JPS62152588A - Treatment of water containing phosphate - Google Patents

Abstract

PURPOSE:To enhance sedimentary properties of sludge formation and reduce treatment cost by heat treating calcium silicate hydrate carrying a specific molar ratio of CaO/SiO2 and adding the same to water containing phosphate. CONSTITUTION:A raw material comprising CaO as main component and a raw material comprising SiO2 are mixed to make a 1.5-5.0 molar ratio of CaO/SiO2. Next, after being calcined at the temperature of 1,300-1,600 deg.C, said mixture is crushed into less than 149mum of grain diameter. Water as much as 1-7 times of weight of calcined substance and the crushed substance are mixed and hydrate reaction is carried out. Then, a hydrate substance carrying calcium silicate as main component is separated from water and heat aged at the temperature of 50-70 deg.C. The compound thus prepared is divided into two or three pieces and added to contaminated water containing phosphate. Said process makes better sedimentary properties of sludge formation and also makes an after treatment such as calcination and the like easier.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to various sewage, human waste water, factory water, factory wastewater,
This article relates to a method for removing phosphates present in water such as boiler water.

[Background Art] In recent years, environmental conservation and securing water resources have become very important social issues, and the technical contents and scope required for water treatment have become increasingly sophisticated and diverse.

In general, undefeated phosphates such as orthophosphates and various condensed phosphates exist in various forms in water such as various types of sewage, human waste water, factory water, factory wastewater, and boiler water. When these phosphates are discharged into natural water systems, the progress of eutrophication in closed or stagnant waters such as lakes and marshes and inland seas is a serious problem.

Against this background, various methods have been recently developed to remove phosphorous salts from water that require 2a, for example, as described in the magazine [Environmental Technology J Vol.
(1982), P. 826, P. 834 and P. 841, the lime coagulation precipitation method and the metal salt coagulation precipitation method using aluminum salt, iron salt, Magnesium cum salt, etc. are in practical use. It is served to.

[Problems to be Solved by the Invention] However, neither the lime coagulation precipitation method nor the metal salt coagulation precipitation method can be said to be a satisfactory method. For example, phosphorus III in the water to be treated! Since the salt removal performance is low, a large amount of flocculant is required, and a large amount of sludge is generated, resulting in high treatment costs.

In addition, there is a problem in that the sludge produced has poor settling properties, making it extremely difficult to treat the sludge.

[Means for Solving the Problems] The present inventors have previously discovered that a calcium silicate water treatment agent exhibits excellent adsorption and removal performance for pollutants contained in wastewater. The inventors of the present invention have conducted intensive research to solve the above-mentioned problems using this water treatment agent, and as a result, have come up with an industrially advantageous method for treating water containing phosphate.

The present invention has a CaO/S i 02 molar ratio of 1.5 to 5.0.
A water treatment in which a calcium silicate compound obtained by heating a substance whose main component is a calcium silicate hydrate within the range of 50 to 700'C is added in portions to water containing phosphate. It's a method. With this method, even if the amount of water treatment agent used is reduced, the original phosphate removal performance is not affected in any way; on the contrary, the amount of generated sludge is reduced, and the amount of water that has adsorbed phosphates is reduced. Excellent effects such as good sedimentation properties of the processing agent are produced.

Next, a preferred water treatment method according to the present invention will be explained in detail.

Raw materials whose main component is CaO and S! Cab/S! 02 is the main ingredient. They are mixed so that the Oz molar ratio is in the range of 1.5 to 5.0, preferably 2.0 to 4.0. CaO
Examples of raw materials whose main ingredients are calci carbonate, cum, and slaked lime; examples of raw materials whose main ingredients are 5iOz include, for example, silica,
Clay, fly ash, blast furnace slag, etc. can be used as appropriate.

After mixing these raw materials, they are fired at a temperature of 1300 to 1600°C. The calcined product of calcium silicate thus obtained is preferably crushed to a particle size of 149 μm or less using a crusher. Next, water in an amount of 1 to 7 times the amount of the fired product is mixed with the crushed product of the fired product to cause a hydration reaction. A substance whose main component is calcium silicate hydrate produced by the reaction is separated from water and
Heat ripening at a temperature of ~700°C, preferably 70-600'C. The water adhering to the substance containing calcium silicate hydrate as a main component is substantially removed by heating and aging. Although the time required for heat aging varies depending on the temperature, 3 hours or more is usually appropriate.

