JP2009255050A - Removing agent and method using the same for removing heavy metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new removing agent capable of easily and efficiently removing harmful heavy metals such as arsenic, cadmium, lead and chromium at a low cost and a method for removing heavy metals. <P>SOLUTION: The removing agent for removing heavy metals contains an amorphous Ti-Fe hydroxide containing amorphous Ti(IV) and amorphous Fe(III) or contains a precipitate obtained by neutralizing an aqueous solution of ferric nitrate and titanium tetrachloride with alkali metal hydroxide. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a removing agent for removing heavy metals such as arsenic (As), cadmium (Cd), lead (Pb), chromium (Cr), and a method for removing the same. The removing agent of the present invention is suitably used for treating pollutants such as water contaminated with heavy metals (surface water, groundwater, wastewater, etc.) and soil.

  It is known that heavy metals discharged from mines and factories contaminate soil and groundwater and are taken into the human body and cause serious damage. In addition, heavy metals are easily mixed into groundwater due to natural phenomena such as hot springs and leaching from the geology, and groundwater contamination by heavy metals is a serious problem especially in developing countries. Among these, arsenic is determined to be 100 μg / L or less in the drainage standard (pH 5.8 to 8.6) of the Water Pollution Control Law by the Ministry of the Environment because of its high toxicity. In WHO, it is stricter and is set to a drinking water reference value of 10 μg / L or less. Similarly to arsenic, cadmium and lead are also set to a WHO drinking water reference value of 10 μg / L or less. Moreover, the drinking water reference value of Cr is 50 μg / L or less.

  Known methods for removing heavy metals include, for example, precipitation separation (coprecipitation) and adsorption. Among these, the precipitation separation method is a method in which iron hydroxide is added to water contaminated with heavy metals, and the heavy metals are coprecipitated together with iron. However, the heavy metal removal efficiency by the precipitation separation method is low.

Specifically, arsenic will be described as an example. More than 80% of arsenic contained in environmental water is an inorganic arsenic compound, which has a stronger toxicity than an organic arsenic compound. Inorganic arsenic exists in two forms, arsenic [As (V)] and arsenous acid [As (III)], and arsenous acid As (III) is more toxic than arsenic acid As (V). About twice as strong and highly soluble. Under oxidizing conditions such as surface water, As (V) is the dominant chemical species (H ₃ AsO ₄ , H ₂ AsO ₄ ⁻ , HAsO ₄ ²⁻ ), but the oxidation-reduction potential decreases in groundwater. Therefore, it is often present in the form of As (III) (H ₃ AsO ₃ , H ₂ AsO ₃ ⁻ , HAsO ₃ ²⁻ ). As (III) is said to be difficult to remove from water because it exists as a H ₃ AsO ₃ molecule in the neutral to acidic range. Actually, the coprecipitation efficiency of As (III) in the precipitation separation method is lower than that of As (V), and it is necessary to oxidize and remove As (III) to As (V). The removal efficiency is low.

  Furthermore, in the precipitation separation method, disposal of sludge generated after the treatment is a problem. Therefore, removal of heavy metals by an adsorption method has been studied, but the ability to adsorb heavy metals such as activated alumina and activated carbon used as an adsorbent is low and is not practical.

  In view of the above circumstances, the present inventor has disclosed amorphous iron (III) hydroxide that can be produced inexpensively and easily as a novel heavy metal adsorbent. Specifically, Patent Document 1 discloses a method for removing Se (selenium), and Patent Document 2 discloses a method for removing heavy metals such as arsenic, cadmium, and lead.

Japanese Patent No. 3830878 JP 2006-218359 A

  An object of the present invention is to provide a novel removal agent that can adsorb and remove harmful heavy metals easily and efficiently at low cost and a method for removing the same. Preferably, the present invention provides a novel adsorbent that is particularly excellent in the adsorption ability of As (III) and can efficiently remove both As (III) and As (V) simultaneously and a method for removing the same.

  The remover of the present invention that has been able to solve the above-mentioned problems is a remover for removing heavy metals and contains amorphous Ti-Fe hydroxide; or iron (III) nitrate or chloride The gist is that it contains a precipitate obtained by neutralizing a mixed aqueous solution of iron (III) and titanium (IV) chloride with an alkali metal hydroxide.

  In a preferred embodiment of the invention, the Ti: Fe molar ratio ranges from 1: 1 to 1: 5.

  In a preferred embodiment of the present invention, the heavy metal is at least one selected from the group consisting of arsenic, cadmium, lead, and chromium.

  Moreover, the removal method of the present invention that has solved the above-mentioned problems is a method for removing heavy metals from pollutants contaminated with heavy metals, and has a gist in that the above-mentioned removing agent is brought into contact with the pollutants. ing.

  In a preferred embodiment of the present invention, the contaminant is contaminated water or contaminated soil.

  In a preferred embodiment of the present invention, the contaminant is arsenic or chromium, and the remover is brought into contact with the contaminant at a pH of 3-10.

  In a preferred embodiment of the present invention, the contaminant is lead, and the remover is brought into contact with the contaminant at a pH of 4 to 6.5.

  In a preferred embodiment of the present invention, the contaminant is cadmium, and the remover is contacted with the contaminant under pH 4-8.

