JPH0261409B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for obtaining purified monoammonium phosphate in high yield. More particularly, the present invention relates to the method for producing purified monoammonium phosphate, usable as industrial grade, directly from wet phosphoric acid in high yield. Ammonium phosphate obtained by reacting wet phosphoric acid with ammonia contains many impurities derived from the phosphoric acid, so although it can be used as a fertilizer, it cannot be used as is for industrial purposes. In order to produce industrial purified ammonium phosphate from wet phosphoric acid, it is necessary to purify the phosphoric acid in advance as follows. That is, phosphoric acid is extracted from wet phosphoric acid by a solvent method, and the extracted material is reacted with ammonia to obtain ammonium phosphorus with less impurities. However, this extraction method involves complicated steps and cannot be said to be an industrially advantageous method. On the other hand, French Patent No. 1248055 (Preyon method)
According to , by reacting wet phosphoric acid with ammonia,
The amount of impurities derived from wet phosphoric acid is reduced by partially forming crystals of dianic acid phosphate in the reaction solution and cutting off a portion of the mother liquor after the crystal separation, and then concentrating the mother liquor. By doing so, crude crystals are crystallized, and by recrystallizing the crude crystals, industrial purified products are obtained. The yield of purified diammonium phosphate obtained by this method is about 40-50% for ₅ minutes of P ₂ O in the raw material wet phosphoric acid, and the remaining
P ₂ O for ₅ minutes will eventually become ammonium phosphate** for fertilizer (Note: *NH ₃ -N=20.3~20.7%,
W-P ₂ O ₅ 51.5-52.7%, the theoretical value is NH ₃ −
N21.2%, W- _P2O5 , ** _NH3 -N14~ ₁₆ %, T
-P ₂ O ₅ 43-45%, W-P ₂ O ₅ 39-42% (W means water-soluble, T means total). The yield of ammonium phosphorus to phosphoric acid in the above description is hereinafter defined as R (withdrawal rate) as follows. R (%) = ₅ amount of P ₂ O contained in ammonium phosphorus crystal / ₅ amount of P ₂ O in raw wet phosphoric acid x 100 As mentioned above, when using direct neutralization of wet phosphoric acid, purified phosphoric acid The yield or extraction rate of ammonium to phosphoric acid is quite low. On the other hand, regarding the various compounds that are produced stepwise by the reaction of wet phosphoric acid and ammonia, Ando et al.
According to "Research on Chemical Fertilizers" written by Akiyama and published by Nissin Publishing Co., Ltd. on May 20, 1976, regarding the ammonia neutralization of wet phosphoric acid, the following is stated in relation to the neutralization conditions: It is being In other words, when neutralization is carried out at approximately 100°C for 5 to 10 minutes, if the neutralization is temporarily stopped when the pH of the reaction solution reaches 2 to 3 and the pH and temperature are maintained, the particle size will decrease. Crystalline substance of about 10μ: (FeAl)
NH ₄ H ₂ (PO ₄ ) ₂ ·1/2H ₂ O (abbreviated as Q compound) is formed. When neutralization is resumed and the pH is adjusted to 4 to 6, the Q compound changes into a microcrystalline substance of about 0.02 μm: (FeAl)NH ₄ HF ₂ PO ₄ (abbreviated as S compound). However, Q
It takes a long time for a compound to change into an S compound. Based on the above facts, in order to obtain an ammonia-neutralized slurry with good filterability from wet phosphoric acid, the phosphoric acid is neutralized to pH 2 to 3 and then aged.