If the heating temperature is below 50°C, the water adhering to the substance whose main component is calcium silicate hydrate cannot be removed unless it is under reduced pressure, and it takes a very long time, so it is not practical for industrial use. There's no sex. Furthermore, when the hfl thermal temperature exceeds 700°C, the adsorption and removal performance of phosphates decreases.

For example, if the molar ratio of Cao/s i02 is 3.0, 1
According to the X-ray powder diffraction method, the material obtained by heating the hydrated material by baking at 500°C for 1 hour at 300°C has a ca.
Only the clear diffraction line of (OH)2 is observed, and only the other broad diffraction lines are observed. According to thermal analysis, the Ca(OH)2 content was approximately 18%.

From these facts, it is considered that the calcium silicate compound of the present invention is mainly composed of an amorphous substance.

The method for using this calcium silicate compound is to add the calcium silicate compound to water containing the contaminant to be removed, and to adsorb the phosphate, which is the substance to be removed, on the surface of the compound.

After the adsorption reaction, the calcium silicate compound is removed from the system.

Since the above-mentioned calcium silicate compound is a solid particle,
The reaction between the phosphate, which is the substance to be removed, and the calcium silicate compound proceeds as an adsorption reaction on the particle surface.

The reaction rate tends to be faster as the initial concentration of phosphate is higher, and slower as the initial concentration is lower.

If the surface of the solid particles is covered to some extent with phosphate, the progress of the adsorption reaction will be inhibited. For this reason, even if an attempt is made to carry out an adsorption reaction by adding the mother necessary for removing phosphates from water all at once, there is a phenomenon in which the adsorption reaction slows down as time passes. In order to avoid this phenomenon, the overall speed of the adsorption reaction can be increased by adding the calcium silicate-based compound in small portions, rather than adding the entire amount at once to water containing phosphate. This makes it possible to make the reactor more compact. The amount of adsorbent discharged after water treatment is also greatly reduced.

The specific method of adding the calcium silicate compound in portions can be determined depending on the phosphate removal rate or removal rate.

In the present invention, it is possible to separate the calcium silicate compound water treatment agent from the water each time it is added in portions, but it is not necessary and it is also possible to separate it all at the end, which is more practical. It is.

Regarding the number of divided additions of the calcium silicate compound, the phosphate removal effect improves as the number of divided additions increases, such as 3 divisions rather than 2 divisions, or 4 divisions rather than 3 divisions. Or, if the number of divisions exceeds a certain level, the degree of effectiveness becomes smaller compared to the complexity of the operation. Up to four divisions are used industrially. The operation method for water treatment may be either a batch method or a continuous method.

As the raw material for the above-mentioned calcium silicate compound used in the present invention, CaO/S! The molar ratio of 02 is 1.5 to 5.
0, preferably in the range 2.0 to 4°O. This mixture is calcined and pulverized, and then subjected to the steps of hydration, heat aging, and pulverization to form a silicified calcium-based compound.

Water treatment was carried out by adding the compound thus obtained in portions to water containing phosphate. In the above raw material composition, 3
A part of i 02 is Al 203 and/or Fe
203 may be substituted, and a mixture with such a composition was also prepared into a calcium silicate-based compound by the same operation as described above, and water treatment was performed by adding it in portions to water containing phosphate in the same manner as above. .

In all of the above cases, excellent adsorption and removal performance was exhibited for phosphate, which is a pollutant in water. However, if the raw material composition of the calcium silicate compound is out of the above range, the adsorption/removal performance of phosphate will decrease.

1 Effect 1 The water treatment method of the present invention removes phosphates such as orthophosphoric acid, orthophosphates, pyrophosphates, metaphosphates, and tripolyphosphates, which have been difficult to remove by lime and metal salt coagulation precipitation methods. Various types of sewage containing one or more types;
Calcium silicate compounds are added in divided doses to household sewage, factory water, factory wastewater, boiler water, etc., and it is better to add the calcium silicate compounds in divided doses rather than adding the whole amount at once. Indicates adsorption removal performance.

Although the mechanism of this action has not been clearly elucidated, when the calcium silicate compound of the present invention is added to not only alkaline water but also neutral or acidic water, the water becomes alkaline. Phosphate is generated and precipitates together with the input calcium silicate compound, or the anion portion of the phosphate ions in various phosphates dissociates under alkaline conditions and forms a positively charged calcium silicate compound. It is presumed that it is adsorbed to the surface. By dividing and adding calcium silicate compounds to various types of wastewater, we have realized a highly efficient water treatment method that not only has a high removal rate of pollutants in water, especially phosphates, but also has good sedimentation properties and produces little sludge. It became possible.

