JP2010029760A - Method of preparing iron-oxide adsorbent, and method of cleaning molybdenum-containing waste water using the adsorbent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of preparing an iron-oxide adsorbent suitable for isolating an oxyacid ion of molybdenum contained in acidic waste water of pH2 or lower, and a method of cleaning molybdenum-containing waste water suitable for isolating an oxyacid ion of molybdenum from acidic waste water of pH2 or lower using the adsorbent. <P>SOLUTION: The method of preparing an iron-oxide adsorbent is characterized by adding an alkali into a solution comprising ferric ions and mixing them for neutralizing the solution to form a precipitate, drying the resulting precipitate at a temperature of 60 to 100°C to obtain a ferric hydroxide powder, and further calcining the resulting ferric hydroxide powder at a temperature of 300 to 700°C. The method of cleaning molybdenum-containing waste water comprises treating molybdenum-containing waste water by allowing it to flow through a column filled with the adsorbent and isolating molybdenum anions from the molybdenum-containing waste water. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method for producing an iron oxide-based adsorbent that can be suitably used for wastewater treatment containing molybdenum oxygenate ions and a method for purifying molybdenum-containing wastewater.
More specifically, a method for producing an iron oxide-based adsorbent suitable for separating molybdenum oxygenate ions contained in acidic wastewater having a pH of 2 or lower, and oxygen of molybdenum from acidic wastewater having a pH of 2 or lower using the same. The present invention relates to a method for purifying molybdenum-containing wastewater suitable for separating acid ions.

In recent years, with the development of science and technology, a wide variety of chemical substances are manufactured and used, and many of these substances have harmful effects on human health and ecosystems.
Therefore, in Japan, the water quality environmental standards were revised in March 1993, monitoring items were added, and molybdenum, antimony, nickel, etc. were newly designated as heavy metals.
These are represented by molybdenum, antimony, etc., and there is an urgent need to establish a practical method for removing heavy metal anions containing chromium, selenium, arsenic, etc., that is, oxygenates of heavy metals from wastewater, and various proposals have been made. .

JP 9-323079 A Japanese Patent Laid-Open No. 11-19661 JP 2000-117265 A JP 2003-103265 A JP 2003-62458 A JP 2003-334542 A JP 2005-270933 A

Among the heavy metal anions, the present inventor has focused on molybdenum this time, and has started intensive studies to develop a technique capable of suitably separating molybdenum from waste water containing the anion.
Wastewater containing molybdenum anions, that is, oxygenate ions of molybdenum, includes molybdenum anion-containing wastewater discharged from semiconductor manufacturing plants, stainless steel manufacturing plants, electronic component manufacturing plants, etc. Kinds have been proposed.

  For this purpose, (1) a method of adding sodium dithiocarbamate and activated carbon to wastewater containing molybdenum anions and adjusting the wastewater to pH 5 or lower (Patent Document 1), or (2) wastewater containing molybdenum anions. There is a method in which a sulfide treatment agent is added to release sulfur ions first, and then a water-soluble metal compound is added to convert molybdenum in wastewater into a hardly soluble solid compound (Patent Document 2).

  Furthermore, (3) Suspension in which molybdenum is coprecipitated by adding ferric ions to the molybdenum-containing wastewater in the reaction vessel, and generating ferric hydroxide by adding acid or alkaline agent to pH 4-8 after the addition. Method to circulate part of solid (sludge) obtained by solid-liquid separation after forming turbid material (Patent Document 3) or (4) Containing low concentration molybdenum with iron as anode Electrolyzes the acidic waste water to elute iron ions, precipitates the iron ions as iron or iron compounds at the same time as the eutectoid of molybdenum, and then adjusts the pH to 3.5 to 5.5, followed by electrolytic treatment There is also a method (Patent Document 4) in which wastewater is solid-liquid separated, an alkaline substance is mixed with the separated liquid after separation to adjust the pH to 6 to 8, and solid-liquid separation is performed again to remove the iron compound.

All of these methods are technologies that form solid substances by chemical reaction and remove the molybdenum anions in the wastewater by solid-liquid separation to purify the solid substances, but other methods have already been proposed. It separates heavy metals from water containing heavy metal anions such as arsenic, molybdenum or antimony by using an adsorbent having a specific composition, which includes zeolite and (PbO) _x (FeO) _y (Fe ₂ O ₃ ) _1-xy · aH ₂ O (wherein 0.1 ≦ x ≦ 0.9, 0 ≦ y ≦ 0.9, 0 ≦ a ≦ 10) (Patent Document 5).

