JPS6075394A - Dephosphorizing method - Google Patents

Abstract

PURPOSE:To permit easy production of a dephosphorizing agent and to perform effectively dephosphorizing treatment by bringing zeolite, etc. into contact with a lime soln. then bringing the same into contact with phosphoric acid and passing waste water contg. phosphate through the layer packed with the dephosphorizing agent formed by such contact. CONSTITUTION:A carrier consisting of zeolite or limestone is brought into contact with a soln. contg. lime of an aq. slaked lime soln. and is then separated from the soln. The soln. is then brought into contact with an aq. soln. of phosphoric acid or sodium phosphate to form the crystal of calcium phosphate. The resulted product thereof is packed as a dephosphorizing agent into the packed bed where waste water contg. phosphate is passed under the condition of >=6pH in the presence of Ca ion. The dephosphorizing agent having excellent dephosphorizing performance is stably produced with the simple operation by the above-mentioned method and the effective dephosphorizing treatment is accomplished by using such agent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a dephosphorization method, and particularly to a dephosphorization agent and a dephosphorization method suitable for treating water containing phosphates.

[Prior art]

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

Such as as a way to remove phosphates.

In the presence of water gold calcium ions containing phosphate, phosphate calcium such as phosphate rock7l7m? A method (crystallization dephosphorization method) has been proposed (LJiss
ertation Abstracts
ational+ Vol, 33, Ki xz, Par
t I, p. 5878-8, etc.). This method removes phosphate ions contained in water in the form of calcium phosphate, such as total hydroxyapatite, by crystallizing them into crystal seeds, and the operation method is not only simpler than the conventional flocculation method. In recent years, it has been attracting particular attention because it significantly improves processing efficiency.

By the way, natural phosphate rock is used as the crystal seed, but phosphate rock is not produced on a practical scale in Japan and is dependent on foreign partners, so it is not stable. Supply is in short supply. -Furthermore, phosphate rock has different chemical composition and physical properties depending on its production area, so is phosphate rock used as a crystal seed for crystallization dephosphorization? When used, there are differences in the dephosphorization effect, so in order to obtain a stable dephosphorization effect, various problems arise, such as the need to use a special type of phosphate rock. In order to solve this problem, people have developed an extremely efficient dephosphorizing agent that is obtained by contacting zeolite or lime with an aqueous solution containing phosphoric acid or its salts, and then contacting it with a lime-containing solution. We proposed all the dephosphorization methods to be used and filed a patent application (Japanese Patent Application Laid-Open No. 5F+-13
9784).

When using the dephosphorizing agent gold prepared by this method, a high dephosphorizing effect is fully exerted immediately after the raw water starts flowing, but a new problem was discovered in which the treated wastewater pi (pi) is high immediately after the water starts flowing.

[Purpose of the invention]

The present invention has been achieved as a result of intensive research and molding in order to obtain a dephosphorization method with a low pH of the treated water, based on the entire application method, and its purpose is to VC aims to provide a complete dephosphorization method that can be easily produced, allows efficient dephosphorization treatment, has a low pf of treated water, and does not require re-neutralization treatment of treated water.

[Structure of the invention]

In order to achieve all of these objects, the present invention provides a carrier made of zeolite or limestone that is obtained by contacting with an aqueous solution containing phosphoric acid or a salt thereof after contact treatment with a lime solution to remove lime. After contacting with a solution containing phosphoric acid, the dephosphorizing agent is separated from the solution, and then brought into contact with an aqueous solution containing phosphoric acid or its salt to completely generate calcium phosphate. Water containing acid? The gist of this is a dephosphorization method that involves passing water through the process.

The present invention will be explained in detail below.

The type and thickness of the zeolite and limestone used as carriers in the present invention are not particularly limited, and both naturally occurring and artificial zeolites can be used. Zeolites with high silica content relative to alumina, such as klip tyrolite and mordenite, are preferred, and these can withstand use with a pFi of about 2 #1, compared to other zeolites and limestone, which have a pH of only 4. Wide PTI range. As limestone, marble, pungoite, calcite, etc. are preferable.