In the present invention, the quick-brewing calcium-based compound added in portions is preferably used in the form of a powder with a particle size of 0.149 mm or less, but it can also be used after being granulated to a particle size of 2.5 mm or less.

For example, when treating various types of wastewater with powder, add 2f [! If added, divide into 3 or more parts. At this time, in the batch method, the first calcium silicate compound is added and mixed and left in contact for a predetermined period of time to adsorb phosphate, a contaminant in the water, onto the surface of the calcium silicate compound, and then the next calcium silicate compound is added. and repeat the above operation. Thereafter, the calcium silicate compound that has adsorbed the phosphate is separated.

In addition, in the continuous method, calcium silicate compound powder was added in continuous portions to a predetermined tank of a large number of stirring tanks arranged in series, and the phosphate was sufficiently adsorbed on the surface of the calcium silicate compound. Thereafter, a method is adopted in which solids are separated from the water slurry containing calcium silicate compounds discharged from the final tank.

The contact time of the calcium silicate compound and water, addition charge, and addition ratio are adjusted as appropriate depending on the type and concentration of the phosphate to be removed and the degree to be treated. Next, the slurry containing the calcium silicate compound that has adsorbed the phosphate is concentrated and dehydrated to remove solid matter, which is a conventional process.

When using a granular calcium silicate compound, the granules are divided into various types of water treatment equipment, stirred and mixed, and then treated by a conventional method.

For example, granules having a particle size of 1.0 mm are divided into two or more ports and placed into a stirring tank. At this time, it is necessary to stir and mix the granulated product so that it comes into sufficient contact with the contaminant to be removed. Specifically, it is necessary to adjust the rotational speed to a higher speed than the stirring speed when using powder so that the granulated product does not settle to the bottom of the stirring tank. Further, in the continuous method, the granulated product may be divided and charged into predetermined tanks of a large number of stirring tanks arranged in series.

Alternatively, a method may be adopted in which the granulated material is placed in a bag with an opening smaller than the particle size and placed in a predetermined stirring tank. In this case, under normal conditions, the final step of separating solids from the treated water exiting the stirring tank can be omitted.

Next, the water treatment method of the present invention will be explained in detail with reference to examples.

[Example] Example 1 162 parts by weight of calcium carbonate powder (CaO content 54.5%) and 32.6 parts by weight of silica powder (S!02 content 96.0%) were weighed and mixed thoroughly. After that, in an electric furnace, 15
It was baked at a temperature of 00°C for 1 hour. This was ground in a test mill so that it passed through a standard sieve of 149 μm. Add 100 parts by weight of the above-mentioned pulverized product to 500 ml of water, and heat at 20°
The mixture was hydrated at C for 3 days with stirring. The water-containing solid obtained by filtration was heated in a dryer at 100°C for 8 hours. This was pulverized using a test mill to pass through a jFX Q sieve of 149 μm to prepare a calcium silicate compound.

Next, an experiment for adsorption and removal of phosphates was conducted using factory water containing diluted phosphorus-based rust preventive agent Cryset 15-370J (manufactured by Kurita Water Industries, Ltd.).

The P2O5 equivalent concentration in the factory water was 11.0mM.

0.30 g of the above calcium silicate compound was added to 2000 ml of this factory water, stirred for 60 minutes at 20'C using a magnetic stirrer at a rotation speed of 300 rl), and then 0.30 g of the calcium silicate compound was added. was added, stirred for 60 minutes, and the contents were filtered using filter paper. Regarding the filtrate thus treated, JIS KO102r
The concentration of P2O5 was measured using a spectrophotometer model 220A manufactured by Hitachi Ltd. 11 in accordance with the total phosphorus measurement method (decomposition with perchloric acid and nitric acid) in Section 3.1 of Factory Effluent Test Method 446, and the dephosphorization rate was determined.

The results are shown in Table 1.

Examples 2 to 4, Comparative Examples 1.2 Calcium silicate compounds were calcined and pulverized in the same manner as in Example 1, except that the mixing ratio of calcium carbonate powder and silica cedar was changed. Further, hydration reaction, filtration, heat aging and pulverization were carried out in the same manner as in Example 1 to prepare a calcium silicate compound. Using this preparation, an experiment for adsorption and removal of phosphate was conducted in the same manner as in Practical 1M Example 1.

Table 1 shows the mixing ratio of calcium carbonate powder and silica powder and the experimental results.

