Method for the simple synthesis of birnessite

Abstract

The invention aims to produce Birnessite with minimal effort, without environmentally harmful synthesis byproducts and with the largest possible surface area. The proposed method involves adding lactate as a reducing agent to a permanganate solution instead of the acids and bases used previously. This simple process allows for the production of highly reactive biressite, which can be used, for example, in the remediation of contaminated sites. The large specific surface area, rarely achieved to date, is also particularly noteworthy. Large surface areas can lead to a greater degradation of organic compounds.

Description

[0001] The invention relates to a process for the synthesis of birnessite with a high surface area, which is produced in a simple manner and without strong acids and bases. Permanganate, the only toxic substance, is completely reduced to birnessite during the reaction.

[0002] The classification of birnessite with regard to its CAS registration number is not uniform. A total of five different CAS numbers are used for birnessite. This description refers to the most commonly used CAS number, 12244-32-5.

[0003] The process described here can be used to produce highly reactive birnessite, which can be used in the remediation of contaminated sites. Particularly noteworthy is the large specific surface area, which has rarely been achieved so far. Large surface areas can lead to greater degradation of organic compounds. Barrett and McBride (KA Barrett and MB McBride: Oxidative degradation of glyphosate and aminomethylphosphonate by manganese oxide, Environmental Science & Technology 39, 2005, 9223-9228) suspect that the oxidative degradation of glyphosate is limited by the surface area of ​​birnessite. Jung and colleagues (JW Jung, S. Lee, H. Ryu, KH Kang, and K.Nam: Detoxification of phenol through bound residue formation by birnessite in soil: Transformation kinetics and toxicity, Journal of Environmental Science and Health Part a-Toxic / Hazardous Substances & Environmental Engineering 43, 2008, 255-261) explain a reduced transformation of phenol by the occupation of reactive sites on the surface of the birnessite. A large specific surface also offers more adsorption sites for particulate and dissolved inorganic and organic components (P. Loganath and RG Burau: Sorption of heavy-metal ions by a hydrous manganese oxide, Geochimica Et Cosmochimica Acta 37, 1973, 1277-1293; BA Manning, SE Fendorf, B. Bostick and DL Suarez: Arsenic(III) oxidation and arsenic(V) adsorption reactions on synthetic birnessite, Environmental Science & Technology 36, 2002, 976-981; H. Selig, TM Keinath and WJWeber: Sorption and manganese-induced oxidative coupling of hydroxylated aromatic compounds by natural geosorbents, Environmental Science & Technology 37, 2003, 4122-4127). Furthermore, microporous birnessite is an effective material for the removal of arsenic in drinking water treatment (W. Driehaus, R. Seith, and M. Jekel: Oxidation of arsenate(III) with manganese oxides in water-treatment, Water Research 29, 1995, 297-305). Birnessite also has a high affinity for lead and has already been successfully tested for the immobilization of lead in soils (SE O'Reilly and MF Hochella: Lead sorption efficiencies of natural and synthetic Mn and Fe-oxides, Geochimica Et Cosmochimica Acta 67, 2003, 4471-4487). The reactive surface of birnessite adsorbs lead particularly well, which is thereby immobilized, which is why birnessite can be used for soil remediation (DG Beak, NT Basta, KG Scheckel and SJTraina: Linking solid phase speciation of Pb sequestered to birnessite to oral Pb bioaccessibility: Implications for soil remediation: Environmental Science & Technology 42, 2008, 779-785). Furthermore, this birnessite can be used as a model mineral in scientific studies on manganese biogeochemistry.

