KR790001264B1 - Mehtod of clear ofr fluorine contain of wet phosphoric acic - Google Patents

Abstract

A process for removing F from conventional pond systems of wet process H3PO4 (WPA) plant is described. Thus, liquid effluents from the WPA plant, including scrubber liquor from gas scrubbing operations of the plant was mixed with the defluorination accelerating agent such as diatomaceous earth or silica gel and condensated in the swenson evaporator at 80-90≰C at 75-20mm Hg. Abs. to give the clarified phosphonic acid.

Description

How to remove fluorine in wet phosphoric acid

1 is a process for removing fluorine in wet phosphoric acid of the present invention.

Figure 2 is a chart showing the de-defect rate over time when the non-destimulation accelerator is added and non-injection in the present invention.

3 is a chart showing the defluorination rate with diatomaceous earth at a constant pressure of 200mmHg Ab's in the present invention.

The present invention relates to a method for removing fluorine contained in a phosphoric acid solution prepared by a wet process.

More specifically, diatomaceous earth or silica gel is added to remove fluorine contained in the phosphoric acid solution, and the phosphoric acid solution reaches the optimum concentration under reduced pressure using a Swenson Evaporator process. The present invention relates to a method of removing fluorine to a P / F ratio of 100 or more while continuously supplying water to maintain a constant concentration after heating and concentrating.

As is well known, the production of wet phosphoric acid is prepared by filtering a slurry obtained by reacting phosphate powder with sulfuric acid to separate gypsum, but wet phosphoric acid always contains fluorine, which is attributable to fluorine contained in phosphorite. The fluorine content varies depending on the origin of the phosphate ore.

In addition, when the fluorine content of phosphorus ore is 100%, in general, the income room of wet phosphoric acid manufacturing process shows that 0.5% is released to the atmosphere during the reaction process and 28.2% is released together to the gypsum water. The result is 7.1%, leaving 64.2% of the final wet phosphoric acid solution.

In general, when the method for preparing wet phosphoric acid is represented by the reaction scheme, Ca ₃ (PO ₄ ) ₂ ㆍ CaF ₂ + 4H ₂ SO ₄ + 8H ₂ O → 2H ₃ PO ₄ + 4CaSO ₄ 2H ₂ O + 2HF Phosphoric acid produced is generally 25 to 32% P ₂ O ₅ and 1 to 3% fluorine.

In addition, the components of the phosphoric acid solution produced industrially by the wet process are as follows.

P ₂ O ₅ : 30.0

Glass H ₂ SO ₄ : 2.25

F: 2.28

SiO ₂ : 1.02

Fe ₂ O ₃ and Al ₂ O ₃ : 2.0

As described above, the phosphate solution prepared by the conventional wet process always contains fluorine, so the P / F ratio (based on the fluorine content in the feed phosphate) is generally 3.64 to 17.46, which is used as raw material for livestock feed other than phosphate fertilizer. When used, it is a task to remove fluorine in the phosphoric acid solution at a P / F ratio of 100 or more. Feeding the livestock as a feed without removing fluorine and accumulating in the livestock body causes the growth and growth to be inhibited.

The present invention thus devised a method for removing fluorine contained in wet phosphoric acid in order to use wet phosphoric acid for feed other than fertilizer.

Although many studies and proposals have already been made in the United States, Japan and other countries on the dehydrofluorination method of wet phosphoric acid, all the methods up to now require complex facilities or the operating conditions of the existing phosphate concentration process (all domestic phosphate plants are Swenson Evaporator). There are many problems such as the risk of causing corrosion of the device and damage to the special rubber coating, so that the present inventors can use this existing Swenson concentrator as it is, without decommissioning easily and efficiently under the operating conditions without any electrical problems. To come up with a new way.

That is, the present invention is the most economical and easy way to prevent corrosion in the debulggi by applying a special rubber coating to the debulggi due to the suction pressure and high temperature (90 ℃ or more) according to the ultra-high vacuum degree (75mmHg · Abs) In order to prevent the damage of the special rubber coating, the special rubber coating can be repaired by maintaining the proper pressure (200mmHg · Abs) and temperature (up to 80 ℃) which does not damage the special rubber coating inside the debulgizer. By adjusting the concentration and temperature of the solution to 49% of P ₂ O _{5 and} below 90 ° C, it was possible to prevent corrosion of the device and the device due to high temperature and high concentration. In addition, when the phosphate solution is heated and concentrated by directly contacting superheated steam or combustion gas with the phosphate solution, the phosphate solution is indirectly heated through the heater to prevent the loss of the phosphate solution released together with the heating medium in the scattering state. The emphasis is on minimizing.

