JPH0426919B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating wastewater containing toxic metals. More specifically, the present invention provides ions,
A method for treating wastewater containing toxic metals, which comprises adsorbing toxic metals present in wastewater in the form of oxide colloids onto silica gel, heat-treating the silica gel to vitrify it, and fixing the adsorbed toxic metals. This is related. Conventionally, wastewater containing toxic metals discharged from industrial facilities, research institutes, etc. has been purified by coagulation-sedimentation treatment, ion exchange treatment, etc. to capture and remove the toxic metals, and then discharged into rivers or sea areas where they can be captured. Sludge and ion exchange resins containing toxic metals have been disposed of by incineration or landfill. Furthermore, wastewater containing harmful radioisotope metals discharged from nuclear power plants and medical institutions that handle radioactive materials cannot be rendered harmless through either chemical or physical treatment. The methods used include concentrating it into a small volume, storing it in isolation in water, in the ground, or in a shield, waiting for the radioactivity to decay, then sealing it in a strong container and discarding the entire container into the deep sea. There is. However, in these methods,
It requires a huge amount of coagulant and expensive ion exchange resin, and there are various restrictions on securing landfill space. On the other hand, the treatment of wastewater containing radioactive materials not only requires water concentration equipment, but also requires various materials such as sealed containers, cement and asphalt to solidify the concentrated sludge, making it extremely uneconomical. It is something. The present invention solves the above problems in the treatment of wastewater containing hazardous metals by using silica hydrogel or silica xerogel (hereinafter referred to as silica gel) as an adsorbent. That is, in the present invention, silica gel is immersed in wastewater containing harmful metals to adsorb harmful metals, and the silica gel is mixed with a vitrification promoting substance of 100 to 10,000 ppm per 1 gr of silica gel and 100 to 100 ppm of vitrification accelerator per 1 gr of silica gel.
The gist of this paper is a method for treating wastewater containing hazardous metals, which involves adding 3000 ppm of solubility-reducing substances and vitrifying the toxic metals to immobilize them. To further explain the present invention, harmful metal-containing wastewater to which the present invention is applied includes chromium, cobalt, copper, cadmium, lead, etc. discharged from metal factories, pharmaceutical factories, tanneries, pigment factories, reagent manufacturing factories, etc. Wastewater containing metals harmful to the human body such as silver and mercury ions, and radioisotope metals such as cobalt, plutonium, and uranium discharged from nuclear power plants and medical institutions that use radioactive materials for treatment. Examples include wastewater containing wastewater. The silica gel in the present invention has, for example, a BEL specific surface area of 200 to 900 m ² /g and a pore volume of 0.3 to 1.3 ml/g.
Examples include commercially available products or in-house products with an average pore diameter of 10 to 260 Å. When treating wastewater containing harmful metals by the method of the present invention, both the static adsorption method using silica gel and the dynamic adsorption method described above can be applied. In the static adsorption method, the pH of the wastewater containing toxic metals to be treated is adjusted by adding hydrochloric acid, aqueous ammonia, etc., and the silica gel is immersed in this to adsorb the toxic metals on the silica gel. An example of cobalt adsorption using this method is, for example, when 0.05 ppm to 0.05 ppm of radioisotope metal cobalt is absorbed into wastewater containing harmful metals.
If the pH of water containing 80 ppm concentration is adjusted and silica gel is immersed in this, 1 g of silica gel has a pH of 6.
0.4mg to 1.4mg of cobalt is adsorbed nearby. In the dynamic adsorption method, the silica gel is made into a slurry and packed in a fixed bed adsorption column to prevent air bubbles from entering, and the wastewater containing harmful metals to be treated is circulated after adjusting the pH with hydrochloric acid, aqueous ammonia, etc. To give an example of adsorption of cobalt by this method, for example, when water containing 8 to 80 ppm of cobalt as a radioactive isotope metal is adjusted to pH 6 and distributed at a rate of 1 to 4 ml/min as wastewater containing harmful metals. ,
0.4 mg to 1.2 mg of cobalt is adsorbed to 1 g of silica gel. In the present invention, as described above, silica gel that has adsorbed harmful metals is heated and melted to vitrify it, thereby fixing the metals. For vitrification, silica gel that has adsorbed harmful metals is placed in an electric furnace,
This is done by heating to 0.degree. C. and maintaining that temperature for 0.5 to 10 hours. If the temperature exceeds this range, bubbles will be generated in the produced glass body, which is not preferable. As mentioned earlier, one way to remove harmful metals is to use ion exchange resins, but ion exchange resins are not only expensive materials, but are also susceptible to radioactive substances and easily decompose, whereas silica gel is inexpensive. In addition, it is stable against radioactive substances, and has the advantage that when it is sintered and vitrified, harmful metals adsorbed within its pores are contained and fixed. In the method of the present invention, in the heat treatment for vitrification, monovalent or divalent metal ions such as alkali metals and alkaline earth metals, such as sodium, potassium, calcium, and magnesium, as well as ions of monovalent or divalent metals such as lead and tin, It is characterized by the addition of a vitrification promoting substance consisting of a substance containing valent metal ions. That is, as a result of the studies of the present inventors, in the above-mentioned vitrification, by adding a vitrification-promoting substance to the silica gel that has adsorbed harmful metals, vitrification can be more easily promoted in a short time and at low temperatures. .
