KR20210106336A - Iron carbonate composites for removing heavy metal and preparation method thereof - Google Patents

Abstract

The present invention relates to an iron carbonate composite for removing heavy metals that can be used for purification of heavy-metal-contaminated water in an oxygen-free environment, and a preparation method therefor. The iron carbonate composite for removing heavy metals exhibits an excellent removal performance on cationic and anionic heavy metals, for which adsorbents exhibit low adsorption capacity, by forming a highly reactive surface with a three-dimensional structure through a surface modification of an iron carbonate using citric acid and, in particular, exhibits an excellent adsorption and removal efficiency for trivalent arsenic. In addition, when applied to environmental purification, an oxidation-reduction reaction of heavy metals can be accompanied during the heavy metal removal process, so that the iron carbonate composite can be widely applied to oxygen anions having various oxidation numbers (e.g., As, Cr, Se, Sb, etc.).

Description

Iron carbonate composites for removing heavy metal and preparation method thereof

The present invention relates to an iron carbonate complex for heavy metal removal that can be used for purification of arsenic-contaminated water in an anoxic environment, and a method for manufacturing the same, and more particularly, to heavy metals, In particular, it relates to an iron carbonate complex for heavy metal removal including iron carbonate and an organic acid, which can excellently improve the adsorption capacity of trivalent arsenic as well as pentavalent arsenic.

Arsenic removal technology is applied differently depending on the groundwater quality and arsenic concentration of the contaminated area. In general, technologies for removing arsenic are largely classified into precipitation, membrane, ion exchange, and adsorption treatment technologies. In general, sedimentation treatment technology effectively treats arsenic-contaminated groundwater in large-scale treatment facilities. And in small-scale treatment plants, membrane, ion exchange, and adsorption techniques are suitable for arsenic removal. However, the current trend is a small-scale treatment facility, which has lower installation and operation costs than membrane and ion exchange treatment technologies, and an adsorption treatment technology using an adsorbent that is not affected by the groundwater quality is widely applied to arsenic-contaminated groundwater.

_{Conventional studies and technologies in adsorption treatment technology use iron (II) carbonate (calite, FeCO 3} ) as an adsorbent that has excellent heavy metal reactivity and is harmless to the environment for environmentally friendly and effective purification of arsenic-contaminated natural water and groundwater.

However, in the prior art, natural iron (II) carbonate contains considerable impurities and has a disadvantage in that the adsorption capacity of arsenic is low. In addition, most of the technologies using iron (II) carbonate are focused on the removal of arsenite (As(V)) under oxygen conditions, but the groundwater environment, which is the source of drinking water that causes the greatest exposure to arsenic, is an anaerobic condition, and most Arsenic is present in the form of arsenite (As(III)), which is more difficult to remove and more toxic than arsenic (As(V)). In addition, there is a problem in that the adsorption capacity of As(III)) using iron(II) carbonate under anoxic conditions is very low, so that the applicability of arsenic-contaminated water treatment is poor.

Therefore, there is a demand for the development of an eco-friendly arsenic adsorbent with improved stability and reactivity under anoxic conditions through reforming of iron (II) carbonate.

Republic of Korea Patent Registration No. 10-1961223

An object of the present invention is to provide an iron carbonate composite for heavy metal removal excellent in adsorption capacity of trivalent arsenic when purifying contaminated water containing arsenic even in an oxygen-free environment, and a method for manufacturing the same.

the present invention

As an iron carbonate composite for heavy metal removal,

The iron carbonate complex for heavy metal removal is a complex in which an organic acid and iron carbonate are combined in the form of a complex,

The complex consists of secondary particles formed by aggregation of a plurality of primary particles,

The average diameter of the primary particles is 10 μm or less,

The BET specific surface area of the composite provides an iron carbonate composite for heavy metal removal ^{of 1 to 10 m 2 /g.}

Also, the present invention

heating; and removing oxygen from deionized water by using any one or more of a mixed gas injection method including hydrogen gas;

First and second reactions of preparing a first reaction solution by mixing iron ions and an organic acid with deionized water from which oxygen has been removed, and mixing hydrogen carbonate ions and an organic acid with deionized water from which oxygen has been removed to prepare a second reaction solution solution preparation step; and

Mixing the first and second reaction solutions, filtering and drying to prepare a complex in which an organic acid and iron carbonate are combined in the form of a solid complex,

The first and second reaction solutions are independently mixed with an organic acid having a concentration of 2 mM to 8 mM.

The iron carbonate complex for heavy metal removal according to the present invention exhibits excellent removal performance for cationic heavy metals and anionic heavy metals, which are difficult to adsorb, by forming a highly reactive surface with a three-dimensional structure through surface modification of iron carbonate using citric acid. shows excellent adsorption and removal efficiency for arsenic, and when applied to environmental purification, heavy metal redox reaction can be accompanied in the heavy metal removal process. Widely applicable.

