JPS58139784A - Dephosphorizing agent and dephosphorizing method - Google Patents

Abstract

PURPOSE:To provide a seed crystal for crystallization and removal of phosphates as calcium phosphate from phosphate-contg. water by using zeolite or limestone as a carrier and depositing the crystal of calcium phosphate thereon. CONSTITUTION:Phosphoric acids are removed from eutrophicated water such as sewage and industrial water contg. phosphates by using calcium phosphate as a seed crystal and crystallizing phosphoric acids as calcium phosphate on the surface thereof, whereby said water is purified. Zeolite or limestone is used as a carrier in producing the seed crystal and is brought into contact with an aq. soln. of <6pH contg. phosphoric acid or salts thereof so that phosphorus is deposited thereon at >=0.7mg with respect to 1g carrier. The carrier is then brought into contact with a soln. contg. calcium hydroxide at >=4 times weight of the phosphorus deposited thereon to deposit calcium phosphate on the surface of the carrier. Such carrier is brought into contact with the phosphate-contg. water, whereby the phosphates contained therein are crystallized and removed as calcium phosphate.

Description

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

In recent years, the progress of eutrophication in closed water areas such as lakes, marshes, and inner bays has become a serious problem.

Phosphate present in water has been highlighted as a cause of eutrophication, and its removal has been considered 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 orthophosphates and condensed phosphates, and organic phosphates.

As a method for removing such phosphates, a method has been proposed in which water containing phosphates is brought into contact with crystal species containing calcium phosphate, such as phosphate rock, in the presence of calcium ions (DissertationAbstra
cts International, Vol. 3
3. A12. Part I.

5878-f3 page etc.). This method removes phosphate ions contained in water by converting them into calcium phosphate, such as hydroxyapatite, and crystallizing them into crystal seeds. It has attracted particular attention in recent years because it not only simplifies the process but also greatly improves processing efficiency.

By the way, natural phosphate rock is mainly used as the crystal seed, but the supply of phosphate rock is limited and stable supply is difficult, and the chemical composition and physical properties differ depending on the production area. There are problems such as the difficulty of stable treatment due to differences in dephosphorization effects.

The present invention is intended to solve these conventional problems. By using zeolite or lime as a carrier and supporting crystals of calcium/ium phosphate, it can be easily produced and efficiently desorbed. It is an object of the present invention to provide a dephosphorization agent capable of phosphorization and a dephosphorization method using the same.

This invention includes the following two inventions.

(1) A phase consisting of zeolite or limestone is brought into contact with an aqueous solution containing phosphoric acid or its salt, separated from said solution, and then brought into contact with a solution containing lime to form crystals of calcium/umum. A dephosphorizing agent containing the generated substance.

(2) After contacting a carrier made of 4 or limestone with an aqueous solution containing phosphoric acid or its salt, l'lfJ
Processed by passing water containing phosphate in the presence of calcium ions through a packed bed filled with a dephosphorizing agent that was separated from the A+2 solution and then brought into contact with a lime solution to produce calcium/umium phosphate. A dephosphorization method characterized by:

The type and origin of zeolite and limestone as a 4"11 body are not particularly limited, and both natural and artificial ones can be used. Zeolites include clinoptilolite, mordenite, etc., and silica for alumina. Those with a high content are preferable, and these can withstand use at a pH of about 2-5, while other zeolites and limestone have a pH of about 2-5.
The usable pH range is wider than that of the 4-hole type. As limestone, marble, coral stone, calcite, etc. are preferable.

Both zeolite and limestone have excellent chemical adsorption ability for phosphorus and are suitable as a carrier, and either one or a mixture of both can be used as a carrier.

