Method for determining different forms of chromium in soil in high geological background area and application thereof

Abstract

The application discloses a method for determining different forms of chromium in soil in a high geological background area and application thereof. The method can sequentially extract the same soil sample and analyze the chromium content in the soil after each step of extraction, so that the distribution of chromium in different forms is obtained, including extracting the adsorbed hexavalent chromium in the soil by using an NH4H2PO4 solution, extracting the iron oxide state chromium therein by using a hot ascorbic acid-ammonium oxalate solution, and extracting the silicate state chromium by using hot concentrated hydrochloric acid, so that the chromium in the chromium iron ore can be fully separated, and accurate results of the chromium form distribution in the high geological background soil are obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chromium determination methods, and particularly relates to a method for determining chromium forms in high geological background soil. BACKGROUND

[0002] The high geological background area refers to an area where the heavy metal content in soil is obviously higher than that of other soils developed from the same parent material in the same region. The chromium in the soil of the high geological background area mainly comes from the process of rock weathering into soil. The development of this process determines the distribution of chromium among various components in the soil, affects the occurrence forms and bioavailability of chromium, and leads to large differences in the ecological toxicity effects of chromium in different soils. Therefore, in order to predict and evaluate the biogeochemical behavior and environmental risk of chromium in high geological background soil, it is necessary to understand the occurrence forms of chromium in the soil.

[0003] The existing extraction of chromium in soil is mainly through continuous extraction. The essence of the continuous extraction method is to exchange, dissolve, leach, complex, adsorb and desorb different chemical reagents for different components of soil, so as to separate the chromium combined with different components. However, since the continuous extraction method is mainly developed for the heavy metal forms in the human-polluted soil, there are the following problems when it is applied to analyze the chromium forms in the high geological background soil:(1) Chromium in the high geological background soil usually exists in the form of trivalent chromium Cr(III), and is mainly fixed in iron(hydro)oxide (such as goethite and hematite) in the form of isomorphous substitution. This part of chromium existing in the form of substitution is difficult to be dissolved by the commonly used reducible state extractant, so the proportion of the reducible state of chromium is underestimated;(2) Chromium spinel is an important occurrence mineral of chromium in the high geological background soil, but the existing continuous extraction method lacks the extraction step for this form of chromium;(3) The commonly used exchangeable state extractant is usually for cationic metal elements, and there is a possibility of underestimating the proportion of chromium(VI) containing oxygen anions in the soil.

[0004] Therefore, there is still a lack of a method for accurately extracting and determining different forms of chromium in the soil of the high geological background area in the art. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a method for accurately extracting and determining different forms of chromium in the soil of the high geological background area and the application thereof.

[0006] The technical scheme of the present application is as follows:

[0007] A method for determining different forms of chromium in the soil of the high geological background area, comprising:

[0008] (1) grinding and sieving the soil sample from the high geological background area to obtain a sieved soil sample; adding a first extraction liquid to the sieved soil sample, and after fully oscillating at room temperature, performing first centrifugal separation, adding a first washing liquid, pure water, to the obtained precipitate and performing second centrifugal separation, and then obtaining a first precipitate sample; combining the supernatants obtained from the two centrifugal separations to obtain a first supernatant, determining the chromium content in the first supernatant, and calculating the content of water-soluble and exchangeable chromium in the soil according to formula (1);

[0009] (2) adding a second extraction liquid to the first precipitate sample, and after fully oscillating at room temperature, performing first centrifugal separation, adding a second washing liquid, pure water, to the obtained precipitate and performing second centrifugal separation, and then obtaining a second precipitate sample; combining the supernatants obtained from the two centrifugal separations to obtain a second supernatant, determining the chromium content in the second supernatant, and calculating the content of adsorbed hexavalent chromium in the soil according to formula (1);

[0010] (3) adding a third extraction liquid to the second precipitate sample, and after fully oscillating at room temperature, performing first centrifugal separation, adding a third washing liquid, i.e., the first extraction liquid, to the obtained precipitate and performing second centrifugal separation, and then obtaining a third precipitate sample; combining the supernatants obtained from the two centrifugal separations to obtain a third supernatant, determining the chromium content in the third supernatant, and calculating the content of carbonate-bound chromium in the soil according to formula (1);

[0011] (4) adding a fourth extraction liquid to the third precipitate sample, and after fully oscillating at room temperature, performing first centrifugal separation, adding a fourth washing liquid, i.e., the third extraction liquid, to the obtained precipitate and performing second centrifugal separation, and then obtaining a fourth precipitate sample; combining the supernatants obtained from the two centrifugal separations to obtain a fourth supernatant, determining the chromium content in the fourth supernatant, and calculating the content of manganese oxide-bound chromium in the soil according to formula (1);

[0012] (5) adding a fifth extraction liquid to the fourth precipitate sample, and after fully oscillating at room temperature, performing first centrifugal separation, adding a fifth washing liquid, i.e., the third extraction liquid, to the obtained precipitate and performing second centrifugal separation, and then obtaining a fifth precipitate sample; combining the supernatants obtained from the two centrifugal separations to obtain a fifth supernatant, determining the chromium content in the fifth supernatant, and calculating the content of organic-bound chromium in the soil according to formula (1);

[0013] (6) adding a sixth extracting solution to the fifth precipitate sample, performing first centrifugal separation after fully oscillating at room temperature, adding a sixth washing solution, i.e. the sixth extracting solution, to the obtained precipitate and performing second centrifugal separation, then obtaining a sixth precipitate sample from the obtained precipitate, combining the supernatants obtained from the two centrifugal separations to obtain a sixth supernatant, measuring the chromium content in the sixth supernatant, and calculating the content of amorphous iron oxide and / or hydroxide combined chromium in the soil according to formula (1);

