KR20150085556A - Mn-substituted δ-feooh, synthesis method for the same and water treatment method using the same - Google Patents

Abstract

The present invention relates to an iron-manganese hydroxide, a synthesis method thereof, and a water treatment method using the same. According to the present invention, a synthesis method of an iron-manganese hydroxide mixes and reacts a first aqueous solution comprising an iron ion, a second aqueous solution comprising a manganese ion, and an oxidizing agent, thereby synthesizing an iron-manganese hydroxide of δ-(Fe_(1-X), Mn_x)OOH, wherein x is greater than 0 and less than 1. The synthesized iron-manganese hydroxide is capable of adsorbing and removing after oxidizing trivalent arsenic to pentavalent arsenic. In addition, the iron-manganese hydroxide has magnetism, thus can be easily separated and collected from water by a magnetic force after adsorbing pollutants.

Description

Manganese-substituted iron oxides, synthesis methods thereof, and water treatment methods using the same [Mn-substituted δ-FeOOH, Synthesis method for the same and Water treatment method using same]

TECHNICAL FIELD The present invention relates to a technology for reducing environmental pollution, and more particularly, to a decontamination material capable of treating contaminants such as an anionic heavy metal and organic substances contained in groundwater including arsenic, a method for synthesizing the same, and a water treatment method using the same.

Arsenic is one of the elements of the Group 15 of the Periodic Table of the Elements. It is the 20th most widely distributed element among the earth's surface constituents, and is widely distributed in mineral rock sediments soil and groundwater. Unlike most other cationic metals, arsenic is a metal that exists in a polyatomic state, including oxygen, and changes to different chemical species depending on pH and oxidation or reduction conditions, or behaves differently depending on conditions.

At present, arsenic contamination in groundwater is found in many parts of the world such as Bangladesh, West Bengal, India, Vietnam, Chile, Taiwan and the West. In the EU, Japan and Vietnam, 10 g / L.

The inorganic arsenic in the groundwater mainly exists in the form of 5 ^- and ₃ ^- valent forms. In the case of 5 - valence, oxygen is abundantly oxidized and behaves as an anion such as H ₂ AsO ₄ ^- or HAsO ₄ ^{2 -} in the aerobic environment of microorganisms. Reduction, and anaerobic environments of microorganisms, mainly in the form of H ₃ AsO ₃ . It is generally known that trivalent arsenic is more mobile and more toxic than pentavalent arsenic.

The removal of arsenic using iron oxide is widely used for arsenic with a high toxicity, and 5-arsenic, which behaves more like anion than trivalent arsenic, has a good efficiency . Therefore, in order to increase the removal efficiency, a process of oxidizing trivalent arsenic into pentavalent arsenic is required.

In addition, the oxidation of trivalent arsenic to arsenic and the action of eliminating arsenic can increase the economical efficiency and efficiency of arsenic removal. Accordingly, there is a demand for development of an arsenic remover which can simultaneously perform oxidation and elimination operations.

An important technical issue related to arsenic removal agents is the recovery of arsenic removal agents after arsenic removal. For example, in the case of an adsorbent that removes arsenic through an adsorption process, it is necessary to separate the adsorbent from the groundwater after adsorbing arsenic. If the separation is difficult, it can not be said that arsenic is removed from the groundwater, and the adsorbent with arsenic is again a secondary source. Therefore, it is required to develop an arsenic removal agent which can be easily separated and collected.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method for treating arsenic and arsenic, Manganese hydroxide, a method of synthesizing the same, and a water treatment method using the same.

The method for synthesizing iron-manganese hydroxide according to the present invention comprises the steps of mixing a first aqueous solution containing iron ions, a second aqueous solution containing manganese ions and an oxidizing agent, (Fe _{1 -X} , Mn _X ) OOH, where 0 < x < 1. And the iron-manganese hydroxide is magnetic.

