JP2006075760A - Wastewater purifying treatment material and treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wastewater purifying treatment material for removing heavy metals from wastewater efficiently and economically, and a wastewater treatment method. <P>SOLUTION: A fibrous substance is used as a carrier and a reducible ferrous precipitate being a mixture of iron hydroxide and green rust or green rust and iron ferrite is supported on the carrier to obtain a wastewater purifying treatment material. Preferably, the reducible ferrous precipitate comprising a precipitate based on iron hydroxide (II), green rust alone or a mixture of green rust and iron ferrite and characterized in that the ratio [Fe<SP>2+</SP>/total Fe] of divalent iron to total iron is 0.3 or above is supported on the ferrous substance to obtain the wastewater purifying treatment material. As the ferrous substance, an inorganic fiber such as quartz wool, glass wool, rock wool, ceramic wool, steel wool, slag wool and the like or an organic fiber is used and a container communicating with wastewater is filled with the wastewater purifying treatment material. The wastewater treatment method using the wastewater purifying treatment material is also disclosed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a wastewater purification treatment material excellent in removal effect and economical efficiency of heavy metals contained in wastewater, and a purification treatment method using this treatment material. More specifically, the present invention relates to a wastewater purification treatment material that is used at room temperature, has a simple usage method, and is excellent in the removal effect and economical efficiency of heavy metals contained in wastewater, and a purification treatment method using this treatment material.

As a means of removing heavy metals in the wastewater, a method of adsorbing heavy metals to the chelating agent, a method of generating precipitates of hydroxides and sulfides, taking heavy metals into the precipitates, and coprecipitation, iron powder in the wastewater In addition, methods for precipitating heavy metals are known. However, the method using a chelating agent is inferior in economic efficiency because the chelating agent is expensive, and the chelating agent is not reducible, so that detoxification of heavy metals is insufficient. In addition, chelating agents may remain in the treated water.

On the other hand, the method of generating precipitates of hydroxides and sulfides requires a flocculant and has a heavy burden such as coagulation sedimentation separation by thickener and sludge dehydration treatment. In addition, there is a problem that the amount of sludge increases because a coprecipitation agent is required to perform good solid-liquid separation. Moreover, there is a problem that the burden of starch treatment is large because the dehydrating property of starch is poor.

The method of reducing and precipitating heavy metals by adding iron powder to the wastewater takes a long time because of the slow reaction, and the recovery of the iron powder is troublesome. The pH during the reaction is under acidic condition and returned to neutral after the treatment. Therefore, the burden of post-processing is large, such as the need to process by-products such as hydrogen gas and divalent iron ions, which is troublesome to adjust pH.

As another method using hydroxide precipitation, fine particles contained in drainage are passed through drainage etc. through a layer filled with an adhesive that holds a metal hydroxide gel precipitate on the surface of a fibrous base material. A treatment method for adsorption is known (Patent Document 1: Japanese Patent Laid-Open No. 5-293316). According to this method, it is described that a part of dissolved components contained in waste water and the like, for example, harmful metal ions such as cadmium, arsenic, mercury, and polymer flocculant can be adsorbed. However, this method has a problem that the adsorptive power or the adsorption capacity is not sufficient because it uses a coordination bond-like adsorbing force.

On the other hand, a method of adding a reducing agent to waste water to reduce the heavy metal ions and removing it from the waste water is also known, and iron powder or the like is used as the reducing agent. For example, a method is known in which a layer filled with iron particles is formed in a column-shaped tank, and drainage is passed through the iron particle packed bed to adsorb and remove heavy metals on the surface of the iron particles (patent). Document 2: JP-A-9-262592). Furthermore, there is also known a method of reducing the selenium concentration in the waste water by bringing the waste water into contact with iron powder or iron fine particles and reducing and precipitating selenium in the waste water on the surface of the iron powder or the like (Patent Document 3: Japanese Patent Laid-open No. Hei. 7-2502).

However, the method of using iron powder as a reducing agent requires that the iron powder be replaced in a short period of time because the surface reaction is hindered when the heavy metal is adsorbed on the surface of the iron powder, and the reducing power decreases rapidly. There is a problem of being big. Furthermore, since hydrogen gas is generated particularly under acidic conditions, post-treatment is required. In addition, since a large amount of iron powder is used, the packed bed becomes extremely heavy, and the burden on the device structure is large.
JP-A-5-293316 JP-A-9-262592 JP-A-7-002502

The present invention solves the above-mentioned problems in conventional wastewater treatment methods, is excellent in the effect of removing heavy metals contained in wastewater, etc., and is easy to maintain and economical in wastewater purification treatment material The processing method is provided.

