JP4068532B2 - Method for treating sewage containing hazardous substances - Google Patents

Description

  The present invention relates to a hazardous substance collecting material and a method for treating sewage containing harmful substances, particularly harmful substances contained in sewage containing harmful substances such as volatile organic compounds such as chromium, selenium, arsenic, trichlorethylene and tetrachloroethylene. It is related with the processing method which collects and reduces. In the present invention, “parts” and “%” are based on mass unless otherwise specified.

  Environmental problems are becoming apparent. In particular, hazardous substances in sewage such as heavy metals such as chromium, selenium and arsenic, nitrate nitrogen and nitrite nitrogen, fluorine, boron, dioxins, volatile organic compounds such as trichlorethylene and tetrachloroethylene, etc. Environmental standards based on the above are defined, and it is preferable to maintain a level below this standard value.

  Among these harmful substances, compounds containing chromium, selenium, and arsenic are extremely toxic and are widely recognized as substances that cause serious damage to society, such as pollution diseases, even in trace amounts. Volatile organic compounds such as trichlorethylene and tetrachlorethylene are used in large quantities and cause carcinogenicity, causing serious environmental damage. If harmful substances such as nitrate nitrogen, nitrite nitrogen, fluorine, boron, and dioxins are released into the environment, they may cause environmental pollution.

  As materials for collecting these harmful substances, a method using activated carbon (see, for example, Patent Documents 1 and 2), a method using zeolite (see, for example, Patent Document 3), and a method using hydrotalcites (Patent) Reference 4), a method of reducing and decomposing with reducing iron powder (see Patent Document 5, etc.), a method using ferrous sulfate (see Patent Documents 6-7, etc.), a method using apatites ( Patent Document 8 etc.), a method using calcium sulfoaluminate hydrate or a heated dehydrated calcium aluminate hydrate (see Patent Document 9 etc.), an aluminum compound such as alkali metal aluminate or calcium aluminate , A method for removing nitrate ions, heavy metal ions, etc. by generating hydrocalumite using calcium hydroxide or the like (see Patent Documents 10-12, etc.), anion Atsumarizai (Patent Document 13 reference) are known.

  The method using activated carbon simply adsorbs harmful substances, and is not sufficient from the viewpoint of immobilization of harmful substances.

  The method using zeolite exhibits adsorption and ion exchange reaction and can collect cadmium, lead, etc., but heavy metals such as chromium, selenium, arsenic, nitrate nitrogen, nitrite nitrogen, fluorine There was a problem that almost no ability to collect boron and the like was expected.

  The method using hydrotalcites itself is an expensive material, which is not only economical, but also has a problem that the harmful substances that can be collected are limited.

  The method using reducing iron powder has no immediate effect, and there is a problem that it takes a long time to obtain the effect. Although the method using ferrous sulfate has an immediate effect, it involves adding sulfate ions that it has to the system, resulting in secondary problems and limiting the number of harmful substances. It was.

  The method using apatite, like zeolite, can collect cadmium, lead, etc., but it can collect heavy metals such as chromium, selenium, arsenic, nitrate nitrogen, nitrite nitrogen, boron, etc. There was a problem that the ability was hardly expected.

  The method of using calcium sulfoaluminate hydrate or heated dehydrated calcium aluminate hydrate has a high specific surface area and high reactivity with water, so when used for collecting harmful substances in sewage There is a problem that the heat of hydration reaction is rapidly generated. Furthermore, when calcium sulfoaluminate hydrate is used, since a sulfuric acid component is added into the system, there has been a problem that secondary adverse effects are likely to occur.

It produces hydrocalumite (4CaO ・ Al ₂ O ₃・ nH ₂ O) using aluminum hydroxide such as alkali metal aluminate or calcium aluminate and calcium hydroxide to remove nitrate ions, heavy metal ions, etc. A method is known (see Patent Documents 10 to 12, etc.). Hydrocalmite's ability to collect harmful substances is not always sufficient, and there has been a strong demand for the development of a hazardous substance collection material with a better sorption capacity and the development of an efficient sewage treatment method.

