JPS60110393A - Material for removing phosphoric acid in water - Google Patents

Abstract

PURPOSE:To develop phosphoric acid removing capacity equal to that of a crystallized material based on magnesia clinker being a matrix material, by using a material prepared by fixedly depositing magnesium oxide and calcium salt to the surface of a granular solid substance having absolute specific gravity of a specific value or less and insoluble in water. CONSTITUTION:A granular solid substance having absolute specific gravity of 3.5 or less and insoluble in water, for example, silica sand, silica stone or zeolite is immersed in a slurry containing 10-30% of magnesium oxide while the impregnated solid substance is baked at 1,000-2,000 deg.C to fixedly deposit magnesium oxide to the surface thereof. In the next step, the baked substance is immersed in a solution containing a proper amount of calcium chloride and calcium hydroxide and the impregnated substance is heated and dried at 120-200 deg.C for about 2hr to further fixedly deposit the calcium salts.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of the Invention The present invention relates to a phosphoric acid removal method for removing phosphate from water by crystallizing it under predetermined conditions.

(2) Background technology Various types of wastewater discharged into natural water systems contain various forms of phosphates, and the presence of these phosphates is believed to be a major cause of eutrophication in closed water bodies. There is. A crystallization method is known as one of the methods for removing these phosphates. This method is for example.

The pH of wastewater containing phosphate was adjusted to 7 or higher in the presence of Ca salt, and two grains of phosphate rock were used as seed crystals.

This is filled into a tower, and the phosphate in the waste water is precipitated on the surface of the phosphate rock as calcium phosphate.

It is being adopted.

However, with this method, the natural phosphate rock that is the seed crystal material is relatively expensive, the phosphoric acid processing capacity is not constant because it contains impurities, and the phosphoric acid removal performance is reduced due to carbonic acid components in the water. It had the disadvantage of In order to improve this drawback of phosphate rock, attempts have been made to develop a crystallization material that uses magnesia clinker as a base material and has calcium salt fixed to its surface. However, since the true specific gravity of magnesia clinker, which is the base material for this crystallization, is high at about 35, when backwashing the packed bed, a large amount of water is required for backwashing, and when backwashing, the support layer is The problem was that the small gravel and crystallizing material were upside down, which hindered stable operation.

(3) Purpose of the Invention The present invention eliminates the drawbacks of the prior art, makes use of the advantages of the crystallization material whose base material is magnesia clinker, reduces the amount of water required for backwashing, and allows the support layer and crystallization To provide a material for removing phosphoric acid in water that hardly causes material reversal.

(4) Key Points of the Invention The phosphoric acid removal material according to the present invention is characterized by having magnesium oxide and calcium salts fixed to the surface of a granular solid substance having a true specific gravity of less than 35 and insoluble in water.

The particulate solid material may include SiO2 and/or A
Natural products containing T203 as a main component 1, such as silica sand, pumice, zeolite, etc., are suitably used. A method for fixing magnesium oxide and calcium salts to the surface of this granular solid material is as follows.

After immersing the granular material in a slurry containing 10-30% magnesium hydroxide, it is fired at 1000-2000°C,
First, magnesium oxide is fixed on the surface of two particulate materials. It is more preferable to repeat this operation several times so that the surfaces of the two particulate materials are almost completely covered with magnesium oxide. Next, two particulate substances f:
After soaking for IO~100 minutes, dry, mulberry, and heat. The heating temperature is 1.'j: i20 to 200'C for about 2 hours. Through the above operations, a magnesium oxide film is formed on the surface of one particulate material, and on this magnesium oxide film.

Calcium salts stick together and form numerous active sites. The fixing method is not limited to the above, but a method of forming a coating of magnesium oxide on one granular material is to add 0.3 to 3% water glass as a binder to magnesium hydroxide slurry, and then
The granular material may be soaked and then fired at 300-500°C. In this case, magnesium hydroxide slurry IJ −
If the granular material is immersed in a ratio of 100 to 300 parts per 100 parts, a magnesium oxide film of 50 to 300 microns will be formed on the surface of the two granular materials.

