JPH0760261A - Preparation of dephosphorization agent - Google Patents

Abstract

PURPOSE:To prepare easily and efficiently a particulate dephosphorization agent with a sufficient strength by a method wherein a precipitate of iron hydroxide obtd. by neutralizing a water soln. contg. iron ion is dried and after the semi-dried article is granulated, it is dried at a specified temp. CONSTITUTION:An alkali such as sodium hydroxide and calcium hydroxide is incorporated into a water soln. contg. an iron compd. e.g. a water soln. of an iron compd. such as iron chloride and iron sulfate to neutralize it and to precipitate iron hydroxide. This precipitate is pref. dehydrated by means of a filter press, a centrifugal separator, etc., to make a dehydrated cake with a water content of about 60-80% and then, this dehydrated cake is dried at a temp. of the article of at most 120 deg.C to obtain a semi-dried article with a water content of 20-50%, which is then granulated by means of a centrifugally rotating fluidized bed granulation or an extrusion granulation. Thereafter, a required granulated dephosphorization agent is prepd. by a method wherein the granulated article of iron hydroxide is dried at a temp. of the article of at most 120 deg.C to make the water content to about 5%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a dephosphorizing agent, and more particularly to a method for producing a granular dephosphorizing agent containing iron hydroxide as a main component.

[0002]

2. Description of the Related Art In recent years, in closed water areas such as the Seto Inland Sea, Lake Biwa and Kasumigaura, deterioration of water quality due to eutrophication phenomenon has been further promoted, and obstacles to water utilization have increased, which has become a major social problem. The causative substances are said to be nitrogen and phosphorus, and in particular, the removal of phosphate ions in wastewater has become an important issue to be solved immediately.

Conventionally, as a method of removing phosphorus, coagulation sedimentation method A chemical containing metal ions such as iron, calcium, and aluminum is injected into wastewater containing phosphoric acid to precipitate and remove phosphoric acid as a sparingly soluble phosphate. Crystallization method Calcium is added to the wastewater containing phosphoric acid to make the pH alkaline and water is passed through the phosphate rock to crystallize and dephosphorize it as hydroxyapatite. There is a method such as.

However, the coagulation-sedimentation method has a problem that a large amount of sludge is generated and the operation management is complicated. On the other hand, the crystallization method has a problem that an advanced management technique is required and the apparatus is complicated. However, none of them was industrially advantageous.

As a solution to such a problem, various phosphorus removing techniques utilizing a dephosphorizing agent containing iron hydroxide (iron oxide hydrate) as a main component have been proposed.

The phenomenon in which iron hydroxide adsorbs phosphorus in water is known from literatures and the like, and for example, "Removal of phosphorus by a gel composite adsorbent" (Environmental Technology Vol. 7, No. 4).
(1978) Shigetomi, Watanabe, and Hori), α-oxyhydrated iron, β-oxyhydrated iron, and γ-oxyhydrated iron adsorb anions and cations well, and particularly β-oxyhydrated iron. Has been reported to adsorb phosphate ions well. The α, β, γ-iron oxide hydrate used here is a dry powder.

[0007] Also, "Phosphorus elution mechanism from the bottom material from the viewpoint of iron oxidation, hydroxylation and adsorption processes" (Water Pollution Research, Vo
l. 14, No. 4 (1991) Kobayashi, Nishimura), it is reported that phosphorus is adsorbed on ferric hydroxide and iron (III) hydrate oxide in lake sediments. This is an adsorption phenomenon due to iron compounds in a muddy state.

Further, "Adsorption of phosphorus from water by bottom mud and its factors" (Kumamoto Prefectural Institute of Public Health No. 13 (19)
83) Yoshinaga, Kubo, Tatsuoka, Nagayama) has been reported that ferric hydroxide adsorbs phosphate ions well.