Both zeolite and limestone are suitable as a carrier due to their chemical adsorption ability for phosphorus, and either one or a mixture of both can be used as a carrier. Although these may be used as a carrier in powder form, granular materials are preferred since they can form a filling during the dephosphorization treatment. In the case of granular materials, both zeolite and limestone require a greater powdering strength as a carrier than conventional phosphate rock.

The carrier as described above is first brought into contact with a solution containing lime to support calcium hydroxide. A slaked lime aqueous solution is suitable as the lime-containing solution, but other substances may be mixed therein.

The concentration of calcium hydroxide in the solution is preferably about 0.1 - 10 -. The contact operation may be either a batch operation or a continuous water flow method. The contact time varies depending on the carrier, the type and concentration of the lime-containing solution, and may be about 3 to 50 hours.

Contact treatment with solutions containing lime? The carrier used was

Separate from this solution. Separation is carried out by normal gravity separation, and if necessary, washing with water is performed. The separated solution can be used for the next loading operation. At this time, if necessary, by adding slaked lime or the like, a stable supporting treatment effect can be sustained. If the next operation is carried out without completely separating the solution, the slaked lime in the solution will react with the phosphate ions in the next step, producing a large amount of calcium phosphate precipitate, which will complicate the treatment process. Also, at this time, slaked lime rises. Further, fine calcium phosphate crystal seeds having a weak bonding force to the carrier surface adhere to the carrier surface and are detached during use, which is undesirable because the treatment effect is reduced.

The carrier from which the solution has been separated is then brought into contact with a solution containing phosphoric acid or its salt, causing the calcium hydroxide supported on the carrier surface to react with the phosphorus. Zoru. As the phosphate, various orthophosphates such as sodium phosphate and potassium phosphate can be used. The concentration of the phosphoric acid (salt) solution brought into contact with the carrier can be arbitrarily selected from 100 q/ml to several tens of weight %. The contact time may be about 1 to 7 days. The pH of the aqueous phosphoric acid (salt) solution during contact is not particularly limited, but in order to maintain a good dissociation state of phosphoric acid (salt) and increase reaction efficiency, acidic conditions are preferred, especially pl (less than 6 is desirable). O In order to produce high-quality calcium phosphate crystals, it is preferable that the quantitative ratio of calcium hydroxide to phosphorus is within a certain range, and a dephosphorizing agent with better performance can thereby be obtained.Standard In order to obtain a dephosphorizing agent with a high removal rate under standard dephosphorizing conditions, it is desirable to contact the dephosphorizing agent with a solution containing phosphorus at least twice the weight of the supported calcium hydroxide.

After contact treatment with an aqueous phosphoric acid (salt) solution, the carrier is separated from the total solution and washed with water if necessary to obtain a product.

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 in the case of conventional crystal seeds such as phosphate rock, and if the dephosphorization agent is obtained in powder form, it must be in slurry form and brought into contact with raw water containing phosphate, and if it is obtained in granular form, it must be contacted with raw water containing phosphate. Filling Wt'r shadow formation and water flow treatment. When the activity of the dephosphorizing agent decreases due to continued dephosphorization operation, the above-described operation for generating calcium phosphate crystals is performed again.

Can be reactivated.

In addition, in five or more operations, it is also possible to add other drugs or to use or add other treatments in order to promote the reaction or make it more efficient.

This is a method of dephosphorization by passing water containing water through it to crystallize phosphate ions in the form of all hydroxyapatite in the dephosphorizing excavated soil.The following describes this method. explain.

