Method of preparation of chelate compounds of humic acid and iron(ii / iii) ions, method of utilization of chelate compounds of humic acid and iron(II) ions

Abstract

To provide a method for simply recovering iron(II) and iron(III) ions by humic acid by focusing on the liquid nature of solutions in which iron(II) and iron(III) ions are dissolved and a method for utilizing the recovered iron(II) and iron(III) ions.SOLUTION: A method for preparing aggregate 2 containing chelate compounds of humic acid and iron(II) ions includes a step of obtaining aggregate 1 containing chelate compounds of humic acid and iron(II) ions from a solution containing humic acid and iron(II) ions at a pH of 1 to 5, and an aggregate 22 contains chelate / hydrothermal synthesis of humic acid and iron(III) ions, obtained by further hydrothermal synthesis of aggregate 2 containing chelate compounds of humic acid and iron(III) ions, which is obtained from a solution containing humic acid and iron(III) ions with a pH of 1 to 5.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for preparing a chelate compound of humic acid and iron (II / III) ions, a method for using the chelate compound of humic acid and iron (II) ions, and a hydrothermal synthesis of the chelate compound of humic acid and iron (III) ions. [Background technology]

[0002] When iron ions are dissolved in water, they must be treated to meet the wastewater standards. The most common method of treatment is to remove the iron ions by adsorbing them with an adsorbent.

[0003] Patent Document 1 discloses a method for preventing blockage of collection and drainage pipes in collection and drainage facilities, in which undecomposed organic matter from wood, grass, and residues is soaked in an appropriate amount of strongly acidic organic acid produced in the charcoal manufacturing process and allowed to cure for a long period of time, producing fulvic acid and humic acid, which are then solidified and used to adhere to the blockage, thereby maintaining the ionization of the salts and reducing adhesion to the collection and drainage pipes. Furthermore, Patent Document 2 discloses that the electrolytic cell includes an electrolytic cell into which water to be treated containing humic substances flows, and a first electrode and a second electrode immersed in the water to be treated, and that the first electrode and the second electrode are arranged so that, when a voltage is applied, a first product formed by a reaction between the humic substances and iron ions on the anode side and a second product formed by a reaction between hydroxide ions and iron ions on the cathode side coagulate to form flocs.

[0004] Non-Patent Document 1 describes that when a flocculant is used to recover iron ions, the addition of humic acid affects the formation of flocs. Furthermore, Non-Patent Document 2 describes that iron (III) ions and a carboxyl group of humic acid form a chelate bond. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2022-172037 A [Patent Document 2] JP 2023-050354 A [Non-patent literature]

[0006] [Non-Patent Document 1] X. Li, NJD Graham, W. Deng, M. Liu, T. Liu, W. Yu, The formation of planar crystalline flocs of γ-FeOOH in Fe(II) coagulation ang the influence of humic acid. Water Research, 185 (2020) 116250. [Non-Patent Document 2] SA Boyd, L. Sommers, DW Nelson, Copper (II) and iron (III) complexation by the carboxylate group of humic acid. Soil Science Society of America Journal, 45 (1981) 1241. Summary of the Invention [Problem to be solved by the invention]

[0007] However, there has been a problem in that no effort has been made to recover iron (II) ions or iron (III) ions simply while maintaining their ionic state by focusing on the properties of the solution in which iron (II) ions or iron (III) ions are dissolved. Therefore, the present invention focuses on the properties of the solution in which iron (II) ions or iron (III) ions are dissolved, and aims to provide a method for recovering iron (II) ions and iron (III) ions simply by using humic acid, and a method for utilizing the recovered iron (II) ions. [Means for solving the problem]

