JPS6078692A - Dephosphorization - Google Patents

Abstract

PURPOSE:To perform the dephosphorization of a phosphate-containing water with good efficiency, by passing phosphate-containing water through a packing layer of a deposphorization agent having a calcium phosphate crystal formed to the surface thereof in the presence of a Ca-ion under a condition of pH 6 or more. CONSTITUTION:Zeolite is brought into contact with an aqueous solution containing a calcium agent such as calcium chloride or calcium hydroxide and calcium is collected by zeolite by ion echange. In the next step, zeolite is separated and contacted with an aqueous solution containing phosphoric acid or a salt thereof to support phosphorus while the treated zeolite is brought into contact with a solution containing lime such as slaked lime to form a calcium phosphate crystal to the surface thereof to obtain a dephosphorization agent. Phosphate-containing water such as sewage is passed through a packing layer packed with the dephosphorization agent in the presence of a calcium ion and a phosphate ion is precipitated on the dephosphorization agent in a hydroxyapatite form to perform phosphorization.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dephosphorization method suitable for treating water containing phosphates.

In recent years, the progress of eutrophication in closed water bodies such as lakes, marshes, and inner bays has become a serious problem. Phosphate present in water is considered to be one of the causes of eutrophication, and its removal is an urgent issue. Phosphate, which causes eutrophication, is present in tap water, sewage, industrial water,
It is contained in factory wastewater, boiler water, etc., and exists in the form of inorganic phosphates such as orthophosphates and condensed phosphates, and organic phosphates.

As a method for removing such phosphorus mf-M.

A method has been proposed in which water containing phosphorus salt is brought into contact with crystal seeds containing calcium phosphate, such as phosphate rock, in the presence of calcium ions (Dis-serL+tion).
Abstracts international, V
o1.33゜1'! l12. part l, 587
8 B page etc.). This method removes phosphate ions contained in water by converting them into calcium phosphate such as human mixiapatite and crystallizing them into crystal seeds. ] Not only can it be simplified, but the processing efficiency is also much improved, so in recent years,
It is receiving particular attention.

By the way, natural phosphate rock is mainly used as the crystal seed used in the crystallization dephosphorization method, but phosphate rock is a resource that is not produced in Japan in practical models and is dependent on imports from foreign countries. Because of this, it is difficult to provide a stable supply, and there are differences in chemical composition and physical properties depending on the production area, and the dephosphorization effect of the crystals used as crystal seeds for crystallization dephosphorization differs, so stable treatment effects cannot be obtained. In order to achieve this, it was necessary to use a special phosphate rock.

The present invention is intended to eliminate such conventional problems and achieve a stable dephosphorization effect! The purpose of the present invention is to provide a complete dephosphorization method using a dephosphorization agent.

The present inventors have already used zeolite? proposed a method for preparing a dephosphorizing agent by bringing it into contact with a water bath solution containing a phosphorus enemy or its salt, separating it from said solution, and then bringing it into contact with a solution containing lime (%Request No. 57-23178). There is. The present invention is a further improvement of this proposed method, and by performing crystallization dephosphorization using a dephosphorizing agent that is extremely effective in removing phosphorus, it is more stable than the already proposed method. Phosphorus removal effect can be achieved.

In the present invention, zeolite, which is a carrier, is brought into contact with a water bath solution containing a calcium agent, then with an aqueous solution containing phosphorus or its salt, and then with a solution containing a lime alloy so that all calcium phosphate crystals are formed on the surface. The generated dephosphorization MIJ is used to perform crystallization and dephosphorization.

In the present invention, preferably zeolite t calcium #lJ
*The purpose is to perform crystallization and dephosphorization using zeolite, which has a calcium exchange rate of 20% or more after contact with a water bath solution containing the zeolite, as a carrier.

The type and origin of the zeolite carrier used in the present invention are not particularly limited, and both naturally occurring and artificial zeolites can be used. Among these, those with a high silica content relative to alumina, such as clinoptilolite and mordenite, are preferred, and these can withstand use up to pH 2i degrees,
Compared to other zeolites whose pH is only 4, it can be used in 1) a wider range of H; In addition, these zeolites are precious W, which are produced in large quantities in our country.

It is advantageous in terms of stable supply because it is inexpensive and easily available.

Zeolite has the ability to interact with calcium ions.

It also has excellent chemisorption ability for phosphorus, making it suitable as a carrier. When used, it may be used as a carrier in a powder bed state, but
Particulate matter is preferred because it can form a layer of light during the dephosphorization process. As a particulate material, the powdering strength of zeolite used as a carrier is greater than that of conventional phosphate rock.

