Heavy metal ion adsorbent and heavy metal ion-containing drain water treatment method and apparatus

Abstract

To provide a heavy metal ion-containing drain water treatment method and apparatus which can let no iron ion derived from an adsorbent remain in treatment water or can reduce the iron ions to such a degree that they are ignorable even in heavy metal ion-containing drain water treatment that management of conductivity and ion species is severe, and a heavy metal ion adsorbent.SOLUTION: A heavy metal ion adsorbent contains 48 mass% or more and 68 mass% or less Fe, 20 mass% or more and 50 mass% or less Fe3O4, 6.5 mass% or more and 11.6 mass% or less Fe2O3, 0.3 mass% or more and 1.6 mass% or less SiO2, the balance with unavoidable impurities.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a heavy metal ion adsorbent and a method and apparatus for treating wastewater containing heavy metal ions by using the heavy metal ion adsorbent. [Background technology]

[0002] Treatment technologies for wastewater containing heavy metal ions can be roughly divided into coagulation and precipitation methods, in which metal ions are precipitated and removed as poorly soluble salts such as hydroxides or sulfides, and adsorption methods, in which metal ions are replaced with other ions using ion exchange resins or chelating resins. As coagulation and precipitation methods, the following have been put to practical use: the hydroxide coprecipitation method, in which ferric ions or aluminum ions are added to wastewater containing heavy metal ions, and then an alkali is added to generate ferric hydroxide or aluminum hydroxide to remove the heavy metal components; the ferrite method, in which an alkali is added to a solution containing ferrous ions and oxidation treatment such as aeration is performed to generate ferromagnetic ferrite; and the iron powder method, in which iron pieces or the like are brought into contact with an acidic solution and the coexisting heavy metals are precipitated on the surface of the iron powder due to the difference in ionization tendency.

[0003] In the ferrite method, as described in Non-Patent Document 1, an appropriate amount of ferrous salt is added to wastewater containing heavy metal ions, neutralized with an alkali to generate ferrous hydroxide, and then air oxidation is performed while heating to 60 to 70°C to generate spinel ferrite (magnetite). The element to be treated (ferrous ion or other heavy metal ion) is incorporated into the M part of the structure MOFe2O3, and it exhibits ferromagnetism. The ferromagnetic spinel ferrite particles generated by the above method can be separated using a magnet, and heavy metals can be separated from the wastewater. However, this ferrite requires a temperature of 60 to 70°C for the reaction, so a large amount of energy is required to raise the temperature, and additional equipment is required for oxidation and magnetic separation, which results in a problem of the entire facility being large in size.

[0004] As described in Non-Patent Document 2 and Patent Document 1, the iron powder method applies the reduction action of iron and the coprecipitation action of dissolved iron ions to the treatment of wastewater containing heavy metal ions, and consists of a reduction and precipitation process under acidic conditions and a coagulation and precipitation effect under alkaline conditions. When iron pieces are brought into contact with an acidic solution to dissolve the iron oxide on the surface, a fresh metal surface appears. This metal surface is highly active, and the coexisting heavy metals are reduced and precipitated due to the difference in ionization tendency. The reduced and precipitated heavy metals have good sedimentation characteristics and can be treated collectively with harmful substances. However, elements with a higher ionization tendency than iron (e.g. manganese, zinc, chromium, etc.) are not reduced and precipitated, but become hydroxides, which causes problems such as poor sedimentation, stability, and filterability.

[0005] In the hydroxide coprecipitation method, the filtration resistance increases, making solid-liquid separation an issue, and there is a problem of an increase in sludge (waste volume).

[0006] The ion exchange resins used in the adsorption method are mainly H-type and Na-type, but the pH decreases when exchanging H-type with heavy metal ions, and increases when exchanging with Na-type, so equipment for adjusting the pH is required in the subsequent stage. In addition, when alkali or alkaline earth metal ions (Ca, Mg, etc. in tap water or industrial water) coexist with heavy metal ions, the functional groups of the ion exchange resin also adsorb the alkali metal ions and alkaline earth ions, resulting in an extremely short lifespan of the ion exchange resin.

[0007] In the ion exchange resin method, H ions or Na ions are released into the treated water instead of heavy metal ions. In the iron powder method, the target heavy metal ions are adsorbed onto the surface of the iron powder, and instead, iron ions are released into the treated water. Therefore, it is difficult to use this method in the purification systems of thermal power plants and nuclear power plants, where the management of electrical conductivity and ion species is strict, and care must be taken, and there are problems with its versatility.

[0008] Patent Document 2 describes a method for producing electrolytic iron powder containing metallic iron (electrolytic iron powder having an average particle size of 50 μm), iron oxide (average particle size of 0.07 μm, BET specific surface area of ​​20 m), and 2 / g of Bertholide FeO 1.39 ) and iron oxyhydroxide (BET specific surface area is 230 m2 It is disclosed that a treatment material containing FeO(OH)2 / g was added to a test solution containing hexavalent selenium and hexavalent chromium to insolubilize the hexavalent selenium and hexavalent chromium. Patent Document 2 discloses that a combination of iron, iron oxide, and iron hydroxide is necessary because the iron oxide enhances the reducing power of iron acting as a reducing agent, and tetravalent selenium and trivalent chromium resulting from the reduction of hexavalent selenium and hexavalent chromium are adsorbed by iron hydroxide. In addition, the iron oxide has an average particle size (50% cumulative size) of 0.001 to 0.5 μm and a specific surface area (BET method) of 10 to 90 m 2 / g, and the specific surface area of ​​the iron hydroxide is at least 100 m 2 / g.