Therefore, as a method utilizing the phenomenon that iron hydroxide adsorbs phosphorus in water in this way, a method of removing phosphate ions in waste water by powdered iron hydroxide has been proposed (Japanese Patent Laid-Open No. Sho 61-61). 153192).

However, the powdery dephosphorizing agent requires a solid-liquid separation step after adsorbing phosphorus by mixing with the waste water. Therefore, a granular dephosphorizing agent that can be used in a fixed bed system that does not require a solid-liquid separation step is desired. In this case, in the fixed bed system, backwashing is indispensable for removing the clogging of the dephosphorizing agent, and the granular dephosphorizing agent is required to have a strength capable of withstanding the impact during the backwashing. That is, if the strength of the granular dephosphorizing agent is low, the dephosphorizing agent is destroyed by the impact during backwashing and becomes powdery, which may flow out into the treated water or cause clogging of the dephosphorizing agent. Cause By the way, the required breaking strength of the granular dephosphorizing agent is 8 kgD.
It is WL or more.

Conventionally, various methods have been proposed as a method for producing a granular dephosphorizing agent containing iron hydroxide as a main component. For example,
Regarding "Removal of phosphorus by gel composite adsorbent" (Environmental Technology Vol.7, No.4 (1978) Shigetomi, Watanabe, Hori), an adsorbent obtained by solidifying iron oxyhydrate with an organic polymer gel has been proposed. There is. In addition, Japanese Examined Patent Publication No. 61-47134,
Japanese Patent Publication No. 62-1299 proposes curing with an unsaturated polyester resin or polyurethane resin. These conventional methods for producing granular dephosphorizing agents are methods in which iron hydroxide is once made into a dry powder and then molded and cured.

[0012]

However, in all of the conventional methods for producing a granular dephosphorization agent, in addition to the active ingredient for dephosphorization, an auxiliary raw material component for ensuring strength is required. , I had the following problems. The phosphorus adsorption capacity of the dephosphorizing agent obtained decreases depending on the blending amount of the auxiliary raw material components used for molding and curing. The material cost of the auxiliary raw material components and the processing cost for mixing the auxiliary raw material components are required, and as a result, the manufacturing cost is significantly increased.

The present invention solves the above-mentioned conventional problems and facilitates the preparation of a granular dephosphorizing agent having a sufficient strength substantially only from the active ingredient of the dephosphorizing agent, that is, iron hydroxide, without using auxiliary raw material components. It aims at providing the manufacturing method efficiently.

[0014]

The method for producing a dephosphorizing agent according to claim 1 is a method for producing a dephosphorizing agent, wherein the precipitation of iron hydroxide obtained by neutralizing an aqueous solution containing iron ions is dried at a product temperature of 120 ° C. or lower to obtain a water content. 20
It is characterized in that it is a semi-dried product having a water content of 20 to 50% without being made less than%, and the semi-dried product is granulated and then dried at a product temperature of 120 ° C. or lower.

The method for producing a dephosphorizing agent according to claim 2 is a dried product having a water content of less than 20% obtained by drying an iron hydroxide precipitate obtained by neutralizing an aqueous solution containing iron ions at a product temperature of 120 ° C or lower. While spraying water with a mist diameter of 30 to 300 μm on this dried product, it was granulated by a centrifugal tumbling type or centrifugal tumbling flow type granulator at a granulation time of 5 minutes or more, and then the granulated product was heated to the product temperature. 12
It is characterized by being dried at 0 ° C. or lower.

The present invention will be described in detail below. First, a method for producing the dephosphorizing agent according to claim 1 will be described.

In the method of claim 1, first, the aqueous solution containing iron ions is neutralized to precipitate iron hydroxide. Specifically, an alkali such as sodium hydroxide or slaked lime is added to an aqueous solution of an iron compound such as iron chloride or iron sulfate to precipitate iron hydroxide. Alternatively, since iron ions are contained in the wastewater discharged from the metal surface treatment plant, the wastewater can be neutralized with an alkali to obtain a precipitate of iron hydroxide. Further, since iron ions are also contained in the mine water of the metal mine, it is possible to obtain a precipitate of iron hydroxide by the same neutralization treatment as above. Regarding metal surface-treated wastewater and mine water, iron hydroxide is generally precipitated as wastewater treatment and is disposed of as landfill waste. Therefore, these wastewater and mine water are used in the present invention. By
The amount of waste can be reduced, and the cost of raw materials can be reduced.