[0014] (7) adding a seventh extracting solution to the sixth precipitate sample, performing first centrifugal separation after fully oscillating in dark at 95-97℃, observing the color of the obtained supernatant, if it presents brown color, repeatedly performing the process of adding a seventh extracting solution and oscillating in dark and centrifugal separation until the supernatant presents yellow or colorless, then adding a seventh washing solution, i.e. the sixth extracting solution, to the obtained precipitate and performing second centrifugal separation in dark, then obtaining a seventh precipitate sample from the obtained precipitate, combining the supernatants obtained from the two centrifugal separations to obtain a seventh supernatant, measuring the chromium content in the seventh supernatant, and calculating the content of crystalline iron oxide and / or hydroxide combined chromium in the soil according to formula (1);

[0015] (8) adding an eighth extracting solution to the seventh precipitate sample, performing first centrifugal separation after fully oscillating at 74-76℃, adding an eighth washing solution, i.e. a ninth extracting solution, to the obtained precipitate and performing second centrifugal separation, then obtaining an eighth precipitate sample from the obtained precipitate, combining the supernatants obtained from the two centrifugal separations to obtain an eighth supernatant, measuring the chromium content in the eighth supernatant, and calculating the content of silicate combined chromium in the soil according to formula (1);

[0016] (9) performing heating digestion of the eighth precipitate sample using hydrochloric acid, then adding digestion reagents nitric acid, hydrofluoric acid and perchloric acid in sequence to perform heating digestion, obtaining a digestion solution, measuring the chromium content in the digestion solution after constant volume, and calculating the content of chromium-spinel combined chromium in the soil according to formula (2):

[0017] wherein formula (1) is as follows:

[0018]

[0019] formula (2) is as follows:

[0020]

[0021] w i represents the content of the i th extracted chromium form, mg / kg; p i represents the mass concentration of chromium in the i th supernatant, μg / L, P 0i represents the mass concentration of chromium in the i th blank supernatant, μg / L; V tV represents the volume of the i-th eluent added, mL; j represents the number of times of repeated extraction using the eluent; V represents the volume of the i-th washing solution added, mL; m represents the mass of the soil sample, g; w9 represents the content of silicate-bound chromium in the soil sample, mg / kg; P9 represents the mass concentration of chromium in the digestion solution, μg / L; P x V represents the volume of the i-th eluent added, mL; j represents the number of times of repeated extraction using the eluent; V represents the volume of the i-th washing solution added, mL; m represents the mass of the soil sample, g; w9 represents the content of silicate-bound chromium in the soil sample, mg / kg; P9 represents the mass concentration of chromium in the digestion solution, μg / L; P 09 V represents the volume of the i-th eluent added, mL; j represents the number of times of repeated extraction using the eluent; V represents the volume of the i-th washing solution added, mL; m represents the mass of the soil sample, g; w9 represents the content of silicate-bound chromium in the soil sample, mg / kg; P9 represents the mass concentration of chromium in the digestion solution, μg / L; P

[0022] V represents the volume of the i-th eluent added, mL; j represents the number of times of repeated extraction using the eluent; V represents the volume of the i-th washing solution added, mL; m represents the mass of the soil sample, g; w9 represents the content of silicate-bound chromium in the soil sample, mg / kg; P9 represents the mass concentration of chromium in the digestion solution, μg / L; P

[0023] V represents the volume of the i-th eluent added, mL; j represents the number of times of repeated extraction using the eluent; V represents the volume of the i-th washing solution added, mL; m represents the mass of the soil sample, g; w9 represents the content of silicate-bound chromium in the soil sample, mg / kg; P9 represents the mass concentration of chromium in the digestion solution, μg / L; P

[0024] V represents the volume of the i-th eluent added, mL; j represents the number of times of repeated extraction using the eluent; V represents the volume of the i-th washing solution added, mL; m represents the mass of the soil sample, g; w9 represents the content of silicate-bound chromium in the soil sample, mg / kg; P9 represents the mass concentration of chromium in the digestion solution, μg / L; P

[0025] V represents the volume of the i-th eluent added, mL; j represents the number of times of repeated extraction using the eluent; V represents the volume of the i-th washing solution added, mL; m represents the mass of the soil sample, g; w9 represents the content of silicate-bound chromium in the soil sample, mg / kg; P9 represents the mass concentration of chromium in the digestion solution, μg / L; P

[0026] V represents the volume of the i-th eluent added, mL; j represents the number of times of repeated extraction using the eluent; V represents the volume of the i-th washing solution added, mL; m represents the mass of the soil sample, g; w9 represents the content of silicate-bound chromium in the soil sample, mg / kg; P9 represents the mass concentration of chromium in the digestion solution, μg / L; P

[0027] V represents the volume of the i-th eluent added, mL; j represents the number of times of repeated extraction using the eluent; V represents the volume of the i-th washing solution added, mL; m represents the mass of the soil sample, g; w9 represents the content of silicate-bound chromium in the soil sample, mg / kg; P9 represents the mass concentration of chromium in the digestion solution, μg / L; P

[0028] According to some preferred embodiments of the present application, the amount of the i-th extractant, i=1, 2, …, 8 is 30 mL, and the amount of the i-th washing liquid, i=1, 2, …, 8 is 10 mL.

