JPS5845786A - Treatment of phosphate-contg. water - Google Patents

Abstract

PURPOSE:To enable to effectively remove phosphate, by adding fluoric ion together with a Ca agent or an alkali agent to phosphate-contg. water in the presence of Mg ion. CONSTITUTION:After fluoric ion together with a Ca agent or an alkali agent is added to phosphate-contg water adjusted pH at 3-6 in the presence of Mg ion, the water is brought into contact with Ca phosphate-contg. crystal seeds (e.g. hydroxyappatite, fluoroappatite or trilime phosphate) to perform precipitation. Said fluoric ion is generally added as the aqueous solution of a water-soluble salt such as Na fluoride or K fluoride, but may be prepared by passing water through a layer packed with fluorite, cryolite or the like to dissolve fluoric ion. By the coexistence of Mg ion and fluoric ion in the phosphate-contg. water, the phosphate can be efficiently removed at a high speed while inhibiting the precipitation of impurities such as Ca carbonate even when the water exceeds a semistable zone in a case not-containing Mg ion and fluoric ion.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating water containing phosphate to remove phosphate.

In recent years, the progress of eutrophication in closed water areas such as lakes 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 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 orthophosphates, 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 a crystal rod containing calcium phosphate such as phosphate rock in the presence of calcium ions (Dis@erta'tionAbstr
acts International, Vol.
33, AI2, Part I.

5878-8 etc.). This method removes phosphate ions contained in water by converting them into calcium phosphate such as hydroxyapatite and crystallizing them into crystal seeds.This method not only simplifies the operation method compared to conventional flocculation methods, but also The reaction that occurs when water containing 0 phosphate is brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions has been attracting particular attention in recent years because the treatment efficiency is significantly improved. Although it differs accordingly, it is usually expressed by the following formula.

5Ca"+70H"-+5HhPOa-→Ca, (O
H)(PO,)3+6H,0- (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. must add the required amount of calcium or alkaline agents.

Conventionally, if the amount of these additions is too large, fine precipitates may be formed in places other than the crystal seeds, or calcium carbonate precipitates may be formed, so these should be within a range that does not prevent green sheets. It had been.

That is, the amount F of calcium ions and hydroxide ions
The conditions were such that hydroxyapatite was produced at a concentration higher than the solubility of the hydroxyapatite produced in formula i (1) and lower than its supersolubility, 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.

However, since the metastable region varies depending on the alkalinity of the water to be treated, when operating at the over-solubility limit,
Due to fluctuations in the quality of the raw water, the metastable region is exceeded and the concentration shifts to the unstable region (a concentration region where fine precipitates are formed in places other than crystal seeds in the reaction system), and precipitates such as calcium carbonate precipitate, resulting in It has been reported that there is a tendency to reduce the phosphate removal effect.

This invention is intended to eliminate the above-mentioned drawbacks of conventional methods. By adding fluoride ions to raw water in the presence of magnesium ions, phosphoric acid can effectively remove phosphates. The purpose is to provide a method for treating water containing salt.

This invention is characterized by adding heptadium ions and a calcium agent or an alkali agent to water containing phosphate in the presence of 1 magnesium ion, and then bringing the mixture into contact with crystal seeds containing calcium phosphate to perform crystallization. This is a method for treating water containing acid salts.

In this invention, one of the essential requirements is the presence of magnesium ions in the phosphate-containing water, but as is clear from the experimental examples described later, when magnesium ions are present, the Even when operating beyond the metastable region, precipitation of impurities such as calcium carbonate is suppressed. In other words, we have discovered the effect of widening the metastable region. Regarding this point, in the past, for example, in the above-mentioned omniscient literature, magnesium was only considered to be a factor that deteriorates the phosphate removal efficiency of hydroxyapatite, and as in this invention, magnesium is only considered to be a factor that deteriorates the phosphate removal efficiency of hydroxyapatite. This effect was completely unknown.

The water to be treated in this invention includes secondary treated water such as sewage and human waste. Further, examples of magnesium ions that should be made to coexist include water-soluble magnesium salts such as magnesium chloride, but if magnesium ions already exist in the raw water, it is of course unnecessary to add them from the outside. In this way, examples of water that already contain magnesium ions include sewage diluted with seawater and discharged water from human waste treatment plants.

The presence of magnesium ions in raw water has the advantage of preventing the precipitation of calcium carbonate as described above, but on the other hand, the reaction of formula (1) becomes difficult to proceed. This is because the presence of magnesium ions inhibits the production reaction of hydroxyapatite, and calcium phosphate salts, which have higher solubility than hydroxyapatite, such as Ca4H (P
This is thought to be due to the generation of O, )3, etc.