Continuing to neutralize ammonia, pH 4 to 6
shall be. The above facts suggest the possibility of producing ammonium phosphate mother liquor for industrial use by removing Fe, Al, and F from wet phosphoric acid using a certain neutralization method. . In the above-mentioned book, the authors state that due to the above-mentioned neutralization method, Fe and Al in wet phosphoric acid become insoluble to the maximum at around pH 4.5 of the neutralized solution, so the slurry generated at this pH is filtered. By differentiating, Fe96
%, 86% Al, 48% F, and 16% Si are removed. However, nothing is said about the removal of Ca or Mg groups, which have a significant adverse effect on the crystallization of ammonium phosphate from a wet ammonia-neutralized phosphoric acid solution. In view of the above-mentioned problems with the known techniques, the present inventors have made efforts to find a method for obtaining purified ammonium phosphate for industrial use with a high yield, that is, a high extraction rate, by a wet phosphoric acid direct neutralization method. conducted research. As a result, wet phosphoric acid is neutralized with ammonia to a pH of 4.2 to 6.5, preferably 4.5 to 6, at 70 to 110°C, preferably 80 to 105°C, for 30 to 180 minutes, preferably 60 to 90 minutes, and the resulting sludge is By filtering, most of the impurities in wet phosphoric acid are removed to the extent that they do not interfere with the production of purified ammonium phosphorus;
The filtration properties of the neutralized phosphoric acid containing the sludge described above are extremely good, the attached ammonium phosphate can be recovered by washing the filtrated sludge with water, and the sludge is filtrated. It is known that by successively concentrating and crystallizing a filtrate (ammonium phosphate mother liquor), purified ammonium phosphate for industrial use can be obtained in high yield without the need for recrystallization (hereinafter referred to as the earlier invention). )
was completed and a patent application was filed as Japanese Patent Application No. 59-3749 (Japanese Unexamined Patent Publication No. 60-151203). However, in the purified ammonium phosphate mother liquor obtained in the previous invention, Fe, Al, Ca, F, etc. are still dissolved, although in trace amounts.
As monoammonium phosphate crystals are crystallized and obtained by concentrating and cooling the mother liquor, it becomes clear that Fe, Al, Ca, F, etc. become concentrated in the remaining mother liquor. Ta. This fact indicates that as the above-mentioned R or "extraction rate" is increased by carrying out the crystallization of monoammonium phosphate from the mother liquor in stages, the impurity SS (note , dissolve 10 g of monoammonium phosphate obtained by crystallization in 100 ml of water, filter out the water-soluble substances in the solution, and dry the weight% of the sample relative to R = 70%. It has been found that the R value increases rapidly and it is no longer possible to obtain industrially purified monoammonium phosphate to higher R values. The experimental facts supporting the above recognition regarding the previous invention are as follows. That is, the purified ammonium phosphate mother liquor obtained by neutralizing wet phosphoric acid and filtering the sludge according to the method of the previous invention is concentrated and cooled, and as monoammonium phosphate is crystallized, insoluble sludge is added to the mother liquor. will occur. This mother liquor was diluted with water and filtered, and the filtration residue, that is, the generated sludge, was chemically analyzed, and the result was as shown in A below. In addition, due to the concentration crystallization, the extraction rate R is 0.7
Wash the monoammonium phosphate crystals crystallized at a stage exceeding the above with a saturated aqueous solution of reagent grade monoammonium phosphate crystals, wash away impurities attached to the surface of the crystals, and then dissolve the monoammonium phosphate crystals in water. When this was done, white turbidity (insoluble matter) was generated.
When this cloudy substance was separated and collected and chemically analyzed, it was found to be as shown in B below.