The iron hydroxide precipitate thus obtained is preferably dehydrated by a filter press, a centrifuge, a belt press or the like to obtain a dehydrated cake having a water content of about 60 to 80%, and then the dehydrated cake. The cake is dried at a temperature of 120 ° C. or lower to obtain a semi-dried product having a water content of 20 to 50% without reducing the water content to less than 20%.

When the drying temperature exceeds the product temperature of 120 ° C., the phosphorus removing ability of the obtained dephosphorizing agent decreases, so the drying temperature is set to 120 ° C. or less, preferably 100 ° C. or less. The reason why the phosphorus removing ability decreases when the drying temperature is high is considered to be that iron hydroxide is changed to iron oxide having no phosphorus removing ability. This drying may be air drying with normal temperature air or warm air. Here, even if the temperature of the hot air exceeds 120 ° C., the product temperature of the dehydrated cake does not rise to 100 ° C. or more because heat is taken away by evaporation of water while the water content is high. Therefore, as long as the product temperature of the dehydrated cake does not exceed 120 ° C, the temperature of the warm air can exceed 120 ° C and be set to 150 ° C, for example.

The drying is preferably carried out while kneading the dehydrated cake with a mixer, whereby not only the surface of the dehydrated cake but also the inside of the dehydrated cake can be dried uniformly.

Further, in order to shorten the drying time, the inside of the mixer may be depressurized and dried.

Once the water content of the semi-dried product by such drying is set to less than 20%, the granulated product obtained even if water content is readjusted to 20% or more by adding water in the subsequent granulation step. The strength may be insufficient. On the other hand, a high-strength granulated product can be obtained by using a semi-dried product having a water content of 20% or more without reducing the water content of the semi-dried product to less than 20%. Although the details of the principle of such action and effect are unknown, it is presumed that if the water content of the semi-dried product is 20% or more, the iron hydroxide molecule in the polymer state shown by the following structural formula is cleaved. It is considered that the iron hydroxide molecules retain the polymer state and form high-strength granules without being separated into small iron hydroxide molecules (portions surrounded by broken lines). In the conventional method for producing a granular dephosphorizing agent, since the strength of the granulated product was insufficient, an auxiliary material for ensuring the strength had to be required, but according to the method of the present invention, a sufficiently high strength is obtained. Since such a granulated product can be obtained, such an auxiliary material is unnecessary. On the other hand, when the water content of the semi-dried product exceeds 50%, the amount of water is too large and granulation becomes difficult. Therefore, the water content of the semi-dried product is not less than 20%, that is, the water content is 20 to 50% directly from the wet state without being dried once to less than 20% and then adjusted with water. To adjust the drying conditions.

[0023]

[Chemical 1]

The semi-dried product is then granulated by centrifugal rolling fluidized bed granulation or extrusion granulation to obtain granules. According to centrifugal rolling fluidized bed granulation, spherical granules
Further, extrusion granulation gives a cylindrical granulation product. In the present invention, the particle size of these granules is 0.3 to 10 m.
It is preferably about m.

The iron hydroxide granules thus obtained are dried at a product temperature of 120 ° C. or lower to a water content of about 5% to obtain a granular dephosphorizing agent. Even in this drying
When the drying temperature is higher than the product temperature of 120 ° C, the phosphorus removing ability of the obtained dephosphorizing agent is lowered, so the drying temperature is set to the product temperature of 120 ° C or lower, preferably 100 ° C or lower. This drying may be air drying with normal temperature air or warm air. Similar to the case of the semi-drying described above, this drying is also performed under reduced pressure, so that the drying time can be shortened.

