JPS6014990A - Dephosphorization process - Google Patents

Abstract

PURPOSE:To maintain high rate of dephosphorization of water contg. phosphate for along time by treating the water with acidic soln. in the presence of Ca ion at >=6pH and allowing thereafter the treated water to contact with seed crystals having powder contg. calcium phosphate deposited thereon. CONSTITUTION:Seed crystals having powder contg. calcium phosphate such as hydroxyapatite, fluoroapatite, tricalcium phosphate, etc. deposited thereon, are allowed to contact with soln. contg. 0.1-30% inorg. acid such as HCl or org. acid such as acetic acid for 5min - several hours. The water contg. phosphate is allowed to contact with the above described seed crystals having powder contg. calcium phosphate which has been treated with acid at >=6pH in the presence of Ca ion to perform dephosphorization. By this method, superior activating effect for seed crystals as compared to the conventional method is attained due to synergistic effect of acid treatment and deposition of calcium phosphate powder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dephosphorization method, and more particularly to an improved crystallization dephosphorization method.

In recent years, the problem of eutrophication in closed water areas such as lakes and marshes has become serious, and countermeasures are urgently needed. One of the causes of eutrophication is phosphates present in water, and studies are underway to find ways to prevent phosphates. This phosphate is widely used in detergent builders, fertilizers, etc., and is present in domestic wastewater, industrial G6 water, etc. in the form of inorganic phosphates such as orthophosphates and condensed phosphates, and free phosphates. are doing.

Methods for removing phosphates from water include the loading method using sulfuric acid, the activated sludge method, or a combination of these methods, which have been used in experimental plants and actual plants and have been shown to be effective. However, in recent years, the operation has become more fWi
The crystallization dephosphorization method is attracting attention because it is simple, does not generate sludge, and has high processing efficiency.

In the crystallization dephosphorization method, water containing phosphate is brought into contact with crystal seeds containing calcium phosphate such as hydroxyapatite in the presence of calcium ions, and the phosphorus ions in the water are converted into calcium phosphate and deposited on the surface of the crystal seeds. This is a method of crystallization, and from time to time, the 88 minutes accumulated in the crystallization/dephosphorization equipment is washed and removed.

However, this method has the problem that the surface of the crystal gradually becomes inactive and the dephosphorization performance deteriorates. This is especially noticeable when the raw water contains reaction inhibiting substances such as magnesium ions and organic substances.

Conventionally, as a means of solving such 1iiJ problems,
A method has been proposed in which crystal seeds with reduced dephosphorization performance are treated with an acidic solution to reactivate them.

In addition, the inventors proposed a method of reactivating crystal seeds with reduced dephosphorization performance by supporting powder containing calcium phosphate (4!j Kokusho 57-22
(See No. 9212).

An object of the present invention is to provide a dephosphorization method with high treatment efficiency that employs a novel activation treatment method that has a greater activation treatment effect than the conventional methods described above.9゜The dephosphorization method of the present invention , a method of dephosphorizing water containing phosphorus salts by fusing them with crystal seeds containing calcium phosphate in the presence of calcium ions and under conditions of pI 6 or higher, wherein the crystal seeds include calcium phosphate. It is characterized by the use of crystal seeds supported by powder containing calcium sulfate treated with bath Vill.

First, the method for activating crystal seeds in the present invention will be explained in detail. The crystal seeds to be activated may be new or may be those whose performance has deteriorated after being used for a certain period of time.

For example, in the case of a crystal seed with reduced dephosphorization performance, first, it is fused with an acidic solution to remove reaction inhibitors on the surface of the crystal seed. As the acid, known inorganic acids and organic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, citric acid, acetic acid, oxalic acid, and tartaric acid can be used. The acid concentration may be from 0.1 to 30%, and the contact time may be from 5 minutes to several hours. Note that phosphate rock, bone charcoal, or granules having phosphate calcium crystals on the surface are used for the crystal scoop.