The above-described zeolite is first brought into contact with a water γO solution containing a calcium agent such as calcium chloride or calcium hydroxide, and calcium is captured by the zeolite using ion particles. Whereas the previous application immediately contacted the Rinkan (Hanawa) water bath solution.

In the present invention, calcium 5C3% is added in advance to
At the same time, by adsorbing phosphate ions on zeolite and reacting with phosphoric acid to generate calcium phosphate, and then contacting it with a lime solution, the adsorbed phosphate ions and calcium are reacted to generate phosphoric acid calcium ions. This is because a highly effective dephosphorizing agent can be obtained by aging the phosphorus produced in the 911 stage with calcium. Zeolites can readily absorb ions and capture all calcium, such as those used to soften hard water. The exchange rate of calcium can be easily changed depending on the degree of spread of calcium salt in the water bath, and is usually 20% or more, preferably 40% or more.

The contact time for 1 liter of water-soluble calcium to be brought into contact with the zeolite may be arbitrarily selected in consideration of the total calcium exchange rate. The contacting operation may be either a batch operation or a continuous water flow method.

The finished zeolite is separated from the calcium-containing bath solution. Separation may be carried out by ordinary gravity separation, and if necessary, washing with water may be performed.

The zeolite from which all the lb liquid has been separated is brought into contact with 16 liquids of water containing phosphoric acid or its salt. Zeolite is phosphorus (
Salt) It has the property of adsorbing phosphorus from the water bath liquid, and in the case of the present invention, calcium ions are incorporated into the zeolite, and the syy ions are rapidly adsorbed and react with the calcium ions.

By bringing the zeolite into contact with a phosphoric acid (salt) water bath solution by an impregnation method or the like, it is possible to easily completely adsorb and support phosphorus. As a phosphorus tower, various kinds of orthophosphorus such as sodium phosphate and potassium phosphate can be used.

The phosphorus to be brought into contact with the carrier is (i'A) 9 degrees of the bath solution is 100
You can choose between duty and failure with axis times from m9/8 to several tens of Msu%. The contact operation may be either a batch operation or a continuous water flow method. pH/a of phosphoric acid (salt) aqueous solution during contact
Although not particularly limited, in order to efficiently carry out phosphorus loading, it is preferable to use conditions such that tL<, Lf:fK pH is less than 6. This seems to be because the tendency for adsorption onto the carrier surface is higher at low pH, and at pH 6 or higher it takes time to obtain stable treated water quality. The contact time may vary depending on the carrier, type of phosphate, concentration, pH, etc., and may be about 3 to 50 hours.

The carrier that has been subjected to the phosphorus loading treatment is separated from the phosphorus-containing solution. Separation may be carried out by ordinary gravity separation, and if necessary, washing with water may be performed. The separated solution can be used for the next loading operation. In addition, at this time, by adding phosphate as necessary, a stable mutual treatment effect is maintained. If the solution is moved to the next step without separating it, the phosphate ions in the solution will react with the slaked lime, producing a large amount of calcium phosphate precipitate, which will complicate the treatment process. Moreover, at this time, since slaked lime is consumed, the required amount of slaked lime increases and processing cost increases. Furthermore, fine calcium phosphorus crystal seeds, which have a weak bonding force to the carrier surface, adhere to the carrier surface.

Since these are desorbed during use, the treatment effect is reduced, which is undesirable.

The carrier from which the solution has been separated is brought into contact with a solution containing lime, and the phosphorus supported on the carrier surface reacts with calcium hydroxide to form calcium phosphate crystals with high release rate. Additionally, pre-formed calcium phosphate is aged.

As the solution containing lime, a slaked lime aqueous solution can be used, but other substances may be mixed therein. In order to generate and ripen high-quality calcium phosphate crystals, a certain amount of calcium hydroxide or more is required for the amount of supported phosphorus, and if this is insufficient, the performance of the resulting dephosphorizing agent will be poor. . In order to obtain a dephosphorizing agent with high removal rate under standard dephosphorizing conditions, the amount of phosphorus supported should be reduced.

It is preferable to contact with a solution containing 4 times by weight or more of hydroxide. The concentration of calcium hydroxide in the solution is o,
The weight may be approximately 1 to 5 cm, and the contact time may be approximately 1 to 7 days.

The product obtained by the above operation is left as is.

