JPH09328305A - Method for decomposing and removing organic material in phosphoric acid solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method, solving problems characteristic to conventional techniques, having excellent removing efficiency on organic materials and capable of decomposing and removing them in an effective and efficient manner. SOLUTION: This method for decomposing and removing organic materials in a phosphoric acid solution consists of the addition of a hypochlorite in a weight ratio of <=0.35 in terms of chloride ions based on the hypochlorite ion, to the phosphoric acid solution containing the organic materials. In the method, the hypochlorite is a sodium hypochlorite aqueous solution, and the content of the effective chlorine is >=15wt.%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for decomposing and removing organic substances in a phosphoric acid solution.

[0002]

2. Description of the Related Art Phosphoric acid is roughly classified into fertilizer phosphoric acid mainly used for fertilizer and industrial phosphoric acid mainly used for metal surface treatment, food additives and the like. The former does not require high purity and usually does not require organic matter removal. Since the latter requires high purity, it is necessary to remove not only organic substances but also cationic impurities such as calcium, magnesium and iron and anionic impurities such as fluorine, sulfuric acid and silicic acid to a sufficiently low level suitable for the purpose of use. . For example, when producing condensed phosphoric acid which is used as a food additive or the like by heating dehydration of the industrial phosphoric acid, the product may be colored depending on the content of the organic matter, and its value may be significantly impaired.

As a typical method for producing industrial phosphoric acid, there is a wet purification method using wet phosphoric acid obtained by sulfuric acid decomposition of phosphate rock as a raw material. In this method, the removal of organic substances is carried out by treatment with an adsorbent such as activated carbon, solvent extraction, oxidation treatment and the like, and the above-mentioned means is selected depending on the type and amount of organic substances contained. However, when the organic matter level is extremely high, the above-mentioned treatment technique cannot sufficiently remove the organic matter, and a coloring problem occurs during the production of condensed phosphoric acid. Furthermore, due to organic matter, separation failure between the extraction phase and the extraction residual liquid phase in solvent extraction occurs,
In some cases, the purification operation itself becomes impossible. Therefore, many of the raw materials used in the wet refining method are produced by decomposing a phosphate rock having a reduced organic matter content with sulfuric acid by an artificial firing treatment or the like. The wet phosphoric acid thus obtained has an organic carbon concentration of less than 100 ppm by weight, and the purification treatment is easy, but the raw material is expensive.

In addition to the above-mentioned wet phosphoric acid, attempts have been made to recycle a large amount of phosphoric acid discharged as industrial waste as a raw material for producing industrial phosphoric acid. JP-A-6-16403 describes a technique in which phosphate sludge generated when a metal surface is subjected to chemical conversion treatment with phosphoric acid is used as a raw material for purified phosphoric acid. However, since many organic substances such as fats and oils are usually attached to the sludge, it is difficult to use the phosphoric acid solution as it is as a raw material for the wet refining method.

In order to solve the above problems, techniques for decomposing organic substances using an oxidizing agent have been studied. JP 54
Japanese Patent Publication No. 93695 describes a technique using a mixed oxidant of permanganate and nitric acid. This method
The oxidizing agent used is expensive, and the added manganese must be removed in a subsequent step, and nitrogen oxides are generated by the decomposition of nitric acid, which necessitates the removal of the oxides, causing many problems.

Japanese Unexamined Patent Publication No. 56-109805 discloses a technique of decomposing organic substances with hydrogen peroxide in the presence of a small amount of catalyst. In this treatment, the generated gas is carbon dioxide gas and oxygen, and the residual component in the phosphoric acid solution is water, which is excellent in comparison with the above technique in that it is completely harmless. Therefore, the effect of oxidizing the organic matter becomes insufficient.

Japanese Unexamined Patent Publication No. 55-16893 discloses a method of decomposing organic substances with a chlorate. However, this method has a large effect of decomposing organic substances, and thereby widens the choice of raw materials, resulting in a more efficient industrial process. It becomes possible to produce phosphoric acid for use. However, in this treatment, unreacted chlorate remains in the phosphoric acid solution, and subsequent treatment is necessary. In this method, it is reductively decomposed with hydrochloric acid, but chlorine gas and chlorine dioxide gas, which are difficult to remove, are generated at that time.