[0009] The treatment material disclosed in Patent Document 2 contains iron hydroxide, which has the effect of co-precipitation of metal ions, and the filtration resistance of the coprecipitate of iron hydroxide (for example, the filtration resistance of ferric hydroxide is 1×10 14 m / kg), it is difficult to separate solid from liquid. It has also been reported that selenium and chromium (polyvalent metal ions with an oxidation number of 4 or more) can be insolubilized, but oxygen atoms and anions (e.g., SeO4 2- ), but makes no mention of the treatment of divalent or trivalent cations, which are common heavy metal ions. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Special Publication No. 57-7795 [Patent Document 2] JP 2006-205152 A [Non-patent literature]

[0011] [Non-Patent Document 1] Pollution and Countermeasures Vol.13, No.1, p37~p41 [Non-Patent Document 2] "Wastewater treatment by iron powder method" by Tetsuo Katsura, Flotation, Vol. 23, No. 3 (Autumn 1976), p190-198 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention aims to provide a method and apparatus for treating wastewater containing heavy metal ions, and a heavy metal ion adsorbent, which eliminate the drawbacks of conventional methods and are capable of eliminating or reducing to a negligible level sodium ions and iron ions derived from the adsorbent in the treated water, even in the treatment of wastewater containing heavy metal ions, which requires strict control of electrical conductivity and ion species. [Means for solving the problem]

[0013] As a result of intensive research to solve the above problems, the present inventors discovered that, when no acid is used, magnetite alone does not cause a substitution reaction of heavy metal ions at room temperature, but by mixing magnetite with iron powder having a specific particle size and specific surface area, hematite, and silica, the substitution reaction of magnetite with heavy metal ions proceeds at room temperature without the use of acid, and thus completed the present invention. Specific aspects of the present invention are as follows.

[0014] [1] A heavy metal ion adsorbent characterized by comprising: Fe: 48% by mass or more and 68% by mass or less, Fe3O4: 20% by mass or more and 50% by mass or less, Fe2O3: 6.5% by mass or more and 11.6% by mass or less, SiO2: 0.3% by mass or more and 1.6% by mass or less, and the remainder being unavoidable impurities. [2] The Fe has a median diameter of 50 μm or more and 300 μm or less and a specific surface area of ​​0.003 m as determined by the air permeability method. 2 / g or more 0.2m 2 / g or less, and the specific surface area calculated based on a median diameter of 50 μm is 0.10 m 2 / g or more 0.18m 2 The heavy metal ion adsorbent according to the above [1], characterized in that it contains iron powder having a molecular weight of 1.0 to 1.0 kg / g or less. [3] The median diameter of the heavy metal ion adsorbent is 5 μm or more and 5000 μm or less, and the specific surface area determined by the air permeability method is 0.00002 m 2 / g or more 20m 2 / g or less of the heavy metal ion adsorbent according to [1] or [2] above. [4] A method for treating wastewater containing heavy metal ions, comprising contacting the wastewater containing heavy metal ions with the heavy metal ion adsorbent described in any one of [1] to [3] above, and treating the wastewater under conditions of pH 6 to 8 and an oxidation-reduction potential (hydrogen standard) of -0.50 V or more and +0.55 V or less. [5] The method for treating wastewater containing heavy metal ions according to the above [4], wherein the heavy metal ion adsorbent is present in an amount of 0.5 w / v% or more and 2.0 w / v% or less relative to the wastewater containing heavy metal ions. [6] The treatment method according to the above [4], wherein the wastewater containing heavy metal ions is passed through a column packed with the heavy metal ion adsorbent. [7] A reaction tank in which the heavy metal ion adsorbent according to any one of the above [1] to [3] is mixed with wastewater containing heavy metal ions; A stirring means provided in the reaction tank; a treated water transfer pipe for discharging the treated water from the reaction tank; a heavy metal ion adsorbent discharge pipe for discharging the used heavy metal ion adsorbent from the reaction tank; an oxidation-reduction potentiometer for measuring the oxidation-reduction potential of the heavy metal ion-containing wastewater containing the heavy metal ion adsorbent in the reaction tank; a pH meter for measuring the pH of the heavy metal ion-containing wastewater containing the heavy metal ion adsorbent in the reaction tank; A treatment device for wastewater containing heavy metal ions, comprising: [8] The treatment device for wastewater containing heavy metal ions according to the above [7], further comprising a reducing agent injection device for injecting a reducing agent into the reaction tank, and / or a pH adjuster injection device for injecting a pH adjuster into the reaction tank. [9] A column packed with the heavy metal ion adsorbent according to any one of [1] to [3] above; a heavy metal ion-containing wastewater introduction pipe for introducing heavy metal ion-containing wastewater into the column; a treated water discharge pipe for discharging the treated water from the column; an oxidation-reduction potentiometer for measuring the oxidation-reduction potential of the treated water from the column; a pH meter for measuring the pH of the treated water from the column; A treatment device for wastewater containing heavy metal ions, comprising:

[10] The treatment device for wastewater containing heavy metal ions according to the above [9], further comprising a reducing agent injection device for injecting a reducing agent into the column, and / or a pH adjuster injection device for injecting a pH adjuster into the column. Effect of the Invention

[0015] According to the present invention, there are provided a method and apparatus for treating wastewater containing heavy metal ions, and a heavy metal ion adsorbent, which are capable of eliminating iron ions derived from the adsorbent in the treated water or reducing the amount of iron ions to a negligible level, even in the treatment of wastewater containing heavy metal ions, which requires strict control of electrical conductivity and ion species.

[0016] According to the method for treating wastewater containing heavy metal ions of the present invention, the pre-treatment and post-treatment required in the conventional method are not necessary, there is no need for addition of acid or heating, the generation of red water can be suppressed, and wastewater containing heavy metal ions can be treated easily, efficiently, and at low cost in a single step carried out at room temperature in a neutral range. Therefore, the configuration of the apparatus for carrying out the treatment method of the present invention can be simplified.