According to the invention, the first aqueous solution is FeCl ₂ Aqueous solution, the second aqueous solution is an aqueous solution of MnCl ₂ .4H ₂ O, and the oxidizing agent may be hydrogen peroxide. The solution in which the first aqueous solution, the second aqueous solution and the oxidizing agent are mixed is preferably in a basic range of pH 8 or more.

In one embodiment of the present invention, the x value for the content of iron and manganese can be optimally expressed in the range of 0.05 to 0.25.

Meanwhile, the water treatment method according to the present invention is for treating polluted water containing all pollutants, and the iron-manganese hydroxide synthesized by the above-described synthesis method is put into the polluted water to adsorb the pollutant, It is characterized by elimination.

In the water treatment method according to the present invention, after the iron-manganese hydroxide adsorbs contaminants, the iron-manganese hydroxide can be separated and recovered from the contaminated water by a magnetic force.

Particularly, in the water treatment method according to the present invention, the contaminant includes trivalent arsenic, and the trivalent arsenic is oxidized by the iron-manganese hydroxide to be formed into pentavalent arsenic and then adsorbed on the iron-manganese hydroxide to be removed .

The iron-manganese hydroxide synthesized according to the present invention has an advantage that it can adsorb and effectively remove trivalent arsenic in water after oxidation into pentavalent arsenic.

Further, since the iron-manganese hydroxide according to the present invention is magnetic, it can be easily separated and recovered in water by the magnetic force after the adsorption and removal of the contaminants are completed, and the iron-manganese hydroxide does not cause secondary contamination.

In addition, the iron-manganese hydroxide according to the present invention has an advantage that it can treat various contaminants in water because it can remove and remove anionic contaminants in addition to arsenic, and can decompose organic contaminants.

1 is a schematic flow diagram of a method for synthesizing iron-manganese hydroxide according to an embodiment of the present invention.
2 is a TEM photograph of iron-manganese hydroxide synthesized by an experiment.
FIG. 3 is a table showing the magnetism of the iron-manganese hydroxide synthesized by the experiment according to the manganese substitution ratio.
FIG. 4 is a graph showing the oxidation ability of iron-manganese hydroxide synthesized by the experiment according to the manganese substitution ratio.
FIG. 5 is a table showing Rietveld exponents R _wp (weighted pattern R), R _exp (expected R), S (Goodness of Fitness, R _wp / R _exp ) and crystallization results of iron-manganese hydroxide synthesized by the experiment.
6 is a graph showing the results of Rietvelt crystal structure analysis of iron-manganese hydroxide synthesized by an experiment.
FIG. 7a is a graph showing the adsorption rate of trivalent arsenic of iron-manganese hydroxide according to the type of electrolyte (NaNO ₃ , NaCl, Na ₂ SO ₄ ), and FIG. 7b is a graph showing the concentration of residual pentavalent arsenic FIG. 7C is a graph showing the concentration of residual trivalent arsenic in the solution according to the type of the electrolyte. FIG.
FIG. 8A is a graph showing the rate of arsenic adsorption of iron-manganese hydroxide according to the concentration of trivalent arsenic solution, FIG. 8B is a graph showing the concentration of residual pentavalent arsenic depending on the concentration of trivalent arsenic solution, 3 is a graph showing the rate of change of pH with the concentration of arsenic solution.
9 is a graph showing the arsenic adsorption capacity of iron-manganese hydroxide according to the concentration of arsenic as a result of the isothermal adsorption experiment.
10 is a graph showing the oxidizing ability of iron-manganese hydroxide according to the manganese substitution ratio as a result of the standard chromium oxidation experiment.
11 is a graph showing the adsorption rate of trivalent arsenic and pentavalent arsenic of iron-manganese hydroxide according to the pH of the solution.

The present invention relates to a process for the synthesis of iron-manganese hydroxides, a process for water treatment using iron-manganese hydroxides and iron-manganese hydroxides synthesized by this synthesis process.

