JPS646832B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for removing 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 reduced to 15mg/or less, and in some areas to 8mg/or less. However, in the conventional calcium fluoride precipitation method by adding slaked lime or calcium chloride, 20 to 50 mg/fluoride remains in the treated water, and if a large amount of calcium agent is used to further improve the removal rate, There were problems in that a large amount of fine calcium fluoride was produced, making it difficult to settle and making it difficult to treat the settled sludge. Recently, methods have been used in which fluorine-containing wastewater is brought into contact with solids supporting phosphate rock or calcium fluoride particles, but when the wastewater is passed through a fixed bed packed bed of these solid particles, fluorine-containing wastewater is When the concentration of . 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. It is about providing. 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. The calcium agent is introduced from the lower part of the reaction tank and flows upward while fluidizing the granular solids in the reaction tank, and the calcium agent is directly injected into the circulation return system or into the reaction tank for treatment of the effluent water from the reaction tank. This is a method for treating fluorine-containing wastewater. 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"). It has been discovered that fluorine in fluorine-containing wastewater can be efficiently removed by circulating a portion of the effluent water and flowing 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 along with a portion of reaction tank outflow water from pipe 2, and the water is passed upward. The reaction tank is filled with granular solids 4, and the granular solids are fluidized by the upward 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 cause the reaction to occur. The crystallization reaction of fluorine on the granular solid surface is allowed to proceed throughout the entire layer in the tank. 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 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, the 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 sludge generated as 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 (fluoride removal agent), Ca is removed on the surface of the seed crystal. ²⁺ +2F→CaF ₂ ↓ …The reaction shown in (1) proceeds 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. (ii) The amount of chemicals added can be significantly reduced. (iii) The residence time of the entire process is short, and sludge treatment is not required, making it a space-saving process. To explain the factors that affect the fluorine removal reaction of this method, the ratio between the amount of calcium and fluorine in the reaction tank should be approximately 1 based on equation (1) above, but it is It is necessary to increase the amount of Ca, and according to experimental results, it is desirable to inject the calcium agent so that the Ca/F ratio in the reaction tank is 5 to 20. In the reaction between calcium and fluorine, the pH is 4~
10 is said to be a useful range, so if the wastewater is outside the PH range, it is necessary to adjust the pH of the wastewater and use an alkaline Ca agent, such as slaked lime or calcium carbonate, as a calcium agent. Although it is desirable to use gypsum and calcium chloride, if PH adjustment is not required, gypsum and calcium chloride can also be used. In addition, as shown in Figure 2, the calcium agent is added into the reaction tank by installing a continuous measuring device for the Ca concentration and linking it with the Ca agent injection device.
One preferred application is to inject the Ca agent into the layer while continuously sensing the concentration. Measurement of Ca concentration can be easily performed in conjunction with a Ca agent injection device by using an ion electrode that uses a Ca-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 material packed bed and cause bed blockage, but if it is made into a fluidized bed, the solid particles packed will combine and form a solid. It happened again without incident
SS sticks to solid surfaces. Furthermore, since a fluidized bed has a high contact effect, a fluidized bed is suitable for crystallizing fluorine on the surface of a solid. Granular phosphate or fluorite is most suitable for solids containing calcium and fluorine as fillers, but crystalline ones containing Ca and F and solid substances such as CaF ₂ and Ca ₅ F (PO ₄ ) ₃ are also suitable. You can also use what you hold. In addition, the ratio of the amount of circulating water to the raw water is 1 to 1, as shown in Example 4.
4 is appropriate. 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 C were used in the comparative examples. The raw water is wastewater discharged from the electronics industry (F content: 40
~50mg/), and water was passed through each method at a rate of 1 m ³ /day. In Flow A, granular fluorite with a diameter of 0.2 to 0.3 mm is placed at a height of 100 cm in a column (reaction tank) with an inner diameter of 7 cm and a length of 200 cm.
cm filling (capacity 4.1). The raw water was mixed at a ratio of 1:1 with circulating water obtained by adding 400 mg of slaked lime to the reaction tank outflow water, and the mixture was allowed to flow into the tank from the bottom of the reaction tank (column). Furthermore, 300 mg of slaked lime was injected at a position 30 cm from the bottom of the reaction tank, and a continuous water flow experiment was conducted for two months (Experiment-1). Next, after the experiment was completed, we stopped directly injecting slaked lime into the reaction tank, and added slaked lime to the reaction tank outflow water.
1 in the same manner as Experiment-1 except that 700mg/
A continuous water flow experiment was conducted for several months (Experiment-2). Furthermore, after the experiment was completed, the addition of slaked lime to the reaction tank outflow water was stopped, and slaked lime was added from the bottom of the reaction tank.
A continuous water flow experiment was conducted for 1 month in the same manner as Experiment 1 except that 700 mg of slaked lime was injected at the cm position (Experiment 3). Flow B is a column with an inner diameter of 10 cm and a height of 200 cm, filled with granular fluorite with a diameter of 0.2 to 0.3 mm to a height of 100 cm (volume
8.3) Did. The raw water was added with slaked lime at a rate of 700 mg/hour and was passed through the reactor from the bottom at a water flow rate of 120 m/hr. In Flow C, raw water is introduced into a stirring tank with an effective capacity of 20, and fluorite 4.1 crushed into 100 to 200 meshes is suspended in the tank and continuously stirred (rotation speed: 100 to 150 r.m.).
A continuous water flow experiment was conducted so that the water remained at pm) for 30 minutes. Table 1 shows the results of experiments conducted under the above processing conditions.
Shown below.