  In particular, in recent years, there has been a need for a harmful substance collection material and a method for treating sewage that can effectively collect selenium, arsenic, dioxins, volatile organic compounds such as trichlorethylene and tetrachloroethylene among harmful substances. Yes.

The present inventor has made extensive efforts in view of industrial utilization of 2CaO · Al ₂ O ₃ · nH ₂ O, which is a kind of calcium aluminate hydrate, and as a result, calcium aluminate hydrate 2CaO · Al ₂ O ₃ · nH ₂ O exhibits excellent performance as a trap for various harmful substances such as chromium, selenium, and arsenic, which are extremely important as pollution-causing substances, and volatile organic compounds such as trichlorethylene and tetrachloroethylene. It is also found that the same effect can be obtained by using the process of generating 2CaO · Al ₂ O ₃ · nH ₂ O using alkali metal aluminate salt and calcium oxide and / or calcium hydroxide. The present invention has been completed.

JP 05-076619 A JP 2002-239347 A JP 2001-238980 Japanese Patent Laid-Open No. 10-128313 Japanese Unexamined Patent Publication No. 07-108280 Japanese Unexamined Patent Publication No. 09-085224 Japanese Patent Laid-Open No. 10-034124 Japanese Unexamined Patent Publication No. 08-182984 JP 2001-70926 JP 05-057289 A JP 2001-252648 A JP 2001-252675 A Japanese Unexamined Patent Publication No. 09-248449

Selenium, arsenic can collect various harmful substances including, moreover harmful substances trapping effect than the known material to provide a method of processing sewage comprising hazardous substances Ru remarkable der.

The present invention is a method for treating sewage containing selenium and arsenic as harmful substances, characterized by adding 2CaO · Al ₂ O ₃ · 8 H ₂ O to sewage, and adding 2CaO by adding an aluminum compound and a calcium compound A method for treating sewage containing harmful substances, characterized in that Al ₂ O ₃ · 8 H ₂ O-like hydrates are produced and the harmful substances are collected.

The hazardous substance collecting material of the present invention can collect a lot of harmful substances, and its collecting ability is larger than that of the conventional hydrocalumite, and the chemical formula 2CaO is obtained by adding an aluminum compound and a calcium compound. -Even if the calcium aluminate hydrate of Al ₂ O ₃ · 8 H ₂ O is produced, the same effect can be obtained.

In the present invention, 2CaO · Al ₂ O ₃ · nH ₂ O is a general term for calcium aluminate hydrates, and hydrates whose CaO / Al ₂ O ₃ molar ratio is close to 2 , normally, the value of n is a positive number of about 10 or less, and specific examples thereof include _{2CaO · Al 2 O 3 · 8H} 2 O value is 8 for n a crystalline compound.

2CaO ・ Al ₂ O ₃・ nH ₂ O is a calcium aluminate hydrate that is different from hydrocalumite, which is a conventional material for collecting harmful substances. Hydrocalumite is a hydrate having a composition with a higher calcium content than the calcium aluminate of the present invention, represented by the chemical formula 4CaO · Al ₂ O ₃ · nH ₂ O, etc., and a CaO / Al ₂ O ₃ molar ratio. Is a generic term for hydrates approximated by 4. Hydrocalumite is excellent in collecting harmful substances, but 2CaO, Al ₂ O ₃ and nH ₂ O are more effective in collecting harmful substances than hydrocalumite.

Examples of the method for obtaining 2CaO · Al ₂ O ₃ · nH ₂ O include a method of reacting an alkali metal aluminate salt with calcium oxide and / or calcium hydroxide in the presence of water, calcium chloride and alkali metal aluminate. A method of reacting a salt with water, a method of reacting calcium oxide and / or calcium hydroxide with aluminum hydroxide or aluminum gel in the presence of water, using calcium aluminate as a raw material, and optionally calcium oxide And / or a method of hydrating calcium aluminate in the presence of calcium hydroxide.

