JPS5924724B2 - Method for producing purified phosphoric acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing purified phosphoric acid in which impurities, particularly sulfate groups, in wet phosphoric acid are removed very efficiently using an organic solvent.

Wet phosphoric acid obtained by decomposing phosphate rock with sulfuric acid contains a large amount of excess sulfuric acid, usually as S04, in addition to various metal compounds derived from the raw phosphate rock.

However, the sulfate content of phosphoric acid used for industrial, pharmaceutical, and food additives is required to be of the same quality as dry phosphoric acid, and the JIS standard (K-1449) requires S0
4 is defined as 30 ppm by weight or less.

Moreover, in recent years, user requirements for sulfate content have become stricter, and even lower content, such as 10
There is a growing demand for substances with weight ppm or less.

Therefore, it is necessary to efficiently remove impurities in wet phosphoric acid, especially sulfate groups, but conventional methods are not necessarily satisfactory as described below.

For example, various so-called solvent extraction methods using organic solvents have been proposed as a method for obtaining products equivalent to dry phosphoric acid.

This solvent extraction method can be roughly divided into (1) dissolving phosphoric acid;
(2) A method of extracting phosphoric acid with an organic solvent that is insoluble or slightly soluble in water and then back-extracting with water; and (2) extracting phosphoric acid with an organic solvent that is miscible with phosphoric acid and water in any ratio. After that, there is a method of performing distillation to separate the phosphoric acid and the solvent.

However, although these solvent extraction methods are effective in removing metal impurities, it is extremely difficult to remove sulfuric acid radicals to the level of dry phosphoric acid.

On the other hand, as a method for removing sulfate radicals, a method is generally employed in which a calcium compound is added to wet phosphoric acid prior to solvent extraction, and the sulfate radicals are separated and removed as ceracola.

However, in this method, since Ceracola has a considerable solubility, the concentration of sulfate groups in phosphoric acid is 804, and 500
The limit was to lower the content to about 5000 ppm by weight.

Therefore, a method of adding a barium compound has been proposed as a method of removing sulfate radicals to an even lower concentration.

However, in order to remove a large amount of sulfate groups, this method requires
Appropriate use of separated barium sulfate, which consumes a large amount of expensive barium compounds, and the presence of metal compounds and organic substances in phosphoric acid causes the barium sulfate crystals to become fine and difficult to separate. Even if you don't have it and throw it away,
It was not considered desirable for reasons such as pollution problems.

Therefore, a method is generally adopted in which wet phosphoric acid from which sulfate groups have been removed with a calcium compound as described above is used as a raw material, and extraction is performed using a solvent extraction method, and a step or operation for removing sulfate groups is added at an appropriate stage of the process. has been done.

As such a method, in a process using a solvent that does not dissolve or slightly dissolves in water, so-called extracted phosphoric acid obtained by back extraction with water is
As disclosed in No. 3786 to No. 52-97390, there is a method of adding a barium compound, but in this method, the content of sulfuric acid radicals barely passes the JIS standard, but the high requirement of 10 pp'm or less is met. It was extremely difficult to achieve that standard.

In addition, in processes that use solvents that are miscible with phosphoric acid and water in arbitrary proportions, an aqueous solution of inorganic compounds such as sodium, potassium, magnesium, calcium, and aluminum is added during the extraction process to form an organic phase (extract liquid). It is separated into two phases, an aqueous phase, and most of the impurities in the phosphoric acid are transferred to the aqueous phase.

Moreover, after the extract is separated from the aqueous phase, it can be further washed with an aqueous solution of inorganic compounds, so this method almost completely removes impurities such as metal compounds and sulfate groups in the phosphoric acid extracted. be able to.

However, even in this extraction method using an organic solvent that can be mixed with phosphoric acid and water in any ratio, there is a phenomenon that the removal level of sulfate groups cannot always be maintained at 10 ppm by weight or less, which is the goal of the present inventors. there were.

The present inventors have conducted various studies in order to overcome the drawbacks of these conventional methods and to develop a method that can easily maintain an extremely low content of sulfate groups in wet phosphoric acid of 804 and 10 ppm by weight or less. As a result, when performing extraction purification using an organic solvent that can be mixed with phosphoric acid and water in any ratio,
It was found that the organic matter content in the wet phosphoric acid had a great effect on the removal rate of sulfate radicals.

In particular, the organic matter content in phosphoric acid is 300% as C.
If it is more than 30 ppm by weight, it is difficult to reduce the sulfate group in the extracted phosphoric acid to 30 ppm by weight or less as S04 no matter how you change the extraction conditions, but it is difficult to reduce the organic matter content in phosphoric acid to 200 ppm by weight as C. It has been found that the content of sulfate groups can be easily reduced to 10 ppm by weight or less when the content is as follows.

The present invention has been made based on this knowledge.