Or it can be used as a dephosphorizing agent in a mixed state with other substances. The dephosphorization method is the same as the conventional method of depositing crystal seeds such as phosphate rock, and if the dephosphorization agent is obtained in powder form, it is brought into contact with raw water containing phosphate in the form of a slurry, and if it is obtained in granular form, it is brought into contact with raw water containing phosphate. The entire packed bed is formed and treated with water. When the activity of the dephosphorizing agent decreases due to continued dephosphorization operation, the above-mentioned production rotation of calcium phosphate crystals is carried out again.

Can be reactivated.

In addition, in the above operation, the reaction is promoted.

Alternatively, in order to improve efficiency, it is also possible to add other drugs, or to use or add other treatments in combination.

The present invention is obtained by the above. Water containing phosphate is passed through a packed bed filled with a dephosphorizing agent in the presence of calcium ions to crystallize phosphate ions in the form of hydroxyapatite on the excavated soil for dephosphorization. The method for using a dephosphorizing agent will be explained below.

The raw water to be treated in the present invention is water containing phosphates and organic substances, and includes secondary treated water such as sewage, human waste, and industrial wastewater. Crystallization is performed by bringing such raw water into contact with a dephosphorizing agent in the presence of calcium ions. The reaction that occurs at this time varies depending on the reaction conditions, but is usually expressed by the following formula.

5Ca"+70H-+3H2POj"-+Ca5(OH
)(PO4)+6 H2O・・・・・・・・・・・・
...(1) In order to efficiently remove phosphate from water containing phosphate, it is necessary to allow the reaction in equation (1) to proceed to the whole stone side, and for this purpose, a calcium agent or an alkaline agent is required. It is necessary to add calcium ions and hydroxide ions by adding them.

If the amount of these ions becomes too large, fine precipitates may be formed in areas other than the nojosun agent, or rat calcium precipitates may be formed. Should.

In other words, the amounts of calcium ions and hydroxide ions are (
Conditions are such that hydroxyapatite is produced at a concentration higher than the solubility of hydroxyapatite produced in formula 1) and lower than its extermination solubility, that is, 0 degree hydroxyapatite in the metastable range. Here, the extermination freshness is the concentration at which crystals begin to precipitate when no crystal seeds are present in one reaction system.

To obtain all the above ranges of calcium ions and hydroxide ions, add calcium and/or alkaline agents to phosphate-containing water. The suitable addition amount of calcium agent and alkaline agent can be determined in advance by fID single epidemiological experiment.If the phosphate in the raw water is less than 50 mfl/6, the calcium ion concentration is 10-2 (joIII9/g, pH is It is about 6 to 12.

Calcium agents used in this invention include calcium hydroxide, calcium chloride, etc. Alkali agents include calcium hydroxide, 1lium hydroxide, calcium hydroxide, etc. 5 Water containing phosphate and dephosphorizing agent The contact is carried out by the optical laminated water flow method, or by filling a dephosphorizing agent with a particle size of 9 to 35 mesh in the case of a fixed bed and 36 to 300 mesh in the case of a fluidized bed, and flowing upward at a flow rate of SVI ~ 20 br-1 ( f
Water is passed in a downward direction to precipitate hydroxyanotite crystals. In the case of upward flow, suspended matter can be captured in the large particle size portion of the lower layer, and all crystallization can be performed in the small particle size portion of the upper layer with high activity. Similarly, when water is passed in a downward flow, a filter medium with a smaller specific gravity and larger particle size than the dephosphorizing agent is stacked on top of the dephosphorizing agent packed layer to avoid adhesion of suspended matter to the surface of the dephosphorizing agent. And with this filter material! It is desirable to remove turbid substances. If the surface of the dephosphorizing agent becomes contaminated or clogged during water flow, periodically perform backwashing using an upward flow to develop and clean the dephosphorizing agent and remove impurities attached to the surface. is desirable. Water flow conditions during backwashing include a flow rate of about 20 to 80m/llr, and a backwashing time of 5.
~60 minutes.

When the crystallization is performed as described above, hydroxyapatite with low solubility is mainly generated according to the formula (1), and this crystallizes on the surface of the dephosphorizing agent, thereby lowering the phosphate temperature in the treated water.

In addition, in the above treatment, the raw water is subjected to pre-treatment prior to the dephosphorization operation, the treated water is subjected to post-treatment, or during the dephosphorization treatment.

It is also possible to use other treatments in combination, or to add all chemicals, etc.

As described above, according to the present invention, it is possible to efficiently and stably produce a dephosphorizing agent with excellent dephosphorizing performance with simple operations, and also to perform efficient dephosphorizing treatment using the same. can.