In the present invention, the iron-manganese hydroxide is referred to as iron oxide or iron oxyhydroxides, which means a single-phase oxide formed by substituting a part of iron in manganese in the material represented by the formula FeOOH.

The five major polymorphs of iron hydroxide goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), the high pressure phase (hp (ε) -FeOOH) and feroxyhyde polymorph.

In the present invention, iron hydroxide refers to feroxyhyde (δ-FeOOH) having δ type among the above five homogeneous bodies, and feroxyhyde is the only magnetic substance at room temperature.

Hereinafter, a method for synthesizing iron-manganese hydroxide according to an embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a schematic flow diagram of a method for synthesizing iron-manganese hydroxide according to an embodiment of the present invention.

Referring to FIG. 1, the iron-manganese hydroxide is synthesized by mixing a first aqueous solution and a second aqueous solution to prepare a mixed solution, adding an oxidizing agent to the mixed solution, and stirring.

The first aqueous solution is an aqueous solution containing bivalent iron ions. In this embodiment, an FeCl ₂ .4H ₂ O aqueous solution is used. However, as in the present embodiment, iron may be in the form of various compounds such as a sulfide form instead of a chloride form. The essential function of the first aqueous solution is to be capable of providing divalent iron ions in the form of an aqueous solution. For example, an aqueous solution containing FeSO ₄ or an aqueous solution containing Fe (NO ₃ ) ₂ may be used.

The second aqueous solution is an aqueous solution containing divalent manganese ions. In this embodiment, an aqueous solution of MnCl ₂ .4H ₂ O is used. However, manganese may be formed in various forms such as a sulfide form instead of a chloride form as in the present embodiment. The essential function of the second aqueous solution is to be capable of providing divalent manganese ions in the form of an aqueous solution. For example, an aqueous solution containing MnSO ₄ or an aqueous solution containing Mn (NO ₃ ) ₂ may be used.

 Then, the mixed solution is formed by mixing the first aqueous solution and the second aqueous solution, and the pH of the mixed solution is adjusted by adding an acid and / or a base to the mixed solution. In this embodiment, the pH of the mixed solution was adjusted to pH 12, but the pH of the mixed solution was adjusted in the basic range of pH 8 or more.

After the pH of the mixed solution is adjusted, the oxidizing agent is immediately added and the mixed solution is stirred. In this embodiment, hydrogen peroxide is used as the oxidizing agent. However, a variety of oxidizing agents can be selected. That is, sodium hypochlorite aqueous solution NaClO (aq) or potassium thiosulfate (K ₂ S ₂ O ₈ ), sodium percarbonate (2Na ₂ CO ₃ .3H ₂ O ₂ ) or an aqueous solution thereof can be used.

As described above, when the mixed solution is stirred while the first aqueous solution, the second aqueous solution and the oxidizing agent are mixed, iron-manganese hydroxide is formed by the following reaction.

First, iron hydroxide (FeOOH) is formed. That is, in a water-soluble dihydrate solution, iron hydroxide is produced by the oxidation reaction following hydrolysis as shown in the following reaction formula (1). In general, oxidation reaction by oxidation of oxygen can be expressed by the following equation.

2 Fe ^{2 +} + 3 H ₂ O + 1/2 O ₂ -> 2 FeOOH + 4 H ⁺

Here, the oxidation may be performed by oxygen in the air or by other oxidizing agents (KNO ₃ , H ₂ O ₂ , hydroxylamine, etc.).

After formation of the iron hydroxide, the iron-manganese hydroxide ((Fe _(1-x) , Mn _x ) OOH) is produced by an oxidation reaction following hydrolysis in the same manner as in the above reaction formula (1) (2).

2 (1-x) Fe ²⁺ + 2xMn ^{2 +} + 3H ₂ O + 1 / 2O ₂ -> 2 (Fe _(1-x) , Mn _x ) OOH + 4H ⁺

Here, x is a range of 0 < x < 1.