[0017] In addition, the iron ions derived from the heavy metal ion adsorbent are converted into magnetite and / or hematite, and the iron ions do not remain in the treated water or are reduced to a negligible level. Therefore, the present invention is suitable for use in purification systems, particularly in thermal power generation facilities and nuclear power generation facilities, where control of electrical conductivity and ion species is strict.

[0018] Furthermore, by converting the iron ions derived from the heavy metal ion adsorbent into magnetite and / or hematite, it is possible to regenerate magnetite that acts as a substitution site for the heavy metal ions and / or hematite that acts as an adsorption site, thereby extending the life of the heavy metal ion adsorbent.

[0019] Furthermore, the treatment method of the present invention does not produce hydroxides with high filtration resistance, which reduces the load of the solid-liquid separation in the downstream stage in the case of batch treatment, and suppresses the decrease in water flow rate over time in the case of column water flow treatment. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram showing an embodiment of a batch treatment system for treating wastewater containing heavy metal ions according to the present invention. [Diagram 2] FIG. 2 is a schematic explanatory diagram showing another embodiment of a batch treatment system for treatment of wastewater containing heavy metal ions according to the present invention. [Diagram 3] FIG. 1 is a schematic diagram showing an embodiment of a column water passing system of an apparatus for treating wastewater containing heavy metal ions according to the present invention. [Figure 4] FIG. 2 is a schematic explanatory diagram showing another embodiment of a column water passing system of an apparatus for treating wastewater containing heavy metal ions according to the present invention. [Diagram 5] Graph showing the change in Co ion concentration over time in Example 1 and Comparative Example 1. [Figure 6] Graph showing the change in divalent heavy metal ion concentration over time in Example 3. [Figure 7] Graph showing the change in concentration of various heavy metal ions over time in Example 4. [Figure 8] 13 is a graph showing the relationship between the cobalt ion concentration at the inlet and outlet of the column and the amount of water passing through in Example 5. [Figure 9] 1 is a graph showing the relationship between the removal rate and the amount of water passing through the heavy metal ion adsorbent of Example 5. Preferred Embodiments

[0021] According to the present invention, there are provided a heavy metal ion adsorbent, and a method and apparatus for treating wastewater containing heavy metal ions using said heavy metal ion adsorbent.

[0022] [Heavy metal ion adsorbent] The heavy metal ion adsorbent of the present invention is characterized by comprising iron (Fe): 48% by mass or more and 68% by mass or less, magnetite (Fe3O4): 20% by mass or more and 50% by mass or less, hematite (Fe2O3): 6.5% by mass or more and 11.6% by mass or less, silica (SiO2): 0.3% by mass or more and 1.6% by mass or less, and the remainder being unavoidable impurities.

[0023] The Fe3O4 contained in the heavy metal ion adsorbent of the present invention functions as a substitution site for heavy metal ions, Fe2O3 functions as an adsorption site for heavy metal ions, and Fe functions as an adsorption site for heavy metal ions. 2+ It is believed that SiO2 functions as a catalyst and SiO2 functions as a supply source. It has been confirmed from the examples described below that the heavy metal ion adsorbent of the present invention having the above composition does not leave excess iron ions in the treated water and can suppress the generation of red water (iron hydroxide).

[0024] The iron (Fe) has a median diameter of 50 μm or more and 300 μm or less, preferably 200 μm or less, and a specific surface area of ​​0.003 m as determined by an air permeability method. 2 / g or more 0.2m 2 / g or less, preferably 0.007m 2 / g or more, more preferably 0.01m 2 / g or more, and the specific surface area calculated based on a median diameter of 50 μm is 0.10 m 2 / g or more 0.18m 2 / g or less, preferably 0.16m 2 By setting the median diameter and specific surface area of ​​the iron powder within the above ranges, a small amount of the iron powder dissolves even in desalted water at room temperature in the neutral range, and divalent iron ions (Fe 2+ ) is provided.

[0025] Magnetite (Fe3O4) is not particularly limited, but desirably contains a powder having a median diameter of 5 μm or more and 5000 μm or less, preferably 50 μm or more, more preferably 150 μm or more, preferably 3000 μm or less, and more preferably 800 μm or less. Magnetite is not particularly limited as long as it undergoes a substitution reaction with heavy metal ions, and may be commercially available black iron tetroxide or inexpensive magnetite concentrate obtained by dressing iron ore.

[0026] The median diameter of the heavy metal ion adsorbent is 5 μm or more and 5000 μm or less, preferably 50 μm or more, more preferably 150 μm or more, preferably 3000 μm or less, more preferably 800 μm or less, and the specific surface area determined by the air permeability method is 0.00002 m 2 / g or more 20m 2 / g or less is preferable. If the median diameter of the heavy metal ion adsorbent is less than 5 μm, problems such as difficulty in solid-liquid separation during batch treatment of wastewater containing heavy metal ions and large pressure loss during column water treatment will occur. If the median diameter of the heavy metal ion adsorbent exceeds 5000 μm, problems such as excessive sedimentation during batch treatment of wastewater containing heavy metal ions, resulting in retention at the bottom of the device and difficulty in discharging the treated water, and if the specific surface area is too small, the adsorption reaction of heavy metal ions will not proceed.

[0027] Hematite (Fe2O3) and silica (SiO2) may be powders that do not affect the specified median diameter and specific surface area of ​​the heavy metal ion adsorbent, but it is preferable that the powders have a median diameter and specific surface area similar to those of iron (Fe).

[0028] [Method for treating wastewater containing heavy metal ions] The method for treating wastewater containing heavy metal ions of the present invention is characterized in that the wastewater containing heavy metal ions is contacted with the heavy metal ion adsorbent of the present invention and treated under conditions of a pH of 6 to 8 and an oxidation-reduction potential (hydrogen standard) of -0.50 V to +0.55 V.

