JP4609660B2 - Adsorbent - Google Patents

Description

  The present invention is an environmental purification composition that adsorbs harmful heavy metal ions in a solution. Specifically, it adsorbs harmful heavy metal ions including arsenic, selenium, chromium, lead and the like.

  In recent years, many environmental technologies have been proposed to remove harmful heavy metal ions in water systems and soils, but materials that can be adsorbed and removed economically and efficiently without placing a heavy load on the environment. Is currently unknown.

  Conventionally, biological methods, physicochemical methods, agglomeration methods, crystallization methods, etc. have been used to remove heavy metal ions, etc. in aqueous solutions. Of these, the adsorption / ion exchange method is advantageous. Conventionally, as an adsorption / ion exchange method, it is known to use a chelate resin, a chelate fiber, an ion exchange resin, cerium hydroxide, zirconium ferrite, or the like.

  However, ion exchange resins, chelate resins / chelate fibers, cerium hydroxide, zirconium ferrite, etc. may be able to adsorb and remove heavy metal ions efficiently, but they are expensive and difficult to use in large quantities in the environment. there were. In addition, ion exchange resins, chelate resins / chelate fibers, etc. selectively adsorb and remove heavy metal ions, but they do not decompose naturally, and if they are released into the environment, there is a risk of environmental impact.

  Also, cerium hydroxide and zirconium ferrite are rarely used because they use rare earth elements and expensive metals and are expensive.

  Conventionally, as an adsorbent for heavy metal ions in water, those using magnetic hydrous iron oxide particles, hydrous ferrite of titanium and zirconium (Patent Documents 1, 2, and 3), iron oxide and hydrous oxide in iron hydroxide Adsorbents (Patent Documents 4, 5, and 6) on a lump in which iron or the like is embedded are known.

JP-A-55-13153 Japanese Patent Laid-Open No. 56-118734 JP-A-57-50543 Special table 2004-509750 gazette JP-T-2004-509751 JP-T-2004-509752

  Adsorbs heavy metal ions, and in particular, a highly versatile adsorbent that can adsorb and remove harmful ions including arsenic, selenium, chromium, etc. efficiently even at low concentrations without giving a large load to the environment. Not yet provided.

  That is, in the aforementioned Patent Documents 1 to 6, it is described that heavy metal ions and the like are adsorbed using various iron compounds, but it is difficult to say that a sufficient effect of removing heavy metal ions is recognized, It is hard to say that environmental impact is light and heavy metal ions can be sufficiently reduced economically.

  The technical problem can be achieved by the present invention as follows.

  That is, the present invention is an adsorbent that adsorbs heavy metal ions, characterized in that the adsorbent is hydrous iron oxide particles containing 0.1 to 2.0 wt% of carbon. Invention 1).

  The present invention is also the adsorbent characterized in that the hydrous iron oxide particles are α-FeO (OH) and / or γ-FeO (OH) (Invention 2).

  The present invention also provides hydrous iron oxide particles synthesized in the region where the pH of the reaction solution is 6.0 to 10.0 using an iron raw material and an alkali carbonate aqueous solution or an alkali carbonate / alkali hydroxide mixed aqueous solution as an alkali raw material. It is the said adsorbent characterized by being (Invention 3).

  Further, the present invention is any one of the above adsorbents characterized in that the hydrous iron oxide particles contain one or more elements selected from titanium, zirconium, hafnium, and cerium (Invention 4). .

  The present invention is also the adsorbent according to any one of the above, wherein the heavy metal ion is an ion containing one or more heavy metals selected from arsenic, selenium or chromium (Invention 5).

Since the adsorbent according to the present invention can adsorb and capture harmful ions such as heavy metal ions composed of arsenic, selenium, chromium, lead, etc. in a wide concentration range, it can be used as a treatment agent or harmful ion adsorbent in drinking water, waste water, or groundwater Is preferred. Furthermore, the adsorbent according to the present invention is also effective as a treatment / adsorbent for drinking water, drainage, and groundwater in which heavy metal ions coexist.
Furthermore, since the adsorbent according to the present invention is non-toxic and can be mass-produced economically, it should be used in a large-scale soil purification wall installed to purify heavy metal contamination of groundwater. Is also possible.
Moreover, since the adsorbent according to the present invention does not require a complicated processing step, it is suitable as an adsorbent used in a simple processing method.

