Detailed introduction of free silica analyzer in dust: There are many types of dust in the production environment of the power and coal industries, mainly including silicon dust, coal dust, boiler dust, asbestos dust, cement dust, welding fumes, etc. Its characteristics are that the content of free silica in dust is high, and the dispersion of dust is also relatively high, which is mostly respiratory dust. Therefore, it poses a greater risk to dust personnel. According to the physical and chemical properties of productive dust, the concentration in the air, the amount of dust entering the human body, and the affected areas, the hazards produced also vary, mainly including respiratory diseases such as rhinitis, pharyngitis, tracheitis, bronchitis, etc. The Chinese government, as well as the power and coal industries, attach great importance to dust prevention work. Therefore, strengthening the detection of free silica content in dust is a very important and urgent task. In the past, the detection of free silica content in dust was carried out using the "pyrophosphate gravimetric method" specified in the "Method for Determination of Dust in Workplace Air" (GB5748-85). This method has a series of problems such as complex operating steps, a wide variety of reagents used, long detection cycles, poor accuracy, and strict laboratory conditions, which make it difficult to meet the requirements of on-site batch testing. In order to improve the accuracy of detection and achieve the purpose of batch detection, a FC-2000D free silica analyzer for dust has been specially developed to detect the content of free silica in dust. To meet the needs of different customers, the FC-3000D free silica analyzer for dust has also been launched (using an imported original host) Imported models have advantages such as high precision, faster speed, and more powerful software functions.

Technical parameters of free silica analyzer in dust


Spectral range: 370-7500cm-1
Resolution: ≤ 1cm-1
Signal/noise ratio: better than 20000:1 (peak to peak, 1-minute test) better than 120000:1 (mean square deviation, 1-minute test)
Wave number accuracy: 0.01 cm-1
Interferometer: RockSolidTM patented interferometer, gold-plated optical mirror, 300 optical compensation design,
Scanning speed: 10 times/second
Electromagnetic drive, frictionless bearings, always aligned optical path.
Detector: DLATGS detector using DigiTectTM technology, fully digital design
Infrared light source: ceramic light source, 1550K
Beam splitter: ZnSe beam splitter, can operate normally in high humidity environments
A/D conversion: 24 bit, high-speed Delta SigmaTM A/D converter
Instrument Qualification: Automatic Monitoring
Measurement technology: transmission ATR、 Diffuse reflection, external reflection
Computer interface: Ethernet
Power supply: 100-240 VAC, 50-60 Hz, 20 W; Rechargeable battery, AC/DC power supply, compatible device that can be directly connected to the car's DC power supply.
Phone: 4000294299 Fax: 86-22-86800320
Instrument size: 22 x 30 x 25 cm (w x d x h)
Weight: 7 kg

Main characteristics of free silica analyzer in dust


Spectral analysis system;
Factory calibrated spectral library;
Error range: ± 2% u of the calibrated range;
Capable of automatic search and determination of unknown gases;
Multiple analysis ranges for selection, suitable for different applications;
Capable of outputting test data in text format and using EXCEL for report analysis;
Chinese software manual, Chinese software interface;
Can continuously upgrade the reference spectral library;
Continuous on-site recording and storage, automatic storage of measured spectra;
Can replay historical data;
Data communication interface: Ethernet connection, can be equipped with wireless transmission;
Sample chamber;
Multiple reflections with an optical path length greater than 2.5 meters in a gas pool;
The sample chamber is coated with a corrosion-resistant coating;
Volume: less than 0.1L, with a small absolute volume;

Attached are the national standard testing methods:

GBZ

National Occupational Health Standards of the People's Republic of China

GBZ/T 192.4—2007

Determination of dust in workplace air

Part 4: Free Silicon Dioxide Content

Method for determination of dust in the air of workplace

Part 4: Content of free silica in dust

Released on June 18, 2007 and implemented on December 30, 2007

The Ministry of Health of the People's Republic of China has released

Preface

GBZ/T 192 is divided into the following five parts based on the characteristics of dust measurement in workplace air:

——Part 1: Total Dust Concentration

——Part 2: Concentration of respiratory dust

——Part 3: Dust dispersion

——Part 4: Free Silicon Dioxide Content

——Part 5: Concentration of asbestos fibers

This section is the fourth part of GBZ/T192, revised based on GB 5748-85 "Determination of Dust in Workplace Air", GB16225-1996 "Hygienic Standard for Respiratory Silicon Dust in Workshop Air" Appendix B "X-ray Diffraction Determination of Free Silicon Dioxide in Dust", and GB16245-1996 "Hygienic Standard for Respiratory Coal Dust in Workplace" Appendix B "Infrared Spectroscopy Determination of Free Silicon Dioxide in Respiratory Coal Dust".