  The removing agent of the present invention can be produced inexpensively and easily, and has a high adsorption removing ability regardless of the type of heavy metal. Therefore, the removing agent of the present invention is suitably used as a heavy metal removing agent for As, Cd, Pb, Cr and the like. In particular, the removing agent of the present invention is extremely excellent in the adsorption ability for As (III), which has been difficult to remove so far, and can efficiently remove both As (III) and As (V) simultaneously. By using the removing agent of the present invention, harmful heavy metals can be removed easily, safely and efficiently at low cost. Therefore, the present invention is extremely useful industrially as a technology that can purify pollutants such as polluted water and soil contaminated with heavy metals.

FIG. 1 is a diagram showing the results of X-ray diffraction in Example 1. FIG. 2A is a graph showing the relationship between Ti concentration and pH in the filtrate in Example 2, and FIG. 2B shows the relationship between Fe concentration in the filtrate and pH in Example 2. It is a graph. 3A is a graph showing the Fe concentration in NaCl in Example 3, and FIG. 3B is a graph showing the Ti concentration in NaCl in Example 3. FIG. FIG. 4 is a graph showing the results of residual amounts of As (III) and As (V) in Example 4. FIG. 5A is a graph showing the relationship between the pH and the As (III) adsorption amount in Example 6, and FIG. 5B is the relationship between the pH and the As (V) adsorption amount in Example 6. It is a graph which shows. FIG. 6 is a graph showing the relationship between the Cd concentration (initial concentration) and the Cd adsorption amount in Example 8. FIG. 7 is a graph showing the relationship between the Pb concentration (initial concentration) and the Pb adsorption amount in Example 9. FIG. 8A is a graph showing the relationship between the pH and the Cr (VI) adsorption amount in Example 10, and FIG. 8B is the relationship between the pH and the Cr (III) adsorption amount in Example 10. It is a graph which shows.

  The present invention relates to a technique for improving a heavy metal removing agent containing amorphous iron (III) hydroxide. The heavy metal removing agent of the present invention contains only amorphous iron (III) hydroxide in that it contains amorphous Ti-Fe hydroxide (Bimethal hydroxide). And the removal agent (Monometal hydroxide) described in 2 and 2.

  Hereinafter, for convenience of explanation, the removal agent containing both Ti and Fe as in the present invention is referred to as “amorphous Bimetal hydroxide” or “Bimeta hydroxide”. A heavy metal removing agent that contains only Fe and does not contain Ti is called “amorphous Monometal hydroxide” or “Monometal hydroxide”, and may be distinguished from each other.

Further, in this specification, “heavy metal” means a material having a density of about 4.0 g / cm ³ or more, and generally covers metal elements belonging to groups 11 to 15 of the long-period periodic table. Specific examples include As, Se, Pb, Cr, Cd, Cu, Hg, Zn, Mn, Co, Ni, Mo, Ta, Sn, Bi, and In.

  If the removing agent of the present invention is used, an adsorption removing action equivalent to or better than that of an amorphous monometallic hydroxide of Fe can be obtained for heavy metals such as As, Cd, Pb, and Cr. In particular, the removing agent of the present invention is remarkably excellent in the arsenic adsorption removing action, and such a remarkable effect is not the amorphous Monometal hydroxide of Fe but the amorphous Bimetal hydroxide of Ti and Fe. It is demonstrated for the first time by making it a thing. As confirmed in the above-mentioned Patent Document 2 and the examples described later, the removal agent of Monometal containing only amorphous iron hydroxide (III) is excellent in the adsorption ability of As (V). A tendency to be slightly inferior to the adsorption ability of III) was observed. On the other hand, it was confirmed that the adsorption ability of As (III) was particularly improved by using the removing agent of the present invention (see Examples described later). Therefore, if the remover of the present invention is used, not only can the wastewater standard (pH 5.8 to 8.6, 100 μg / L or less) of the arsenic water pollution prevention method by the Ministry of the Environment be achieved, but also the amount of the remover added. It is considered that the WHO drinking water standard (10 μg / L or less) can be sufficiently achieved by appropriately controlling the pH and pH.

  Moreover, as will be described in detail in the Examples section that follows, the removal agent of the present invention is stable against changes in pH (about 3 to 11) and has a low solubility in the electrolyte (NaCl).・ Excellent physical stability. Therefore, it was also found that the removal agent of the present invention is particularly suitable for adsorption treatment on contaminated water contaminated with heavy metals.

  The composition of the amorphous Ti-Fe hydroxide used in the present invention is unknown in detail. For example, amorphous Ti-Fe hydroxide in which Ti and Fe coexist in the same compound; amorphous A mixture of porous titanium hydroxide and amorphous iron hydroxide; or a mixture thereof may be considered.

  In the present invention, “including amorphous Ti—Fe hydroxide” means containing at least amorphous Ti—Fe Bimetal hydroxide. Therefore, it consists only of amorphous titanium (IV) hydroxide and amorphous iron (III) hydroxide, and it is used in combination with other adsorbents as well as remover composed of the two components. The removed agent is also included in the remover of the present invention. Moreover, in this invention, you may use the removal agent containing 2 or more types of amorphous Ti-Fe hydroxide from which the ratio of Ti and Fe differs. Further, the above-described removing agent may be supported on a commonly used carrier within a range not impairing the action of the present invention, and such a thing is also included within the scope of the present invention.

Among these, details of amorphous iron hydroxide (III) are as described in Patent Document 1 and Patent Document 2 described above. That is, amorphous iron hydroxide (III) is an amorphous material called “amorphous iron (hydr) oxide”, “amorphous ferric (III) iron (hydr) oxide”, “amorphous ferric hydroxide oxide”, etc. It is a kind of iron-containing hydroxide having a composition of Fe ₂ O ₃ .nH ₂ O. More specifically, an amorphous form in which iron hydroxide (III) (Fe (OH) ₃ ), iron oxyhydroxide (III) (FeO (OH)) and hydrogenated iron oxide (III) (FeHO ₂ ) are mixed. belongs to. This amorphous iron (III) hydroxide is a naturally occurring compound and does not contain aluminum or harmful heavy metals, so it can be used safely.

