JPH0712760A - Determination method for mineral - Google Patents

Abstract

PURPOSE:To provide a mineral determination method capable of improving measuring efficiency without any need of adding a standard substance to a sample. CONSTITUTION:A sample is pulverized and the diffracted ray intensity of the sample powder is measured with a powder X-ray diffraction method. Then, the crystallinity index of quartz contained in the sample is obtained from the diffracted ray intensity ratio of each reflection peak due to the quartz. Also, maximum X-ray intensity is measured in the same condition for quartz powder having a known crystallinity index. The maximum X-ray intensity of the power quartz so obtained is corrected, depending upon a relative ratio of the crystallinity index of the quartz powder to the crystallinity index of quartz contained in the sample, thereby obtaining the maximum X-ray intensity of the quartz in the sample. Also, a comparison is made between the diffracted ray intensity of quartz in the sample and the maximum X-ray intensity of the quarts in the sample, thereby obtaining the quartz mass ratio of the sample. Furthermore, the diffracted ray intensity of a target mineral in the sample, the diffracted ray intensity of the quartz in the sample, and the quartz mass ratio of the sample are respectively compared with an analytical curve, thereby obtaining the mass ratio of the object mineral.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for quantifying various minerals contained in a sample such as rock by a powder X-ray diffraction method, and more particularly to a method for using quartz in a sample as a standard substance.

[0002]

2. Description of the Related Art It is possible to identify the mineral species contained in rocks and sediments and to quantify the mass ratio of each mineral. The possibility of landslides and ground collapses, the effect of rock expansion on structures, aggregates, etc. In recent years, the demand for quantitative analysis of minerals in the field of civil engineering is increasing because it is effective in predicting the influence of alkali-aggregate reaction in the environment.

However, since there are minerals having the same elemental composition but different crystal structures and polymorphic substances, qualitative and quantitative determination of minerals cannot be performed by simple chemical analysis, fluorescent X-ray analysis, etc. There is no choice but to rely on powder X-ray diffraction, which can specify the crystal structure of a substance. Prior to the description of the prior art, the basic principle of the powder X-ray diffraction analysis method will be briefly described.

The diffraction intensity of the i component in a sample composed of n types of components is expressed by the following equation (1). (1) Ii = Ki · Vi / μ where Ii: intensity of the diffracted x-ray of the i component Ki: constant depending on the equipment conditions and properties of the i component Vi: volume ratio of the target i component μ: average line of the n-type component Is the absorption coefficient.

The average linear absorption coefficient other than the i component is μm,
Assuming that the content rate (volume ratio) other than the i component is Vm, (2) μ = μi · Vi + μm · Vm (3) Vi + Vm = 1, so equation (1) is expressed as equation (4). It

When the mass ratio is represented by X, Therefore, equation (4) can be transformed into equation (5).
ρ is the density, and μ / ρ is the mass absorption coefficient.

Since (μ / ρ) = (μ / ρ) i · Xi + (μ / ρ) m · (1-Xi), the following equation (6) is finally obtained. Powder X
The quantification method by the line diffraction method is based on this formula.

Conventionally, as a quantitative analysis method for a sample having a multi-component system and different mass absorption coefficients, the following method applying the above equation (6) is known. (A) Absorption diffraction method (b) Internal standard method (c) Standard addition method

However, the absorption diffraction method has a mass absorption coefficient (μ /
ρ) must be obtained by actual measurement, which is difficult to measure with a sample containing multiple components. Although the standard addition method can be easily performed, it is difficult to measure when the mass ratio of the target substance exceeds 10%.

On the other hand, in the internal standard method, a certain amount of the internal standard substance s is added to the sample, the diffraction intensity of the target mineral and the internal standard substance s is measured, and a calibration curve is prepared using the ratio. Is a method for obtaining the mass ratio of the target substance by means of, and is more suitable for quantitative determination of minerals than the other two methods. The outline will be described below.

The mass ratio of the target component (mineral) i in the sample is Xi, and the mass ratio of the component m other than the target mineral is Xm.
When the mass ratio Xs of the internal standard substance s is added to the sample Xi + Xm, the mass ratios of the target component i and the internal standard substance s in the sample after the addition are Xi / (Xi + Xm + Xs),
And Xs / (Xi + Xm + Xs). At this time, for the diffraction line intensity Ii of the target component i and the diffraction line intensity Is of the internal standard substance s, the following formulas (7) and (8) are obtained from the formula (6).