  Furthermore, since the adsorbent according to the present invention is composed of harmless elements or compounds, even when the adsorbent itself is disposed of in landfill, the burden on the environment is small.

  The configuration of the present invention will be described in more detail as follows.

  First, an adsorbent that adsorbs heavy metal ions according to the present invention (hereinafter referred to as “adsorbent”) will be described.

  The adsorbent according to the present invention is a hydrous iron oxide powder containing carbon. For example, α-FeO (OH) (goethite), β-FeO (OH) (akagenite), γ-FeO (OH) (let Pidocrocite), etc., preferably α-FeO (OH) (goethite), γ-FeO (OH) (lepidococsite), more preferably α-FeO (OH) (goethite).

  The carbon content of the adsorbent according to the present invention is 0.1 to 2.0 wt%. In the case of less than 0.1 wt%, adsorption of heavy metal ions is not sufficient. When it exceeds 2.0 wt%, it is not preferable because efficiency (productivity) at the time of mass production is deteriorated and carbon dioxide gas is slightly generated at the time of use. Preferably it is 0.12-1.2 wt%, More preferably, it is 0.15-0.8 wt%.

  The particle shape of the adsorbent according to the present invention is not particularly limited, such as a needle shape, a spindle shape, a granular shape, or a plate shape. The hue of the adsorbent is generally yellow to tan.

The BET specific surface area value of the adsorbent according to the present invention is preferably 30 to 300 m ² / g, more preferably 45 to 300 m ² / g, and still more preferably 60 to 290 m ² / g. When the BET specific surface area value is less than 30 m ² / g, the contact area between harmful ions and the adsorbent becomes small, which is not preferable. If it exceeds 300 m ² / g, there is no problem in the adsorption of harmful ions, but it is difficult to produce industrially, and it is difficult to handle due to severe aggregation.

  The average particle diameter of the adsorbent according to the present invention is preferably 2 to 500 nm. Preferably it is 5-300 nm.

  The adsorbent according to the present invention may contain one or more elements selected from Ti, Zr, Hf, and Ce, and the adsorption ability of heavy metal ions is improved by containing the elements. The content of Ti is preferably 0.1 to 15 wt%, more preferably 1.0 to 15 wt%. The content of Zr, Hf or Ce is preferably 0.2 to 40 wt%, more preferably 1.0 to 30 wt%. Ti, Zr, Hf or Ce is preferably present as a solid solution in the hydrous iron oxide.

  In the adsorbent according to the present invention, the Ti content is preferably 1/50 to 1/3 in terms of molar ratio to Fe (Ti / Fe). The content of Zr, Hf, and Ce is preferably 1/50 to 1/2 in terms of a molar ratio to Fe ((Zr, Hf, Ce) / Fe).

  Next, the manufacturing method of the adsorbent according to the present invention will be described.

  The adsorbent according to the present invention can be obtained by mixing an iron raw material and an alkali raw material containing at least an alkali carbonate, and controlling the pH of the reaction solution to 6.0 to 10.0 to perform an oxidation reaction.

  As an iron raw material in this invention, ferrous sulfate aqueous solution, ferrous chloride aqueous solution, etc. can be used.

  The alkali raw materials are sodium carbonate aqueous solution, potassium carbonate aqueous solution, ammonium carbonate aqueous solution and the like as the alkali carbonate aqueous solution, and sodium hydroxide, potassium hydroxide and the like can be used as the alkali hydroxide aqueous solution.

  The amount of the alkali carbonate aqueous solution or the mixed aqueous solution of alkali carbonate and alkali hydroxide used is 1.3 to 3.5, preferably 1.5 to 2.5 as the equivalent ratio to the total Fe in the ferrous salt aqueous solution. It is. When it is less than 1.3, magnetite (ferrite) may be mixed, and when it exceeds 3.5, the cost tends to increase, which is not industrially preferable. In addition, if magnetite (ferrite) is mixed, the adsorption performance is lowered, which is not preferable.