[0029] The contact between the heavy metal ion adsorbent and the wastewater containing heavy metal ions may be by a batch treatment method or a column water passing method. In the batch treatment method, the heavy metal ion adsorbent is added to the wastewater containing heavy metal ions, and the wastewater is stirred under conditions of pH 6 to 8 and an oxidation-reduction potential of -0.50 V to +0.55 V. When the heavy metal ion concentration in the treated water falls to a predetermined concentration, the stirring is stopped, the heavy metal ion adsorbent is allowed to settle, and the supernatant is discharged as treated water.

[0030] In the case of the batch treatment method, it is desirable to adjust the heavy metal ion adsorbent to 0.5 w / v% to 2.0 w / v%, preferably 1.0 w / v% to 1.5 w / v%, of the heavy metal ion-containing wastewater. 2+ Since the supply source of is small, the redox potential is not likely to decrease, and if the concentration exceeds 2.0 w / v%, solid-liquid separation to obtain treated water becomes difficult.

[0031] In the case of the column water flow method, an appropriate median diameter is selected from the viewpoints of packing into the column, water permeability during column water flow treatment, and prevention of heavy metal ion adsorbent outflow from the column. For example, when packing into a glass column with a diameter of 50 mm and a height of 150 mm, it is preferable to use a heavy metal ion adsorbent with a median diameter of 5 μm to 300 μm. In addition, in the case of the column water flow method, the wastewater containing heavy metal ions is passed through SV10h. -1 More than 30h -1 It is preferable to pass the water at a flow rate of 1000 rpm.

[0032] In the treatment method of the present invention, the pH of the heavy metal ion adsorbent when it comes into contact with the wastewater containing heavy metal ions is set to 6 or more and 8 or less. If the pH is less than 6 or exceeds 8, the pH is adjusted to 6 or more and 8 or less by automatic control such as a pH stat or by adding an acid or alkali pH adjuster. However, it is not necessary to strictly maintain the pH at 6 or more and 8 or less throughout the entire treatment period. Since some variation occurs depending on the concentration of various ions in the wastewater containing heavy metal ions to be treated, for example, the pH may be allowed to drop to about 5.6 or rise to about 8.4. In the pH range of 6 or more and 8 or less, the heavy metal ions contained in the wastewater containing heavy metal ions are present in the form of metal cations or anions such as chromate.

[0033] In the treatment method of the present invention, the redox potential at the time of contact between the heavy metal ion adsorbent and the wastewater containing heavy metal ions is set to -0.50 V or more and +0.55 V or less, preferably +0.50 V or less. If the redox potential becomes less than -0.50 V during treatment, magnetite may be added, and if it exceeds +0.55 V, iron powder (Fe) may be added to adjust it. However, this adjustment is not always necessary, and even if the redox potential temporarily deviates from the above range during treatment, it is not necessary if it is determined that the reaction is proceeding smoothly without a large amount of heavy metal ions being detected in the treated water.

[0034] When the heavy metal ion adsorbent of the present invention is brought into contact with wastewater containing heavy metal ions, the reaction represented by the following formula (1) occurs under conditions of a pH of 6 to 8 and an oxidation-reduction potential (hydrogen standard) of -0.50 V to +0.55 V, converting Fe to Fe. 2+ is eluted.

[0035] [ka]

[0036] The redox potential is expressed by the following formula (2): 2+ The more ions there are, the lower the potential.

[0037]

number

[0038] In the treatment method of the present invention, divalent and trivalent iron ions are eluted from magnetite by replacing them with heavy metal ions. 3+ ) on the Fe(III) site of magnetite, and equation (4) represents the substitution of divalent heavy metal ions (M 2+ ) for the Fe(II) site of magnetite.

[0039] [ka]

[0040] In the above formula (4), when M is cobalt (Co), manganese (Mn), or nickel (Ni), the following reaction occurs:

[0041] [ka]

[0042] The trivalent iron ion (Fe 3+ ) comes into contact with iron powder (Fe) having a specific particle size and specific surface area, and converts divalent iron ions (Fe) into the corresponding ions as shown in formula (5). 2+ ) becomes.

[0043] [ka]

[0044] As described above, the substitution of the Fe(II) site of magnetite with divalent heavy metal ions increases the Fe 2+ The Fe(III) sites of magnetite were replaced by trivalent heavy metal ions, and the Fe(III) sites were replaced by trivalent heavy metal ions. 3+ But Fe 2+ As a result, a large amount of divalent iron ions is dissolved, and the redox potential decreases.

[0045] According to the treatment method of the present invention, it is possible to treat not only heavy metal cations such as those of cobalt, nickel, manganese, chromium, copper and zinc, but also anions such as those of chromate.

[0046] Wastewater containing heavy metal ions is chromated (CrO4 2- ), the Fe produced by the heavy metal ion adsorbent of the present invention 2+ As a result, the redox potential decreases according to formula (2), and the redox reaction of chromic acid in formula (6) proceeds, producing trivalent chromium. Trivalent chromium substitutes for the Fe(III) site of magnetite as shown in formula (7), and dissolves the trivalent iron ions (Fe 3+ ) is converted to divalent iron ions (Fe 2+ ) The divalent iron ion (Fe 2+ ) is generated, the redox potential decreases according to equation (2). This circulation makes it possible to reduce hexavalent chromium to trivalent chromium even in the neutral pH range of 6 to 8 without adding acid.

[0047] [ka]

[0048] Since magnetite contains Fe(II) and Fe(III) in a molar ratio of 1:2, trivalent chromium is more easily adsorbed by magnetite than divalent cations.

[0049] The reaction of chromic acid proceeds rapidly in the presence of divalent cations. The Fe(II) in magnetite is replaced by the divalent cation and dissolved. 2+ The reduction of chromic acid is promoted by lowering the redox potential. When chromic acid and divalent cations do not coexist, a reducing agent may be added to promote the substitution reaction.

