JPH09173735A - Regeneration of filter cloth - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and in excellent reproductivity regenerate a filter cloth deteriorated in the performance, in filtering of an alkali silicate aqueous solution. SOLUTION: The filter cloth used to filtering the alkali silicate aqueous solution obtained by dissolving alkali silicate glass cullet such as sodium silicate glass cullet into water, is generally regenerated by joint washing with an acid solution such as inorganic acid at 0-100 deg.C and with an alkali solution such as alkali hydroxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating a filter cloth used in a filtration step during the production of an aqueous alkali silicate solution. Specifically, in the step of producing a clear alkaline silicate aqueous solution obtained by dissolving an alkaline silicate glass cullet in water to obtain a clear alkaline silicate aqueous solution, the filter cloth whose performance is lowered by the filtration is effectively regenerated. Is the way to do it.

[0002]

2. Description of the Related Art An aqueous solution of alkali silicate has the general formula M ₂ O.
nSiO ₂ · xH ₂ O (M = Na, K and n = 2 to
It is generally about 3.5). Civil engineering fields such as soil hardening stabilizers and cement quick-setting agents; for molding sand molds for casting; bleaching agents for pulp and deinking of waste paper. It is used in a wide range of applications such as papermaking fields such as chemicals; raw materials such as white carbon, silica gel, silica carriers for catalysts; cleaning agents, adhesives, raw materials for fire-resistant paints, chemicals for the electronic industry, etc.

In the above applications, it is desired that the aqueous solution of alkali silicate does not substantially contain fine solid matter in terms of quality such as turbidity and stability.

Generally, an aqueous solution of an alkali silicate is prepared by mixing silica sand with an alkali carbonate or an alkali hydroxide to obtain 1300
After heating and melting at about ℃ to make a homogeneous melt, cooling
It is obtained by solidifying to obtain an alkali silicate glass cullet (hereinafter, also simply referred to as cullet), and dissolving the cullet with water in an autoclave under pressure at 150 to 180 ° C. Such an aqueous solution of alkali silicate is usually turbid due to the presence of solid matter derived from impurities in the cullet.

For the purpose of removing these solid matters, generally, a filter aid such as diatomaceous earth is mixed with the aqueous alkali silicate solution and filtered with a filter such as a filter press.

The solid matter produced when the cullet is dissolved contains fine particles having a particle size of about several μm, and even when a filter aid is used, the fine particles cause clogging of the filter cloth. Therefore, it has been a problem that the filtration resistance of the filter cloth increases and the filtration rate decreases while the filtration of the alkaline silicate aqueous solution is repeated.

As a treatment method when the filtration resistance of the filter cloth increases due to the clogging of such fine particles, we have
We proposed a method to recycle the filter cloth by washing with an alkaline solution such as an aqueous solution of sodium hydroxide.

[0008]

However, although washing with an alkaline solution has some effect on the regeneration of the filter cloth, there is still room for improvement in the regeneration effect.
Further, when the regenerating treatment of the filter cloth having the lowered filtration ability is repeatedly carried out by the alkali washing, the filtration performance of the filter cloth is gradually lowered, and finally the filter cloth is hardly regenerated by the alkali washing, so that the filter cloth becomes unusable. It turns out that there is.

Therefore, when a solution of alkali silicate glass cullet in water to produce an aqueous solution of alkali silicate, a method for more effectively and reproducibly reproducing the filtration performance of the filter cloth used in the filtration step has been developed. Was wanted.

[0010]

The inventors of the present invention have conducted extensive studies in order to solve the above-mentioned problems, and as a result, fine particles of about several μm generated when the cullet is dissolved are found in the cullet. Impurities, specifically, alkaline earth metals, especially when a large amount of calcium is contained, are often produced,
We have found that such fine particles are one of the causes of clogging of the filter cloth. That is, when the present inventors collected and analyzed the clogging particles of the filter cloth, it was found to be an amorphous and crystalline silica and a calcium silicate alkali compound that is produced mainly when calcium is dissolved due to the impurity calcium. found.

Therefore, when the filter cloth is regenerated by washing only with alkali, only amorphous and crystalline silica is dissolved and removed, whereas calcium silicate alkali is insoluble in alkali, so clogging particles As a result, it is considered that they remained on the filter cloth and the filtration resistance of the filter cloth was not sufficiently reduced.

Repeating such inadequate regeneration treatment of the filter cloth results in successively accumulating the residual amount of calcium silicate alkali, and the filtration resistance gradually increases as the filtration is repeated, resulting in alkali cleaning. It is presumed that this caused the phenomenon that the filter cloth could not be regenerated.

Therefore, as a result of further studies, the inventors of the present invention have solved the above problems by using a filter cloth whose filtration performance is deteriorated in combination with cleaning with an acid solution and cleaning with an alkaline solution. The inventors have found that the filtration performance of the filter cloth can be reproducibly reproduced to the same level as that of a new filter cloth, and have completed the present invention.