1 is a schematic view showing a method for manufacturing an iron carbonate composite for heavy metal removal according to an embodiment of the present invention.
2 is a flowchart illustrating a method for manufacturing an iron carbonate composite for heavy metal removal according to an embodiment of the present invention.
3 is an image showing an arsenic removal experiment and device analysis process using an iron carbonate complex for heavy metal removal according to an embodiment of the present invention.
4 is an X-ray diffraction (XRD) graph of the iron carbonate complex for heavy metal removal according to oxygen removal and citric acid concentration according to an embodiment of the present invention.
5 is a scanning electron microscope (SEM) image according to the citric acid concentration of the iron carbonate complex for heavy metal removal according to an embodiment of the present invention.
6 is a Fourier-transform infrared analysis (Fourier Transform Infrared spectroscopy, FT-IR) result graph according to the citric acid concentration of the iron carbonate complex for heavy metal removal according to an embodiment of the present invention.
7 is a graph showing the results of Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) according to the citric acid concentration of the iron carbonate complex for heavy metal removal according to an embodiment of the present invention.
8 is a graph showing an adsorption isotherm test result of an iron carbonate composite for heavy metal removal according to an embodiment of the present invention.
9 is a scanning electron microscope image and Energy Dispersive Spectrometry (EDS) graph before and after arsenic adsorption of the iron carbonate complex for heavy metal removal according to an embodiment of the present invention.
10 is an X-ray photoelectron spectroscopy (XPS) graph before and after arsenic adsorption of the iron carbonate complex for heavy metal removal according to an embodiment of the present invention.
11 is a graph showing the results of an oxygen anion adsorption experiment having various oxidation numbers of the iron carbonate complex for heavy metal removal according to an embodiment of the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in more detail with reference to the accompanying drawings in order to describe the present invention in more detail. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms.

The present invention is an iron carbonate complex for heavy metal removal, wherein the iron carbonate complex for heavy metal removal is a complex that exists in the form of a solid complex in which an organic acid and iron carbonate are combined, and the complex is a heavy metal composed of secondary particles formed by aggregation of a plurality of primary particles An iron carbonate complex for removal is provided.

As an example, the average diameter of the composite according to the present invention is from 20 μm to 100 μm, from 20 μm to 80 μm, from 25 μm to 70 μm or from 30 μm to 50 μm.

In addition, the average diameter of the primary particles of the composite according to the present invention is characterized in that 10 ㎛ or less. Specifically, the average diameter of the primary particles is 10 μm or less, 2 μm to 7 μm, or 3 μm to 5 μm.

The surface of the primary particles has a three-dimensional porous surface structure in the form of a honeycomb. By having the honeycomb three-dimensional porous surface structure as described above, the iron carbonate composite for heavy metal removal of the present invention may have an excellent BET specific surface area, total pore volume and/or pore diameter.

The organic acid includes two or more carboxyl groups, and the organic acid includes any one or more of citric acid, oxalic acid, tartaric acid, fumaric acid, malic acid, malonic acid, and maleic acid. Specifically, the organic acid may be citric acid.

The complex may be formed by combining an organic acid and iron carbonate to form a complex. The iron carbonate may be iron (II) carbonate or iron (II) carbonate mixed with iron (III).

The organic acid may be 10 wt% to 20 wt% based on the iron carbonate composite for heavy metal removal. Specifically, the organic acid may be 10 wt% to 19 wt%, 11 wt% to 19 wt%, or 14 wt% to 18 wt% based on the iron carbonate composite for heavy metal removal.

The iron carbonate complex for heavy metal removal according to the present invention forms a porous surface by including an organic acid as described above, and can provide a medium for electron transfer, so that it has excellent adsorption capacity for cationic heavy metals and anionic heavy metals, particularly trivalent arsenic adsorption capacity this is excellent

For example, the BET specific surface area of the iron carbonate composite for heavy metal removal ^{may be 1 to 10 m 2} /g. Specifically, the BET specific surface area of the iron carbonate composite for heavy metal removal is 1 to 9 m ² /g, 1 to 7 m ² /g, 1 to 6 m ² /g, 2 to 6 m ² /g, or 2 to 5 m ² /g.

In addition, the total pore volume of the iron carbonate composite for heavy metal removal ^{may be 0.01 to 0.05 cm 3} /g. Specifically, the total pore volume of the iron carbonate composite for heavy metal removal may be 0.015 to 0.05 cm ³ /g, 0.01 to 0.04 cm ³ /g, or 0.01 to 0.03 cm ³ /g.

In addition, the average pore diameter of the iron carbonate composite for removing heavy metals may be 10 to 15 nm. Specifically, the average pore diameter of the iron carbonate composite for heavy metal removal may be 10 to 14 nm, 11 to 14 nm, or 11 to 13 nm.