[0050] The treatment method of the present invention is carried out under conditions of pH 6 to 8 and redox potential -0.50 V to +0.55 V. According to the pH-potential diagram of iron, the conditions of pH 6 to 8 and redox potential -0.50 V to +0.55 V are2+ , magnetite (Fe3O4) and hematite (Fe2O3) regions.

[0051] The iron ions (Fe) released by replacing the Fe(II) and Fe(III) sites of magnetite with heavy metal ions were 2+ or Fe 3+ ) is easily converted to magnetite and / or hematite under conditions of pH 6 or more and 8 or less and an oxidation-reduction potential of -0.50 V to +0.55 V. Therefore, in the treatment method of the present invention, first, heavy metal ions are substituted at the Fe(II) site and Fe(III) site of magnetite, and then excess iron ions eluted from magnetite are converted to magnetite and / or hematite, thereby adsorbing heavy metal ions well and promoting regeneration of magnetite and / or hematite, thereby achieving a long life of the heavy metal ion adsorbent.

[0052] In addition, iron ions are converted into magnetite and / or hematite, so the Fe in the treated water 2+ Residual and excess Fe 2+ This can prevent the occurrence of red water caused by the formation of Fe(OH)3 through air oxidation.

[0053] Therefore, the treatment method of the present invention is characterized by the adsorption and removal of heavy metal ions by replacing magnetite with heavy metal ions, and the removal of iron ions (Fe 2+ , Fe 3+ By regenerating the heavy metal ion adsorbent by converting the ferrous metal ions into magnetite and / or hematite, it is possible to adsorb and remove heavy metal ions without leaving excess iron ions in the treated water, and it is possible to effectively treat wastewater containing heavy metal ions even in reactor water purification systems, where electrical conductivity and ion species are strictly controlled.

[0054] [Treatment equipment for wastewater containing heavy metal ions] 1 to 4 are schematic diagrams illustrating embodiments of the apparatus for treating wastewater containing heavy metal ions according to the present invention. Figures 1 and 2 show an embodiment of a batch treatment system, and Figures 3 and 4 show an embodiment of a column water flow system.

[0055] [Batch processing method] The batch treatment type treatment apparatus of Figure 1 comprises a reaction tank 11 for mixing the heavy metal ion adsorbent of the present invention with heavy metal ion-containing wastewater, an agitation means 12 provided in the reaction tank 11, a treated water transfer pipe 13 for discharging treated water from the reaction tank 11, a heavy metal ion adsorbent discharge pipe 14 for discharging used heavy metal ion adsorbent from the reaction tank 11, an oxidation-reduction potentiometer 15 for measuring the oxidation-reduction potential of the heavy metal ion-containing wastewater containing the heavy metal ion adsorbent in the reaction tank 11, and a pH meter 16 for measuring the pH of the heavy metal ion-containing wastewater containing the heavy metal ion adsorbent in the reaction tank 11.

[0056] 1 further includes a reducing agent injection device 17 that injects a reducing agent into the reaction tank 11, and a pH adjuster injection device 18 that injects a pH adjuster into the reaction tank 11. However, the reducing agent injection device 17 and the pH adjuster injection device are not essential and are installed as necessary.

[0057] 1, the treated water transfer pipe 13 further includes a treated water transfer pump 20 for pumping the treated water from the reaction tank 11, and a purification device 21 such as a filter for removing turbid components of the treated water provided in the treated water transfer pipe 13. In addition, the heavy metal ion adsorbent discharge pipe 14 further includes a heavy metal ion adsorbent discharge pump 21 for sucking the heavy metal ion adsorbent from the bottom of the reaction tank 11. However, these pumps and purification devices are not essential and are installed as necessary.

[0058] The stirring means 12 may be any means capable of mixing in water, such as bubbling with nitrogen gas, a vibration type stirrer, a propeller or paddle stirrer, or an underwater mixer, but bubbling with air is not preferred as this may promote the oxidation of the heavy metal ion adsorbent and the oxidation of various ions during the treatment reaction.

[0059] The treated water transfer pump 20 provided in the treated water transfer pipe 13 is not particularly limited, but a skimming pump, a submersible pump, a diaphragm pump, etc. are preferable. The purification device 21 attached to the treated water transfer pipe 13 is not particularly limited, but a membrane filter, a hollow fiber cartridge, a metal mesh, a bag filter, a magnetic separation device, etc. are preferable when the particle size of the heavy metal ion adsorbent that may accompany the treated water is large and there is a concern about clogging of the filter. A metal mesh, a bag filter, and a magnetic separation device are preferable.

[0060] The treatment device shown in Fig. 2 comprises a reaction tank 111 for mixing the heavy metal ion adsorbent of the present invention with heavy metal ion-containing wastewater, an agitation means 112 provided in the reaction tank 111, a treated water transfer pipe 113 for discharging treated water from the reaction tank 111, a heavy metal ion adsorbent discharge pipe 114 for discharging used heavy metal ion adsorbent from the reaction tank 111, an oxidation-reduction potentiometer 115 for measuring the oxidation-reduction potential of the heavy metal ion-containing wastewater containing the heavy metal ion adsorbent in the reaction tank 111, and a pH meter 116 for measuring the pH of the heavy metal ion-containing wastewater containing the heavy metal ion adsorbent in the reaction tank 111. The reaction tank 111 in Fig. 2 has an inverted bottom, and is connected to the used heavy metal ion adsorbent discharge pipe 114.

[0061] The treatment apparatus shown in FIG. 2 further includes a reducing agent injection device 117 that injects a reducing agent into the reaction tank 111, and a pH adjuster injection device 118 that injects a pH adjuster into the reaction tank 111, but these may be omitted.