[0012] Ii, Is: Diffraction line intensity of i, s component Ki, Ks: Constant depending on equipment conditions and properties of i, s component Xi, Xs: Mass ratio of target i, s component μ: Average line absorption coefficient ρ: Density

Taking the ratio of the equations (7) and (8), the coefficient depending on the apparatus conditions when s is added and the properties of the i and s components is Ki.
When s is given, the equation (9) is obtained.

Since Xs is constant, if K = (1− / Kis) · Xs, then (10) Xi = K · Ii / Is That is, Ii / Is is the mass ratio of the target component i regardless of the mass absorption coefficient. Proportional to Xi. Therefore, the mass ratio of the minerals to be obtained can be obtained by preparing a sample that has been mixed at a specific ratio in advance and creating a calibration curve.

[0015]

However, in the method for quantifying minerals by the internal standard method, measurement cannot be performed when the reflection peak of the standard substance overlaps with the reflection peaks of the minerals in the sample, and therefore, depending on the composition of each sample. There is a problem that the standard substance must be carefully selected, and it takes time and effort to add the standard substance to the sample, and it takes a long time to perform measurement for each sample.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for quantifying minerals that does not require addition of a standard substance to a sample and can improve the measurement efficiency per sample.

[0017]

First, the theory of the method for quantifying minerals according to the present invention will be described. When the target mineral i to be quantified in the sample has a mass ratio Xi, the quartz s has a mass ratio Xs, and the other components m have a mass ratio Xm, the mass ratio of the target mineral i and the quartz s in the sample is: Xi / (Xi + Xs
+ Xm) and Xs / (Xi + Xs + Xm). Therefore, for the diffraction line intensities Ii and Is of the target mineral i and quartz s, the equation (9) explained in the internal standard method can be applied as it is.

[0018] Here, if K = 1 / Kis Is.

As shown in the equation (11), (Xi / X
If the relationship between (s) and (Ii / Is) is made into a calibration curve,
By obtaining the value of (Ii / Is) and the quartz mass ratio Xs in the sample, the mass ratio Xi of the target mineral can be obtained regardless of the absorption coefficient K.

In the method of the present invention, the quartz index method is used to measure the quartz mass ratio Xs. The quartz index (QI) is the diffraction line intensity of quartz in a sample expressed as a percentage of the strongest X-ray intensity Iq (cps) of pure quartz measured under the same experimental conditions. As shown by the equation, in this method, the mass ratio of quartz in the sample is meant. (12) QI ＝ Is / Iq × 100

However, since the diffraction line intensity of minerals changes due to the output (kw) at the time of measurement and deterioration of the tube, in order to obtain the mass ratio Xs of quartz in the sample, before measuring the sample in advance. It is necessary to measure the standard pure quartz under the same conditions and check the strongest X-ray intensity (cps).

Further, the characteristics of quartz contained in rock samples, in particular the crystallinity, differ from sample to sample,
Affects the intensity of diffraction lines. Therefore, if the quartz mass ratio of the sample is calculated using the strongest X-ray intensity measured from quartz having different crystallinity, a quantitative error will occur. Therefore, originally, it is desirable to separate pure quartz from the sample to be quantified in advance to prepare pure quartz, and to obtain the strongest X-ray intensity using this pure quartz, but it is troublesome and difficult.
Furthermore, it is difficult to directly determine the crystallinity of quartz in the sample.

Therefore, the present inventors measured the strongest X-ray intensities of a plurality of types of quartz having different crystallinities and the crystallinity index, which will be described later, to obtain a function of the crystallinity index and the strongest X-ray intensity. I asked. As a result, if only the crystallinity index of quartz in the sample is measured, the strongest X due to quartz with different crystallinity is obtained.
It was found that the strongest X-ray intensity of quartz in the sample can be estimated from the line intensity.

The crystallinity index can be easily measured, for example, by the following method. First, the diffraction line intensity of a powdered sample (it is not necessary to separate quartz) is measured by a usual powder X-ray diffraction method. The X-ray diffraction peak of quartz is shown in Fig. 1.
As shown in Fig. 5, 5 lines appear between 2θ = 67-69 ° (called a quintet). Of these, using the height b of the diffraction peak appearing at 2θ = 67.65 ° and the height a of the diffraction peak from the valley appearing at 2θ = 67.93 °, the crystallinity index defined by the following equation Calculate (CI). (13) CI = 10 × 1.67 × a / b

This crystallinity index CI is a value that reflects the crystallinity of quartz, and by using this value to correct the strongest X-ray intensity, the accuracy of quantifying quartz by the quartz index method can be improved.