Amorphous iron hydroxide (III) is excellent in affinity with heavy metals such as arsenic, mainly because of its wide specific surface area. As shown in Table 1, the specific surface area of amorphous iron hydroxide (III) is magnetite, hematite, and phosphorus, which are other (water) iron (III) oxides (Fe ₂ O ₃ .nH ₂ O). Bigger than iron ore.

Amorphous titanium (IV) hydroxide is a kind of titanium-containing hydroxide having a composition of TiO ₂ · nH ₂ O. More specifically, titanium hydroxide (IV) (Ti (OH) ₄ ), titanium oxyhydroxide (IV) (TiO (OH) ₂ ) and hydrogenated titanium oxide (IV) (TiH ₂ O ₃ ) are mixed. It is amorphous.

  In the present invention, “amorphous” refers to a material in which no crystal structure is observed when X-ray diffraction is performed by a method described later. Specifically, the X-ray diffraction method has a broad scattering band having a peak at a 2θ value of 10 ° to 80 °, and may have a crystalline diffraction line. Preferably, the strongest intensity among the crystalline diffraction lines seen from 2 ° to 10 ° to 80 ° is the intensity of the diffraction line at the peak of the broad scattering band seen from 2 ° to 10 ° to 80 °. It is preferably 500 times or less, more preferably 100 times or less, particularly preferably 5 times or less, and most preferably no crystalline diffraction line.

  In the present invention, in order to obtain an excellent heavy metal adsorption capacity, the content ratio of Ti and Fe is generally better when the ratio of Fe is high. Especially for arsenic, as demonstrated in the examples described later, the As removal ability of amorphous Ti tends to be inferior to the As removal ability of amorphous Fe, and the ratio of Fe decreases and the ratio of Ti increases. Then, it is presumed that the active site of Fe is covered with Ti and the adsorption ability of Fe is lowered. Specifically, it may be appropriately set depending on the type and concentration of the heavy metal to be treated, the nature of the pollutant, etc., but the molar ratio of Ti: Fe is generally 1: 1 to 1: 5. preferable.

  For example, the Bimetal hydroxide is prepared by mixing a mixed aqueous solution of an Fe supply source (such as iron (III) nitrate and iron chloride (III)) and a Ti supply source (such as titanium (IV) chloride) with an alkali metal hydroxide. It is obtained by adding and precipitating. Therefore, in the present invention, the precipitate thus obtained can be used as the removing agent of the present invention. Specifically, an aqueous solution of iron nitrate (III) and an aqueous solution of titanium chloride (IV) are mixed so that the ratio of Ti and Fe is a predetermined ratio, and an alkali metal hydroxide such as NaOH, What is necessary is just to adjust and adjust so that it may become about pH7 (for example, the range of pH7 +/- 1), and freeze-dry the obtained precipitate.

  The removal method of the present invention is characterized in that the above-mentioned removal agent is brought into contact with a heavy metal contaminant. Thereby, the heavy metal in the pollutant is adsorbed by the removal agent and insolubilized.

  The heavy metal contaminant to be treated in the present invention may be in any state of solid, liquid, and gas. For example, soil contaminated with at least one heavy metal selected from the group consisting of As, Cd, Pb, and Cr, contaminated groundwater, drainage from mines and factories, smoke discharged from factories, etc. it can.

  Heavy metals such as As, Cd, Pb, and Cr may exist as simple substances in the environment, but most exist in the form of salts or ions. Since the method of the present invention is excellent in the performance of adsorbing these heavy metals in an ionic state, it is necessary to take a treatment mode according to the object to be treated. For example, when processing soot, it is also conceivable to pass soot through a filter carrying the removing agent of the present invention.

  As a specific treatment method, for example, when treating contaminated soil, it is preferable to add water and the removal agent of the present invention to the contaminated soil and to insolubilize by stirring. When the treatment target is a liquid, the removal agent of the present invention may be added as it is and stirred.

  Although the temperature in process is not specifically limited, For example, about 5-50 degreeC may be sufficient. It is because elution efficiency of heavy metals in water and heavy metal adsorption efficiency to the removal agent of the present invention can be increased by setting the temperature to 5 ° C. or higher. Moreover, by making it 50 degrees C or less, alteration of a process target substance can be suppressed and reuse can be performed.

  The appropriate value of pH when processing contaminants varies depending on the type of heavy metal to be removed. For example, when a substance contaminated with at least one of As and Cr is treated, it is preferable to mix the removing agent of the present invention and the contaminant in water having a pH of 3 to 10. Specifically, as shown in the examples described later, the optimum pH depends on the types of As (III) and As (V) for arsenic, and the types of Cr (III) and Cr (VI) for chromium. Is different. For example, As (III) and Cr (III) have a maximum adsorption amount around an alkali of pH 8-10, while As (V) and Cr (VI) adsorb around an acidity around pH 2-3. The amount is maximized. In any case, it was confirmed that when the removing agent of the present invention is used, it exhibits a good adsorption ability for any form of heavy metal in the pH range (pH 5.8 to 8.6) of the drainage standard.

