CN111551522B - Method for quantifying ratio of goethite to hematite in sediment by diffuse reflection spectrum - Google Patents
Method for quantifying ratio of goethite to hematite in sediment by diffuse reflection spectrum Download PDFInfo
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- CN111551522B CN111551522B CN202010556006.2A CN202010556006A CN111551522B CN 111551522 B CN111551522 B CN 111551522B CN 202010556006 A CN202010556006 A CN 202010556006A CN 111551522 B CN111551522 B CN 111551522B
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Abstract
The invention discloses a novel method for quantifying the ratio of goethite to hematite in sediment based on diffuse reflection spectroscopy, which comprises the following steps: (1) selecting a typical malan loess and tertiary red clay sample in a loess plateau area as a substrate, and grinding the materials into powder; (2) adding samples with different contents of hematite and goethite and proportioning loess and red clay substrates; (3) the sample is tested by a Lambda 900 ultraviolet/visible light/near infrared spectrophotometer; (4) obtaining continuum removal data for each sample from the post-test data; (5) wavelength lambda at equal part of areahCalculating; (6) using the known wavelength lambda at the equal part of the goethite/hematite ratio and the areahRegression analysis was performed. The method has the advantages of simple pretreatment, reliable quantification, no substrate effect, capability of quickly, effectively and accurately quantifying the ratio of goethite to hematite in various sediments, time and cost saving, and suitability for large-scale quantitative test of the ratio of goethite to hematite in the sediments.
Description
Technical Field
The invention belongs to a novel method for measuring the ratio of goethite to hematite in diffuse reflection spectrum quantitative sediment, and belongs to the field of environment.
Background
Goethite and hematite are two kinds of iron oxides associated therewith, widely affect the color of soil, are one of the most important factors determining the color of soil, and are commonly used for classification of soil and the like. In addition, the change of the ratio is mainly controlled by the change of the climate environment, goethite favors a cold and wet environment, hematite is more preferentially formed in a warm and dry environment, namely, more goethite is formed in the cold and wet environment than in the warm and dry environment, more hematite is formed than in the goethite, the ratio represents the change of the dryness and the wetness, and the goethite is widely applied to loess, lakes and marine sediment carriers and is used for reconstructing the past climate environment change. There is therefore a great need for research efforts to quantify the ratio of goethite/hematite in deposits.
At present, the traditional method for testing the ratio of goethite/hematite in the sediment mainly comprises a diffuse reflection spectrum technology, but has greater unreliability, and the main method comprises the following steps: one method is to obtain a second derivative after the measured diffuse reflection spectrum is converted by a Kubelka-Munk function to reflect the content of minerals, wherein the characteristic peak values of goethite and hematite are respectively 425nm and 535nm, and the valley-to-top heights of the characteristic peaks are respectively I425nmAnd I535nmGoethite/hematite ratio of 1.56 × (I)425nm/I535nm) In the method, hematite also has an absorption peak at 425nm, and the second derivatives of different contents of goethite and different sediment types at 535nm are changed, so that the quantification of the hematite is influenced. In addition, the content of hematite is calculated by using the red degree of a diffuse reflection spectrum, the content of free iron in a sample is extracted by using sodium citrate-sodium bicarbonate-sodium dithionite, the content of hematite is subtracted from the content of free iron to obtain the content of goethite, and the ratio of the content of goethite is calculated. In addition, a large amount of amorphous iron is present in the free iron, and therefore, the goethite content obtained is greatly overestimated. In addition, X-ray diffraction is also commonly used for quantifying the goethite/hematite ratio, but the detection line is high, and the requirement on the crystal form of the goethite/hematite in a sample is high, so that the method is widely considered as a qualitative and semi-quantitative method.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects in the prior art, the invention provides a novel method for quantifying the ratio of goethite to hematite in sediment based on diffuse reflection spectroscopy, which has the advantages of simple pretreatment, convenient test, high efficiency, accurate quantification and no influence from the type of the sediment.