As described above, the 隆 -type iron-manganese hydroxide is generated when the oxidation reaction following hydrolysis is very rapid in an alkaline environment of pH 8 or more. At this time, a strong oxidizing agent such as H ₂ O ₂ is required .

We have synthesized single-phase minerals with the conditions of x = 0, 0.1, 0.3 and 0.5 for the characterization and crystallographic study of iron-manganese hydroxide [δ- (Fe _{1 -x} , Mn _x ) OOH] The synthesis process is as follows.

1 L of 0.1 M FeCl ₂ 4H ₂ O was prepared and adjusted to pH 12 with 5M NaOH. The mixture was immediately stirred for 30 minutes in a magnetic stirrer with 30% H ₂ O _{2 for} 10 minutes, (Fe _{1 -x} , Mn _x ) OOH. For the samples with x = 0.1, 0.3 and 0.5, 1L of 0.1M FeCl ₂ 4H ₂ O and 0.1M MnCl ₂ 4H ₂ O solution were prepared at 9: 1, 7: 3, 5: 0 were synthesized in the same manner. After the reaction, all the synthesized samples were sufficiently washed with distilled water and lyophilized. TEM photographs of the synthesized iron-manganese hydroxides are shown in FIG.

The properties of synthesized iron - manganese hydroxides were tested.

(1) Magnetic and oxidative capacity analysis

The magnetic properties of the composite were measured using a Bartington magnetic susceptibility meter (UK) with 36 mm internal diameter calibration vol. (SCNOT) (Barlett & James, 1996) was used to measure the oxidative capacity of the compound. The results are shown in the table of FIG. 3 and the graph of FIG.

Referring to FIG. 3 and FIG. 4, as the Mn substitution ratio increases, the magnetic property decreases sharply and the oxidizing ability increases. When the manganese substitution ratio is increased, the oxidation ability is increased, but the iron content is decreased and the magnetic property is lowered. In the reverse case, the oxidation ability is lowered and the magnetic property is increased.

From the above results, when the present invention focuses on the treatment of trivalent arsenic in the present invention, the optimum Mn replacement ratio is estimated to be about 10%. That is, to remove trivalent arsenic, trivalent arsenic must be oxidized to pentavalent arsenic and the pentavalent arsenic must be adsorbed to iron.

(2) Determination of the shape and size of the composite by transmission electron microscopy (TEM) analysis

2, the iron-manganese hydroxide synthesized as a result of the transmission electron microscopic observation shows a particle size distribution of several hundreds of nanometers and has a hexagonal plate shape morphology. The c-axis corresponding to the thickness of the hexagonal plate was crystallographically very thin with a few nm, and it was confirmed that the crystal was mainly formed in the lateral a-axis direction. It was observed that there was almost no change in the shape and size of the compound according to the Mn substitution ratio.

(3) Crystal structure change of iron-manganese hydroxide according to manganese substitution ratio

The crystal structures of δ- (Fe _{1 -x} , Mn _x ) OOH single-phase oxides were analyzed by high-resolution X-ray diffraction and Rietveld method in order to investigate the crystal structure changes depending on the degree of substitution and degree of Mn substitution. The X-ray diffraction data for this study were acquired using D8 Advance (Bruker, Cu target) under the conditions of step interval 0.01 ° (2θ) and 1 second per step in 10-95 ° (2θ) section.

The software used for the crystal structure analysis to identify the change of the crystal structure depending on the substitution degree and degree of Mn substitution in the δ- (Fe _{1 -x} , Mn _x ) OOH single phase oxide is version 4.2 as TOPAS (Bruker, Germany) The initial input structure model of Refinement is Patrat et al. (1983) were used. The order of refinement was performed by increasing the variables by taking into account the structural and experimental parameters, one by one, from the fixed values of the initial model.

