JP4007890B2 - Water purification material - Google Patents

Description

【発明の効果】
低コストで製造でき、かつ栄養塩類、特にリンを吸着させ得る水質浄化材料を得ることができる。また、覆砂される場所の底質の条件に適するように製造できる水質浄化材料が得られる。また、低コストで良好な覆砂性能を得る水質浄化材料を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a material that reuses coal ash (fly ash), which is industrial waste discharged from a thermal power plant, or a construction method using the same, and in particular, it can purify water quality in rivers, lakes, sea areas, and the like. It relates to materials or construction methods that can be used.
[0002]
[Prior art]
One of the water pollution factors in rivers, lakes and marshes is the elution of organic matter, nutrients such as nitrogen and phosphorus from the bottom of the ground. There is a sand-capping method as a typical countermeasure for water purification against these elutions. In this method, natural sand or viscous soil is used to form a layer with an almost uniform thickness on the organic sediment. In many cases, natural sand is used, and thick on top of the bottom mud containing a large amount of nutrients. Scrape out about 30 to 150 cm so that nutrients are prevented from leaching from the bottom mud. According to the sand-capping method, the elution prevention effect can be obtained at a lower cost as compared with a method of removing organic sediment by dredging or insolubilizing phosphorus by spraying chemicals.
[0003]
There are various theories about the mechanism of the effect of inhibiting the dissolution of nutrient salts by sand-capping, but it is said that the following effects are exhibited in combination.
(1) Nutrient salts are adsorbed on the surface of sand material, and elution is suppressed.
(2) By covering the surface with sand material, it is possible to prevent the surface floating mud from being rolled up and diffused by the water flow, and to reduce the elution of nutrient salts into the water.
(3) Although the elution of nutrients increases dramatically in anaerobic conditions, aerobic conditions are maintained and the elution of nutrients is suppressed by constructing a sand layer with high quality and high water permeability (water exchange capacity) on the surface layer. .
[0004]
However, with respect to (1), it is a fact that conventional natural sand is hardly expected to adsorb nutrient salts, so it is necessary to increase the thickness of the sand cover to prevent the dissolution of nutrient salts. As a result, there is a problem that it is difficult to maintain the aerobic state (3) and the cost is increased.
[0005]
By the way, the enforced sand-capping layer is affected by various external factors. For example, the water flow that is constantly generated on the seabed or river bottom may move the sand-capping material and cause the sand-capping layer to flow out, and if the sediment is soft, the sand-capping material will sink into the sediment. May not be effective. Moreover, the sand-covering layer may be used for the purpose of promoting the growth of benthic organisms. These conditions differ depending on the water area where sand covering is performed, and the conditions of the optimum sand covering material are also different. However, when conventional natural sand is used as a sand-capping material, it must be used in the state collected from the cost side, and a sand-clad material suitable for the conditions of the place where sand is covered should be selected. Is difficult.
[0006]
In addition, as a sand covering material that can be substituted for natural sand, artificial zeolite obtained by hydrothermal chemical treatment of coal ash (fly ash) discharged from a thermal power plant is used as it is or molded into a plate shape, etc. The invention of the purification method is disclosed (for example, see Patent Document 1).
[0007]
However, this material requires considerable manufacturing costs for hydrothermal chemical treatment and the like. Usually, a large amount of sand covering material is required for laying the sand covering layer on the upper surface of the water bottom ground, so that the cost for sand covering work is also great.
[0008]
On the other hand, the invention of the ground improvement material which solidified and granulated the coal ash collect | recovered from the boiler of the thermal power plant with cement etc. is disclosed. This ground improvement material is used for drainage material, compaction material or drainage laying sand because of its water permeability and strength (see, for example, Patent Document 2).
[0009]
[Patent Document 1]
JP 2000-29951 A (columns 0010 to 0012)
[Patent Document 2]
JP 2000-154526 A (column 0005)
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a water purification material that can be produced at a low cost and can reliably adsorb nutrients, particularly phosphorus. It is another object of the present invention to provide a water purification material that can be manufactured so as to be suitable for the condition of the bottom sediment of the place to be covered with sand. Furthermore, it is an object of the present invention to provide a sand-capping method capable of obtaining good sand-capping performance at a low cost in the sand-capping method on the contaminated sediment.