That is, according to the present invention, a filter cloth whose performance has been lowered by filtering an alkali silicate aqueous solution obtained by dissolving alkali silicate glass cullet in water is washed with an acid solution and an alkali solution. It is a method of regenerating a filter cloth, which is characterized in that it is carried out in combination.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the alkali silicate glass cullet used in the preparation of the aqueous alkali silicate solution to be filtered is not particularly limited. Specific examples thereof include sodium silicate glass cullet and potassium silicate glass cullet.

The above-mentioned aqueous solution of alkali silicate is prepared by
Generally, it is obtained by dissolving alkali silicate glass cullet in an autoclave together with water under pressure at a temperature of about 150 to 180 ° C.

The filter cloth to which the recycling method of the present invention is applied is not particularly limited in its material as long as it is a filter cloth used for filtering an aqueous solution of alkali silicate. For example, a filter cloth made of synthetic resin fiber such as polyethylene, polypropylene, nylon, polyester, polyacrylonitrile, polyfluoroethylene is suitable. Further, natural fibers such as cotton and wool, alkali resistant metal fibers such as stainless fibers, glass fibers, ceramic fibers, and carbon fibers can also be used. Furthermore, the weaving method of the filter cloth is not particularly limited, and plain weave, twill weave,
There are no restrictions on twill weave, satin weave, etc.

The filter used for filtering the aqueous solution of alkali silicate is not particularly limited as long as it uses the above filter cloth. For example, a pressure filter such as a filter press or a pressure nutche is generally used, but a rotary cylindrical vacuum filter,
A vacuum filter such as a horizontal belt vacuum filter can be used without any limitation.

In the present invention, as the acid solution, known inorganic acid and organic acid solutions can be used without particular limitation. As the inorganic acid, hydrochloric acid, nitric acid, sulfuric acid, boric acid, phosphoric acid or the like can be used. Organic acids include acetic acid, propionic acid,
Examples thereof include oxalic acid, maleic acid, fumaric acid, benzoic acid and the like. Among them, from the viewpoint of easy handling and waste liquid treatment,
The use of inorganic acids is preferred.

In the present invention, as the alkaline solution, a known alkaline solution may be used without particular limitation.
Specific examples of alkaline solutions include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; amines such as methylamine and ethylamine; anilines such as aniline and methylaniline; pyridine such as pyridine and methylpyridine. Kinds; solutions of organic ammonium hydroxide such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide and the like. Of which,
From the viewpoint of waste liquid treatment, it is preferable to use an alkali metal hydroxide solution.

Water is generally used as a solvent for the acid solution and the alkaline solution, and is preferably used.

The concentration of the acid solution or alkali solution used in the present invention depends on the type of acid or alkali used and cannot be specified unconditionally.
Generally 0.01 to 18 N, preferably 0.1 to 15
The specified range can be preferably used because it is easy to handle.

The method of using acid washing and alkali washing together in the method for recycling the filter cloth of the present invention is not particularly limited.
If the acid or alkali remaining on the filter cloth after the washing process is washed off and care is taken not to reduce the washing effect due to the neutralization reaction between the acid and the alkali, a combination method of acid washing and alkali washing, after alkali washing The combined use method of acid washing or the combined use method of alternately repeating acid washing and alkali washing can be carried out without any limitation. Of these, if the cleaning is performed with an acid solution and then the cleaning with an alkaline solution is used in combination, the regeneration effect of the filter cloth becomes higher, including the case where acid cleaning and alkaline cleaning are alternately repeated. preferable.

Means for washing with an acid solution or washing with an alkali solution in the present invention is not particularly limited, but means for circulating the acid or alkali solution through a filter such as a filter press holding a filter cloth, or a filter. Means for directly immersing the cloth in an acid or alkali solution can be used. The latter means of direct immersion is preferable because it facilitates the stirring and heating of the acid or alkali solution, and the regeneration treatment effect is enhanced.

The temperature of the acid cleaning and the alkali cleaning of the present invention is generally from 0 to 100 ° C., preferably,
10 to 90 ° C, more preferably 30 to 90 ° C, and further preferably 40 to 80 ° C. If the temperature of the washing with the acid solution and the washing with the alkaline solution is lower than 0 ° C., the dissolution of calcium silicate alkali, which is the clogging particles of the filter cloth, becomes insufficient, and the regeneration effect tends to decrease. In particular, the cleaning time can be significantly shortened by performing the cleaning at 30 ° C. or higher. However, if it exceeds 100 ° C., the acid or alkali concentration becomes too high due to the volatilization of water, and the filter cloth itself is deteriorated, which is not preferable.

[0026]

The action of acids and alkalis in the present invention is unclear, but the following may be considered.

Calcium silicate alkali, which is one of the clogging particles of the filter cloth, is insoluble in alkali,
When treated with an acid, the calcium and alkali components in the calcium silicate alkali are dissolved and the structure can be destroyed. Furthermore, because acid alone is incomplete,
When the alkali treatment is carried out after the acid treatment, the residual silicic acid component from which the calcium and alkali components have come off is dissolved, and the clogging particles of the filter cloth can be removed more effectively.

Alkali also dissolves amorphous and crystalline silica, which is another cause of clogging of filter cloth,
Also acts to remove.