In this invention, in order to overcome the reaction inhibiting aspect of magnesium ions, it is an essential component to further add fluoride ions.

Normally, when fluoride ions are present, a reaction represented by the following formula occurs.

5Ca"+ F"+60H-+ 3H2P04'-, →
Ca5F(PO4)1+ 6H,O・(2) Fluoroapatite produced in formula (2) has lower solubility and is a more stable form than hydroxyapatite. The concentration of phosphate will be lower. In addition, the presence of heptatide ions has the effect of increasing the crystallization reaction rate under the same conditions as compared to the case where fluoride ions are not present.

The method of adding fluoride ions is not particularly limited, and it is common to add water-soluble salts such as sodium heptadide and potassium fluoride in the form of an aqueous solution, but filling with fluorite, cryolite, etc. Water may be passed through the layer to dissolve the fluorine ions.

The amount of fluoride ion added is generally 0.5 to 101
It is about Q/l. If it exceeds 10rn971, depending on the phosphate content, it may remain in the treated water and cause secondary pollution.
becomes. If it is within the above range, the added fluoride ions become fluoroapatite and are removed by crystallization, so a new fluoride ion removal device is not required. Immediately after discontinuing the addition of fluoride ions, the phosphate concentration in the treated water gradually increases and becomes the same level as when no fluoride ions are added after about a month, so adding fluoride ions does not affect water quality. Although it can be done intermittently while monitoring the water, it is preferable to use continuous injection as it provides more stable water quality.

When a method of passing water through a packed bed of rock, cryolite, etc. is adopted, the required amount of fluoride ions can be dissolved simply by adjusting the water passing rate. The barrel stone is CaF2
, Cryolite U Na5AI! Minerals mainly composed of F6, all of which have low solubility, are suitable for eluting low concentrations of fluoride. These minerals may be used alone or in combination to form a packed bed, and raw water is passed through and brought into contact with the packed bed.

The method of contact between the raw water and these packed beds may be either a fixed bed water flow method or a fluidized bed water flow method.

When treating water that contains suspended matter, if you use a fixed bed water flow system filled with fluorine-containing minerals that are about the size of the filter media used in normal filtration, the suspended matter in the water will be removed by the filtration action. Since the influence of suspended matter in the subsequent crystallization step K" can be ignored, a more stable treatment effect can be achieved. In particular, in the crystallization step, crystal seeds containing calcium phosphate and a fixed bed water flow method are used. In the case of contact, the trapping of suspended matter in the crystal seed packed bed can be ignored, so the frequency of backwashing of the crystal seed packed bed is reduced, and a more stable treatment effect can be obtained. Backwashing the bed disturbs the packed bed, and even if the treatment is restarted, the quality of the treated water will be affected for several hours, and the quality of the treated water will deteriorate. - When the suspended AML II degree is low, such as when raw water is filtered in the pretreatment stage, a fluidized bed water flow system may be adopted.The water flow direction is not particularly limited, and upward flow , or downward flow.

The flow rate when water is passed is determined by the particle size of the packed bed, the bed height, and the raw water, and the flow rate is such that the necessary fluoride ions can be eluted. The water velocity is approximately Sv1 to 10 (1/hr).

Raw water when flowing through a packed bed of 5 fathoms of stone and ice crystals -
There is no limit to this, and it may be within a range where fluoride ions can be eluted, but if the raw water has a high pH, add acid in advance to adjust the pH to 5 to 6.
It is preferable to adjust to Acid addition treatment can be incorporated into the main treatment process as necessary, taking into account the quality of the target wastewater and the target phosphate concentration of the treated water. If the - of the raw water is too low, excessive fluoride ions will be eluted and the
is required.

To perform crystallization, it is necessary to add calcium ions or an alkaline agent to the fluoride ions and adjust the calcium ion concentration to the level necessary for the reaction of formula (2). When adding heptadide ions in the form of water-soluble salts, there is no restriction on the order of addition of calcium agents, alkaline agents, etc., but the place where water is passed through a packed bed of #matamaru stone, cryolite, etc. should be filled. If added before water passing through the layer, the elution of fluoride ions will be impaired, so it should be added after water passing through the optical layer.

The amount of calcium agent or alkaline agent to be added to raw water should be in excess of the reaction equivalent expressed by equation (2), but if it is added in an extremely large amount, fine precipitates will precipitate in places other than crystal seeds. In addition, impurities such as calcium carbonate may be produced, so it should be within a range that does not produce any impurities.

