JP2650616B2 - Method for producing phosphoric acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing phosphoric acid, and more particularly to a method for producing phosphoric acid by efficiently removing and recovering phosphorus from phosphorus-containing wastewater.

[0002]

2. Description of the Related Art Phosphorus is contained in agricultural chemicals, detergents, fertilizers, manure, etc., and phosphorus contained in various industrial wastewaters and domestic wastewater is discharged together with nitrogen in water quality due to eutrophication of river water. It is necessary to release phosphorus after removing phosphorus in the phosphorus-containing wastewater because it causes deterioration and environmental pollution.

[0003] Conventionally, phosphorus in phosphorus-containing wastewater is adsorbed and removed using a dephosphorizing agent such as iron hydroxide or subjected to a biological dephosphorization treatment.

On the other hand, phosphoric acid, which is a raw material of agricultural chemicals, detergents, fertilizers and other various treating agents, is conventionally produced from a dry method: yellow phosphorus. Or Wet method: Produced by decomposing phosphate rock with sulfuric acid or a mixed acid of sulfuric acid and phosphoric acid. It is manufactured by.

Conventionally, among these methods for producing phosphoric acid,
Although high purity phosphoric acid can be obtained by the dry method,
Due to the high cost, the wet method is mainly used.

[0006]

The wet method can produce phosphoric acid at a lower cost than the dry method, but phosphorus ore, which is a raw material of the wet method, is hardly produced in Japan.
There is a problem with the source. Further, even if the wet method is used, the cost is not sufficiently low, and further cost reduction is desired.

On the other hand, in the phosphorus removal treatment of phosphorus-containing wastewater, it is preferable from the viewpoint of effective use of resources if the phosphorus removed from the wastewater can be recovered and reused. At present, no recovery and reuse method has been proposed.

[0008] It is an object of the present invention to solve the above-mentioned conventional problems and to provide a method for producing phosphoric acid that can efficiently remove phosphorus from phosphorus-containing wastewater and recover it as phosphoric acid.

[0009]

According to a first aspect of the present invention, there is provided a method for producing phosphoric acid, wherein phosphorus-containing water is passed through a packed bed of calcium-based particles containing calcium oxide and / or calcium hydroxide.
Thereby, the calcium-based particles are brought into contact with phosphorus-containing water to form calcium phosphate on the particle surfaces, then the particle surfaces are peeled off, the peeled materials are classified, and the resulting fine powder is contacted with sulfuric acid to obtain phosphorus. Generate acid and calcium sulfate,
It is characterized in that it is separated and the phosphoric acid is recovered.

[0010] The method for producing phosphoric acid according to claim 2 is based on claim 1.
Wherein the calcium-based particles are granules of cement and / or fluidized bed ash or pulverized ALC.

Hereinafter, the present invention will be described in detail.

In the present invention, the calcium-based particles containing calcium oxide and / or calcium hydroxide include:
There is no particular limitation as long as it contains lime, and for example, the following can be used.

[I] Granules obtained by granulating cement such as Portland cement and alumina cement and / or fluidized bed ash. The granulated raw material may be used by mixing fine coal ash in order to reduce the weight and increase the specific surface area of the granulated material. When granulating cement and fluidized bed ash, the use ratio of the fluidized bed ash is preferably about 100 to 10% by weight based on the cement. When pulverized coal is further used, pulverized coal is 900 to 700% by weight based on cement, 30 to 20% by weight based on fluidized bed ash, and 30 to 10% by weight based on total cement and fluidized bed ash. Is preferred. When foaming, an aluminum powder as a foaming agent is further added. The addition amount of the aluminum powder is 0.1 to 0.2% by weight based on the total amount of cement or cement and fluidized bed ash, or cement, fluidized bed ash and pulverized coal. Is preferred.

[II] Pulverized ALC. ALC is especially AL
Advantageously, C waste is used. Of the ALC crushed materials,
Those having a large particle size can be used as calcium-based particles as they are. Moreover, if it is a finely pulverized product of ALC, cement or quick lime can be added and granulated as necessary before use.

[0015] Cured particles are produced by adding an appropriate amount of water to the calcium-based powder, granulating and drying. That is, hard particles are produced by a hydration reaction of lime contained in the granulated particles (formation of tobermorite and ettringite). The hydration reaction can be promoted by performing steam curing, and the strength of the granulated product can be increased. When aluminum powder is added, the specific surface area of the granulated material increases due to hydrogen gas generated during the reaction between slaked lime and aluminum powder. Thereby, the contact area with the phosphorus in the phosphorus-containing wastewater increases, and the phosphorus can be efficiently removed. After primary curing,
It is preferable to perform high-pressure curing.

The general composition of cement, fluidized bed ash, ALC, and pulverized coal ash, which are the main raw materials of the calcium-based particles, is as follows.

[0017]

[Table 1]

Such calcium-based particles have a particle size of 5 to 5 from the viewpoints of handleability and contact efficiency with phosphorus-containing water.
It is preferably about 30 mm.

[0019] In the present invention, contact between the calcium-based particles and phosphorus-containing water is performed by passing water a phosphorus-containing water to the reactor to form a packed bed of calcium-based particles in a downflow or upflow .

When the calcium-based particles come into contact with the phosphorus-containing water, the lime in the calcium-based particles reacts with the phosphoric acid in the phosphorus-containing water to form calcium phosphate on the surface of the calcium-based particles. Since the calcium phosphate generating layer on the surface of the calcium-based particles is brittle and easily peeled off, the calcium-based particles having calcium phosphate generated on the surface are taken out and treated with a ball mill, a rod mill, etc., so that the calcium phosphate generating layer on the particle surface is easily peeled off. Can be taken.