That is, in the present invention, when extracting and purifying wet phosphoric acid using an organic solvent that can be mixed with phosphoric acid and water in an arbitrary ratio, the organic matter content in phosphoric acid is determined in advance as C, and 2
The purpose of the present invention is to provide a method for producing purified phosphoric acid, which is characterized in that the concentration of phosphoric acid is reduced to 0.00 ppm by weight or less, and then solvent extraction is performed.

The method of the present invention can be carried out by treating wet phosphoric acid according to the following steps: (1) pretreatment, (2) organic matter removal, (3) extraction, (4) washing, and (5) post-treatment.

The wet phosphoric acid pretreatment in (1) above can be carried out arbitrarily by a conventional method, and is carried out by treating the wet phosphoric acid with a calcium compound such as phosphate rock, slaked lime, or calcium carbonate.

In this pretreatment, conventionally known methods have been used to increase the sulfate radical content, S
O, is reduced to about 500 to 5000 ppm by weight, but such strictness is not required in the pretreatment of the method of the present invention.

However, it is more preferable to have a lower sulfate content, so in this pretreatment, the S04 content should be between 500 and 5000 wt.
It is often reduced to pm.

If the sulfate group content after pretreatment is high (for example, if it exceeds 5000 wt PPm), the inventors can reduce the sulfate group content in the extracted phosphoric acid by increasing the number of washing stages in the extraction process described below. It can be reduced to 10 ppm by weight or less.

The wet phosphoric acid pretreated in this manner is concentrated as necessary, and then subjected to the organic matter removal treatment described in (2) above to reduce the organic matter content to 200 ppm by weight in terms of C.

This organic matter removal treatment involves not only treating wet phosphoric acid with activated carbon, but also adding oxidizing agents such as hydrogen peroxide, chlorates, perchlorates, dichromates, permanganates, and nitric acid. Various methods such as decomposition and removal methods can be applied, and two or more methods can be combined if necessary.

That is, a generally known method can be applied to this organic matter removal itself.

The concentration of wet phosphoric acid during this organic matter removal treatment is:
It is practical to carry out the extraction at the same concentration as the next extraction process.

In the above (3) extraction process of wet phosphoric acid from which organic substances have been removed, an organic solvent that is optionally miscible with phosphoric acid and water is added to the wet phosphoric acid, stirred to form a homogeneous solution, and then an inorganic compound is added. Thereafter, it is carried out according to a conventional method in which it is left to stand and separated into an organic phase (extract) and an aqueous phase (raffinate).

At this time, most of the impurities in the phosphoric acid migrate to the aqueous phase side.

The concentration of wet phosphoric acid in this case is 30~30 as P2O5.
A range of 55% by weight is preferred.

The amount of organic solvent added is determined by the amount of solvent 2 P20. 1 = weight ratio of
A range of 1 to 20:1 is suitable, and a range of 5:1 to 10:1 is preferred.

Examples of organic solvents include methanol, ethanol, and n-fluorocarbons.
Conventionally used lower alcohols such as alcohol, isopropanol, and ketones such as acetone can be used.

Inorganic compounds to be added include those that are soluble in water and do not form precipitates during extraction, such as hydroxides of sodium, potassium, magnesium, calcium, aluminum, zinc, ammonia, or inorganic salts of these alkalis. One or more of these compounds can be added in the form of a concentrated aqueous solution, but among these compounds, hydroxides and phosphates do not introduce foreign anions into the extract. preferable.

The amount of the inorganic compound added is determined when a homogeneous solution of wet phosphoric acid and an organic solvent is divided into an organic phase (extract liquid) and an aqueous phase (raffinate liquid).
It is necessary to have an amount that completely separates into phases, and the weight ratio to the extract is usually in the range of 1/10 to 1/250.

The separated extract is subjected to multi-stage countercurrent washing or multi-current washing using a concentrated aqueous solution of the same inorganic compound as used in the extraction process, and the resultant liquid is derived from the wet phosphoric acid entrained in the extract. Residual impurities are removed.

Next, since some of the inorganic compounds used in the extraction process and washing process are mixed in the extract, this is removed by an ion exchange method or the like.

However, when the inorganic compound used is the above-mentioned hydroxide or phosphate, only the cations need to be removed.

By distilling the extract thus obtained and separating the solvent, extremely pure phosphoric acid is obtained.

According to the method of the present invention, in which the organic matter content in wet phosphoric acid is reduced to 200 p'm or less in terms of C before extraction and purification using an organic solvent, impurities such as metal compounds are present. Instead, the content of sulfate radicals can be extremely low, that is, 10 ppm by weight or less as S04.

Next, the present invention will be explained in more detail based on examples.

In addition, the ratio and ppm in the examples and comparative examples are weight ratio, respectively.
Weight ppm is shown.

Example 1 The organic content of wet phosphoric acid obtained by decomposing phosphate rock (from Morocco) with sulfuric acid was about 800 pp'm as C, so 35% hydrogen peroxide solution was added to the wet phosphoric acid.
1% was added and boiled for 2 hours to obtain wet phosphoric acid having the composition shown in Table 1.