[0008] The present invention which solves the above problems is as follows. [1] A method for preparing an aggregate containing a humic acid-iron (II) ion chelate compound, the method comprising the step of obtaining an aggregate containing a chelate compound of humic acid and iron (II) ions from a solution containing humic acid and iron (II) ions and having a pH of 1 to 5. Here, the aggregate containing a humic acid-iron (II) ion chelate compound describes the properties of a humic acid-iron (II) ion chelate compound, and in chemical substance means a humic acid-iron (II) ion chelate compound. [2] The method for preparing an aggregate containing a humic acid-iron (II) ion chelate compound according to [1], wherein the pH is 2 to 4. [3] A method for using the aggregate containing a chelate compound described in [1] or [2], comprising a step of supplying the aggregate containing the chelate compound into water. [4] [3] The water in the water includes a water body having a seaweed bed, and the method of using the aggregate containing the chelating compound in [1] or [2] is also provided. [5] An aggregate containing a humic acid-iron(III) ion chelate hydrothermal compound is obtained by further hydrothermally synthesizing an aggregate containing a chelate compound of humic acid and iron(III) ion obtained from a solution containing humic acid and iron(III) ion and having a pH of 1 to 5. The term "aggregate containing hydrothermal synthesis product of humic acid-iron(III) ion chelate" refers to an aggregate containing hydrothermal synthesis product of humic acid and ferric ion chelate compound. The term "aggregate containing hydrothermal synthesis product of humic acid-iron(III) ion chelate" refers to a description of the properties of the hydrothermal synthesis product of humic acid-iron(III) ion chelate, and in chemical substance refers to the hydrothermal synthesis product of humic acid-iron(III) ion chelate. [6] A method for preparing an aggregate containing a chelate compound of humic acid and iron(III) ions, the method comprising: obtaining an aggregate containing a chelate compound of humic acid and iron(III) ions from a solution having a pH of 1 to 5 containing humic acid and iron(III) ions; and further hydrothermally synthesizing the aggregate. Effect of the Invention

[0009] According to the method of the present invention for preparing an aggregate containing a humic acid-iron(II) ion chelate compound and an aggregate containing a humic acid-iron(III) ion chelate compound, iron(II) ions and iron(III) can be efficiently recovered using humic acid. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing a method for preparing an aggregate containing a chelate compound of humic acid and iron (II) ions and an aggregate containing a chelate compound of humic acid and iron (III) ions, which is one embodiment of the present invention. [Diagram 2] FIG. 1 shows (a) the recovery rate of iron (II) ions and (b) the recovery rate of iron (III) ions using humic acid. [Diagram 3] FIG. 1 shows XPS spectra of (a) an aggregate containing a chelate compound obtained from iron(II) ions, and (b) an aggregate containing a chelate compound obtained from iron(III) ions. [Figure 4] FIG. 1 shows the effect of (a) iron(II) nitrate nonahydrate and (b) iron(III) chloride hexahydrate on the recovery of iron(III) ions by humic acid. [Diagram 5] FIG. 1 is a graph showing the temperature dependence of iron (III) ion recovery rate by humic acid. [Figure 6] FIG. 1 shows a method for preparing aggregates containing humic acid-iron(III) ion chelate-hydrothermal synthesis. [Figure 7] This figure shows the results of an XRD study of the crystallinity of aggregates containing humic acid-iron(III) ion chelate-hydrothermal synthesis products. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be made without departing from the scope of the invention.

[0012] A chelate compound of humic acid and iron (II) ions or iron (III) ions (hereinafter sometimes referred to as "iron (II / III) ions") can be prepared (obtained) as aggregates 1 or 2 containing the chelate compound, and aggregates 3 or 4 of aggregates 1 or 2, respectively (see FIG. 1), by mixing an iron (II / III) ion-containing solution with a humic acid-containing solution and allowing to stand at a pH of 1 to 5. In the case of iron (II) ions, the pH of the solution containing humic acid and iron (II) ions is preferably 2 to less than 5, and more preferably 2 to 4, from the viewpoints of the oxidation degree of the iron ions and the solubility of humic acid.

[0013] The concentration of iron(II / III) ions in the iron(II / III) ion-containing solution is preferably 10 to 1000 ppm, more preferably 10 to 40 ppm, from the viewpoint of reaction efficiency with humic acid, while the concentration of humic acid in the humic acid-containing solution is preferably 5 to 1200 ppm, more preferably 5 to 100 ppm, from the viewpoint of aggregate formation efficiency.

[0014] The properties (state) of aggregate 3 of aggregate 1 are as follows (see Figure 1). It can be recovered as a precipitate and is brown in color. The amount produced varies depending on the mixed amounts of humic acid and the iron (II) ion-containing solution. The properties (state) of aggregate 4 of aggregate 2 are similar to those of aggregate 3 of aggregate 1, and no difference in properties due to the difference in the valence of the iron ions is observed.

[0015] Iron(II / III) ions can be supplied as ferric salts, e.g. chloride, nitrate or their hydrates, while humic acids can be supplied as reagents or extracted and purified from soils or streams.

[0016] The humic acid and iron (III) ion chelate hydrothermal synthesis product can be prepared by adding an aggregate containing a humic acid and iron (III) ion chelate compound (sometimes abbreviated as "humic acid-iron (III) ion aggregate") 2 to water (distilled water) preferably having a pH of 2 to 5, and then heating the mixture through hydrothermal synthesis. The synthesis temperature is preferably 80 to 260°C, more preferably 120 to 260°C. Through this synthesis, the humic acid-iron (III) ion aggregate 2 can be converted into α-Fe at temperatures of 180°C or higher. 2 O 3 As the temperature increases, the crystallinity and amount of precipitation change, resulting in a composite material containing humic acid.