It is known that some minerals other than quartz (such as montmorillonite and sericite) have different relative intensities of diffraction peaks due to the difference in crystallinity. However, with respect to minerals other than quartz, the relationship between crystallinity and diffraction line intensity has not been accurately investigated, unlike quartz, and quartz can be said to be excellent as a standard mineral from this point as well.

Next, the method for quantifying minerals according to the present invention will be described by following a specific procedure. In this method, first, a sample to be measured is powdered. The sample used for powder X-ray diffraction needs to be crushed to have an average particle size of about 3 to 30 μm. When the average particle size of the sample is larger than this range, the number of crystals contributing to the analysis is small and the reproducibility is deteriorated. On the other hand, when the average particle size is smaller than this range, the volume ratio of the amorphous phase on the particle surface increases and the diffraction line intensity decreases.

In a general rock sample, since soft and hard minerals are mixed, it is difficult to grind all minerals to the same particle size. However, it has been confirmed by the experiments by the present inventors that the X-ray diffraction results are almost the same when the average particle size of the powder is within the above range, when the powder is carefully ground and when it is not. The grinding method for powdering rock may be any conventionally used method.

Next, the intensity of the diffraction line of the sample powder was measured by the powder X-ray diffraction method. From the height b of the diffraction peak appearing at 2θ = 67.65 ° and the valley appearing at 2θ = 67.93 °. Using the height a of the diffraction peak of
3) Calculate the crystallinity index (CI) defined by the equation. Then, the obtained crystallinity index is substituted into a previously calculated function of the crystallinity index and the strongest X-ray intensity, and the strongest X-ray intensity of quartz contained in the sample is estimated.

FIG. 2 is a graph showing the relationship between the crystallinity index and the strongest X-ray intensity measured by the present inventors. The horizontal axis is the crystallinity index, and the vertical axis is the intensity rate. This intensity rate is the other pure quartz when the strongest X-ray intensity of the artificial quartz having the highest crystallinity index is 100. The ratio of the strongest X-ray intensity of If this graph is used as a calibration curve, the intensity ratio can be easily obtained from the crystallinity index. Therefore, use that intensity ratio to correct the strongest X-ray intensity of pure quartz measured under the same conditions as the measurement conditions of the sample. Thus, the strongest X-ray intensity of quartz contained in the sample can be obtained.

Next, with respect to the quartz powder whose crystallinity index is known, the strongest X-ray intensity is measured by the powder X-ray diffraction method under the same conditions as the sample. The average particle size of the quartz powder used here is preferably equal to the average particle size of the sample. The crystallinity index is preferably closer to that of quartz in the sample. The strongest X-ray intensity of the quartz powder thus obtained is corrected using a calibration curve as shown in FIG. 2 to find the strongest X-ray intensity of the quartz contained in the sample.

Further, the diffraction line intensity of quartz in the sample is compared with the strongest X-ray intensity of quartz in the sample, and (1
The mass ratio of quartz in the sample is calculated using the equation (2). Then, the diffraction line intensity of the target mineral contained in the sample, the diffraction line intensity of quartz contained in the sample, and the quartz mass ratio of the sample are compared with a calibration curve obtained in advance, and Calculate the mass ratio.

As the calibration curve, for example, a diffraction curve of a calibration curve preparation sample obtained by mixing powders of minerals of the same species as the target mineral and quartz powders of which the crystallinity index is known in different ratios are used. By measuring the intensity, the diffraction line intensity ratio between quartz and the target mineral whose crystallinity index is known, and in the sample for preparing a calibration curve between quartz and the target mineral whose crystallinity index is known. A plot of the mass ratio of is used.

An example of the calibration curve is shown in FIG. This is used when quantifying plagioclase, where the vertical axis is the common logarithm of (diffracted ray intensity of plagioclase / diffraction line intensity of quartz), and the horizontal axis is (mass ratio of plagioclase wt% / The common logarithm of the mass ratio of quartz (wt%) is shown. In the figure, line (A) is a graph for the reflecting surface (040) of the crystal, and line (B) is a graph for the reflecting surface (201) of the crystal. Details of the experiment will be described later.