[0029] According to some preferred embodiments of the present application, the method for determining different forms of chromium in soil in a high geological background area further comprises: obtaining the ratio of the content of each form of chromium in the soil to the total chromium content according to formula (3):

[0030]

[0031] wherein f i represents the ratio of the content of the i-th form of chromium in the soil to the total chromium content.

[0032] According to some preferred embodiments of the present application, the determination of the chromium content in the i-th supernatant is achieved by an inductively coupled plasma mass spectrometer.

[0033] According to some preferred embodiments of the present application, the determination comprises: passing the i-th supernatant through a 0.45 μm filter membrane, and then determining the chromium content by an inductively coupled plasma mass spectrometer.

[0034] The present application further provides an application method of the above-mentioned method for determining different forms of chromium in soil in a high geological background area, which is to apply the method to the assessment of the risk of chromium pollution in soil in a high geological background area.

[0035] The present application has the following advantages:

[0036] The present application uses NH4H2PO4 to extract the adsorbed hexavalent chromium in the soil, uses hot ascorbic acid-ammonium oxalate solution to quickly extract the iron oxide state chromium, and uses hot concentrated hydrochloric acid to extract the silicate state chromium, so that the chromium in the chromite is fully separated.

[0037] The present application can sequentially extract the same soil sample and analyze the chromium content in the soil after each step of extraction, so as to obtain the distribution of chromium in different forms.

[0038] The present application improves the steps of the commonly used continuous extraction method, solves the problem that the existing method is not suitable for chromium form analysis in high geological background soil, and can obtain accurate results of the distribution of chromium forms in this type of soil.

[0039] The application can reveal the variation law of key chromium forms (such as hexavalent chromium adsorption state, crystalline iron oxide combined state, silicate combined state and chromium-iron combined state) in soil with weathering degree by accurately analyzing the chromium forms in representative soil in high geological background area, and then a multidimensional correlation model of chromium form-weathering degree-parent rock type is constructed, so that the chromium form and migration potential in soil can be directly evaluated according to the rock type and weathering degree in high geological background area, without a large amount of soil collection and a large amount of analysis and detection, and the application is especially suitable for soil chromium pollution risk assessment in high geological background area, and has important application value in the fields of soil remediation and safe use of arable land. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The flowchart of the determination method used in the embodiments of the application is shown.

[0041] Figure 2 The determination results of the embodiments 1-4 of the application are shown in the graphs. DETAILED DESCRIPTION

[0042] The technical solutions in the application will be further described below with reference to the embodiments of the application. The embodiments described below are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor should fall within the protection scope of the application.

[0043] The calculation formula used in the following embodiments includes:

[0044] Formula (1):

[0045]

[0046] Formula (2):

[0047]

[0048] w i represents the content of the extracted chromium form, mg / kg; p i represents the mass concentration of chromium measured, μg / L, P 0i represents the mass concentration of chromium in the blank solution, μg / L; V t represents the volume of the extraction liquid added, mL; j represents the number of times of repeated extraction using the extraction liquid; V x represents the volume of the washing liquid added, mL; m represents the mass of the soil sample, g; w9 represents the content of silicate combined chromium in the soil sample, mg / kg; P9 represents the mass concentration of the digestion liquid, μg / L; P 09 represents the mass concentration of chromium in the corresponding blank solution, μg / L, and V represents the constant volume of the digestion liquid, mL.

[0049] The blank solution is obtained by performing the same steps as in the embodiments, but without adding the supernatant obtained from the soil sample.

[0050] Example 1

[0051] The following steps were used to determine different forms of chromium in the soil of a weakly weathered basalt high geological background area:

[0052] (1) After drying and grinding the soil sample, pass it through a 10-mesh sieve to obtain the sieved sample;

[0053] (2) Accurately weigh 1.00g of sieved sample into a centrifuge tube, add 30mL of solution I, shake at room temperature (22±1℃) for 16h, then centrifuge at 7000rpm / min for 15min, extract the supernatant, add 10mL of pure water into the tube, shake and centrifuge briefly to obtain the washing supernatant and precipitate, combine the two supernatants, filter through a 0.45μm filter membrane, and detect chromium with an inductively coupled plasma mass spectrometer. Calculate the water-soluble and exchangeable chromium content in the soil according to formula (1).

[0054] (3) Add 30 mL of solution II to the precipitate obtained in step (2), shake at room temperature for 16 h, centrifuge at 7000 rpm / min for 15 min, extract the supernatant, add 10 mL of pure water to the tube, shake and centrifuge briefly to obtain the washing supernatant and precipitate, combine the two supernatants, filter through a 0.45 μm filter membrane, detect chromium with inductively coupled plasma mass spectrometry, and calculate the content of adsorbed hexavalent chromium in the soil according to formula (1);

[0055] (4) Add 30 mL of solution III to the precipitate obtained in step (3), shake at room temperature for 24 h, centrifuge at 7000 rpm / min for 15 min, extract the supernatant, add 10 mL of solution I to the tube, shake briefly and centrifuge to obtain the washing supernatant and precipitate, combine the two supernatants, filter through a 0.45 μm filter membrane, detect chromium with inductively coupled plasma mass spectrometry, and calculate the carbonate-bound chromium content in the soil according to formula (1);

[0056] (5) Add 30 mL of solution IV to the precipitate obtained in step (4), shake at room temperature for 0.5 h, centrifuge at 7000 rpm / min for 15 min, extract the supernatant, add 10 mL of solution III to the tube, shake briefly and centrifuge to obtain the washing supernatant and precipitate, combine the two supernatants, filter through a 0.45 μm filter membrane, detect chromium with inductively coupled plasma mass spectrometry, and calculate the content of manganese oxide-bound chromium in the soil according to formula (1);