Table 1” ea7111 (7) Attachment 7 JDI 0.015
<Split! 711! 1st stage) + O, O + 5 (2nd stage of divided addition) = 0.030 W/V%lI2 P before treatment
20s Concentration 110■/Example 5 Calcium carbonate powder (CaO content @ 55.0%) 324 parts by weight, silica powder (S!02 content 96% > 40 parts by weight) and fly ash (SiO2 content 55%, A I 2
44 parts by weight (33% Fe2O3 content, 4% maximum Fe2O3 content, 2% CaO content) were weighed out, thoroughly mixed, and fired at a temperature of 1500°C in an electric furnace. This was ground in a test mill so that it passed through a standard sieve of 149 μm.

Further, in the same manner as in Example 1, a calcium silicate compound was prepared by performing a hydration reaction, cracking, heat aging, and pulverization. Using this preparation, the same phosphate adsorption and removal experiment as in Example 1 was conducted.

The results and the IDH measurement results of the filtrate are shown in Table 2.

Comparative Example 3 Calcium silicate compound prepared in Example 5.
The process was carried out in the same manner as in Example 5, except that 6() was added at once without dividing and stirred for 120 minutes.

The results are shown in Table 2.

Example 6.7 Heat aging conditions in Example 5 (100'C 18 hours)
at 300°C for 4 hours (Example 6) and 600'C1
The treatment was carried out in the same manner as in Example 5, except that the time was changed to 3 hours (Example 7).

The results are shown in Table 2.

Example 8 A calcium silicate-based compound was prepared in the same manner as in Example 5, except that the hydration reaction was carried out in warm water adjusted to 65 ± 1°C for 7 hours using the pulverized product obtained in Example 5 after firing. was prepared. A phosphate adsorption experiment similar to that in Example 1 was conducted using this preparation.

The results are shown in Table 2.

Table 2 Example 9 Reaction tank with crusher (diameter 30 cm, height 43 cm,
-I-Effect Yosen 259〉 was installed in a water system with 4 tanks installed in series.
It was fed continuously at a rate of OR/h.

In addition, the calcium silicate compound prepared in Example 5 was
The water was supplied to each of the tanks and the third tank at a rate of 1.8 J/h to treat industrial water containing phosphates.The treated water discharged from the fourth tank was continuously The mixture was filtered to obtain a filtrate.

When the steady state is reached, the degree of P2O5 in the filtrate is 0.
The dose was 1mM.

Example 10 In Example 9, using recovered water from the fertilizer factory, 50% of the total amount of calcium silicate compounds added to the 1st tank was added to the 24th tank. ! ,
After continuously adding 25% of the total amount to each of the third tanks, the samples were treated using the same method and equipment as in Example 1.

In addition, P 205 '+H before 2a burial of fertilizer factory recovered water
The concentration is 40mM Q, with addition of calcium silicate compound.
Oa was 30 (]/h. Also, the P 20 S temperature in the filtrate when steady state was reached was 0.2 mg/h.
It was 9 degrees.

Comparative Example 4 A treatment was carried out using the same method and apparatus as in Example 9, except that the industrial water used in Example was used and the entire amount of the lucium silicate compound was added to the first tank.

When the steady state is reached, the P2O5 concentration in the filtrate is 1.
The dose was 5mM.

[Effects of the Invention] As is clear from the above explanation, the water treatment method of the present invention in which quick-brewing calcium-based compounds are added in portions to water containing phosphates removes lime and metal salts by coagulation and precipitation. Excellent in adsorption and removal of phosphates such as orthophosphoric acid, orthophosphates, pyrophosphates, metaphosphates, tripolyphosphates, etc. contained in various types of sewage, human waste water, factory water, factory wastewater, etc., which have been difficult to remove. This shows the performance achieved.

Since the sludge produced has good settling properties and the amount of sludge produced is small, post-processing such as firing and dumping becomes easy.

Claims (4)

[Claims] (1) For water containing phosphate, CaO/SiO_
By adding in portions a calcium silicate-based compound obtained by heating a substance mainly composed of calcium silicate hydrate having a molar ratio of 1.5 to 5.0 at 50 to 700°C, A method for treating water containing phosphate, characterized by removing phosphate. (2) A method for treating water containing phosphate according to claim (1), wherein a calcium silicate compound in which a portion of SiO_2 is replaced with Al_2O_3 and/or Fe_2O_3 is added in portions. (3) The method for treating water containing phosphate according to claim (1), wherein the calcium silicate compound is added in 2 to 4 portions. (4) The method for treating water containing phosphate according to claim (2), wherein the calcium silicate compound is added in 2 to 4 portions.