As an example, the iron carbonate composite for heavy metal removal according to the present invention has excellent ability to adsorb heavy metals under anoxic conditions. The anaerobic conditions may be O ₂ < 1 ppm, H ₂ = 2-3%, CO ₂ = 500 ~ 600 ppm. Specifically, the heavy metal includes a cationic heavy metal or an anionic heavy metal, and the cationic heavy metal is at least one selected from the group consisting of cadmium (Cd), copper (Cu) and lead (Pb), zinc (Zn), and anionic heavy metal The silver may be at least one selected from the group consisting of arsenic (As), chromium (Cr), selenium (Se), and antimony (Sb). More specifically, the heavy metal may be an anionic heavy metal, and may be trivalent arsenic, pentavalent arsenic, trivalent chromium, hexavalent chromium, trivalent selenium, hexavalent selenium, tetravalent antimony, or pentavalent antimony. .

For example, the iron carbonate composite for heavy metal removal of the present invention has excellent adsorption capacity for trivalent arsenic as well as pentavalent arsenic under _{anoxic conditions (O 2} < 1 ppm, H ₂ = 2-3%, CO _{2 = 500-600 ppm).} do.

In addition, the heavy metal adsorption rate of the iron carbonate composite for heavy metal removal of the present invention may be 60% or more under anoxic conditions. Specifically, the heavy metal adsorption rate of the iron carbonate composite for heavy metal removal may be 70% or more, 80% or more, 85% or more, or 85% to 95% under anoxic conditions. More specifically, the iron carbonate composite for heavy metal removal may have an adsorption rate of trivalent arsenic of 80% or more or 85% to 95% under anoxic conditions.

Specifically, the heavy metal removal performance of the iron carbonate composite for heavy metal removal may be improved through a redox reaction with the heavy metal. For example, the iron carbonate complex for heavy metal removal may be removed by accelerating an adsorption reaction while reducing heavy metals in cations and oxyanions in a process in which iron (II) of iron carbonate is oxidized to iron (III). In addition, according to the oxygen content under anoxic conditions, a portion of iron (III) in the pre-oxidized iron carbonate is reduced back to Fe (II), thereby accelerating the oxidation of heavy metals, thereby accelerating and removing the heavy metals.

In addition, the present invention comprises the steps of removing oxygen from deionized water by using any one or more methods of a mixed gas injection method including heating and hydrogen gas; preparing a first reaction solution by mixing iron (II) ions and an organic acid with deionized water from which oxygen has been removed; preparing a second reaction solution by mixing hydrogen carbonate ions and an organic acid with deionized water from which oxygen has been removed; and mixing the first and second reaction solutions, filtering and drying to prepare a complex in which an organic acid and iron carbonate are combined in a solid complex form.

1 is an image showing a method for manufacturing an iron carbonate composite for heavy metal removal according to the present invention, and FIG. 2 is an image showing a flowchart of a method for manufacturing an iron carbonate composite for heavy metal removal according to the present invention. 1 and 2, the manufacturing method of the iron carbonate composite for heavy metal removal of the present invention includes 1) heating deionized water to primarily remove oxygen (S100), 2) primary oxygen removal A step of removing oxygen secondary by purging with injection and stirring of a mixed gas containing hydrogen and nitrogen while cooling the ionized water (S100), 3) bivalent iron (Fe ²⁺ ) in deionized water from which oxygen has been removed Dissolving ions and hydrogen carbonate (HCO ₃ ⁻ ) ions, respectively, and adding citric acid to prepare first and second reaction solutions (S200), 4) iron ions in the first and second reaction solutions prepared above After injecting the first reaction solution containing the first reaction solution into the second reaction solution containing hydrogen carbonate ions at a constant rate and stirring for a certain time, preparing a complex in which an organic acid and iron carbonate are combined in the form of a solid complex (S300), 5) Separating the precipitate from the mixed solution containing the reaction complex using a filtration device and a vacuum pump and washing to separate the precipitate, 6) Heating the filtered precipitate and storing it in a vacuum with silica gel to remove moisture drying step.

Hereinafter, the manufacturing method of the iron carbonate composite for heavy metal removal shown in FIG. 1 will be described in detail.

As an example, in the step of primarily removing oxygen, oxygen may be primarily removed by heating deionized water to a temperature of 100° C. to 150° C. for 10 to 25 minutes. Specifically, the dissolved oxygen concentration ( DO) of 0.5 to 3 ppm deionized water can be prepared. A simple hydrogen and nitrogen gas purging may be added to the solution during this heating step.

In addition, the second step of removing oxygen is a mixed gas containing hydrogen and nitrogen using a needle-type gas injector while putting the heated deionized water solution into a sealed bottle through the step of first removing oxygen and cooling it. An oxygen-free deionized water solution can be prepared by purging together with injection and stirring, and it can be prepared by injecting a mixed gas for a long time. The method can also be used outside the anaerobic chamber. Alternatively, an anaerobic deionized water solution may be prepared by directly injecting and purging a mixed gas containing hydrogen and nitrogen using a microbubble in the anaerobic chamber with stirring. The mixed gas may include 2 vol% to 8 vol% hydrogen gas and 92 vol% to 98 vol% nitrogen gas, and the mixed gas injection may be performed for 5 to 30 minutes at a rate of 1 to 10 L/min. have.