Next, examples and comparative examples of the present invention will be described.

Example 1 Clinoptilolite yarn natural zeolite 2uomA' (195i%
) into a 1B Erlenmeyer flask and add 51 J u m1 at a time.
Washing was repeated 5 times using tap water from No. 3 using the decanting method.

Next, it was transferred into an aqueous solution of calcium chloride containing 7.32 wt % of the above Ceolite and subjected to contact treatment for 5 hours. After 5 hours, the zeolite and calcium chloride aqueous solutions were completely separated.

The amount of calcium trapped in the zeolite is determined by contact treatment with the aqueous solution of calcium chloride, and the calcium ion exchange rate of the zeolite is calculated by taking into account the i-K4 of calcium originally contained in the zeolite.
It was 7 yen.

Next, after washing with tap water, the phosphorus concentration s, o o.

ml/8 or 7 fy-NaH
2PO4) water bath solution (pH 4,3), transferred to 5 ounces,
Contact treatment was carried out for 1 day.

After 3 days of contact treatment, the residual liquid from the first reaction was separated and washed with tap water. Next, 3.2% slaked lime emulsion 5 u u r
After contact treatment for 3 days in nl; further.

Rinse thoroughly with tap water and fC.

150 rILl of the dephosphorizing agent prepared in this way was packed into an acrylic column with an inner diameter of 30 mm, and the phosphorization degree ->
2 mg/9, total a/l/27 degrees approximately 1001
At the column inlet, add calcium chloride water bath solution and sodium hydroxide aqueous solution to synthetic water adjusted to 119/8. i, all added to bring the calcium ion concentration to about 45m9/13. pHk
8, 8-9. The water was continuously passed for 22 days in an upward flow at a flow rate of SV 2 hr-'' (1).

The average value of constant viscosity was 0.13 m97&. The results of the determination of the phosphorus concentration of the treated water are shown in Table 1 together with the #1 results of Example 2 and Comparative Example.

Example 2 The same conditions as in Example 1 except that zeolite was pretreated using 4.88 wt% slaked lime emulsion soumJi instead of 5 ut + mg of 7.32 wt% calcium chloride water bath solution. Considering the sum of the calcium trapped by the dephosphorizing agent, and also considering the amount of calcium originally contained in the zeolite, what is the calcium ion exchange rate of the zeolite? z J'J- was 42.8%.

Subsequently, a dephosphorization experiment was conducted under the same conditions as in Example 1 using the dephosphorization agent prepared in nl.4. The average value of the measurement results of treated water phosphor box 4 degree on day 22 after the start of water flow was 0. '1ll
It was i/e.

Comparative Example 200 Tπg (195 g.) of the same clinobutyrolite thread natural zeolite (calcium ion exchange rate 16.7%) as used in Examples 1 and 2 was taken into 18 Erlenmeyer flasks, and 500- 6 was purified by repeating the decantation method five times using tap water.

i iC riff (1m f 8.000 In9'
! The mixture was transferred into 500 ml of a sodium phosphate aqueous solution (pH 4,3) containing 3 t'cifMI and subjected to contact treatment for 1 day, after which the residual liquid from the reaction was separated from the zeolite. continue,
The cells were transferred to a 3.2 wt% slaked lime emulsion at 500 mA and subjected to contact treatment for 3 days.

After 381 nl of contact treatment, the reaction residue was separated and further washed with tap water.

In this way, the entire dephosphorization process was created.

A dephosphorization experiment was conducted in the same prefecture as in Example 1. The average value of the measurement results of phosphorus concentration in treated water up to 22 days after the start of flooding was 0.
．． It was 16m9/lj.

Table 1 Measurement results of phosphorus CI degree of treated water From this result, in the example, 18.
The iWt improvement rate in such a low erosion degree range is estimated to be 8 to 31.3% (1).
This is more than m times.

Milk' + 1 person Kurita Industries Co., Ltd.

Claims (2)

[Claims] (1) Dephosphorization by contacting zeolite with an aqueous solution containing a calcium agent, then with an aqueous solution containing phosphoric acid or its salt, and then with a solution containing lime to form calcium phosphate crystals on the surface. A dephosphorization method characterized by passing water containing gold phosphate through a packed layer containing the agent in the presence of calcium ions and at a pH of 6 or more. (2) The dephosphorization method according to claim 1, wherein the zeolite has a calcium ion exchange rate of 20% or more after being brought into contact with an aqueous solution containing a calcium agent.