Moreover, when processing the substance contaminated with Pb, it is preferable to mix this removal agent and a pollutant in the water of pH 4-6.5 (more preferably pH 5-6). If pH4 or plant viability, etc. Soil is not being deactivated, also, since ^{Pb 2+} is eluted from the Pb (OH) ₂ at pH6.6 or less, the present invention removing agent the elution ^{Pb 2+} This is because it can be efficiently adsorbed and insolubilized. The excellent effects of the removing agent of the present invention and the method of the present invention within the above range are well demonstrated in the examples described later.

Moreover, when processing the substance contaminated by Cd, it is preferable to mix this removal agent and a contaminant in water of pH 4-8 (more preferably pH 6-8). If pH4 or plant viability, etc. Soil is not being deactivated, and because ^{the Cd 2+} is eluted from Cd (OH) ₂ at pH8 or less, the present invention removing agent The eluted ^{Cd 2+} efficiency This is because it can be well adsorbed and insolubilized. The excellent effects of the removing agent of the present invention and the method of the present invention within the above range are well demonstrated in the examples described later.

  The addition amount of the removal agent of the present invention may be appropriately determined depending on the concentration and pH of the contaminant to be treated.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

  In Examples 1 to 3 below, the following four types of samples (a) to (d) were used, and the crystal structure of each sample, and the stability to pH and electrolyte were examined.

(1) Sample production method As shown below, two types of amorphous Bimetal hydroxides containing Ti and Fe in a molar ratio of 0.5: 0.5 or 0.2: 0.8 (present Samples of Invention Examples 1 and 2) were produced. For comparison, amorphous Monometal hydroxide containing only Ti and not containing Fe, and amorphous Monometal hydroxide containing only Fe and not containing Ti (non-described in Patent Document 1 and Patent Document 2) A sample of (crystalline iron hydroxide) was prepared in the same manner.
(A) Invention Example 1 (abbreviated as “1-1-s” in the figures and tables to be described later)
Amorphous Bimetal hydroxide with Ti: Fe = 0.5: 0.5 (A) Invention Example 2 (abbreviated as “1: 4-s” in the figures and tables described later)
Ti: Fe = 0.2: 0.8 amorphous Bimetal hydroxide (c) Comparative example 1 (abbreviated as “Ti-s” in the figures and tables described later)
Amorphous Monometal hydroxide with Ti: Fe = 1.0: 0.0 (D) Comparative Example 2 (abbreviated as “Fe-s” in the figures and tables described later)
Amorphous Monometal hydroxide with Ti: Fe = 0.0: 1.0

Specifically, first, the iron (III) nitrate nonahydrate (manufactured by Wako Pure Chemical Industries, Ltd. _{Fe (NO 3) 3 · 9H} 2 O) and titanium tetrachloride (manufactured by Wako Pure Chemical Industries, Ltd. TiCl ₄₎ Each solution was diluted with 5000 mL. Next, the electrode of the pH meter was immersed in the above solution, and the pH was adjusted to 7.0 with 1M NaOH. After standing for 3 hours, the pH was adjusted again to 7.0 ± 0.1 with 1 M NaOH, and when the precipitate and water separated after standing for 4 hours, the supernatant was removed by decantation. The resulting precipitate was placed in a dialysis membrane and immersed in deionized water for dialysis. The deionized water was changed twice a day until the electrical conductivity (EC) of the deionized water did not change. The dialyzed precipitate was transferred to a freeze-drying beaker, frozen while rotating the sample in the ethanol layer, and when completely frozen, freeze-drying was started using a freeze-dryer (TOKYO TIKAKIKAI CO. LTD., FD-1). . After lyophilization, the obtained powder sample was placed in a glass bottle and stored in a desiccator until the experiment was conducted.

Example 1 Confirmation of Crystal Structure by X-Ray Diffraction Four types of samples (a) to (d) obtained by the method (1) above were placed in holes in an aluminum sample plate, pressed flatly, and excess powder. The sample was removed. The crystal structure of each sample thus treated was measured under the following measurement conditions using an X-ray diffractometer (SIMAZDU XD-D1w).
<Measurement conditions>
・ Voltage: 30kV
・ Current: 20 mA
-Scan mode: Continuous scan-High angle: 80 deg
・ Low angle: 10deg
・ Integration time: 1 sec
Scanning speed: 2 deg / min
・ Full scale: 5.0 kcps
・ Drive shaft of goniometer: θ-2θ
・ Fixed shaft & angle: 10.0000deg

The result of X-ray diffraction is shown in FIG. For reference, the X-ray diffraction results of commercial TiO ₂ (Wako Pure Chemical Industries) are also shown in FIG.

As shown in FIG. 1, the commercial TiO ₂ showed a peak showing crystallinity, whereas the four types of samples produced by the above method did not show any peak showing crystallinity. Presumed to be crystalline.

Example 2 Stability test (effect of pH)
In this example, the stability to pH (pH 3 to 11) was examined.

  First, 40 mL of 0.05 M NaCl solution is placed in a 100 mL bottle with a lid, and this solution is stirred with a stirrer, and pH = 3, 5, 7, 9, 11 with 0.1 M HCl and 0.1 M NaOH. Adjusted. 10 mg (250 mg / L) of each sample was added to each of the pH adjustment solutions thus obtained, shaken for 24 hours, and then filtered through a 0.45 μm membrane filter. The concentrations of Ti and Fe in the filtrate were measured with a high-frequency plasma optical emission spectrometer (SHIMADZU ICP-1000IV), and the dissolution rates of Ti and Fe were examined.