[0004] Birnessit ist in der Lage anorganische und organische Bodenkontaminanten wie z. B. Eisencyanide (T. Rennert, A. Pohlmeier and T. Mansfeldt: Oxidation of ferrocyanide by birnessite: Environmental Science & Technology 39, 2005, 821-825), Arsenit (B.A. Manning, S.E. Fendorf, B. Bostick and D.L. Suarez: Arsenic(III) oxidation and arsenic(V) adsorption reactions on synthetic birnessite: Environmental Science & Technology 36, 2002, 976-981), Phenole (S.W.C. Chien, H.L. Chen, M.C. Wang and K. Seshaiah: Oxidative degradation and associated mineralization of catechol, hydroquinone and resorcinol catalyzed by birnessite: Chemosphere 74, 2009, 1125-1133) oder Atrazin (D.J. Wang, J.Y. Shin, M.A. Cheney, G. Sposito, G. and T.G. Spiro: Manganese dioxide as a catalyst for oxygen-independent atrazine dealkylation: Environmental Science & Technology 33, 1999, 3160-3165) zu oxidieren.The reaction products formed alongside birnessite during the synthesis described here are not environmentally harmful and can also serve as nutrients for soil microorganisms, potentially accelerating the degradation of organic contaminants. To remediate large-scale soil contamination by these contaminants with birnessite, a cost-effective, industrially viable, low-effort, and reproducible production method is required, as described below.

[0005] It is well known that the currently available methods for the synthesis of birnessite are complex, usually involving strong bases and acids under high temperature and pressure conditions, and often require long reaction times. Most methods are based on the chemical reduction of permanganate. The most common and frequently applied method according to McKenzie (R.M. McKenzie: Synthesis of birnessite, cryptomelane, and some other oxides and hydroxides of manganese, Mineralogical Magazine 38, 1971, 493-502) involves the reduction of permanganate in concentrated hydrochloric acid. The method according to Cheney and colleagues (M.A. Cheney, P.K. Bhowmik, S. Moriuchi, M. Villalobos, S.Z. Qian and S.W.According to Joo: The effect of stirring on the morphology of birnessite nanoparticles, Journal of Nanomaterials, 2008, Article ID 168716), birnessite is produced by the reduction of permanganate with concentrated sulfuric acid under standard conditions followed by aging for up to 20 days. In both processes, the synthesis product must be freed from potassium permanganate residues after the reaction. It has been known since 1915 (EJ Witzemann: A new method of preparation and some interesting transformations of colloidal manganese dioxide, Journal of the Chemical Society 37, 1915, 1079-1091) that manganese (hydr)oxides can be produced in alkaline solution using organic compounds and potassium permanganate. The reaction products of this study were not determined. In more recent studies, organic species such as ethanol, various sugars or propylene oxide are used as reducing agents for permanganate to synthesize birnessite. Ma and colleagues used ethanol to reduce a strongly alkaline potassium permanganate solution to obtain birnessite. Temperatures between 60 °C and 95 °C were reported for a period of 3 to 90 days (Y. Ma, J. Luo and S. L. Suib: Syntheses of birnessites using alcohols as reducing reagents: Effects of synthesis parameters on the formation of birnessites, Chemistry of Materials 11, 1999, 1972-1979). Purification of the product is necessary to significantly lower the strongly alkaline pH.

[0006] Another complex production method involves the reaction of sugars such as glucose or sucrose with permanganate and subsequent phase separation at 110 °C to form a xerogel, which is heated to 400 °C - 450 °C and then washed to obtain birnessite (S. Ching, DJ Petrovay, ML Jorgensen and SL Suib: Sol-gel synthesis of layered birnessite-type manganese oxides, Inorganic Chemistry 36, 1997, 883-890).

[0007] The method developed by Zhang and colleagues (X. Zhang, X. Chang, N. Chen, K. Wang, L. Kang, and Z. Liu: Synthesis and capacitive property of d-MnO2 with large surface area, Journal of Materials Science 47, 2011, pp. 999-1003) is based on the reduction of permanganate using toxic propylene oxide. The process is very complex, requiring temperatures of 90 °C and a minimum time of 48 hours, but it does not require strong acids or bases.

[0008] To date, only a few processes for the production of birnessite are known that do not rely on the reduction of permanganate. In such processes, Mn 2+ In very alkaline solutions, oxygen is blown into the solution at low temperatures over several hours to form birnessite. While McKenzie (RM McKenzie: Synthesis of birnessite, cryptomelane, and some other oxides and hydroxides of manganese, Mineralogical Magazine 38, 1971, 493-502) uses manganese sulfate and potassium hydroxide, the method of Cai and colleagues (J. Cai, J. Liu and SL Suib: Preparative parameters and framework dopant Effects in the synthesis of layer-structure birnessite by air Oxidation, Chemistry of Materials 14, 2002, 2071-2077) uses manganese chloride and sodium hydroxide.