The present invention relates to a wastewater purification treatment material having the following constitution and a treatment method thereof.
(1) Wastewater purification treatment material characterized by carrying a reducing iron-based precipitate, which is a fibrous substance as a carrier, and is iron hydroxide, green last, or a mixture of green last and iron ferrite. .
(2) Reducing iron comprising iron hydroxide, green last, or a mixture of green last and iron ferrite and having a ratio of divalent iron to total iron [Fe ²⁺ / total Fe] of 0.3 or more The waste water purification treatment material according to (1) above, wherein the system precipitate is supported on a fibrous material.
(3) Wastewater purification as described in (1) or (2) above, wherein the fibrous material is inorganic fiber such as quartz wool, glass wool, rock wool, ceramic wool, steel wool, or slag wool, or organic fiber Treatment material.
(4) A wastewater purification treatment material obtained by filling a wastewater purification treatment material described in any one of (1) to (3) above into a container through which wastewater flows.
(5) Filling a container with the waste water purification treatment material described in any one of (1) to (3) above and bringing the container into contact with the waste water purification treatment material through waste water, selenium and copper contained in the waste water , Hexavalent chromium, molybdenum, boron, antimony, lead, arsenic, zinc, cadmium, nickel, manganese, fluorine, tin, phosphorus, cobalt, or any one or more of organic chlorine compounds such as trichlorethylene and dichloroethylene Wastewater purification treatment method.

[Specific description]
The waste water purification treatment material according to the present invention comprises a fibrous substance as a carrier and carries a reducing iron-based precipitate that is iron hydroxide, green last, or a mixture of green last and iron ferrite. It is a featured wastewater purification treatment material. Specifically, for example, a reducing iron-based precipitate composed of an iron hydroxide mainly composed of divalent iron (II) hydroxide, or green last alone, or a mixture of green last and iron ferrite. Is a wastewater purification treatment material that is supported on a fibrous material.

Green last is a blue-green substance in which a hydroxide of ferrous iron and ferric iron forms a layer, and has a structure in which an anion is taken in between layers, and is represented by, for example, the following formula (1).
_{^{[Fe II (6-x) Fe}} III x (OH) 12 ] ^{x +} [A _x / n · yH ₂ O] ^x- ... (1)
(0.9 <x <4.2, Fe ²⁺ / total Fe = 0.3 to 0.85)
(A: anion, SO ₄ ²⁻ , Cl ^−, etc.)
For example, when A = SO ₄ ²⁻ and x = 2, it is called green last (II) [GR (II)]. Green rust becomes iron ferrite by slowly oxidizing.

The iron ferrite is mainly composed of magnetite (Fe ^II OFe ^III ₂ O ₃ ), but may be partially substituted with heavy metal by Fe (II) or Fe (III). As the iron-based precipitate having reducibility according to the present invention, for example, a ferritic iron precipitate in a state in which heavy metal ions in waste water are taken into the green rust and partially include heavy metals can be used.

Reducing iron hydroxide is a precipitate mainly composed of iron (II) hydroxide of divalent iron. For example, by adding alkali to a ferrous salt solution in a non-oxidizing atmosphere to form a precipitate. Obtainable. This iron (II) hydroxide gradually changes to green last by slowly oxidizing under alkaline conditions.

In the iron-based precipitate of the present invention, the ratio of divalent iron to the total iron in the precipitate [Fe ²⁺ / total Fe] is at least 0.3 or more so as to have a reducing power. If the ratio of divalent iron in the iron-based precipitate is smaller than this, the reducing power is weak, which is not suitable. Incidentally, as described above, in the green last or a mixture of green last and iron ferrite, the ratio of the divalent iron [Fe ²⁺ / total Fe] is 0.3 to 0.85, and the amount of divalent iron is large. The stronger the reduction, the stronger. In addition, since green last is iron-ferrite by being oxidized slowly, the ratio of the divalent iron is usually 0.4 to 0.65, preferably 0.5 to 0.6.

The wastewater purification treatment material of the present invention uses a fibrous substance as a carrier and carries the above-described reducing iron-based precipitate thereon. As the fibrous material of the carrier, for example, inorganic fibers such as quartz wool, glass wool, rock wool, ceramic wool, steel wool, or slag wool can be used. Alternatively, organic synthetic fibers may be used. The thickness and density of the fibrous substance, or the weight ratio of the iron-based precipitate and the fibrous substance are appropriately selected according to the use environment.

The waste water purification treatment material of the present invention, for example, prepared a precipitate slurry mainly composed of iron (II) hydroxide, a slurry of green last alone, or a slurry of a mixture of green last and iron ferrite, to these slurries It can be produced by soaking the fibrous material, stirring well to allow the slurry to conform to the fiber and coating the fiber surface with a slurry precipitate. Alternatively, the wastewater purification treatment agent of the present invention is produced by impregnating a fibrous material into a divalent iron-based salt aqueous solution, adding an alkali thereto to form a precipitate, and covering the fiber surface with this precipitate. Can do.