[Table] From the analytical values and comparison of the above-mentioned sludge A and white turbidity B, it is found that trace amounts of impurities dissolved in the purified ammonium phosphate mother liquor according to the method of the previous invention are precipitated in the sludge as the mother liquor is concentrated. However, it was found that the monoammonium phosphate crystals were incorporated into the crystallized monoammonium phosphate crystals. In order to solve the above-mentioned technical problem that became clear through re-examination of the previous invention, the present inventors conducted extensive research. As a result, the reaction solution (note: phosphorus mother liquor) neutralized to pH 4.5 to 4.8 in the previous invention is not filtered immediately, but kept at 80 to 110°C for 1 to 10 hours, aged, and then filtered. Alternatively, ammonium fluoride and/or acidic ammonium fluoride are added and mixed in an amount of 0.3 to 2 times the amount of dissolved calcium in the neutralized reaction solution, and the resulting sludge is filtered after holding for 1 to 10 hours. When monoammonium phosphate is crystallized by a method such as concentration cooling using purified ammonium phosphate obtained separately, surprisingly, the above-mentioned R (Note: extraction rate, ie, phosphoric acid yield) is 81%. The present invention was completed knowing that it is possible to increase the height even closer to that level. As is clear from the above description, an object of the present invention is to provide a method for obtaining purified industrial monoammonium phosphate directly from wet phosphoric acid in high yield. More precisely, the object of the invention is to
The object of the present invention is to provide a process for producing industrially purified monoammonium phosphate in significantly higher yields than in the previous invention. Other purposes will become clear from the description below. The present invention (second invention) has the following main configuration (1) or (3) and the following embodiment configuration (2) or (4). (1) In a method for obtaining monoammonium phosphate by reacting wet phosphoric acid with ammonia, the reaction temperature is maintained at 70 to 110°C, and ammonia is
React for ~180 minutes and adjust the pH of the reaction solution to 4.5~4.8
A method for obtaining purified ammonium phosphate in high yield, characterized in that a purified ammonium phosphate mother liquor obtained by filtering the sludge produced after holding the sludge at 80 to 110°C for 1 to 10 hours is used. (2) The method according to item (1) above, wherein monoammonium phosphate is obtained by concentrating the purified ammonium phosphate mother liquor. (3) In a method for obtaining monoammonium phosphate by reacting wet phosphoric acid with ammonia, the reaction temperature is maintained at 70 to 110°C, and ammonia is
React for ~180 minutes and adjust the pH of the reaction solution to 4.5~4.8
and the amount of dissolved calcium in the reaction solution is
0.3 to 2 equivalents of ammonium fluoride and/or
Or add and mix acidic ammonium fluoride to 1
A method for obtaining purified ammonium phosphate in high yield, characterized by using purified ammonium phosphate mother liquor obtained by filtering the sludge produced after holding for ~10 hours. (4) The method according to item (3) above, wherein monoammonium phosphate is obtained by concentrating the purified ammonium phosphate mother liquor. The structure and effects of the present invention will be explained in detail below. The wet phosphoric acid used in the present invention is the so-called wet phosphoric acid obtained by treating phosphate rock with mineral acid. It may be manufactured by any method. Such phosphoric acid contains the aforementioned impurities other than phosphoric acid derived from the raw phosphate rock and the inorganic acid for decomposition. This phosphoric acid is placed in a reaction tank and reacted with ammonia. It is easiest to blow ammonia in gas form directly into phosphoric acid, but
For example, it may be added as aqueous ammonia with a concentration of 20 to 30% by weight. The essential features of the method of the present invention are the combination of wet phosphoric acid neutralization conditions with ammonia and high-temperature aging after neutralization or addition of ammonium lofted (and/or acidic ammonium fluoride) and high-temperature thermal formation. and filtration of the sludge produced after the thermal formation. The neutralization temperature is maintained at 70-110°C, preferably 85-105°C throughout. The necessary heating or heat removal is carried out for this purpose by heat transfer through the walls of the reaction vessel or by other known methods. If the neutralization temperature is outside the above range, the filtration performance of the sludge, which will be described later, will decrease and the amount of impurities in the target product (phosphorus ammonium) will increase. The neutralization time is 30 to 180 minutes, preferably 60 minutes.
~90 minutes. If the time required for neutralization is outside the above range, the formation of a sludge with good filtration properties and effective in removing impurities in the mother liquor will be insufficient. However, the predetermined final pH value is 4.5 to 4.8.
