JPS60206485A - Treatment of fluorine-containing waste water - Google Patents

Abstract

PURPOSE:To obtain high fluorine removal capacity generating no clogging, by packing a reaction tank with solid particles containing calcium and fluorine, and adding a calcium agent to a recirculation system or tank to allow fluorine-containing waste water to reversely flow to the packed tank. CONSTITUTION:Fluorine-containing waste water from a pipe 1 is introduced into a reaction tank 5 along with a part of the outflow water of the reaction tank 1 from a pipe 2. The reaction tank 5 is packed with solid particles 4 of fluorite or phosphate rock and said solid particles are fluidized by the upwardly flowing waste water. A calcium agent 3 is injected in the recirculation line 2 of the outflow water from the reaction tank 5 or the reaction tank 5 and the concn. of calcium in the tank is held to a predetermined amount while the contact reaction of fluorine in waste water and solid particles is promoted and fluorine is crystallized on the surfaces of solid particles in a calcium fluoride form over the entire region in the tank. A part of treated water 6, from which fluorine is removed, is re-utilized as recirculation water and the remainder thereof is discharged out of the system.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing a proportion of fluorine from fluorine-containing wastewater discharged from electronic industries, aluminum industries, phosphoric acid industries, etc.

In recent years, from the standpoint of environmental conservation and pollution prevention, the emission regulations for fluorine contained in wastewater have been set to 15"76 or less, and in some areas to 8 or less.

However, in the conventional calcium fluoride precipitation method by adding slaked lime or calcium chloride, 20 to 5,014 fluorides remain in the treated water, and if a large amount of calcium agent is used to further improve the removal rate, a large amount of fluorine remains. There was a problem in that fine calcium fluoride was generated, which was difficult to settle, and the treatment of the settled sludge was difficult. Recently, a method has been used in which fluorine-containing wastewater is brought into contact with a solid supporting phosphate rock or calcium fluoride particles, but when the I solution is passed through a fixed bed packed bed of these solid particles, fluorine High concentrations often result in large amounts of suspended solids, which can clog the packed bed and require frequent backwashing. Furthermore, even when these solids are suspended, the same problems as those of the conventional calcium fluoride precipitation method described above remain unsolved.

The invention of the present application improves the above-mentioned problems and provides a treatment method that can significantly reduce the amount of sludge generated while maintaining a high fluorine removal rate even when the fluorine concentration is in a relatively high concentration range. There is a particular thing.

The present invention provides a method for treating fluorine-containing wastewater by introducing it into a reaction tank filled with solid particles containing calcium and fluorine. Fluorine-containing wastewater is introduced from the reaction tank and passed upward while fluidizing the granular solids in the reaction tank, and is treated by injecting a calcium agent directly into the circulation return route of the reaction tank effluent or into the reaction tank. This is the processing method.

As a result of various studies in order to solve the problems of the conventional method described above, the present inventor used a fluidized reaction tank for granular solids containing calcium and fluorine (hereinafter abbreviated as "granular solids") to prevent the flow out of the reaction tank. It has been discovered that fluorine in fluorine-containing wastewater can be efficiently removed by circulating and returning a portion of the water while maintaining the calcium concentration in the reaction tank at a predetermined level.

Next, embodiments of the present invention will be described based on the following drawings.

First, referring to FIG. 1, fluorine-containing waste water from pipe 1 is introduced into reaction tank 5 together with a portion of reaction tank outflow water from pipe 2, and the water is passed in an upward flow. The reaction tank is filled with granular solids 4, which are fluidized by the upwardly flowing water of the waste water. A calcium agent is injected into the reaction tank effluent circulation line 2 or into the reaction tank to maintain the calcium concentration in the reaction tank at a predetermined level, promote the contact reaction between fluorine in the wastewater and granular solids, and Ruts throughout the inner layer.

□ to advance the crystallization reaction of fluorine on the surface of the granular solid. A portion of the treated water 6 from which fluorine has been removed is reused as circulating water, and the rest is discharged outside the system.

The principle of the present invention utilizes the crystallization phenomenon of calcium fluoride produced by the reaction between fluorine and calcium in a liquid.

That is, fluorine in the liquid is fixed in the form of calcium fluoride to the surface of the granular solid containing calcium and fluorine, and the fluorine in the liquid is removed accordingly.

Therefore, there is no generation of sludge, which is seen in conventional sedimentation methods.

