JPS5919046B2 - Phosphoric acid treatment method - Google Patents

Description

[Detailed description of the invention] The present invention relates to the treatment of phosphoric acid, particularly its cleaning.

Industrial phosphoric acid production from phosphate-bearing rocks always suffers from the problem that certain metal ions, especially magnesium, iron, and aluminum ions, are carried into the final product as impurities.

The abundance of these impurities clearly depends on the specific type of rock used.

So, for example, the local Pharabo
rwa) The ore has a high magnesium content (Mg01.5
%), but the iron content (Fe2O3O, 3%) and aluminum content (Al2030.2%) are relatively low, while typical American mineral ores, such as Florida ore, usually contain aluminum, Fe2O3O, 3%), and iron content (Al2030.2%). Fe
2031.25), and the magnesium content is relatively low (MgOo, 3%).

Hereinafter, in this specification, unless otherwise specified, all terms refer to (mass/mass), and farapolvic acid (Ph
The term alaborwa acid) is used to refer to phosphoric acid produced from typical Phalaborwa phosphate ore, with the following components: MgO-2.5%, P
2O5-54%, CaO-0,03%.

5o4-3.4%, Fe203-0.64%, Al□0
3-0.17%, F-0,30 section.

The above impurities are often part of the unrefined final product.
The sum of the percentages of g02Fe203 and A I 203 is present in an amount of more than 4 parts.

On average this number varies from 0.5 to 10%.

The presence of these impurities is undesirable for various reasons.

Thus, for example, precipitates form in acids during storage or transportation, especially at the low temperatures experienced in winter in many parts of the world.

AI-F whose precipitates cannot be clearly defined
The e-F-Mg-PO4 compound gradually settles out, usually over a period of one week to several months, and this behavior of impurities in the acid makes it impractical to utilize this behavior as a means of cleaning the acid before shipment.

The presence of these impurities in the acid can also cause various problems when the phosphoric acid is used in fertilizer production.

For example, acids high in magnesium tend to form gel-like products when ammonia is added, possibly resulting in insoluble M
g-NH4-PO4 compounds, which are unsuitable for use as liquid fertilizers, for example, as they pose serious handling problems.

Furthermore, when ammonia ions are added during the ammonification of -, an AI-Fe-Mg-NH4-F-P04 complex, whose composition and properties vary greatly depending on the origin and the individual wet acid treatment method, is formed. The possibility of undesirable insoluble compound precipitation, including .

As a result of these disadvantages, strict requirements have been placed on the permissible percentages of such impurities, and the specifications are determined by the type of acid in question and the end use of the acid.

For example, in the case of magnesium, the P2O570 phosphoric acid is usually required to not exceed 0.5% Mg.

Furthermore, acids with low R2O3 values (sum of the percentages of A1203 and Fe2O3), such as those with a coefficient of less than 2, are preferred over those with higher iron and aluminum contents.

In addition, the present invention particularly applies when P2O5 of pharabolwaic acid is 50 to 50.
This was done in consideration of the fact that it is a section 75, and P2
The target is phosphoric acid containing O550 to 75%.

Various attempts have been made to remove such impurities from wet process phosphoric acid, but all previously proposed solutions have some drawback.

As the quality of phosphate ore processed around the world is gradually deteriorating, there will be a need in the future for an economically viable refining process for wet phosphoric acid in order to prepare acid of acceptable quality for the production of highly concentrated fertilizers. It is expected to increase considerably.

Below is a summary of some of the methods currently available in the fertilizer industry for phosphoric acid purification.

(1) Solvent Extraction Several methods based on the extraction of inorganic impurities from acids with organic solvents have been developed, and some are used industrially.

Phosphoric acid of suitable quality is thus obtained, but the process is expensive.

So, for example, the cost of carrying out the necessary modifications to an existing medium-sized phosphoric acid plant can be enormous, with the result that the refining cost is 3.3 lb/ton of P2O due to phosphate losses and solvent losses in the purified product.
It will be on the order of $0-$40.

