JPS6130838B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a seed crystal material for crystallization treatment for crystallizing a phosphoric acid compound dissolved in a liquid and separating it from the liquid. The present invention relates to a method for producing a seed crystal material suitable for efficiently crystallizing phosphoric acid compounds contained in wastewater such as sewage.

Various wastewaters discharged into natural water systems contain various forms of phosphate compounds such as inorganic orthophosphates, various condensed phosphates, and organic phosphates. The presence of compounds is a major cause of eutrophication in closed water bodies such as rivers, lakes, and inner bays.

One of the methods for removing phosphoric acid compounds dissolved in these liquids is a crystallization treatment method. In this method, water to be treated whose pH has been adjusted to 7 or higher in the presence of calcium ions is passed through a packed bed of phosphate rock whose main component is calcium phosphate salt, and the phosphate in the liquid is converted to calcium phosphate and applied to the surface of the phosphate rock. Basically, it is precipitated. At this time, phosphate rock acts as a seed crystal material, and an intermediate product of a calcium phosphate compound is initially formed on the surface of phosphate rock, but it is said to change into stable hydroxyapatite over time. This crystallization treatment method has the advantages of generating little sludge and simple treatment operations, and has recently been adopted as a tertiary treatment for sewage with relatively low phosphoric acid concentrations. .

By the way, this crystallization treatment method is difficult because the naturally produced phosphate rock that is the seed crystal material is relatively expensive, contains impurities, so the ability to treat phosphate in the liquid is not constant, and the treatment process is difficult during operation. This method had drawbacks such as a decrease in performance. In addition, the composition and properties of phosphate rock itself vary significantly depending on the production area, and there have been problems with unstable factors in terms of performance guarantee and suitability of physical properties as a filler.

An object of the present invention is to eliminate the drawbacks of the above-mentioned conventional techniques and to provide a method for producing a seed crystal material for crystallizing phosphoric acid in a liquid that is inexpensive and has stable processing performance, instead of the above-mentioned phosphate rock. .

To achieve this objective, the method for producing a seed crystal material according to the present invention involves adsorbing phosphoric acid onto a magnesia-based or zirconia-based carrier, and then adsorbing a calcium compound selected from calcium chloride, calcium hydroxide, and calcium oxide. It is characterized by carrying at least one kind of.

Here, the term "carrier" refers to a granular material that serves as a matrix for the seed crystal material, and a substance that has an affinity for phosphate is selected. The granules include both spherical and crushed particles. For example, those whose main component is an oxide of magnesium or zirconium are preferably used. Adsorption of phosphoric acid onto these carriers can be achieved, for example, by immersing the carrier in a 0.01-5% phosphate solution whose pH is adjusted to 5.5 or less. The immersion time is usually 2 to 50 hours. The amount of phosphoric acid adsorbed on the carrier is 2 to 20 mg per 1 g of carrier.
is preferred. Lowering the concentration of the phosphate solution and increasing the soaking time results in higher stability of the adsorbed phosphoric acid than vice versa. It is preferable to perform dry heating for stabilization after immersion.

Next, a calcium compound is fixed to the carrier (hereinafter referred to as adsorption carrier) on which phosphoric acid has been adsorbed in the manner exemplified above. The following methods can be used to fix the calcium compound.

(1) Method of immersing an adsorption carrier in a calcium compound solution In this method, the adsorption carrier is immersed in a 0.05 to 10% calcium compound solution for 10 to 100 hours, either while being wet or after dry heating. Through this treatment, the adsorbed phosphoric acid and calcium ions react, and a large number of active sites are distributed on the surface of the carrier. Although the chemical composition of these active sites is not clear, they are presumed to be calcium phosphate or its intermediate products. As with the phosphoric acid adsorption treatment, this treatment is preferably performed by immersing the adsorption carrier in a low concentration calcium compound solution for a long period of time. There is relatively little dependence on PH. The amount of calcium fixed on the carrier is usually preferably 4 to 50 mg per gram of carrier.

(2) A method of thoroughly mixing a wet adsorption carrier and fine powder of a calcium compound, and then drying this method. Especially in the drying process, phosphoric acid and calcium ions adsorbed on the carrier gradually react with each other. Forms active points on the surface. After drying,
Further, it is preferable to heat at 120 to 200°C for about 2 hours. Heating makes the calcium fixation stronger.