The technical scheme is as follows: in order to solve the technical problem, the novel method for quantifying the ratio of the goethite to the hematite in the sediment based on the diffuse reflection spectrum comprises the following steps:
(1) selecting a typical malan loess and a tertiary red clay sample in a loess plateau area as a substrate, grinding the original sample by using an agate mortar to prepare a powder sample, weighing about 11-16g of the sample, adding 500ml of 0.3mole/L sodium citrate solution and 50ml of 1mole/L sodium bicarbonate solution, adding 2 +/-0.2 g of sodium hydrosulfite to ensure excessive reaction, placing the sample in a shaking table at 80 ℃ for oscillation reaction for 90 minutes until the sediment is grey, namely complete reaction, centrifuging the sample in a centrifuge at the rotating speed of 5000 r/minute for 15 minutes, pouring out the supernatant, washing the sample with secondary distilled water for three times, drying the residue at room temperature, and grinding the residue into powder; (ii) a
(2) Adding samples with different contents of hematite and goethite based on loess or red clay base according to the proportion: firstly, weighing a substrate sample by using a ten-thousand-position high-precision electronic balance, pouring the substrate sample into an agate mortar, weighing goethite and hematite samples, pouring the goethite and hematite samples into the agate mortar filled with the substrate, grinding for more than 10 minutes to ensure that the goethite and hematite samples are uniformly mixed without obvious color difference, and sequentially matching 31 samples with different goethite and hematite ratios to form a loess substrate and a red clay substrate;
(3) testing the proportioned sample by using a Lambda 900 diffuse reflection spectrometer, wherein the scanning wavelength is 400-700nm and the interval is 2nm, when the proportioned sample is tested, firstly grinding the sample by using an agate mortar to prepare a powder sample, taking a proper amount of the powder sample on a glass slide, adding a few drops of distilled water to mix the powder sample into paste, uniformly stirring and smearing the paste, lightly knocking the glass slide on a table top to flatly spread the sample, and naturally drying the sample; and then testing the barium sulfate white board on a computer, wherein the barium sulfate white board is used as a color background, the barium sulfate white board is placed at a sample placing position of the instrument, a cover is covered, Lambda 900 software in a computer is clicked, the wavelength range is 400-700nm, and the interval is 2 nm. Modifying the sample number, clicking an AUTOZORO button, after the test is finished, clicking a START button to test, wherein the test result is required to be within 100 +/-1%, if the test result does not reach the standard, the test result is required to be repeatedly carried out, when the sample is tested, a glass slide coated with the sample is placed in a sample bin, the sample number is filled, the START button is clicked, the test time of one sample is 2 minutes, and the data is automatically stored after the test is finished;
(4) obtaining continuum removal data for each sample from the post-test data;
(5) wavelength lambda at equal part of areahCalculating by using PAST3.0 software to perform 0.1nm interpolation on the continuous system removal data, and based on Microsoft EXCEL software calculation program, finding out the reflectivity R at 450nm450nmThen, the nearest R is found out between 450-600nm450nmWavelength λ of valuemaxRemoval curve for continuum starting from 450nm to λmaxThe area integral calculation is carried out at intervals of 0.1nm, and the cumulative area, lambda, is calculatedmaxIs arranged asThe maximum cumulative area, then the cumulative area at each wavelength divided by the maximum area, the wavelength position at which the value is 50% is the area-dividing wavelength λhA value;
(6) using the known wavelength lambda at the equal part of the goethite/hematite ratio and the areahPerforming regression analysis, wherein the quantitative relationship is the goethite/hematite ratio of 0.003251 lambdah 2-3.609264*λh+996.742926，λhThe wavelength at which the area is equally divided.
Preferably, the specific contents of step (4) are as follows: the tested data format is CSV, the ENVI Classic5.1 version is utilized to carry out Continuum removal, firstly, the Spectral Library Builder under the Spectral Libraries under the Spectral menu of the ENVI Classic5.1 is clicked, then, the First Input Spectrum is selected, the data are led in batch, the Plot is clicked, the Endmember Collection Spectra window is popped up, the continuous Removed data under the Plot _ Function is selected for processing, then, the data are led out, and the Continuum Removed data of each sample can be obtained
Has the advantages that: the method for quantifying the ratio of goethite to hematite in the sediment based on the diffuse reflection spectrum has the advantages of simple pretreatment, capability of quickly, effectively and accurately quantifying the ratio of goethite to hematite in the sediment, time saving and cost saving, and suitability for large-scale quantitative test of the ratio of goethite to hematite in the sediment.
Drawings
Figure 1 is a continuous system removal spectrum of goethite and hematite standard minerals (top) versus different goethite/hematite ratios added (bottom).
FIG. 2 is a schematic flow chart of the present invention.
FIG. 3 is a schematic diagram showing the correlation between the wavelength at the equal part of the area and the goethite/hematite ratio in the present invention.
Detailed Description
The present invention will be further described with reference to the accompanying drawings.