(II) Solvent Precipitation In this, for example, an acid is mixed with a miscible solvent such as methanol to precipitate impurities as phosphates.

Small amounts of inorganic salts, ammonia, etc. are often added to promote the formation of insoluble varieties.

The solids are separated and the solvent is distilled from the liquid phase and recycled, leaving behind the purified acid.

This is also an expensive method that requires a large amount of energy.

For example, one such process requires 3.5 Ky of methanol, 9- and 0.04 Ky of ammonia per P2O5KP.

The loss of phosphorus in the solid content is on the order of 10 times the amount of P2O5 in the raw material.

(Indirect purification) This type of process separates the phosphate in the acid from impurities as a salt or organic adjunct compound and converts it into the desired product.

In one method of this type, urea-phosphate is converted into P2O554%
Precipitate from acid.

The urea phosphate crystals were then separated from the mother liquor by centrifugation.
It is decomposed at 21° C. or higher to form a melt of ammonium polyphosphate and undecomposed urea.

Add ammonia and water to this mixture to make a fertilizer solution with a nitrogen content of 15, phosphorus content of 28, and potassium content of 0, which contains, for example, 85 parts of phosphate in the raw material, but only 15 parts of pure middle-aged raw material. Can be done.

The mother liquor obtained by centrifugation can be processed into a suspension fertilizer.

Recovery of phosphoric acid from urea-phosphate requires nitric acid treatment to precipitate the urea-nitrate.

Nitrates can be neutralized with ammonia to make ammonium urea nitrate.

As can be seen, this procedure is rather tedious and therefore time consuming and expensive.

OV) Ion exchange This is also an acid with dilute acid impurities, such as P2O53.
From 0%, it is absorbed into an ion exchange resin and removed from the resin with another acid such as sulfuric acid.

This method produces high quality acid, but apart from the cost,
Some problems with this method include the difficulty of clarifying the acid sufficiently in advance to prevent poisoning of the resin, deposition of solids from the acid onto the resin, and blockage of the exchange tower with gypsum and other soluble residues. Make it unattractive.

In contrast to these complex and therefore expensive and time consuming existing processes, it is an object of the present invention to provide a simple yet effective phosphating process for removing impurities such as magnesium.

According to the present invention, a method for treating phosphoric acid containing one or more impurities including ions of at least one metal belonging to the group of magnesium, iron, and aluminum can be used to treat phosphoric acid containing at least one type of impurity including ions of at least one metal belonging to the group of magnesium, iron, and aluminum. Including the process of heating the acid under conditions of temperature, pressure, time, and concentration such that when the main component of magnesium is 60 (mass/mass) or more), the acid is precipitated as a pyrophosphate of the metal ion. .

That is, in the present invention, in order to reduce metal ions, particularly magnesium ions, in the phosphoric acid to be treated to a specified value or less, P2 of the phosphoric acid is
We investigated the correlation between O5 concentration and treatment conditions, namely temperature, pressure, and time, and based on this knowledge, we treated a P2O5 concentration of about 50% with about 75% phosphoric acid to precipitate the contained magnesium as pyrophosphate. Temperature and pressure conditions are specified to bring the % to a desired value, for example, less than 0.5%.

The applicant has discovered that, for example, when pharabolwaic acid is heated above room temperature, especially above 100°C, after a certain time a precipitate containing more than 63 parts (mass/mass) of magnesium as acidic magnesium pyrophosphate MgH2P2O7.xH20 is formed. I found out.

Furthermore, according to the invention, the process comprises, in the case of acids containing magnesium as the main impurity, the step of precipitating at least 70 φ (mass/mass) of the magnesium as acidic magnesium pyrophosphate.

In one form of the invention, the method may include adding acid pyrophosphate nuclei of the metal ion to the acid to induce precipitation.

The inducing agent may be, for example, part of a precipitate formed by heating an acid previously, or in another version of the invention may be a synthetic equivalent to such a precipitate.

The present invention involves heating the acid under high pressure to induce precipitation.

