A stepwise extraction method and application of manganese species from soil

Abstract

This invention belongs to the field of soil manganese extraction technology, and discloses a stepwise extraction method and application for manganese species in soil. First, exchangeable manganese is extracted using magnesium chloride; then, manganese carbonate and sulfides are extracted using hydrochloric acid; next, active Mn(III) bound to organic matter is extracted using pyrophosphate solution under alkaline pH; then, manganese oxides are dissolved using hydroxylamine hydrochloride; and finally, manganese bound to crystalline iron and manganese oxides is extracted using sodium dithionite solution. This stepwise extraction scheme accurately quantifies the concentration of active Mn(III) species bound to organic matter in the soil. Experimental results show that the extraction method of this invention can effectively separate different forms of manganese in soil. In particular, PP extraction successfully distinguishes Mn(III) bound to organic matter without introducing interfering substances such as iron minerals that may interfere with dissolution.

Description

Technical Field

[0001] This invention relates to the field of soil manganese extraction technology, and in particular to a stepwise extraction method and application of manganese species in soil. Background Technology

[0002] Manganese (Mn) is a redox-sensitive transition metal widely distributed in the natural environment, mainly existing in three oxidation states: Mn(II), Mn(III), and Mn(IV). These oxidation states and the electron exchanges between them play a crucial role in various environmental processes and element cycling. Mn(II) is typically found in primary minerals, released into the soil through weathering, and is the only form available to plants. In contrast, Mn(IV) usually exists in oxide form, possessing strong oxidizing and metal adsorption capabilities, significantly influencing the behavior of trace metals and organic matter in the environment. Solid Mn(III) is commonly found in manganese oxides or exists as a substitute cation in other mineral structures; while dissolved Mn(III) tends to undergo disproportionation reactions to form Mn(II) and Mn(IV), but can also exist when forming stable complexes with ligands.

[0003] Because Mn(III) is an intermediate valence state and readily undergoes disproportionation reactions in the absence of ligands, making it difficult to capture / detect, it did not receive widespread attention in biogeochemical research before the 20th century. The formation mechanisms of Mn(III) are diverse, but the reaction kinetics of oxidizing Mn(II) to Mn(III) with oxygen in the absence of catalysts are slow. Therefore, in terrestrial ecosystems, the conversion of Mn(II) to Mn(III) is mainly achieved through biological processes. Fungi and heterotrophic bacteria can catalyze this conversion process by secreting extracellular enzymes (such as polycopper oxidases) to generate soluble, reactive Mn(III) intermediates. These reactive Mn(III) intermediates play an important role in promoting the decomposition of litter and twigs in forest ecosystems, especially in carbon oxidation at the redox interface. Furthermore, recent studies have shown that manganese plays a significant role in influencing the abiotic and biotic oxidation processes and decomposition of soil organic matter (SOM). However, the complex chemical properties and distribution patterns of manganese in soil make a comprehensive understanding of its role in these processes challenging. To gain a deeper understanding of its role in biogeochemical cycles, it is necessary to accurately quantify Mn(III) species in soil and use more comprehensive and advanced analytical methods to accurately characterize the distribution of manganese species in soil.

[0004] Current research commonly employs X-ray diffraction (XRD), synchrotron radiation-based X-ray absorption spectroscopy (XANES and EXAFS), and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS) to interpret the complex distribution of manganese in soil. While these techniques provide detailed analytical results, their procedures are relatively cumbersome and often require simultaneous measurement of wet chemical data as a supplement, highlighting the importance of geochemical analysis for studying manganese species. Although various single-step and stepwise manganese extraction methods exist, methods for extracting active, organically bound Mn(III) species are still lacking. Lenstra et al. (Lenstra W. K., Klomp R., Molema F., Behrends T., Slomp CP A sequential extraction procedure for particulate manganese and its application to coastal marine sediments [J]. Chemical Geology, 2021, 584: 120538.) proposed a five-step sequential extraction method for manganese in marine sediments, which can effectively separate manganese bound to pyrite, which is of great significance in sedimentary environments. However, this method cannot be directly applied to the extraction of manganese from soil because the distribution of manganese in soil varies greatly, and it fails to capture an important component of the soil manganese pool—organically bound Mn(III). Summary of the Invention