[Table] In implementing the present invention, the fluorine concentration of the treated water was stably maintained at 10 mg/or less in all methods. Furthermore, the amount of SS generated was less than 20mg/, which was significantly reduced compared to the comparative example. In implementing the present invention, it has been found that the most excellent method is to separately inject slaked lime, which is a calcium agent, into the circulating water and into the reaction tank. On the other hand, in the comparative example using flow B, the fluorine concentration in the treated water can be reduced to 9 to 12 mg/day, but on the other hand, the packed bed becomes clogged in a short period of time, and the backwash frequency is once/12 hours. And so. Due to this backwashing, the SS trapped in the reaction tank flowed out of the system, resulting in a high amount of SS generated at 40 to 50 mg/.
In addition, in the comparative example using Flow C, the quality of the treated water was poorer and the amount of SS generated was higher than in the present invention. 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 400% was added to the reaction tank outflow water.
mg/, gypsum (CaSO ₄ .2H ₂ O) was injected at a position 30 cm from the bottom of the reaction tank. When injecting gypsum, a portion of the treated water is taken and its concentration is detected.
The injection pump was controlled so that the Ca concentration was 400 mg/. As a result, the fluorine concentration in the treated water could be maintained at 6-8 mg/in contrast to the raw water fluorine concentration in the range 40-50 mg/in. The amount of SS generated was 8 to 12 mg/. Example 3 Five units of the apparatus of Example 1 were manufactured, and granular fluorite with a particle size of 0.2 to 0.4 mm, phosphate rock from Jordan, and fluoride sand were added to each column, each of which was designed to allow 1 m ³ /day of wastewater to flow. It was filled with calcium-supported materials, marble, and sand supported with magnesium fluoride, and water was passed under the conditions of Example 1. Each piece of wood was pulled out at regular intervals and its weight was measured to determine the growth rate of the wood. 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, fluorite containing Ca and F,
The sand supporting Jordanian phosphate rock and calcium fluoride had a good thickening rate (corresponding to the rate of fixing fluorine) of 90 g/day or more. On the other hand, marble containing calcium carbonate as a main component and sand supporting magnesium fluoride had a significantly slow growth 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 smaller than 1 or larger than 4, the fluorine concentration of the treated water deteriorated significantly.

[Brief explanation of the drawing]

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 wood 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... Material (calcium,
Fluorine-containing solid particles), 5... Reaction tank, 6... Treated water, 8... Treated water sampling pipe, 9... Ca concentration continuous measurement recording device.

Claims (1)

[Scope of Claims] 1. A method for treating fluorine-containing wastewater by introducing it into a reaction tank filled with solid particles containing calcium and fluorine, in which a part of the reaction tank effluent that is circulated and returned is combined with the wastewater. , introduced from the bottom of the reaction tank,
The treatment is carried out by passing water upward while fluidizing the granular solids in the reaction tank, and directly injecting a calcium agent into the circulation return system path and/or into the reaction bed in the outflow water from the reaction tank. A method for treating fluorine-containing wastewater. 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.