[0011]
[Means for Solving the Problems]
The present invention contains coal ash in the range of 80 to 97 parts by weight, solidified material in the range of 2 to 15 parts by weight, bentonite in the range of 2 to 5 parts by weight and an average particle size of 0. the following crushing strength .1mm~20mm is Ri Do from granules above 2 MPa, and a water purification material comprising a Ru coating der of the sea bed soil. Thereby, the water purification material which can adsorb | suck nutrients, especially phosphorus reliably can be obtained. Moreover, the water purification material can be produced at a relatively low cost and has a high adsorption performance for nutrient salts such as phosphorus.
[0012]
The second aspect of the invention is that the coal ash is 80 to 97 parts by weight, the solidified material is 2 to 15 parts by weight, the bentonite is 2 to 5 parts by weight, and the water is 15 to 25 parts by weight. In the method for producing a water purification material described above, the mixture is put into a mixer within the following range, stirred and mixed to form a granulated product, and dried at 10 to 40 ° C. for 1 day to 1 month. is there.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described below.
The water purification material according to the present invention uses coal ash that is discarded as industrial waste from a thermal power plant. Furthermore, among coal ash, it is desirable to use fly ash collected by an electric dust collector before exhausting from a thermal power plant from the viewpoint of adsorption removal performance of nutrient salts contained in water to be treated.
[0014]
The water purification material is obtained by granulating this coal ash, preferably fly ash. Although when the granulation is mixed with solidifying material and water such as cement, coal ash, particularly fly ash poor water retention, when the granulation, water-retaining material also Ru addition to solidifying material and water. These are put into a mixer and agitated and mixed at around room temperature for granulation.
[0015]
In granulating, it is desirable to granulate the coal ash using the state recovered from the electric dust collector without any chemical treatment in advance. It becomes possible to keep the production cost of the granulated product low.
[0016]
As the solidifying material that can be used, cement or cement and dihydrate gypsum are used, and as the water retaining material, bentonite is used from the viewpoint of stably producing a granulated product.
[0017]
Here, the blending ratio of each component, the coal ash Ru der 80 parts by weight or more 97 parts by weight or less. When the amount is 80 parts by weight or more, adhesion of the granulated material at the outlet of the mixer used at the time of granulation hardly occurs and handling becomes easy, and when it is 97 parts by weight or less, sufficient strength as a sand covering material is obtained. More desirably, it is 85 parts by weight or more and 95 parts by weight or less, and further desirably 87 parts by weight or more and 93 parts by weight or less.
[0018]
Solidifying material, Ru der than 15 parts by weight 2 parts by weight or more. The strength required for the material can be obtained at 2 parts by weight or more, and the trouble that the granulated material adheres at the outlet of the mixer used at the time of granulation at 15 parts by weight or less is less likely to occur. It becomes easy. More desirably, it is 7 parts by weight or more and 13 parts by weight or less, and further desirably 9 parts by weight or more and 11 parts by weight or less.
[0019]
When dihydrate gypsum is included in the solidifying material, it is desirable to blend so that the dihydrate gypsum is 7 parts by weight or more and 10 parts by weight or less. When the amount is 7 parts by weight or more, the amount of other solidifying material used can be reduced to reduce the manufacturing cost, and when the amount is 10 parts by weight or less, granulation can be stably performed.
[0020]
Water-retaining material is Ru added at 5 parts by weight or less than 2 parts by weight. If it is 5 parts by weight or less, adhesion troubles during granulation hardly occur and handling becomes easy. More desirably, it is 4 parts by weight or less. In addition, it is possible to perform granulation without using a water retaining material, but adding it tends to make the granulation more stable. Therefore, it is more desirably 2 parts by weight or more and 3 parts by weight or less.
[0021]
Water may be added so that granulation becomes stable and the strength of the particles falls within a necessary range. For example, the water can be added in an amount of 15 to 25 parts by weight. If it is 15 parts by weight or more, the shape of the granulated product is easily stabilized, and if it is 25 parts by weight or less, it becomes easy to obtain a granulated product having the required strength. More desirably, it is 18 parts by weight or more and 25 parts by weight or less.
[0022]
Each of the above blends is put into a mixer and stirred and mixed at room temperature for granulation. The mixer used for the stirring and mixing process is not particularly limited as long as the process can be performed.For example, a cylindrical drum is placed horizontally, a stirring blade is provided on a rotating main shaft provided in the center of the drum, and It is desirable to use a high-speed rotary mixer having an independent drive chopper provided inside the side surface of the drum. The operation conditions when this mixer is used are that the stirring blade is rotated at around 50 to 100 rpm, and at the same time the chopper is rotated at a high speed around 1000 to 2000 rpm and operated for about 3 to 10 minutes. Thereby, a uniform granulated product having an average particle size of 2 mm to 10 mm can be obtained in a short time. An example of such a mixer is described in, for example, Japanese Patent Application Laid-Open No. 2000-154526.
