This standard specifies the determination of calcium oxide and magnesium oxide by complexometric titration and the determination of magnesium oxide by atomic absorption spectrometry. This standard is applicable to the determination of calcium oxide and magnesium oxide in limestone and dolomite, and also to the determination of calcium oxide and magnesium oxide in metallurgical lime. The first part is complexometric titration, the determination range: calcium oxide content greater than 25%, magnesium oxide content greater than 2.5%; the second part is atomic absorption spectrometry, the determination range: magnesium oxide content 0.10% to 2.50%. GB/T 3286.1-1998 Chemical analysis method for limestone and dolomite Determination of calcium oxide content and magnesium oxide content GB/T3286.1-1998 Standard download decompression password: www.bzxz.net

GB/T 3286. 1- 1998
This standard amends GB/T3286.1-1982 "Chemical analysis method for limestone and dolomite - EGTA-CyDTA volumetric method for determination of calcium oxide and magnesium oxide" and GB/T3286.11-1993 "Chemical analysis method for limestone and dolomite - flame atomic absorption spectrometry for determination of magnesium and iron content". This revision combines the magnesium oxide content determination part in GB/T3286.1-1982 and GB/T3286.11-1993 into one standard, which is described in two parts, the first part is complexometric titration method, and the second part is flame atomic absorption spectrometry method. The first part is complexometric titration method, which is not equivalent to the method of EDTA titration of calcium oxide and magnesium oxide content in JISM8850:1994 "Chemical analysis method for limestone". The second part of the flame atomic absorption spectrometry method adopts the method of determining magnesium oxide content by atomic absorption spectrometry in JISM8850:1994 "Chemical Analysis Methods for Limestone".
The "Model Diagram" clearly states that this standard is also applicable to the determination of calcium oxide and magnesium oxide in metallurgical lime. The "Allowable Difference" adds the laboratory allowable difference.
The sample decomposition in the complexometric titration method is changed from the acid-soluble residue alkali fusion recovery in the original standard to the decomposition method of direct alkali fusion and dilute acid leaching of the sample. The prepared test solution can be used for the determination of calcium oxide, magnesium oxide, silicon dioxide, lead oxide and iron oxide at the same time, making the analysis method more practical. The method adds a method of titrating calcium oxide and magnesium oxide with EDTA, which is parallel to the method of titrating calcium oxide and magnesium oxide with EGTA and CyDTA in the original standard. For the determination of calcium oxide in high-magnesium samples, since the "blank value" of the dispersant tartaric acid-sucrose solution added in the original method is difficult to control, the dispersant is no longer added in the revised method. The volume of the test solution and the fractionation were adjusted in the flame atomic absorption spectrometry. In view of the simplicity, high sensitivity and accuracy of this method, the original GB/T3286.2-1982 "Chemical analysis method of limestone and dolomite - Determination of magnesium oxide by chrome black T photometric method" was replaced by flame atomic absorption spectrometry.
GB/T3286 "Chemical analysis methods for limestone and dolomite" includes the following nine substandards: GB/T3286.1 Determination of calcium oxide content and magnesium oxide content; GB/T 3286. 2
Determination of silicon dioxide content;
GB/T 3286. 3
GB/T3286.4
Determination of aluminum oxide content;
Determination of iron oxide content;
GB/T 3286.5
Determination of manganese oxide content;
GB/T3286.6 Determination of phosphorus content,
GB/T3286.7 Determination of sulfur content;
GB/T3286.8 Determination of loss on ignition;
GB/T 3286. 9
Determination of carbon dioxide content.
This standard replaces GB/T3286.1-1982, GB/T3286.2-1982 and GB/T3286.11-1993 from the date of implementation. This standard was proposed by the former Ministry of Metallurgical Industry of the People's Republic of China. This standard is under the jurisdiction of the Information Standards Institute of the former Ministry of Metallurgical Industry. This standard was drafted by Wuhan Iron and Steel (Group) Corporation. The drafting units of this standard are: Wuhan Iron and Steel (Group) Corporation Technology Center, Anshan Iron and Steel (Group) Corporation Quality Inspection Center and Shanghai First Iron and Steel (Group) Co., Ltd.