For example, the present applicant has been able to reduce the magnesium content of an acid to a specified concentration P2O5 in a relatively short time by simply pressurizing the acid under high pressure.
It has been found that at 70% Mg OO can be lower than the value of 5%.

The applicant has further discovered that the acidic magnesium pyrophosphate precipitate thus obtained is superior to the acidic magnesium pyrophosphate precipitate obtained by precipitation at normal pressure in terms of p and crystallinity.

Applicants have also found that the rate of formation of metal ion acid pyrophosphate precipitates increases with increasing temperature and pressure.

For example, the applicant has found that a temperature range of 100°C or higher is suitable, but good results can be obtained at any temperature of 180°C.

Further, at a pressure higher than normal pressure, particularly at a pressure higher than 10 atm (gauge pressure, the same applies hereinafter), preferably at a pressure higher than 21 to 35 atm, the precipitation rate increased considerably.

Even if the temperature is set to 180° C. or higher and the pressure is set to 35 atm or higher, no great technical effect can be obtained, and it is rather disadvantageous in terms of equipment.

Note that the above pressure range of 10 to 35 atm is 7 to 35 atm when inoculating acidic magnesium pyrophosphate as described later.
Atmospheric pressure is valid.

be.

The applicant has discovered that the wet phosphoric acid produced from the Phalaborwa ore purified by the above-mentioned method has certain properties of important commercial value, particularly low viscosity, high clarity, low total impurity content (i.e. percentage of Mg02A1203°Fe2O3). low fluorine content (total of 1.5%), extremely low fluorine content (0.05%)
%) and normal behavior regarding the change from orthophosphate to polyphosphate.

Therefore, far fewer handling problems are encountered with acids purified in this way than with other commercially available phosphoric acids.

According to the present invention, the method also includes converting the precipitate into calcium carbonate,
This includes treatment with neutralizing agents such as calcium hydroxide, sodium hydroxide, and ammonia.

In this way, it is possible to produce a high-quality slow-release fertilizer that is non-hygroscopic and appears to have good granulation properties (P205 approximately 60%).

The invention will now be described with reference to the following experiments.

These experiments were carried out at the Applicant's phosphoric acid plant in Pothefström, Transvaal, to remove magnesium from wet phosphoric acid produced from phosphate ore produced at Phalabolwa, Northern Transvaal.

■ The first series of experiments was conducted to determine and describe the effects of temperature, concentration, and inoculation of acidic magnesium pyrophosphate in removing magnesium from Phalaborwa's phosphoric acid under normal pressure as a magnesium acid pyrophosphate precipitate.

In these experiments, 800 g portions of acid extracted from the same stock solution were placed in glass speakers and heated in a furnace.

Samples were taken periodically to follow the progress of the precipitation reaction.

The results are presented in Table 1, which contains only those details deemed appropriate to explain the factors mentioned above.

In Table 1, "inoculation" means that the acidic magnesium pyrophosphate precipitate obtained from the previous precipitation was inoculated at 1% to the treated phosphoric acid.

In addition, for these experiments, the factory-produced acid was used at approximately 60 MH
g to the starting concentration shown in the table, i.e. P
2O556,1,60,4.

Various concentrations were obtained: 64.2 and 69.1%.

The results in Table 1 show that if acid is inoculated with acidic magnesium pyrophosphate and given enough time, magnesium can be precipitated down to 0.5% Mg even at 100°C, but on the other hand, it is difficult to precipitate at high temperature and high concentration. The progress is rapid, and as shown in No. 10 in Table 1, Mg00 is reduced within 24 hours.
．． It can be precipitated to 5% or less, indicating that inoculation with acidic magnesium pyrophosphate is a preferable condition for reducing the MgO content of the acid to less than 0.5%.

At temperatures higher than 160°C, the MgO content can be reduced to less than 0.5% in some cases without acid inoculation, but the P separation of the product is difficult and reproducible due to the poor crystallinity of the precipitate. was found to be low.