  These results are shown in Table 2. Moreover, the result of Ti residual density | concentration and Fe residual density | concentration in the filtrate in each sample is shown to Fig.2 (a) and FIG.2 (b), respectively. It means that the lower the residual concentration of Ti / Fe in the filtrate, the less the Ti / Fe dissolved from the sample and the more stable it is.

  First, the Fe concentration will be considered. As is clear from FIG. 2 (b), Examples 1 and 2 of the present invention had the highest Fe concentration at pH 3 as in Comparative Examples 1 and 2, but both were 10 mg / L or less, and the Ministry of the Environment The water drainage standard value (10 mg / L or less) of the iron water pollution prevention method by the above was satisfied. The Fe dissolution rate from Example 2 of the present invention having the highest Fe concentration at pH 3 was about 6% or less of the total Fe amount (40 mg), and it was confirmed that the Fe dissolution rate was generally stable against changes in pH.

  Next, the Ti concentration will be considered. As is clear from FIG. 2 (a), Examples 1 and 2 of the present invention, as in Comparative Examples 1 and 2, are almost stable regardless of the change in pH, and both are very low at 1 mg / L or less. It was found to be extremely stable compared to. Moreover, the Ti dissolution rate from the inventive examples was about 1% of the total Ti amount (40 mg), and it was confirmed that the Ti dissolution rate was extremely stable against changes in pH.

Example 3 Stability test (effect of electrolyte)
In this example, the stability against the electrolyte (NaCl) was examined.

  First, 40 mL of 0.05 M NaCl solution was added to a 100 mL bottle with a lid, and the pH was adjusted to 5.0 ± 0.1 using 0.1 M HCl and 0.1 M NaOH while stirring with a stirrer. 10 mg of each sample was added to this pH adjusting solution (pH 5), shaken for 24 hours, and then filtered through a 0.45 μm membrane filter. Ti concentration and Fe concentration in the filtrate were measured in the same manner as in Example 2 described above.

  For comparison, deionized water was prepared instead of the 0.05M NaCl solution, and an experiment was performed in the same manner as described above, and the Ti concentration and Fe concentration in the filtrate were measured.

  These results are shown in FIG. FIG. 3A and FIG. 3B show the results of Fe concentration and Ti concentration in the filtrate in each sample, respectively.

  First, the Fe concentration will be considered. As is clear from FIG. 3 (a), the Fe concentrations in Invention Examples 1 and 2 are as low as about 0.5 mg / L or less, as in Comparative Example 2. The drainage standard value (10 μg / L or less) was sufficiently satisfied.

  Next, the Ti concentration will be considered. As is clear from FIG. 3B, the Ti concentrations in Examples 1 and 2 of the present invention were very low, about 0.5 mg / L or less, as in the case of Fe.

  From the above results, it was confirmed that the samples of Invention Examples 1 and 2 were hardly dissolved in NaCl and extremely stable in the electrolyte.

  In Examples 4 to 7 below, arsenic adsorption tests were performed under various conditions using the samples (A) to (D). The method for preparing the arsenic solution used in the experiment is as follows.

Arsenic acid [As (V)] and arsenous acid [As (III)] were prepared by diluting NaHAsO ₄ .7H ₂ O and NaAsO ₂ with deionized water to 1000 mg / L, respectively. . In the adsorption experiments described later, an aqueous solution obtained by appropriately diluting this stock solution with deionized water was used.

Example 4 Arsenic adsorption test (1)
In this example, the adsorption treatment was performed as follows under the constant conditions of arsenic concentration: 5 mg / L, sample addition amount: 10 mg, pH 7.0, 0.05 M NaCl.

  First, 0.05 ml of NaCl was used as an electrolyte to prepare 40 ml of a 5.0 mg / L arsenic solution. While stirring this solution with a stirrer, the pH was adjusted to 7 ± 0.1 using 0.1 M HCl and 0.1 M NaOH. 10 mg of each sample was added to this pH adjusting solution, shaken for 24 hours, and then filtered through a 0.45 μm membrane filter.

  The As (V) concentration in the filtrate thus obtained was measured with a high-frequency inductively coupled plasma optical emission spectrometer (SHIMADZU ICP-1000IV). Further, the As (III) concentration in the filtrate was measured with an atomic absorption photometer (SHIMAZU: AA-6800) connected to a pretreatment apparatus for as-analyzed As analysis (SHIMAZU: ASA-2sp). As (III) was subjected to adsorption treatment in a glove box (As-600BR AS ONE Co., Ltd.) filled with nitrogen gas so that the form of As did not change due to oxidation, and a silicon plug was used until just before analysis.

  These results are shown in FIG. The concentrations of As (V) and As (III) in the filtrate indicate the residual ratio, and the higher the residual ratio, the smaller the amount of adsorption.

  Table 3 shows the removal rates of As (V) and As (III) calculated from the results of FIG.

  First, As (III) will be considered. The As (III) removal rates of Invention Examples 1 and 2 are both as high as 90% or more. In particular, the present invention example 2 (1: 4-s) having a high Fe ratio in the amorphous hydroxide was very high at about 96.5%, which was higher than the comparative example 2 of amorphous Fe.

  Next, As (V) will be considered. The As (V) removal rates of Invention Examples 1 and 2 were both as high as about 85% or more.

  Therefore, when bimetallic samples such as the present invention 1 and the present invention 2 are used, not only an excellent removal rate with respect to As (V) can be obtained, but also extremely excellent that cannot be achieved with the monometal samples of Comparative Examples 1 and 2. In addition, it was confirmed that the removal rate for As (III) was very useful. Furthermore, it was also confirmed that the excellent As adsorption ability according to the present invention example tends to improve as the ratio of Fe in the bimetal increases.