The adsorbent has a complicated composition containing lead and iron oxides in addition to zeolite. However, an adsorbent for separating heavy metals composed of iron hydroxides having a simpler composition has already been proposed. Yes.
For this purpose, an anion adsorbent composed of an amorphous iron hydroxide-based precipitation product obtained by adding an alkali to an iron ion solution (Patent Document 6) or obtained by drying the precipitated organism at 60 to 100 ° C. There is an anion adsorbent or the like supported on a continuous porous molded body obtained by heating and baking the obtained microcrystalline iron hydroxide material with synthetic resin powder (Patent Document 7).

The above-mentioned adsorbents for iron hydroxide-based materials have been developed by the present inventors, and were developed by focusing mainly on the separation of arsenic among heavy metal anions.
In addition, separation of heavy metal anions by an adsorbent is a simple process that can separate heavy metal anions simply by passing wastewater containing heavy metal anions through a column packed with adsorbent, whereas patent literature The methods described in 1 to 4 all involve precipitation formation by a chemical reaction and subsequent solid-liquid separation treatment, and thus are complicated and require a lot of treatment time compared to adsorption separation treatment. .

Separation of heavy metal anions with adsorbents has the above-mentioned advantages, so that separation of the same anions from wastewater containing molybdenum anions, especially acidic wastewater, using the adsorbent of iron hydroxide-based material described above. As a result, it was found that the adsorption performance as expected could not be exhibited, and that the adsorbent dissolved as the acidity of the wastewater increased.
However, the separation of heavy metal anions using an adsorbent has the advantages as described above, and the adsorbent of the iron hydroxide-based material has a composition compared to the adsorbent described in Patent Document 5 as described above. Since it has the advantage of simplicity, we decided to proceed with further studies.

As a result, since the adsorbent of the iron hydroxide-based material does not contain lead like the adsorbent of Patent Document 5, it has also been found that there is an advantage that it is possible to avoid adverse effects on the environment due to the elution. .
Since the adsorbent for iron hydroxide-based materials has the advantages or advantages as described above, the inventors have continued research and development in the range of adsorbents for iron hydroxide-based materials in order to solve the above problems. The present invention is a result of diligent efforts and successful development as a result.

That is, the present inventors, in the previous research, when the hydroxide iron-based material was dried at a temperature exceeding 100 ° C., as described in paragraph [0015] of Patent Document 7, It was considered unsuitable for adsorption of heavy metal anions.
However, with regard to the adsorbent for iron hydroxide materials, we have intensively studied from various viewpoints in order to take advantage of the advantages, and unexpectedly heat-treated at a temperature in a specific range exceeding 300 ° C. It has been found that the adsorbent does not dissolve even in sewage under strong acidity and exhibits excellent adsorption performance for separating heavy metal anions, especially molybdenum anions.

  Therefore, the present invention has been successfully developed based on this new knowledge, and the production of an iron oxide-based adsorbent suitable for separating molybdenum oxyacid ions contained in acidic wastewater having a pH of 2 or lower. It is an object of the present invention to provide a method and a method for purifying molybdenum-containing wastewater suitable for separating molybdenum oxyacid ions from acidic wastewater having a pH of 2 or less using the method. .

  The present invention provides a method for producing an iron oxide-based adsorbent for achieving the above-mentioned problems, and a method for purifying molybdenum-containing wastewater using the same, and the former method for producing an iron oxide-based adsorbent comprises: A solution containing ferric ions is mixed with an alkali agent and neutralized to form a precipitate, and the obtained precipitation product is dried at 60 to 100 ° C. to obtain ferric hydroxide powder. 2 iron powder is further baked at 300-700 degreeC.