Fine powder obtained by classifying the exfoliated product with a sieve,
Usually, fine powder having a particle size of 600 μm or less contains calcium phosphate at a high concentration.

Therefore, by contacting the fine powder with sulfuric acid, a precipitate of phosphoric acid and calcium sulfate can be obtained.
Phosphoric acid can be recovered by filtering and separating the precipitated calcium sulfate.

In order to precipitate calcium phosphate having good filterability, the sulfuric acid used here has a concentration of 5%.
A high concentration of about 0 to 100% by weight is suitable, and the processing temperature is preferably 60 to 100 ° C.

In the present invention, the calcium-based particles from which the calcium phosphate-forming layer on the surface has been peeled off can be reused for treating the phosphorus-containing water. In addition, the one whose particle size becomes excessively small by repeated use may be used as a granulation raw material for producing calcium-based particles, or may be used for another purpose.

Further, particles on a sieve obtained by classifying the exfoliated product and fractionating the fine powder can also be used as a granulation raw material for producing calcium-based particles.

[0026]

The calcium-based particles containing lime react with the phosphoric acid in the phosphorus-containing water to form calcium phosphate on the surface. Since the calcium phosphate generating layer on this surface is a brittle layer, it can be easily peeled off.

The fine powder obtained by classifying the exfoliated material contains calcium phosphate at a high concentration. By contacting the fine powder with sulfuric acid, a precipitate of phosphoric acid and calcium sulfate can be obtained. By separating the precipitate of calcium sulfate, high-purity phosphoric acid can be efficiently recovered.

According to the method of claim 2, phosphoric acid can be produced more efficiently.

That is, as the calcium-based particles, cement containing a relatively large amount of excess CaO, fluidized bed ash,
ALC and the like are preferable, and these are easy to granulate, and are excellent in the reaction efficiency with phosphoric acid in phosphorus-containing water.

In particular, when fluidized bed ash or ALC waste material is used, waste can be effectively used, which is industrially advantageous.

[0031]

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

In the following, the following calcium-based particles were used.

A: Cement granulated material = 250 g of water added to 1 kg of cement, kneaded, and granulated to an average particle diameter of 10 mm.

B: Cement + fine coal ash granules = 100 g of cement and 900 g of fine coal ash, 1 kg of water is added and kneaded,
Granulated to an average particle size of 10 mm.

C: Fluidized bed ash granulated product: 450 g of water was added to 1 kg of fluidized bed ash and kneaded, and the mixture was granulated to an average particle diameter of 10 mm.

D: Cement + fluidized bed ash granulated product = 500 g of cement and 500 g of fluidized bed ash, 1 kg of water is added and kneaded.
Granulated to an average particle size of 10 mm.

E: Granulated cement (foamed) = Cement 1
250 g of water was added to the kg and kneaded, 1.2 g of aluminum powder was further added, and the mixture was granulated to an average particle diameter of 10 mm.

F: cement + fluidized bed ash granulated product (foamed) =
1 kg of water was added and kneaded to 500 g of cement and 500 g of fluidized bed ash, and 1.2 g of aluminum powder was further added to granulate to an average particle diameter of 10 mm.

G: Cement + fluidized bed ash + fine coal ash (foamed) = 200 g of cement, 200 g of fluidized bed ash and 600 g of fine coal ash, 1 kg of water was added and kneaded, and 1.2 g of aluminum powder was further added, and the average particle size was adjusted. Granulated to a diameter of 10 mm.

H: ALC crushed material = ALC waste material crushed to an average particle size of 10 mm.

The composition of the materials used is as follows.

[0042]

[Table 2]

Example 1 A reactor was charged with 2 kg of each of the calcium-based particles A to E, and phosphorus-containing wastewater (phosphoric acid concentration: 2 mg / l) was added to a reactor.
Water was passed in a downward flow at a rate of ml / min for 1 hour.

Thereafter, the calcium-containing particles having a brittle layer formed on the surface were taken out of the reactor by passing phosphorus-containing wastewater, and treated with a ball mill to peel off the surface layer.
The exfoliated material was classified with a sieve, and fine powder having a particle size of 600 μm or less was collected.

After adding 75% by weight of sulfuric acid to the obtained fine powder and stirring at 100 ° C., the mixture was filtered with filter paper.

As a result, calcium sulfate was filtered off on the filter paper, and phosphoric acid was recovered in the filtrate.

The phosphoric acid recovery rate was calculated from the ratio of the recovered phosphoric acid to the total amount of phosphoric acid in the phosphorus-containing wastewater passed through the reactor, and the results are shown in Table 3.

[0048]

[Table 3]

As is clear from Table 3, according to the present invention, phosphoric acid can be efficiently produced using phosphorus-containing wastewater.

[0050]

As described in detail above, according to the method for producing phosphoric acid of the present invention, phosphoric acid can be produced efficiently from phosphorus-containing water.

According to the method of the present invention, the phosphoric acid contained in the phosphorus-containing wastewater can be removed and recovered and effectively reused, which is industrially extremely advantageous.

According to the method of claim 2, phosphoric acid can be produced more efficiently.

Claims (2)

(57) [Claims] 1. A method according to claim 1 , wherein phosphorus-containing water is passed through a packed bed of calcium-based particles containing calcium oxide and / or calcium hydroxide.
By watering, the calcium-based particles are brought into contact with the phosphorus-containing water to form calcium phosphate on the particle surfaces, then the particle surfaces are peeled off, the peeled materials are classified, and the resulting fine powder is brought into contact with sulfuric acid. Producing a phosphoric acid and calcium sulfate, and separating and recovering the phosphoric acid. 2. The method according to claim 1, wherein the calcium-based particles are granulated cement and / or fluidized bed ash.
A method for producing phosphoric acid, which is a pulverized product of ALC.