The present invention is based on such a principle, and when a calcium agent is added as necessary to wastewater containing fluorine and brought into contact with a substance that becomes a seed crystal (a fluorine removal agent), Ca'' is removed on the surface of the seed crystal. ” + 2 F−CaF2↓ ・−・(1)
The reaction shown in will proceed effectively.

The features of the processing method of the present invention can be summarized as follows.

(i) The amount of sludge generated is not significantly small.

(11) The amount of chemicals added can be significantly reduced.

(111) It is a space-saving process because the residence time of the entire process is short and sludge treatment is not required.

To explain the factors that affect the fluoride removal reaction of this method, the ratio of the amount of calcium to fluorine in the reaction tank should be approximately 1 based on the above equation (1), but in the measurement, CaO According to experimental results, it is desirable to inject the calcium agent in a large amount so that the Ca/F ratio in the reaction tank is 5 to 20.

In the reaction between calcium and fluorine, it is said that a pH range of 4 to 10 is a useful range.
If the wastewater is outside the PH range, it is necessary to adjust the pH of the wastewater, and it is preferable to use an alkaline Ca agent, such as slaked lime or calcium carbonate.
If H adjustment is not required, gypsum and calcium chloride can also be used.

Furthermore, as shown in Figure 2, the calcium agent is added into the reaction tank by installing a continuous measuring device for Ca concentration and linking it with the Ca agent injection device to continuously detect the Ca concentration in the treated water. However, one preferred application is to inject Ca agent into the layer. Measurement of Ca9 degree can be easily performed in conjunction with a Ca agent injection device by using an ion electrode that uses a C, a selective electrode.

The upward flow velocity within the packed bed is set to be equal to or higher than the fluidization velocity required to fluidize the packed solid particles.

This is because if the SS generated during the reaction process is placed in a fixed bed, it will be trapped in the packed bed of the reactor material and cause clogging of the reactor bed, but if it is made into a fluidized bed, the solid particles packed will combine and form a solid bed. The generated SS adheres to the solid surface. Furthermore, since a fluidized bed has a high contact effect, a fluidized bed is suitable for crystallizing fluorine on the surface of a solid.

The best calcium and fluorine-containing solid fillers are granular phosphate rock and fluorite, but crystalline ones containing Ca and F and c a F21 c a, F (p O,)3
Supported on a solid substance can also be used. Further, the ratio of the circulating water amount of the effluent to the raw water is suitably 1 to 4 as shown in Example 4.

Examples of the present invention are shown below.

Example 1 An example and a comparative example of the present invention carried out according to the flow shown in FIG. 3 will be described. Flow A was used in the examples of the present invention, and flows B and C1 were used in the comparative examples.

The raw water is wastewater discharged from the electronics industry (F content 40-50
℃), and water was passed through each method at a rate of 1'/8.

In flow A, a column (reaction tank) with an inner diameter of 7 crrL and a length of 200 ctn was filled with granular fluorite with a diameter of 0.2 to 0.3 B to a height of 100 cm (volume 4.1 e). The raw water was mixed with circulating water containing 400"/3 of slaked lime added to the reaction tank 2 outflow water at a ratio of 1=1, and was allowed to flow into the lower part of the reaction tank (column). 30
Slaked lime was injected at a position of 300 cm, and a continuous water flow experiment was conducted for 2 months (Experiment-1).

Next, after the above experiment was completed, we stopped directly injecting slaked lime into the reaction tank, and conducted a continuous water flow experiment for one month in the same manner as in Experiment 1, except that slaked lime 700"/6 was added to the reaction tank outflow water. (Experiment-2).

Furthermore, after the experiment was completed, the addition of slaked lime to the reaction tank outflow water was stopped, and 700 μ/e of slaked lime was injected into the reaction tank at a position 30 minutes from the bottom. A water flow experiment was conducted (Experiment-3).

Flow B is a column with an inner diameter of 10 crn and a height of 200 cm.
It was filled (volume 8.31). Raw water is slaked lime 700
7g was added and water was passed from the bottom of the reaction tank at a water flow rate of 120 m/hr.

Flow ○ introduces raw water into a stirring tank with an effective capacity of 201.
In a tank in which fluorite 4.1e crushed into 0 to 200 meshes was suspended and continuously stirred (rotation speed 100 to 150 r,
A continuous water flow experiment was conducted so that the water remained at > p, m for 30 minutes.

Table 1 shows the results of experiments conducted under the above processing conditions.