Next, a method for producing the dephosphorizing agent of claim 2 will be described. Also in the method of claim 2, first, a precipitate of iron hydroxide is obtained in the same manner as the method of claim 1 described above.

The obtained iron hydroxide precipitate is preferably dehydrated by a filter press, a centrifuge, a belt press or the like to give a dehydrated cake having a water content of about 60 to 80%, and the dehydrated cake is then dried. The product is dried at a temperature of 120 ° C. or lower to obtain a dried product having a water content of less than 20%.

Here, if the drying temperature exceeds the product temperature of 120 ° C., the phosphorus removing ability of the obtained dephosphorizing agent decreases, as described above. Therefore, the drying temperature is 120 ° C. or less, preferably 1.
The temperature is set to 00 ° C or lower. The drying may be air drying with normal temperature air or warm air, but the drying time can be shortened by performing the drying under reduced pressure. As described above, even if the temperature of the hot air exceeds 120 ° C., the product temperature of the dehydrated cake does not rise to 100 ° C. or higher because heat is taken away by evaporation of water while the water content is high. Therefore, as long as the product temperature of the dehydrated cake does not exceed 120 ° C, the temperature of the warm air can exceed 120 ° C and be set to 150 ° C, for example. The drying does not have to be performed while kneading the dehydrated cake with a mixer.

The dried product is then pulverized with a particle size of 5 to 50 mm.
After pulverizing to a certain degree, while granulating with water having a mist diameter of 30 to 300 μm, granulation is performed with a centrifugal tumbling type or centrifugal tumbling fluid type granulator.

In this granulation, when the mist diameter of the sprayed water exceeds 300 μm, the water does not reach the entire dry matter (dry powder), and the water-containing particles and dry powder are mixed. Therefore, the resulting granulated product is such that the dry powder adheres to the surface of the particle, and the strength of the granulated product surface becomes weak. Further, regarding the size of the particles, a mixture of large particles and small particles is obtained, and the granulated product has a nonuniform particle diameter. It is possible to increase the amount of water sprayed to completely eliminate dry powder and increase the strength of the granulated product, but in this case, the granulated product will have a very large particle size, so destroy this. It is necessary to make granules with a small particle size, and there is a drawback that the granulation time becomes long. On the contrary, when the mist diameter is less than 30 μm, the mist drifts in the air like the mist of the ultrasonic humidifier, and the dry powder cannot be sufficiently sprayed. Further, the mist drifting in the air increases the humidity in the container of the granulator and causes dew condensation on the inner wall of the container to cause the same problem as in the case where the large-diameter mist is sprayed.

For this reason, the mist diameter of the sprayed water is 30 to 300 μm, preferably about 50 to 100 μm.

The amount of water sprayed is preferably such that the water content of the dried product (dry powder) is about 35-40%. If the amount of water spray is too small or too large, it is difficult to granulate, and it is difficult to obtain a strong granulated product.

Further, the granulation time in the centrifugal tumbling type or centrifugal tumbling flow type granulator is 5 minutes or more. That is, in the normal case,
The granulation time by this type of granulator is about 1 to 3 minutes, but in the method of claim 2, the granulation time is 5 minutes or more,
It is preferably about 6 to 10 minutes. By adopting such a relatively long granulation time, the following effects are exhibited. That is, the primary particles formed within 1 to 3 minutes from the start of granulation collide with each other as the granulation continues, and the bubbles in the particles escape to gradually become dense particles. Also,
The surfaces of the particles are rubbed against each other and subjected to a force such as stroking the surfaces to form a granulated product having a smooth and strong surface.