[0009] An overview of other, also considerably more complex, preparation methods is provided in Brock, SL et al.: A Review of Porous Manganese Oxide Materials. In: Chem. Mater., Vol. 10, 1998, No. 10, pp. 2619-2628. The authors divide the production of manganese oxides into three processes: the conventional route via precipitation, ion exchange, or hydrothermal formation; the high-temperature route; and the formation route based on sol-gel alteration (see also the above comments, S. Ching, DJ Petrovay, ML Jorgensen, and SL Suib: Sol-gel synthesis of layered birnessite-type manganese oxides, Inorganic Chemistry 36, 1997, 883-890). All three processes are characterized by considerably more complex process steps. What all processes have in common is that several heating steps are necessary for the targeted production of birnessite: for drying the gel, for calcination / tempering, and for drying the final product which has been purified with water.

[0010] The washing step with water is necessary to remove excess potassium. The described processes are technically complex and require temperatures of over 100 °C to dry the gel, over 400 °C for annealing / calcining, and again over 100 °C to dry the product after removing unwanted foreign ions such as potassium with water, strong acids, or bases. None of the processes described in this review article is based on the use of lactate in the production process. None of the described processes utilize freeze-drying. None of the described processes incorporates Na-K ion exchange as an intrinsic process step to reduce excess potassium in the final product, birnessite.

[0011] Another complex method for producing birnessites for use in battery electrodes, based on the sol-gel alteration route, is described in DE 195 32 073 A1. For this purpose, KMnO4 is dissolved in water with various metal salts and then mixed with organic reducing agents such as fumaric acid. The resulting gel is dried for 72 hours and then annealed / calcined at 450 °C. The potassium is then removed in a two-hour treatment with 1 M H2SO4. This process is very complex, requiring temperatures of 450 °C, a minimum of 74 hours, and strong acids. Furthermore, the products synthesized in this way pose human and ecotoxicological concerns due to the incorporation of semimetals or heavy metals and are unsuitable for environmental applications, e.g., for the remediation of contaminated groundwater.

[0012] The invention is based on the object of producing birnessite with low effort, without environmentally harmful synthesis by-products and with a large surface area.

[0013] This problem is solved in a process for the synthesis of birnessite using a permanganate solution, for example, potassium permanganate, by adding lactate as a reducing agent to the permanganate solution instead of the usual acids and bases. By avoiding strong acids and bases, the reaction of the permanganate solution with the reducing agent lactate does not produce any byproducts of the synthesis reaction that are harmful to the environment or require disposal as hazardous waste. Permanganate, the only toxic substance, is completely reduced to birnessite during the reaction.

[0014] Furthermore, the reaction with lactate to produce birnessite can now be carried out under standard conditions, eliminating the need to maintain defined and controlled pressure and temperature conditions. The inventive effect occurs (without limitations) even at standard ambient temperature and pressure (SATP) conditions of 25 °C and 101.3 kPa, so the manufacturing effort required by the invention is significantly lower than with the methods described above.

[0015] By adding the reducing agent according to the invention, a molar ratio of lactate to permanganate of greater than 0.5, advantageously from 0.5 to 2, in particular from 0.7 to 1, is advantageously achieved for the synthesis reaction, the lactate preferably being added as a 50% sodium lactate solution and reacted.

[0016] Further process features are listed in the subclaims.

[0017] The method for producing birnessite according to the invention is low-effort and cost-effective, rapid, reliable, reproducible, easy to handle, and technologically feasible. Not only the birnessite produced in this way, but also the oxidation products of the lactate can be used together for the remediation of contaminated sites. Lactate and its oxidation products serve as nutrients for microorganisms, which is expected to accelerate the degradation of organic contaminants. Purification is not required for such an application, and the reaction suspension can be used directly.

[0018] The synthesized birnessite can be synthesized in high purity and exhibits all the properties described for this mineral in the literature. Particularly noteworthy is the surprisingly large specific surface area, which has rarely been achieved before.

[0019] The invention is explained in more detail below using an embodiment.