A slurry of green last or a mixture of green last and iron ferrite can be prepared as follows.
(Ii) Slaked lime is added to the ferrous sulfate aqueous solution to make it alkaline at about pH 9.0 to produce an iron-based precipitate.
(B) The precipitate is recovered by solid-liquid separation, and further slaked lime is added to adjust to a strong alkali around pH 12.
(C) This strong alkali starch is added to the ferrous sulfate aqueous solution, adjusted to around pH 9.0, and stirred to form a slurry. At this time, the ratio of divalent iron to the total iron in the slurry [Fe ²⁺ / T-Fe] is 0.4 to 0.65, and the redox potential (Ag / AgCl electrode standard) is -620 mV to -680 mV. Thus, the contact area with the air interface of the stirring device is adjusted.
(D) The produced precipitate is solid-liquid separated to obtain a concentrated starch.
By repeating the steps (b) to (d), an iron-based precipitate used for the wastewater purification treatment material of the present invention can be prepared.

Moreover, the iron-type deposit used for the waste water purification treatment material of this invention can be prepared using the aqueous solution containing bivalent iron and trivalent iron as follows.
(B) The following operations (b) to (d) are carried out under an inert gas atmosphere (99.99% N ₂ or the like).
(B) The deionized water is aerated with an inert gas such as 99.99% N ₂ .
(C) FeSO ₄ .7H ₂ O and Fe ₂ (SO ₄ ) ₃ are added to the ion exchange water, and Fe ²⁺ and Fe ³⁺ are added at a ratio of Fe ²⁺ / Fe ³⁺ = 2 (molar ratio). A solution containing is prepared.
(D) NaOH is added to the aqueous iron sulfate solution and mixed. The amount of NaOH added is adjusted so that NaOH / total Fe = 2 (molar ratio). As a result, green last (II) is produced as shown in the following reaction formula.
4Fe ²⁺ + 2Fe ³⁺ + 12OH ⁻ + SO ₄ ²⁻ → Fe ₄ Fe ₂ (OH) ₁₂ SO ₄
(E) The precipitate is recovered by solid-liquid separation, and further slaked lime is added to adjust to a strong alkali around pH 12.
(F) Add this strong alkali starch to the ferrous sulfate aqueous solution, adjust the pH to around 9.0, and stir to make a slurry. At this time, the ratio of divalent iron to total iron in the slurry (Fe ²⁺ / total Fe) is 0.4 to 0.65, and the oxidation-reduction potential (Ag / AgCl electrode standard) is −620 mV to −680 mV. The contact area with the air interface of the agitator is adjusted.
(G) The produced precipitate is solid-liquid separated to obtain a concentrated starch.
The concentrated starch obtained by repeating the steps (e) to (g) can be used for the wastewater purification treatment material of the present invention.

The starch slurry thus obtained is sufficiently impregnated with the fibrous substance and supported on the fibrous substance, whereby the waste water purification treatment material of the present invention can be obtained.

Also, the waste water purification treatment material of the present invention can be manufactured as follows.
(A) Impregnating a ferrous sulfate aqueous solution with a fibrous material.
(B) An aqueous sodium hydroxide solution is added here to adjust the pH to 9.0, and a precipitate is deposited on the surface of the fibrous material.
Through the above steps, the waste water purification treatment material of the present invention can be obtained.

The waste water purification treatment material of the present invention can be used, for example, by filling the treatment material in a container such as a column through which waste water passes. A column or the like filled with a fibrous substance carrying the iron-based precipitate has a larger surface area and a higher porosity than a spherical carrier or a block-like carrier. It becomes intertwined with each other and the iron-based precipitate is stably maintained. Therefore, when drainage is passed through a column or the like, the ratio of the iron-based precipitates falling off from the fibrous material and flowing out is small, and a stable treatment effect can be obtained.

A column packed with a fibrous substance carrying an iron-based precipitate is preferably used under alkaline pH 8-11, and more preferably pH 9-10. When this pH is lower than the above range, divalent iron ions are eluted and the water quality deteriorates. On the other hand, when the pH is higher than the above range, the reducing ability decreases.

The waste water purification treatment material of the present invention is preferably used in a state where the oxidation-reduction potential in the column through waste water is -500 mV to -800 mV as an Ag / AgCl electrode reference, and more preferably -620 mV to -680 mV. If this oxidation-reduction potential is higher than the above range, the reduction ability is lowered, and thus heavy metal removal treatment becomes impossible.

When using the waste water purification treatment material of the present invention, a divalent iron-based salt such as ferrous sulfate or ferrous chloride is added as necessary, and the reduction reaction is performed by adjusting to a non-oxidizing atmosphere. Can be further promoted.