In addition, the presence of solubility-reducing substances such as aluminum, boron, and chromium reduces the solubility of vitrified silica gel in water, which is a new technology that has the effect of suppressing the elution of harmful metals that have been adsorbed and fixed. I gained knowledge. In this case, the amount of vitrification promoting substances such as alkali metals and alkaline earth metal salts added as metal ions is 100 to 1g per 1g of silica gel adsorbing harmful metals.
It is desirable to add 10,000 ppm, particularly preferably in the range of 500 to 10,000 ppm. Generally, meso- and macropore-type silica gels are vitrified at temperatures of about 1000°C, but they become foamy at higher temperatures. However, if metal ions such as sodium ions of an alkali metal salt are present in advance, this phenomenon does not occur, and sodium ions such as
When it is present in an amount of 1000 ppm or more, a dense vitrified sintered body without foaming can be obtained. However, on the other hand, if the amount of sodium ions added exceeds 3000 ppm,
When vitrified silica gel that has adsorbed harmful metal ions is immersed in water, the liquid phase pH increases; for example, when 3000 ppm or more of sodium ions are added, the pH value shows a pH value of 9. That is, there is a possibility that the silica gel will dissolve and the fixed harmful metal ions will be eluted. Therefore, the amount of vitrification promoting substances such as alkali metal salts and alkaline earth metal salts added is 100 to 100% as metal ions per 1gr of silica gel.
The amount is preferably 10,000 ppm, preferably in the range of 500 to 3,000 ppm, thereby making it possible to obtain a vitrified silica gel in which the elution rate of fixed harmful metals is suppressed to the maximum, and also to promote vitrification. . Typical substances containing metal ions such as alkali metal salts and alkaline earth metal salts include:
Examples include sodium chloride. Further, the addition method can be carried out, for example, by dropping a predetermined amount of a sodium chloride solution onto dry toxic metal-adsorbing silica gel. A typical example of the solubility-reducing substance is aluminum salt, such as aluminum chloride, which can be added, for example, by dropping a predetermined amount of an aluminum chloride solution onto dry toxic metal-adsorbing silica gel. The amount added is 100 to 3000 ppm, preferably 100 to 3000 ppm, per 1 g of silica gel as aluminum ions.
It is in the range of 2000ppm. The addition of this metal ion,
For example, by adding 1000 ppm of aluminum ions, the elution rate of harmful metals from vitrified silica gel adsorbed with harmful metals can be suppressed to 0.1% or less. It should be noted that if the amount of metal ions added exceeds 3000 ppm, it is not preferable because the elution rate increases. As described above, the present invention is capable of adsorbing toxic metals using silica gel when treating wastewater containing toxic metals, particularly wastewater containing radioactive toxic metals discharged from nuclear power plants, medical institutions, etc. By trapping the silica gel and sintering and vitrifying the silica gel, harmful metals are sealed in the silica gel pores, and by adding vitrification promoting substances such as alkali and alkaline earth metals during sintering and vitrification. , it is possible to save the thermal energy required for sintering, and it also firmly fixes the adsorbed toxic metals and prevents them from leaching out, making it extremely useful as a method for treating wastewater containing toxic metals. Next, the present invention will be explained with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 BET specific surface area is 475m ² /g, pore volume is 0.8
Commercially available silica gel with an average pore diameter of 67 Å per ml/g was purified by adding hydrochloric acid to pure water to remove impurities.
After 48 hours of immersion in a solution with a temperature of 2, it was taken out, washed thoroughly with pure water, and dried at 170°C. This material was immersed in a cobalt chloride solution of about 3 times the weight of 0.017 mol/for about 20 hours, taken out and dried at 170°C to obtain a silica gel adsorbed with 541 ppm of cobalt. A solution of sodium chloride was added dropwise to this silica gel, and sodium ions were added so that the concentration was as shown in Table 1.The temperature was raised at a rate of 10°C/min to 900°C.
After reaching this temperature, this temperature was maintained for 3 hours to effect vitrification. The obtained glass sintered body was cooled and crushed to 32
It was classified into ~48 meshes, and fine powder was removed with absolute ethanol. 1g of this material, 50ml of pure water and PH with hydrochloric acid.
It was sealed in a pirate glass ampoule together with a solution adjusted to =5.5 and boiled at 98 to 100°C for 20 hours, and the concentration of cobalt ions transferred to the solution was determined. The results are shown graphically in Table 1 and FIG.