If the pH value is less than 4.5, the yield of the target product (monoammonium phosphate) will decrease, and if the pH value exceeds 4.8, diammonium phosphate will be mixed into the monoammonium phosphate. After the neutralization is completed, the above-mentioned high-temperature ripening in (A) or combination of addition of ammonium fluoride, etc. and high-temperature aging in (B) is carried out. The high-temperature aging is carried out by heating the monoammonium phosphate mother liquor after the neutralization reaction to 80 to 110%
The temperature is preferably maintained at 80 to 105°C for 1 to 10 hours, preferably 1 to 5 hours. Furthermore, when adding ammonium fluoride or the like, it is added prior to the ripening. The additive is ammonium fluoride (NH ₄ F) or acidic ammonium fluoride (NH ₄ F.HF) or a mixture thereof. The temperature during addition is the same as the temperature during neutralization, and there is no need for particular cooling or heating. The amount added is 0.3 to 2 times equivalent, preferably 0.5 to 1.5 times equivalent, relative to dissolved calcium in the neutralization reaction solution. If it is less than 0.3 times, the effect is insufficient;
Even if the amount is doubled, the effect will not improve. After addition, stir to uniformly dissolve ammonium fluoride, etc. During the above-mentioned neutralization prior to the ripening according to the present invention, the wet phosphoric acid neutralized mother liquor contains the T compound (Fe, Al) (NH ₄ ) ₂ ·H ₂ F(PO ₄ ) ₂ ·nH mentioned in the above-mentioned book. ₂ The main component is a mixture of O and Q compounds (described above), and also contains Ca,
A sludge consisting of salt or double salt containing Mg or Fe is generated. It is believed that the crystal growth of the crystal portion inside the sludge continues during the ripening according to the present invention, and as a result, the amount of impurities in the mother liquor after filtration, which will be described later, is reduced. This reduction effect is particularly remarkable when an appropriate amount of ammonium fluoride or the like is added and mixed and dissolved before ripening. After the above aging, the wet phosphoric acid neutralized mother liquor is filtered or centrifuged using a known method to obtain a filtrate and a sludge. Collect P ₂ O for ₅ min. The difference in effectiveness between the previous invention and the method of the present invention clearly appears in the amount of latent sludge in the mother liquor after filtration and the amount of impurities in the mother liquor, which will be described below. Whether this relationship has matured or not,
Examples according to the presence or absence of addition of ammonium fluoride, etc. before ripening are as follows: A (method of the previous invention): No aging, no addition of ammonium fluoride B (first invention of the present invention): Aging, no addition of ammonium fluoride (Second invention of the present invention): With aging, with addition of ammonium fluoride etc. A Filtration speed (-500mmHg gauge vacuum filtration) A 6-8ton/m ² , Hr B 4-6〃 H 3-4〃 As mentioned above, the earlier invention is superior, but
Both B and C are not disadvantageous in terms of industrial implementation. B Potential sludge volume of filtration mother liquor (up to PH8
Neutralized with NH ₃ and then filtered) A. Standard amount (40-30Kg/P ₂ O ₅ ton) B. 10-20% reduction of standard amount (30-26Kg/
(P ₂ O ₅ ton) C. 50% reduction from the standard amount (30-4Kg/P ₂ O ₅ ton) The amount of potential sludge ultimately depends on the amount of impurities in the target material (monoammonium phosphate) and the amount of impurities mentioned above. It is related to the level of R (return rate). C Amount of impurities in mother liquor As shown in Table 1 below.

[Table] As shown in Table 1, aging alone does not reduce Ca, but significantly reduces Fe, F, and Mg. When aging and fluoride addition are combined, Fe, Mg
Not only that, but Ca also decreased significantly, while the increase in F was not significant. Note that the presence of F does not adversely affect the crystallization of monoammonium phosphate. The filtered mother liquor of RUN No. 5 described above is evaporated and concentrated and cooled to produce monoammonium phosphate crystals, which are centrifuged and washed with water to produce monoammonium phosphate with a yield of R=0.81. Obtained ammonium. Water-insoluble content (SS ^* ) of this product is 0.1
Weight%, _SO3 was 0.07%. These values are significantly superior to those in Example 1 of the previous invention, in which SS = 0.3% and SO ₃ = 0.28% when R = 58.5 (Note: *SS is
Dissolve 100 g of the obtained ammonium phosphoric acid in 100 ml of water, filter out water-insoluble substances in the solution, and dry the solution (% by weight based on the sample). As detailed above, according to the method of the present invention,
Without extracting the phosphoric acid content from the wet phosphate mother liquor, it is directly neutralized with ammonia under specific conditions, and impurities can be reduced by aging after neutralization or by adding ammonium fluoride etc. and aging, followed by filtration of the sludge. A wet phosphoric acid neutralized mother liquor can be obtained. By concentrating and crystallizing this mother liquor using a known method, industrial purified phosphoric acid can be obtained in high yield. In the method of the previous invention, this yield has an upper limit of R value of about 70.
