). You can

The method for separating salt (c) from seawater will be briefly described below. As the strong acid containing a sulfate ion used to bring the seawater to a low pH, dilute sulfuric acid of several% can be used, but 3 to 5% concentrated sulfuric acid is added to an aqueous solution in which activated calcium phosphate is dissolved. In addition, an aqueous solution from which precipitates have been removed (hereinafter abbreviated as P-S acid) can be used. Add a few% of dilute sulfuric acid or P-S acid to seawater,
Leave the seawater at a pH of 2 or lower by leaving it for 2 to 3 hours.
It can be adjusted to H. At this time, almost no precipitate is generated, but some precipitate is removed together with the suspended matter in the original seawater by means such as filtration.

The strong alkaline agent precipitates alkaline earth metals such as calcium and magnesium whose solubility decreases at high pH and salts such as sulfates of other metals. As such a strong alkaline agent, sodium hydroxide, potassium hydroxide, calcium oxide, or a mixture thereof is used. The amount of strong alkaline agent is high pH, that is, p
H12 or more, preferably pH 13 or more, for example, in the case of sodium hydroxide (solid) 3% to seawater,
In the case of an aqueous solution of sodium hydroxide added to an aqueous solution of calcium oxide, about 5% is added, and the mixture is left for 10 hours or more. By adding the amounts of these exemplified alkalis, the seawater exhibits a basicity of pH 13 or higher, and the first precipitate (a) is formed.

The precipitate (a) can be mixed with dilute lime and added to the high pH aqueous solution of the present invention.
The addition amount is about several% to 50% with respect to water. By adding the mixture of precipitate (a) and dilute lime (d),
The high pH aqueous solution of the present invention can exhibit a decolorizing action. The mixing ratio of the precipitate (a) and the dilute lime can be appropriately selected, but is usually 3: 7 to 7: 3, preferably 4: 6.
It is in the range of to 6: 4.

The residual seawater after removing the precipitate (a) is further concentrated to a volume of about 10% to 15% and cooled. A second precipitate forms upon cooling. The residual liquid (b) after removing this precipitate is alkaline having a pH of 13 or more and can be used as it is as the high pH aqueous solution of the present invention. Further, the seawater (b) after this treatment may be diluted with water if necessary, and then the mixture (d) of the above-mentioned precipitate (a) and dilute lime may be added thereto. Further, a salt (c) obtained by removing water from the seawater (b) after this treatment, a mixture of the precipitate (a) and dilute lime (d) dissolved in water is used as the high pH aqueous solution of the present invention. It is also possible.

The high pH aqueous solution of the present invention shows a pH of 13 or more in any of the above cases, decomposes the paper into fibers without heating, and penetrates into the paper fibers to release the ink from the paper to be submerged in water. It can be dispersed. Furthermore, the high pH aqueous solution of the present invention has a bleaching action without using a bleaching agent, especially when the mixture (d) of the salt (a) after acid-alkali treatment of seawater and dilute lime is added. Show. To further enhance the bleaching action, the above-mentioned P-S acid can be added after defibration. In order to defibrate with the high pH aqueous solution of the present invention, the used paper is immersed in a high pH aqueous solution several times in weight and stirred for about 0.5 to 2 hours. As a result, the paper is decomposed into almost fibrous form, and the ink in the paper fibers is dispersed in water. If necessary, a surfactant may be added appropriately.

After that, deinking is performed by a flotation method or a cleaning method. Preferably, the ink is adhered to the bubbles by the flotation method to float and separate, and then washed with water. The pulp raw material obtained by the method for producing used paper of the present invention does not need to be bleached for ordinary use, but may be bleached with a bleaching agent such as hydrogen peroxide or side loss sulfite depending on the use.

The aqueous solution used for defibration can be recycled and a new aqueous solution can be appropriately added and used several times. In addition, what becomes the final waste liquid becomes clean drainage that meets drainage standards by adding a mixture (d) of precipitate (a) and dilute lime produced by treating seawater with acid-alkali, Can be reduced to

[0016]

【Example】

Example 1 10 liters of P-S acid was added to 500 liters of seawater, left for 3 hours, and then impurities were removed by filtration. This brought the pH of seawater to 1.6. Next, 3% of NaOH was added to 500 liters of seawater having a lowered pH, and the mixture was left for 10 hours. At this time, the seawater after removing the formed precipitate (a) was further heated to a volume of 1
The water was removed to 0% and the mixture was concentrated and cooled to cause precipitation. Residual liquid (b) obtained by removing this precipitate
Was above pH 14.

Into the remaining 7 l of seawater (b), 500 g of finely cut old newspaper was put and stirred for about 30 minutes to decompose it into fibers. After removing the water content of this fiber, P-S acid was added and bleached by mixing and stirring, and then the water content was removed by a centrifugal separator to obtain 310 g of pulp material. This pulp material has long fibers and can be applied to high-quality paper. Example 2 Water was removed from the treated seawater (b) obtained in Example 1 to obtain salt (c). On the other hand, the precipitate (a) generated during seawater treatment and dilute lime were mixed and stirred at a weight ratio of 4: 6 to obtain a mixture (d). The salt (c) and the mixture (d) were dissolved in tap water at 20% by weight and 10% by weight, respectively. The pH of this supernatant water was 13.6.

Old supernatant paper was put into this supernatant water in the same manner as in Example 1 and stirred for about 30 minutes to decompose it into fibers. The resulting pulp material was decolorized and white, had long fibers and was applicable to high quality papers. Example 3 The seawater (b) after the acid-alkali treatment obtained in Example 1 was diluted with about 4 times the amount of water, and the mixture (d) in which the mixing ratio of the precipitate (a) and dilute lime was 4: 6. Was dissolved by 10% by weight. The pH of this supernatant water was 13.6.

In the same manner as in Example 1, old newspaper was placed in this supernatant water and stirred for about 30 minutes to decompose it into fibers. The resulting pulp material had long fibers and was applicable to high quality paper.

[0020]

As is apparent from the above description, according to the present invention, the paper is decomposed by the high pH aqueous solution using the salt separated from the seawater, and therefore, the paper is not decomposed as in the case of using sodium hydroxide. High quality pulp material can be obtained without breaking the fibers of the paper. Further, according to the present invention, since the heating step is unnecessary, the regenerated pulp raw material can be easily manufactured with a relatively simple apparatus. Further, according to the present invention, a high-quality pulp raw material with almost no coloring can be obtained without using a bleaching agent, etc., and there is no problem of environmental pollution due to waste liquid.

Claims (2)

[Claims] 1. The seawater is adjusted to a low pH with a strong acid containing a sulfate ion, and then a strong alkaline agent is added to bring it to a high pH, and the seawater after removing the first precipitate generated at that time is further concentrated,
A method for recycling used paper, which comprises dissolving the used paper in an aqueous solution having a high pH and containing a salt obtained from the residual liquid obtained by removing the second precipitate generated by cooling, deinking, and taking out a pulp raw material. 2. The high pH aqueous solution further comprises a mixture of the first precipitate and dilute lime.
How to recycle the described waste paper.