When the present invention will be described with reference to the drawings for ease of understanding, the diatomaceous earth solution and the wet phosphate solution are filled up to the operation level of the deaerator (3) through the diatomaceous earth tank 2 and the wet phosphate supply pipe 1 in FIG. After operating (4), saturated steam (9) is applied to the heater (8) while controlling the internal pressure of the degassing machine (3) by the gypsum water (6) and the automatic pressure regulating valve (7) supplied to the pressure condenser (5). After supplying the phosphate solution by heating for about 3 hours to concentrate and then the water corresponding to the amount of water vapor evaporated thereafter through the pipe (10) which is supplied to the de-bulder until the completion of de-fluorination (P / F 100 or more) Continue to feed over about 5 hours.

Fluorine in the phosphoric acid solution reacts with silicon in diatomaceous earth to boil off in the form of silicon fluoride (SiF ₄ ) and hydrogen fluoride by heat, blocking the supply of saturated steam (9) when the final P / F ratio is above 100 and forcing After stopping the circulation pump (4) and sending the defluorination phosphate solution to the product movement tank (12) through the product discharge pump (11) while making the internal pressure of the degassing machine (3) to atmospheric pressure, and then the product transport pump (13). It is sent to the product storage tank (14).

Diatomaceous earth (or silica gel) added to the phosphoric acid solution as a defluorination promoter used in the present invention is hydrated in water to make a 15-20% aqueous solution in consideration of increased diffusion of diatomaceous earth in the phosphoric acid solution and ease of handling. Put it in.

Addition amount of SiO ₂ / F equivalent ratio based on the fluorine content in the phosphoric acid solution is 1 ~ 1.1 (that is, 1g equivalent F = 19g SiO ₂ 1g equivalent = 15g Therefore SiO ₂ 1 equivalent / F1 equivalent = 15 ~ 16.5 / Add diatomaceous earth to the phosphate solution at the ratio of 19 = 0.8 ~ 0.87g / 1g).

At this time, there is no need to overfeed diatomaceous earth in order to further enhance the defluorination effect.

This is because part of the diatomaceous earth contained in the raw material phosphorite remains in the phosphate solution as it is, the oversupply of the diatomaceous earth does not have any effect on the promotion of deinflammation.

2 is a result of measuring the defluorination efficiency according to the time when the defluorination promoter is added to the wet phosphoric acid solution and the non-injection using an experimental apparatus, and the purpose is to determine whether or not to enter the defluorination promoter in connection with the present invention.

The experiment was performed by concentrating the P ₂ O ₅ 32% ((F: 2.4%) phosphate solution prepared by the wet process to 40.9% (F: 0.7%) and performing the following method.

Silica gel was added to the concentrated phosphoric acid solution by 1%, 1.5%, and 2.0%, respectively, as a defluorination promoter, and the dephosphorization experiment was performed while heating for 3 hours in the absence of a dehydrogenation accelerator on the other side.

As shown in FIG. 2, the defluorination rate of the non-deactivation accelerator was not more than 60%, but the defluorination rate of the silica gel was 1.0%, 1.5%, and 2.0%, respectively, as 86.4%, 87.6%, and 85.6%. As a result, it showed a significant increase of 25.6% ~ 27.6% than non-injection.

However, when comparing the defluorination rate according to the rate of defluoridation accelerator addition, the defluorination rate of 2.0% addition was lower than that of 1.0-1.5% addition. As a result, excessive dehydrogenation agent addition had an adverse effect on the defluorination rate.

The phosphoric acid solution in the deaerator is heated and deaerated by water vapor supplied to the heater.

Saturated water vapor is supplied to the shell side of the heater, and the phosphoric acid solution is flowed to the tube side to be heated to minimize the phosphate loss due to the direct heating method by conventional superheated steam and hot air. There are advantages to it.

The pressure inside the deaerator is controlled by the suction (vacuum) principle caused by the drop of water supplied to the barometric condenser, the suction by the ejector, and the valve for automatic pressure control. In this case, the pressure of saturated steam used in the heater is 3.5 ~ 4.2㎏ / ㎠ saturated steam when using the graphite tube according to the material of the tube, and the saturated steam pressure in the heater is 0.1 ~ 0.6㎏ / Maintain cm 2.

The defluorination effect in the phosphate solution depends on the internal pressure and the phosphate concentration of the deaerator.

The optimum concentration of phosphate solution at each pressure inside the deaerator is shown in the table below.

Degassing Internal Pressure and P ₂ O ₅ Optimal Concentration Table

Deaerator P ₂ O ₅ P ₂ O ₅ Titration

Internal pressure concentration range

760mmHg, Abs 38.6 27.6 ~ 40.1

600 ˝ 40.8 39.8 ~ 42.3

500 ˝ 42.2 41.4 ~ 43.2

400 ˝ 43.5 43.0 ~ 44.0

300 ˝ 44.9 44.5 ~ 45.5

200 ˝ 46.3 46.0 ~ 48.0

100 ˝ 47.7 47.0 ~ 49.0

75 ˝ 48.0 48.0 ~ 49.5

That is, the defluorination effect at a constant pressure depends on the concentration of phosphoric acid. Therefore, when the concentration that gives the maximum defluorination effect of the phosphoric acid solution is reached during heating and concentration of the phosphoric acid solution, water corresponding to the amount of water evaporated to prevent further concentration ( Or hot water, condensed water) by continuously supplying the following effects can be obtained.