By removing oxygen from the deionized water solution as described above, a solution of iron in which iron is not oxidized in the deionized water solution (Fe ²⁺ ) can be prepared, and then, when pure iron carbonate and organic acid are added using this solution, the surface is Modified iron carbonate can be prepared.

Specifically, the dissolved oxygen concentration (DO) of the deionized water solution that has undergone the secondary oxygen removal step is 0.00 to 0.05 ppm or 0.00 to 0.01 ppm, and the pH of the deionized water solution is 4 to 7 or 5 to 6 days. can

In the first and second reaction solution preparation steps, the prepared anaerobic deionized water solution is transported into a chamber in which an anaerobic atmospheric condition is formed to dissolve iron ions and hydrogen carbonate ions, respectively, and organic acids are added to the first and second reaction solutions, respectively. can be manufactured. Specifically, the first reaction solution contains iron (II) ions and an organic acid, and the second reaction solution contains hydrogen carbonate ions and an organic acid.

For example, the first reaction solution contains 0.01 M to 1.5 M, 0.01 M to 1 M, or 0.05 M to 1.5 M Fe ²⁺ ions, and the second reaction solution is 0.01 M to 1.5 M, 0.01 M to 1 M or 0.05 M to 1.5 M HCO ₃ ⁻ ions.

The organic acid includes two or more carboxyl groups, and the organic acid includes any one or more of citric acid, oxalic acid, tartaric acid, fumaric acid, malic acid, malonic acid, and maleic acid. Specifically, the organic acid may be citric acid.

The first and second reaction solutions each contain 2.0 mM to 8 mM, 2.5 mM to 7 mM, or 2.5 mM to 5 mM organic acid. By including the organic acid of the above concentration in the reaction solution, the prepared iron carbonate composite for heavy metal removal has a three-dimensional porous structure, exhibits a high specific surface area, and can provide a medium for electron transfer, thereby providing an excellent heavy metal adsorption rate. can indicate

As an example, in the step of preparing the complex, a first reaction solution containing iron (II) ions is injected into a second reaction solution containing hydrogen carbonate ions for a predetermined time with stirring, and then an organic acid and iron carbonate are combined. Complexes existing in the form of solid complexes can be synthesized. In this case, the composite may be composed of secondary particles formed by aggregation of a plurality of primary particles. The iron carbonate may be iron (II) carbonate or iron (II) carbonate mixed with some iron (III) depending on oxygen conditions.

Specifically, the step of preparing the complex comprises injecting the first reaction solution into the second reaction solution with stirring for 1 hour to 6 hours or 3 hours to 5 hours, then aging for 20 hours to 30 hours or 22 hours to 26 hours can do. At this time, the temperature of the mixed solution may be maintained at 25±0.1° C. through a circulating constant-temperature water bath and a heated magnetic stirrer with a temperature sensor, and the complex may be prepared at room temperature or in the range of 10 to 45° C.

Separation and drying of the precipitate may be further included after the step of preparing the complex. In the step of separating the precipitate, the mixed solution containing the iron carbonate complex after the reaction is separated into a precipitate and a solution using a membrane filtration device and a vacuum pump, and then the precipitate can be washed. For the washing, deionized water from which secondary oxygen has been removed or a mixed solution of deionized water from which secondary oxygen has been removed for oxidation prevention and methanol may be used as a solvent. A solid iron carbonate composite from which impurities such as electrolytes remaining in the sediment are removed can be obtained through the sediment separation and washing steps as described above.

In addition, it may further include the step of drying after the step of separating the precipitate. In the drying step, the precipitate prepared in the previous step is heated at a temperature of 40 ℃ to 80 ℃ or 50 ℃ to 60 ℃ for 20 hours 27 hours or 23 hours to 25 hours to remove the primary moisture, and remove the residual moisture Secondary vacuum drying may be performed to The second vacuum drying is performed by putting the first heat-dried precipitate in a vacuum desiccator containing silica gel, and vacuuming the inside of the desiccator using a vacuum pump to remove residual moisture in the precipitate and prevent deterioration of the precipitate can do.

Examples of the present invention will be described below. However, the following examples are only preferred examples of the present invention, and the scope of the present invention is not limited by the following examples.