In the seed crystal material for crystallization treatment according to the present invention that has undergone the above operations, the amount of the adsorbed phosphoric acid and the fixed calcium compound is extremely small relative to the weight of the carrier, which is the base material. Rather than covering the surface of the crystal, it is distributed as a large number of active points as described above, and exhibits properties suitable as a seed crystal material. There is a wide selection of carriers, natural or artificial carriers with uniform properties and low cost can be used, and uniform processing can be carried out. Therefore, the seed material resulting from the present invention is physically and chemically uniform. Demonstrates stable processing performance. In addition, the particle size of the carrier,
By arbitrarily selecting the particle size, specific gravity, mechanical strength, etc., the seed crystal material can be filled and used as either a fixed bed or a fluidized bed.

Note that the seed crystal material produced by the method of immersing the carrier in a solution in which phosphate and calcium salt coexist, which is not a method of the present invention, does not exhibit sufficient treatment performance. Although the reason for this is not clear, it is presumed that in the present invention, adsorption of phosphoric acid with affinity to the carrier as a first step produces good results.

Adsorption experiments were conducted to confirm the affinity of various carriers for phosphoric acid. The adsorption isotherm is shown in Figure 1. It can be seen from FIG. 1 that the amount of phosphorus adsorbed by zirconium hydroxide and magnesium oxide is large, followed by aluminum oxide, activated carbon, and sand, and the amount of phosphorus adsorbed decreases in that order.

Example 1 Four types of seed crystal materials were prepared according to the following conditions.

Sample A Seawater magnesia clinker with a particle size of 0.3 to 0.6 mm was (i) immersed in a 0.5% sodium phosphate solution adjusted to pH 5 for 20 hours, and (ii) dried and heated at 120°C for 3 hours. (iii) This adsorption carrier was immersed in a 1% calcium chloride solution for 20 hours, and (iv) dried at 120°C.
It was heated for 3 hours.

Sample B It was prepared in the same manner as Sample A except that the drying and heat treatment in (iv) in Sample A were omitted.

Sample C Prepared in the same manner as Sample A except that the drying and heat treatment in (ii) in Sample A were omitted.

Sample D Prepared in the same manner as Sample A except that the drying and heating treatments (ii) and (iv) in Sample A were omitted.

A column packed with each of these four types of seed crystal materials had a phosphorus concentration of approximately 3.5 mg/day and a calcium concentration of approximately 3.5 mg/day.
35~45mg/, simulated sewage adjusted to pH8.0~8.5
The phosphorus removal performance was examined by passing water at SV = 5h ^-1 .
The results are shown in FIG. The phosphorus concentration in the treated water for all seed crystal materials was less than 0.7 mg/d, demonstrating stable phosphorus removal performance even during long-term operation. Sample A had good removal performance, followed by sample B,
The removal performance decreased slightly in the order of sample C and sample D.

Example 2 A seed crystal material was prepared in the same manner as in Sample A of Example 1, except that zirconium oxide hydrate was used as a carrier. A water flow experiment was carried out on this seed crystal material in the same manner as in Example 1, and as a result, the phosphorus concentration of the treated water showed a value equivalent to that of Sample A shown in FIG.

Comparative example Seawater magnesia clinker (particle size 0.3-0.6mm)
Add the carrier to a mixed solution containing 0.5% sodium phosphate, 1.0% calcium chloride, and adjusted to pH 8.
It was soaked for 40 hours and used as a seed crystal material. As a result of conducting a water flow experiment on this seed crystal material in the same manner as in Example 1,
The phosphorus concentration in the treated water was around 1.6mg/at the beginning of operation, and showed a gradual decreasing trend as the operation time progressed, but even after 1500 hours, it remained high at around 1.2mg/.

[Brief explanation of the drawing]

Figure 1 is a diagram showing phosphorus adsorption isotherms of various carriers,
FIG. 2 is a diagram showing the operational results when simulated sewage water was passed through a column filled with the seed crystal material according to the present invention.

Claims (1)

[Claims] 1. Phosphoric acid in a liquid is characterized by adsorbing phosphoric acid onto a magnesia-based or zirconia-based carrier, and then supporting at least one calcium compound selected from calcium chloride, calcium hydroxide, and calcium oxide. A method for producing seed crystal material for crystallization.