JP2016187795A - Heavy metal adsorbent and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heavy metal adsorbent that prevents manganese oxide produced by microorganisms from becoming an anaerobic state with a lapse of time and thus prevents decrease in cation adsorption ability, and a method for producing the same.SOLUTION: The present invention provides a heavy metal adsorbent in which manganese oxide produced by microorganisms is subjected to heat treatment and organic matter derived from microorganisms is sufficiently removed. In the heat treatment, manganese oxide produced by microorganisms is heated in the range of 300-500°C, and the heating temperature is regulated at a fixed temperature (500°C) or less, so that the cation adsorption ability of manganese oxide can be maintained.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a heavy metal adsorbent that adsorbs metal cations such as cadmium and a method for producing the same.

  Waste and natural soil may contain hazardous substances such as heavy metals such as lead, mercury, and cadmium. Metals pollute the environment as a result of leaching into the leachate as they are washed out by rainwater infiltration. For such environmental pollution countermeasures, that is, heavy metal countermeasures, various methods are known such as insolubilization using chemicals such as chelating agents, calcium compounds, sulfides, iron powder, and suppression of elution from soil by cement solidification.

  Among the measures for heavy metals, a method using a heavy metal adsorbent is known. Among heavy metals, cadmium is known to be removed from the environment using manganese oxide as a cadmium adsorbent. It is known that manganese oxide to be used as a cadmium adsorbent is particularly slow in chemical oxidation of manganese in the natural environment and requires a catalytic action of microorganisms (Non-patent Document 1). Non-Patent Document 1 describes the structure and characteristics of manganese oxide produced by microorganisms.

  Non-Patent Document 2 describes that an oxide having a similar structure to a manganese oxide produced by a microorganism is chemically synthesized. However, it has been pointed out that chemically synthesized manganese oxide has lower cadmium adsorption ability than manganese oxide produced by microorganisms (Non-patent Document 3).

Tebo, BM, Bargar, JR, Clement, BG, Dick, GJ, Murray, KJ, Parker, D., Verity, R., Webb, SM (2004) Biogenic manganese oxides: properties and mechanisms of formation.Annu. Rev. Earth Planet Sci., 32, 287-328. Villalobos, M., Toner, B., Bargar, J., Sposito, G. (2003) Characterization of the manganese oxide produced by Pseudomonas putida strain MnB1. Geochim. Cosmochim. Acta, 67, 2649-2662. Tani, Y., Ohashi, M., Miyata, N., Seyama, H., Iwahori, K., Soma, M. (2004) Sorption of Co (II), Ni (II), and Zn (II) on biogenic manganese oxides produced by a Mn-oxidizing fungus, strain KR21-2. J. Environ. Sci. Health A, 39, 2641-2660.

  However, manganese oxide produced by microorganisms tends to become anaerobic over time. When manganese oxide is placed in an anaerobic state, it is reductively dissolved by the action of microorganisms, so that there is a problem that the cations contained in the object to be treated cannot be sufficiently removed or the cations once adsorbed are released.

  Then, in view of the practical use mentioned above, an object of this invention is to provide the heavy metal adsorbent which prevented the fall of cation adsorption ability, and its manufacturing method.

  As a result of intensive studies by the present inventors in order to achieve the above-described object, when manganese oxide is produced by a microorganism, anaerobic reaction is caused because oxygen in the environment is consumed when organic matter derived from the microorganism is decomposed. It has been found that it is easy to be in a state, and that organic substances derived from microorganisms and the like can be removed by heating to prevent a decrease in cation adsorption capacity, and the present invention has been completed. The present invention includes the following.

(1) A heavy metal adsorbent obtained by heat-treating manganese oxide produced by a microorganism.
(2) The heavy metal adsorbent according to (1), wherein the heat treatment heats manganese oxide produced by a microorganism to a range of 300 to 500 ° C.
(3) A method for producing a heavy metal adsorbent, comprising a step of heat-treating manganese oxide produced by a microorganism.
(4) The method for producing a heavy metal adsorbent according to (3), wherein the heat treatment heats manganese oxide produced by a microorganism to a range of 300 to 500 ° C.