By treatment with this acidic solution, crystals 4. ! It is believed that the surface area of II surface blood increases, and that fine particles of calcium phosphate are carried thereon, creating a lily-like appearance. On the other hand, when treated with an acidic bath solution, the crystal seed surface dissolves and a waste liquid containing phosphorus is generated, but this phosphorus-containing waste liquid can be effectively used when supporting powdered calcium phosphate. That is, phosphorus-containing 1 generated in the acid treatment step
In addition to phosphorus, a large amount of calcium ions are also dissolved in the solution.
Therefore, when the pH of this Bi solution is adjusted, calcium phosphorus crystals precipitate. Therefore, when the waste liquid generated in the acid treatment step is raised to pH 7 or more and water is passed through the waste liquid while the powdered calcium phosphate is in contact with the crystal seeds, the calcium phosphate in the liquid is precipitated by a crystallization reaction. Then, the precipitated phosphorus acts to bind the yarn/f-product and the powder. In other words, by this operation, powdered phosphorus 1-wave calcium is made into crystals 149 using the precipitated crystals as a binder.
It will be carried on the surface.

After the acid solution treatment, a powder containing calcium phosphate is supported. The supporting treatment may be carried out by passing water using the above-mentioned hostile waste liquid, or by passing water using a separate liquid containing phosphorus and calcium ions.

Powders containing calcium phosphate include hydroxyapatite, fluoroapatite, tricalcium phosphate, phosphate rock, 11' carbon, or calcium phosphate as a main component and 1-
A flocculation method JHjQ product, for example, a powder such as calcium phosphate precipitated by adding calcium to phosphorus-containing water can be used. 7 anti-powder containing calcium phosphate has a particle size of 0.4 tu
It is preferable to have a particle size of less than + (approximately 36 meshes or less).Those originally obtained in the form of ar powder can be used as they are, and those obtained as granules or lumps are used after being made into a powder. As a powdering means, a known means is used.

The crystallization and dephosphorization process 11 is carried out by passing raw water through a packed bed consisting of the activated crystal seeds and the like.

The reaction that occurs when water containing phosphate is brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions varies depending on the reaction conditions, but is usually expressed by the following formula.

5Ca -1-70H+3H2PO4→Ca! (OH)
(PO4)3 +G If20-' (1) As can be seen from equation (1), in order to increase the removal rate of phosphorus salt,
It is necessary for the reaction to proceed to the right, and in order to crystallize the calcium phosphate produced at the same time, it is necessary to keep the surface of the crystal seeds clean and maintain high activity. Therefore, in the present invention, water passing treatment is performed in the presence of calcium ions and under conditions of pH 6 or higher.

In order for the reaction to proceed, it is desirable to have a large amount of calcium ions and aqueous ions present in the reaction system.
If these are present in excess, fine precipitates such as calcium phosphate will occur in areas other than crystal A5I, blocking the filling H1 consisting of rigidity, crystal secretion, etc., and reducing the water flow treatment efficiency.
Sometimes I give it away.

In Equation (1), the degree of j17 of the produced "twoi" calcium phosphate is higher than the common understanding and lower than the excess r6'Ai degree (the concentration at which 111 products start to precipitate when there are no crystal seeds in the reaction system). In the range of calcium ion concentration and pH, that is, in the mulberry stable range, the phosphorous calcium produced precipitates on the surface of the crystal seeds and no fine precipitates are produced. However, calcium ions and/or pTI
is high < 1.1: In the unstable region where the produced calcium phosphate exceeds the overmelting intensity, the calcium phosphate precipitates as fine precipitates. Therefore, the range of the metastable region varies depending on the L degree of phosphate ions contained in the raw water.
The phosphorus ridge ion expansion at 61°C is broadly based on a', 4, or 1. Therefore, if the degree of phosphate ion O1 is high, increasing the degree of calcium ion ridge and/or pl-i will result in an unstable region where precipitation is likely to occur;
When the ζ7 value is low, crystallization can occur in the metastable region even if the calcium ion concentration and/or pI+4 is increased, so the reaction rate can be increased without forming a precipitate.

(Filling) Calcium ions are made to exist in the raw water passed through the sock so that the reaction of the above formula (1) proceeds. If calcium ions are absent or insufficient in the raw water, add a calcium agent from the outside. The pH of the reaction system is 6 or higher,
Usually it is 6 to 12, and an alkaline agent is added if necessary. In this way, the calcium ion concentration and pH present in the water to be treated are adjusted to be within the metastable range.

The packed bed is filled with crystal seeds containing the above-mentioned calcium phosphate powder, and these AJi crystal seeds themselves may be used as granules to form the filling f7fl. It may be filled in a state in which it is trapped in a layer. Furthermore, the method of contacting the raw water with the crystal seeds may be either a fixed bed method or a fluidized bed method.

The dephosphorized water is neutralized by known means, if necessary, and then discharged.