The general order is somewhat different according to the literature, but as described by Young (1993), the scale factor, the zero point aiming factor, the four baseline function factors, the unit cell and the bias factor, and the asymmetry factor, The factor, the total thermal vibration factor, was fixed at the initial value. The instrumental peak shape function parameters were initially used as instrumental calibration factors using diffraction data obtained under identical conditions using the LaB ₆ standard sample (SRM 660a, NIST). And refined to take into account the bias factor in the direction of the deflection direction of the composite (010). Items of the occupancy rate of cations such as Fe and Mn contained in the octahedral site M were not included in the calculation and were calculated by distributing and fixing them on the M1 and M2 sites based on the ratio of the synthesis conditions without preference. The degree of crystallinity was calculated for one peak using the peaks phase mode of the TOPAS program in order to take into account the amorphous patterns present in the diffraction data. The peak shape function was determined using the Fundamental Parameter Approach (Cheary and Coelho , 1992). A spherical harmonics function was used to consider the anisotropic peak broadening, which depends on the hkl observed prominently in the diffraction results of δ- (Fe _{1 -x} , Mn _x ) OOH (J, 1993). In addition, halite, which is a small amount of impurities left in the synthesis solution and washing process, is also included in the structural analysis to enhance the completeness of the final crystal structure refining. R _wp (weighted pattern R), R _exp (expected R), S (Goodness of Fitness, R _wp / R _exp ) and the crystallinity results indicating the completeness of the Rietveld refinement are shown in the table of FIG. Respectively.

Looking at Fig R index, which indicates the completeness of Refinement in Table 5, the theoretical index R _exp is 3.796% -4.309% is expected after a calculated, weighted index R _wp is found to be 4.414% -5.521%. The index indicating how well the actual refinement is done is S (Goodness of fitness), where R _wp / R _exp And the difference between the two indices is smaller, the refinement is better. After the refinement calculation, the S value was 1.163 - 1.281, which is sufficient to compare these data with each other.

(4) Results

As a result of Rietveld crystal structure analysis of δ- (Fe _{1 -x} , Mn _x ) OOH (x = 0, 0.1, 0.3, 0.5) synthesized in a single phase, the proportion of a unit cell and unit cell The volume V is decreased because the ion radius of Mn is relatively smaller than that of Fe (see the graph of FIG. 6). This indicates that Mn can be generated by substitution of Fe in the Fe position of the feroxyhyde.

The change of the crystal structure due to the change of ionic radius size of Fe and Mn was not the same in unit cell a and b. In the case of a, the content decreases proportionally as the Mn content increases, whereas the case of c does not show a large displacement from the point of fine increase or Mn content of 10% or more. This is because the octahedral shape distortion is accompanied by the change of the ion radius according to the degree of Mn substitution while maintaining the octahedral plate which is the basic skeleton of δ- (Fe _{1 -x} , Mn _x ) OOH .

In addition, the present invention provides a water treatment method using iron-manganese hydroxide synthesized as described above. The iron-manganese hydroxide performs the decontamination action in three respects.

The most important action is the treatment of trivalent arsenic.

As described in the prior art, trivalent arsenic has a greater effect on the ecological environment as compared with the pentavalent arsenic, and also has great mobility. Unlike the 5-valent arsenic, which is negatively charged on the surface, it is electrically neutral, which makes it difficult to remove by adsorption.

The iron-manganese hydroxide according to the present invention oxidizes trivalent arsenic to pentavalent arsenic in water as shown in the following reaction formula (3) by the action of manganese, and the pentavalent arsenic is adsorbed on the surface of iron of iron-manganese hydroxide Removed.

2Mn ^{3 +} + H ₃ AsO ₃ + H ₂ O → 2Mn ^{2 +} + HAsO ₄ ^{2 -} + 4H ⁺

Another contaminant removal action of iron-manganese hydroxide is that of anionic contaminants (AsO ₄ ^{3 -} , AsO ₃ ^3- , Cr ₂ O ₇ ² -, PO ₄ ^{3 -} , F ^- , NO ₃ ^- Adsorbs and removes hydroxides on iron surfaces, and decomposes organic contaminants.