  Preferably, in the method for producing the iron oxide-based adsorbent, a solution containing ferric ions is mixed with an alkali agent and neutralized to form a precipitate, and the obtained precipitation product is formed at 60 to 100 ° C. In order to obtain ferric hydroxide powder, which is further calcined at 300 to 700 ° C., and the adsorbent is for separating oxygenate ions of molybdenum, More preferably, a solution containing ferric ions is mixed with an alkali agent and neutralized to form a precipitate, and the obtained precipitation product is dried at 60 to 100 ° C. to obtain ferric hydroxide powder. The ferric hydroxide powder is further calcined at 400 to 600 ° C., and the adsorbent is for separating oxygenate ions of molybdenum in an acidic pH of 2 or less.

  And the latter purification method of molybdenum-containing wastewater is obtained by mixing a neutralizing agent with a solution containing ferric ions to neutralize it to form a precipitate, and drying the obtained precipitation product at 60 to 100 ° C. Wastewater containing iron oxide adsorbent obtained by obtaining ferric hydroxide powder and further baking this ferric hydroxide powder at 300 to 700 ° C., and containing molybdenum oxygenate ions in the column It is characterized by separating molybdenum oxyacid ions by passing the liquid through and contacting.

Further, the purification method preferably comprises mixing a neutralizing agent with a solution containing ferric ions to neutralize to form a precipitate, and drying the obtained precipitation product at 60 to 100 ° C. The iron oxide adsorbent obtained by obtaining two iron powders and calcining this ferric hydroxide powder at 400 to 600 ° C. is filled in the column, and the waste water containing molybdenum oxyacid ions having a pH of 2 or less is contained in the column. It is characterized by separating molybdenum oxyacid ions by passing the liquid through and contacting.

The method for producing an iron oxide-based adsorbent and the method for purifying molybdenum-containing waste water according to the present invention can provide the following excellent effects.
(1) The iron oxide-based adsorbent produced by the production method of the present invention is sintered at a high temperature of 300 ° C. or higher, preferably 400 ° C. or higher. In comparison, the adsorption performance is excellent, and in particular, the adsorption separation performance of molybdenum anions is excellent.
(2) The iron oxide-based adsorbent can stably exhibit excellent adsorption performance without dissolving in an acidic solution, particularly an acidic solution having a pH of 2 or less.
(3) In particular, the iron oxide-based adsorbent is used to purify strongly acidic wastewater containing low-concentration molybdenum that is generated during the production of tungsten filaments used for automobile headlamps described in Patent Document 4. Can be suitably used.

Furthermore, the present invention can provide the following excellent operational effects.
(4) A column packed with an adsorbent as compared with a method in which a solid substance is formed by a chemical reaction, such as separation of molybdenum anions described in Patent Documents 1 to 4, and this solid substance is further separated into solid and liquid. Wastewater treatment can be performed simply by passing wastewater containing heavy metal anions inside, and wastewater purification treatment is simple.
(5) Since the adsorbent described in Patent Document 5 does not have a complicated composition, and the adsorbent does not contain lead, it has a simple composition and elutes lead during or after the adsorption treatment. There is no need to worry about adverse environmental impacts.

Hereinafter, the present invention will be described in detail with respect to an embodiment including the best mode for carrying out the invention, but the present invention is not limited in any way by this embodiment, and is specified by the scope of claims. Needless to say, it is something.
As described above, the present inventor mixes an alkali agent with a solution containing ferric ions and neutralizes it to form a precipitate. The obtained precipitation product is dried at 60 to 100 ° C. A method for producing an iron oxide-based adsorbent characterized by obtaining iron powder and further firing the ferric hydroxide powder at 300 to 700 ° C., and a method for purifying molybdenum-containing wastewater using the iron oxide-based adsorbent It is.

  That is, an alkaline agent is mixed in a solution containing ferric ions and neutralized to form a precipitate, and the obtained precipitation product is dried at 60 to 100 ° C. to obtain ferric hydroxide powder. An iron oxide-based adsorbent obtained by further firing ferric hydroxide powder at 300 to 700 ° C. is packed in a column, and a wastewater containing molybdenum oxyacid ions is passed through the column for contact with molybdenum. This is a method for purifying molybdenum-containing wastewater, characterized by separating oxygenate ions.

  Regarding the solution containing ferric ions used in the method for producing an iron oxide-based adsorbent of the present invention, various compounds are used without particular limitation as long as they are compounds that dissolve in water to form ferric ions. Examples thereof include ferric sulfate, ferric nitrate, ferric chloride, polyferric sulfate, etc., and alkali is also particularly limited as long as it is a compound that dissolves in water and exhibits basicity. Various compounds can be used without being treated, such as hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, etc. An example is carbonate.