[0017] For example, seaweed denudation is a problem in Japanese fishing grounds. Seaweed denudation is a phenomenon in which seaweed drastically decreases and disappears in coastal waters where it grows abundantly, causing seaweed to stop growing. This leads to a decrease in abalone, turban shells, and other organisms, dealing a major blow to coastal fishing. Iron (II) ions are effective in restoring seaweed beds. However, iron (II) ions are easily oxidized, and even in water, iron (II) ions are easily oxidized to iron (III) ions.

[0018] Therefore, if iron (II) ions are supplied to water areas with seaweed beds where coastal denudation is a problem, the supplied iron (II) ions can restore the seaweed beds. In other words, the supply of aggregates containing the chelate compound of humic acid and iron (II) ions according to the present invention can restore the seaweed beds. EXAMPLES

[0019] (Preparation of aggregates of humic acid and iron (II / III) ions) As shown in Fig. 1, 15 mL of the iron (II / III) ion-containing solution and 30 mL of the humic acid-containing solution were mixed and allowed to stand (pH 3 after mixing, standing time 48 hours) in a capped sample tube container (hereinafter sometimes simply referred to as "container") to prepare aggregates of humic acid and iron (II) ions (aggregates containing a chelate compound) 1 and aggregates of humic acid and iron (III) ions (aggregates containing a chelate compound) 2. Then, supernatants 51 from the preparation of aggregate 1 and 52 from the preparation of aggregate 2 were collected. The iron(II) ion-containing solution was prepared by dissolving iron(II) chloride tetrahydrate (reagent) in water, and the iron(III) ion-containing solution was prepared by dissolving iron(III) chloride hexahydrate (reagent) in water. The iron(II) ion and iron(III) ion concentrations were 10, 20, and 40 ppm. On the other hand, humic acid-containing solutions were prepared by dissolving humic acid (reagent) in water, and the humic acid concentrations were 5, 10, 20, 30, 50, and 100 ppm.

[0020] The iron (II) ions and iron (III) ions in the supernatants 51 and 52 were quantified as follows to determine the recovery rates of the iron (II) ions and iron (III) ions. The iron (II / III) ion concentrations in the supernatants 51 and 52 obtained by centrifugation were determined using a high-frequency inductively coupled plasma emission spectrometer (Shimadzu Corporation, ICPS-7000), and the recovery rates were calculated from the difference from the initial concentrations.

[0021] (Recovery rate of iron (II / III) ions) The results of the iron (II) ion recovery test using humic acid are shown in Figure 2(a) for the recovery rate of iron (II) ions, and the results of the iron (III) ion recovery test using humic acid are shown in Figure 2(b) for the recovery rate of iron (III) ions. As shown in Figure 2(a), the iron(II) ion concentration (10, 20, 40 ppm) is used as a parameter, with the iron(II) ion recovery rate on the vertical axis and the humic acid concentration (0, 5, 10, 20, 30, 50, 100 ppm) on the horizontal axis. When the iron(II) ion concentration was 20 or 40 ppm, the iron(II) ion recovery rate tended to increase as the humic acid concentration increased. When the iron(II) ion concentration was 10 ppm, the iron(II) ion recovery rate tended to increase up to a humic acid concentration of 30 ppm, and became almost constant above 30 ppm. On the other hand, when the humic acid concentration was the same, the recovery rate of iron (II) ions increased in the order of iron (II) ion concentrations of 10 ppm, 40 ppm, and 20 ppm. From this, it is estimated that there is an optimal iron (II) ion concentration for improving the recovery rate of iron (II) ions (between 20 and 40 ppm in the example).

[0022] As shown in Figure 2(b), the iron(III) ion concentration (10, 20, 40 ppm) is used as a parameter, the vertical axis shows the recovery rate of iron(III) ions, and the horizontal axis shows the humic acid concentration (0, 5, 10, 20, 30, 50, 100 ppm). When the iron(III) ion concentration is 10 ppm and the humic acid concentration is 10 ppm, the recovery rate of iron(III) ions is 100%, but when the humic acid concentration changes from 20 ppm to 30 ppm, the recovery rate of iron(III) ions drops dramatically from about 80% to about 2%, and the recovery rate is nearly 0% up to higher humic acid concentrations.