  The pH during the reaction is preferably 6.0 to 10.0. When the pH is less than 6.0, the amount of carbon contained in the hydrous iron oxide is 0.1 wt% or less, and the adsorption ability of heavy metal ions is lowered, which is not preferable as an adsorbent. When the pH exceeds 10.0, the carbon content may be 0.1 wt% or more, but the adsorption capacity for heavy metal ions is low, which is not preferable as an adsorbent.

The reaction temperature may usually be a temperature of 80 ° C. or lower at which hydrous iron oxide particles are generated. When it exceeds 80 ^degreeC , the magnetite particle | grains containing Fe2 ⁺ are mixed and are not preferable. In addition, if magnetite (ferrite) is mixed as described above, the adsorption performance is lowered, which is not preferable.

  The carbon content may be adjusted by aging with decarboxylation by blowing nitrogen before the oxidation reaction.

  The oxidation means in the reaction for generating the hydrous iron oxide particles is performed by venting an oxygen-containing gas (for example, air) through the liquid.

  In producing the hydrous iron oxide powder containing Ti according to the present invention, in the reaction, a Ti raw material may be added, mixed and aged. Examples of the Ti raw material include titanyl sulfate.

  In producing the hydrous iron oxide powder containing Zr according to the present invention, a Zr raw material may be added, mixed and aged in the reaction. The Zr raw material is a tetravalent zirconium salt such as zirconium sulfate.

  In producing the hydrous iron oxide powder containing Hf according to the present invention, the Hf raw material may be added, mixed and aged in the reaction. The Hf raw material is a tetravalent hafnium salt such as hafnium sulfate. Hafnium may be contained as an impurity in a zirconium salt such as zirconium sulfate.

  In producing the hydrous iron oxide particles containing Ce according to the present invention, in the reaction, a Ce raw material may be added, mixed and aged. The Ce raw material is a tetravalent cerium salt such as ceric sulfate.

  Moreover, the reactivity with harmful ions in an aqueous system can be controlled by subjecting the hydrous iron oxide particles to a dry surface treatment with an organic substance or the like. Examples of the surface treatment agent include rosin compounds, silane coupling agents, higher fatty acids and the like. The coating amount of the adsorbent powder by the surface treatment agent is preferably 0.1 to 5% by weight in terms of C with respect to the hydrous iron oxide particles. As a dry surface treatment machine, a rough machine, a vibration mill, a roller type mixer, or the like can be used.

  Next, a method for treating heavy metal ions in water using the adsorbent according to the present invention will be described.

  The adsorbent according to the present invention exhibits a high adsorbing ability for heavy metal ions such as arsenic, selenium, and chromium.

  In the heavy metal ion treatment process of the present invention, the heavy metal ions are released to the aqueous system by immobilizing an adsorbent in the case of immobilizing / separating the dissolved heavy metal ions and those that may release the heavy metal ions. A distinction is made when it is suppressed. Hereinafter, the process of the dissolved heavy metal ion in this invention is demonstrated.

  In the present invention, the method for bringing the water to be treated into contact with the adsorbent is not particularly limited. A method in which water to be treated is circulated through a column or filtration tank filled with an adsorbent and / or an adsorbent granule, a method in which a stirring tank using powdered hydrous iron oxide particles and a precipitation tank are combined can be used.

  There is no restriction | limiting in particular about the liquid temperature at the time of making an adsorbent contact, It is 5-90 degreeC of the temperature range normally used, Preferably it is 10-50 degreeC.

  Although the pH of the aqueous solution at the time of adsorbing heavy metal ions varies depending on the target ions, it is generally preferable to be in the acidic to neutral range.

  In addition, the adsorbent according to the present invention can adsorb the adsorbed heavy metal ion by a usual method, for example, a method of adding a desorption accelerator or the like by making the pH of the aqueous solution strong alkali. It may be detached and reused.