Example 5 Arsenic adsorption test (2)
In this example, the adsorption ability when the arsenic concentration (initial concentration) was changed in the range of 1 to 50 mg / L was examined. Specifically, the sample addition amount (10 mg) and pH (pH 7.0 for As (III) and pH 6.0 for As (V)) were kept constant, and the arsenic concentration was variously changed as shown in Table 4 to obtain the following: Adsorption treatment was performed.

  First, 0.05 mL of NaCl was used as an electrolyte to prepare 40 mL of various arsenic solutions of 1.0 mg / L, 2.0 mg / L, 5.0 mg / L, 7.5 mg / L, 10.0 mg / L. While stirring this solution with a stirrer, using 0.1 M HCl and 0.1 M NaOH, the As (V) solution was adjusted to pH 6 ± 0.5, the As (III) solution was adjusted to pH 7 ± 0.1, The pH was adjusted respectively. 5 mg of each sample was added to this pH adjusting solution, shaken for 24 hours, and then filtered through a 0.45 μm membrane filter. The As (V) concentration and As (III) concentration in the filtrate thus obtained were measured in the same manner as in Example 4 described above.

  The As residual concentration in the filtrate thus obtained is shown in Table 4. Bold diagonal lines in the table satisfy the wastewater standard value (100 μg / L or less) of the Ministry of the Environment (the same applies to the following tables).

  First, when As (III) was examined, when the As concentration was the same, the adsorptive capacity of Inventive Example 1 and Inventive Example 2 tended to increase as compared to the case of using other samples. When the As concentration is 2 mg / L or less, the wastewater standard value (0.1 mg / L or less) of the Ministry of the Environment can be achieved if the samples of Invention Examples 1 and 2 are used, and in particular, the ratio of Fe in the bimetal is high. It was confirmed that the use of Invention Example 2 exhibited higher As (III) adsorption ability than Comparative Example 2. Focusing on the ratio of Ti to Fe in the bimetal, it can be seen that the present invention example 2 having a higher Fe ratio has higher As (III) adsorption capacity than the present invention example 1 having a lower Fe ratio.

  A tendency similar to the above was also observed for As (V).

  Furthermore, the maximum adsorption amount of As (III) and As (V) in each sample was calculated from the results of Table 4 based on the adsorption isotherm obtained by the Langmuir model formula. The results are shown in Table 5.

  From Table 5, the maximum adsorption amount of As (III) was 93.6 mg / g in Invention Example 2 and 88.0 mg / g in Invention Example 1, which was very high, showing a higher value than any of Comparative Examples. . Moreover, the maximum adsorption amount of As (V) in Invention Examples 1 and 2 was 41.9 mg / g, which was as high as Comparative Example 2. Thus, the maximum adsorption amount of arsenic of the present invention example is very high, and is significantly higher than that of conventionally used adsorbents such as activated alumina.

  Considering the above results, it is confirmed that the adsorbent of the present invention example is particularly excellent in the adsorption ability of As (III), and that the adsorption capacity for arsenic increases as the ratio of Fe in the bimetal increases. It was.

Example 6 Arsenic adsorption test (3)
In this example, the adsorption ability when the pH was changed between 3 and 10 was examined. Specifically, the amount of sample added (10 mg) and arsenic concentration (5.0 mg / L) were kept constant, the pH was changed between 3 and 10, and the following adsorption treatment was performed.

  First, 0.05 ml of NaCl was used as an electrolyte to prepare 40 ml of a 5.0 mg / L arsenic solution. While stirring this solution with a stirrer, the pH was adjusted to 3, 5, 7, 9, 10 (all within ± 0.1) using 0.1 M HCl and 0.1 M NaOH. . Next, 5 mg of each sample was added to each pH adjusting solution, shaken for 24 hours, and then filtered through a 0.45 μm membrane filter. The As (V) concentration and As (III) concentration in the filtrate thus obtained were measured in the same manner as in Example 4 described above, and the amount of adsorption was calculated from each arsenic concentration (residual rate) in the filtrate. did.

  These results are shown in FIG.

  FIG. 5A shows the results of As (III) adsorption amount. In Example 1 of the present invention, the amount of As (III) adsorbed markedly increased as the pH increased, whereas in Example 2 of the present invention, the change due to pH was smaller than that of the present invention 1, and the alkali side (pH 8-9). ) Showed a high adsorption amount.

  FIG. 5B shows the results of As (V) adsorption amount. Inventive example 1 was hardly affected by pH, while in inventive example 2, the highest was at pH 3, and the amount of adsorption decreased with increasing pH.

  Further, paying attention to the pH range (pH 5.8 to 8.6) of the drainage standard, the adsorption amount of As (III) is the highest in Invention Example 2, and the adsorption amount of As (V) is higher than that in Invention Example 2. Invention Example 1 was higher.

  Taking these results into consideration, it has been found that the adsorbent of the present invention is very effective particularly in the pH range of the drainage standard. It was also suggested that when two or more kinds of adsorbents having different ratios of Ti and Fe in the bimetal were used in combination, more excellent characteristics were exhibited.

Example 7 Arsenic adsorption test (4)
In this example, the adsorption ability when the amount of adsorbent added was changed to 2 to 30 mg was examined. Specifically, arsenic concentration (5.0 mg / L) and pH (7 ± 0.1) were kept constant, the amount of sample added was changed as shown in Table 6, and the following adsorption treatment was performed.