These may be used as a carrier in powder form, but granules are preferable because they can form a packed bed during dephosphorization. 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 phosphoric acid or a salt thereof to support phosphorus. Both zeolite and limestone have the property of adsorbing phosphorus from phosphoric acid (salt) solutions, and by bringing them into contact with each other by impregnation, etc.
Phosphorus can be easily adsorbed and supported. The phosphate salt can be arbitrarily selected from various orthophosphoric trq/l, such as sodium phosphate and potassium phosphate, to several tens of trq/l by weight. The contact operation may be either a batch operation or a continuous water flow method. pH of phosphoric acid (salt) aqueous solution during contact
Although not particularly limited, acidic conditions are preferred in order to efficiently support phosphorus, and conditions with a pH of less than 6 are particularly desirable. This seems to be because the state of dissociation of phosphate differs depending on the pH, and the tendency for adsorption to the carrier surface is higher at lower weights.At p)'16 or higher, it takes time to obtain stable treated water quality. Garu. The contact time varies depending on the carrier, the type of phosphate, the concentration, etc., but 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. At this time, by adding +)7fR salt as necessary, a stable mutual treatment effect is maintained. If the next operation is carried out without separating the solution, the phosphate ions in the solution will react with the slaked lime and a large amount of calcium phosphate precipitate will be produced, complicating the treatment process. Also, at this time, since slaked lime is consumed, the amount of slaked lime required increases,
Processing costs increase. Furthermore, 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 brought into contact with a solution containing lime, and the phosphorus supported on the carrier surface reacts with calcium hydroxide to produce calcium phosphate crystals with high dephosphorizing properties. As the solution containing lime, a slaked lime aqueous solution can be used, but other substances may be mixed therein. In order to produce high-quality calcium phosphate crystals, it is necessary to have a certain amount of hydroxide or more relative to 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 dephosphorization agent with a high removal rate under standard dephosphorization conditions, it is desirable to contact the dephosphorization agent with a solution containing hydroxide in an amount of 4 times or more by weight relative to the amount of supported phosphorus.

The cal/rum hydroxide concentration of the solution may be o, i~5 weight ratio, and the contact time may be about 1 to 7 days.

The product obtained by the above operation can be used as a dephosphorizing agent as it is or 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,
When the dephosphorizing agent is obtained in powder form, it is brought into contact with raw water containing phosphate in the form of a slurry, and when it is obtained in granular form, a packed bed is formed and water is passed through it. When the activity of the dephosphorizing agent decreases due to continued dephosphorization, it can be reactivated by performing the above-described calcium phosphate crystal production operation again.

In addition, in the above operation, it is also possible to add other chemicals, or to use or add other treatments in order to promote the reaction or make it more efficient.

The second aspect of the present invention is to pass water containing phosphate in the presence of calcium ions through the packed bed filled with the de-1 non-removal agent obtained above, thereby converting phosphate ions in the form of hydroxyapatite. This is a method of dephosphorizing by crystallizing on a dephosphorizing agent, and the usage of the dephosphorizing agent will be explained below regarding this method.

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-+ 3H2PO4-→Ca5(O
)()(POJ + 6H20-(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 right, and for this purpose, a calcium agent It is necessary to add calcium ions and alkaline agents as necessary to make calcium ions and hydroxide ions exist.If the amount of these ions becomes too large, fine precipitates may form in places other than the dephosphorizing agent. Since precipitates of calcium carbonate may be formed, the amount of calcium ions and hydroxide ions should be within a range that does not form.In other words, the amounts of calcium ions and hydroxide ions should be higher than the solubility of hydroxyapatite formed in equation (1), and These are conditions under which hydroxyapatite is produced at a concentration lower than its solubility, that is, at a concentration in the metastable range.

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

In order to keep the amounts of calcium ions and hydroxide ions within the above ranges, a calcium agent and/or an alkaline agent is added to the phosphate-containing water as necessary. Suitable addition amounts of calcium agents and alkaline agents can be determined in advance by simple experiments, but when the phosphate in the raw water is less than soi/l, the calcium ion concentration is 10 to 200 ■/l,...
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.

゛ The contact between the water containing phosphate and the dephosphorizing agent is carried out by a packed bed water flow system, but in the case of a fixed bed, the dephosphorizing agent is packed with a particle size of 9 to 55 mesh, and in the case of a fluidized bed, it is packed with a dephosphorizing agent of 36 to 500 mesh. , at a flow rate of 8 V1 to 2 [1 hr-', water is passed in an upward flow or a downward flow to precipitate hydroxyapatite crystals. In the case of upward flow, suspended matter can be trapped in the large particle size portion of the lower layer, and 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, in order to avoid the adhesion of suspended matter to the surface of the dephosphorizing agent, a filter medium with a smaller specific gravity and larger particle size than the dephosphorizing agent is filled with the dephosphorizing agent. It is desirable to remove suspended solids using this filter medium.