  When mixing the solution containing ferric ions and the alkali agent, a solid alkali agent may be mixed in the solution containing ferric ions, but the alkali agent is dissolved in water in advance to form an aqueous solution. The reaction may be carried out after mixing, and the concentration at that time is preferably about 10 to 30%. At the time of mixing, it is preferable to add an alkali agent to a solution containing ferric ions. Conversely, mixing is performed by adding a solution containing ferric ions to an aqueous solution of an alkali agent. You can also. The pH after neutralization is preferably about 6-8.

The drying of the precipitate formed by neutralization is not particularly limited, and various dryers can be used, and examples thereof include a hot air dryer, a ventilating dryer, a spray dryer, and an air dryer. The precipitate may be dried as it is, but drying after solid-liquid separation in advance has a lower water content in the precipitate and is excellent in energy efficiency. Therefore, drying is preferably performed after solid-liquid separation.
Various solid-liquid separation means can be used for solid-liquid separation at that time without particular limitation, and examples thereof include a vacuum dehydrator, a centrifugal dehydrator, a filter press, and the like.

  After drying, the obtained ferric hydroxide powder is sintered, and the heat treatment temperature at that time is required to be 300 to 700 ° C. The ferric powder is sintered to become a ferric oxide compound having a crystal structure, and an adsorbent excellent in heavy metal anion adsorption performance is obtained. Moreover, by heat-treating in a temperature range of 400 to 600 ° C., a sintered product of a ferric oxide compound having higher crystallinity is obtained, and an adsorbent having higher adsorption performance of heavy metal anions is obtained.

As described above, the iron oxide-based adsorbent produced by the production method of the present invention can be suitably used for adsorption separation of molybdenum anions and exhibits excellent adsorption performance, but heavy metal anions other than molybdenum Of course, since it can be adsorbed, it can of course be used for purification treatment of waste water containing heavy metal anions other than molybdenum.
The iron oxide-based adsorbent produced by the production method of the present invention can be separated into heavy metal anions by filling the column and letting the waste water containing heavy metal anions flow into and contact the column. This is a preferable waste water treatment, and this is adopted in the purification method of the present invention. Of course, heavy metals can be separated even if waste water containing heavy metal anions is brought into contact with an adsorbent by other methods.

[Method for producing adsorbent]
Ferric chloride hexahydrate (FeCl ₃ .6H ₂ O) crystals are dissolved in pure water at 25 ° C. to a Fe ³⁺ concentration of 1 mol / L. An aqueous solution of (NaOH) was added dropwise at a constant rate to adjust the pH to 7. The obtained suspension was filtered while washing with pure water to obtain a precipitate. The precipitate was dried at 70 ° C. for 72 hours and then pulverized in an agate mortar to obtain a fine powder. The obtained fine powder was heat-treated individually at each temperature at intervals of 100 ° C. in the range of 200 ° C. to 800 ° C. for about 1 hour, and a fired product was prepared at each heat treatment temperature.

[Adsorption performance test]
(1) Test method To 1 L of HNO ₃ solution (HNO ₃ : 630 g / L) containing 10 mg / L of Mo in the form of anion, 10 g of the calcined product heat-treated at each of the predetermined temperatures described above is added. The mixture was stirred at room temperature with a magnetic stirrer for 2.5 hours. Thereafter, the membrane was filtered, and each filtrate was analyzed for Mo concentration by ICP-MS.

(2) Test Results FIG. 1 shows the Mo adsorption rate and the residual concentration of Mo in the HNO ₃ solution after the Mo adsorption by each fired product obtained at each heat treatment temperature.
From the results of FIG. 1, each adsorbent made of each calcined product obtained at a firing temperature of 300 to 700 ° C. has a high Mo anion adsorption rate of 80% or more, and at less than 300 ° C. and 700 ° C. or more, Mo It turns out that the adsorption rate of an anion falls rapidly. Moreover, it turns out that each adsorbent which consists of each baked product obtained by the temperature of the range of 400-600 degreeC of firing temperature has much higher adsorption rate of Mo anion.