The present phosphoric acid removal material produced by the method described above has a phosphoric acid removal performance equivalent to that of a crystallization material whose base material is magnesia clinker, and is not affected by carbonic acid components in waste water. In addition, since the true specific gravity is lower than the crystallization material whose base material is magnesia clinker, the amount of backwash water can be reduced during backwashing.

Example 1 The concentration of magnesium hydroxide is 10% in each case.

Silica sand with an effective diameter of 0.6 mm was immersed in 20% and 30% magnesium hydroxide slurry, and then heated to 1000°C, 1500°C, and 2000°C, respectively.

It was fired at 2500°C. This calcined silica sand was immersed in a 5% calcium chloride solution, dried, and then heated at 180° C. for 2 hours to obtain a phosphoric acid removal material. POa P 3.5 in a 500m Erlenmeyer flask! / l, Ca, 50m
A test solution having a pH of 8.5 and a pH of 8.5 g/l was added thereto, the above phosphoric acid removing material 1yk was added thereto, and the mixture was shaken for 24 hours.

As a result, the concentrations of PO4-P in the test solutions were as shown in Table 1, and good phosphoric acid removal performance was exhibited in all cases. In addition, the true specific gravity of the above phosphoric acid removal material is 2.6~
; 27, and the true specific gravity is about 30% lower than that of crystallized materials whose base material is magnesia clinker.

The amount of water during backwashing can be reduced accordingly.

Table 1 Example 2 When forming a coating of magnesium oxide on the surface of one of the granular substances of the phosphoric acid removal material of Example 1, magnesium hydroxide! Li"520% and a calcination temperature of 1500°C was packed in a 27.φ column with a bed height of 50ctn, and the same sample solution as in Example 1 was passed through the column at 5V=30. .

Changes in phosphorus removal performance over time were investigated. As a result, the concentration of PO4-P in the treated water remained stable at less than 0.5 TIF/l- even after 2,500 hours, and compared with crystallization using magnesia clinker as a base material, which was conducted as a comparative experiment. It showed performance equivalent to that of wood.

Example 3 An experiment was conducted under the same conditions as in Example 1 and Example 2, except that natural pumice was used as the granular material. As a result, Example 1 using silica sand. Processing results equivalent to those of Example 2 were obtained. The true specific gravity of the phosphoric acid removing material according to this example is 23 to 24, and the amount of backwash water can be further reduced.

Example 4 A water flow experiment was conducted under the same conditions as in Example 2, except that various M-alkalinity levels were added to the test solution. The concentration of PO4-P in the treated water after 500 hours of water flow time is shown in Figure 1 in comparison with a conventional water flow experiment using phosphate rock as a crystallizer. When the phosphoric acid removal material according to the present invention is used, it exhibits stable phosphoric acid removal performance without being affected by 1■-alkalinity in any case where the M-alkalinity is 500ηIr/ or less. Ta. On the other hand, when conventional phosphate rock is used, it is strongly influenced by 9M-alkalinity, and when +n-alkalinity is 5oomy7t, the concentration of PO4-P in the test solution is 3.5 my /
1, but PO4-P in the treated water is 2.
It was as high as 8 mg/t, and the phosphoric acid removal performance was significantly reduced.

[Brief explanation of drawings]

The figure is a graph showing the experimental results in Run I+ll4.

Claims (1)

[Claims] (]) A material for removing phosphoric acid in water, characterized in that magnesium oxide and calcium salts are fixed to the surface of a granular solid substance having a true specific gravity of less than 35 and insoluble in water. (2) The phosphoric acid removing material is characterized in that a magnesium oxide film is formed on the surface of two granular solid substances, and a calcium salt is fixed to the magnesium oxide film. The phosphoric acid removal material in water described in .11N.