[Example]

Examples 1 to 4 and Comparative Examples 1 to 4

Deionized water using an electric pot was heated for 20 minutes to remove primary oxygen (DO concentration 7-12 ppm→0.5-1 ppm). The solution from which the primary oxygen has been removed is transferred to a sealed bottle, sealed, and cooled while the mixed gas (6%H ₂ /94%N ₂ ) is injected and purged into the solution using a needle-type gas injector to remove secondary oxygen. (O ₂ + 2H ₂ → 2H ₂ O) An oxygen-free deionized water solution was prepared (DO concentration 0.5-1 ppm → 0.00 ppm, pH 5-6). Then, the oxygen-free deionized water solution was _{transferred into a chamber in which an anaerobic atmospheric condition (O 2} <1 ppm) was formed and used to prepare an iron carbonate synthesis reaction solution. At this time, Fe ²⁺ and HCO ₃ ^- Each solution concentration range is within 0.03 ~ 1.2M. When citric acid was mixed, Fe ²⁺ and HCO ₃ ^- concentrations of each solution were fixed at 0.1M, and citric acid/carbonic acid was dissolved by dissolving citric acid (CA) of various concentrations (0-5 mM) as shown in Table 1 below. A reaction solution for synthesizing iron complex was prepared (pH conditions of each solution Fe ²⁺ =2.0~2.5, HCO ₃ ^- =7.0~8.3). ^{The Fe 2+} solution in the synthetic reaction solution prepared above is put in a syringe, and using a single or multiple syringe injection pump, the HCO ₃ ^- solution stirred in a beaker at a constant rate of 0.25 mL/min is injected for 4 hours and then the agitation is maintained. Aged for 1 day. At this time, the temperature of the mixed solution was maintained at 25±0.1 ℃ through a circulating water bath and a heated magnetic stirrer equipped with a temperature sensor. After the reaction was completed, the precipitate was separated into solid and liquid using a filtration device and a vacuum pump. The filtered precipitate is placed in a petri dish, dried by heating (50 to 60 ° C.) for 1 day on a heated magnetic stirrer, and placed in a vacuum desiccator containing silica gel to prevent deterioration and remove residual moisture to obtain an iron carbonate complex for heavy metal removal. prepared.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 citric acid concentration 5 mM 4 mM 3 mM 2.5 mM 2 mM 1 mM 0.5 mM 0 mM

[Experimental example]

3 is an image showing an arsenic removal experiment and device analysis process of the iron carbonate composite for heavy metal removal according to the present invention.

Referring to FIG. 3, ① carbonic acid for heavy metal removal invented in a 50 mL centrifuge tube container containing an arsenic solution (40 mL) of a certain concentration prepared using an anaerobic deionized water solution ([DO] = 0.00 ppm) in an anaerobic chamber After the iron composite (0.04 g) was injected, _{the lid was closed to maintain an anaerobic atmosphere (O 2} <1 ppm), and then the lid was closed and then sealed with parafilm to thoroughly block contact with the external atmosphere.

② The sealed adsorption experiment vessel was subjected to adsorption reaction while maintaining a constant temperature and rotational speed (25 ℃, 200 rpm) in a constant temperature incubator stirrer outside the chamber.

③ After the reaction for a set time, the adsorption experiment vessels are first separated through high-speed centrifugation (5500 rpm, 10 min), then transported into the chamber and subjected to secondary solid-liquid separation using a syringe-filter (0.2 μm pore size). About 10 mL of the solution thoroughly separated from the solid was extracted. This solution sample was acid-treated with 70% nitric acid to accurately measure the residual arsenic concentration in the solution using the instrument without the effect of deterioration.

④ The solid sample remaining in the adsorption vessel (iron carbonate complex for heavy metal removal that adsorbed arsenic) was again filtered using a vacuum pump and a membrane filtration device and dried.

⑤ Additionally, high-performance liquid chromatography (HPLC) analysis for measuring the content of citric acid contained in the iron carbonate complex for heavy metal removal of the present invention, inductively coupled plasma emission for calculating the amount of arsenic adsorbed to the iron carbonate complex for heavy metal removal Spectroscopy (ICP-OES) analysis, characterization of solid adsorbed samples (X-ray diffraction (XRD), scanning electron microscopy/energy dispersion) to elucidate the physicochemical properties and arsenic removal mechanism of the invented iron carbonate complex for heavy metal removal Spectroscopy (SEM/EDS), Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS)) were performed.

Experimental Example 1

In order to confirm the characteristics of the iron carbonate composite for heavy metal removal according to the present invention, high performance liquid chromatography (HPLC), X-ray diffraction analysis (XRD) and Fourier- Analyzed by transform infrared analysis (FT-IR), and photographed with a scanning electron microscope (SEM), the results are shown in Table 2 and FIGS. 4 to 6 .

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 citric acid concentration 5 mM 4 mM 3 mM 2.5 mM 2 mM 1 mM 0.5 mM 0 mM Citric acid content in iron carbonate complex for heavy metal removal 17.9 wt% 15.9 wt% 14.4 wt% 11.4 wt% 7.8 wt% 2.8 wt% 2.3 wt% 0 wt%