It is a schematic block diagram which shows the application example of the heavy metal adsorbent which concerns on this invention. It is a schematic block diagram which shows the other application example of the heavy metal adsorbent which concerns on this invention. It is a characteristic view which shows the relationship between heat processing temperature and the amount of organic substances contained in manganese oxide, and the relationship between heat processing temperature and cation adsorption ability. It is a characteristic view which shows the change of crystallinity with heat processing temperature.

Hereinafter, the heavy metal adsorbent according to the present invention will be described in detail with reference to the drawings.
The heavy metal adsorbent according to the present invention is obtained by heat-treating manganese oxide produced by a microorganism. Here, the manganese oxide produced by the microorganism means manganese oxide produced by culturing a microorganism having manganese oxidizing ability in the presence of manganese.

  It does not specifically limit as microorganisms which have manganese oxidation ability, A conventionally well-known microorganism can be used. For example, a newly isolated U9-1i strain (Miyata, N., Saito, K., Okano, K., and Ozaki, Y .: Manganese () that is believed to be widely involved in manganese oxidation in the environment. II) oxidation by a unique alphaproteobacterium that grows symbiotically in cocultures with a broad range of microorganisms, 19th International Symposium on Environmental Biogeochemistry, Environmental Changes and Sustainability of Biogeochemical Cycling (Hamburg, Germany), Abstract, p. 166 (September 18, 2009) ) Can be used.

  In addition, manganese-oxidizing bacteria and manganese-oxidizing fungi can be used as microorganisms having manganese oxidizing ability.

  Manganese-oxidizing bacteria are ubiquitous in the environment (rivers, lakes, soils, oceans, etc.) (BM Tebo, HA Johnson, JK McCarthy, AS Templeton (2005). Geomicrobiology of manganese (II) oxidation. Trends in Microbiology, 13, 421-428. HL Ehrlich, DK Newman (2009). Geomicrobiology, 5th ed. CRC Press, New York.

Furthermore, as a manganese-oxidizing bacterium, Leptothrix discophora (LF Adams, WCGhiorse (1987). Characterization of extracellular Mn ²⁺ -oxidizing activity and isolation of an Mn ²⁺ -oxidizing protein from Leptothrix discophora SS-1 Journal of Bacteriology, 169, 1279-1285.).

  Furthermore, as manganese-oxidizing bacteria, Pseudomonas putida (M. Okazaki, T. Sugita, M. Shimizu, Y. Ohode, K. Iwamoto, EW de Vrind-de Jong, JPM de Vrind, PLAM) Corstjens (1997). Applied and Environmental Microbiology, 63, 4793-4799.).

  Furthermore, as manganese-oxidizing bacteria, Pedomicrobium sp. (EI Larsen, LI Sly, AG McEwan (1999). Manganese (II) adsorption and oxidation by whole cells and a membrane fraction of Pedomicrobium sp. ACM 3067. Archives of Microbiology, 171, 257-264.

  Furthermore, examples of manganese-oxidizing bacteria include Arthrobacter sp. (H.L. Ehrlich, D.K. Newman (2009). Geomicrobiology, 5th ed. CRC Press, New York.).

  Examples of manganese-oxidizing fungi include various incomplete fungi such as Acremonium strictum (Ascomycota) that are widely inhabited in soil and water environments (N. Miyata, K. Maruo, Y. Tani, H. Tsuno, H. Seyama, M. Soma, K. Iwahori (2006). Production of biogenic manganese oxides by anamorphic ascomycete fungi isolated from streambed pebbles. Geomicrobiology Journal, 23, 63-73.).

  Microorganisms having manganese oxidizing ability usually produce manganese oxide outside the cell, and the cell surface layer is covered with manganese oxide. The heavy metal adsorbent according to the present invention is derived from microorganisms having manganese oxidizing ability by culturing microorganisms having manganese oxidizing ability in the presence of manganese and then heating the dehydrated or dried culture at a predetermined temperature. Organic matter is removed. Here, the removal of organic matter means removal of 50% or more, preferably 60% or more, more preferably 70% or more, more preferably 80% or more, and most preferably 90% or more of the organic matter contained before the temperature treatment. Means. The amount of organic matter contained in the manganese oxide produced by the microorganism is not particularly limited, but can be measured as the carbon content using an elemental analyzer, for example.