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. All crystallization is carried out 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 determined by the following formula.

sCa"+70H-+3nzP04--sCa5(On
)(PO2)r+6hl#=(1) In order to efficiently remove phosphorus from water containing phosphates, it is necessary for the reaction in equation 11 to proceed completely to the right, and for this reason, VC is used as a calcium agent or alkaline agent. It is necessary to add calcium ion 2 and hydroxide ion gold as necessary.

If the amount of these ions becomes too large, fine precipitates may form in areas other than the dephosphorizing agent.

Since calcium carbonate precipitates are bound to form, the range should be set so that these do not form.

In other words, the amount of calcium ions and hydroxide ions is (
This is a condition in which hydroxyapatite having a degree of welding higher than the degree of welding of hydroxyapatite produced in Equation 11 and lower than its supersolubility, that is, degree # of metastable region, is produced.

Here, the over-dissolution is the concentration at which crystals begin to precipitate when no crystal seeds are present in the reaction system.

In order to maintain the above range of calcium ions and hydroxyl ions, a calcium agent and/or an alkaline agent may be added to the water containing phosphate, if necessary. Suitable amounts of calcium and alkaline agents to be added can be determined in advance through simple experiments;
In the following case, calcium ion is lO ~ 2005 ahead, p
H is about 6 to 12.

Calcium agents used in this invention include calcium hydroxide and calcium chloride, and alkaline agents include sodium hydroxide, potassium hydroxide, calcium hydroxide, and the like.

Phosphate? The contact between the contained water and the dephosphorizing agent depends on the packed bed water flow system, but in the case of a fixed bed, the dephosphorizing agent has a particle size of 9 to 35 mesh, and in the case of a fluidized bed, it is 36 to 300 mesh, and the flow rate is Svl to 20 hr. −', water flows upward R or downward;
All crystals of hydroxyapatite are precipitated. In the case of upward flow, suspended matter can be captured in the large particle size portion of the tort layer, and crystallization can be performed in the small particle size and highly active portion of the upper layer.

Similarly, when water is passed in a downward flow, in order to avoid adhesion of suspended matter to the surface of the dephosphorizing agent, material F, which has a smaller specific gravity and larger particle size than the dephosphorizing agent, is placed on top of the dephosphorizing agent packed bed. It is desirable to remove the suspended solids from the door material. If the surface of the dephosphorizing agent becomes contaminated or clogged during water flow, periodically backwash the dephosphorizing agent with an upward flow to spread out the dephosphorizing agent and remove gold impurities attached to the surface. It is desirable to do so. What are the conditions for water flow during backwashing?

The flow rate is about 20 to 80 m/hr, and the backwashing time is about 5 to 60 minutes.

When the crystallization is carried out as described above, hydroxyapatite with a low solubility percentage is mainly produced according to the formula (1), which crystallizes on the surface of the desulfurizing agent, and the phosphate concentration in the treated water decreases. It gets lower.

In addition, in the above treatment, prior to the dephosphorization operation, the raw water may be pretreated, the treated water may be post-treated, or other treatment metals may be used together with the dephosphorization treatment, or chemicals, etc. may be added altogether. is also possible.

[Examples of the Invention] The present invention will be described in more detail below using Example 2 of the present invention and a comparative example, but the present invention is not limited to the following Examples unless the gist of the invention is completely diminished.

Example 200ml (195i) of clinoptilolite natural zeolite with particle size of 16 to 32 mesh (1 to 0.5 mm)
The mixture was placed in an Erlenmeyer flask and washed 5 times by decantation using 500 grams of tap water each time.

Next, the above zeolite was transferred into a slaked lime emulsion sooml containing 4.8F 1% by weight and subjected to a contact treatment for 5 hours.

After the contact treatment, the zeolite and slaked lime emulsion were separated and washed with tap water. Obtained Ceolite) K-phosphorus production ROOO
Phosphate monosodium (Na & PU4 prepared at wq/g)
) Water bath solution (pH 4,3) 50 om! It was moved into a container and subjected to contact treatment for 3 days. After the treatment, the reaction residue was completely separated and washed with tap water to obtain a dephosphorizing agent.