[0005] The purpose of this invention is to provide a stepwise extraction method and application for manganese species in soil, which solves the problem that existing technologies cannot achieve quantitative extraction of Mn(III) species in soil.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a stepwise extraction method for manganese species in soil, comprising the following steps: (1) Extraction of exchangeable manganese: Soil samples were mixed with magnesium chloride solution for extraction, and then centrifuged to obtain the first extract and the first residue; the manganese species in the first extract were analyzed by inductively coupled plasma mass spectrometry. (2) Extraction of manganese carbonate and manganese sulfide: The first residue was mixed with hydrochloric acid solution for extraction, and then centrifuged to obtain the second extract and the second residue; the manganese species in the second extract were analyzed by inductively coupled plasma mass spectrometry. (3) Extraction of organically bound active Mn(III): The second residue was mixed with pyrophosphate solution for extraction, and then centrifuged to obtain the third extract and the third residue; the manganese species in the third extract were analyzed by inductively coupled plasma mass spectrometry. (4) Extraction of manganese oxides: The third residue was mixed with hydroxylamine hydrochloride solution for extraction, and then centrifuged to obtain the fourth extract and the fourth residue; the manganese species in the fourth extract were analyzed by inductively coupled plasma mass spectrometry. (5) Extraction of manganese bound in crystalline iron and manganese oxides: The fourth residue is mixed with sodium dithionite solution for extraction, and then centrifuged to obtain the fifth extract and the fifth residue; the manganese species in the fifth extract are analyzed by inductively coupled plasma mass spectrometry; that is, the stepwise extraction of manganese species in the soil is completed.

[0007] Preferably, the concentration of the magnesium chloride solution in step (1) is 1~2 mol / L; the ratio of the amount of soil sample to magnesium chloride solution in step (1) is 0.1~0.5g:30~50mL.

[0008] Preferably, the concentration of the hydrochloric acid solution in step (2) is 1~2 mol / L; the ratio of the first residue to the hydrochloric acid solution in step (2) is 0.1~0.5g:30~50mL.

[0009] Preferably, the concentration of the pyrophosphate solution in step (3) is 0.1~0.5 mol / L; the pH of the pyrophosphate solution in step (3) is 10~10.5; and the ratio of the second residue to the pyrophosphate solution in step (3) is 0.1~0.5 g: 30~50 mL.

[0010] Preferably, the concentration of the hydroxylamine hydrochloride solution in step (4) is 0.1~1 mol / L; the ratio of the third residue to the hydroxylamine hydrochloride solution in step (4) is 0.1~0.5 g: 30~50 mL.

[0011] Preferably, the concentration of the sodium dithionite solution in step (5) is 50 g / L; the ratio of the fourth residue to the sodium dithionite solution in step (5) is 0.1~0.5 g: 30~50 mL.

[0012] Preferably, the extraction time in steps (1) to (5) is 60 to 360 min.

[0013] This invention also provides a stepwise extraction method for manganese species in soil, which is applied to the quantification of active Mn(III) species in soil.