First, the partial pressure of silicon fluoride (SiF ₄ ) gas is relatively decreased since the partial pressure of steam in the deaerator is increased.

Second, the decrease in the partial pressure of silicon fluoride results in a decrease in solubility according to Henry's law, resulting in the promotion of defluorination.

Third, it is possible to maintain an appropriate concentration showing the maximum defluorination effect at a given pressure.

3 shows the defluorination rate with time at a constant pressure of 200 mmHg · Abs.

As shown in this table, the defluorination rate is accelerated up to 3 hours after heating the phosphate solution, and 60% or more of fluoride is removed, but 25 ~ 30% of fluorine is added until 3 ~ 6 hours later. The defluorination rate is slowed down, and all the fluorides that can be removed (after 8 ~ 9 hours total) are removed (94 ~ 95%), and after that, they are almost horizontal, affecting the removal of fluoride in the phosphate solution. Do not give.

The process of removing fluorine is represented by chemical reaction formula as follows.

CaF ₂ + 2H ₂ SO ₄ 2H ₂ O ㅡ CaSO ₄ ㆍ 2H ₂ O + 2HF

2Al⁺²+4HF2AlF ₂ + 4H ⁺ +

2Al ⁺² + 4HF

6HF + SiO ₂ (diatomaceous earth) ㅡ H ₂ SiF ₆ + 2H ₂ O ㅡ (1)

H ₂ SiF6 + Heating ㅡ SiF ₄ + 2HF ㅡ (2)

(1) Equation + (2) Equation

4HF + SiO ₂ → SiF ₄ + 2H ₂ O

The silicon fluoride gas generated at this time is remarkably helpful in preventing pollution because it is absorbed and discharged into water in the form of the following product while reacting with water supplied to the pressure condenser.

3SiF ₄ + 2H ₂ O → SiO ₂ + 2H ₂ SiF ₆

Example 1

74.6 tons of P ₂ O ₅ 26.8% wet phosphoric acid solution (F: 1.07%) added with 490 kg of diatomaceous earth was added to ₂₀₀ mmHg.Abs. After concentrating to 44.6% of P ₂ O ₅ (F: 0.47%) under reduced pressure, and maintaining the temperature of the phosphoric acid solution at 85 to 86 ° C. while supplying water at a rate of 174 L per minute, the final P ₂ O ₅ concentration was 47.7%, The fluorine content was 0.2% (P / F Ratio 104), which took a total of 11 hours.

Example 2

Phosphoric Acid Solution Temperature 80 ~ 86 ℃, Pressure 190 ~ 200mmHg.Abs. 78 tons of wet phosphoric acid solution containing 28.7% P ₂ O ₅ concentration and 760 kg of diatomaceous earth under reduced pressure were concentrated to 42%, and condensed water was continuously supplied at 142 L / min. The final P ₂ O ₅ concentration was 48.4. It took 11 hours with% ~ 0.19% (P / F Ratio: 111).

Example 3

60 tons of a wet phosphoric acid solution having a concentration of 30.5% fluorine and 2.25% P ₂ O ₅ containing 1,700 kg of diatomaceous earth was degassed at 200 mmHg. Abs. After concentrating to 49.2% P ₂ O ₅ concentration under reduced pressure, condensate was fed at a rate of 116 L per minute. The final P ₂ O _{5 was} 47.7% fluorine: 0.17% (P / F Ratio 122).

The operating status range using the actual industrial scale apparatus for the present invention is as follows.

(1) P ₂ O ₅ concentration range

Initial concentration: 25.0 ~ 32.0%

Final concentration: 47.0 ~ 55%

(2) Fluorine Content

Initial Condition: 0.8 ~ 3%

Final condition: 0.168 ~ 0.24%

(3) P / F ratio

Initial Condition: 3.64 ~ 17.46

Final Condition: 100 ~ 122

(4) De-energizer internal pressure: 75 ~ 210

(5) Phosphate solution temperature range: 80 ~ 90 ℃

(6) One-time phosphoric acid throughput (100% P ₂ O ₅ ): 18.0 ~ 22.4 tons

Claims (1)

In removing fluorine contained in wet phosphoric acid, diatomaceous earth or silica gel, which is a non-inflammation accelerator, is added in an equivalent ratio according to the content of fluorine. Concentrating up to 49% and then defluorination to maintain a phosphate concentration in water, condensed water, hot water or steam while maintaining a constant P / F ratio of 100 ~ 122, characterized in that the removal of fluorine contained in the wet phosphoric acid.

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