The obtained dephosphorizing agent 150IrLlt was packed into an acrylic column with an inner diameter of 30 m, and synthesized water (phosphor fIk degree 2tq/8
．． 1#, alkaline irreducible 100wq7B) (D de'J
I processed the money. In addition, calcium chloride aqueous solution and sodium hydroxide aqueous solution were added to the synthetic water at the column inlet.
Calcium ion concentration total approximately 45K/13°pH'z 8
．． R ~ 9.0, and the upward R of the flow rate zhr-/(8V)
Continuous water flow treatment was carried out for 22 days.

Measurement results of phosphorus concentration and p)l of the obtained treated water ft
It is shown in Table 1.

Table 1 From Table 1, according to the present invention, the phosphorus UU of the obtained treated water
After day 1, the phosphorus oIJc becomes 0.3η/6 or less, confirming that the treatment effect is extremely stable and the pH of the treated water is low.

Hii? Ill A dephosphorizing agent was prepared in the same manner as in Example 1 except that 5 ood2 of a 7.32% by weight calcium chloride aqueous solution was used instead of the slaked lime emulsion, and 4 dephosphorizing treatments of synthetic water were carried out under the same conditions. Table 2 shows the phosphorus level and pH of the resulting treated water.

Clothes 2 From Table 2, the phosphorus concentration of the treated water is around 2■/, and is calcium chloride used instead of slaked lime? It is clear that when prepared using this method, it shows almost no dephosphorized young fruit.

Comparative Example 2 Clinoptilolite natural zeolite 2007+17 (195i
) Pour 500IfLl of tap water into an Erlenmeyer flask at a time. Washing was repeated five times using the decantation method.

Next, 8,000 liters of phosphoric acid was added.
Sodium (Na&POi) aqueous solution (p[4,3)
The above carrier was transferred to 500 ml of water and left in contact for 1 day.
The reaction residual liquid and the zeolite carrier were completely separated.

The obtained zeolite was then transferred into a slaked lime emulsion 500-3.2% by weight and subjected to contact treatment for 3 days. After the treatment, the reaction residue was separated and thoroughly washed with tap water to obtain a dephosphorizing agent.

Using the dephosphorizing agent thus prepared, synthetic water was completely dephosphorized in the same manner as in the experimental crab. Table 3 shows the phosphorus content of the treated water and the pdO 1j fixed ayu pot. From Table 3, the phosphorus concentration of the treated water was 0.2η/e or less, and a stable dephosphorization treatment effect was achieved. However, the p of the treated water
It is clear that i( is high, and especially at the 58th point of water flow, the pH becomes 9 or more.

As described in detail above, according to the present invention, a carrier made of zeolite or limestone is brought into contact with a lime-containing solution and then brought into contact with an aqueous phosphoric acid (salt) solution. A dephosphorizing agent with excellent dephosphorizing performance? Not only can it be produced efficiently and stably, but it can also be used to perform all efficient dephosphorization treatments. In addition, the pH of the treated water obtained by the dephosphorization treatment is low, making re-neutralization of the treated water unnecessary, which is extremely advantageous industrially.

Claims (3)

[Claims] (1) Zenkou is a dephosphorizing agent in which a carrier made of zeolite and limestone is brought into contact with a solution containing lime, separated from the solution, and then brought into contact with an aqueous solution containing phosphorus IR or its salt to form a calcium phosphate solution. Treatment is carried out by passing water containing phosphates through the provided Kofu layer in the presence of calcium ions and under conditions of p) 16 or more f:
Characteristic dephosphorization method. (2) A phosphorus method characterized in that the lime-containing bath liquid is a slaked lime bath liquid. (3) The aqueous solution containing "phosphoric acid" or its salt must have a pH of less than 60%.
Dephosphorization method described in Section.