  First, 0.05 ml of NaCl was used as an electrolyte to prepare 40 ml of a 5.0 mg / L arsenic solution. While stirring this solution with a stirrer, the pH was adjusted to 7 ± 0.1 using 0.1 M HCl and 0.1 M NaOH. 2 mg, 5 mg, 10 mg, 30 mg, and 50 mg of each sample were added to this pH adjusting solution, shaken for 24 hours, and then filtered through a 0.45 μm membrane filter. The As (III) concentration and As (V) concentration in the filtrate thus obtained were measured in the same manner as in Example 4 described above.

  These results are summarized in Table 6.

  From the table, as the adsorbent addition amount increased, the residual concentrations of As (III) and As (V) decreased and the adsorption amount increased.

  Specifically, the adsorption capacity of As (III) was most excellent in Inventive Example 2, and was higher than Comparative Example 2. The As (III) adsorption capacity of the present invention 1 was also high, and both of the present invention examples 1 and 2 were able to reduce the As (III) concentration below the effluent standard value with an addition amount of 20 mg.

  Moreover, although the adsorption capacity of As (V) is slightly inferior to that of Comparative Example 2, both of Inventive Examples 1 and 2 can reduce the As (V) concentration below the drainage standard value with an addition amount of 20 mg. did it. That is, it was found that the arsenic concentration can be suppressed to a drainage standard value or less by adding about 0.5 to 1 g / L of the sample of the present invention to a solution having an arsenic concentration of 5 mg / L.

  From the results of these Examples, the As adsorption capacity of Examples 1 and 2 of the present invention is very excellent. In particular, the adsorption ability for As (III) is remarkably improved. It has been sufficiently demonstrated that the higher the ratio of Fe, the more effective. Considering the presence of both As (III) and As (V) in water, the present invention example 2 having a high Fe ratio has a high adsorption amount, so that it is extremely useful as an As adsorbent. It was suggested. In addition, from these results, it is possible to keep the As concentration of treated water below the WHO drinking water reference value (10 μg / L) by appropriately adjusting treatment conditions such as the amount of adsorbent added and pH. It was suggested that Furthermore, it is possible to more completely remove both As (V) and As (III) by performing a two-step adsorption treatment such as using the present invention example 1 and the present invention example 2 in combination. Conceivable.

Example 8 Cd adsorption test In this example, the above three types of samples (a) to (c) were used, the sample addition amount (10 mg) and pH (7 ± 0.1) were kept constant, and the Cd concentration The Cd adsorption capacity of each sample when the (initial concentration) was changed in the range of 5 to 50 mg / L was examined.

First, CdCl ₂ was diluted with deionized water and adjusted to 1000 mg / L, and used as a stock solution. This stock solution was further appropriately diluted with deionized water to prepare 40 mL of Cd solutions having various concentrations of 5 mg / L, 10 mg / L, 20 mg / L, 30 mg / L and 50 mg / L.

  Next, after adding 40 mL of 0.05M NaCl solution to a 100 mL bottle with a lid, 40 mL of each of the above-mentioned various Cd solutions was added while stirring this solution with a stirrer. The pH was adjusted to 7 ± 0.1 using NaOH. 10 mg of each sample was added to this pH adjusting solution, shaken for 24 hours, and then filtered through a 0.45 μm membrane filter. The Cd concentration in the filtrate thus obtained was measured using an atomic absorption photometer (SHIMAZU: AA-6800), and the adsorption amount was calculated from the Cd concentration (residual rate) in the filtrate.

  The Cd adsorption amount thus obtained is shown in FIG. Table 7 shows the residual Cd concentration in the filtrate.

  From these results, the Cd adsorption ability of Example 1 of the present invention (“1: 1-s” in the table and drawings) and Example 2 of the present invention (“1: 4-s” in the tables and drawings) was found to be a comparative example. 1 ("Fe-s" in the table and the figure) or better than that, Cd adsorption ability superior to Comparative Example 1 was confirmed when the Cd initial concentration was 5 to 30 mg / L.

  Further, based on the adsorption isotherm obtained by the Langmuir model formula, the maximum adsorption amount of Cd in each sample was calculated from the results in Table 7. As a result, the maximum adsorption amount of Cd is about 33 mg / g in the present invention example 1 where the ratio of Fe is small, while the maximum adsorption amount of the present invention example 2 and the comparative example 1 where the ratio of Fe is high is the same. About 26 mg / g.

Example 9 Pb adsorption test In this example, the three types of samples (a) to (c) above were used, the sample addition amount (10 mg) and pH (6 ± 0.1) were kept constant, and the Pb concentration The Cd adsorption capacity of each sample when the (initial concentration) was changed in the range of 5 to 250 mg / L was examined.

First, PbCl ₂ diluted with deionized water to a concentration of 1000 mg / L was used as a stock solution. This stock solution was further appropriately diluted with deionized water to prepare 40 mL of various Pb solutions of 5 mg / L, 10 mg / L, 100 mg / L, 150 mg / L, 200 mg / L and 250 mg / L.

  Next, 40 mL of 0.05M NaCl solution was added to a 100 mL bottle with a lid, and then 40 mL of the Pb solution having each concentration described above was added. While stirring this solution with a stirrer, the pH was adjusted to 6 ± 0.1 using 0.1 M HCl and 0.1 M NaOH. 10 mg of each sample was added to this pH adjusting solution, shaken for 24 hours, and then filtered through a 0.45 μm membrane filter. The Pb concentration in the filtrate thus obtained was measured using an atomic absorption photometer (SHIMAZU: AA-6800), and the adsorption amount was calculated from the Pb concentration (residual rate) in the filtrate.