We have investigated the effects of iron - manganese single phase oxides on the removal of arsenic in aqueous solutions and their efficiency.

(1) Comparison of removal rate of arsenic adsorption by electrolyte

In order to select the electrolytes required for the arsenic adsorption experiment for iron - manganese single phase oxides with different manganese ratios, we examined the arsenic adsorption removal ratio and the concentration of 5 - arsenic remaining. The experimental procedure is as follows. A 1L 1000 mg / L As (III) 3 arsenic solution was prepared and the trivalent arsenic solution was adjusted to pH 6 using 1 M HCl, NaOH. Then, 10 mM of each electrolyte (NaNO ₃ , NaCl, Na ₂ SO ₄ ) was added to the three solutions by dividing the trivalent arsenic solution into three (A, B, C). The trivalent arsenic solution containing the electrolyte was diluted to 20 mg / L, and 20 ml of the ferrous-manganese single phase oxide containing 0.02 g was added to the vial to make the iron-manganese hydroxide capacity 1 g / L. And the reaction was carried out at 150 rpm for 24 hours. After the reaction, the iron-manganese hydroxide and the solution were separated using a 0.45 μm syringe filter. The separated solution was divided into halves and the half was separated 5 times slowly using a 5-point arsenic filter and added with 2 drops of nitric acid. Respectively. After pretreatment, it was analyzed by ICP (Inductively Coupled Plasma) analyzer.

The results are shown in the graphs of Figs. 7a to 7c.

Referring to the graphs of FIGS. 7a to 7c, there was no significant influence depending on the type of electrolyte, but overall, NaNO ₃ >NaCl> Na ₂ SO ₄ was found to affect arsenic adsorption. The arsenic adsorption rate was high up to 10% manganese ratio, but the arsenic adsorption amount was greatly decreased from 30%. As the manganese ratio increased, the concentration of residual pentavalent arsenic increased without adsorption, and trivalent arsenic was not observed. However, when the manganese substitution ratio is low, it can be seen that a relatively large amount of arsenic is retained in the solution. From this, it can be predicted that the manganese ion substituted with iron - manganese hydroxide reacts with trivalent arsenic and oxidized into pentavalent arsenic.

In conclusion, the adsorption capacity decreases as the proportion of iron hydroxide, which can provide the site of arsenic adsorption, decreases although the manganese ratio increases and the minerals having sufficient oxidizing power are formed. In this experiment, the NaNO ₃ electrolyte with high adsorption efficiency was determined. The trivalent arsenic was oxidized to pentavalent arsenic and the oxide synthesized with 9: 1 iron-manganese which could adsorb to the iron oxide was determined at an optimum ratio Respectively. That is, although the x value in the chemical formula is 0.1, if the x value is 0.05 to 0.25, both the oxidation ability and the adsorption capacity can be satisfied.

(2) Trivalent arsenic adsorption reaction rate experiment

To investigate the amount of iron - manganese monohydrate removed at each hour in the arsenic adsorption reaction, the removal rate of trivalent arsenic adsorption and the concentration of residual 5 - arsenic were investigated. The experimental procedure is as follows. In this experiment, the removal efficiency of arsenic adsorbed on the electrolyte was determined to be NaNO ₃ , and an oxide with an iron / manganese ratio of 9: 1 was selected and used. 1 L of 1000 mg / L As (III) was prepared and used as a storage solution. PH was adjusted to 6 with 1 M HCl and NaOH, and 10 mM NaNO ₃ electrolyte was added. Dilute 3 mg of arsenic 1000 mg / L stock solution to 20, 50 and 100 mg / L, add 20 ml of 0.02 g of oxide synthesized at an iron-manganese ratio of 9: 1 in 20 ml of vial, L, and the reaction was carried out at 150 rpm for up to 24 hours in a water bath.