Referring to Table 2, it can be seen that the content of citric acid in the iron carbonate composite for heavy metal removal according to the concentration of citric acid during the production of the iron carbonate composite for heavy metal removal. Specifically, it can be seen that the citric acid content in the iron carbonate composite for heavy metal removal prepared in Examples 1 to 4 (citric acid concentration = 2.5 to 5 mM) is 11.4 wt% to 17.9 wt%. As an XRD analysis result of the iron carbonate complex for heavy metal removal of the present invention according to the conditions and citric acid concentration conditions, referring to FIG. 4 , iron carbonate and other iron oxide minerals are mixed in the primary oxygen removal, whereas in the secondary oxygen removal, pure Since iron carbonate can be obtained, it can be seen that the control of dissolved oxygen concentration is one of the important factors in determining the purity and physical properties of iron carbonate. In the iron carbonate complex for heavy metal removal of Examples 3, 4 and Comparative Example 1 having a citric acid concentration of 2 mM to 3 mM, the crystallinity of iron carbonate (mite, siderite) was greatly reduced, and the citric acid concentration was 3 mM or more. It can be seen that the iron carbonate composites for removing heavy metals of Examples 1 to 3 show characteristics similar to amorphous ones by disappearing the XRD peak of rhombite.

5 is a scanning electron microscope image of the iron carbonate complex for heavy metal removal according to the present invention. Referring to FIG. 5, in the absence of citric acid, single crystals having a size of several tens of nm are aggregated and grown to have a diameter of 3 to 5. A spherical rhombite of ㎛ is formed, and as the concentration of citric acid in the solution increases, spherical particles with a diameter of 3 to 5 ㎛ having a honeycomb-like three-dimensional porous surface structure are gradually reassembled, resulting in a particle size of 30 to 50 It can be confirmed that the change in the form of μm.

In addition, as a result of BET specific surface area analysis, the average value of the three samples prepared under the condition of 5 mM citric acid concentration was 2.87±1.25 m ² /g, total pore volume 0.017±0.007 cm ³ /g, and average pore diameter 12.67±1.52 nm. was measured.

6 is a Fourier-transform infrared analysis result of the iron carbonate complex for heavy metal removal according to the present invention. Referring to FIG. 6, as the concentration of citric acid increases, the carboxyl group (-COOH), which is the main constituent and functional group of citric acid, means the presence to -COO ^- peak is gradually increased, and the surface properties of the functional group of the complex, particularly, more than 2.5 mM of citric acid at a concentration -COO CO ₃ ^- can confirm that the change significantly with. The iron carbonate complex for heavy metal removal of Examples 1 and 2 prepared at a citric acid concentration of 4 to 5 mM by comparison with the iron citrate complex (Fe-citrate) was an iron citrate (II) complex (Fe(II)-citrate) It is confirmed that it has a surface functional group very similar to that of the present invention. Accordingly, it can be seen that the iron carbonate composite for heavy metal removal of the present invention is a composite material in which Fe(II)-citrate is incorporated in the iron carbonate surface structure.

Through this, in the iron carbonate composite for heavy metal removal according to the present invention, the properties of the material can be controlled by controlling the citric acid concentration during manufacture. It can be seen that the surface reactive properties are changed in the form of Fe(II)-citrate, and the crystal shape is also changed to a three-dimensional form favorable for catalytic reaction. The surface reactivity of the iron carbonate composite for heavy metal removal of the present invention can be greatly improved through the amorphous three-dimensional porous surface structure and the increase of highly reactive functional groups, and it is very effective for adsorption and removal of ionic contaminants in aqueous solution such as arsenic. can be seen to be advantageous.

Experimental Example 2

In order to confirm the adsorption performance of the iron carbonate composite for heavy metal removal according to the present invention to As(III) under anoxic conditions, Examples 1 to 4 and Comparative Examples 1 to 4 were subjected to As(III) adsorption under anoxic conditions. An experiment was performed, and the results are shown in FIG. 7 . In addition, in order to confirm the adsorption characteristics and adsorption capacity for As(III) and As(V), Example 1 and Comparative Example 4 were subjected to the iron carbonate composite for heavy metal removal, which showed the highest adsorption performance of As(III). Adsorption isotherm experiments and inductively coupled plasma spectroscopy (ICP-OES) were performed with this method, and the results are shown in Table 3 and FIG. 8 .

adsorption model parameter Types of iron carbonate composites for heavy metal removal Pure iron carbonate (II)
pure-FeCO ₃ Citric Acid/Iron Carbonate (Ⅱ)
citric-FeCO ₃ As(III) As (V) As(III) As (V) Langmuir q _m 9.5669 77.0462 187.9267 256.7356 k _L 0.7865 0.0173 0.0409 0.1664 R ² 0.9621 0.9080 0.9940 0.9808 RMSE 0.6002 7.0567 4.7900 12.6748 Freundlich q _m 4.6533 6.9355 18.9926 52.9716 k _L 0.1532 0.4061 0.4354 0.3608 R ² 0.8619 0.9797 0.9483 0.9742 RMSE 1.1454 3.3117 14.1122 14.6951

- Calculation formula for adsorption rate R(%) and adsorption capacity q _e (mg/g):

- Calculation formula for adsorption capacity through adsorption isotherm experiment:

7 is an ICP-OES analysis result according to a trivalent arsenic (As(III)) adsorption experiment using an iron carbonate complex for heavy metal removal (citrate/iron carbonate) prepared under different citric acid concentration conditions. Referring to FIG. 7 , it can be seen that As(III) adsorption increases as the citric acid concentration increases. Specifically, it can be seen that the arsenic adsorption rate is 74% or more when the citric acid concentration is 2.5 to 5 mM. In particular, it can be seen that the increase in citric acid concentration was small in the range of 0 to 1 mM, but greatly increased in the range of 2 to 3 mM, and the highest adsorption rate (85% or more) was maintained in the condition of 4 to 5 mM. Therefore, the present invention The iron carbonate complex for heavy metal removal according to It can be confirmed that the iron carbonate complex for removal.