[0014] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: This invention employs a modified stepwise extraction method to evaluate the distribution of different forms of manganese in soil samples. First, exchangeable manganese is extracted using magnesium chloride (MgCl2), followed by extraction of manganese carbonates and sulfides using hydrochloric acid (HCl). Then, under alkaline conditions, active Mn(III) bound to organic matter is extracted using pyrophosphate (PP) solution. Next, manganese oxides are dissolved using hydroxylamine hydrochloride. Finally, manganese bound to crystalline iron and manganese oxides is extracted using sodium dithionite (DCB) solution. This stepwise extraction scheme accurately quantifies the concentration of active Mn(III) species bound to organic matter in the soil. The accuracy and reliability of the extraction method are enhanced by comparison with X-ray absorption near-edge structure (XANES) spectroscopy and linear combination fitting (LCF) analysis results. Experimental results show that the extraction method of this invention can effectively separate different forms of manganese in soil. In particular, PP extraction successfully distinguishes Mn(III) bound to organic matter without introducing interfering substances such as iron minerals into the dissolution process. Furthermore, PP has unique advantages in extracting Mn(III) species bound to organic matter. Compared with other oxidants such as hydrogen peroxide (H2O2) and sodium hypochlorite (NaClO), PP is better able to maintain the original oxidized state of Mn(III) species and can distinguish organically bound Mn(III) species with different activities, thus improving the specificity and accuracy of extraction and providing a new tool for studying the distribution of manganese species in soil. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0016] Figure 1 This is a schematic diagram of the step-by-step extraction process of manganese species from soil according to the present invention; Figure 2 The distribution maps of different forms of manganese obtained by stepwise extraction in Examples 1 and 2 are shown below; where a) is the distribution map of manganese concentration of different forms, b) is the correlation map between different forms of manganese and manganese of different valence states, c) is the distribution map of manganese forms in soil samples from the Maui sampling point, and d) is the distribution map of manganese forms in soil samples from the Kohala sampling point. Figure 3 The diagram shows the solubility characteristics of the seven manganese minerals in Example 3. Figure 4 The percentage of different manganese minerals dissolved in PP solution in Example 4 and Comparative Example 1; where a is a PP solution with pH=7.0 and b is a PP solution with pH=10.5; Figure 5 The percentage of different manganese minerals dissolved in water for Comparative Examples 2 and 3 is given; where a is water with pH=7.0 and b is water with pH=10.5. Detailed Implementation

[0017] This invention provides a stepwise extraction method for manganese species from soil, the flowchart of which is shown below. Figure 1 As shown, it includes the following steps: (1) Extraction of exchangeable manganese: Soil samples were mixed with magnesium chloride solution for extraction, and then centrifuged to obtain the first extract and the first residue; the manganese species in the first extract were analyzed by inductively coupled plasma mass spectrometry. (2) Extraction of manganese carbonate and manganese sulfide: The first residue was mixed with hydrochloric acid solution for extraction, and then centrifuged to obtain the second extract and the second residue; the manganese species in the second extract were analyzed by inductively coupled plasma mass spectrometry. (3) Extraction of organically bound active Mn(III): The second residue was mixed with pyrophosphate solution for extraction, and then centrifuged to obtain the third extract and the third residue; the manganese species in the third extract were analyzed by inductively coupled plasma mass spectrometry. (4) Extraction of manganese oxides: The third residue was mixed with hydroxylamine hydrochloride solution for extraction, and then centrifuged to obtain the fourth extract and the fourth residue; the manganese species in the fourth extract were analyzed by inductively coupled plasma mass spectrometry. (5) Extraction of manganese bound in crystalline iron and manganese oxides: The fourth residue is mixed with sodium dithionite solution for extraction, and then centrifuged to obtain the fifth extract and the fifth residue; the manganese species in the fifth extract are analyzed by inductively coupled plasma mass spectrometry; that is, the stepwise extraction of manganese species in the soil is completed.

[0018] In this invention, the concentration of the magnesium chloride solution in step (1) is preferably 1~2 mol / L, more preferably 1~1.5 mol / L, and even more preferably 1 mol / L; the ratio of the amount of soil sample to magnesium chloride solution in step (1) is preferably 0.1~0.5g:30~50mL, more preferably 0.3~0.5g:30~40mL, and even more preferably 0.5g:30mL.

[0019] In this invention, the concentration of the hydrochloric acid solution in step (2) is preferably 1~2 mol / L, more preferably 1~1.5 mol / L, and even more preferably 1 mol / L; the ratio of the first residue to the hydrochloric acid solution in step (2) is preferably 0.1~0.5g:30~50mL, more preferably 0.3~0.5g:30~40mL, and even more preferably 0.5g:30mL.

[0020] In this invention, the concentration of the pyrophosphate solution in step (3) is preferably 0.1~0.5 mol / L, more preferably 0.1~0.2 mol / L, and even more preferably 0.1 mol / L; the pH of the pyrophosphate solution in step (3) is preferably 10~10.5, more preferably 10.2~10.5, and even more preferably 10.5; the ratio of the second residue to the pyrophosphate solution in step (3) is preferably 0.1~0.5g:30~50mL, more preferably 0.3~0.5g:30~40mL, and even more preferably 0.5g:30mL.