Some iron and aluminum are found in the magnesium pyrophosphate precipitate, and the applicant believes that the reason these impurities do not coprecipitate further with the magnesium is due to the presence of sulfate ions in the acid. .

■ Further experiments were carried out to determine and explain the effect of pressure on the rate of removal of magnesium from phosphoric acid by the process according to the invention.

In this experiment, pre-concentrated phosphoric acid (P2O570, 3%
, Mg03.04) was placed in a 14 pressure vessel, and 150
It was heated to 0.degree. C. and a pressure of 21 atmospheres was applied using compressed air.

After 1.5 hours, the pressure was reduced and the product was suction filtered through a Bunona funnel using a polypropylene oven cloth with a throughput area of 255 cr.

The pass was over in 50 seconds. The analysis result of acidic p liquid is P2O
, 71.2%, and Mg 0.38%, which corresponded to the 19th section of the sample.

The second concentrated acid 1e was inoculated with acid pyrophosphate and heated to 150° C. under normal pressure in a furnace.

Although precipitation started quite early, i.e. at about 3 o'clock,
The magnesium content of the acid reaches the specified M after 200 hours.
gO less than 0.5% was reached.

It took 3 minutes to filter the product through the Buchna funnel.

Analysis of the p-liquid showed that P2O was 569.2% and Mg was 0.48%, and the p-filter cake was equivalent to 2.4% of the mixed product.

From these results, it is clear that the rate of production of acidic magnesium pyrophosphate from acid is significantly increased by applying pressure to the acid while heating it to a selected temperature.

This observation applies to both inoculated and uninoculated acids.

This is important when applying this method to the production of acid sugars on an industrial scale, since shortening the reaction time means reducing the size of the container.

In addition, the precipitate thus produced has a coarse crystalline appearance and has excellent filterability, which is considerably better than that of a precipitate produced under normal pressure.

It has also been found that a significant improvement in the precipitation rate of magnesium acid pyrophosphate is possible at a pressure higher than 10 atm without inoculation of magnesium acid pyrophosphate, and at a pressure higher than 7 atm when inoculated.

The maximum pressure tested was 24.5 atmospheres.

However, higher pressures are believed to only improve the settling rate.

Temperatures above 120°C are desirable and 150-180°C is maximum.

However, temperatures higher than this could not be achieved using manual equipment.

However, higher temperatures, perhaps above 200°C, may lead to excessive polyphosphate formation and sequester metal ions, including magnesium, in the acid, thereby inhibiting the formation of an insoluble magnesium acid pyrophosphate precipitate or It is considered to be limited.

Regarding the influence of acid concentration on magnesium precipitation under pressure, it has been found that when pressures in the range of 10-21 atmospheres are applied, the lowest concentration that has a favorable effect on the purification of the farapollic acid used is a concentration of about 63% P2O5. Confirmed.

Also, by changing the temperature and pressure, P lower than 63
The method is effective for acids with 2O5 concentrations, for example about 50%.

■ Another series of experiments was conducted to evaluate the method as it is applied on a much larger scale.

In these experiments, a kneaded-lined tank with a capacity of about 60,006 mm was used, which was equipped with a liquid level control, a thermocouple, a heating corrugated tube made of a heat-resistant alloy, and an agitator.

This tank is filled with commercially produced acid (P2O550, 2%) from the Applicant's Pothefström phosphoric acid factory, the temperature of the acid is maintained at 135-145°C by controlling the steam flow, and the acid is stirred and tested. The purpose of the first part was simply to concentrate the acid at normal pressure to such an extent that inoculation would induce precipitation.

The liquid level in the tank was kept constant by introducing new acid to compensate for evaporation loss.

Samples were taken from the acid periodically to monitor its progress.

The results are presented in Table 3, which again contains only a summary of the important measurements for the purpose of explaining the test results.

The acid reached a concentration of 2.6% P2056 only after 500 hours.