When the waste water is brought into contact with the waste water purification treatment material, the heavy metal contained in the waste water is taken into the iron-based precipitate, becomes a starch, and is removed from the waste water. For example, heavy metal ions such as cadmium, lead, zinc, nickel and manganese are taken in between layers of green last. In addition, oxyanions such as hexavalent selenium and hexavalent chromium are reduced to tetravalent selenium, metal selenium, or trivalent chromium, and incorporated into the iron-based precipitate. Furthermore, oxyanions other than selenium and chromium, for example, pentavalent arsenic and trivalent arsenic, are all taken into the loose lamellar structure of green last and are removed from the waste water as starch.

If the reducing power of the waste water purification treatment material is reduced by repeatedly passing the waste water through the waste water purification treatment material or continuously passing it, and the heavy metal in the waste water is taken into the iron-based precipitate, What is necessary is just to take out a waste water purification processing material from a column etc. and replace | exchange for the new waste water purification processing material with a strong reduction power.

Since the wastewater purification treatment material of the present invention takes in heavy metals contained in wastewater into iron-based precipitates, heavy metals can be effectively removed from wastewater. Moreover, when using the waste water purification treatment material of this invention, it is not necessary to heat, and the heavy metal of a waste water is taken in at normal temperature, and precipitation of iron progresses. In addition, since the precipitate is mainly composed of magnetite, it is magnetic and can be treated by adsorbing the precipitate to a magnet. Furthermore, since it can be taken out and removed integrally with the fibrous material, it is easy to handle, the post-treatment burden of starch is small, and it is excellent in economic efficiency and handleability.

By using slag wool, which is a by-product of metal smelting, as a fibrous material, wastewater treatment with low cost and low environmental impact is possible. In addition, the wastewater purification treatment material of the present invention can be used under neutral to weak alkalinity, is easy to adjust pH, and achieves detoxification and concentration separation by reduction of heavy metals in a single packed bed. Can do. For example, when treating contaminated wastewater with a low concentration of heavy metals, conventionally, a large amount of sludge is generated due to the use of a coprecipitation agent such as iron chloride, and a solid-liquid separation means such as a thickener is required. According to the purification treatment material, conventional solid-liquid separation means is not required, and the heavy metal in the wastewater becomes starch and deposits on the fibrous material. And post-processing is much easier.

〔Example〕
1000 mL of a slurry containing 20 g / L of a precipitate made of a mixture of green last and iron ferrite and prepared such that the ratio of divalent iron to total iron [Fe ²⁺ / T-Fe] is 0.4 to 0.65. 20 g of slag fiber is dipped, thoroughly agitated to adjust the fiber, and the surface of the fiber is covered with the precipitate. The slag fiber covered with the precipitate (weight after coating 25 g) is recovered and uniformly packed in a column (diameter 5 cm × height 6 cm). Waste water was allowed to flow from the top of the column through the interior at a liquid flow rate of 2 mm / min. Table 1 shows the heavy metal concentration contained in the wastewater before flowing down and the heavy metal concentration after flowing down.

As shown in Table 1, the amount of heavy metal ions in the wastewater that passed through the wastewater purification treatment material of the present invention is greatly reduced, and this treatment effect is not significantly different between the flow-down amounts of 500 mL and 2000 mL. Even if the flow rate increases, heavy metals can be removed stably.

Claims (5)

A wastewater purification treatment material comprising a fibrous substance as a carrier and carrying a reducing iron-based precipitate, which is iron hydroxide, green last, or a mixture of green last and iron ferrite.
A reducing iron-based precipitate comprising iron hydroxide, green last, or a mixture of green last and iron ferrite and having a ratio of divalent iron to total iron [Fe ²⁺ / total Fe] of 0.3 or more. The waste water purification treatment material according to claim 1, which is supported on a fibrous material.
The wastewater purification treatment material according to claim 1 or 2, wherein the fibrous substance is an inorganic fiber such as quartz wool, glass wool, rock wool, ceramic wool, steel wool, or slag wool, or an organic fiber.
A wastewater purification treatment material obtained by filling a wastewater purification treatment material according to any one of claims 1 to 3 into a container through which wastewater flows.
The selenium, copper, hexavalent chromium contained in the wastewater is filled by filling the wastewater purification treatment material according to any one of claims 1 to 3 into the container and contacting the wastewater purification treatment material through the wastewater. , Molybdenum, Boron, Antimony, Lead, Arsenic, Zinc, Cadmium, Nickel, Manganese, Fluorine, Tin, Phosphorus, Cobalt, or any one or more of organic chlorine compounds such as trichlorethylene and dichloroethylene Method.