JPS58210893A - Treatment of waste water containing phosphoric acid - Google Patents

Abstract

PURPOSE:To treat waste water contg. phosphate from a low concn. to a high concn. efficiently by passing the water to be treated through a layer of a filter medium consisting of a granular magnetic material formed with an insoluble Ca salt film in the presence of Ca salt while fixing the downstream part thereof in a magnetic field. CONSTITUTION:Waste water contg. phosphate is introduced into a crystallization tank 3 while said waste water is mixed with Ca salt 2 contg. Ca of reaction equiv. or above in accordance with the content of phosphate through a line 1. A magnet 4 and a metallic screen 5 which excites a magnetic field with said magnet are provided in the tank 3, and a granular filter medium 6 formed of a film of insoluble Ca salt prior to passing of the water to be treated is packed in said tank. Therefore, the phosphates in the waste water, the added Ca salt 2 and the film on the surface of the medium 6 react in the tank 3 and form hydroxy apatite which deposits as a crystal on the surface film of the medium 6. The upper part is fixed by the magnetic field formed by the magnet 4 and the screen 5 in this state, thereby forming a fixed bed 6a and a fluidized bed 6b.

Description

[Detailed description of the invention] The present invention applies to tap water, sewage, Shihara wastewater, and industrial water.

It relates to a method for removing phosphates present in liquids such as industrial wastewater and boiler water.

Inorganic phosphates generally present in wastewater include 1) IJ salts and various polymeric phosphates.

Furthermore, organic phosphates are said to cause eutrophication in closed water bodies, and when used as water, they can cause slime and scale formation in equipment piping, leading to accidents.

As a method of removing these phosphates, water containing phosphates is mixed with calcium phosphate-containing ores (for example, phosphate rock) in the presence of Cal/Rum.

Bone ash, etc.) has been proposed.
sserpation Abstracts Inte
national, Vol, 3o, Nn12゜part T). This method removes phosphate ions contained in water by converting them into calcium phosphate compounds such as hydroquinoapatite and crystallizing them into crystal seeds.
Processing efficiency is also excellent.

However, the phosphate rock used in this method varies depending on the production area, and many have inconsistent compositions and cannot be used as crystal seeds. In other words, phosphate rock itself is brittle and easily turns into fine powder when external force is applied, and when suspended in water to be treated,
, it has the property that solid-liquid separation is extremely difficult. Therefore, in order to use the ore as a crystal seed, collisions between the crystal seeds,
In order to avoid wear, a fixed bed type method is used in which the water is brought into contact with the water to be treated. However, even in this case, the amount of water to be treated! As the ratio of the water flow rate to the filling phase increases, phosphorus leaks into the treated water without being removed, and the filling material has to be replaced periodically. Further, when the above-mentioned ore is used in a fluidized state, it is difficult to increase the concentration of crystal seeds because it is easily crushed. Therefore, the crystallization rate is slow,
This has the disadvantage that the scale of the device also increases. The crystal seed concentration in this case is high h2-10 W/l.

The present invention provides at least a downstream portion of the filter medium layer in a phase layer made of a powdery or granular magnetic material or a solid material containing a magnetic material on which an insoluble calcium salt rupture film is formed on the surface in the presence of a calcium salt. Phosphoric acid-containing wastewater, characterized in that IIJ acid in the water to be treated is removed by passing through the water to be treated in a fixed state in a magnetic field and causing crystals of hydroxyapatite to precipitate on the surface of the filter medium. The purpose of the treatment method is to eliminate the shortcomings of conventional methods, to be applicable to both low to high concentration phosphate-containing υ1 water, and to improve the flow rate of the water to be treated. As a result, the phosphate concentration in the treated water can be stably maintained at a low level, making it possible to significantly downsize and simplify the treatment equipment, as well as generating extremely little sludge, making it possible to fill the water without stopping the operation of the equipment. The objective is to propose a processing method that allows for the exchange of materials.

Next, an embodiment of the method of the present invention will be explained based on the drawings.