This section was proposed by the National Occupational Health Standards Committee.

This section is approved by the Ministry of Health of the People's Republic of China.

Drafting units for this section: School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Industrial Hygiene Technology Research Institute of Wuhan Iron and Steel Company, Institute of Occupational Disease Prevention and Control of Dongfeng Motor Corporation, Wuhan Institute of Occupational Disease Prevention and Control, Hubei Provincial Center for Disease Control and Prevention, Fujian Provincial Center for Disease Control and Prevention, Liaoning Provincial Center for Disease Control and Prevention, Wuhan Analytical Instrument Factory.

The main drafters of this section are Yang Lei, Chen Weihong, Liu Zhanyuan, Chen Jingqiong, Li Jichao, Yi Guilin, Yang Jingbo, Mei Yong, Peng Kailiang, Liu Jiafa, and Ye Bingjie.

GBZ/T 192.4—2007

Determination of dust in workplace air

Part 4: Free Silicon Dioxide Content

1 Scope

This section specifies the method for determining the content of free silica in workplace dust.

This section is applicable to the determination of free silica content in workplace dust.

2 Normative References

The clauses in the following documents become clauses of this standard by reference. Any referenced document marked with a date shall not be subject to any subsequent amendments (excluding errata) or revisions to this standard. However, parties to agreements based on this standard are encouraged to study whether the latest versions of these documents can be used. The latest version of any referenced document without a date is applicable to this standard.

GBZ 159 Sampling Specification for Monitoring Harmful Substances in Workplace Air

GBZ/T XXX. 1 Determination of Dust in Workplace Air Part 1: Total Dust Concentration

GBZ/T XXX. 2 Determination of Dust in Workplace Air Part 2: Concentration of Respiratory Dust

3 Terms and definitions

This section uses the following terms:

Free silica

Refers to crystalline silica, also known as quartz.

4. Phosphoric acid method

4.1 Principle

Silicates and metal oxides in dust can dissolve in pyrophosphate heated to 245 ℃~250 ℃, while free silica is almost insoluble, achieving separation. Then weigh the separated free silica and calculate its percentage content in the dust.

4.2 Instruments

4.2.1 Sampler: Same as GBZ/T XXX. 1 and GBZ/T XXX. 2.

4.2.2 Constant temperature drying oven.

4.2.3 Drying machine, filled with color changing silicone gel.

4.2.4 Analytical balance with a sensitivity of 0.1mg.

4.2.5 Cone flask, 50ml.

4.2.6 Adjustable electric furnace.

4.2.7 High temperature electric furnace.

4.2.8 Ceramic or platinum crucible, 25ml, with lid.

4.2.9 Crucible pliers or platinum tipped crucible pliers.

4.2.10 Measuring cylinder, 25ml.

4.2.11 beaker, 200ml~400ml.

4.2.12 Agate mortar.

4.2.13 Slow quantitative filter paper.

4.2.14 Glass funnel and its rack.

4.2.15 Temperature gauge, 0 ℃~360 ℃.

4.3 Reagents

The experimental reagent is analytical grade.

4.3.1 Phosphoric acid, heat 85% (W/W) phosphoric acid to boiling until no bubbles appear at 250 ℃, cool down, and store in a reagent bottle.

4.3.2 Hydrofluoric acid, 40%.

4.3.3 Ammonium sulfate.

4.3.4 Hydrochloric acid solution, 0.1mol/L.

4.4 Sample Collection

On site sampling shall be carried out in accordance with GBZ 159.