The allowable concentration of chlorine is 199, Japan Society for Occupational Health.
1 ppm (3 mg / m ³ ) according to the recommendation of the 5th fiscal year, and the American Industrial Hygiene Council (ACGIH 1994-1995)
The short-term exposure limit (15 minutes or less) according to the annual edition) is 1 pp
m, time weighted average (8 hours) is 0.5 ppm. These values mean that the abatement treatment must be performed almost completely. Chlorine can be efficiently removed by absorbing it in an alkaline aqueous solution such as caustic soda, but chlorine dioxide has a low absorption efficiency by alkali, and it is difficult to sufficiently remove it unless a reducing agent is used. Therefore, when chlorine and chlorine dioxide gas are discharged at the same time, a two-stage facility for absorbing chlorine by the alkali in the first stage and chlorine dioxide by the reducing agent in the second stage is required. This leads to complicated operations and increased equipment costs. Literature (TAPPI Pulpi
ng Conf (Tech Assoc Pulp Pup Ind) VOL.1982 PAGE 365-
370 1982) describes an example in which exhaust gas consisting of chlorine and chlorine dioxide discharged from a pulp bleaching plant is treated in two stages by a packed tower.

British Patent 1215664 and JP-A-5
Japanese Patent No. 3-88691 describes a method using hypochlorite as an oxidizing agent. The former aims at decolorizing wet phosphoric acid, and many organic substances still remain in the phosphoric acid solution after treatment, and it is difficult to use it as a raw material for industrial phosphoric acid. In the latter method, hypochlorite is used as an optional additional item in the method of separating and removing the organic matter in the wet phosphoric acid as a solid carbide by high-temperature heat treatment. A considerably high temperature is required to obtain a sufficient effect by this method, which is industrially difficult in terms of the material of the device.

[0010]

SUMMARY OF THE INVENTION The object of the present invention is to solve the problems of the above-mentioned conventional techniques and to provide a novel method which has a large effect of removing organic substances and can decompose and remove organic substances effectively and efficiently. To do.

[0011]

Among various oxidizing agents, hypochlorite is considered to have a relatively high oxidizing power. The present inventors have examined the effect of decomposing organic matter in the phosphoric acid solution using commercially available sodium hypochlorite water solution.
Unexpectedly, the result was extremely low. Therefore, when further investigation was conducted to clarify the cause, an actually interesting fact was found. That is, in place of the sodium hypochlorite aqueous solution used until then, a fresh sodium hypochlorite aqueous solution obtained by filtering out the sodium chloride crystals that are simultaneously precipitated when chlorine is blown into the high-concentration sodium hydroxide aqueous solution. As a result of a study using the above, a new fact was found that the effect was dramatically improved, and the present invention was completed.

That is, the present invention is characterized by adding hypochlorite having a weight ratio of chloride ion to hypochlorite ion of 0.35 or less to a phosphoric acid solution containing an organic substance. This is a method of decomposing and removing organic substances in the phosphoric acid solution.

Hereinafter, the present invention will be described in detail.

The hypochlorite that can be used in the method of the present invention must have a chloride ion content with respect to hypochlorite ion of 0.35 or less by weight. The smaller the amount of coexisting chloride ions, the greater the effect of decomposing organic matter,
This weight ratio is particularly preferably 0.25 or less. When chloride ions are contained in excess of this level, the effect of decomposing organic matter is significantly impaired, and the effect of the present invention cannot be obtained. For example, sodium hypochlorite aqueous solution commonly called industrial hypochlorous acid or commonly used hypochlorous acid is produced by chlorinating a low-concentration aqueous solution of caustic soda. Is 0.69 or more in weight ratio with respect to hypochlorite ion. In addition, there is a calcium salt of hypochlorous acid called soda powder or soy sauce liquid produced by causing chlorine gas to act on slaked lime or milk of lime, but these also have an amount of chloride ion relative to hypochlorite ion. Since the weight ratio is 0.69 or more, a satisfactory organic substance decomposition effect cannot be obtained.

The hypochlorite which can be used in the present invention is preferably an alkali metal and / or alkaline earth metal hypochlorite, particularly preferably a sodium salt or a calcium salt. In the case of a phosphoric acid solution containing sulfate such as wet phosphoric acid,
When calcium salt is used, the operability may be reduced, such as the precipitation of calcium sulfate crystals and the formation of scale.
In such a case, sodium salt is preferably used.

As the sodium salt, a low-concentration sodium hypochlorite aqueous solution (low salt hypochlorous acid) obtained by chlorinating a high-concentration caustic soda aqueous solution and filtering out precipitated sodium chloride, and a coexisting sodium chloride content Very low low salt products (ultra low salt hyposodium) correspond. The effective chlorine concentration of the sodium hypochlorite aqueous solution is preferably 15% by weight or more,
20% by weight or more is more preferable. If it is too low, the handling amount increases, and the phosphoric acid solution is diluted by the addition, and the effect of decomposing organic substances decreases.