  In the heavy metal adsorbent according to the present invention, organic substances derived from microorganisms are sufficiently removed, so that an anaerobic state is prevented even when used over a long period of time. Structural change / decomposition can be suppressed. In addition, although it does not specifically limit in the heat processing for removing the organic substance derived from the microorganisms which have manganese oxidation ability at this time, it heats more than the temperature which can remove an organic substance. In the heat treatment for removing organic substances derived from microorganisms having manganese oxidizing ability, for example, the temperature is preferably 300 ° C. or higher, more preferably 350 ° C. or higher, and further preferably 400 ° C. or higher. Most preferably, the temperature is set to ° C or higher. On the other hand, when manganese oxide is heated at a high temperature, the decrease in cation adsorption ability of manganese oxide may become significant. Therefore, in the heat treatment for removing organic substances derived from microorganisms having manganese oxidizing ability, for example, the temperature is preferably less than 700 ° C., more preferably less than 650 ° C., and further preferably less than 600 ° C. Preferably, it is less than 550 degreeC.

  The heavy metal adsorbent according to the present invention configured as described above can be used in an environment contaminated with heavy metals. Examples of the environment contaminated with heavy metals include groundwater, soil (including rocks), waste, drainage, rivers, lakes, the sea, or water that has passed through the contaminated environment.

  The heavy metal adsorbent according to the present invention can remove heavy metals contained in the environment by adsorbing metal cations such as cadmium contained in the environment described above with manganese oxide.

  As an example of applying the heavy metal adsorbent according to the present invention to an environment contaminated with heavy metals, for example, as shown in FIG. 1, a facility in which wastes containing heavy metals are accumulated can be mentioned. In the application example shown in FIG. 1, the heavy metal adsorbent according to the present invention can be used as the purification wall 1 buried in the ground between the facility site and the outside. When the heavy metal adsorbent according to the present invention is used as the purification wall 1, even if heavy metal is eluted from the waste accumulated in the facility site into the groundwater (showing the flow of groundwater as indicated by arrows in FIG. 1), Heavy metal can be removed when groundwater passes through the purification wall 1.

  Moreover, as another example to which the heavy metal adsorbent according to the present invention is applied, as shown in, for example, FIG. In the application example shown in FIG. 2, a so-called excavation ladle 3 containing heavy metal is placed on the heavy metal adsorbent 2 according to the present invention, and the slope of the excavation ladle 3 is impermeable, and the surface of the excavation ladle 3 Paving. Thereby, even if heavy metal elutes from the excavation ladle 3 including heavy metal, it is possible to prevent heavy metal from reaching the ground 4 below the heavy metal adsorbent 2 by being adsorbed by the heavy metal adsorbent 2.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, the technical scope of this invention is not limited to a following example.

[Example 1]
In this example, changes in carbon content and changes in cadmium adsorption ability when heat treatment was performed on manganese oxide produced by microorganisms were examined, and changes in crystallinity due to heat treatment were also examined.

<Preparation of manganese oxide-containing sludge>
An integrated culture system of manganese-oxidizing bacteria prepared using riverbed biofilm as a seed was used as a test for manganese sludge. The composition of the culture solution at the time of accumulation is shown in Table 1. Using a 20 L polybucket, 15 L of medium was added and large-scale culture was performed. For aeration, two air pumps for raising ornamental fish were used, and aeration and agitation were performed from the bottom of the bucket with an air balloon. Culturing was carried out at room temperature using a batch method. When the medium was changed, the culture was allowed to stand for about 15 minutes to settle the culture (hereinafter referred to as Mn-adapted sludge), the supernatant was removed by decantation, and a fresh medium was added. The frequency of medium exchange was 2-3 times a week. At the time of medium exchange, the Mn (II) concentration in the supernatant was simply monitored using a pack test, and it was confirmed that all dissolved Mn (II) was oxidized and removed from the aqueous phase. Manganese oxide-containing sludge (hereinafter referred to as manganese sludge) was prepared by the above culture operation. In the experiment, manganese sludge freeze-dried was used. The Mn content of manganese sludge subjected to the following experiment was 23.2%.