Then add 20g of acidic magnesium pyrophosphate precipitate prepared in advance in the laboratory to the acid, i.e. about 0.35% of the acid in the tank.
Gravimetric apparatus inoculation.

Precipitation started after 5 hours and after the next 10 hours the acid was Mg0
It reached a level of 0.38%.

Precipitation stopped at a level of about 0.3% MgO.

Only little or no iron and aluminum were removed from the acid, which Applicant believes may be for the same reasons as above.

The precipitate obtained under these conditions has good filterability and the filtrate/
The cake ratio was 78,722 on a weight basis.

The Applicant has discovered that the phosphoric acid of Phalaborwa ore purified by the method according to the invention has the following properties which make it a superior acid in terms of quality compared to most other commercially available wet superphosphoric acids on the world market. do.

([) Viscosity The viscosity of superphosphoric acid can be extremely high, creating serious handling problems.

Solidification occurs at room temperature.

Removal of magnesium has a significant effect on the viscosity of superphosphate from Phalaborwa ore.

For example, a sample of acid from this phosphoric acid plant is P2O56
It was concentrated to 9.1 part and MgO2.8 part and the viscosity was measured with a Brookfield viscometer, and it was 2650 cp at 40°C.
Met.

The same acid sample was then treated with acidic magnesium pyrophosphate from the previous experiment and heated to 140°C for 24 hours.

When the p liquid was separated and analyzed, it was found that P2O5688, Mg
The viscosity was 236 cp at 40°C.

It is known that when the aluminum content in phosphoric acid is high, the viscosity of the acid becomes high.

This explains the exceptionally low viscosity of South African phosphoric acid.

When magnesium is removed from this acid, the aluminum content of the acid is exceptionally low (0.1 to 0.2%) compared to products made overseas, so the viscosity becomes extremely low, resulting in an acid that is easy to handle.

After purification, the acid has a very high residual impurity content. low.

Superphosphoric acid can have a total content of MgO, Fe2O3 and A I 203 of 1.5%, which is extremely low by world standards.

P2O570% superphosphoric acid produced and refined from Phalaborwa ore would then have the following composition: P20.70%
, Mg00.4, A12030.2%, Fe2030
．． Section 8 and Fo, 05%.

(11) Clarity When commercially available pharabolwic acid is concentrated and purified, its color usually becomes darker and becomes amber, but it is still much more visually appealing than those made from phosphate rock of organic origin, such as Florida acid in the United States. Attractive.

Foaming during concentration is a serious problem with the latter acids, but on the other hand, pharabolwaic acid has a low carbon content and does not require an antifoaming agent even when concentrated to the superphosphoric acid range.

Carbon analysis of faraforwaic acid with P2O554% shows only o,
oot% carbon, while the US Florida acid contained 0.25% carbon.

The applicant has found that the process according to the invention does not adversely affect these properties of pharabolwic acid.

Since it is often necessary to specify the polyphosphate content of polyphosphate superphosphates, it is important to note the polyphosphate formation of the acid purified by this method, i.e. the conversion of orthophosphate to polyphosphate during heat treatment. It is necessary to show how the behavior of

The phosphates in wet phosphoric acid are normally present as orthophosphates, but as the acid is being concentrated to the superphosphate range, the phosphates polymerize, and the conditions under which the polymerization took place and the origin of the acids involved That is, polyphosphates with various compositions and distributions are produced depending on factors such as their composition.

Applicant's interest in polyphosphates stems from the fact that polyphosphates have the ability to sequester cations such as calcium, magnesium, iron and aluminum, thus preventing the formation of undesirable insoluble precipitates in acids. do.

This performance is also responsible for determining the properties of fertilizer products made from superphosphoric acid in an advantageous manner by improving the desired physical properties of the product.

End users of superphosphate typically produce 25-40% polyphosphate (
Suffice it to say that the content (or non-ortho phosphate) content, possibly even higher, is specified.

The examples below demonstrate that acids purified by the method described above can be processed to produce acids of specified polyphosphate content.