[0057] (6) To the precipitate obtained in step (5), 30 mL of solution V was added, and after oscillation at room temperature for 1.5 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution III was added to the tube, and after short oscillation and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of chromium in the organic combination state in the soil was calculated according to formula (1);

[0058] (7) To the precipitate obtained in step (6), 30 mL of solution VI was added, and after oscillation in the dark at room temperature for 4 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution VI was added to the tube, and after short oscillation and centrifugation in the dark, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of chromium in the amorphous iron oxide and / or hydroxide combination state in the soil was calculated according to formula (1);

[0059] (8) To the precipitate obtained in step (7), 30 mL of solution VII was added, and after oscillation in the dark at 96℃ for 0.5 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution VI was added to the tube, and after short oscillation and centrifugation in the dark, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of chromium in the crystalline iron oxide and / or hydroxide combination state in the soil was calculated according to formula (1);

[0060] (9) To the precipitate obtained in step (8), 30 mL of solution VIII was added, and after oscillation at 75℃ for 24 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted; 10 mL of solution IX was added to the tube, and after short oscillation and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of chromium in the silicate combination state in the soil was calculated according to formula (1);

[0061] (10) The precipitate obtained in step (9) was washed and transferred to a crucible with hydrochloric acid, heated and digested on a hot plate, and then nitric acid, hydrofluoric acid and perchloric acid were added in sequence and heated and digested, and after constant volume, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of chromium in the chromium-spinel combination state in the soil was calculated according to formula (2).

[0062] Among them, the solutions used are respectively:

[0063] Solution I: 0.02 mol / L CaCl2 solution;

[0064] Solution II: 0.01 mol / L NH4H2PO4 solution (pH = 8.0);

[0065] Solution III: 1 mol / L ammonium acetate solution (pH = 6.0);

[0066] Solution IV: mixed solution of 0.1 mol / L hydroxylamine hydrochloride and 1 mol / L ammonium acetate (pH = 6.0);

[0067] Solution V: 0.025 mol / L EDTA solution (pH = 4.6);

[0068] Solution VI: 0.2 mol / L ammonium oxalate solution (pH = 3.25);

[0069] Solution VII: mixed solution of 0.1 mol / L ascorbic acid and 0.2 mol / L ammonium oxalate (pH = 3.25);

[0070] Solution VIII: 12 mol / L hydrochloric acid solution;

[0071] Solution IX: 1 mol / L hydrochloric acid solution.

[0072] Example 2

[0073] The different forms of chromium in the basalt strongly weathered high geological background area soil were determined by the following steps:

[0074] (1) After the soil sample was dried, ground and passed through a 10-mesh sieve, a sieved sample was obtained;

[0075] (2) 1.00 g of the sieved sample was accurately weighed into a centrifuge tube, 30 mL of solution I was added, and after oscillation at room temperature (22±1℃) for 16 h, centrifugation at 7000 rpm / min for 15 min was performed, the supernatant was extracted, 10 mL of pure water was added to the tube, and after short oscillation and centrifugation, the washing supernatant and the precipitate were obtained, the two supernatants were combined, filtered through a 0.45 μm filter membrane, and then chromium was detected by an inductively coupled plasma mass spectrometer, and the content of water-soluble and exchangeable chromium in the soil was calculated according to formula (1);

[0076] (3) 30 mL of solution II was added to the precipitate obtained in step (2), oscillation was performed at room temperature for 16 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of pure water was added to the tube, and after short oscillation and centrifugation, the washing supernatant and the precipitate were obtained, the two supernatants were combined, filtered through a 0.45 μm filter membrane, and then chromium was detected by an inductively coupled plasma mass spectrometer, and the content of adsorbed hexavalent chromium in the soil was calculated according to formula (1);

[0077] (4) To the precipitate obtained in step (3), 30 mL of solution III was added, and after oscillation at room temperature for 24 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution I was added to the tube, and after short oscillation and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of carbonate-bound chromium in the soil was calculated according to formula (1);

[0078] (5) To the precipitate obtained in step (4), 30 mL of solution IV was added, and after oscillation at room temperature for 0.5 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution III was added to the tube, and after short oscillation and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of manganese oxide-bound chromium in the soil was calculated according to formula (1);

[0079] (6) To the precipitate obtained in step (5), 30 mL of solution V was added, and after oscillation at room temperature for 1.5 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution III was added to the tube, and after short oscillation and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of organic-bound chromium in the soil was calculated according to formula (1);

[0080] (7) To the precipitate obtained in step (6), 30 mL of solution VI was added, and after oscillation in the dark at room temperature for 4 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution VI was added to the tube, and after short oscillation and centrifugation in the dark, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of amorphous iron oxide and / or hydroxide-bound chromium in the soil was calculated according to formula (1);

[0081] (8) To the precipitate obtained in step (7), 30 mL of solution VII was added, and after oscillation in the dark at 96℃ for 0.5 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, and the extraction was repeated once, 10 mL of solution VI was added to the tube, and after short oscillation and centrifugation in the dark, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of crystalline iron oxide and / or hydroxide-bound chromium in the soil was calculated according to formula (1);