As shown in fig. 2, in the novel method for quantifying the ratio of goethite to hematite in the deposit based on the diffuse reflection spectrum, the continuous and systematic removal technology based on the principal principle can better obtain the characteristic spectrograms of goethite and hematite, the characteristic peak of the goethite is mainly 486.5nm, the peak types are symmetrical, the characteristic peak of the hematite is about 545nm, the peak type of the goethite is obviously blue-shifted, and the peak types of the goethite and the hematite are not influenced by the type of the deposit, so that the method for quantitatively measuring the ratio of the goethite to the goethite by using the peak types of the characteristic peaks is reliable, and the method comprises the following steps:
(1) selecting a typical malan loess and tertiary red clay sample in a loess plateau area as a substrate: grinding an original sample by using an agate mortar to prepare a powder sample, weighing about 11-16g of the sample, firstly adding 500ml of 0.3mole/L sodium citrate solution and 50ml of 1mole/L sodium bicarbonate solution, then adding 2 +/-0.2 g of sodium hydrosulfite, placing the sample in a shaking table at 80 ℃ for oscillation reaction for 90 minutes until the deposit is grey white, namely the reaction is complete, centrifuging the sample in a centrifuge at the rotating speed of 5000 r/min for 15 minutes, then pouring out the supernatant, washing the sample with secondary distilled water for three times, drying the residue in an oven at 40 ℃ and grinding the residue into powder;
(2) adding samples proportioning loess and red clay bases and different contents of hematite and goethite: firstly, weighing a loess or red clay substrate sample by using a ten-thousand-position high-precision electronic balance, pouring the loess or red clay substrate sample into an agate mortar, weighing goethite and hematite samples, pouring the goethite and hematite samples into the agate mortar with the substrate, grinding for more than 10 minutes to ensure that the goethite and hematite samples are uniformly mixed without obvious color difference, and sequentially proportioning 31 samples with different goethite and hematite ratios for forming the loess substrate and the red clay substrate;
(3) the sample added with the mixture ratio is tested by a Lambda 900 diffuse reflection spectrometer, the scanning wavelength is 400-700nm, and the interval is 2 nm. During testing, a proper amount of powder sample is placed on a glass slide, a few drops of water are added to mix the powder sample into paste, the paste is evenly stirred and smeared, the glass slide is slightly knocked on a table to flatly spread the sample, the sample is naturally dried, and then the sample is tested on a machine. Firstly, testing a barium sulfate white board which is used as a color background, wherein the testing steps comprise that the barium sulfate white board is placed at a sample placing position of an instrument, a cover is covered, Lambda 900 software in a computer is clicked, the wavelength of 400-. When testing samples, only the number needs to be modified and the START button needs to be clicked, the testing time of one sample is 2-3 minutes, and the samples are automatically stored after the testing is finished;
(4) the data format after the test is CSV, and the ENVI Classic5.1 version is used for removing the continuum: firstly clicking the Spectral Library Builder under Spectral Libraries under the Spectral menu of ENVI Classic5.1, then selecting First Input Spectrum, importing CSV format data obtained by testing a diffuse reflection spectrometer in batches, clicking Plot, popping up an Endmember Collection Spectra window, selecting continuous Removed under Plot _ Function for processing, and then exporting data, thus obtaining continuous system removal data of each sample.