As the calcium salt, the high-grade ground bean powder obtained by chlorinating high-concentration lime milk and filtering and drying the precipitated calcium hypochlorite dihydrate crystals corresponds to this.

As the phosphoric acid solution to be treated in the present invention, one having an organic carbon concentration of 100 to 1500 ppm by weight can be preferably used. For example, in the case of wet phosphoric acid, those obtained from phosphate rocks in production areas such as Morocco, Taiba, Jordan and China fall under this category. Further, the above-mentioned JP-A-6
A crude phosphoric acid solution obtained from the phosphoric acid sludge described in JP-A-16403 is also an example of the solution to be treated in the present invention.
These wet phosphoric acid and crude phosphoric acid solutions are used as they are,
Alternatively, they may be mixed and used. When the organic matter concentration is high, the method of the present invention may be combined with another method. For example, the organic matter concentration is 100 to 100 by means such as activated carbon adsorption.
It is more efficient to treat it in the range of 1500 ppm by weight.

The phosphoric acid concentration of the phosphoric acid solution to be treated is 75 or 85% by weight (P ₂
Since it is 54 or 62% by weight as O ₅ , if it is too low, it is not preferable in terms of energy cost for concentration and productivity. The concentration of the phosphoric acid solution used in the method of the present invention is preferably that containing 30 to 60% by weight as P ₂ O ₅ .

The amount of hypochlorite used varies depending on the concentration of organic substances in the phosphoric acid solution, the treatment temperature and the treatment method and is not uniquely determined, but 10 to 200 g of effective chlorine is added per 1 g of organic carbon. To do.

The treatment may be carried out under normal pressure or under pressure, and may be a batch, semi-batch, or continuous reaction type, but a continuous type is preferable from the viewpoints of operability and processing ability, and a complete mixing tank type continuous type is preferable. When a reaction device is used, it is preferable to connect and use a plurality of reaction tanks in series because the efficiency is high. A tubular type continuous reaction is also suitable. The reaction can be controlled by the redox potential.

The higher the treatment temperature, the greater the effect of decomposing organic substances, which is advantageous. Therefore, a preferred temperature range for carrying out the process of the present invention is 80 to 150 ° C, more preferably 1
The temperature is from 00 to 130 ° C.

Further, in the method of the present invention, a chlorine-based gas is generated during the treatment, but it is substantially chlorine gas, and its detoxification treatment can be easily carried out by contact with an alkali. It is a feature. As the absorption device, any of a stirring tank type in which exhaust gas is blown into an alkaline solution, a bubble column, a plate column, or a packed column may be used.

[0024]

The present invention will be described in more detail with reference to the following examples.

Example 1 Wet phosphoric acid (P ₂ O ₅ 54%, organic carbon concentration 600% by weight) obtained by decomposing a Chinese ore with sulfuric acid in a closed container of 150 ml equipped with a Teflon inner cylinder and then concentrating it. pp
m) 160 g and 27 g (effective chlorine concentration: 3.5 g) of low-salt hypochlorous acid (effective chlorine concentration: 13% by weight) having a chloride ion content of 0.22 by weight ratio to hypochlorite ion. Set in a heating oven at 130 ℃
Was treated for 5 hours. As a result of this treatment, the organic carbon concentration was 185 ppm by weight.

Comparative Example 1 Sodium hypochlorite having a chloride ion content of 0.69 with respect to hypochlorite ions, that is, so-called ordinary hyposodium (effective chlorine concentration: 13% by weight) was used. The same process as in Example 1 was performed. This treatment resulted in an organic carbon concentration of 380 ppm.

Comparative Example 2 An example was carried out except that 45 g by weight of sodium chlorate, 3.7 g (effective chlorine equivalent 3.3 g, equivalent to Example 1), was used as an oxidizing agent in place of the low-salt hypochlorous acid. The same process as 1 was performed. The organic carbon concentration after the treatment was 210 ppm.

Example 2 A wet phosphoric acid (P) obtained by decomposing a Chinese ore with sulfuric acid and then concentrating it in a processing device in which a 2 liter reaction tank made of Teflon equipped with a stirring blade was connected in a two tank series by an overflow method.
₂ O ₅ 54%, organic carbon concentration 600 weight ppm) 40
It was fed at a flow rate of 0 ml (640 g) / hour. 76 g / hour of sodium hypochlorite (effective chlorine concentration: 25% by weight) having a chloride ion content of 0.22 with respect to hypochlorite ion in a weight ratio to the first reaction tank,
Further, it was fed to the second reaction tank at a flow rate of 38 g / hour (the total amount of effective chlorine added was 27 g / hour). The heating of the reaction tank was performed by an oil bath. The temperature in the steady state was 120 ° C. in both the first and second reaction tanks. This treatment resulted in an organic carbon concentration of 98 ppm by weight.