[0023] On the other hand, when the iron(III) ion concentration was 20 ppm, the recovery rate of iron(III) ions increased up to a humic acid concentration of 20 ppm, and remained almost constant at about 95% at higher humic acid concentrations. In particular, when the humic acid concentration was between 10 ppm and 20 ppm, the recovery rate of iron(III) ions increased rapidly. Furthermore, when the iron(III) ion concentration was 40 ppm, the recovery rate of iron(II) ions increased as the humic acid concentration increased. In particular, when the humic acid concentration was between 20 ppm and 50 ppm, the recovery rate of iron(III) ions increased rapidly from about 15% to about 100%, and even at higher humic acid concentrations, the recovery rate remained nearly 100%.

[0024] (Fe ion valence evaluation) The valence of the iron ions was evaluated by XPS spectrum analysis of aggregates 1 and 2. The XPS analysis conditions were as follows. Dried aggregates 1 and 2 were analyzed using a photoelectron spectrometer (ULVAC-PHI PHI5000 VersaProbe) with Al Kα radiation, a spot size of 100 μm, and a take-off angle of 45°. At this time, the bond energy was normalized by C1s.

[0025] As shown in Figure 3(a), a peak derived from iron (II) ions was detected at approximately 717 eV in Aggregate 1, confirming that Aggregate 1 retained the state of iron (II) ions. As shown in Figure 3(b), a peak derived from iron (III) ions was detected at approximately 719 eV in Aggregate 2, confirming that Aggregate 2 retained the state of iron (III) ions.

[0026] (Effect of anions on iron(III) ion recovery) In the iron(III) ion recovery test using humic acid, iron(III) nitrate nonahydrate (reagent) was used as the solute instead of iron(II) chloride tetrahydrate (reagent), and the iron(III) concentration was set to 10, 20, 30, 40, and 50 ppm, and the iron(III) ion recovery rate was determined in the same manner. By changing iron(II) chloride tetrahydrate (reagent) to iron(III) nitrate nonahydrate (reagent), the anion was changed from chloride ion to nitrate ion, and the effect of the anion on the iron(III) ion recovery rate was investigated.

[0027] As shown in Figure 4(a), the recovery rate trends at iron(III) concentrations of 10, 20, 30, and 40 ppm were almost the same as those in Figure 2(b). That is, the recovery rate patterns of iron(III) ions at iron(III) concentrations of 10, 20, 30, and 40 ppm were similar to those at iron(III) concentrations of 10, 20, 30, and 40 ppm. In addition, when the iron(III) ion concentration was 50 ppm, the recovery rate tended to be almost the same as that at an iron(III) ion concentration of 40 ppm, but the recovery rate was slightly lower up to a humic acid concentration of 50 ppm. Meanwhile, Figure 4(b) also shows the case of an iron(III) ion concentration of 50 ppm in addition to Figure 2(b). The tendency of the recovery rate at an iron(III) ion concentration of 50 ppm was similar to that at an iron(III) ion concentration of 40 ppm, but the recovery rate was slightly lower at humic acid concentrations other than 100 ppm.

[0028] (Temperature dependence of iron(III) ion recovery rate) In a test to recover iron (III) ions using humic acid, iron (III) nitrate nonahydrate (reagent) was used as the solute, and the recovery rate of iron (III) ions was determined (n=3) when the humic acid concentration was 50 ppm, the iron (III) concentration was 50 ppm, the recovery time was 24 hours, the pH after mixing was 3, and the temperatures were 20, 25, 30, 35, and 40°C. As a result, as shown in Figure 5, the recovery rate of iron (III) ions improved with increasing temperature. This is presumably because the diffusivity of humic acid and iron ions improves with increasing temperature, promoting the formation of chelate compounds and their aggregation.

[0029] (Functionalization of humic acid-iron(III) ion aggregates) Unlike humic acid-iron(II) ion aggregates (aggregates containing humic acid-iron(II) ion chelate compounds), humic acid-iron(III) ion aggregates are not very useful as they are. Therefore, as shown in Figure 6, we synthesized a humic acid-iron(III) ion chelate hydrothermal compound to functionalize the humic acid-iron(III) ion aggregates. Unlike humic acid-iron(III) ion aggregates, the humic acid-iron(III) ion chelate hydrothermal compound can be used to, for example, 2+ It can be assumed that the humic acid-iron(III) ion chelate hydrothermal synthesis can adsorb Cu ions. 2+ Contains iron oxide that adsorbs ions, etc., and Cu 2+ This is because it contains a carboxyl group that forms a chelate bond with an ion.