[0082] (9) To the precipitate obtained in step (8), 30 mL of solution VIII was added, and after oscillation at 75°C for 24 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution IX was added to the tube, and after short oscillation and centrifugation, the washing supernatant and precipitate were obtained, the two supernatants were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the silicate-bound chromium content in the soil was calculated according to formula (1);

[0083] (10) The precipitate obtained in step (9) was washed with hydrochloric acid and transferred to a crucible, and then heated and digested on a hot plate, followed by the sequential addition of nitric acid, hydrofluoric acid and perchloric acid for heating and digestion, and after constant volume, chromium was detected by an inductively coupled plasma mass spectrometer, and the chromium content in the soil was calculated according to formula (2);

[0084] Among them, the used solutions are respectively:

[0085] Solution I: 0.02 mol / L CaCl2 solution;

[0086] Solution II: 0.01 mol / L NH4H2PO4 solution (pH = 8.0);

[0087] Solution III: 1 mol / L ammonium acetate solution (pH = 6.0);

[0088] Solution IV: 0.1 mol / L hydroxylamine hydrochloride and 1 mol / L ammonium acetate mixed solution (pH = 6.0);

[0089] Solution V: 0.025 mol / L EDTA solution (pH = 4.6);

[0090] Solution VI: 0.2 mol / L ammonium oxalate solution (pH = 3.25);

[0091] Solution VII: 0.1 mol / L ascorbic acid and 0.2 mol / L ammonium oxalate mixed solution (pH = 3.25);

[0092] Solution VIII: 6 mol / L hydrochloric acid solution;

[0093] Solution IX: 1 mol / L hydrochloric acid solution.

[0094] Example 3

[0095] The different forms of chromium in the weakly weathered soil in the high geological background area of the serpentine rock were determined by the following steps:

[0096] (1) After the soil sample was dried, ground and passed through a 10 mesh sieve, a sieved sample was obtained;

[0097] (2) Accurately weigh 1.00 g of the sieved sample into a centrifuge tube, add 30 mL of solution I, after oscillation for 16 h at room temperature (22±1℃), centrifuge at 7000 rpm / min for 15 min, extract the supernatant, add 10 mL of pure water into the tube, after short oscillation and centrifugation, obtain the washing supernatant and the precipitate, combine the two supernatants, filter through a 0.45 μm filter membrane, and then detect the chromium by an inductively coupled plasma mass spectrometer, to calculate the water-soluble and exchangeable chromium content in the soil according to formula (1);

[0098] (3) Add 30 mL of solution II to the precipitate obtained in step (2), oscillate for 16 h at room temperature, centrifuge at 7000 rpm / min for 15 min, extract the supernatant, add 10 mL of pure water into the tube, after short oscillation and centrifugation, obtain the washing supernatant and the precipitate, combine the two supernatants, filter through a 0.45 μm filter membrane, and then detect the chromium by an inductively coupled plasma mass spectrometer, to calculate the adsorbed hexavalent chromium content in the soil according to formula (1);

[0099] (4) Add 30 mL of solution III to the precipitate obtained in step (3), oscillate for 24 h at room temperature, centrifuge at 7000 rpm / min for 15 min, extract the supernatant, add 10 mL of solution I into the tube, after short oscillation and centrifugation, obtain the washing supernatant and the precipitate, combine the two supernatants, filter through a 0.45 μm filter membrane, and then detect the chromium by an inductively coupled plasma mass spectrometer, to calculate the carbonate-bound chromium content in the soil according to formula (1);

[0100] (5) Add 30 mL of solution IV to the precipitate obtained in step (4), oscillate for 0.5 h at room temperature, centrifuge at 7000 rpm / min for 15 min, extract the supernatant, add 10 mL of solution III into the tube, after short oscillation and centrifugation, obtain the washing supernatant and the precipitate, combine the two supernatants, filter through a 0.45 μm filter membrane, and then detect the chromium by an inductively coupled plasma mass spectrometer, to calculate the manganese oxide-bound chromium content in the soil according to formula (1);

[0101] (6) Add 30 mL of solution V to the precipitate obtained in step (5), oscillate for 1.5 h at room temperature, centrifuge at 7000 rpm / min for 15 min, extract the supernatant, add 10 mL of solution III into the tube, after short oscillation and centrifugation, obtain the washing supernatant and the precipitate, combine the two supernatants, filter through a 0.45 μm filter membrane, and then detect the chromium by an inductively coupled plasma mass spectrometer, to calculate the organic-bound chromium content in the soil according to formula (1);

[0102] (7) To the precipitate obtained in step (6), 30 mL of solution VI was added, and after oscillation in the dark at room temperature for 4 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution VI was added to the tube, and after short oscillation in the dark and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of chromium combined with amorphous iron oxide and / or hydroxide in the soil was calculated according to formula (1);

[0103] (8) To the precipitate obtained in step (7), 30 mL of solution VII was added, and after oscillation in the dark at 96℃ for 0.5 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, and the extraction was repeated once, 10 mL of solution VI was added to the tube, and after short oscillation in the dark and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of chromium combined with crystalline iron oxide and / or hydroxide in the soil was calculated according to formula (1);

[0104] (9) To the precipitate obtained in step (8), 30 mL of solution VIII was added, and after oscillation at 75℃ for 24 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution IX was added to the tube, and after short oscillation and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of chromium combined with silicate in the soil was calculated according to formula (1);

[0105] (10) The precipitate obtained in step (9) was washed and transferred to a crucible with hydrochloric acid, heated and digested on a hot plate, and then nitric acid, hydrofluoric acid and perchloric acid were added in sequence for heating and digestion, and after constant volume, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of chromium combined with chromium iron ore in the soil was calculated according to formula (2);