The amount of dust sample required for this method should generally be greater than 0.1g. A 75mm diameter filter membrane can be used to collect dust in the air at a high flow rate, or fresh settling dust at the breathing zone height can be collected at the sampling point, and the sampling method and sample source should be recorded.

4.5 Measurement steps

4.5.1 Dry the collected dust samples in an oven at 105 ℃± 3 ℃ for 2 hours, cool them slightly, and store them in a dryer for later use. If the dust particles are large, they need to be ground with an agate mortar until they feel smooth when twisted by hand.

Accurately weigh 0.1000g~0.2000g (G) of dust sample into a 25ml conical flask, add 15ml of pyrophosphate and several milligrams of ammonium sulfate, stir until the sample is completely moist. Place the conical flask on an adjustable electric furnace and quickly heat it to 245 ℃~250 ℃, while continuously stirring with a glass rod equipped with a thermometer for 15 minutes.

4.5.3 If the dust sample contains coal, other carbon and organic matter, it should be placed in a porcelain crucible or platinum crucible and ashed at 800 ℃~900 ℃ for more than 30 minutes to completely ashe the carbon and organic matter. After cooling, wash the residue with phosphoric acid into a conical flask. If containing sulfide minerals such as pyrite, chalcopyrite, chalcopyrite, etc., a few milligrams of crystalline ammonium sulfate should be added to a conical flask. Heat treatment with pyrophosphate and several milligrams of ammonium sulfate according to 4.5.2.

4.5.4 Remove the conical flask and cool it to 40 ℃~50 ℃ at room temperature. Add distilled water at 50 ℃~80 ℃ to about 40ml~45ml and stir evenly while adding distilled water. Carefully transfer the contents of the conical flask into a beaker and rinse the thermometer, glass rod, and conical flask with hot distilled water. Pour the washing solution into the beaker and add distilled water to about 150ml~200ml. Fold the slow quantitative filter paper into a funnel shape, place it in the funnel, and moisten it with distilled water. Boil the contents of the beaker on an electric stove, let it stand for a while, and allow the suspension to settle slightly. Filter while hot, and the filtrate should not exceed 2/3 of the filter paper. After filtration, wash the beaker with 0.1mol hydrochloric acid and transfer it into a funnel. Rinse the sediment on the filter paper 3-5 times, then rinse with hot distilled water until there is no acidic reaction (tested with pH test paper). When using a platinum crucible, it should be washed three times until there is no phosphate reaction. The above process should be completed on the same day.

4.5.5 Fold the filter paper with sediment several times, place it in a porcelain crucible that has been weighed to a constant amount (m1), dry and carbonize it on an electric furnace; Cover and leave a small gap when carbonizing. Then put it into a high-temperature electric furnace and ash it at 800 ℃~900 ℃ for 30 minutes; Take it out, cool it slightly at room temperature, and place it in a dryer to cool for 1 hour. Weigh it to a constant amount (m2) on an analytical balance and record it.

4.5.6 Calculate the content of free silica in dust according to equation (1):

．．．（1）

In the formula: SiO2 (F) - free silica content,%;

M1- crucible quality, g；

M2- mass of crucible and sediment, g；

G - Quality of dust sample, g。

4.5.7 Treatment of insoluble substances in pyrophosphate

If the dust contains substances that are insoluble in pyrophosphate, such as silicon carbide, beryl, tourmaline, yellow jade, etc., hydrofluoric acid should be used to treat them in a platinum crucible. The method is as follows:

Place the filter paper with sediment into a platinum crucible, burn it to a constant amount (m2) as in step 4.5.5, and then add a few drops of 9mol/L sulfuric acid solution to moisten all sediment. Add 5ml~10ml of 40% hydrofluoric acid into the fume hood, heat slightly to dissolve the free silica in the sediment, and continue heating until no white smoke is emitted (to prevent boiling). Burn again at 900 ℃ and weigh to a constant volume (m3). The content of free silicon dioxide after hydrofluoric acid treatment is calculated according to equation (2):

．．．（2）

In the formula: SiO2 (F) - free silica content,%;

M2- The mass of sediment (a substance insoluble in free silica and pyrophosphate) added to the crucible before hydrofluoric acid treatment, g；

M3- mass of sediment (insoluble substance in pyrophosphate) added to the crucible after hydrofluoric acid treatment, g；

G - Quality of dust sample, g。

4.6 Precautions

4.6.1 When dissolving silicates with phosphoric acid, the temperature should not exceed 250 ℃, otherwise it is easy to form a gel like substance.