[0020] The drawing shows: Fig. 1: X-ray powder diffraction patterns of birnessite, prepared according to McKenzie (a) and according to the synthesis according to the invention (b) Fig. 2: Fourier transform infrared spectra of birnessite prepared according to McKenzie (a) and according to the synthesis according to the invention (b) Fig. 3: Energy dispersive X-ray spectrum of birnessite, prepared by the synthesis according to the invention

[0021] In a typical embodiment, all process steps, including purification, are preferably carried out under SATP conditions (T = 25 °C; p = 101.3 kPa).

[0022] First, 1 g of potassium permanganate is dissolved in ultrapure water (R = 18.2 MΩ, OC < 1 µg 1 -1) and then made up to a total volume of 100 ml to obtain a 62.8 mM potassium permanganate solution. 1 ml of a 50% sodium lactate standard solution is added to this solution. After combining both reagents, the solution is mixed vigorously for approximately one minute and then allowed to stand. The reaction is complete when a clear, colorless supernatant forms after approximately 90 minutes. To obtain pure birnessite, lactate residues and the low-molecular-weight organic salts formed as by-products must be washed out using ultrapure water. This is first done by centrifuging the reaction solution, in which the organic salts are dissolved. Birnessite settles as a sediment during centrifugation and is then further purified by resuspending and centrifuging five times so that the concentration of dissolved organic carbon is less than 1 mg 1 -1Leaching of the organic salts by pressure filtration is also possible. The resulting birnessite is then freeze-dried. Air drying under SATP conditions is also possible. After freeze-drying, birnessite is present as a loose powder.

[0023] In the following, the birnessite synthesized in this way according to the invention is compared with other birnessite produced in a known manner.

[0024] The comparison of two X-ray powder diffractograms in Fig. 1 shows four broad diffraction reflections, which are characteristic of birnessite with a turbostratic crystal structure (E. Silvester, A. Manceau and VA Drits: Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite. 2. Results from chemical studies and EXAFS spectroscopy, American Mineralogist 82, 1997, 962-978).

[0025] The broad diffraction reflections with lower intensity reflect the nanocrystalline structure of the particles. In the birnessite synthesized according to the invention (see Fig. In Figure 1, curve b), the reflections of the 001 and 002 lattice planes are only vaguely visible. This can be explained in particular by the smaller crystallite size of the birnessite, which leads to a coherence problem and thus lower diffraction intensity (M. Villalobos, B. Lanson, A. Manceau, B. Toner and G. Sposito: Structural model for the biogenic Mn oxide produced by Pseudomonas putida, American Mineralogist 91, 2006, 489-502).

[0026] The broad, low-intensity diffraction peaks and the coherence problem indicate that individual crystallites are significantly smaller than 1 µm. The FTIR spectra of both birnessites in Fig. 2 are very similar to each other. The absorption bands at 3358 and 1625 cm -1can be assigned to the hydroxyl groups of the weakly bound H2O molecules of birnessite. The other bands at 506 and 445 cm -1 are caused by the vibrations of the MnO6 octahedra (RM Potter and GR Rossman: Tetravalent manganese oxides - identification, hydration, and structural relationships by infrared spectroscopy, American Mineralogist 64, 1979, 1199-1218). The sharpness of the band at 435 cm -1 is an indicator of the crystalline order of birnessite (CM Julien, M. Massot, and C. Poinsignon: Lattice vibrations of manganese oxides - Part 1. Periodic structures, Spectrochimica Acta Part a-Molecular and Biomolecular Spectroscopy 60, 2004, 689-700).

[0027] Since this band is less pronounced in the birnessite synthesized according to the invention than in the birnessite according to McKenzie, a lower crystalline order can be assumed, which is also in agreement with the results of X-ray powder diffraction (cf. Fig.1). The absence of further absorption bands indicates the successful purification of the birnessite synthesized according to the invention. The weak band at 930 cm -1 , which is only observed in birnessite synthesized according to McKenzie (see Fig. 2, curve a), is caused by potassium permanganate residues.