[0062] 2, the treated water transfer piping 113 further includes a treated water transfer pump 120 for pumping the treated water from the reaction tank 111, and a purification device 121 such as a filter for removing turbid components of the treated water provided in the treated water transfer piping 113. The heavy metal ion adsorbent transfer piping 114 further includes a heavy metal ion adsorbent discharge pump 121 for sucking the heavy metal ion adsorbent from the bottom of the reaction tank 111. However, these may be omitted.

[0063] The treatment device shown in Fig. 3 is an upward flow column water passing type, and the treatment device shown in Fig. 4 is a downward flow column water passing type. The upward flow column water passing type is preferable because gas may accumulate during treatment, reducing the treatment efficiency. The treatment device shown in Fig. 4 has the same device configuration as the treatment device shown in Fig. 3, except for the water passing direction, so Fig. 3 will be used as a representative example.

[0064] The treatment apparatus shown in Fig. 3 comprises a column 1 filled with the heavy metal ion adsorbent of the present invention, a heavy metal ion-containing wastewater inlet pipe 2 for introducing heavy metal ion-containing wastewater into the column 1, a treated water discharge pipe 3 for discharging the treated water from the column 1, an oxidation-reduction potentiometer 4 for measuring the oxidation-reduction potential of the treated water from the column 1, and a pH meter 5 for measuring the pH of the treated water from the column 1. Note that, although the oxidation-reduction potentiometer 4 and the pH meter 5 are shown in the same place in Fig. 3, the installation place is not limited as long as they are provided in the treated water discharge pipe 3. Also, a liquid delivery pump 9 is provided in the heavy metal ion-containing wastewater inlet pipe 2.

[0065] The treatment device shown in Fig. 3 further includes a reducing agent injection device 7 for injecting a reducing agent into the column 1 and / or a pH adjuster injection device 8 for injecting a pH adjuster into the column 1, but these may be omitted. Note that in Fig. 3, the reducing agent injection device 7 and the pH adjuster injection device 8 are shown in the same location, but the installation location is not limited as long as they are provided in the heavy metal ion-containing wastewater introduction pipe 2 near the column 1. EXAMPLES

[0066] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

[0067] [Example 1, Comparative Example 1] Cobalt sulfate heptahydrate (special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in pure water to prepare simulated wastewater containing Co ions. A heavy metal ion adsorbent (Example 1) which is a mixed powder of 50% by mass of magnetite (manufactured by Fujifilm Wako Pure Chemical Industries, iron oxide) with a median diameter of about 10 μm, 43% by mass of iron with a median diameter of about 50 μm, 6.9% by mass of hematite, and 0.1% by mass of silica, and magnetite powder alone (Comparative Example 1) were added to simulated wastewater containing Co ions, and the mixture was stirred slightly using a propeller stirrer, and the change in Co concentration over time was measured. The Co ion concentration was measured by flame atomic absorption spectrometry using the filtrate filtered through a 0.45 μm syringe membrane filter. The results are shown in FIG. 5.

[0068] In Example 1, in which the heavy metal ion adsorbent of the present invention was used, the initial Co ion concentration of 11.7 mg / L decreased to 1.4 mg / L after 1 hour, and to 0.0 mg / L after 4 hours, whereas in Comparative Example 1, in which only magnetite powder was used, no decrease in the Co concentration was observed. This example confirmed that by using the heavy metal ion adsorbent of the present invention, heavy metal ions that cannot be reduced by magnetite powder alone can be removed.

[0069] [Example 2, Comparative Examples 2 to 3] A heavy metal ion adsorbent, which is a mixed powder of 50% by mass of 2-5 mm flake magnetite (manufactured by Kojundo Chemical, iron oxide), 43% by mass of iron, 6.9% by mass of hematite, and 0.1% by mass of silica, was used to treat simulated wastewater containing hexavalent chromium. The median diameter of the components of the heavy metal ion adsorbent, excluding magnetite, was approximately 50 μm, and the specific surface area measured by the air permeability method in accordance with JIS R5201 was 0.116 m. 2 / g.

[0070] In Comparative Examples 2 and 3, a mixed powder of 50 mass% of various commercially available iron powders having the particle size and average specific surface area shown in Table 1 and 50 mass% of flaky magnetite (manufactured by Kojundo Chemical, iron oxide black) of 2 to 5 mm was used as the iron powder. Note that the particle size and specific surface area of ​​the various commercially available iron powders are catalog values.

[0071] A potassium chromate (Fujifilm Wako Pure Chemical Industries, Ltd.) aqueous solution was used as the simulated wastewater containing hexavalent chromium. The mixed powder was added to the simulated wastewater containing hexavalent chromium at 2 w / v% and stirred with a propeller stirrer. To perform an accelerated test, ferrous sulfate (Fe10mg / L) was added three times, and the Cr ion concentration and redox potential were measured after 4.5 hours of treatment, and the occurrence of red water was observed. The Cr ion concentration was measured by flame atomic absorption spectrometry using the filtrate filtered through a 0.45μm syringe membrane filter. The results are shown in Table 2.

[0072] [Table 1]

[0073] [Table 2]

[0074] In the treatment method using the heavy metal ion adsorbent of the present invention, Cr ions could be removed down to 0.1 mg / L without generating red water (iron hydroxide), but in Comparative Examples 2 and 3, Cr ions remained at 35 mg / L or more and could not be removed, and further the generation of red water (iron hydroxide) was observed.

[0075] [Example 3] Batch processing Heavy metal ion-containing simulated wastewater was prepared using nickel sulfate hexahydrate, zinc sulfate heptahydrate, and cobalt sulfate heptahydrate (all Fujifilm Wako Pure Chemical Industries, Ltd., special grade).

[0076] Using magnetite powder and iron powder sieved to a particle size of 150 μm or more, a mixed powder of 25 mass % magnetite, 64 mass % iron powder, 10 mass % hematite, and 1 mass % silica was prepared as a heavy metal ion adsorbent.