P2O567, 1% 2M purified by applying a pressure of 21 atm at 150°C for 1.5 hours to a concentrated factory-produced acid sample.
g 00-32 section.

Al2030.2%, Fe2O30,72% acid 11
About 60aH,! It was further concentrated at a pressure of i' and samples were periodically withdrawn and analyzed for total and orthophosphate.

The boiling point of the acid was recorded each time a sample was taken.

The results are shown in Table ①.

Furthermore, in an experiment conducted to explain the preparation of magnesium pyrophosphate fertilizer by the method of the present invention, the acidic magnesium pyrophosphate cake obtained by the above method was pulverized with 1 Kp containing 567% P2O and 11.4% Mg0. 300 g of limestone was mixed well.

The product is a non-hygroscopic white powder with no free acids and its analysis is as follows: total P2O 560.1 parts, citric acid soluble P2O 549.0 parts, water soluble P2O 515.1%, Mg.
010.1%, Ca014.3, pH==3.6
The product remained fluid even after being exposed to the atmosphere for several months.

When moistened with a small amount of water and then dried, it forms a hard mass.

The material thus obtained is considered to have good granulation properties.

The analysis of this product makes it suitable for use as an agricultural slow-release phosphate fertilizer that also provides nutrients calcium and magnesium to plants.

It will be appreciated that phosphoric acid purified by the method of the invention as well as fertilizers produced by the method of the invention are also intended to be included within the framework of the invention.

It will be appreciated that although the above examples relate to the removal of only magnesium from the acid being treated, the present invention is not intended to be limited to only magnesium removal.

Claims (1)

[Claims] 1. Containing magnesium ions as impurities in the solution,
In a method for treating phosphoric acid with a P2O5 concentration of 50% to 75%, nucleic acid is heated to a temperature of 100°C to 180°C at a pressure of 10 to 35 atmospheres, the nucleic acid is maintained at the temperature at the pressure, and the magnesium is A phosphoric acid treatment method characterized by precipitation as a pyrophosphate. 2. Claim 1, characterized in that the acid is heated to a temperature of 100° C. to 180° C. and maintained at the temperature until at least a factor of 60 (mass/mass) of the magnesium is precipitated as a pyrophosphate. Treatment method described in. 3. The nucleic acid is concentrated until the acid contains 70% of P2O5, and then heated at a pressure of 21 atm and a temperature of 150°C for 1.5 hours to form a precipitate of acidic magnesium pyrophosphate. Treatment method described in Scope 1. 4 For nucleic acids, aluminum is Ag303, iron is Fe2O3
The treatment method according to claim 1, characterized in that the total amount of the total amount is less than one factor (mass/mass). 5 The acid is Mgo; ratio 2.5; P2O5; ratio 54. CaO; 0.03%, SO4; 3.4%, Fe
2O3; 0.64%, Ae203; 0.17%,
and F; Phalaborwa (pha) with a composition of 0.3%
The treatment method according to claim 1, characterized in that the treatment method is an acid (laborwa) acid. 6 Contains magnesium ions as impurities in the solution,
In a method for treating phosphoric acid with a P2O5 concentration of 50 to 75, nucleic acids are heated from 100°C to 100°C at a pressure of 7 to 35 atm.
The nucleic acid is heated to a temperature of 80° C., the nucleic acid is maintained at the temperature under the pressure, and acidic magnesium pyrophosphate is inoculated to induce the formation of a precipitate, and the magnesium is precipitated as a pyrophosphate. Phosphoric acid treatment method. 7. The above-mentioned acidic magnesium pyrophosphate is added as a nucleus until an amount of acidic magnesium pyrophosphate is precipitated such that the magnesium remaining after welding in the acid becomes less than 0.5'% (mass/mass) as MgO. Process according to claim 6, characterized in that the acid is heated to a temperature in the range 100°C to 145°C. 8 Nucleic acids are exposed to P2O at temperatures between 135°C and 145°C.
Claim No. 5, characterized in that the nucleic acid is heated until the concentration of No. Treatment method described in Section 6.