To 1 kg of this wet phosphoric acid, 3 kg of ethyl alcohol with a concentration of 95% and 100 g of ammonia water with a concentration of 28% were added, mixed for 5 minutes, and separated into two phases after standing for 20 minutes.

Thereafter, the extract was washed five times with 28% ammonia water using 50 g each time.

Next, this washed extract was passed through a strongly acidic cation exchange resin, the solvent was removed by distillation, and the extract was further concentrated to obtain extracted phosphoric acid having the composition shown in Table 2.

Comparative Example 1 The oxidative decomposition treatment with hydrogen peroxide solution was omitted, and all other operations were the same as in Example 1. The composition of the extracted phosphoric acid was as shown in Table 3.

Comparative Example 2 Wet phosphoric acid of Example 1 (organic content is about 80% as C)
0ppm) to 1% hydrogen peroxide solution to wet phosphoric acid.
When the mixture was heated at 80° C. for 30 minutes, the organic matter content was 270 ppm as C.

When the same operation as in Example 1 was carried out using this wet phosphoric acid, S04 in the obtained extracted phosphoric acid was 25p.
It was pm.

Example 2 Wet phosphoric acid with an organic matter content of 520 pp'm as C obtained by decomposing phosphate rock (produced in Florida) with sulfuric acid was added with dichromic acid at a weight ratio of 0.5% to the wet phosphoric acid. After adding potassium and boiling for 1 hour, iron powder was added and reduced until the phosphoric acid solution turned green, thereby obtaining a phosphoric acid solution having the composition shown in Table 4.

Next, the present inventors added a phosphoric acid solution having a composition shown in Table 4 and an azeotropic composition to a perforated plate extraction column (20 plates).
Noisopropyl alcohol (concentration 87.6%) upflow at 20 g/min and 100 g/min, respectively.
Further, an acidic magnesium phosphate aqueous solution with a concentration of 20 is supplied at a flow rate of 3 g/min in the opposite direction (countercurrent) to the phosphoric acid solution and isopropyl alcohol,
Continuous extraction was performed.

The thus obtained extract was then subjected to ion exchange, distillation, and concentration treatment in the same manner as in Example 1 to obtain extracted phosphoric acid having the composition shown in Table 5.

Comparative Example 3 4 kg of water-saturated n-butyl alcohol was added to 1 kg of wet phosphoric acid having the same composition as that shown in Table 1 of Example 1, and the resulting extract was extracted with extracted phosphorus having a P2O5 concentration of 20 parts. After washing the acid 5 times with an amount of 50 g each time, back-extracting with water,
Further concentration was performed to obtain phosphoric acid having the composition shown in Table 6.

Barium carbonate was added to this phosphoric acid in an amount equivalent to the sulfate groups in the phosphoric acid (approximately 0.062% amount relative to the phosphoric acid), stirred for 30 minutes, left for 24 hours, and filtered. The content was 30 ppm as SO4.

Example 3 Wet phosphoric acid before potassium dichromate treatment, similar to that used in Example 2, was added to a glass column with an inner diameter of 30 mm and a height of 1 m packed with 600 ml of granular activated carbon at a rate of 10 ml/m.
The phosphoric acid solution having the composition shown in Table 7 was passed through the solution at a flow rate of 3 in.
I got 1.

Extraction using this phosphoric acid 11 in the same manner as in Example 1,
Through ion exchange, distillation, and concentration operations, the sulfate radical content was reduced to 80%.
4 ppm of extracted phosphoric acid could be obtained.

Comparative Example 4 When the flow of wet phosphoric acid through the granular activated carbon layer in Example 3 was further continued, the organic matter content increased, and wet phosphoric acid 11 containing 350 ppm as C was obtained.

After using this wet phosphoric acid, the same operation as in Example 3 was carried out, and the content of sulfate groups in the extracted phosphoric acid solution was found to be SO4
It was 35 ppm.

Example 4 Wet phosphoric acid obtained by decomposing phosphate rock (produced in Morocco) with sulfuric acid, and 35% hydrogen peroxide solution was added to the wet phosphoric acid.
1 part was added and boiled for 2 hours to obtain wet phosphoric acid having the composition shown in Table 8.

The same extraction operation as in Example 1 was performed on this wet phosphoric acid.

However, the number of times of washing with ammonia water was 7 times.

After passing this extract through a strongly acidic cation exchange resin, the solvent was removed by distillation to obtain extracted phosphoric acid having the composition shown in Table 9.

Claims (1)

[Claims] 1. When extracting and purifying wet phosphoric acid using an organic solvent that can be mixed with phosphoric acid and water in any ratio, the organic matter content in phosphoric acid is set in advance to 200 pp by weight as C.
A method for producing purified phosphoric acid, the method comprising: reducing the amount of phosphoric acid to less than m and then performing solvent extraction.