<Heat treatment>
Tens of mg of the test manganese sludge was dispensed into a quartz crucible, heat-treated at 100, 300, 500, and 700 ° C. for 1 hour using a muffle furnace, respectively, and then allowed to cool in a desiccator.

<Measurement of carbon content>
The carbon content was measured using a CHN coder 2400CHN manufactured by PerkinElmer.

<Measurement of cadmium adsorption amount>
10 mg of test sample was dispensed into 125 mL hardened hard vials (V-100 manufactured by Nidec Rika Glass Co., Ltd., sealed with PTFE-coated butyl rubber stoppers and aluminum seals), and cadmium standard solution (manufactured by Wako Pure Chemical Industries, Ltd.) adjusted to the appropriate concentration 50 After adding mL, the pH was adjusted to 5.8 ± 0.1, and the mixture was shaken for 24 hours with a vertical rotary shaker. The sample after shaking was centrifuged at 10,000 rpm for 10 minutes, and the supernatant was filtered through a 0.45 μm syringe filter, and the cadmium concentration was measured. The cadmium concentration was measured using ICP / MS (Agilent: 7700e). The amount of cadmium adsorbed at each equilibrium concentration was plotted on a graph, approximated by the Freundlich type adsorption isotherm, and the amount of cadmium adsorbed when the environmental standard of 0.01 mg / L was used as the equilibrium concentration was calculated.

  FIG. 3 shows changes in carbon content and cadmium adsorption amount (equilibrium concentration = 0.01 mg / L) at each heating temperature measured by the above experimental method. As can be seen from FIG. 3, organic substances contained in the manganese oxide produced by the microorganisms could be significantly removed by the heat treatment. It was also found that when the heating temperature was 300 ° C. or higher, almost all organic substances contained in manganese oxide produced by microorganisms could be removed.

  On the other hand, when the temperature of heat treatment was high, it became clear that cation adsorption ability fell. In other words, it has been clarified that the cation adsorption ability by manganese oxide can be maintained by setting the temperature of the heat treatment to a certain temperature or lower (for example, 500 ° C.).

<Examination of crystallinity by X-ray diffraction>
XRD analysis of manganese sludge heat-treated under each condition was performed using an X-ray diffractometer (Rigaku RINT-2500). CuKα rays (40 kV, 20 mA) were used as X-rays, and the scan speed was 1.0 ° / min.

The results are shown in FIG. As can be seen from FIG. 4, the XRD pattern of untreated and heat-treated manganese sludge at 100 ° C. was consistent with the pattern of layered manganese (IV) oxide (bernite; δ-MnO ₂ ). On the other hand, when heated to 300 ° C. or higher, phase conversion to (Mn ₃ O ₄ ; Mn (II, III) oxide) was observed. It was also found that when the heating temperature is further increased, the peak intensity corresponding to Mn ₃ O ₄ is relatively increased, and the crystallinity is greatly increased. In combination with the results shown in FIG. 3, it was considered that when the temperature of the heat treatment is high, the crystallinity of manganese oxide greatly increases, so that the cation adsorption ability decreases.

DESCRIPTION OF SYMBOLS 1 ... Purification wall, 2 ... Heavy metal adsorbent, 3 ... Excavation, 4 ... Ground

Claims (4)

  A heavy metal adsorbent obtained by heat-treating manganese oxide produced by microorganisms.   The heavy metal adsorbent according to claim 1, wherein the heat treatment heats manganese oxide produced by a microorganism to a range of 300 to 500 ° C.   A method for producing a heavy metal adsorbent, comprising a step of heat-treating manganese oxide produced by a microorganism.   4. The method for producing a heavy metal adsorbent according to claim 3, wherein the heat treatment heats manganese oxide produced by the microorganism to a range of 300 to 500C.

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