Table 1 In implementing the present invention, the fluorine concentration of the treated water was stably maintained at 10''/6 or less in all methods.

Further, the amount of SS generated was 20° C.g or less, which was significantly reduced compared to the comparative example. In the implementation of the present invention, it has been found that the method in which slaked lime, which is a calcium agent, is separately injected into the circulating water and the reaction tank is the most destructive.

On the other hand, in the comparative example using Nro B, the fluorine concentration of the treated water was 9 to 9.
Although it was possible to reduce the amount to 12-1, the packed bed became clogged in a short period of time, and the backwashing frequency required 1 time/12 hours of water flow. Due to this backwashing, the SS trapped in the reaction tank flowed out of the system, resulting in an increase in the amount of SS generated by 40 to 50". Also, in the comparative example with flow 〇, compared to the present invention, The quality of the treated water was poor, and the amount of SS generated was large.

Example 2 Using the same raw water as in Example 1, a similar continuous water flow experiment was conducted using the treatment flow A of the present invention in Example 1. In this experiment, slaked lime 4001 was added to the reaction tank outflow water, and 30 c of calcium was added from the bottom of the reaction tank.
Gypsum (CaSO3.2H20) was injected at position m. When injecting gypsum, a portion of the treated water was taken, its concentration was detected, and the injection pump was controlled so that the Ca concentration was 400♂l/l.

As a result, for raw water fluorine concentration of 40-50''/6,
The fluorine concentration in treated water can be maintained between 6 and 81.

The amount of SS generated was 8 to 12 shg.

Example 3 Five units of the apparatus of Example 1 were manufactured, and the drainage was 17/8 each.
Particle sizes of 0.2-0.
4B granular fluorite, Jordanian phosphate rock, sand carrying calcium fluoride, marble, and sand carrying magnesium fluoride were filled, and water was passed under the conditions of Example 1. Each swamp material was extracted at regular intervals and its weight was measured to determine the expansion rate of material F.

This hypertrophy rate was considered to be the same as the fixation rate of calcium fluoride. The processing results are shown in Figure 4.

As shown in Figure 4, the sand loaded with fluorite containing Ca and F, Jordanian phosphate rock, and calcium fluoride has an enlargement rate (corresponding to the rate of fixing fluorine) of 90 g/
A score of 8 or higher was good and rare. On the other hand, marble containing calcium carbonate as a main component and sand supporting magnesium fluoride had a significantly slow enlargement rate.

Example 4 In Flow A of Example 1, the influence of the circulation ratio was investigated by changing the circulation ratio from 0.5 to 5 while keeping the water flow rate and contact time constant. The results are shown in Figure 5.

As shown in the figure, when the circulation ratio was made smaller than 1 or made larger than 4, the fluorine concentration of the treated water deteriorated significantly.

[Brief explanation of drawings]

FIG. 1 shows an apparatus according to an embodiment of the present invention. FIG. 2 shows an embodiment in which a Ca concentration continuous measuring device is added to the device shown in FIG. 1. FIG. 3 shows a flow pattern of an example of the present invention and a comparative example. Figure 4 shows the relationship between the type of door material and the rate of enlargement. Figure 5 shows the relationship between the ratio of the amount of circulating water to the amount of raw waste water and the fluorine concentration of the treated water. 1... Fluorine-containing wastewater introduction pipe 2... Circulating water introduction pipe 3... Slaked lime 4... P material (calcium, 5...
Reaction tank Fluorine-containing solid particles) 6... Treated water 8...
- Treated water sampling pipe 9...Ca concentration continuous measurement recording device Tadashi Shiozaki, Patent Attorney, Hirochan l/27 3rd m 4th Figure Higashi 7zu Uino Cliff (M9/I) Figure 5

Claims (1)

[Scope of Claims] 1. In a method for treating fluorine-containing wastewater by introducing it into a reaction tank filled with solid particles containing calcium and fluorine, a part of the reaction tank effluent that is circulated and returned to the wastewater is subjected to a reaction. Water is introduced from the bottom of the tank and flows upward while fluidizing the granular solids in the reaction tank, and a calcium agent is directly injected into the circulation return system path in the reaction tank effluent and/or into the reaction tank. 1. A method for treating fluorine-containing wastewater, the method comprising: 2. The method according to claim 1, wherein the injection of the calcium agent is controlled while continuously measuring the amount of calcium in the reaction effluent. 3. The method according to claim 1 or 2, wherein the granular solid containing calcium and fluorine is fluorite and/or phosphate rock.