Next, when the effective chlorine remaining in the treatment liquid was subjected to a reductive decomposition treatment with HCl, 1.4 g of 35 wt% HCl was consumed for 1 kg of the oxidation treatment liquid.

The gas generated in the above processing is set to 144
Absorption tower (packing: Raschig ring (3 mm
φ)) is introduced from the bottom and 1N caustic soda solution (2
Liter / hour). When the gas discharged from the top of the tower was introduced into an absorption bottle filled with a 10% potassium iodide aqueous solution, no coloring due to the release of iodine was observed, and it was confirmed that chlorine was not present in the exhaust gas. The chlorine-based gas generated in the reductive decomposition treatment of residual available chlorine could be removed by the caustic soda absorbent.

Comparative Example 3 Treatment with sodium chlorate was carried out using the same phosphoric acid raw material and apparatus as in Example. The phosphoric acid solution was supplied to the first reaction tank at 400 ml (640 g) / hour, and a 45 wt% sodium chlorate aqueous solution was added to the first reaction tank at a flow rate of 20 g / hour and to the second reaction tank at a flow rate of 10 g / hour. (The total amount of effective chlorine added is 27.5 g / hour). The temperature in the steady state was 120 ° C. in both the first and second reaction tanks. Organic concentration is 100 ppm by weight
It became.

The concentration of undecomposed sodium chlorate remaining in the obtained treatment liquid was 0.21% by weight.
As a result of reductive decomposition treatment at 110 ° C. with
The required amount of wt% HCl was 4.1 g per 1 kg of the treatment liquid.

The gas generated in the above treatment was introduced into the same packed tower as in the example to carry out a detoxification treatment. When the exhaust gas from the tower top was introduced into an absorption bottle filled with a 10% potassium iodide aqueous solution, the liquid turned reddish brown due to the release of iodine, and the chlorine-based gas was not absorbed and removed by the caustic soda aqueous solution. all right. Even if the concentration and flow rate of the aqueous solution of caustic soda as the absorbent were increased, they could not be completely removed. It is considered that this is because the generated gas contains chlorine dioxide due to the decomposition of chlorate, so that sodium sulfite, which is a reducing agent, coexists in the caustic soda aqueous solution fed from the top of the packed column to absorb the generated gas. I went. By this operation, the exhaust gas from the tower top did not liberate iodine, and the chlorine-based gas could be removed.

[0034]

According to the method of the present invention, the effect of removing organic substances in the phosphoric acid solution is large, and the organic substances can be decomposed and removed effectively and efficiently. Hereinafter, the effects of the present invention will be listed.

(1) When decomposing and removing organic substances in the phosphoric acid solution, the use of hypochlorite having a chloride ion to hypochlorite ion content of 0.35 or less by weight gives:
Compared with the case of using normal hypochlorous acid or ordinary hypochlorous acid with a weight ratio of 0.69 or more, the effect of decomposing organic matter is remarkably improved, and the amount of oxidizing agent required to obtain the same effect is small. In addition, it is economically advantageous and efficient processing is possible.

(2) In the conventional method using a chlorate,
A large amount of chlorate remains in the treated phosphoric acid solution, and a large amount of HCl is required for the reduction treatment. Further, not only chlorine gas but also chlorine dioxide, which is difficult to remove harm, is discharged during the decomposition and reduction treatment of organic substances, so that the harm removal equipment is complicated and the operation is complicated. However, according to the method of the present invention, the residual amount of available chlorine compounds remaining in the treated phosphoric acid solution is small,
It can be easily reduced with a small amount of HCl. Also, the chlorine-based gas generated during operation is essentially only chlorine,
It can be easily treated with a simple decontamination facility using alkali.

Claims (2)

[Claims] 1. A phosphoric acid solution containing an organic substance having a chloride ion to hypochlorite ion content of 0.35 by weight.
A method for decomposing and removing organic matter in a phosphoric acid solution, which comprises adding the following hypochlorite. 2. The method according to claim 1, wherein the hypochlorite is an aqueous solution of sodium hypochlorite, and the effective chlorine content is 15% by weight or more.