[Table] Note: Comparative examples are marked with * From the above results, the addition of alkali metal ions has the effect of suppressing the elution of adsorbed metal ions and promotes the formation of a dense glass body of silica gel, and especially at around 3000 ppm, the adsorption It can be seen that the metal is sealed within the pores to the extent that almost no metal is eluted. Example 2 Cobalt prepared in the same manner as Example 1 was
A solution of sodium chloride was dropped onto the silica gel that had absorbed 541 ppm of sodium chloride, 3000 ppm of sodium ions was added, and the temperature was raised at a rate of 10°C/min to the temperature shown in Table 2. Hold for an hour and vitrify. After cooling, the obtained glass sintered body was immersed in pure water at room temperature for 70 days, and the concentration of cobalt ions transferred to the liquid was determined. The results are shown graphically in Table 2 and FIG.

[Table] From the above results, the addition of alkali metal ions results in sintering at a relatively low temperature, with almost no elution of the adsorbed metal ions. FIG. 2 is a graph showing the relationship between sintering temperature and elution rate of metals adsorbed on silica gel when the sodium ion concentration is kept constant (3000 ppm). Example 3 Cobalt prepared in the same manner as Example 1
A solution of aluminum chloride was dropped onto metal-adsorbed silica gel that had adsorbed 541 ppm, and sodium ions
1000 ppm was added, and an aluminum chloride solution was added so that the aluminum ion concentration was as shown in Table 3, and the mixture was heated and vitrified in the same manner as in Example 1. After cooling, the obtained glass sintered body was immersed in pure water at room temperature for 70 days, and the concentration of cobalt ions transferred to the liquid was determined. The results are shown graphically in Table 3 and FIG.

[Table] Note: Comparative examples are marked with *. From the above results, in addition to the addition of alkali metal ions, the addition of aluminum ions within a certain range, for example, 2000 ppm or less, produces a more dense glass than when only alkali metal ions are added. It can be seen that the adsorbed metal is sealed in the pores to such an extent that it hardly elutes. Example 4 Commercially available spherical silica gel (particle size 30-20 mesh,
Suspend 10 or 20 g (surface area 475 m ² /g, pore volume 0.8 ml/g, average pore diameter 70 Å) in ion-exchanged water, degas it, and place it in a glass column with an inner diameter of 0.8 cm to prevent air bubbles from entering. to create a column fixed bed. Next, a cobalt solution was prepared by dissolving cobalt chloride in ion exchange water so that the cobalt concentration was 2.8 to 80 ppm. Add this cobalt solution to 1.3
The liquid was passed through the column at a flow rate of ml/min to 4.1 ml/min, and the column effluent was collected, for example, every 50 ml. The concentration of cobalt in each fraction of the effluent was measured by atomic absorption spectrometry. The results are shown in Table 4.

[Table] Figure 4 shows the breakthrough curve when the cobalt solution concentration is 47 ppm. The vertical axis shows the cobalt concentration in the fractionated effluent, and the horizontal axis shows the amount of the effluent. The breakthrough point was clearly observed, and the large cobalt ion concentration gradient at the front end of the adsorption zone indicated that the separation efficiency was good. Similar breakthrough curves were obtained from low to high cobalt ion concentrations. Next, FIG. 5 shows an effluent breakthrough curve obtained when a chromium solution was passed through the column in the same manner. The chromium solution was prepared by dissolving chromium chloride in ion-exchanged water and adjusting the chromium ion concentration to 4 ppm. The flow rate is
0.5ml/min, chromium ion adsorption amount is 0.4mg/gsio ₂
It was hot. In this case as well, a clear breakthrough curve was obtained as in the cobalt solution. As described above, it was found that adsorption and removal of metal ions using a silica gel column fixed bed is very efficient and effective for separation.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the amount of sodium ions added and the elution rate of metals adsorbed on silica gel in vitrification of silica gel adsorbing harmful metals in Example 1. A graph showing the relationship between the sintering temperature and the elution rate of metals adsorbed on silica gel when the ion concentration is kept constant (3000 ppm). Figure 3 shows the relationship between the elution rate of metals adsorbed on silica gel when the ion concentration is kept constant (1000 ppm). A graph showing the relationship between the concentration and the elution rate of metals adsorbed on silica gel, Figure 4 shows the cobalt solution concentration of 47 ppm in Example 4.
Figure 5 shows the breakthrough curve for the same example when the chromium solution concentration was 4 ppm.

Claims (1)

[Claims] 1. Silica gel is immersed in wastewater containing toxic metals to adsorb the toxic metals, and the silica gel is
Treatment of wastewater containing toxic metals, characterized by adding vitrification promoting substances of 100 to 10000 ppm per 1gr and solubility reducing substances of 100 to 3000ppm per 1g of silica gel and vitrifying the mixture by heating to 500 to 1200°C. Method.