[0021] In this invention, the concentration of the hydroxylamine hydrochloride solution in step (4) is preferably 0.1~1 mol / L, more preferably 0.1~0.5 mol / L, and even more preferably 0.1 mol / L; the ratio of the third residue to the hydroxylamine hydrochloride solution in step (4) is preferably 0.1~0.5 g: 30~50 mL, more preferably 0.3~0.5 g: 30~40 mL, and even more preferably 0.5 g: 30 mL.

[0022] In this invention, the concentration of the sodium dithionite solution in step (5) is preferably 50 g / L; the ratio of the fourth residue to the sodium dithionite solution in step (5) is preferably 0.1~0.5 g: 30~50 mL, more preferably 0.3~0.5 g: 30~40 mL, and even more preferably 0.5 g: 30 mL.

[0023] In this invention, the extraction time in steps (1) to (5) is preferably 60 to 360 min; the extraction process also includes stirring; the stirring speed is preferably 60 rpm.

[0024] In this invention, the centrifugation speed in steps (1) to (5) is preferably 8000 rpm; the centrifugation time is preferably 10 min.

[0025] In this invention, before analyzing manganese species by inductively coupled plasma mass spectrometry in steps (1) to (5), the extract is acidified with 2% nitric acid solution for 12 hours.

[0026] In this invention, the first residue, the second residue, the third residue, and the fourth residue are all washed twice with deionized water before use.

[0027] This invention also provides a stepwise extraction method for manganese species in soil, which is applied to the quantification of active Mn(III) species in soil.

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] Soil samples were collected from Haleakala Mountain on Maui, referred to as the Maui sampling point. Three subsurface soil samples were collected from areas at this sampling point with average annual precipitation of 1.5 m, 2.5 m, and 5.0 m, respectively, and named MS 0.5, MS 2, and MS 6. The key parameters of these soil samples are shown in Tables 1 and 2. The following methods were used to extract manganese from each soil sample stepwise, and the corresponding proportions of different manganese forms are shown in Table 3.

[0031] (1) Extraction of exchangeable manganese: 0.5 g of soil sample was mixed with 30 mL of 1 mol / L magnesium chloride solution in a 50 mL centrifuge tube. The mixture was extracted by mixing at 60 rpm for 60 min in a rotary mixer, and then centrifuged at 8000 rpm for 10 min to obtain the first extract and the first residue. The first extract was acidified with 2% nitric acid solution for 12 h and then the manganese species were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). (2) Extraction of manganese carbonate and manganese sulfide: 0.5 g of the first residue was mixed with 30 mL of 1 mol / L hydrochloric acid solution in a 50 mL centrifuge tube. The mixture was then extracted by mixing at 60 rpm for 60 min in a rotary mixer. After that, it was centrifuged at 8000 rpm for 10 min to obtain the second extract and the second residue. The manganese species in the second extract were analyzed by ICP-MS. (3) Extraction of organically bound active Mn(III): 0.5 g of the second residue was mixed with 30 mL of 0.1 mol / L sodium pyrophosphate solution with pH=10.5 in a 50 mL centrifuge tube. The mixture was extracted by mixing at 60 rpm for 360 min in a rotary mixer, and then centrifuged at 8000 rpm for 10 min to obtain the third extract and the third residue. The manganese species in the third extract were analyzed by ICP-MS. (4) Extraction of manganese oxides: 0.5 g of the third residue was mixed with 30 mL of 0.1 mol / L hydroxylamine hydrochloride solution in a 50 mL centrifuge tube. The mixture was extracted by mixing at 60 rpm for 120 min in a rotary mixer, and then centrifuged at 8000 rpm for 10 min to obtain the fourth extract and the fourth residue. The manganese species in the fourth extract were analyzed by ICP-MS. (5) Extraction of manganese bound in crystalline iron and manganese oxides: 0.5 g of the fourth residue was mixed with 30 mL of 50 g / L sodium dithionite solution (specifically, a composite solution of 0.3 M sodium citrate + 1 M sodium bicarbonate + 50 g / L sodium dithionite) in a 50 mL centrifuge tube. The mixture was extracted by mixing at 60 rpm for 360 min in a rotary mixer, and then centrifuged at 8000 rpm for 10 min to obtain the fifth extract and the fifth residue. The manganese species in the fifth extract were analyzed by ICP-MS.