When obtaining 2CaO.Al ₂ O ₃ .nH ₂ O, the reaction temperature is preferably 30 ° C. or lower, more preferably 20 ° C. or lower. Exceeds _{30 ℃, 2CaO · Al 2 O} 3 · nH 2 No addition to _{3CaO · Al 2 O 3 · 6H} 2 O in O by-harmful substances trapping effect is reduced in some cases.

In the present invention, 2CaO · Al ₂ O ₃ · 8 H ₂ O can be used as a hazardous substance collecting material, and this can be added to sewage containing the toxic substance to perform sewage treatment. Moreover, an aluminum compound and a calcium compound can be added to wastewater to produce 2CaO · Al ₂ O ₃ · 8 H ₂ O to treat wastewater containing harmful substances.

  As the aluminum compound, alkali metal aluminate, aluminum hydroxide, aluminum gel, calcium aluminate and the like are suitable.

The alkali metal aluminate is a general term for R ₂ O—Al ₂ O ₃ compounds and is not particularly limited. Here, R ₂ O represents Na ₂ O or K ₂ O. Specific examples thereof include sodium aluminate and potassium aluminate. The sodium salt is preferable from the economical aspect, and the potassium salt is preferable from the viewpoint of an excellent effect of collecting harmful substances. In the present invention, these can be used in combination according to the purpose and application.

These alkali metal aluminates do not have a specific composition, and there are various R ₂ O / Al ₂ O ₃ molar ratios, and the R ₂ O / Al ₂ O ₃ molar ratio ranges from 0.5 to 2.0. Are well known. Alkali metal aluminates include anhydrous salts and hydrated salts. In the case of a hydrated salt, the ratio of the crystal water is often within 10 mol with respect to 1 mol of Al ₂ O ₃ . The alkali metal aluminate can be used in any R ₂ O / Al ₂ O ₃ molar ratio or in the number of water of crystallization.

Examples of calcium aluminate include CaO · Al ₂ O ₃ , 12CaO · 7Al ₂ O ₃ , 11CaO · 7Al ₂ O ₃ · CaX ₂ (X is halogen), 3CaO · Al ₂ O ₃ , and these crystalline calcium aluminum Amorphous calcium aluminate can also be mentioned in addition to nates, and one or more of these can be used in combination. In this case, it is necessary to use a calcium compound or an aluminum compound together so that the CaO / Al ₂ O ₃ molar ratio is about 2. For example, when using CaO · Al ₂ O ₃ or 12CaO · 7Al ₂ O ₃ having a CaO / Al ₂ O ₃ molar ratio smaller than ₂ , so that the CaO / Al ₂ O ₃ molar ratio is about 2, it must be adjusted in combination with the calcium compound such as calcium hydroxide, in the case of using a 3CaO · Al ₂ O ₃ greater than CaO / Al ₂ O ₃ molar ratio of 2, aluminum hydroxide and aluminate It is necessary to adjust the CaO / Al ₂ O ₃ molar ratio to about ₂ by using an aluminum compound such as an alkali metal salt in combination.

  In the present invention, from the viewpoint of reactivity, it is preferable to use, for example, aluminum hydroxide or aluminum gel as the aluminum compound. Examples of calcium compounds include calcium oxide, calcium hydroxide, and calcium chloride, and any of them can be used, but it is not necessary to raise the temperature of the system, and it is not necessary to add a coexisting anion into the system. Therefore, it is preferable to use calcium hydroxide.

  The toxic substances referred to in the present invention are not particularly limited, but toxic substances for which environmental standards are established, for example, heavy metals such as chromium, selenium, arsenic, cadmium, lead, mercury, all cyan, nitrate Nitrogen, nitrite nitrogen, fluorine, boron, phosphorus, and organic substances include dioxins, volatile organic compounds such as trichloroethylene and tetrachloroethylene, PCB, dichloromethane, carbon tetrachloride, 1,2-dichloroethane, 1 1,1-dichloroethylene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, benzene, organic phosphorus and the like. Examples of environmental standards not defined include copper, zinc, molybdenum, amine compounds, various environmental hormones, endocrine disrupting substances, and the like.