[0028] The elemental compositions for the birnessite synthesized according to the invention and for the birnessite synthesized by McKenzie were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Both birnessites were digested according to the method described by Schwertmann (U. Schwertmann: Differentiation of the iron oxides of the soil by extraction with acidic ammonium oxalate solution: Journal of Plant Nutrition, Fertilization and Soil Science 105, 1964, 194-202) for dissolving poorly crystalline iron oxides. The determined weight percentages, along with other elemental compositions of various birnessites from the literature, are listed in Table 1 below and demonstrate that the birnessite produced according to the invention always lies within the range of the values ​​reported in the literature for known synthesis methods. Table 1: Elemental composition of synthetically produced birnessites sample Mn (wt%) K (wt%) Na (wt%) O+H (wt%) inventive Birnessite 55,5 5,1 0,9 38,5 according to McKenzie 55,7 4,8 < 0,02 39,5 Gaines et al. (1997) 52,9 - 6,3 40,8 Ching et al. (1997) 54,9 10,9 - 38,2 Ma et al. (1999) 50,8 11,9 - 37,3 (RV Gaines, CW Skinner, EE Foord, B. Mason and A. Rosenzweig: Dana's new mineralogy: The system of mineralogy of James Dwight Dana and Edward Salisbury Dana, John Wiley & Sons, 1997) (S. Ching, DJ Petrovay, ML Jorgensen and SL Suib: Sol-gel synthesis of layered birnessite-type manganese oxides, Inorganic Chemistry 36, 1997, 883-890) (Y. Ma, J. Luo and SL Suib:,syntheses of birnessites using alcohols as reducing reagents: Effects of synthesis parameters on the formation of birnessites, Chemistry of Materials 11, 1999, 1972-1979)

[0029] The elemental composition was additionally investigated by energy-dispersive X-ray spectroscopy (EDS). EDS quantification revealed the presence of oxygen, sodium, potassium, and manganese in the same proportions as determined by ICP-OES data. A characteristic EDS spectrum of the birnessite produced according to the invention is shown in Fig.3. The concentrations of other elements were below the detection limit using the methods. The specific surface area of ​​the birnessite produced according to the invention is 249.15 ± 0.05 gm -2 and is therefore significantly larger than the one produced by McKenzie (32 gm -2 ) is specified.

[0030] Using secondary electron images (not shown), a microporous structure of aggregated birnessite colloids was demonstrated, which is consistent with the large specific surface area.

[0031] The oxidation products of lactate, pyruvate (1351 mg 1 -1 ), acetate (1250 mg 1 -1 ), formate (44.5 mg 1 -1 ) and oxalate (12.1 mg 1 -1 ), in the centrifuged reaction solution were determined by ion chromatography. The oxidation of lactate is not quantitative for the selected concentrations, and 643 mg 1 -1Lactate was detected in the reaction solution. The concentration of dissolved organic carbon in the centrifugate of the fifth wash solution was at the limit of detection of 0.5 mg 1 -1 The total carbon content of the purified and dried birnessite was below the detection limit of 1 mg kg -1 Both carbon content measurements indicate that the purification by washing five times is successful.

[0032] The birnessite obtained by the synthesis according to the invention can be used as a model mineral for laboratory experiments and also has the potential to serve as an electron acceptor for remediation purposes.

Claims

[1] Process for the synthesis of birnessite using a permanganate solution, characterized by , that - lactate is added to the permanganate solution as a reducing agent - the permanganate solution is then mixed with the lactate - the mixture is left to rest to form the birnessite - and the birnessite formed is separated and purified, wherein the addition of lactate achieves a molar ratio of lactate to permanganate of greater than 0.5, preferably from 0.5 to 2, in particular from 0.7 to 1. [2] Method according to claim 1, characterized by that potassium permanganate solution is used as permanganate solution. [3] Method according to claim 1, characterized by that lactate is added as a 50% sodium lactate solution. [4] Method according to claim 1, characterized by that the lactate is added and reacted under standard conditions without controlled pressure and temperature conditions. [5] Method according to claim 1, characterized by that the birnessite is air dried. [6] Method according to claim 1, characterized by that the birnessite is freeze-dried. [7] Method according to claim 1, characterized by that the birnessite is separated by pressure filtration. [8] Method according to claim 1, characterized by that the birnessite is purified by resuspension and centrifugation.

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