[0023]
Another desirable mixer has a vertical mixing layer having a bottom surface and a funnel-inclined side surface that descends toward a discharge port provided at the center of the bottom surface. A high-speed rotating shaft attached with a spiral inner kneading blade rotating at the center of the mixing tank, and an outer kneading blade via an arm so that the outer kneading blade rotates close to the inner side surface of the mixing layer. An example is a mixer in which the attached low-speed rotation shafts are arranged concentrically, and a drive device is provided so that the rotation directions of these high-speed rotation shafts and low-speed rotation shafts are opposite.
[0024]
Using these mixers, it is possible to produce a sand covering material using a particle size distribution that is most suitable for the bottom sediment condition and water flow condition of the water area where sand covering is performed. Specifically, after adjusting the mixer operating conditions so as to obtain the desired particle size distribution and granulating, the granulated product is taken out of the mixer and dried for a certain period of time near the room temperature. A solidified granule is obtained. The drying temperature is preferably 5 ° C or higher, more preferably 10 ° C or higher and 40 ° C or lower. Most preferably, it is performed at around 20 ° C. What is necessary is just to select a drying period suitably according to the conditions of the solidification material to be used and temperature between about 1 day to 1 month.
[0025]
The average particle diameter of the solidified granulated product state, and are 20mm or more or less 0.1 mm, preferably is 0.5mm or more 15mm or less. More desirably, it is 0.5 mm or more and 10 mm or less. In this range, good performance as a sand-capping material can be obtained, but it goes without saying that the average particle size or particle size distribution of the sand-capping material should be selected according to the place and purpose of sand-capping.
[0026]
The crushing strength of the solidified granule obtained in this way is about 2 MPa or more on average after drying for 28 days, and can be obtained at the same cost as natural sand. It can be handled in the same way as natural sand. Further, this solidified granulated product is excellent in the adsorption ability of nutrient salts such as ammonia nitrogen, and in particular, excellent in the adsorption ability of phosphorus. Therefore, it is useful as a purification material for water quality contaminated with nutrient salts.
[0027]
Next, the sand covering method performed using this granulated material is demonstrated.
The granulated product obtained above can in principle be covered with sand in the same manner as when natural sand is used, and is not particularly limited.
[0028]
By the way, in the solidified granule obtained above, it is possible to appropriately adjust the average particle size and particle size distribution in the production stage. Therefore, the thing which adjusted the manufacturing conditions of the solidified granulated material according to the conditions of the place where sand covering is performed, and the purpose of sand covering in addition to the elution prevention of organic salts is used. For example, if the purpose of sand-capping is only water purification, fine particles may be included. Moreover, if emphasis is placed on workability, it is preferable that the average particle size from medium sand to fine sand is as narrow as possible. Also, if you want to grow benthic organisms, it is better to include some silt. Furthermore, if it is important to prevent the sand-covering material from flowing out by the bottom water flow or to prevent the sand-covering material from sinking into the soft sediment, it is desirable to use a material having a coarse average particle diameter.
[0029]
In transporting the solidified granulated material for covering sand, it may be carried out by a dry construction method in which the dried solidified granulated product is transported as it is, or a wet construction method in which the solidified granulated product is transported hydraulically in a slurry state.
[0030]
In covering sand using this solidified granulated material, it has a greater effect of preventing the elution of nutrients than natural sand. Although it differs depending on the like, it is possible to obtain an effect of preventing the elution of nutrient salts similar to natural sand, particularly phosphorus, at a thickness of about 1/3 to 4/5 as compared with the case of using only natural sand.
[0031]
The solidified granulated product can be mixed with natural sand or other known sand-capping material and used for sand-capping. In particular, when there is a possibility that the alkali component may ooze out from the solidified material, other known sand-covering materials such as natural sand that do not have such a risk are mixed and prevented. The blending ratio of natural sand or other sand-capping material may be appropriately determined according to the contamination concentration of the target soil, but it can usually be used up to about 20 times the weight of the solidified granulated product. An adsorption effect of nutrient salts can be obtained within this range. Preferably it is 5 times weight or less, More preferably, it is 2 times weight or less.