  The toxic water collecting material and the method for treating sewage containing toxic substances of the present invention are particularly excellent in the collection effect of volatile organic compounds such as selenium, arsenic, chromium, trichlorethylene and tetrachloroethylene.

  In the present invention, a known water treatment material can be used in combination. Specific examples include calcium aluminoferrites, calcium ferrites, calcium aluminosilicates, various portland cements, filler cements mixed with limestone powder, etc. Type cement (eco-cement), granulated blast furnace slag, blast furnace slow-cooled slag, fly ash, converter slag, electric furnace reduction period slag, electric furnace oxidation period slag, etc., and hydraulic materials contained in these powders Represented by all hydrates generated from latent hydraulic materials and pozzolanic materials, magnesium compounds such as magnesium oxide, magnesium hydroxide, dolomite and hydrotalcite, carbonaceous materials such as activated carbon, montmorillonite and kaolinite Bentonites and zeolites that are layered compounds , Sepiolite, phosphates such as apatite and zirconium phosphate, activated carbon, sulfur compounds such as polysulfides, sulfides, thiosulfates and sulfites, thiourea, amalgam, reduced iron powder, ferrous sulfate, ferric chloride The object of the present invention is to use one or more of iron compounds such as ferrous iron, water-soluble polymers such as celluloses, polyvinyl alcohol and chitosan, dialkyldithiocarbamic acids, quinoline compounds, polyamines and saccharides. They can be used in combination as long as they are not substantially inhibited.

  The water treatment material described above may be used in combination with the harmful substance collection material of the present invention, or may be used separately. It is also possible to perform the secondary treatment with the above-mentioned material after performing the primary treatment with the hazardous substance collecting material of the present invention. As described above, it is preferable to treat a plurality of harmful substances from the viewpoint of collecting the harmful substances in a multifaceted and reliable manner.

The specific surface area of calcium aluminate hydrate (2CaO · Al ₂ O ₃ · nH ₂ O) is not particularly limited, but is usually in the range of 5 to 100 m ² / g as a BET specific surface area value, Many are about 10-50 cm ² / g. If it is less than 5 m ² / g, the effect of collecting harmful substances may not be sufficient, and if it exceeds 100 m ² / g, handling may be difficult.

  The method of using the hazardous substance collecting material of the present invention is not particularly limited. For example, if it is used for water treatment, it may be used in powder form and then separated into solid and liquid, or it may be processed into pellets, columns, etc., and the treated water may be run and used as a filter. Can also be used.

  As a method for producing pellets and filters, for example, the method for pressure-molding the harmful substance-collecting material of the present invention, or the precursor, that is, the step of hydrating and curing the material based on calcium aluminate is used. Methods and the like. At this time, it may be hydrated and hardened together with other hydraulic materials such as various Portland cements.

  1 g of various calcium aluminate hydrates were put into 50 ml of a solution containing the harmful substances shown in Table 1, stirred for 5 minutes, and then separated into solid and liquid. And the density | concentration of the harmful substance which remains in a liquid phase was measured, and the reduction rate of the harmful substance was calculated | required. The results are also shown in Table 1.

<Materials used>
Calcium hydroxide: Reagent grade 1 Sodium aluminate: Reagent grade 1
2CaO ・ Al ₂ O ₃・ 8H ₂ O: synthesized by reacting 1 mol of sodium aluminate and 1 mol of calcium hydroxide in 1,000 cc of pure water while keeping at room temperature (25 ° C). BET specific surface area 31 m ² / g.
4CaO · Al ₂ O ₃ · 13H ₂ O: Synthesized by mixing 1 mol of C ₃ A and 1 mol of calcium hydroxide and hydrating them at a water / powder ratio of 100% in an environment of 50 ° C. BET specific surface area 19m ² / g, mainly hydrocalumite.
3CaO · Al ₂ O ₃ · 6H ₂ O: synthesized by reacting 0.5 mol of sodium aluminate and 1 mol of calcium hydroxide in 1,000 cc of pure water while heating to 50 ° C. BET specific surface area 5 m ² / g.
Hazardous substance Cr: Chrome standard solution, chromium concentration 1,000mg / liter solution, Kanto Chemical's hazardous substance Se: Selenium standard solution, selenium concentration 1,000mg / liter solution, Kanto Chemical's hazardous substance As: Arsenic standard solution, arsenic concentration 1,000mg / L solution, Kanto Chemical's hazardous substance F: Sodium fluoride, powder, reagent grade 1, Wako Pure Chemical's hazardous substance B: Boric acid, powder, reagent grade 1, Wako Pure Chemical's hazardous substance NO ₃ : Nitric acid Sodium, reagent grade 1, Wako Pure Chemical's hazardous substance P: Sodium orthophosphate (Na ₃ PO ₃ ), powder, reagent grade 1, Wako Pure Chemical's hazardous substance TCE (trichloroethylene): reagent grade 1, Wako Pure Chemical