[0032] Example 2

[0033] Soil samples were collected from Kohala Mountain on the island of Hawaii, referred to as the Kohala sampling point. Five soil samples were collected from the surface and subsurface soils at this point. The surface soil samples were from areas with average annual precipitation of 2.043 m and 2.165 m, respectively, and were labeled SP 1 and SP 229. The subsurface samples were from areas with average annual precipitation of 0.255 m, 0.818 m, and 3.505 m, respectively, and were labeled SP 138, SP 188, and WTH21. Key parameters of the above soil samples are shown in Tables 1 and 2. The method of Example 1 was used to perform stepwise extraction on each soil sample, and the corresponding proportions of different manganese forms and valence states are shown in Table 3.

[0034]

[0035] The concentration distribution of different forms of manganese obtained through stepwise extraction in Examples 1 and 2 are as follows: Figure 2 As shown in a), the correlation between different forms of manganese and manganese in different valence states is as follows: Figure 2 As shown in b), the distribution of manganese speciation in soil samples from the Maui sampling site is as follows. Figure 2 As shown in c), the distribution of manganese speciation in soil samples from the Kohala sampling site is as follows. Figure 2 As shown in d). Figure 2 Correlation analysis showed a high positive correlation between manganese extracted by MgCl2 and Mn(II) content, and a strong positive correlation between manganese extracted by DCB and Mn(IV) content. This is because MgCl2 and DCB are widely proven to effectively extract exchangeable and crystalline manganese fractions, respectively. Furthermore, only in PP and Mn(III)... OMA strong positive correlation was observed between the two, indicating that manganese extracted by PP is strongly associated with organically bound Mn(III). Conversely, manganese extracted by HCl or hydroxylamine showed no significant correlation with any particular manganese oxidation state. This lack of correlation may be because HCl primarily targets Mn(II) minerals and poorly crystalline manganese oxides, in which manganese may be in a mildly oxidized state between +2 and +3. Similarly, hydroxylamine can extract manganese oxides with mixed +3 and +4 valence states, reflecting the presence of this transitional state common in soils, such as Mn3O4 and biogenic naphthoic acid manganese ore.

[0036] Example 3

[0037] Different manganese minerals were used as samples, including five manganese oxides: δ-MnO2, β-MnO2, γ-MnOOH, rhodochrosite (Mn2O3), and malachite (Mn3O4); one manganese carbonate (MnCO3, rhodochrosite); and one manganese sulfide (MnS, manganese sulfide); for a total of seven manganese minerals. For specific extraction methods, please refer to Example 1. The solubility characteristics of the seven manganese minerals are as follows: Figure 3 As shown.