If the surface of the dephosphorizing agent becomes contaminated or clogged during water flow, backwashing is performed periodically using an upward flow to develop and clean the dephosphorizing agent and remove impurities attached to the surface. It is desirable to do so. The water flow conditions during backwashing are as follows:
The speed is about 0 to 80 m/hr, and the backwashing time is about 5 to 60 minutes.

As described above, when crystallization is performed in [7], hydroxyapatite with low solubility is mainly produced according to formula (1), which crystallizes on the surface of the dephosphorizing agent, and the phosphate concentration in the treated water becomes low.

In addition, in the above treatment, the raw water is pretreated 1-7 prior to the dephosphorization operation, and the treated water is post-treated.
Alternatively, during the dephosphorization treatment, it is also possible to use other treatments together, or to add a chemical or the like.

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. A similar technique is to obtain a dephosphorizing agent by contacting granular P materials such as sand, anthracite, and activated carbon with a solution containing phosphates that has been adjusted to pH 6 or higher in the presence of calcium salts. In this method, calcium phosphate is difficult to crystallize, so the dephosphorization performance cannot be said to be good. In contrast, in the present invention, phosphorus is strongly adsorbed chemically or physicochemically in advance on zeolite or limestone, which has good phosphorus adsorption properties, and then crystallization is performed.
Generates uniform crystals and exhibits excellent dephosphorization activity.

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

Example 1 200m (195F) of clinosatyrolite natural zeolite with a particle size of 16-52 mesh (1-0.5♂〆) was taken into 14 Erlenmeyer flasks and decanted using tap water of 5DDm/time. Washing was repeated 5 times.

Next, a sodium phosphate (NaH2PO4) aqueous solution (pH 4,5) adjusted to a phosphorus concentration of 8.000 ■/l 50
The carrier was transferred to 0 vtl and impregnated for 1 day, and then the reaction residual liquid and the zeolite carrier were separated.

The amount of phosphorus supported on the zeolite carrier in the above impregnating and supporting treatment operation was calculated from the amount of decrease in phosphorus concentration in the phosphoric acid solution, and was found to be 44 -p/r-carrier.

Subsequently, the above carrier was subjected to a contact treatment for 6 days in 500 ml of a 3.2 Wt % slaked lime emulsion. The amount of slaked lime used,
The weight ratio of the amount of iIJn supported is about 15.

After 6 days of contact treatment, the reaction residue was separated and thoroughly washed with tap water.

Prepared in this way, 150 ml of dephosphorizing agent was added to the
Packed into a 01n1n acrylic column, the phosphorus concentration was set to 2.
At the column inlet, calcium chloride aqueous solution and sodium hydroxide aqueous solution were added to synthetic water whose total alkalinity was adjusted to approximately 100 ■/l, and the calcium ion concentration was approximately 45 ■/l and the pH was adjusted to 85 ~ As 88, SV 2hr=
The liquid was continuously passed for about two weeks in an upward flow at a flow rate of .

After the water flow started, the average value of the phosphorus concentration of the stable treated water was 0.18 μ/l.

Example 2 The conditions were the same as in Example 1, except that aqueous phosphate-sodium solutions (pH 4, 4 to 4.7) with different phosphorus concentrations were brought into contact with zeolite, and the amount of phosphorus supported was changed. A dephosphorizing agent was prepared. Also, replace with zeolite, 16~
A dephosphorizing agent was prepared in the same manner as above using limestone (coralstone) with a particle size of 32 mesh. The obtained dephosphorizing agent was subjected to a liquid passage treatment under the same conditions as in Example 1, and the results regarding the amount of phosphorus supported and the phosphorus concentration of the treated water are shown in the graph of the drawing together with the results of Example 1.

Comparative Example 1 A dephosphorizing agent was prepared in the same manner as in Example 2 using activated carbon having a particle size of 16 to 2 mesh, and the results of the liquid passage treatment are also shown in the graph of the drawing. Compared to Example 1.2, the dephosphorization performance is lower, and the phosphorus removal rate is about 40%.