<Measurement method>
Hazardous substance concentration: Measured according to Environmental Agency Notification No. 46.
Hazardous substance reduction rate: Calculated by the following formula based on the concentration of harmful substances measured based on Environmental Agency Notification No. 46.
Hazardous substance reduction rate (%) = C / C ₀ × 100
However, C ₀ : Total amount of harmful substance elution when no hazardous substance collector is added, C: Total amount of harmful substance elution when a hazardous substance collector is added.

注：(1)有害物質のTCEはトリクロロエチレン
(2)C₂AH₈は2CaO・Al₂O₃・8H₂O、C₃AH₆は3CaO・Al₂O₃・6H₂O、C₄AH₁₃は4CaO・Al₂O₃・13H₂Oである。

Note: (1) TCE of hazardous substances is trichlorethylene
₍₂₎ C 2 AH ₈ is _{2CaO · Al 2 O 3 · 8H} 2 O, C 3 AH 6 is _{3CaO · Al 2 O 3 · 6H} 2 O, C 4 AH 13 is _{4CaO · Al 2 O 3 · 13H} 2 O It is.

Wastewater containing harmful substances was treated using calcium hydroxide and sodium aluminate. Calcium hydroxide and sodium aluminate with a CaO / Al ₂ O ₃ molar ratio of 1 for 50 ml of a solution containing the hazardous substances shown in Table 2 so that 2CaO · Al ₂ O ₃ · 8 H ₂ O is formed. 1 g of the mixture was used. The results are shown in Table 2.

注：(1)有害物質のTCEはトリクロロエチレン
(2)C₂AH₈は2CaO・Al₂O₃・8H₂ Oである。

Note: (1) TCE of hazardous substances is trichlorethylene
(2) C ₂ AH ₈ is 2CaO · Al ₂ O ₃ · 8H ₂ O.

  The experiment was conducted in the same manner as in Experiment No. 2-11 of Example 2 except that potassium aluminate was used instead of sodium aluminate. The results are shown in Table 3.

<Materials used>
Potassium aluminate: Grade 1 reagent

注：(1)有害物質のTCEはトリクロロエチレン
(2)C₄AH₁₃は4CaO・Al₂O₃・13H₂Oである。

Note: (1) TCE of hazardous substances is trichlorethylene
(2) C ₄ AH ₁₃ is 4CaO · Al ₂ O ₃ · 13H ₂ O.

The hazardous material collection material of the present invention is a hazardous material such as chromium, selenium, arsenic, volatile organic compounds, etc., which is discarded from the chemical industry, electronics industry, medical facilities, and various research facilities, regardless of the type. The effect is that it can be collected quickly and efficiently.

Claims (3)

In a method for treating sewage containing harmful substances, wherein 2CaO · Al ₂ O ₃ · 8 H ₂ O is added to sewage, the sewage containing one or two of selenium and arsenic is treated as the harmful substance. Wastewater treatment method. In the wastewater treatment method for collecting toxic substances by adding aluminum compound and calcium compound to sewage to produce 2CaO ・ Al ₂ O ₃・8 H ₂ O, one or two of selenium and arsenic as the toxic substances A method for treating sewage, comprising treating sewage containing seeds.   The method for treating sewage according to claim 2, wherein the aluminum compound and the calcium compound are alkali metal aluminate and calcium hydroxide, respectively.