According to the method for quantifying minerals comprising the above procedure, it is not necessary to add the standard substance to the sample as in the conventional internal standard method, so that the reflection peaks of the target mineral and the standard substance should not be overlapped carefully. There is no need to select a standard substance or add the standard substance to the sample uniformly.
The quantitative analysis work can be simplified.

Since the calibration curve is used after the strongest X-ray intensity of the standard pure quartz is made to match the quartz component in the sample by using the crystallinity index, a large number of calibration curves are prepared. It has an advantage that the sample can be efficiently quantified.

[0037]

[Embodiments] Next, the effectiveness of the present invention was confirmed by quantifying the minerals in simulated samples by the mineral quantification method according to the present invention and the internal standard method.

(Preparation of Sample for Creating Calibration Curve) Plagioclase, calcite, and amphibole were prepared as target minerals, and artificial quartz was prepared as pure quartz for standard. These minerals were crushed for 45 minutes with a grinder and 10 minutes with a handrail to obtain a powder having an average particle size of 10 μm. Each target mineral and quartz powder were mixed in several ratios for each target mineral, and the total weight was 2.0 g to prepare a sample for preparing a calibration curve.

(Preparation of calibration curve used in the quantification method of the present invention) The obtained calibration curve preparation sample was subjected to the powder X-ray diffraction method under the same measurement conditions as the simulated sample to be quantified. Considering the accuracy of the equipment and sample settings, each calibration curve preparation sample was measured 5 times, and the approximate expression of the calibration curve was obtained from the average value. As a method of measuring the intensity of the diffraction line, there are a method of obtaining the area and height of the reflection peak and a method of obtaining from the count value. In this test, Ii and Is are respectively calculated using the count value (unit: cps) by the scintillation counter. I asked. Any counting method may be used in the practice of the present invention.

An example of the prepared calibration curve is shown in FIG. The vertical axis of the calibration curve represents the common logarithm of (diffraction line intensity of target mineral / diffraction line intensity of quartz), and the horizontal axis represents the common logarithm of (wt% by weight of target mineral / wt% of quartz). .

(Crystallinity Correction by Quartz Index) Five kinds of quartz having different crystallinities were prepared, and a calibration curve for crystallinity correction was prepared from the crystallinity index and the intensity ratio of the strongest X-ray intensity. The results are shown in Figure 2. The intensity ratio is the ratio of the strongest X-ray intensities of the other four samples, where 100 is the strongest X-ray intensity of "artificial quartz" having the highest crystallinity index. As shown in FIG. 2, there is a clear correlation between the crystallinity index and the intensity ratio, and the correlation coefficient at four points is r = 0.
It was 9731.

(Preparation of Calibration Curve for Internal Standard Method) On the other hand, zinc oxide (ZnO) was used as an internal standard substance, and a calibration curve for use in the internal standard method was prepared. 0.5 g of each zinc oxide powder was added to 2.0 g of each of the calibration curve preparation samples after the calibration curve preparation for the mineral quantification method of the present invention was performed to prepare a calibration curve preparation sample under the same conditions as above. The diffraction line intensity was measured.

Desirable characteristics for the internal standard substance are that the mass absorption coefficient is small, the number of reflection peaks is small, and a clear reflection peak is obtained at an appropriate position (a position where it does not overlap with other reflection peaks). Zinc oxide satisfies these conditions, although it is a substance that is not contained. That is, the reflection peak of the diffraction surface (002) of zinc oxide is located at 2θ = 34.5 °, does not overlap with the reflection peaks of the main constituent minerals of rock, and the diffraction line intensity is high. Table 1 shows an example of the measurement results of the calibration curve preparation sample.

[0044]

[Table 1]

(Verification test) All the samples for preparing a calibration curve containing zinc oxide used for preparing the calibration curve for the internal standard method were mixed to prepare a simulated sample for verification. The composition of this simulated sample is as shown in Table 2.

[0046]

[Table 2] (Note) Since the mass ratio obtained by the internal standard method is calculated excluding zinc oxide, the numerical value becomes large.

The X-ray diffraction measurement was carried out by the quarter method to check whether the samples were uniformly mixed.
Was divided into 1.5 to 2.0 g of samples 1 to 4, and the X-ray diffraction was measured for each. Some of the results are shown in Table 3.