%, it is possible to easily obtain an R value of 80% or more, so it can be said that this is an extremely effective improvement method for the previous invention. The present invention will be explained below with reference to Examples. Example 1 Wet phosphoric acid obtained by decomposing Florida phosphate ore with sulfuric acid (analytical values: P ₂ O ₅ 29.44%, SO ₃ 0.51%,
F0.38%, Ca0.23%, Mg0.15%, Fe0.58%,
Gas ammonia was blown into 2038 g of Al0.21%) over 70 minutes to neutralize the pH to 4.67. During this time, the temperature of the neutralization reaction solution was maintained at 90 to 100°C. The obtained sample was divided into four equal parts and subjected to aging and filtration treatment under the following conditions. RUN No. Aging conditions (all filtration after aging) 1 Aging at 90-100℃ for 1 hour 2 〃 , 5 〃 3 〃 , 1 〃 (Addition of NH ₄ F in an amount equivalent to dissolved Ca before the start of aging) 4 Aging at 90 to 100°C for 5 hours (adding NH ₄ F equivalent to dissolved Ca before starting aging) Filtration rate and impurity analysis values of the filtrates obtained in RUN No. 1 to 4 above, and The potential sludge amount was measured and is shown in Table 2 below.

【table】

[Table] Example 2 Using the purified monoammonium phosphate mother liquor obtained by processing in RUN No. 4 of Example 1, stepwise crystallization by evaporation concentration and cooling was repeated to obtain monoammonium phosphate at each step. Obtained crystals. These crystals are
After removing liquid by centrifugation, the liquid was removed in a centrifuge, and then washed with 80 ml of water per 1 kg of monoammonium phosphate, and the washing liquid was combined with the filtered mother liquor. As a result, the relationship between the extraction rate R (note: yield of P ₂ O ₅ ) and the quality of the crystallized product (note: monoammonium phosphate) at each stage was as follows.

[Table] As shown above, even when the extraction rate exceeds 80%, there is no rapid increase in water-insoluble components, and only a trace amount of SO ₃ is observed.

Claims (1)

[Claims] 1. A method for obtaining monoammonium phosphate by reacting wet phosphoric acid with ammonia, in which the reaction temperature is maintained at 70 to 110°C, and ammonia is reacted at 30 to 180°C.
to adjust the pH of the reaction solution to 4.5 to 4.8,
A method for obtaining purified ammonium phosphate in high yield, characterized in that a purified ammonium phosphate mother liquor obtained by filtering a sludge produced after being maintained at 80 to 110°C for 1 to 10 hours is used. 2. The method according to claim 1, wherein monoammonium phosphate is obtained by concentrating purified ammonium phosphate mother liquor. 3 In a method of obtaining monoammonium phosphate by reacting wet phosphoric acid with ammonia, the reaction temperature is maintained at 70 to 110 °C, and ammonia is reacted at 30 to 180 °C.
to adjust the pH of the reaction solution to 4.5 to 4.8,
Purified ammonium phosphate obtained by adding and mixing ammonium fluoride and/or acidic ammonium fluoride in an amount of 0.3 to 2 times the amount of dissolved calcium in the reaction solution, holding for 1 to 10 hours, and then filtering the resulting sludge. A method for obtaining purified ammonium phosphate in high yield, characterized by using a mother liquor. 4. The method according to claim 3, wherein monoammonium phosphate is obtained by concentrating purified ammonium phosphate mother liquor.