[0077] Heavy metal ion adsorbent was added at 2 w / v% to the simulated wastewater containing heavy metal ions, and the mixture was treated for 7 hours while stirring with a stirrer. After stopping the stirring every hour and leaving the mixture to stand for 1 minute, the supernatant was filtered through a 0.45 μm membrane filter for syringes, and the filtrate was used to measure the ion concentrations of nickel, zinc, cobalt, and iron by flame atomic absorption spectrometry. The results are shown in Table 3 and Figure 6.

[0078] [Table 3]

[0079] It was confirmed that nickel, zinc, and cobalt decreased over time. Zinc (Zn) achieved the target value after 7 hours of treatment. It is estimated that nickel (Ni) and cobalt (Co) could achieve the target value by extending the treatment time. Iron (Fe) was dissolved from the heavy metal ion adsorbent, and increased for up to 3 hours, but began to decrease after 3 hours, and is thought to have converted to magnetite and / or hematite.

[0080] [Example 4] Batch processing Heavy metal ion-containing simulated wastewater was prepared using manganese sulfate tetrahydrate, nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and potassium chromate (VI) (all Fujifilm Wako Pure Chemical Industries, Ltd., special grade).

[0081] Using magnetite powder and iron powder sieved to a particle size of 150 μm or more, a mixed powder of 25 mass % magnetite, 64 mass % iron powder, 10 mass % hematite, and 1 mass % silica was prepared as a heavy metal ion adsorbent.

[0082] Heavy metal ion adsorbent was added at 2 w / v% to simulated wastewater containing heavy metal ions, and the mixture was treated for 6 hours while stirring with a stirrer. After stopping the stirring every hour and leaving the mixture to stand for 1 minute, the supernatant was filtered through a 0.45 μm syringe membrane filter, and the filtrate was used to measure the ion concentrations of manganese, nickel, cobalt, chromium, and iron by flame atomic absorption spectrometry. The results are shown in Table 4 and Figure 7.

[0083] [Table 4]

[0084] It was confirmed that manganese, nickel, cobalt and chromium decreased over time. The target value for chromium (Cr) was achieved after 1 hour of treatment. The target values ​​for nickel (Ni) and cobalt (Co) were achieved after 3 hours of treatment. It is estimated that the target value for manganese (Mn) can be achieved by extending the treatment time further. Iron (Fe) was not detected until 5 hours, and Cr was immediately released after elution from the heavy metal ion adsorbent. 6+ From Cr 3+ It is believed that the amount was consumed in reducing it to

[0085] [Example 5] Column water flow treatment A heavy metal ion-containing simulated wastewater with a target Co ion concentration of 1 mg / L was prepared using cobalt sulfate heptahydrate (special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0086] Using magnetite powder and iron powder sieved to a particle size of 150 μm or more, a mixed powder of 25 mass % magnetite, 64 mass % iron powder, 10 mass % hematite, and 1 mass % silica was prepared as a heavy metal ion adsorbent.

[0087] A glass column (inner diameter 50 mm x height 100 mm) was filled with heavy metal ion adsorbent to a height of 50 mm and a filling volume of 97 mL, and simulated wastewater containing heavy metal ions was poured into the column for 10 h. -1 The water was passed through the column in an upward flow. Samples were taken of the heavy metal ion-containing wastewater at the inlet of the column and the treated water at the outlet of the column, and the Co ion concentration was measured by flame atomic absorption spectrometry. Treatment was continued until the Co ion concentration in the treated water measured at the outlet of the column reached 80% of the Co ion concentration at the inlet of the column (removal rate of 20%). The measurement results are shown in Figure 8, and the transition of the removal rate in Figure 9. Note that when the removal rate of the heavy metal ion adsorbent falls to 20%, it is time to replace the heavy metal ion adsorbent.

[0088] 8 and 9 show that when the Co ion concentration at the column inlet rises to 1.2 mg / L, the Co ion concentration in the treated water also rises, but the removal rate remains at 100% up to a water flow rate of 2000 BV, at a water flow rate of 3950 BV, and at a water flow rate of 12800 BV, the removal rate reaches 20%. It can be said that the heavy metal ion adsorbent of the present invention is capable of treating large volumes of wastewater containing heavy metal ions.

[0089] [Examples 6 to 8, Comparative Example 4] Batch processing A simulated wastewater containing heavy metal ions with a target Cr concentration of 90 mg / L was prepared using potassium chromate (VI) (special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0090] A heavy metal ion adsorbent having the composition shown in Table 5 was prepared using magnetite powder and iron powder sieved to a particle size of 150 μm or more.

[0091] [Table 5]

[0092] Heavy metal ion adsorbent was added to the simulated wastewater containing heavy metal ions at 2 w / v%, and the mixture was stirred with a propeller stirrer. Ferrous sulfate (Fe) was added as a reducing agent at 10 mg / L four times for an accelerated test. After stopping the stirring every 30 minutes and leaving the mixture to stand for 1 minute, the supernatant was filtered through a 0.45 μm syringe membrane filter to measure the chromium ion concentration using the filtrate by flame atomic absorption spectrometry, and the treatment time until the concentration reached 1.0 mg / L was measured. The results are shown in Table 6.

[0093] [Table 6]

[0094] From Tables 5 and 6, it can be seen that the more the iron powder content of the heavy metal ion adsorbent is increased, the shorter the time required for removing chromium ions becomes, and the more the reaction proceeds (Examples 6 to 8). However, when the iron powder content is too high, as in Comparative Example 4, the generation of red water was confirmed. Therefore, it can be said that the magnetite content of the heavy metal ion adsorbent is preferably 20 mass% or more. [Industrial Applicability]

[0095] The heavy metal ion adsorbent, and the method and apparatus for treating wastewater containing heavy metal ions of the present invention are useful for wastewater treatment at various sites.