Also in the method of claim 2, the particle size of the granulated product thus obtained is preferably about 0.3 to 10 mm. The obtained iron hydroxide granules have a product temperature of 12
A granular dephosphorizing agent is obtained by drying at 0 ° C. or lower to a water content of about 5%. Also in this drying, if the drying temperature exceeds the product temperature of 120 ° C., the phosphorus removing ability of the obtained dephosphorizing agent decreases, so the drying temperature is set to 120 ° C. or less, preferably 100 ° C. or less. This drying may be air drying with normal temperature air or warm air. Similar to the case of the semi-drying described above, this drying is also performed under reduced pressure, so that the drying time can be shortened.

The granular dephosphorizing agent thus obtained is
The dephosphorization treatment can be easily performed by filling the column or the like with water to be treated. In this dephosphorization treatment, if the particle size of the granular dephosphorization agent is too small, clogging by suspended substances in the raw water is likely to occur, and conversely if it is too large, the specific surface area will be small, and the surface area ratio that contributes to the dephosphorization reaction. Becomes smaller, the dephosphorization performance decreases. Therefore, the particle size of the granular dephosphorizing agent is 0.3 to 10 m as described above.
It is preferably m.

[0036]

[Function] Once iron hydroxide is completely dried, granulation is difficult even if water is added again, and the strength after molding is often low. On the other hand, according to the method of claim 1, the semi-dried product which is not completely dried and has a certain amount of water is granulated and then dried, without using an auxiliary raw material for granulation. It is possible to obtain a granular material having a strength that can be industrially sufficiently used as a granular dephosphorizing agent.

On the other hand, in the method of claim 2, once the water content is 2
Although it is dried to less than 0%, a sufficiently high-strength granular material can be obtained by granulating with a specific granulator for a specific time or longer while spraying water with a specific mist diameter on it.

According to the present invention, normally, 8 kg DW
A granular dephosphorizing agent having a breaking strength of L or more can be produced.

[0039]

EXAMPLES The present invention will be specifically described below with reference to experimental examples, examples and comparative examples, but the present invention is not limited to the following examples unless it exceeds the gist.

Experimental Example 1 To a pH of 7 was added caustic soda to a 10 wt% iron sulfate aqueous solution, and the obtained iron hydroxide precipitate was dehydrated, then at 20 to 300 ° C.
Was dried at each temperature. Then, it grind | pulverized with the mortar and classified with the sieve, and obtained the particle | grains of 250-500 micrometers. 1 g of the particles was added to 1 liter of an aqueous Na ₂ HPO ₄ solution (50 mg-P / l), and the mixture was stirred with a stirrer for 3 hours in a beaker. After filtration at 5C, the phosphorus concentration of the filtrate was measured. For each dry powder, from the decrease amount of phosphorus concentration,
The phosphorus removal amount (mg-P / g) per 1 g of iron hydroxide particles was calculated, and the results are shown in FIG.

As shown in FIG. 1, when the drying temperature exceeds the product temperature of 120 ° C., the phosphorus removing ability decreases, so that the drying temperature is the product temperature of 120 ° C.
It can be seen that the temperature needs to be kept at or below ° C.

Examples 1 to 4, Comparative Examples 1 and 2 Caustic soda was added to a 10% by weight aqueous solution of iron sulfate to adjust the pH to 7, and the resulting iron hydroxide precipitate was dehydrated with a filter press to a water content of 61% and then dehydrated cake. While being kneaded in a mixer, it was semi-dried at 90 ° C. under reduced pressure so that the water content shown in Table 1 was obtained. When drying 10 kg of the dehydrated cake having a water content of 61% to a water content of 38%, the inner wall of the mixer was heated to 90 ° C. and the vacuum degree was reduced to −600 mmHg. Met.

The obtained semi-dried product was granulated with a centrifugal tumbling fluidized granulator to a size such that 90% or more of the particles had a particle size of 1 to 2 mm. Water content 18, 20, 25%
The semi-dried product (1) was granulated after adding water to adjust the water content to 38%, which is suitable for granulation. Next, the granulated product was air-dried at room temperature for 2 days to be dried to a water content of about 5%. In Comparative Example 2 in which a semi-dried product having a water content of 52% was obtained by semi-drying, granulation could not be performed.