4.6.2 When mixing acid with water, it should be stirred slowly and thoroughly to avoid the formation of a gel like substance.

4.6.3 When carbonate is present in the sample, bubbles may form upon contact with acid. It is advisable to heat slowly to prevent sample splashing.

4.6.4 When treating with hydrofluoric acid, it must be operated in a fume hood, taking care to prevent skin contamination and inhalation of hydrofluoric acid vapor.

4.6.5 When processing samples with a platinum crucible, the filtered sediment must be washed until there is no phosphate reaction, otherwise the platinum crucible will be damaged.

The method for testing phosphate ions is as follows:

Principle: Phosphoric acid and ammonium molybdate are reduced to blue with ascorbic acid at pH 4.1.

Reagents: ① Acetate buffer solution (pH 4.1): Mix 0.025mol of sodium acetate solution with 0.1mol of acetic acid solution by equal volume, ② 1% ascorbic acid solution (stored at 4 ℃), ③ ammonium molybdate solution: Take 2.5g of ammonium molybdate and dissolve it in 100ml of 0.025mol sulfuric acid (prepared before use).

Testing method: Dilute reagents ② and ③ with ① to a ratio of 10, take 1ml of filtrate, add 4.5ml of each dilution reagent, mix well, and let it stand for 20 minutes. If there are phosphate ions, the solution will turn blue.

5 Infrared spectrophotometry

5.1 Principle

Alpha quartz exhibits specific absorption bands in infrared spectra at 12.5 μ m (800cm-1), 12.8 μ m (780cm-1), and 14.4 (694cm-1) μ m. Within a certain range, its absorbance values are linearly related to the mass of alpha quartz. Quantitative determination is carried out by measuring absorbance.

5.2 Instruments

5.2.1 Ceramic crucibles and crucible clamps.

5.2.2 Box type resistance furnace or low-temperature ashing furnace.

5.2.3 Analytical balance with a sensitivity of 0.01mg.

5.2.4 Drying oven and dryer.

5.2.5 Agate milk bowl.

5.2.6 Tablet press and ingot mold.

5.2.7 200 mesh dust sieve.

5.2.8 Infrared spectrophotometer. Record the spectra from 900cm-1 to 600cm-1 on the X-axis, calibrate the zero point and 100% at 900cm-1, and represent the absorbance on the Y-axis.

5.3 Reagents

5.3.1 Potassium bromide, of superior purity or spectral purity, passes through a 200 mesh sieve, is ground using a wet method, dried at 150 ℃, and stored in a dryer for later use.

5.3.2 Anhydrous ethanol, analytical grade.

5.3.3 Standard alpha quartz dust, with a purity of over 99% and a particle size of<5 μ m.

5.4 Sample Collection

According to the measurement purpose, the sample collection method can refer to GBZ 159 and GBZ/T XXX. 2 or GBZ/T XXX. 1. When the amount of dust collected on the filter membrane is greater than 0.1mg, it can be directly used for the determination of free silica content in this method.

5.5 Determination

5.5.1 Sample processing: Accurately weigh the mass (G) of dust on the filter membrane containing dust. Then fold the dust receiving surface inward three times, place it in a porcelain crucible, and place it in a low-temperature ashing furnace or resistance furnace (less than 600 ℃) for ashing. After cooling, place it in a dryer for later use. Weigh 250mg of potassium bromide and the ashed dust sample, grind and mix them together in an agate mortar, and then place them in a drying oven (110 ℃± 5 ℃) for 10 minutes along with the tablet mold. Place the dried mixed sample in a compression mold, apply pressure of 25MPa for 3 minutes, and prepare the ingot as the test sample. At the same time, take a blank filter membrane and process it as a blank control sample.