It is considered that, due to such action, the regeneration effect of the filter cloth is enhanced by the combined use of acid cleaning and alkali cleaning.

[0030]

As can be understood from the above description, according to the present invention, a filter cloth having a deteriorated performance, which is used for filtering an aqueous solution of alkali silicate obtained by dissolving alkali silicate glass cullet, is used as a new filter. It can be reproducibly reproduced with the same performance as cloth. Therefore, an aqueous solution of alkali silicate can be produced with high production efficiency using a filter cloth having low filtration resistance, and the filter cloth can be repeatedly used, so that the life of the filter cloth can be significantly extended.

[0031]

EXAMPLES The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to the following examples.

Example 1 A circular sample filter cloth having a diameter of 55 mm was cut from a used filter cloth (made of polypropylene) used for filtering an aqueous sodium silicate solution. The sample filter cloth was fixed to a Buchner funnel, and an aqueous sodium silicate solution (JIS standard: 3, 2,
Filtration under reduced pressure (Battle degree 41) at 5 ° C (210 Torr)
Then, the filtration resistance of the filter cloth was evaluated by measuring the time (t) required to obtain 300 ml of the filtrate.

As a result, t was 75 minutes.

Then, the sample filter cloth was immersed in 200 ml of 1N hydrochloric acid at 25 ° C. for 20 hours. Then, after washing with water to remove the hydrochloric acid, it was immersed in 200 ml of a 1N sodium hydroxide aqueous solution at 25 ° C. for 20 hours. The sodium hydroxide was removed by washing with water.

The filter cloth thus treated was evaluated for filtration resistance in the same manner as above, and as a result, t was 3.6 minutes.

For reference, a sample filter cloth of the same size was cut out from a new filter cloth and the filtration resistance was measured in the same manner. As a result, t was 2.1 minutes. From this result, it is understood that the filter cloth to which the method of the present invention is applied can be regenerated to a filtration performance close to that of a new filter cloth. It was also confirmed that there was almost no deterioration in the separation performance of the regenerated filter cloth.

Example 2 The filter cloth was regenerated in the same manner as in Example 1 except that the temperature at the time of acid cleaning and alkali cleaning was 70 ° C., and the time of acid cleaning and alkali cleaning was 3 hours each. Moreover, the filtration resistance was evaluated.

As a result, t was 3.0 minutes. Also,
It was confirmed that there was almost no deterioration in the separation performance of the regenerated filter cloth.

Example 3 5N hydrochloric acid was used for acid cleaning, 5N aqueous sodium hydroxide solution was used for alkaline cleaning, and acid cleaning and alkaline cleaning were performed at 70 ° C.
The filter cloth was regenerated and the filtration resistance was evaluated in the same manner as in Example 1 except that the time was 3 hours each.

As a result, t was 2.4 minutes. Also,
It was confirmed that there was almost no deterioration in the separation performance of the regenerated filter cloth.

Example 4 Example 4 except that the order of performing alkali washing with 1N aqueous sodium hydroxide solution and then acid washing with 1N hydrochloric acid and alkali washing and acid washing at 70 ° C. for 3 hours each. The filter cloth was regenerated in the same manner as in 1, and the filtration resistance was evaluated.

As a result, t was 6.0 minutes. Also,
It was confirmed that there was almost no deterioration in the separation performance of the regenerated filter cloth.

Comparative Example 1 The filter cloth was regenerated and filtered in the same manner as in Example 1 except that acid washing was not carried out and only alkali washing with a 1N sodium hydroxide aqueous solution was carried out at 25 ° C. for 40 hours. The resistance was evaluated.

As a result, t was 8.5 minutes.

Comparative Example 2 The filter cloth was regenerated and filtered in the same manner as in Example 1 except that acid washing was not carried out and only alkali washing with a 1N aqueous sodium hydroxide solution was carried out at 70 ° C. for 6 hours. The resistance was evaluated.

As a result, t was 8.1 minutes.

COMPARATIVE EXAMPLE 3 Alkali cleaning was not carried out, and only acid cleaning with 1N hydrochloric acid was carried out.
The filter cloth was regenerated and the filtration resistance was evaluated in the same manner as in Example 1 except that the treatment was performed at 5 ° C. for 40 hours.

As a result, t was 31 minutes.

Comparative Example 4 The filter cloth was regenerated in the same manner as in Example 1 except that the washing with water at 25 ° C. was carried out for 40 hours without carrying out the acid washing and the alkali washing, and the filtration resistance was increased. An evaluation was made.

As a result, t was 75 minutes.

The results of the above Examples and Comparative Examples are summarized in Table 1.

[0052]

[Table 1]

Claims (3)

[Claims] 1. A filter cloth whose performance has deteriorated by filtering an alkali silicate aqueous solution obtained by dissolving alkali silicate glass cullet in water is subjected to both washing with an acid solution and washing with an alkali solution. A method for recycling a filter cloth, comprising: 2. The method for regenerating a filter cloth according to claim 1, wherein after washing with an acid solution, washing with an alkaline solution is carried out. 3. The temperature of washing with an acid solution and washing with an alkaline solution is 0 to 100 ° C.
A method for recycling the described filter cloth.