[0048]

[Table 3] * Indicates the diffraction line intensity of plagioclase (reflection surface: 201). The strongest X-ray intensity of artificial quartz in this test is 37917 cps
Met.

(Results of Measurement by Internal Standard Method) The mass ratio of each mineral by the internal standard method should be 10% for feldspar, calcite and amphibole and 70% for quartz (zinc oxide is excluded). ). The quantitative value (B) of each mineral in the verification sample obtained by using the calibration curve after the X-ray diffraction measurement is shown in Table 4 below.

[0050]

[Table 4]

The ratio (B / A) between the quantitative value and the true value was determined. The quantitative value by the internal standard method was 1.03 times the true value for quartz, and the other components were 1.29 for feldspar. It was 1.25 times that of calcite and 1.38 times that of amphibole. Further, when the correction value (C) is obtained by correcting the quantitative value (B) so that the total of the quantitative values becomes 100 wt%, the correction value (C) is 0.93 to 1 of the true value (A). It fluctuated in the range of 24 times.

(Results of the Quantitative Method of the Present Invention) The mass ratio of minerals according to the present invention is 8 wt% for feldspar, calcite and amphibole, since 20 wt% of zinc oxide is mixed in the simulated sample of the verification test. , Quartz should be 56 wt%. The quantitative values (B) obtained by the method of the present invention are as shown in the following table.

[0053]

[Table 5]

The quantitative value (B) according to the method of the present invention is 0.58 times that of calcite and 0.80 of feldspar as compared to the true value (A).
Double, amphibole 0.86 times, and quartz 0.87 times. Contrary to the internal standard method, there was a tendency to quantify less than the true value. However, when the correction value (C) is obtained by correcting the quantitative value (B) so that the total of the quantitative values becomes 100 wt%, the correction value (C) is 0.69 to 1 of the true value (A). .0
It was in the range of 5 times.

[0055]

According to the mineral quantification method of the present invention,
Since it is not necessary to add the standard substance to the sample, it is not necessary to carefully select the standard substance so that the reflection peaks of the target mineral and the standard substance do not overlap, or to add the standard substance uniformly to the sample. The quantitative analysis work can be simplified. In addition, the calibration curve is used after the strongest X-ray intensity of pure quartz, which is the standard, is matched with the quartz component in the sample by using the crystallinity index, so once the calibration curve is created, many samples are sampled. It is possible to quantify efficiently.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction graph of pure quartz.

FIG. 2 is a graph showing the relationship between the crystallinity index and the strongest X-ray intensity.

FIG. 3 is a calibration curve of plagioclase by the mineral quantification method of the present invention.

Claims (3)

[Claims] 1. A method for quantifying minerals, which comprises the following steps. (A) a step of pulverizing a sample to be measured; (b) a powder X-ray diffraction method to measure the diffraction line intensity of the sample powder; The step of obtaining the crystallinity index of quartz, (c) the step of measuring the strongest X-ray intensity by the powder X-ray diffraction method under the same conditions for the quartz powder of which the crystallinity index is known, (d) the quartz powder A step of correcting the strongest X-ray intensity according to the relative ratio between the crystallinity index of the quartz powder and the crystallinity index of quartz contained in the sample to obtain the strongest X-ray intensity of the quartz contained in the sample; e) a step of comparing the diffraction line intensity of quartz in the sample with the strongest X-ray intensity of quartz in the sample to obtain the quartz mass ratio of the sample, (f) the diffraction line of the target mineral contained in the sample Intensity and diffraction line intensity of quartz contained in the sample A quartz mass ratio of the sample, compared to the previously determined calibration curve, obtaining a weight ratio of interest minerals. 2. The diffraction line intensity of a calibration curve preparation sample in which powders of minerals of the same kind as the target minerals and quartz powders of which the crystallinity index is known are mixed at different ratios. Thus, the diffraction line intensity ratio of quartz and the target mineral whose crystallinity index is known, and the mass ratio of the quartz and the target mineral whose crystallinity index are known in the sample for preparing the calibration curve are plotted. 2. The method for quantifying minerals according to claim 1, wherein a substance is used as the calibration curve. 3. The crystallinity index of quartz contained in the sample is
The ratio is defined by using the ratio of the diffraction peak height of 2θ = 67.65 ° obtained by powder X-ray diffraction and the height of the diffraction peak from the valley appearing at 2θ = 67.93 °. The method for quantifying mineral according to 1 or 2.