[0038] Depend on Figure 3It was found that in the first step, using 1M MgCl2 solution to extract exchangeable manganese, only a very small portion of MnS (3.9%) and MnCO3 (0.7%) were dissolved, as these two minerals were more soluble than other manganese mineral samples tested at pH 7.0. In the second step, 1M HCl solution completely dissolved the remaining MnCO3 and partially dissolved MnS (14.3%), as well as small amounts of γ-MnOOH and Mn3O4, consistent with previous studies (Lenstra WK, Klomp R., Molema F., Behrends T., Slomp CP A sequential extraction procedure for particulate manganese and its application to coastal marine sediments [J]. Chemical Geology, 2021, 584: 120538.). In the third step, using PP solution as the extractant, only 1.9% of Mn3O4 was dissolved, while the dissolution of all other manganese mineral samples was less than 1%. This indicates that the PP solution at pH 10.5 does not introduce errors due to the dissolution of manganese oxides, manganese carbonate, and manganese sulfide during the extraction of organically bound active Mn(III) substances. The fourth step uses hydroxylamine hydrochloride solution, which has low solubility for manganese oxide minerals other than pyrolusite; the solubility rates for δ-MnO2, γ-MnOOH, Mn2O3, and Mn3O4 are 73.8%, 66.5%, 91.1%, and 70.9%, respectively. Finally, the DCB solution further dissolves the remaining manganese oxides and also dissolves a certain amount of β-MnO2 (12.8%). By applying the stepwise extraction method of this invention to seven manganese mineral samples, the results show that this method has high selectivity in distinguishing manganese minerals with different reactivity and structures. Using 1M hydrochloric acid as a pretreatment step reduces the human error caused by the trace dissolution of manganese minerals by the PP solution, thus facilitating the quantitative analysis of organically bound active Mn(III) species. In these manganese mineral samples, β-MnO2 and MnS could not be completely extracted. β-MnO2, as a highly crystalline manganese oxide, was difficult to completely dissolve with the extractant used in this invention; while the insufficient dissolution of MnS was more attributable to the formation and deposition of a sulfur-rich layer on its surface, which hindered dissolution. This phenomenon was also observed during separate pyrophosphate extraction.

[0039] Example 4

[0040] This embodiment provides the dissolution efficiency of a single PP solution as an extractant for various manganese minerals, specifically: A 0.1 mol / L PP solution with pH=10.5 was used as the extraction solvent. The manganese minerals included five manganese oxides: δ-MnO2, β-MnO2, γ-MnOOH, rhodochrosite (Mn2O3), and malachite (Mn3O4); one manganese carbonate (MnCO3, rhodochrosite); and one manganese sulfide (MnS, manganese sulfide), for a total of seven manganese minerals. The specific extraction method is described in step (3) of Example 1. The solubility percentages of different manganese minerals in the PP solution at pH=10.5 are as follows: Figure 4 As shown in b.

[0041] Comparative Example 1

[0042] This example demonstrates the dissolution efficiency of a single PP solution as an extractant for various manganese minerals, as detailed in Example 2, except that the pH of the PP solution is 7.0. The dissolution percentages of different manganese minerals in a PP solution at pH 7.0 are shown below. Figure 4 As shown in Figure a.

[0043] Comparative Example 2

[0044] This example demonstrates the solubility efficiency of water as an extractant for various manganese minerals, as shown in Example 2, except that the PP solution is replaced with water at pH 10.5. The solubility percentages of different manganese minerals in the PP solution at pH 10.5 are as follows: Figure 5 As shown in b.

[0045] Comparative Example 3

[0046] This example demonstrates the solubility efficiency of water as an extractant for various manganese minerals, as shown in Example 2, except that the PP solution is replaced with water at pH 7.0. The solubility percentages of different manganese minerals in the PP solution at pH 7.0 are as follows: Figure 5 As shown in Figure a.