Tables 3 and 8 show the heavy metal removal iron carbonate composite of Comparative Example 4 (pure iron carbonate, pure-FeCO ₃ ) and the heavy metal removal iron carbonate composite of Example 1 (citric acid/iron carbonate, citric-FeCO ₃ ) Experimental conditions: [As] _i = 1-350 mg/L, pH _i = 7.0, T = 25 ℃, 200 rpm, 48 hours and anaerobic conditions (O _{2 (g)} < 1 ppm, [DO] = 0.00 ppm) These are the results obtained by performing adsorption isotherm experiments for trivalent arsenic and pentavalent arsenic. Referring to FIG. 8, the maximum adsorption capacity (qm, mg/g) of the iron carbonate composite for heavy metal removal of Example 1 and Comparative Example 4 can be compared, and the maximum adsorption capacity calculated through the adsorption isotherm experiment is shown in Table 3 In the case of pure iron carbonate of Comparative Example 4 based on the Langmuir adsorption model, q _{m =9.6 mg/g for As(III), q m} = 77 mg/g for As(V), heavy metal removal of Example 1 For the molten iron carbonate complex (citrate/iron carbonate), it _{is confirmed that q m} =188 mg/g _{for As(III) and q m} =257 mg/g for As(V). Therefore, it can be seen that the adsorption performance is improved by about 19.6 times for As(III) and by about 3.3 times for As(V).

Experimental Example 3

In order to confirm the characteristic change of the iron carbonate composite for heavy metal removal according to the present invention before and after arsenic adsorption, SEM/EDS analysis and XPS analysis were performed on Example 1 and Comparative Example 4 before and after arsenic adsorption, and the results were 9 to 10 are shown.

9 is a scanning electron microscope image and elemental component analysis results before and after arsenic adsorption of the iron carbonate composite for heavy metal removal of Comparative Example 4 (pure-FeCO ₃ ) and the heavy metal removal composite iron carbonate composite (citric-FeCO _{3 ) of Example 1;} am. Referring to FIG. 9 , it can be seen that the content of arsenic detected on the surface of the iron carbonate composite for heavy metal removal is different depending on whether or not the iron carbonate composite for heavy metal removal contains citric acid, which is similar to the trend shown in the adsorption isotherm experiment. Specifically, compared to the iron carbonate composite for heavy metal removal of Comparative Example 4, which is pure iron carbonate, the iron carbonate composite for heavy metal removal prepared in 5 mM citric acid of Example 1 had a very high concentration of arsenic detected by adsorption to the surface of 11.16 wt%. level, and through this, it can be seen that the iron carbonate complex for heavy metal removal can adsorb/remove a larger amount of arsenic by including a certain amount of citric acid or more in the structure.

10 is a graph of the results of XPS analysis for confirming the change in the oxidation number of the iron carbonate complex for removing arsenic and heavy metals during the arsenic adsorption process and evaluating the possibility of a redox reaction catalyst of the iron carbonate complex for removing heavy metals according to the present invention. Specifically, high resolution before and after arsenic adsorption of the iron carbonate composite for heavy metal removal of Comparative Example 4 (pure iron carbonate, pure-FeCO ₃ ) and the iron carbonate composite for heavy metal removal of Example 1 (citric acid/iron carbonate, citric-FeCO _{3 )} As a result of XPS analysis, the spectral range is (A) As3d, (B) Fe2p binding energy range.

Referring to FIG. 10 , the As3d binding energy of As(III) and As(V) adsorbed to the (citrate/iron carbonate) iron carbonate complex for heavy metal removal of Example 1 was greatly reduced compared to the pure iron carbonate of Comparative Example 4 As can be seen, As is reduced. In addition, as a result of the Fe2p binding energy analysis, it can be seen that Fe(II), a component of iron carbonate, is oxidized as the binding energy of Fe2p increases after As adsorption.

The results of the reduction of As and the oxidation of Fe indicate that the redox reaction is included as the removal mechanism of As using the citrate/iron carbonate complex, and the effect is very superior to that of pure iron carbonate for heavy metal removal according to the present invention. It can be seen that the iron carbonate complex can also be utilized as a redox catalyst.