[Acid adsorption acid resistance test (dissolution test)]
(1) Test method An aqueous solution containing 10 mg / L of anionic form of Mo was adjusted to an acidic side of pH 0.5 to 3 by adding sulfuric acid or hydrochloric acid to prepare test solutions of various pHs, and various pHs prepared. 10 g of a fired product obtained by heat treatment at various temperatures for 1 hour was added to 1 L of the test solution, and stirred at room temperature with a magnetic stirrer for 2 hours. Thereafter, the membrane was filtered, and each filtrate was analyzed for Fe concentration by ICP-MS.

(2) Test result The result of the dissolution test with respect to each baked product obtained in each heat processing temperature by the test solution of various pH obtained as a result is illustrated in FIG.
From the results of FIG. 2, it can be seen that the adsorbent composed of the calcined product at the heat treatment temperatures of 300 ° C. and 500 ° C. hardly dissolves the adsorbent even when the test solution is strongly acidic at pH 0.6 to 0.9.
At heat treatment temperatures of 70 ° C. and 200 ° C., it can be confirmed that the adsorbent is dissolved by about 10 to 20%.

[Survey of crystal structure of adsorbent]
An X-ray diffraction test was performed on the fired products obtained by heat treatment at temperatures of 70 ° C, 300 ° C, 500 ° C, and 700 ° C. The results obtained are illustrated in FIG.
According to FIG. 3, the fact that the crystal structure of hematite (Fe ₂ O ₃ ) is slightly formed can be confirmed for the fired product heat-treated at a temperature of 300 ° C. or higher. It can be confirmed that a large number of hematite crystal structures are formed at ℃.

The X-ray diffraction test result of the fired product obtained by heat treatment at 700 ° C. is almost the same as that of the fired product obtained at 500 ° C. as described above.
However, the fired product obtained by heat treatment at 700 ° C. has an adsorption performance similar to that of the fired product obtained at 300 ° C. according to FIG. Although the adsorption performance is inferior to that of the fired product obtained in step 1, the reason has not been elucidated so far.

The Mo adsorption rate and the residual concentration of Mo in the HNO ₃ solution after Mo adsorption by each fired product obtained at each heat treatment temperature are illustrated. The result of the dissolution test with respect to each baked product obtained in each heat processing temperature by the test liquid of various pH is illustrated. The result of having performed the X-ray-diffraction test about the baked material etc. which were heat-processed at each temperature is shown in figure.

Claims (5)

  A solution containing ferric ions is mixed with an alkali agent and neutralized to form a precipitate, and the obtained precipitation product is dried at 60 to 100 ° C. to obtain ferric hydroxide powder. A method for producing an iron oxide-based adsorbent, wherein the ferric iron powder is further fired at 300 to 700 ° C.   A solution containing ferric ions is mixed with an alkali agent and neutralized to form a precipitate, and the obtained precipitation product is dried at 60 to 100 ° C. to obtain ferric hydroxide powder. A method of producing an iron oxide-based adsorbent for separating oxygenate ions of molybdenum, wherein the ferric iron powder is further fired at 300 to 700 ° C.   A solution containing ferric ions is mixed with an alkali agent and neutralized to form a precipitate, and the obtained precipitation product is dried at 60 to 100 ° C. to obtain ferric hydroxide powder. A method for producing an iron oxide-based adsorbent for separating oxygenate ions of molybdenum in an acidic pH of 2 or less, wherein the ferric iron powder is further calcined at 400 to 600 ° C.   A solution containing ferric ions is mixed with an alkali agent and neutralized to form a precipitate, and the obtained precipitation product is dried at 60 to 100 ° C. to obtain ferric hydroxide powder. The iron oxide adsorbent obtained by further firing the ferric iron powder at 300 to 700 ° C. is filled in the column, and the wastewater containing molybdenum oxyacid ions is passed through the column and brought into contact therewith. A method for purifying molybdenum-containing wastewater, characterized by separating acid ions.   A solution containing ferric ions is mixed with an alkali agent and neutralized to form a precipitate, and the obtained precipitation product is dried at 60 to 100 ° C. to obtain ferric hydroxide powder. By filling the column with iron oxide-based adsorbent obtained by further firing ferric powder at 400 to 600 ° C., and passing the waste water containing molybdenum oxygenate ions having a pH of 2 or less into the column for contact. A method for purifying molybdenum-containing wastewater, characterized by separating oxygenate ions of molybdenum.

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