5.5.2 Drawing of Quartz Standard Curve: Accurately weigh different masses of standard alpha quartz dust (0.01mg~1.00mg), add 250mg of potassium bromide separately, and place them in an agate mortar for thorough grinding. Prepare transparent ingots according to the above sample preparation method. Place standard quartz ingots of different qualities in the sample chamber optical path for scanning, with absorbance values at 800cm-1, 780cm-1, and 694cm-1 as the vertical axis and quartz mass (mg) as the horizontal axis. Draw three different wavelength alpha quartz standard curves and calculate the regression equation of the standard curve. In the absence of interference, the 800cm-1 standard curve is generally used for quantitative analysis.

5.5.3 Sample Measurement: Scan the sample ingot and blank control sample ingot separately in the optical path of the sample chamber, record the absorbance value at 800cm-1 (or 694cm-1), repeat the scanning measurement 3 times, subtract the absorbance mean of the blank control sample from the absorbance mean of the measured sample, and obtain the mass (m) of free silica in the sample from the alpha quartz standard curve.

5.5.4 Calculate the content of free silica in dust according to equation (3):

（3）

In the formula: SiO2 (F) - the content of free silica (α - quartz) in dust,%;

M - the mass of free silica in the measured dust sample, mg；

G - Quality of dust sample, mg。

5.6 Precautions

5.6.1 The detection limit of alpha quartz in this method is 0.01mg; The relative standard deviation (RSD) is 0.64%~1.41%. The average recovery rate is 96.0% to 99.8%.

5.6.2 The particle size of dust has a certain impact on the measurement results. Therefore, the sample and quartz dust used to make the standard curve should be thoroughly ground to ensure that more than 95% of the particles have a particle size less than 5 μ m before analysis and measurement can be carried out.

5.6.3 The ashing temperature has a certain impact on the quantitative results of coal mine dust samples. If the coal dust sample contains a large amount of kaolin components, decomposition occurs when ashing is above 600 ℃, and interference occurs near 800cm-1. If the ashing temperature is below 600 ℃, this interference band can be eliminated.

5.6.4 If the dust contains components such as clay, mica, amphibole, feldspar, etc., interference can occur around 800cm-1, and a standard curve of 694cm-1 can be used for quantitative analysis.

To reduce random measurement errors, the laboratory temperature should be controlled between 18 ℃ and 24 ℃, and the relative humidity should be less than 50%.

The analysis conditions for preparing quartz standard curve samples should be completely consistent with the conditions of the tested sample to reduce errors.

X-ray diffraction method

6.1 Principle

When X-rays are irradiated on free silica crystals, X-ray diffraction will occur; Under certain conditions, the intensity of the diffraction line is directly proportional to the mass of the irradiated free silica. Qualitative and quantitative determination of free silica in dust by measuring diffraction line intensity.

6.2 Instruments

6.2.1 Dust filter membrane.

6.2.2 Dust sampler.

6.2.3 Filter membrane slicer.

6.2.4 Sample board.

6.2.5 Analytical balance with a sensitivity of 0.01mg.

6.2.6 Tweezers, rulers, stopwatches, compasses, etc.

6.2.7 Agate milk bowl or agate ball mill.

6.2.8 X-ray diffractometer.

6.3 Reagents

The experimental water is double distilled water.

6.3.1 Hydrochloric acid solution, 6mol/L.

6.3.2 Sodium hydroxide solution, 100g/L.

6.4 Sample Collection

According to the measurement purpose, the sample collection method can refer to GBZ 159 and GBZ/T XXX. 2 or GBZ/T XXX. 1. When the amount of dust collected on the filter membrane is greater than 0.1mg, it can be directly used for the determination of free silica content in this method.

6.5 Measurement steps

6.5.1 Sample processing: Accurately weigh the mass (G) of dust on the filter membrane containing dust. Cut the filter membrane into 4-6 test samples according to the scale of the rotating sample rack.

6.5.2 Standard Curve

6.5.2.1 Preparation of standard alpha quartz dust: After crushing high-purity alpha quartz crystals, soak them in hydrochloric acid solution for 2 hours to remove impurities such as iron, and then wash and dry them with water. Then grind with agate mortar or agate ball mill until the particle size is less than 10 μ m, soak in sodium hydroxide solution for 4 hours to remove amorphous substances on the surface of quartz, rinse thoroughly with water until the washing solution is neutral (pH=7), dry and set aside. Or prepare using commercially available standard alpha quartz dust that meets the requirements of this article.