The sampling interval was divided into 11 sections (10, 20, 30, 50, 70, 90, 120, 180, 360, 600 and 1440 minutes). The reaction samples for each time were taken out from the water bath, To separate the oxide and the solution. The separated solution was again divided into halves, and the semi-detached solution was slowly separated 5 times using an arsenic filter, and 2 drops of nitric acid was added thereto. After pretreatment, they were analyzed using ICP analyzer.

The results of the analysis are shown in Figs. 8A to 8C.

8A to 8C, it took 360 minutes to reach the adsorption equilibrium at the three concentration conditions, and the adsorption reaction gradually occurred after 50% of arsenic was removed in the initial 10 minutes. At the three conditions, the concentration of arsenic remaining after the adsorption was found to be about 1.2, 8.0, 41.4 mg / L, respectively, and the arsenic concentrations of 5 were found to be 0.8, 1.5 and 5.0 mg / . Initial pH was controlled to 6, and 96.7 mg / L 3 was observed under pH in the presence of arsenic. In the absence of arsenic, the pH of the solution rapidly increased to about 9.14 when the iron-manganese single phase oxide was injected, but when the amount of trivalent arsenic was increased, the increase was small and was less than 8 ). This can be an indirect evidence that trivalent arsenic is oxidized to pentavalent arsenic and releases hydrogen ions.

(3) Trivalent arsenic adsorption experiments

The removal rates of arsenic adsorption on iron - manganese single phase oxides were investigated in order to investigate the amounts of iron - manganese oxides removed by different concentrations in arsenic adsorption. In this experiment, the preparation of a trivalent arsenic 1000 mg / L stock solution is the same as in the previous experiments. The storage solution of trivalent arsenic (1000 mg / L) was divided into 10 groups of 10, 20, 30, 50, 70, 90, 120, 150, 200 and 250 mg / Was put into a 25 mL vial containing 0.02 g to make a mineral volume of 1 g / L, and the mixture was placed in a water bath and reacted at 150 rpm for 24 hours. After the reaction, the oxide and the solution were separated using a 0.45 μm syringe filter. The separated solution was added with 2 drops of nitric acid and stored in the refrigerator. After pretreatment, they were analyzed using ICP analyzer. The results are shown in Fig.

9, the adsorption capacity changes of iron-manganese monohydrate hydroxides to trivalent arsenic were observed by varying the initial trivalent arsenic concentration from 10.2 to 264 mg / L. As the initial concentration of trivalent arsenic increased, the amount of arsenic adsorption increased. The maximum adsorption amount was 83.8 mg / g at the initial trivalent arsenic concentration of 264 mg / L.

(4) Standard chromium oxidation experiments

To investigate the precise oxidizing ability of iron - manganese monohydrate in oxidation reaction, we investigated oxidizing ability by using standard chromium oxidation test method. The experimental procedure is as follows. 500 mL of 1 mM CrCl ₃ was prepared and 20 mL of each of the vials containing 0.1 g of the iron-manganese monohydrate hydroxide having different manganese ratios was added, and the mixture was reacted at 150 rpm for 1 hour in a water bath. After the reaction, 0.2 mL of phosphate buffer (1M, pH 7.2, phosphate solution) was added, and the reaction was carried out for 15 seconds to remove the adsorbed Cr (VI). The supernatant was then extracted using a centrifuge and then filtered through a 0.45 μm syringe filter. The filtered solutions were analyzed using the CHROMIUM, Hexavalent 1560 (1,5-Diphenycarbohydrazide Method) program of the UV-vis Spectrophotometer (DR / 4000) analyzer. Referring to the result table in FIG. 10, it was found that the oxidation ability was increased as the manganese ratio was increased