Experimental Example 4

In order to confirm the adsorption performance of the iron carbonate composite for heavy metal removal according to the present invention for various heavy metals, an additional heavy metal adsorption experiment was performed on Example 1, and the results are shown in FIG. 11 .

11 is a heavy metal adsorption performance test result of the iron carbonate composite for heavy metal removal according to the present invention. The iron carbonate composite for heavy metal removal (citrate/iron carbonate) prepared in Example 1 is not only arsenic (As(III, V)); It can also be seen that the removal performance for elements having various oxidation numbers, such as chromium (Cr(III, VI)), selenium (Se(IV, VI)), and antimony (Sb(III, V)), is also excellent.

Through this, it can be seen that the iron carbonate composite for heavy metal removal according to the present invention can be applied to adsorption and removal of other heavy metals in addition to arsenic, in particular, oxygen anions whose removal mechanism can be promoted by redox reaction.

Claims (17)

As an iron carbonate composite for heavy metal removal,
The iron carbonate complex for heavy metal removal is a complex in which an organic acid and iron carbonate are combined in the form of a complex,
The complex consists of secondary particles formed by aggregation of a plurality of primary particles,
The average diameter of the primary particles is 10 μm or less,
The BET specific surface area of the composite is 1 to 10 m ² /g of heavy metal removal iron carbonate composite. According to claim 1,
The average diameter of the composite is 20 μm to 100 μm of the iron carbonate composite for heavy metal removal. According to claim 1,
The heavy metal is an iron carbonate complex for heavy metal removal comprising a cationic heavy metal or an anionic heavy metal. According to claim 1,
The surface of the primary particles is an iron carbonate composite for heavy metal removal having a three-dimensional pore structure such as a honeycomb shape. According to claim 1,
The organic acid is an iron carbonate complex for heavy metal removal including two or more carboxyl groups. 6. The method of claim 5,
The organic acid is an iron carbonate complex for heavy metal removal comprising at least one of citric acid, oxalic acid, tartaric acid, fumaric acid, malic acid, malon and maleic acid. According to claim 1,
The iron carbonate composite for heavy metal removal has an organic acid content of 10 wt% to 20 wt% of the iron carbonate composite for heavy metal removal. According to claim 1,
The heavy metal adsorption rate of the iron carbonate composite for heavy metal removal is 60 wt% or more under anoxic conditions. 9. The method of claim 8,
The anaerobic condition is O ₂ < 1 ppm, [DO] = 0.00 ~ 0.05 ppm, H ₂ = 2-3%, CO ₂ = iron carbonate composite for heavy metal removal of 500 ~ 600 ppm. According to claim 1,
The complex is an iron carbonate complex for heavy metal removal including redox reaction with heavy metals as a heavy metal removal mechanism. heating; and removing oxygen from deionized water by using any one or more of a mixed gas injection method including hydrogen gas;
First and second reactions of preparing a first reaction solution by mixing iron ions and an organic acid with deionized water from which oxygen has been removed, and mixing hydrogen carbonate ions and an organic acid with deionized water from which oxygen has been removed to prepare a second reaction solution solution preparation step; and
Mixing the first and second reaction solutions, filtering and drying to prepare a complex in which an organic acid and iron carbonate are combined in the form of a solid complex,
The first and second reaction solutions are independently mixed with an organic acid having a concentration of 2 mM to 8 mM. 12. The method of claim 11,
The step of removing oxygen from deionized water may include heating the deionized water to a temperature of 100° C. to 150° C. for 10 minutes to 30 minutes to primarily remove oxygen; and
A method of manufacturing an iron carbonate complex for heavy metal removal, comprising: injecting and purging a mixed gas containing hydrogen and nitrogen into deionized water from which oxygen has been primarily removed to secondaryly remove oxygen. 12. The method of claim 11,
In the preparation of the first and second reaction solutions, the first reaction solution contains 0.01 M to 1.5 M of iron ions. 12. The method of claim 11,
In the first and second reaction solution preparation steps, the second reaction solution contains 0.01 M to 1.5 M hydrogen carbonate ions. 12. The method of claim 11,
The reaction solution mixing step of preparing the complex includes injecting the first reaction solution into the second reaction solution with stirring for 1 to 6 hours, and aging with stirring for 20 to 30 hours. Iron carbonate complex for heavy metal removal manufacturing method.
The organic acid is citric acid, oxalic acid, tartaric acid, fumaric acid, malic acid, a method of manufacturing an iron carbonate complex for heavy metal removal comprising any one or more of malon and maleic acid. 12. The method of claim 11,
The composite prepared in the step of preparing the composite consists of secondary particles formed by aggregation of a plurality of primary particles,
The average diameter of the primary particles is 10 μm or less,
The surface of the primary particles is a three-dimensional honeycomb (honeycomb) form of a method of manufacturing an iron carbonate composite for heavy metal removal. 12. The method of claim 11,
The method of manufacturing an iron carbonate composite for heavy metal removal further comprising the step of separating, washing and drying the precipitate after the step of preparing the composite.

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