The breaking strength of the obtained granules is shown in Table 1. In addition, 1 g of the granules obtained in Examples 1 to 4 and Comparative Example 1 was added to 1 liter of an aqueous solution of Na ₂ HPO ₄ (50 mg-
P / l), the phosphorus removal amount was determined in the same manner as in Experimental Example 1, and the results are shown in Table 1.

[0045]

[Table 1]

The obtained granular material was packed in a column at a height of 1 m as a dephosphorizing agent, and secondary treated water for domestic wastewater of a condominium (phosphorus concentration: about 3 mg-P / l) was used as raw water for SV.
= 3 (m ³ / m ³ · hr). The changes over time in the phosphorus concentration of raw water and treated water (column outflow water) are shown in FIG.

The following is clear from Table 1 and FIG. That is, once the dehydrated cake is dried to a water content lower than 20%, the strength of the granulated product is insufficient even if water is added again.
On the contrary, if the water content by semi-drying is higher than 50%, the amount of water is too large to granulate. Also, regarding dephosphorization performance,
It is preferable to granulate a semi-dried product having a water content of 20 to 50%.

Examples 5 and 6 and Comparative Examples 3 to 5 Caustic soda was added to a 10 wt% iron sulfate aqueous solution to adjust the pH to 7, and the resulting iron hydroxide precipitate was dehydrated with a filter press to a water content of 61% and then dehydrated cake. Was dried in a dryer at 90 ° C. to a water content of 10%.

The dried product thus obtained was subjected to a centrifugal tumbling fluidized granulator to give water having a mist diameter shown in Table 2 to a water content of 3 suitable for granulation.
While spraying at 8%, 90% or more of the particles were granulated within the range of 1 to 2 mm for the granulation time shown in Table 2. Next, the granulated product was air-dried at room temperature for 2 days to be dried to a water content of about 5%. The breaking strength of the obtained granules is shown in Table 2.

[0050]

[Table 2]

From Table 2, it is clear that the method of claim 2 can provide high strength granules. On the other hand, in Comparative Example 3 in which the mist diameter is small, the dry powder remains, and high-strength granular material cannot be obtained. Further, even in Comparative Example 4 having a large mist diameter, high-strength granular material cannot be obtained. Furthermore, in Comparative Example 5 in which the granulation time was short, the properties of the granules were inferior.

[0052]

As described in detail above, according to the method for producing a dephosphorizing agent of the present invention, a granular dephosphorizing agent consisting essentially of iron hydroxide can be used without using an auxiliary raw material component for granulation. Therefore, a product having sufficient strength can be easily and efficiently manufactured.

The granular dephosphorizing agent produced by the present invention can be packed in a column and subjected to dephosphorization treatment, and is extremely excellent in workability and handleability.

[Brief description of drawings]

FIG. 1 is a graph showing the results of Experimental Example 1.

FIG. 2 is a graph showing the results of a water flow test in Examples 1 to 4 and Comparative Example 1.

Claims (2)

[Claims] 1. A semi-drying method in which a precipitate of iron hydroxide obtained by neutralizing an aqueous solution containing iron ions is dried at a product temperature of 120 ° C. or lower to have a water content of 20 to 50% without reducing the water content to less than 20%. A method for producing a dephosphorizing agent, which comprises granulating the semi-dried product and then drying at a product temperature of 120 ° C. or less. 2. A precipitate of iron hydroxide obtained by neutralizing an aqueous solution containing iron ions is dried at a product temperature of 120 ° C. or lower to obtain a dried product having a water content of less than 20%, and the dried product has a mist diameter of 30 to 30.
The method is characterized by granulating for 5 minutes or more with a centrifugal tumbling type or centrifugal tumbling flow type granulator while spraying water of 300 μm, and then drying the granulated product at a product temperature of 120 ° C. or less. Method for producing dephosphorizing agent.