Comparative Example 2 The zeolite, limestone, and activated carbon used in Example 1.2 and Comparative Example 1 were packed untreated, and the dephosphorization ability of the carrier itself was tested by passing liquid under the same conditions as Example 1. In all cases, the phosphorus removal rate was less than 10%.

Example 6 In Example 1, a dephosphorizing agent was prepared and tested under the same conditions as in Example 1, except that the weight ratio of the amount of slaked lime during slaked lime treatment and the amount of supported phosphorus was changed. The results are shown in Table 1.

Example 4 Table 2 shows the results of preparation and testing under the same conditions as in Example 1, except that sodium hydroxide was added to the phosphate solution to change the pH.

Comparative Example 3 Example 1 except that the method of Example 1 was brought into direct contact with the slaked lime emulsion without contacting with the sulfur/acid aqueous solution.
processed in the same way. As a result, treated water of the same level as that of the present invention was obtained up to the 4th day, but after the 5th day, the quality of the treated water deteriorated rapidly, reaching 0.64 μ/l on the 7th day and 0.64 μ/L on the 100th day. 0.86■/1115th day Te 1.18 m9/12.

After 15 days, the same lime treatment as above is performed again.
Continuous operation was performed again. As a result, treated water was still of good quality until the 7th day, but after that the quality deteriorated significantly.

The following results can be found from the above results.

■The dephosphorizing agent of the present invention has much higher dephosphorizing performance than those in which the carrier is not specially treated, only lime is treated, or activated carbon is treated in the same manner as in the present invention. Are better.

(2) From the results shown in the drawings, there is a tendency for the dephosphorization performance to improve as the amount of phosphorus supported increases, and this is particularly noticeable when the amount of phosphorus supported is greater than 0,7rq-PA-carrier, and more preferably when the amount of phosphorus is more than 1 tq-P/carrier.

■From the results in Table 1, even if the amount of supported phosphorus is large, if the amount of calcium hydroxide is insufficient, excellent dephosphorization performance cannot be obtained. It is desirable to do so.

(2) From the results in Table 2, it is desirable that the aqueous solution containing phosphoric acid or its salt that comes into contact with the carrier has a concentration of less than I) H6.

[Brief explanation of drawings]

The drawings are graphs showing the results in Examples. Agent: Patent attorney Sei Yanagi Hara

Claims (1)

[Claims] (1) A carrier made of zeolite or limestone is brought into contact with an aqueous solution containing phosphoric acid or its salt, separated from the solution, and then brought into contact with a solution containing lime to produce calcium phosphate crystals. A dephosphorizing agent containing a substance that has been (2) The dephosphorizing agent according to claim 1, wherein the amount of phosphorus supported by the carrier upon contact with an aqueous solution containing phosphoric acid or a salt thereof is greater than or equal to 07■-P/7- carrier. (3) The dephosphorizing agent according to claim 1 or 2, wherein the aqueous solution containing phosphoric acid or its salt that contacts the carrier has a pH of less than 6. +4) The dephosphorizing agent according to any one of claims 1 to 6, wherein the amount of calcium hydroxide relative to the amount of phosphorus supported in the lime-containing solution is 4 times or more by weight. (5) A carrier made of zeolite or limestone is brought into contact with an aqueous solution containing phosphorus agility or its salt, separated from the solution, and then brought into contact with a lime solution to produce calcium phosphate. Cal/
A dephosphorization method characterized by launching and treating water containing phosphate in the presence of udon ions. (6) The dephosphorization method according to claim 5, wherein the amount of the phase supported by contacting with an aqueous solution containing phosphoric acid or a salt thereof is greater than or equal to 07■-P/f- carrier. (7) The pH of the aqueous solution containing phosphoric acid or its salt that comes into contact with the carrier is 6 or less.
Dephosphorization method described in section. (8) The dephosphorization method according to any one of claims 5 to 7, wherein the amount of calcium hydroxide relative to the amount of phosphorus supported in the lime-containing solution is 4 times the amount or more.