  The amount of Cd adsorption obtained in this way is shown in FIG. Table 8 shows the Pb residual concentration (mg / L) in the filtrate.

  From these results, the Pb adsorbing ability of Example 1 of the present invention (“1: 1-s” in the table and figure) and Example 2 of the present invention (“1: 4-s” in the table and figure) are comparative examples. The Pb adsorption capacity tended to be higher than that of Comparative Example 1 (“Fe-s” in the table and the figure) when the Pb initial concentration was around 250 mg / L. .

  Further, the maximum adsorption amount of Pb in each sample was calculated based on the adsorption isotherm obtained by the Langmuir model formula. As a result, the maximum adsorption amount of Pb was the highest in Invention Example 2 and was 257.4 mg / g, and then 216.3 mg / g of Invention Example 1, both of which were Comparative Example 1 (187.7 mg / g). g) higher than.

Example 10 Cr adsorption test In this example, the three types of samples (a) to (c) described above were used, the sample addition amount (10 mg) and the Cr concentration (5.0 mg / L) were kept constant, and the pH was adjusted. Cr adsorption ability when V was changed between 2 and 10 was examined.

_{First, Cr (NO 3) 3 ·} 9H 2 O [Cr (III)] and _K 2 _Cr 2 _O 7 was diluted [(Cr (VI)] in deionized water respectively, the stock solution which was adjusted to 1000 mg / L And diluted with deionized water to prepare 5.0 mg / L of each Cr solution.

  Next, 40 mL of 0.05 M NaCl solution was added to a 100 mL bottle with a lid, and then 40 mL of each Cr solution was added. While stirring this solution with a stirrer, the pH was adjusted to 2, 4, 6, 8, 10 (all within ± 0.1) using 0.1 M HCl and 0.1 M NaOH. Next, 10 mg of each sample was added to each pH adjusting solution, shaken for 24 hours, and then filtered through a 0.45 μm membrane filter. The Cr (III) concentration and the Cr (VI) concentration in the filtrate thus obtained were measured using an atomic absorption photometer (SHIMAZU: AA-6800), and each Cr concentration (residual rate) in the filtrate was measured. The amount of adsorption was calculated from

  The result of the Cr (VI) adsorption amount is shown in FIG. 8 (a), and the result of the Cr (III) adsorption amount is shown in FIG. 8 (b).

  As shown in FIG. 8, all of the inventive examples (“1: 1-s” and “1: 4-s” in the figure) are almost the same as Comparative Example 1 (“Fe-s” in the figure). The present invention example 2 has a good Cr adsorbing ability, and in the case of Cr (VI), the inventive example 2 was confirmed to have a better adsorbing action.

  Further, when the pH of the Cr solution and the Cr adsorbing ability of each sample were examined in detail, differences were observed depending on the type of Cr ions. Specifically, the amount of adsorption increases with increasing pH in Cr (III), and the amount of adsorption is maximum in any sample in the range of pH 8 to 10, whereas the pH is lower in Cr (VI). As the amount of adsorption increased, the amount of adsorption reached a maximum in the vicinity of pH 2 to 3, and the amount of adsorption decreased as the pH increased. The behavior of Cr (VI) is similar to As (V) described above, and the behavior of Cr (III) is similar to As (III) described above.

The reason why the reverse phenomenon occurs depending on the kind of Cr ions is considered to be due to the difference in ion form between the two. That is, Cr (VI) is present in an anionic form such as HCrO ₄ ⁻ , CrO ₄ ²⁻ , Cr ₂ O ₇ ²⁻ in water, while Cr (III) is in water and Cr (OH) ₂ ^2+. , Cr (OH) ₂ ⁺ , Cr ₂ (OH) ₂ ⁴⁺ , Cr ₃ (OH) ₄ ^{5+ and the} like. In general, as the pH increases, negative charge increases on the surface of the adsorbent, so that Cr (III) ions, which are cations, are attracted and the amount of Cr (III) adsorbed increases. Conversely, when the pH is lowered, the surface of the adsorbent increases in positive charge, so that Cr (VI) ions that are anions are attracted, and the adsorption amount of the Cr (VI) increases. As a result, it is considered that Cr (III) and Cr (VI) showed the opposite behavior.

  From the above experimental results of 8 to 10, it was confirmed that the removing agent of the present invention has a good adsorption removing action on Cd, Cr and Pb in addition to As.

Claims (9)

  A remover for removing heavy metals, comprising an amorphous Ti-Fe hydroxide.   A removal agent for removing heavy metals, containing precipitates obtained by neutralizing iron (III) nitrate or mixed aqueous solution of iron (III) chloride and titanium (IV) with alkali metal hydroxide A remover characterized by that.   The removal agent according to claim 1 or 2, wherein the molar ratio of Ti: Fe is 1: 1 to 1: 5.   The removal agent according to any one of claims 1 to 3, wherein the heavy metal is at least one selected from the group consisting of arsenic, cadmium, lead, and chromium.   A method for removing heavy metal from a pollutant contaminated with heavy metal, wherein the removing agent according to claim 1 is brought into contact with the pollutant.   The removal method according to claim 5, wherein the contaminant is contaminated water or contaminated soil.   The removal method according to claim 5 or 6, wherein the contaminant is arsenic or chromium and is contacted at a pH of 3 to 10.   The removal method according to claim 5 or 6, wherein the contaminant is lead and is brought into contact under pH 4 to 6.5.   The removal method according to claim 5 or 6, wherein the contaminant is cadmium and is contacted at a pH of 4 to 8.