<Action>
An important point in the present invention is the fact that the adsorbent according to the present invention can adsorb harmful ions such as ions containing heavy metals over a wide range from a low concentration to a high concentration.

The reason why the adsorbent according to the present invention has a high adsorption capacity for heavy metal ions is not yet clear, but as shown in the examples and comparative examples described later, carbon is contained in the hydrated iron oxide particles constituting the adsorbent. The inventor presumes that it is due to the existence.
That is, since the adsorbent according to the present invention is obtained by using a carbonate-based alkaline raw material as a starting material and controlling the pH during the production of hydrous iron oxide particles, the surface state in which carbon derived from carbonate ions is present. As a result, the present inventor presumes that it has a high adsorption capacity for heavy metal ions.

  Since the adsorbent according to the present invention has high adsorption ability for ions containing heavy metals and has ion adsorption selectivity, it maintains high adsorption ability even when it contains coexisting ions. can do.

  The adsorbent according to the present invention can adsorb heavy metal ions from the acidic region to the neutral region and separate the adsorbed heavy metal ions according to a conventional method to regenerate the adsorbent and reuse it as an adsorbent. is there.

  A typical embodiment of the present invention is as follows.

  The crystal phase of the adsorbent according to the present invention is identified by “X-ray diffractometer RINT2500 (manufactured by Rigaku Corporation)” (tube: Cu, tube voltage: 40 kV, tube current: 300 mA, goniometer: wide angle goniometer. , Sampling width: 0.010 °, scanning speed: 4.00 ° / min, diverging slit: 1/2 °, scattering slit: 1/2 °, light receiving slit: 0.15 mm).

  The BET specific surface area value of the adsorbent according to the present invention was indicated by a value measured by the BET method.

  Analysis of the content of metal elements such as Fe, Ti, Zr, Hf, and Ce of the adsorbent according to the present invention was performed by dissolving the powder with hydrochloric acid or the like, and “Plasma emission spectroscopic analyzer SPS4000 (Seiko Electronics Co., Ltd.) To measure.

  The carbon content (% by weight) and the sulfur content (% by weight) of the adsorbent according to the present invention were measured by a carbon sulfur analyzer: EMIA-2200 (manufactured by HORIBA).

Example 1: Production of adsorbent In a reaction vessel maintained in a non-oxidizing atmosphere by flowing nitrogen gas at a rate of 40 l / sec, 1.60 mol / l Na ₂ CO ₃ aqueous solution 22 l and 1.60 mol / l After adding 6 l of NaOH aqueous solution, Fe ²⁺ 0.8 mol / l ferrous sulfate aqueous solution 25 l (Na ₂ CO ₃ is 1.76 equivalents for the reaction with Fe, NaOH is for the reaction with Fe 0.24 equivalents and a total of 2.0 equivalents) was added and mixed to form a suspension containing FeCO ₃ at pH 8.5 at a temperature of 50 ° C.

  The suspension was aged by continuously flowing nitrogen gas at a rate of 40 liters per second while maintaining the temperature at 50 ° C for 60 minutes, and then the temperature of the suspension was 40 ° C. The suspension was aerated for 5.5 hours to produce tan precipitated particles. The yellowish brown precipitated particles were adjusted for pH, filtered, washed with water, dried and pulverized.

As a result of X-ray diffraction, the obtained yellowish brown particle powder is goethite (α-FeO (OH)), is composed of particles having a spindle shape with a BET specific surface area of 87 m ² / g, and has an iron content ( T-Fe) was 58.7 wt%, carbon amount (TC) was 0.46 wt%, and sulfur amount (TS) was 0.26 wt%.

Examples 2-7, Comparative Examples 1-2
Except for various changes in the type, concentration and usage of the alkaline aqueous solution, the concentration and usage of the aqueous ferrous salt solution, the type, concentration, and usage of the iron replacement raw material in the adsorbent production reaction, Example 1 and Similarly, hydrous iron oxide particles were produced.