The water to be treated containing phosphates is introduced into a crystallization tank 3 through a line 1 after being mixed with a calcium salt 2 containing more than the reaction equivalent amount of calcium corresponding to the phosphate content. The crystallization tank 3 is equipped with a magnet 4 and a metallic screen 5 that excites a magnetic field. In addition, before passing the water to be treated, the crystallization tank 3 is filled with insoluble calcium salts (for example, Ca
CO5, Ca5Oa, CaFy, preferably hydroquine apatite CIL! (PO,)s(OH), fluoroano; tight Ca1t(PO4)IF) Powdered or granular Shisatsuki 6 is filled. The filter medium 6 is a powdery or granular magnetic material (for example, α-
1γ-1δ-Fe*Os, Fe5Oa, FeooH
Suitable materials are those with low water solubility such as

A powdery or granular solid material containing a magnetic material (such as magnetite), or a powdery or granular solid material supporting a magnetic material (polyethylene, polystyrene, etc.).

A material with a magnetic material fixed to the surface of a solid material such as PVC is suitable. ). The particle size of these filter media is preferably 2 mm or less from the viewpoint of fluidization in the tank, and the corresponding mesh of the metal screen 5 is suitably 50 to 200 meSh.

In the crystallization tank 3, the phosphates contained in the water to be treated react with the added calcium 2 and the surface coating of the filter medium 6, and hydroxyapatite is produced.

It precipitates on the surface coating of the filter medium 6 as crystals. At this time, the lower and middle portions of the filter medium 6 flow due to the water to be treated.
The second part is fixed due to the magnetic field formed by the magnet 4 and the suction layer 75, and the fixed layer 68 and the fluidized layer 6 respectively.
form b. As hydroquinapatite crystals precipitate, the phosphate concentration in the water to be treated is reduced and flows out from the crystallization tank 3 to the line 9 as treated water.

The pH in the crystallization tank can be between 7 and IO, but is preferably maintained at between 80 and 85. The reason for this is.

Hydroxyapatite production reaction occurs at pH 7 or higher,
This is because when the pHI becomes 0 or more, metal hydroxides are generated and scales other than hydroxyapatite are generated, increasing excess sludge welfare. In addition, since the pH regulation value of effluent water is usually 58 to 86, the pH of the crystallization reaction must be adjusted in advance.
If it is set to 80 to 85, there is an advantage that there is no need to adjust the pH after the crystallization reaction.

As the flow rate of treated water increases, if there is a possibility that the phosphate concentration in the treated water will increase, the filter media in the tank will be continuously or intermittently replenished with new filter media from line 7. It will be used from line 8.

Is the concentration of the filter medium in the crystallization tank between 50 and 200? Adjust within the range of /l.

In such a method, phosphates in the water to be treated react on the surface coating of the filter medium as follows.

(: In the case of aCOm film The initial reaction is as follows.

5Ca(,Os+70H-+3HtPO4--Cas
(OH) (P(L)s + 6HtO+5COs'-
(Produced crystals) ■ In the case of CaSO4 film The initial reaction is as follows.

5C1lSO1+ 70H-+3H, P04″″→Ca
s, (OH)(PO4), +6H10-4-5SOa
”-(Crystal produced) ■ In case of CaF, film The initial reaction is as follows.

5CaFt+60H-+3114'0<-→Ca*(P
O4)sF+611+O+9F- (produced crystal) Then, the above hydroquine apatite Ca5(OH)(P
64) Tricrystalline or fluoroapatite caw (PO4
F acts as a seed crystal on the surface coating.

5 Ca" +70H-+ 3 lit P Oa"-
→Promotes the crystallization reaction of hydroxy avatar represented by Ca5(0n)(PO4)s + 6HtO from the water to be treated, and generates hydroquine apatite crystal groups on the coating.

If the ruptured membrane on the surface of the filter medium is already covered with hydroxyapatite, the initial reactions described in (1), (2), and (2) do not occur, and hydroxyapatite crystals immediately precipitate on the surface film.

In addition, magnetic components such as iron undergo the crystallization reaction vc t
Nit is not involved at all (the iron is dissolved in the water and does not react with the phosphate) and acts as a carrier for the insoluble Cal/Rum salt.