6.5.2.2 Preparation of standard curve: Standard alpha quartz dust is generated in the dust chamber, and the standard quartz dust is collected on a filter membrane of known mass using the same sampling method as the working environment. The collection amount is controlled between 0.5mg and 4.0mg, and 5-6 different mass points are collected within this range. After dust collection, the filter membrane is weighed and the incremental value is recorded. Then, 5 standard samples are taken from each filter membrane, and the size of the standard samples is consistent with the size of the rotating sample table. Before measuring the alpha quartz dust standard sample, the diffraction intensity (CPS) of the standard silicon on the (111) plane is first measured. Then measure the diffraction intensity (CPS) of each standard sample separately. Calculate the arithmetic mean of 5 alpha quartz dust samples at each point, and plot a standard curve of diffraction intensity (CPS) mean against quartz mass (mg).

6.5.3 Sample determination

6.5.3.1 Qualitative Analysis Before conducting phase quantitative analysis, the collected sample should first undergo qualitative analysis to confirm the presence of alpha quartz in the sample. Reference conditions for instrument operation:

Target: CuKα；

Scanning speed: 2 °/min;

Tube voltage: 30kV;

Recording paper speed: 2cm/min;

Tube current: 40mA;

Divergent slit: 1 °;

Range: 4000CPS;

Receiving slit: 0.3mm;

Time constant: 1s;

Angle measurement range: 10 ° ≤ 2 θ ≤ 60 °

Phase identification: Place the sample to be tested on the rack of an X-ray diffractometer for measurement, compare its diffraction pattern with the alpha quartz pattern in the Joint Committee on Powder Diffraction Standards (JCPDS) card, and when its diffraction pattern is consistent with the alpha quartz pattern, it indicates the presence of quartz in the dust.

6.5.3.2 Quantitative analysis

The measurement conditions of X-ray diffractometer are completely consistent with the conditions for making standard curves.

6.5.3.2.1 Firstly, measure the diffraction intensity of the sample (101) mesh, and then measure the diffraction intensity of the standard silicon (111) mesh; The measurement result is calculated according to equation (4):

．．．（4）

In the formula: IB - diffraction intensity of quartz in dust, CPS；

Ii - diffraction intensity of quartz on the dust collection filter membrane, CPS；

Is - the diffraction intensity of the standard silicon (111) mesh when formulating the quartz standard curve, CPS；

I - When measuring the diffraction intensity of quartz on the dust collection filter membrane, the standard silicon (111) mesh diffraction intensity is measured, CPS。

If the instrument accessories are not equipped with standard silicon, the diffraction intensity (CPS) of standard quartz (101) mesh can be used to represent the I value.

The calculated IB value (CPS) is used to determine the mass (m) of quartz in the dust on the filter membrane from the standard curve.

6.5.4 Calculation of Free Silica (α - Quartz) Content in Dust
Calculate according to equation (5):

（5）

In the formula: SiO2 (F) - content of free silica (α - quartz) in dust,%;

M - the mass of free silica (α - quartz) in the dust on the filter membrane, mg；

G - mass of dust sample, mg. Change M2-M1 to G, consistent with infrared method!

6.6 Precautions

6.6.1 The free silica in dust determined by this method refers to alpha quartz, and its detection limit is greatly affected by instrument performance and the crystalline state of the substance being measured; In a general X-ray diffractometer, the detection limit of alpha quartz content can reach 1% when the filter membrane dust collection amount is 0.5mg.

6.6.2 The particle size of dust affects the intensity of diffraction lines. When the particle size is above 10 μ m, the diffraction intensity decreases; Therefore, the dust particle size used to create the standard curve should be consistent with the particle size of the measured dust.

6.6.3 The X-ray diffraction intensity of quartz varies greatly depending on the dust mass per unit area. Therefore, the amount of dust collected on the filter membrane is generally controlled within the range of 2mg~5mg.

6.6.4 When there are substances that interfere with the alpha quartz diffraction line or affect the alpha quartz diffraction intensity, correction should be made according to the actual situation.