  The production conditions at this time are shown in Table 1, and the characteristics of the obtained hydrous iron oxide particles are shown in Table 2.

<Heavy metal ion adsorption test>
Example 1
First, a solution in which a very small amount of sulfuric acid was added to ion-exchanged water was prepared, and sodium selenite (Na ₂ SeO ₃ ; reagent grade manufactured by Wako Pure Chemical Industries, Ltd.) was added therein, and Se = 11. An adsorption test solution containing a heavy metal of 0 mg / L, pH 6.7 was prepared (Se was estimated to be ionized as SeO ₃ ^2- ). Pour 100 ml of the adsorption test solution into a resin bottle, add 0.2 g (2 g / L) of the adsorbent obtained in Example 1, shake for 6 hours using a horizontal shaker, and remove 5C filter paper. As a result of measuring the concentration of heavy metals in the liquid using a “plasma emission spectroscopy analyzer SPS4000 (Seiko Electronics Co., Ltd.)”, the Se concentration was 0.5 mg / L or less and below the detection limit. (Hereinafter abbreviated as ND).

Use Examples 2-6, Comparative Use Examples 1-3:
Except for the pH of the adsorption test solution, the type of adsorbent, the type and concentration of the heavy metal contained in the solution, a heavy metal adsorption test was carried out in the same manner as in Use Example 1, and the results are shown in Table 3.
As arsenic heavy metal ions, an arsenic standard solution (As ₂ O ₃ and NaOH in water pH 5.0 with HCl; a measurement standard reagent manufactured by Wako Pure Chemical Industries, Ltd.) was used (As is AsO ₃ ³⁻ or AsO ₂ ⁻ As a heavy metal ion of chromium, potassium dichromate (K ₂ Cr ₂ O ₇ ; Wako Pure Chemical Industries reagent special grade) was dissolved and used in the same manner as described above (Cr is Cr ₂ Estimated to be ionized as O ₇ ^2- ). The As concentration is 0.5 mg / L or less and below the detection limit (hereinafter abbreviated as ND), and the Cr concentration is 0.5 mg / L or less and below the detection limit (hereinafter abbreviated as ND). ).

Use examples 7-9
The heavy metal adsorption test was carried out in the same manner as in Use Example 1 except that the adsorption test solution pH, the type of adsorbent, and the heavy metal contained in the solution were changed to multiple types, and the results are shown in Table 3. Show.

Use Example 10 and Comparative Use Example 4
Sodium selenate (Na ₂ SeO ₄ ), a special grade reagent that is hexavalent Se, which is difficult to adsorb and remove heavy metals contained in the solution by changing the pH of the adsorption test solution and the type of adsorbent; A heavy metal adsorption test was carried out in the same manner as in Use Example 1 except that Wako Pure Chemical Industries, Ltd. Wako Standard Grade 1 acceptable product) was dissolved and used (estimated to be ionized as SeO ₄ ^2- ). The results are shown in Table 3.

  As is clear from the above examples, the adsorbent according to the present invention exhibits a high adsorbing ability for heavy metal ions in an aqueous solution (present as anions in an aqueous solution).

Since the adsorbent according to the present invention can easily adsorb heavy metal ions in a wide concentration range, it is suitable as an adsorbent for heavy metal ions.

Claims (4)

An adsorbent that adsorbs one or more heavy metal ions selected from arsenic, selenium or chromium , wherein the adsorbent is hydrous iron oxide particles containing 0.1 to 2.0 wt% of carbon. Adsorbent. The adsorbent according to claim 1, wherein the hydrous iron oxide particles are α-FeO (OH) and / or γ-FeO (OH). The hydrous iron oxide particles synthesized using an iron raw material and an alkali carbonate aqueous solution or an alkali carbonate / alkali hydroxide mixed aqueous solution as an alkali raw material in a pH range of 6.0 to 10.0. The adsorbent according to claim 1 or 2. The adsorbent according to any one of claims 1 to 3, wherein the hydrous iron oxide particles contain one or more elements selected from titanium, zirconium and cerium.