In this way, according to the present method, the filter medium flows in the lower and middle parts of the crystallization tank, while being fixed by the magnetic field in the upper illumination, so that the concentration of the filter medium as a seed crystal can be significantly increased. part becomes a fixed layer and can filter CaFt microcrystals without escaping.

Furthermore, the filter material flows in the lower and middle portions of the crystallization tank, making it possible to discharge and replenish the material even while the water to be treated is flowing.

As described in detail in the embodiments above, the method of the present invention has the following advantages.

lit The crystallization rate of hydroquinapatite is expressed by the following formula.

1-=K(C-C")"
・・・・・・・・・(IIt Here: Crystallization rate constant (t/m9-n) l( is proportional to seed crystal surface area A and seed crystal concentration Cd K. That is, K (CA , A 6eCd ,' , COCCd
t: Elapsed time (H) C: F concentration when t=t (da/1) C": F concentration when L2ω (Ill&#) - above (1
), the crystallization rate is proportional to the seed crystal concentration and the seed crystal surface area. ′Z) The larger the specific surface area of the broken seed crystal, the more
That is, the smaller the particle size is, the more advantageous it is, and the higher the seed crystal concentration is, the more advantageous it is. In the present invention, the specific surface area of the seed crystal can be increased, and the seed crystal concentration can be increased by 5 to 20 times compared to the conventional method, so that the device can be made smaller.

In addition, the crystallization rate can be reduced by 1 even in wastewater containing a low 1 degree IJ 7-salt salt, and since the insoluble phosphate salt comes into contact with the seed crystals frequently, it is easy to precipitate on the 1-seed crystal.

It is less likely to generate fine hydroquine apatite floating in the liquid.

(2) Enlarged seed crystals can be replaced continuously or intermittently without stopping the flow of water to be treated, and as a result, phosphates in the water to be treated can be Stable concentrations are obtained at low levels.

Note that in the fixed layer formed on the downstream side, the 4ζ material may be replaced in the flow of pH water to be treated, but since the fixed layer is a thin zone, its proportion to the whole is very small.

(3) Since hydroquinoapatite crystals are solid substances, there is very little sludge formation.

(4) Hydroxyano(・
Even if tight microcrystals are formed, they can be prevented from leaking into the treated water. Thereby, the phosphate concentration of the water to be treated can be stably obtained. No post-treatment is required.

A treatment comparison 1+11 between the conventional phosphate rock contact method and the present invention is shown in Table 1, 17C. In addition, in the method of the present invention, in order to form a hydroxyapatite film on magnetite, 60 to 200 meshes of magnetite are added to the water to be treated (
It was adjusted by contacting PO4'-5pp) with CaCl2140p- while adding it. A magnetite whose surface visually changed from black to white was used as a seed crystal.

Adjusted to Table 1 10011jN11. The added Ca salt was CaC1y and was adjusted to 140 ppH1.

2) 150-200 metsushi from Jordan. Water residence time is 20 minutes (space velocity 5v-3r7h).

3) 60~20t + Metsuyu Red sea bream tight (Fes
O+) on which a hydroxyapatite film is formed. The strength of the magnetic field is 0.5 to + (Oe). Water residence time was 5 minutes (SV = 121/h).

[Brief explanation of drawings]

FIG. 1 is a flowchart showing one embodiment of the method of the present invention. 3... Crystallization tank, 4... Magnet, 5... Metal screen. fi a...Fixed bed, 6b...Fluidized bed. 1 flash

Claims (1)

[Claims] In a magnetic field, at least the downstream part of the entrained layer is identified in a layer of a filter medium made of a powdered or granular magnetic material or a solid material containing a magnetic material, on which an insoluble salt film is formed on the surface in the presence of a calcium salt. 1. A method for treating phosphoric acid-containing wastewater, characterized in that phosphoric acid in the water to be treated is removed by allowing the water to be treated to pass through and come into contact with the water in an oxidized state to precipitate crystals of hydroxyapatite on the surface of the opening material.