[0030] First, the humic acid-containing solution and the iron (III) ion-containing solution were mixed in a container to prepare humic acid-iron (III) ion aggregate 12 (preparation for one batch). The iron (III) ion-containing solution used iron (III) nitrate nonahydrate (reagent) as a solute, and the iron (III) ion concentration was 20 ppm. On the other hand, the humic acid-containing solution had a humic acid concentration of 30 ppm. Next, the aggregate 12 for 12 batches was added to 13.5 mL of distilled water (pH 3) in a container, and hydrothermal synthesis was performed to prepare aggregate 22 containing a humic acid-iron (III) ion chelate-hydrothermal synthesis product. The synthesis temperatures in the hydrothermal synthesis were 120, 180, 200, and 260 °C, and the reaction time was 24 hours. Figure 6 shows that the humic acid-iron(III) ion aggregate 12 becomes a humic acid-iron(III) ion chelate-hydrothermal synthesis aggregate (humic acid-iron(III) ion hydrothermal synthesis aggregate) 22, and the collection of humic acid-iron(III) ion aggregates 14 becomes a collection of humic acid-iron(III) ion chelate-hydrothermal synthesis aggregate (humic acid-iron(III) ion hydrothermal synthesis aggregate) 24. The properties (state) of the collection 24 of the aggregates 22 were as follows: The amount of the aggregates produced varied depending on the hydrothermal synthesis and iron ion recovery conditions, and the aggregates were black or reddish brown powder.

[0031] (Investigation of crystallinity by XRD) The XRD patterns of the samples prepared under each temperature condition shown in Figure 7 reveal the following. For example, when the synthesis temperature is 260°C, Fe 3 O 4 and α-Fe 2 O 3 In detail, the crystal phase of the obtained sample was α-Fe 2 O 3 is the main component, Fe 3 O 4 Each crystal had no anisotropy. As the synthesis temperature increased from 120°C to 260°C, the half-width became smaller and the crystallinity became higher. The XRD analysis conditions were as follows: The prepared samples were analyzed using an X-ray diffractometer (MiniFlex manufactured by Rigaku Corporation) with a tube voltage of 40 kV and a tube current of 15 mA using Co Kα radiation. [Industrial Applicability]

[0032] Since divalent iron ions have an effect on the recovery of coastal barren areas, they can contribute to improving the water quality environment in marine areas. On the other hand, trivalent iron ions can be presumably recycled as iron oxide through heat treatment. With the expected increase in ESG investments in the future that address environmental issues in addition to water treatment, this invention can contribute to the growth of the market to which it is applicable. [Explanation of symbols]

[0033] 1: Humic acid - aggregates containing chelates of iron(II) ions 2: Humic acid - aggregates containing chelates of iron(III) ions 3: Humic acid - a collection of aggregates containing chelated compounds of iron(II) ions 4: Humic acid - a collection of aggregates containing chelated compounds of iron(III) ions 12: Humic acid - aggregates containing chelates of iron(III) ions 14: A collection of aggregates containing humic acid-iron(III) ion chelate-hydrothermal synthesis products 22: Humic acid-iron(III) ion chelate-hydrothermal synthesis aggregates 24: A collection of aggregates containing humic acid-iron(III) ion chelates and hydrothermal compounds 51: Supernatant from preparation of humic acid-iron(II) ion chelate aggregates 52: Supernatant from preparation of humic acid-iron(III) ion chelate aggregates

Claims

1. A method for preparing an aggregate containing a humic acid-iron (II) ion chelate compound, the method comprising the step of obtaining an aggregate containing a chelate compound of humic acid and iron (II) ions from a solution having a pH of 1 to 5 containing the humic acid and iron (II) ions.

2. The method for preparing an aggregate containing a humic acid-iron (II) ion chelate compound according to claim 1, wherein the pH is 2 to 4.

3. A method for using the aggregate containing a chelate compound according to claim 1 or 2, comprising the step of supplying the aggregate containing the chelate compound into water.

4. A method for utilizing the aggregate containing the chelate compound according to claim 1 or 2, wherein the water according to claim 3 includes a water area having a seaweed bed.

5. An aggregate containing a humic acid-iron (III) ion chelate hydrothermal synthesis product is obtained by further hydrothermally synthesizing an aggregate containing a chelate compound of humic acid and iron (III) ions obtained from a solution containing humic acid and iron (III) ions and having a pH of 1 to 5.

6. A method for preparing an aggregate containing a hydrothermal synthesis product of a chelate of humic acid and iron (III) ions, comprising: obtaining an aggregate containing a chelate compound of humic acid and iron (III) ions from a solution containing humic acid and iron (III) ions and having a pH of 1 to 5; and further hydrothermally synthesizing the aggregate.

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