[0032]
Therefore, a conventionally known construction method can be used as the sand covering method, and it is not particularly limited. However, a method capable of covering sand as uniformly as possible with a thin layer is more suitable. For example, sand is poured into a blind dropping device installed on a trolley, leveled to a predetermined thickness with a sand top leveling device, then the blinds are opened at the same time, and the sand is leveled and the sea floor is flattened. The so-called "floating conveyor + spreader" that is used in combination with the so-called blind-type sand-capping method, single ship or floating conveyor system, which transports the sand-carrying material with the conveyor on the trolley and continuously carries out the sand-clad material with the spreader ship at the tip. It is desirable to use (FCS) type sand-capping method.
[0033]
Hereinafter, the present invention will be specifically described with reference to examples.
The phosphorus quantification method used in the examples is the potassium peroxodisulfate decomposition method described in JIS K 0102 46.3.1, and the ammoniacal nitrogen quantification method is the indophenol blue absorbance of JIS K 0102 42 2. It is a photometric method. The crushing strength was determined by measuring 10 points of solidified granulated material according to JIS Z8841-1993 and taking a simple average of them.
[0034]
(Example 1) Using the coal ash (fly ash) collected from the electrostatic precipitator of the thermal power plant, 90 parts by weight of coal ash, 10 parts by weight of ordinary Portland cement, 3 parts by weight of bentonite, and 21 parts by weight of water were added to the above drum. The mixture was put into a horizontal mixer, and the stirring blade was operated at 83 rpm and the chopper was operated at 1500 rpm for 5 minutes to form a granulated product having a substantially spherical shape and an average particle diameter of about 5 mm. Next, this granulated product was taken out from the mixer and dried at 20 ° C. for 28 days to obtain a desired solidified granulated product. The crushing strength of the solidified granulated product was about 2.1 MPa.
[0035]
Next, using a beaker, a salt solution was prepared by dissolving 50 mg of ammonium chloride, 146 mg of potassium dihydrogen phosphate and 11 mg of potassium dihydrogen phosphate in water to make 1 liter, and 100 g of the solidified granulated product obtained above was added to this salt. The solution was poured into the solution and stirred for about 1 minute, and then allowed to stand at 20 ° C. for 72 hours, after which the supernatant was collected. The salt concentration of this salt solution and supernatant was measured, and the amount of adsorption per unit weight of the solidified granulated product and the removal rate of salts from the salt solution were determined. The experimental results are shown in Table 1. Excellent values were obtained for both phosphorus removal and ammoniacal nitrogen removal. In addition, when the solidified granulated product was added to the salt solution, there was no particular problem and the handleability of the solidified granulated product was good.
[0036]
(Comparative example 1) It replaced with 100g of the solidified granulated material of Example 1, and obtained | required the adsorption amount per unit weight of natural sand and the removal rate of salts similarly to Example 1 except having used 100g of natural sand. It was. The experimental results are shown in Table 1. Although natural sand also has some salt adsorbing ability, it can be seen that its ability is considerably lower than that of solidified granules.
[0037]
(Comparative example 2) It replaces with the solidified granulated material 100g of Example 1, and uses the coal ash 100g as it is, it carries out similarly to Example 1, and sets the adsorption amount per unit weight of coal ash, and the removal rate of salts. Asked. The experimental results are shown in Table 1. When coal ash was introduced, the coal ash repelled water and easily scattered in the air, resulting in a worse working environment. The phosphorus removal rate of coal ash was similar to that of the solidified granulated product, but the removal rate of ammonia nitrogen was inferior.
[0038]
[Table 1]

【The invention's effect】
A water purification material that can be produced at low cost and can adsorb nutrient salts, particularly phosphorus, can be obtained. Moreover, the water purification material which can be manufactured so that it may be suitable for the condition of the bottom quality of the place covered with sand is obtained. Moreover, the water purification material which obtains favorable sand covering performance at low cost can be obtained.

Claims (2)

Contains 80 to 97 parts by weight of coal ash , 2 to 15 parts by weight of solidified material, 2 to 5 parts by weight of bentonite, and an average particle size of 0.1 mm to 20 mm water purification material less in the crushing strength, characterized in that Ri Do from granules above 2 MPa, and Ru coating der of the sea bed soil. 80 to 97 parts by weight of coal ash, 2 to 15 parts by weight of solidified material, 2 to 5 parts by weight of bentonite, and 15 to 25 parts by weight of water 2. The method for producing a water purification material according to claim 1, wherein the mixture is stirred and mixed to form a granulated product and dried at 10 ° C. to 40 ° C. for 1 day to 1 month.