(5) trivalent arsenic removal pH effect experiment

In order to compare the amounts of iron - manganese monohydrate hydroxides removed by different pH in arsenic adsorption reaction, the removal rate of arsenic adsorption by pH was investigated. The experimental procedure is as follows. 1 L of 1000 mg / L As (III) was prepared and used as a stock solution. 10 mM NaNO ₃ electrolyte was added and diluted to 50 mg / L. After adjusting the pH to 3 ~ 10 with 1M HCl and NaOH, 20 mL of the solution was added to a 25 mL vial containing 0.02 g of oxide synthesized at an iron-manganese ratio of 9: 1, and the mineral content was adjusted to 1 g / L. bath, and reacted at 150 rpm for 24 hours. After the reaction, the oxide and the solution were separated using a 0.45 μm syringe filter, and the separated solution was immediately analyzed using an ICP analyzer. As shown in the graph of FIG. 11, the adsorption rate of trivalent arsenic was constant regardless of the change of pH, while the adsorption rate of arsenic 5 was abruptly decreased at pH 6 ~ 7. Based on this, iron - manganese hydroxide is more suitable for the treatment of acid wastewater.

As described above, it was confirmed that the δ type iron-manganese hydroxide was synthesized through the synthesis method according to the present invention, and the crystallographic characteristics and the characteristics of the iron-manganese hydroxide as the adsorbent were also determined.

Based on this, it was confirmed that the iron-manganese hydroxide according to the present invention can effectively adsorb and remove trivalent arsenic and pentavalent arsenic in water. In addition, iron-manganese hydroxides according to the present invention have an advantage of being capable of adsorbing other anionic contaminants in the water as well as arsenic removal and treating organic contaminants.

In the present invention, it is possible to remove contaminants in the water through the use of iron-manganese hydroxide as a reaction wall or a method in which the iron-manganese hydroxide is introduced into a carrier. Further, after adsorbing the contaminants, there is an advantage that the recovery can be performed using magnetic force in water by using magnetic property which is a characteristic of iron-manganese hydroxide.

Therefore, the present invention can be effectively used for water treatment in that it can effectively remove trivalent arsenic contaminants having a great influence on mobility and ecology, and can easily separate and recover from secondary contamination.

In the present invention, iron-manganese hydroxide, iron-manganese oxide, iron-manganese oxide, iron hydroxide substituted with manganese have the same meanings as the formula δ- (Fe _{1 -X} , Mn _x ) OOH ≪ 1)).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation and that those skilled in the art will recognize that various modifications and equivalent arrangements may be made therein. It will be possible. Accordingly, the true scope of protection of the present invention should be determined only by the appended claims.

Claims (10)

And a first aqueous solution containing iron ions, by reacting a mixture of the second aqueous solution and the oxidizer comprises manganese ions iron-manganese hydroxide _{(δ- (Fe 1 -X, Mn} X) OOH, where 0 <x <1) &Lt; / RTI &gt; is synthesized. The method according to claim 1,
Wherein the first aqueous solution is an FeCl ₂ .4H ₂ O aqueous solution. The method according to claim 1,
Wherein the second aqueous solution is an aqueous solution of MnCl ₂ .4H ₂ O. The method according to claim 1,
Wherein the x value of the content of iron and manganese is 0.05 to 0.25. The method according to claim 1,
Wherein the solution in which the first aqueous solution and the second aqueous solution are mixed is a basic one having a pH of 8 or more. The method according to claim 1,
Wherein the iron-manganese hydroxide is magnetic. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The iron-manganese hydroxide synthesized by the synthesis method according to any one of claims 1 to 6. It is intended to treat polluted water containing all contaminants,
Characterized in that iron-manganese hydroxide synthesized by the synthesis method according to any one of claims 1 to 6 is added to the polluted water to adsorb and remove the pollutant. Way. 9. The method of claim 8,
After the iron-manganese hydroxide adsorbs contaminants,
Wherein the iron-manganese hydroxide is separated and recovered from the contaminated water by magnetic force. 9. The method of claim 8,
Wherein the contaminant comprises trivalent arsenic,
Wherein the trivalent arsenic is oxidized by the iron-manganese hydroxide to form the pentavalent arsenic, and then the iron-manganese hydroxide is adsorbed and removed.

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