(5) Calculating the wavelength lambda at the equal division of the area: firstly, the PAST3.0 software is utilized to carry out 0.1nm linear interpolation on the continuous system removal data, and based on the calculation program of the Microsoft EXCEL software, the reflectivity R at 450nm is found out firstly450nmThen, the nearest R is found out between 450-600nm450nmWavelength λ of valuemaxCurve at R450nmAnd λmaxThe area between them is the area stated in the present invention. Curve for continuum removal starting from 450nm to λmaxThe area integral calculation is carried out at intervals of 0.1nm, and the cumulative area, i.e. lambda, is calculatedmaxIs the maximum cumulative area, then the cumulative area per wavelength is divided by the maximum area, and the wavelength position at which the value is 50% is the area-dividing wavelength lambdahValues, as shown in FIG. 1;
(6) regression analysis was performed using the known goethite/hematite ratio and the wavelength λ at the equal part of the area, with the quantitative relationship being the goethite/hematite ratio 0.003251 × x2-3.609264 x +996.742926, x being the wavelength λ at which the area is equally dividedhR of which2At 0.96 with an RMSE of 0.29, the correlation was very good and the quantification was extremely reliable, as shown in FIG. 3. By utilizing the quantitative relation, the ratio of the goethite to the hematite in the sediment can be calculated reversely.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (2)
1. A method for quantifying the ratio of goethite to hematite in a sediment based on diffuse reflectance spectroscopy is characterized by comprising the following steps:
(1) selecting a typical malan loess and a tertiary red clay sample in a loess plateau area as a substrate, grinding the original sample by using an agate mortar to prepare a powder sample, weighing about 11-16g of the sample, adding 500ml of 0.3mol/L sodium citrate solution and 50ml of 1mol/L sodium bicarbonate solution, adding 2 +/-0.2 g of sodium hydrosulfite to ensure excessive reaction, placing the sample in a shaking table at 80 ℃ for oscillation reaction for 90 minutes until the sediment is grey, namely complete reaction, centrifuging the sample in a centrifuge at the rotating speed of 5000 r/min for 15 minutes, pouring out the supernatant, washing the sample with secondary distilled water for three times, drying the residue at room temperature, and grinding the residue into powder;
(2) adding samples proportioning loess or red clay base and different contents of hematite and goethite: firstly, weighing a substrate sample by using a ten-thousand-position high-precision electronic balance, pouring the substrate sample into an agate mortar, weighing goethite and hematite samples, pouring the goethite and hematite samples into the agate mortar filled with the substrate, grinding for more than 10 minutes to ensure that the goethite and hematite samples are uniformly mixed without obvious color difference, and sequentially matching 31 samples with different goethite and hematite ratios to form a loess substrate and a red clay substrate;
(3) testing the proportioned sample by using a Lambda 900 diffuse reflection spectrometer, wherein the scanning wavelength is 400-700nm and the interval is 2nm, when the proportioned sample is tested, firstly grinding the sample by using an agate mortar to prepare a powder sample, taking a proper amount of the powder sample on a glass slide, adding a few drops of distilled water to mix the powder sample into paste, uniformly stirring and smearing the paste, lightly knocking the glass slide on a table top to flatly spread sample particles, and naturally drying the sample particles in the air; then, testing on a computer, firstly testing a barium sulfate white board which is used as a color background, wherein the testing steps comprise that the barium sulfate white board is placed at a sample placing position of an instrument, a cover is covered, Lambda 900 software in the computer is clicked, the wavelength range is 400-700nm, the distance is 2nm, the sample number is modified, an AUTOZORO button is clicked, after the testing is finished, a START button is clicked again for testing, the testing result is required to be 99-100%, if the testing result does not reach the standard, the testing is required to be carried out repeatedly, when the sample is tested, a glass slide coated with the sample is placed in a sample bin, the sample number is filled, the START button is clicked, the testing time of one sample is 2 minutes, and the data is automatically stored after the testing is finished;
(4) processing original data of the diffuse reflection spectrometer by utilizing ENVI Classic5.1 software to obtain continuum removal data of each sample;
(5) calculating the wavelength lambda of the equal parts of the area, firstly utilizing PAST3.0 software to carry out 0.1nm interpolation on the continuous system removal data, and firstly finding out the reflectivity R of 450nm based on the calculation program of EXCEL software450nmThen, the nearest R is found out between 450-600nm450nmWavelength λ of valuemaxRemoval curve for continuum starting from 450nm to λmaxThe area integral calculation is carried out at intervals of 0.1nm, and the cumulative area, lambda, is calculatedmaxIs the maximum cumulative area, then the cumulative area per wavelength is divided by the maximum area, and the wavelength position at which the value is 50% is the area-dividing wavelength lambdahA value;
(6) using the known wavelength lambda at the equal part of the goethite/hematite ratio and the areahPerforming regression analysis, wherein the quantitative relationship is goethite/hematite ratio =0.003251 lambdah 2-3.609264* λh+996.742926，λhThe wavelength at which the area is equally divided.
2. The method for quantifying the ratio of goethite to hematite in the sediment based on the diffuse reflection spectroscopy as claimed in claim 1, wherein the step (4) comprises: the tested data format is CSV, the ENVI Classic5.1 version is used for removing the Continuum, firstly, the Spectral Library Builder under the Spectral Libraries under the Spectral menu of the ENVI Classic5.1 version is clicked, then, the First Input Spectrum is selected, the data are led in batch, the Plot is clicked, the Endmember Collection Spectra window is popped up, the continuous Removed under the Plot _ Function is selected for processing, and then, the data are led out, so that the Continuum Removed data of each sample can be obtained.
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