However, in the conventional method, as mentioned above, it was necessary to determine the amount of addition within the metastable region of hydroxyapatite and operate, but in this invention, by coexisting magnesium ions and fluoride ions, it is possible to avoid the coexistence of hydroxyapatite. It is possible to operate beyond the metastable region of , and even in the region conventionally known as the unstable region. and,
The reaction rate can be increased accordingly, which brings about many benefits.

However, even in this invention, caution should be taken not to add an excessive amount of calcium or alkaline agents to the amberjack, as fine crystals will form in areas other than the crystal seeds.

The preferred amount of calcium and alkaline agents added is 50% phosphate in water. m9/l or less, when coexisting magnesium ions are 5o, my/11, calcium ions are 10~
200In9/A, pH is about 6-12.

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.

Crystal species containing calcium phosphate include hydroxyapatite (Ca5(OH)(Po4)s), fluoroapatite (Ca5(F)(PO4)!), and tricalcium phosphate (,Caa(PO+)t). Crystalline species containing calcium phosphate' can be used, and natural phosphate rocks contain these phosphates. Furthermore, crystal seeds in which calcium phosphate is precipitated on the surface of a filter medium such as sand can also be used.

If the main component is fluoroapatite, which is the same type as calcium phosphate produced by the reaction, as the crystal seed, new crystals will be deposited smoothly, phosphate will be removed efficiently, and the removal rate will increase.

The method of contacting the water containing phosphate with the crystal seeds may be either a fixed bed method or a fluidized bed method, but when the fluidized bed water is passed through a layer of stones etc. in the first stage, suspended matter is also removed at the same time. Therefore, a fixed bed type is preferable, and a fluidized bed type may be used when the ion exchanger packed bed is a fixed bed.

Preferably, if water is passed through a fixed bed filled with fluorite or the like, and suspended matter is also removed at the same time, the particle size of the crystal seeds filled in the crystal seed packed bed can be made smaller, and as described above, Additionally, the number of times the crystal seeds are backwashed can be reduced, and as a result, treated water with more stable quality can be obtained.

Generally, the smaller the size of the crystal seeds, the larger the specific surface area, so that new crystals are more likely to precipitate. However, if the size of the crystal seeds is too small, it becomes difficult to contact or separate the crystal seeds from water. Also, if the particle size is too large, the specific surface area per unit filling amount will be small.
Usually, about 9 to 300 meshes are used. Among these, the larger one is suitable for a fixed bed, and the smaller one is suitable for a fluidized bed.

In the case of a fixed bed, crystal seeds having a particle size of 9 to 65 mesh are packed, and water is passed upwardly or downwardly at a flow rate of SV1 to 10 hr-' to precipitate fluoroapatite crystals. In addition, if the first step is a fluidized bed, in the second step, suspended matter is captured in the lower layer with large particle size and crystallized in the upper layer with high activity of small particle size. I can do it. Similarly, when water is passed in a downward direction, it is necessary to avoid the adhesion of suspended matter to the surface of the crystal seeds.

It is desirable to layer a filter medium with a small specific gravity and a large particle size on the crystal seed fixing layer, and to remove suspended matter with this filter medium. If the surface of the crystal seeds becomes contaminated or clogged during water flow, it is recommended to periodically backwash the crystal seeds using an upward flow to develop and clean the crystal seeds and remove impurities attached to the surface. desirable.

Water flow conditions during backwashing include a flow rate of 20 to 80 m/hr.
The backwashing time is about 5 to 60 minutes.

When crystallization is carried out in the above manner, fluorite, oroa/gutite, which has low solubility according to equation (2), is mainly produced, and this crystallizes on the surface of the crystal seeds, and the phosphate concentration in the treated water decreases. Despite the presence of magnesium ions, they are extremely low. The action of magnesium ions is considered to be a kind of negative catalyst, and they remain in the treated water and are discharged. The heptadide ion becomes fluoroapatite and also acts as a catalyst for the formation of hydroxya/ξtite! Therefore, it is assumed that a positive catalyst and a negative catalyst coexist in the aqueous system, and that the positive catalyst becomes predominant and the reaction proceeds.

As described above, according to the present invention, by allowing magnesium ions and heptadide ions to exist in water containing phosphate, impurities such as calcium carbonate can be precipitated even beyond the metastable range when they are not present. It is possible to remove phosphates quickly and efficiently while preventing this, and the phosphate concentration in treated water can be extremely reduced.

Next, experimental examples and examples of the present invention will be explained.