[0106] Among them, the used solutions are respectively:

[0107] Solution I: 0.02 mol / L CaCl2 solution;

[0108] Solution II: 0.01 mol / L NH4H2PO4 solution (pH=8.0);

[0109] Solution III: 1 mol / L ammonium acetate solution (pH=6.0);

[0110] Solution IV: 0.1 mol / L hydroxylamine hydrochloride and 1 mol / L ammonium acetate mixed solution (pH=6.0);

[0111] Solution V: 0.025 mol / L EDTA solution (pH=4.6);

[0112] Solution VI: 0.2 mol / L ammonium oxalate solution (pH = 3.25);

[0113] Solution VII: 0.1 mol / L ascorbic acid and 0.2 mol / L ammonium oxalate mixed solution (pH = 3.25);

[0114] Solution VIII: 12 mol / L hydrochloric acid solution;

[0115] Solution IX: 1 mol / L hydrochloric acid solution.

[0116] Example 4

[0117] The different forms of chromium in the soil in the strong weathering high geological background area of the serpentine rock were determined by the following steps:

[0118] (1) After the soil sample was dried, ground and passed through a 10-mesh sieve, a sieved sample was obtained;

[0119] (2) 1.00 g of the sieved sample was accurately weighed into a centrifuge tube, 30 mL of solution I was added, and after oscillation at room temperature (22±1℃) for 16 h, centrifugation at 7000 rpm / min for 15 min was performed, the supernatant was extracted, 10 mL of pure water was added to the tube, and after short oscillation and centrifugation, the washing supernatant and the precipitate were obtained, the two supernatants were combined, filtered through a 0.45 μm filter membrane, and then chromium was detected by an inductively coupled plasma mass spectrometer, and the content of water-soluble and exchangeable chromium in the soil was calculated according to formula (1);

[0120] (3) 30 mL of solution II was added to the precipitate obtained in step (2), oscillation was performed at room temperature for 16 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of pure water was added to the tube, and after short oscillation and centrifugation, the washing supernatant and the precipitate were obtained, the two supernatants were combined, filtered through a 0.45 μm filter membrane, and then chromium was detected by an inductively coupled plasma mass spectrometer, and the content of adsorbed hexavalent chromium in the soil was calculated according to formula (1);

[0121] (4) 30 mL of solution III was added to the precipitate obtained in step (3), oscillation was performed at room temperature for 24 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution I was added to the tube, and after short oscillation and centrifugation, the washing supernatant and the precipitate were obtained, the two supernatants were combined, filtered through a 0.45 μm filter membrane, and then chromium was detected by an inductively coupled plasma mass spectrometer, and the content of carbonate-bound chromium in the soil was calculated according to formula (1);

[0122] (5) To the precipitate obtained in step (4), 30 mL of solution IV was added, and after oscillation at room temperature for 0.5 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution III was added to the tube, and after short oscillation and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of manganese oxide-bound chromium in the soil was calculated according to formula (1);

[0123] (6) To the precipitate obtained in step (5), 30 mL of solution V was added, and after oscillation at room temperature for 1.5 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution III was added to the tube, and after short oscillation and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of organic-bound chromium in the soil was calculated according to formula (1);

[0124] (7) To the precipitate obtained in step (6), 30 mL of solution VI was added, and after oscillation in the dark at room temperature for 4 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution VI was added to the tube, and after short oscillation and centrifugation in the dark, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of amorphous iron oxide and / or hydroxide-bound chromium in the soil was calculated according to formula (1);

[0125] (8) To the precipitate obtained in step (7), 30 mL of solution VII was added, and after oscillation in the dark at 96℃ for 0.5 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, and the extraction was repeated once, 10 mL of solution VI was added to the tube, and after short oscillation and centrifugation in the dark, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of crystalline iron oxide and / or hydroxide-bound chromium in the soil was calculated according to formula (1);

[0126] (9) To the precipitate obtained in step (8), 30 mL of solution VIII was added, and after oscillation at 75℃ for 24 h, centrifugation was performed at 7000 rpm / min for 15 min, the supernatant was extracted, 10 mL of solution IX was added to the tube, and after short oscillation and centrifugation, the washing supernatant and precipitate were obtained, the supernatants of the two times were combined, and after filtration through a 0.45 μm filter membrane, chromium was detected by an inductively coupled plasma mass spectrometer, and the content of silicate-bound chromium in the soil was calculated according to formula (1);

[0127] (10) The precipitate obtained in step (9) is washed with hydrochloric acid and transferred to a crucible, heated and digested on a hot plate, and then nitric acid, hydrofluoric acid and perchloric acid are added in sequence and heated and digested, and after being diluted to volume, chromium is detected by an inductively coupled plasma mass spectrometer, and the content of chromium in chromite combined state in the soil is calculated according to formula (2);

[0128] The solutions used are as follows:

[0129] Solution I: 0.02 mol / L CaCl2 solution;

[0130] Solution II: 0.01 mol / L NH4H2PO4 solution (pH = 8.0);

[0131] Solution III: 1 mol / L ammonium acetate solution (pH = 6.0);

[0132] Solution IV: mixed solution of 0.1 mol / L hydroxylamine hydrochloride and 1 mol / L ammonium acetate (pH = 6.0);

[0133] Solution V: 0.025 mol / L EDTA solution (pH = 4.6);

[0134] Solution VI: 0.2 mol / L ammonium oxalate solution (pH = 3.25);

[0135] Solution VII: mixed solution of 0.1 mol / L ascorbic acid and 0.2 mol / L ammonium oxalate (pH = 3.25);

[0136] Solution VIII: 6 mol / L hydrochloric acid solution;

[0137] Solution IX: 1 mol / L hydrochloric acid solution.