[0096] -Application to nuclear reactor cleaning systems In Gibbs free energy, except for chromium, the reaction tends to be easier at higher temperatures, so the present invention is considered to be applicable to the treatment of wastewater containing heavy metal ions in the reactor water purification system of a nuclear reactor. Currently, the treatment of wastewater from the reactor purification system is carried out using ion exchange resins. Since ion exchange resins have poor heat resistance, it is necessary to cool the reactor water at 280°C to 330°C to less than 100°C before treatment. However, since the purified water is reused as reactor water, it is necessary to heat it again to the reactor water temperature, which requires a huge amount of energy. Since the heavy metal ion adsorbent of the present invention has excellent heat resistance, it can treat the reactor water purification system wastewater at a high temperature and does not require reheating. Therefore, it is expected that there will be little energy loss, and that it will increase the power generation efficiency and contribute to the SDGs.

[0097] - Suppression of insoluble scale formation in thermal boilers Gahnite (ZnAl2O4), a type of thermal boiler scale, has a low thermal conductivity and is one of the factors that reduce power generation efficiency. Magnetite and other scales can be dissolved and removed by chemical cleaning, but gahnite does not dissolve even in strong acids and remains. Gahnite is generated when Zn and Al are partially dissolved in the material of a preboiler such as a high-pressure feed water heater, so its generation tends to be suppressed by lowering the Zn concentration. However, since the water temperature in the preboiler already exceeds 200°C and ion exchange resin cannot be applied, it cannot be removed at present. The heavy metal ion adsorbent of the present invention has excellent heat resistance and can be used even at high temperatures downstream of the preboiler, and it is expected to remove Zn ions and suppress the generation of gahnite scale.

[0098] - Column water treatment for wastewater containing radioactive Co, such as reactor water When the amount of Co captured in Example 5 was converted to radioactive Co-60, the result exceeded the L2 concentration of low-level radioactive waste, so it can be used as a radioactive Co removal material. Radioactivity is rate-limiting, and concentration adjustment is possible, such as stopping treatment near the upper limit of the L2 or L3 radioactivity concentration standard [Bq / kg], so it is thought that it can contribute to reducing the amount of radioactive waste. Since the waste is stable in a clad-like form such as cobalt ferrite, there is no need to worry about heavy metal elution. Since the waste does not contain organic matter even in final disposal, the transition to disposal as miscellaneous solids is smooth, and low costs can be expected.

Claims

1. Fe: 48% by mass or more and 68% by mass or less, Fe ３ O ４ : 20% by mass or more and 50% by mass or less, Fe ２ O ３ : 6.5% by mass or more and 11.6% by mass or less, SiO ２ : A heavy metal ion adsorbent characterized by being composed of 0.3 mass% or more and 1.6 mass% or less, with the remainder being unavoidable impurities.

2. The Fe has a median diameter of 50 μm or more and 300 μm or less and a specific surface area of ​​0.003 m as determined by an air permeability method. ２ / g or more 0.2m ２ / g or less, and the specific surface area calculated based on a median diameter of 50 μm is 0.10 m ２ / g or more 0.18m ２ 2. The heavy metal ion adsorbent according to claim 1, further comprising iron powder having a molecular weight of 1:1 or less.

3. The heavy metal ion adsorbent has a median diameter of 5 μm or more and 5000 μm or less, and a specific surface area determined by an air permeability method of 0.00002 m ２ / g or more 20m ２ 3. The heavy metal ion adsorbent according to claim 1, wherein the adsorption capacity of the heavy metal ion adsorbent is 1 / g or less.

4. A method for treating wastewater containing heavy metal ions, comprising contacting the wastewater containing heavy metal ions with the heavy metal ion adsorbent according to claim 1 or 2, and treating the wastewater under conditions of pH 6 to 8 and an oxidation-reduction potential (hydrogen standard) of −0.50 V or more and +0.55 V or less.

5. 5. The method for treating wastewater containing heavy metal ions according to claim 4, wherein the heavy metal ion adsorbent is present in an amount of 0.5 w / v % to 2.0 w / v % based on the amount of the wastewater containing heavy metal ions.

6. 5. The treatment method according to claim 4, wherein the wastewater containing heavy metal ions is passed through a column packed with the heavy metal ion adsorbent.

7. A reaction tank for mixing the heavy metal ion adsorbent according to claim 1 or 2 with wastewater containing heavy metal ions; A stirring means provided in the reaction tank; a treated water transfer pipe for discharging the treated water from the reaction tank; a heavy metal ion adsorbent discharge pipe for discharging the used heavy metal ion adsorbent from the reaction tank; an oxidation-reduction potentiometer for measuring the oxidation-reduction potential of the heavy metal ion-containing wastewater containing the heavy metal ion adsorbent in the reaction tank; a pH meter for measuring the pH of the heavy metal ion-containing wastewater containing the heavy metal ion adsorbent in the reaction tank; A treatment device for wastewater containing heavy metal ions, comprising:

8. 8. The apparatus for treating wastewater containing heavy metal ions according to claim 7, further comprising a reducing agent injector for injecting a reducing agent into the reaction tank, and / or a pH adjuster injector for injecting a pH adjuster into the reaction tank.

9. A column packed with the heavy metal ion adsorbent according to claim 1 or 2; a heavy metal ion-containing wastewater introduction pipe for introducing heavy metal ion-containing wastewater into the column; a treated water discharge pipe for discharging the treated water from the column; an oxidation-reduction potentiometer for measuring the oxidation-reduction potential of the treated water from the column; a pH meter for measuring the pH of the treated water from the column; A treatment device for wastewater containing heavy metal ions, comprising:

10. 10. The apparatus for treating wastewater containing heavy metal ions according to claim 9, further comprising a reducing agent injector for injecting a reducing agent into said column, and / or a pH adjuster injector for injecting a pH adjuster into said column.

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