Experimental example Sodium bicarbonate with total alkalinity of 1.00 da/l
Calcium chloride is added as calcium to distilled water added to give a concentration of 150 μ/l, 45 μ/11 magnesium chloride is added as magnesium, 0 da/i, 20 my/l, s
Further addition was made to give om9/i, aomy/lt, and then the temperature was adjusted to 95 using sodium hydroxide. The solution thus obtained was stirred and reacted at room temperature. After 1 hour, the solution was filtered, and the calcium ion concentration in the filtrate was measured by EDTA titration. Table 1 shows the results.
Shown below.

Table 1 As is clear from Table 1, the presence of magnesium ions increases the concentration of calcium ions in the filtrate, and a particularly remarkable effect is obtained with magnesium ions of soq,'z or higher.゛Example 1 Inner diameter 3. Jordanian phosphate rock (with a particle size of 16 to 32 mesh) was placed in an acrylic column with a length of Q cm and a length of 50 cIIL.
Filled with 150 mJ of water that had become steadily active after being used for water flow treatment for about 100 days in a magnesium ion concentration of 40 to 501n9/7δ coexistence system, synthetic water (phosphorus concentration of 1 to 1/l,
Total alkalinity approximately 100+9/J, magnesium ion concentration 50 Da/1. pH 7,0) Add an aqueous solution of calcium chloride and sodium hydroxide at the inlet of the IIC column to adjust calcium ion si to so~85 da/l and - to 8.8~9.
．． OK! After preparing the phosphate rock, the packed bed of phosphate rock was filled with 2" (j/
Water was passed continuously for 7 days using an upward flow fixed bed water flow method at a flow rate of hrlr. From the 7th day, in addition to adding calcium chloride and sodium hydroxide at the column inlet, a treatment according to the present invention was performed by adding an aqueous solution of sodium fluoride as fluorine ions to a concentration of about 1 tny/l. For comparison, we also used a column packed with Jordanian phosphate rock similar to the one above to confirm the effect of treatment in the absence of magnesium ions (no fluorine added). These results are shown in Table 2.

Table 2 From the above results, it is clear that in the system without magnesium ions, the phosphorus concentration in the treated water is always o12myZl.
A stable treatment effect was achieved under i.
．． It varied in the range of 24 to 0.62 m971, and a stable high phosphorus removal effect could not be achieved.

On the other hand, even when containing 50~/l of magnesium ions,
After the 7th day of water treatment using the treatment method based on the present invention, the phosphorus concentration of the treated water gradually decreased, and after the 14th day, it decreased to the level of the treated water that was almost the same as that of the system in which magnesium ions did not coexist. On day 0, we were able to achieve a stable treatment effect, which was even better than the non-coexistence system.

The fluoride ion concentrations in the treated water were all below the detection limit.

Example 2 A column was filled with 5 CJtl of 1 to 2 square stones, and another column was filled with 150 l of the same phosphate rock as in Example 1 (however, it had been subjected to water flow treatment for 250 days), and the columns were placed in series. I contacted. The same raw water as in Example 1 was added to this device! ('I
The sample was first passed through the fluorite layer using an upward flow fixed bed method at a flow rate of /, by), and then treated in the same manner as in Example 1. The results are shown in Table 6. The case where the fluorite layer is bypassed is also shown.

Table 6 □ From the above results, it can be seen that, despite the high flow velocity of the SV of the stone layer of 10, there is a significant difference in effectiveness between when the flow goes through the stone layer and when it does not go through the stone layer.

Agent: Patent attorney Sei Yanagi Hara

Claims (6)

[Claims] (1) The method is characterized by adding an alkaline agent to water containing phosphate in the presence of magnesium ions, and then crystallizing the mixture by bringing it into contact with crystal seeds containing calcium phosphate. How to treat water containing phosphates (2) A method for treating water containing phosphate according to claim 1, wherein the heptadium ion is added as an aqueous solution of a water-soluble salt. (3) The method for treating water containing phosphate according to claim 2, wherein the water-soluble salt is sodium fluoride or potassium heptafluoride. (4) The method for treating phosphate-containing water according to claim 1, in which the addition of fluoride ions is carried out by passing the water through a packed bed of marble or cryolite. (5) A method for treating water containing phosphates as set forth in claim 4, which comprises reducing the raw water to 6-6 and passing the water through a packed bed. (6) The method for treating water containing phosphate according to any one of claims 1 to 5, wherein the crystal seeds containing calcium phosphate are hydroxyapatite, fluoroanotite, takelin, and acid trilime.