According to the present invention, due to the synergistic effect of the bar treatment and the calcium phosphate powder loading treatment, a more effective activation effect on crystal seeds can be obtained than in the conventional method. Therefore, the cylinder phosphorus removal rate can be maintained over a long period of time. Moreover, the waste liquid from the acid treatment process can be effectively used for the calcium phosphate powder supporting treatment. In addition, since the pI (pI) of the treated water after dephosphorization treatment is low, it is possible to omit the neutralization treatment car for the treated water compared to conventional methods, or the amount of pear agent required for neutralization can be reduced.

Example This product was used for about 2 years to dephosphorize secondary treated sewage water containing 40-60 my/l of magnesium ions, 50 mg/l of sulfate ions, and 1-2 mvl of phosphorus by the crystallization method. Phosphate crystal fjn 150 tall with grain layer 16 to 32 mesh,
Acrylic (ii:t Bii column) with a tube size of 500 pieces was packed. To this packing M2, 7 colors (pH 2,5) 750- in vinegar sprinkled at 0.5 mol/l were added at 100 nm, l/mm of 0I.
1. , for 1 hour.

After 1 hour, the waste liquid used for acid treatment was extracted, and the particle size was 0.
．． ] A solution prepared by suspending 2 g of hydroxyapatite powder below trm in 5.00 ml of tap water was
Water was circulated at a flow rate of 0 ml 7 mm to trap the hydroxyapatite powder in the packed bed.

Next, an aqueous sodium hydroxide solution was continuously added at the inlet of the column to the water in which the flattened liquid generated in the acid treatment step was diluted 30 times. Water was passed through the packed M at a countercurrent flow rate of 300 mJ/hr for 3 days. After 3 days, the water flow was stopped, and the packed bed of the ore crystal pile was developed and washed (backwashed), and the unsupported powder was discharged outside the packed bed, and the reactivation was completed.

Next, the phosphorus concentration is 2/13. m alkalinity approximately 100
Continuously add an aqueous solution of calcium chloride (hydroxidized with a calcium chloride water bath solution) to the synthesized water of Jn97 at the column inlet to adjust the calcium ion concentration to approximately 4 snrg/6, pH
After harmonics are adjusted to 88 to 9.0, the upward flow a o
Water was continuously passed through the LA layer for 35 days at a flow rate of 0 mli/br to perform dephosphorization by crystallization.

The phosphorus content and pH of the treated water during the water flow period are shown in Cloth-1. In addition, as Comparative Example 1, the same phosphate rock was reactivated 1
The treatment results when used for dephosphorization under the same conditions without - are shown. As Comparative Example 2, the same phosphate rock was subjected to reactivation treatment by performing only the acid treatment step of the above example, and the M ratio was shown when it was used for dephosphorization under the same conditions. Furthermore, as Comparative Example 3, the same phosphate rock was subjected to ladle activation treatment by a method of supporting hydroxyapatite powder without performing the acid treatment step of the above example, and was used for dephosphorization under the same conditions. The results were shown.

(Margins below) As shown in Table 1, in the case of no reactivation (Comparative Example 1
The average phosphorus concentration of treated water in
was 8.5 or higher. On the other hand, when reactivated by the method of the present invention (Example), the average phosphor density was 0.21
my/l.

The pfl was also as low as 8.21, indicating a significant treatment effect. Even compared to the conventional methods shown in Comparative Examples 2 and 3, the quality of the treated water is much better, and it can be seen that the reactivation treatment achieved by the method of the present invention is significant.

Claims (1)

[Claims] 1. In the presence of calcium ions and at a pH of 6.
In the method of dephosphorizing water containing phosphate by contacting it with crystal seeds containing calcium phosphate under the above conditions, the crystal seeds are treated with an acidic solution and then supported with powder containing calcium phosphate. A dephosphorization method characterized by using. 2. The method according to claim 1, wherein the crystal seeds are phosphate rock, bone char, or granules having calcium phosphate crystals on the surface. 1 Powder containing calcium phosphate is hydroxyapatite, fluoroapatite, phosphorus is trilime, phosphate rock,
The method according to claim 1 or 2, which is a coagulated precipitate mainly composed of bone char or calcium phosphate. 4. The -μ retention of the powder containing calcium phosphate is carried out using calcium phosphorus precipitated from the waste liquid generated during treatment with an acidic solution as a binder. Claims 1m to 3. The method described in.