[0138] The determination process of the above examples is shown in FIG. 1, and the determination results are shown in FIG. 2. Figure 1 The determination process of the above examples is shown in FIG. 1, and the determination results are shown in FIG. 2. Figure 2 The determination process of the above examples is shown in FIG. 1, and the determination results are shown in FIG. 2.

[0139] It can be seen that the present application can accurately analyze the chromium forms of the soil developed on different rock types, and can also analyze the differences in chromium forms in different weathered soils. For example, compared with the basalt weakly weathered soil of Example 1, the strongly weathered soil of Example 2 has a significant increase in the crystalline iron oxide combined state of chromium (from 55.78% to 71.82%), indicating that weathering promotes the transformation of amorphous iron oxides to more stable crystalline states, and the content of amorphous iron oxides decreases from 12.06% to 4.42%; the silicate combined state decreases (from 22.46% to 19.46%), indicating that weathering leads to the decomposition of silicate minerals, and the released chromium is fixed by crystalline iron oxides; the content of chromite combined state decreases (from 9.61% to 4.21%), indicating that part of the chromite is also oxidized and decomposed.

[0140] However, in the serpentine weathered soil, the silicate-bound state of chromium in the strongly weathered soil of Example 4 is significantly reduced compared to the silicate-bound state of chromium in the weakly weathered soil of Example 3 (from 47.60% to 20.80%), indicating that weathering destroys the silicate structure and releases chromium to other forms; the crystalline iron oxide-bound state increases significantly (from 6.60% to 22.48%), reflecting the transformation of chromium in the soil to the stable crystalline iron oxide state; the chromite-bound state increases significantly (from 44.87% to 54.73%), indicating that the parent rock is rich in primary chromite and is stably present in the soil; the hexavalent chromium adsorption state increases significantly (from 0.20% to 1.46%), indicating that the weathering process promotes the oxidation of chromium.

[0141] As can also be seen by comparing Examples 1-4, there are significant differences in the chromium forms in basalt and serpentine developed soils. In basalt developed soils, chromium is mainly in the form of crystalline iron oxide-bound state (content of 55-72%); while in serpentine developed soils, chromium is mainly in the form of stable chromite-bound state (content of 45-55%); and strong weathering increases the risk of hexavalent chromium compared to weak weathering. The results show that the degree of weathering and the type of parent rock jointly affect the distribution of chromium binding states, and the determination method of the present application can clearly distinguish them, achieving targeted management of the environmental risk of chromium in different soil types.

[0142] It should be noted that the above only describes the preferred embodiments of the present application, which should not limit the protection scope of the technical solutions of the present application. Any modifications made by those skilled in the art to the technical solutions described in the foregoing embodiments, equivalent replacements of technical features, etc., should be included in the protection scope of the present application, as long as they are within the spirit and principles of the present application.