[0047] Depend on Figures 4-5The results at pH 7.0 revealed unique dissolution patterns among different manganese minerals. For example, rhodochrosite (Mn3O4) dissolved completely within 8 hours, while rhodochrosite (MnCO3) and manganese sulfide (MnS) achieved high manganese extraction rates of 54.8% and 48.0% respectively within the first 2 hours, with no further dissolution observed thereafter. On the other hand, γ-MnOOH and δ-MnO2 showed lower dissolution rates, only 7.5% and 7.6% respectively. Rhodochrosite (Mn2O3) and pyrolusite (β-MnO2) were almost insoluble, with dissolution rates below 1% throughout the process. At pH 10.5, rhodochrosite (MnCO3) dissolved completely within 6 hours, and manganese sulfide (MnS) achieved a manganese extraction rate of 25% in the first 4 hours, which did not increase thereafter. In contrast to the complete dissolution at pH 7.0, the solubility of rhodochrosite (Mn3O4) decreased dramatically to only 2%. The solubility of γ-MnOOH, δ-MnO2, Mn2O3, and β-MnO2 remained very low, all below 0.5%. These results clearly indicate that the PP extraction method at pH 10.5 significantly improves the efficiency of separating active organically bound Mn(III) species from soil, primarily due to the significantly lower dissolution rate of manganese oxides at this pH compared to neutral pH conditions. While the application of PP in the extraction of active Mn(III) species is recognized, comprehensive studies on the effect of PP on manganese mineral dissolution are insufficient, especially when it is used as the sole extractant or part of a sequential extraction process. As a moderately potent complexing agent, PP can replace weaker natural ligands such as acetates and oxalates, making it an important tool for distinguishing between weakly and strongly complexed active Mn(III) species. This distinction is particularly important because the decomposition of soil organic matter typically begins with a ligand exchange reaction in which SOM replaces the ligand originally bound to Mn(III), thereby promoting electron transfer between Mn(III) and SOM. If the original ligand bound to Mn(III) is too stable, it will hinder ligand exchange, leading to a decrease in the reactivity of the ligand-bound Mn(III) species.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for stepwise extraction of manganese species from soil, characterized in that, Includes the following steps: (1) Extraction of exchangeable manganese: Soil samples were mixed with magnesium chloride solution for extraction, and then centrifuged to obtain the first extract and the first residue; the manganese species in the first extract were analyzed by inductively coupled plasma mass spectrometry. (2) Extraction of manganese carbonate and manganese sulfide: The first residue is mixed with hydrochloric acid solution for extraction, and then centrifuged to obtain the second extract and the second residue; The second extract was analyzed for manganese species using inductively coupled plasma mass spectrometry. (3) Extraction of organically bound active Mn(III): The second residue was mixed with pyrophosphate solution for extraction, and then centrifuged to obtain the third extract and the third residue; The third extract was analyzed for manganese species using inductively coupled plasma mass spectrometry. (4) Extraction of manganese oxides: The third residue was mixed with hydroxylamine hydrochloride solution for extraction, and then centrifuged to obtain the fourth extract and the fourth residue; the manganese species in the fourth extract were analyzed by inductively coupled plasma mass spectrometry. (5) Extraction of manganese bound in crystalline iron and manganese oxides: The fourth residue is mixed with sodium dithionite solution for extraction, and then centrifuged to obtain the fifth extract and the fifth residue; the manganese species in the fifth extract are analyzed by inductively coupled plasma mass spectrometry; that is, the stepwise extraction of manganese species in the soil is completed.

2. The method for stepwise extraction of manganese species from soil according to claim 1, characterized in that, The concentration of the magnesium chloride solution in step (1) is 1~2 mol / L; the ratio of soil sample to magnesium chloride solution in step (1) is 0.1~0.5g:30~50mL.

3. The method for stepwise extraction of manganese species from soil according to claim 2, characterized in that, The concentration of the hydrochloric acid solution in step (2) is 1~2 mol / L; the ratio of the first residue to the hydrochloric acid solution in step (2) is 0.1~0.5g:30~50mL.

4. The method for stepwise extraction of manganese species from soil according to claim 1, characterized in that, The concentration of the pyrophosphate solution in step (3) is 0.1~0.5 mol / L; the pH of the pyrophosphate solution in step (3) is 10~10.5; the ratio of the second residue to the pyrophosphate solution in step (3) is 0.1~0.5 g: 30~50 mL.

5. The method for stepwise extraction of manganese species from soil according to claim 4, characterized in that, The concentration of the hydroxylamine hydrochloride solution in step (4) is 0.1~1mol / L; the ratio of the third residue to the hydroxylamine hydrochloride solution in step (4) is 0.1~0.5g:30~50mL.

6. The method for stepwise extraction of manganese species from soil according to claim 5, characterized in that, The concentration of the sodium dithionite solution in step (5) is 50 g / L; the ratio of the fourth residue to the sodium dithionite solution in step (5) is 0.1~0.5 g: 30~50 mL.

7. The method for stepwise extraction of manganese species from soil according to claim 1, characterized in that, The extraction time for steps (1) to (5) is independently 60 to 360 minutes.

8. The application of the stepwise extraction method for manganese species in soil according to any one of claims 1 to 7 in the quantification of active Mn(III) species in soil.

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