Claims

1. A method for determining different forms of chromium in soils of high geological background areas, characterized in that, It includes: (1) Grind and sieve the soil sample from the high geological background area to obtain the sieved soil sample. Add the first extract to the sieved soil sample, shake it fully at room temperature and then perform the first centrifugation. Add the first washing solution (pure water) to the precipitate and perform the second centrifugation. The precipitate obtained thereafter is the first precipitate sample. Combine the supernatants obtained from the two centrifugations to obtain the first supernatant. Determine the chromium content in the first supernatant and calculate the content of water-soluble and exchangeable chromium in the soil according to formula (1). (2) Add the second extract to the first precipitate sample, shake it thoroughly at room temperature and then perform the first centrifugation. Add the second washing solution (pure water) to the precipitate and perform the second centrifugation. The precipitate obtained thereafter is the second precipitate sample. Combine the supernatants obtained from the two centrifugations to obtain the second supernatant. Determine the chromium content in the second supernatant and calculate the adsorbed hexavalent chromium content in the soil according to formula (1). (3) Add the third extract to the second precipitate sample, shake it thoroughly at room temperature and then perform the first centrifugation. Add the third washing liquid, i.e. the first extract, to the precipitate and perform the second centrifugation. The precipitate obtained thereafter is the third precipitate sample. Combine the supernatants obtained from the two centrifugations to obtain the third supernatant. Determine the chromium content in the third supernatant and calculate the carbonate-bound chromium content in the soil according to formula (1). (4) Add the fourth extract to the third precipitate sample, shake thoroughly at room temperature and then centrifuge for the first time. Add the fourth washing liquid, i.e. the third extract, to the precipitate and centrifuge for the second time. The precipitate obtained thereafter is the fourth precipitate sample. Combine the supernatants obtained from the two centrifugations to obtain the fourth supernatant. Determine the chromium content in the fourth supernatant and calculate the chromium content in the soil in the manganese oxide bound state according to formula (1). (5) Add the fifth extract to the fourth precipitate sample, shake thoroughly at room temperature and then centrifuge for the first time. Add the fifth washing liquid, i.e. the third extract, to the precipitate and centrifuge for the second time. The precipitate obtained thereafter is the fifth precipitate sample. Combine the supernatants obtained from the two centrifugations to obtain the fifth supernatant. Determine the chromium content in the fifth supernatant and calculate the organic chromium content in the soil according to formula (1). (6) Add the sixth extract to the fifth precipitate sample, shake thoroughly at room temperature and then centrifuge for the first time. Add the sixth washing solution, i.e. the sixth extract, to the precipitate and centrifuge for the second time. The precipitate obtained thereafter is the sixth precipitate sample. Combine the supernatants obtained from the two centrifugations to obtain the sixth supernatant. Determine the chromium content in the sixth supernatant and calculate the content of amorphous iron oxide and / or amorphous iron hydroxide bound chromium in the soil according to formula (1). (7) Add the seventh extract to the sixth precipitate sample, and perform the first centrifugation after shaking in the dark at 95-97℃. Observe the color of the supernatant obtained. If it is brown, repeat the process of adding the seventh extract, shaking in the dark and centrifuging until the supernatant is yellow or colorless. Then add the seventh washing solution, i.e. the sixth extract, to the precipitate and perform the second centrifugation in the dark. The precipitate obtained is the seventh precipitate sample. Combine the supernatants obtained from the two centrifugations to obtain the seventh supernatant. Determine the chromium content in the seventh supernatant and calculate the content of crystalline iron oxide and / or crystalline iron hydroxide bound chromium in the soil according to formula (1). (8) Add the eighth extract to the seventh precipitate sample, shake thoroughly at 74-76℃ and then centrifuge for the first time. Add the eighth washing solution, i.e. the ninth extract, to the precipitate and centrifuge for the second time. The precipitate obtained thereafter is the eighth precipitate sample. Combine the supernatants obtained from the two centrifugations to obtain the eighth supernatant. Determine the chromium content in the eighth supernatant and calculate the silicate-bound chromium content in the soil according to formula (1). (9) The eighth precipitate sample was heated and digested with hydrochloric acid, followed by the addition of nitric acid, hydrofluoric acid and perchloric acid as digestion agents for further heating and digestion to obtain a digestion solution. After adjusting the volume, the chromium content in the digestion solution was determined, and the chromium content in the soil bound to chromite was calculated according to formula (2): Equation (1) is as follows: Equation (2) is as follows: w i p represents the content of the i-th chromium form extracted, in mg / kg; i This indicates the measured mass concentration of chromium in the i-th supernatant, in μg / L, p. 0i V represents the mass concentration of chromium in the i-th blank supernatant, in μg / L; t V represents the volume of the i-th extract added, in mL; j represents the number of times the extract was repeated using that extract; V x The volume of the i-th washing solution added is represented in mL; m represents the mass of the soil sample in g; w9 represents the content of chromite-bound chromium in the soil in mg / kg; p9 represents the mass concentration of chromium in the digestion solution in μg / L; p 09 V represents the mass concentration of chromium in the corresponding blank digestion solution, in μg / L; V represents the final volume of the digestion solution, in mL; and i represents any ordinal number from one to nine. Wherein, the i-th blank supernatant is the supernatant obtained by combining two centrifugations after performing the same operation in steps (1)-(i) but without adding soil samples, and the blank digestion solution is the digestion solution obtained by performing the same operation in step (9) but without adding the eighth precipitated sample. The first extract is a 0.02 mol / L calcium chloride solution; the second extract is a 0.01 mol / L ammonium dihydrogen phosphate solution with pH adjusted to 8.0-8.2; the third extract is a 1 mol / L ammonium acetate solution with pH adjusted to 6.0-6.2; the fourth extract is a mixed solution of 0.1 mol / L hydroxylamine hydrochloride and 1 mol / L ammonium acetate with pH adjusted to 6.0-6.2; and the fifth extract is a solution with pH adjusted to... The sixth extract is a 0.025 mol / L ethylenediaminetetraacetic acid solution with a pH adjusted to 3.25-3.30; the seventh extract is a mixed solution of 0.1 mol / L ascorbic acid and 0.2 mol / L ammonium oxalate with a pH adjusted to 3.25-3.30; the eighth extract is a 6-12 mol / L hydrochloric acid solution; and the ninth extract is a 1 mol / L hydrochloric acid solution.

2. The method for determining different forms of chromium in soils of high geological background areas according to claim 1, characterized in that, The room temperature is 22-25℃, and the oscillation condition is 150-170 rpm / min.

3. The method for determining different forms of chromium in soils of high geological background areas according to claim 1, characterized in that, The centrifugation rate is 6500-7500 rpm, and the time is 13-17 min.

4. The method for determining different forms of chromium in soils of high geological background areas according to claim 1, characterized in that, The mass of the soil sample after sieving is 0.99-1.01g, and the sieving is through a 10-mesh sieve.

5. The method for determining different forms of chromium in soils of high geological background areas according to claim 1, characterized in that, It also includes: obtaining the ratio of the content of each form of chromium in the soil to the total chromium content according to formula (3): Among them, f i This represents the ratio of the content of the i-th chromium form in the soil to the total chromium content.

6. The method for determining different forms of chromium in soils of high geological background areas according to claim 1, characterized in that, in, The chromium content in the i-th supernatant was determined by inductively coupled plasma mass spectrometry.

7. The method for determining different forms of chromium in soils of high geological background areas according to claim 6, characterized in that, The determination includes: passing the i-th supernatant through a 0.45 μm filter membrane, followed by determination of chromium content using inductively coupled plasma mass spectrometry.

8. The application of the method for determining different forms of chromium in soils of high geological background areas as described in any one of claims 1-7, comprising: The method for determining different forms of chromium in soils with high geological backgrounds was applied to the assessment of chromium pollution risk in soils with high geological backgrounds.

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