The main drafters of this standard are: Liu Jixian, Cao Hongyan, Ma Fuyang, Wei Kuangqun, Chen Yasen, Yu Guizhi. This standard was first issued in July 1982, and the flame atomic absorption spectrometry was revised in March 1993. 34
1 Scope
National Standard of the People's Republic of China
Chemical analysis method of limestone and dolomite
The determination of calcium oxide andmagnesium oxide content
GB/T 3286. 1-1998
Replaces GB/T 3286. 1-1982
GB/T 3286.2--1982
GB/T 3286. 11-~1993
This standard specifies the determination of calcium oxide and magnesium oxide by complexometric titration and the determination of magnesium oxide by atomic absorption spectrometry. This standard is applicable to the determination of calcium oxide and magnesium oxide in limestone and dolomite, and also to the determination of calcium oxide and magnesium oxide in metallurgical lime. The first part is complexometric titration, with a determination range of calcium oxide greater than 25% and magnesium oxide greater than 2.5%. The second part is atomic absorption spectrometry, with a determination range of magnesium oxide 0.10% to 2.50%. 2 Reference standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T2007.21987 General rules for sampling and sample preparation of bulk mineral products Manual sample preparation method GB/T3286.21998 Chemical analysis method of limestone and dolomite Determination of silicon dioxide content GB/T3286.3-1998 Chemical analysis method of limestone and dolomite Determination of aluminum oxide content GB/T3286.4-1998 Chemical analysis method of limestone and dolomite Determination of iron oxide content GB/T7728--1987 General rules for chemical analysis of metallurgical products by flame atomic absorption spectrometry Part I Complexometric titration
3 Method shortcut
The sample is melted with sodium carbonate-boric acid mixed flux and leached with dilute hydrochloric acid. Take part of the test solution, mask the iron, aluminum, manganese ions with triethanolamine, and titrate the calcium oxide content with EDTA or EGTA standard solution in a strong alkaline medium with calcium indicator as indicator. For high-magnesium samples, pre-place 90% to 95% EDTA or EGTA standard solution before adjusting the test solution to alkalinity to eliminate the influence of large amounts of magnesium. Take another part of the test solution, mask the iron, aluminum, manganese ions with triethanolamine, use acid chrome blue K and phenol green B as mixed indicators in an ammonia buffer solution, filter the calcium oxide and magnesium oxide content with EDTA standard solution, or mask calcium with a slightly excessive amount of EGTA standard solution, and titrate the magnesium oxide content with CyDTA standard solution.
If the sample contains iron oxide, aluminum oxide content greater than 2.0%, or aluminum oxide content greater than 0.10%, use copper reagent to precipitate and separate iron, aluminum, manganese ions, and take the filtrate and titrate the calcium oxide and magnesium oxide content with EDTA or EGTA, CyDTA standard solution. Approved by the State Administration of Quality and Technical Supervision on December 7, 1998, implemented on July 1, 1999
4 Reagents
GB/T 3286. 1--1998
4.1 Mixed flux: Grind two parts of anhydrous sodium carbonate and one part of boric acid and mix. 4.2 Hydrochloric acid (1+5).
4.3 Triethanolamine (1+4).
Ammonia water (1+1).
4.5 Potassium hydroxide solution (200g/L), stored in a plastic bottle, needs to be left overnight before use. Diethylamine sodium dithiocarbamate (copper reagent) solution (50g/L.), prepared when needed. 4.6
Ammonia buffer solution: weigh 67.5g ammonium chloride and dissolve it in water, add 570mL ammonia water (0.90g/mL), dilute with water to 1L, mix 4.7
Calcium indicator: grind 1g calcium indicator with 100g sodium chloride and mix. 4.9
Acid chrome blue K solution (5 g/L), prepared with triethanolamine (1+1). 4.10 Naphthol green B solution (5g/L), prepared with triethanolamine (1+1). Calcium oxide standard solution: weigh 0.8924g high-purity calcium carbonate (not less than 99.99%) that has been dried at 105-110℃ for 1h and cooled to room temperature, put it in a 250mL beaker, add about 100mL water, and cover with a watch. Slowly add 10mL of hydrochloric acid (1+1) until the reagent dissolves, heat to boil to drive out carbon dioxide, remove and cool to room temperature. Transfer to a 1000mL volumetric flask, dilute to scale with water and mix well. This solution contains 0.50mg of calcium oxide in 1.00mL.
4.12 Magnesium oxide standard solution: weigh 0.5000g of high-purity magnesium oxide (not less than 99.99%), place in a 250mL beaker, add about 100mL water, and cover with blood. Slowly add 15mL hydrochloric acid (1+1) until the reagent is dissolved, heat to boil, remove, and cool to room temperature. Transfer to a 1000mL volumetric flask, dilute to scale with water, and mix. This solution contains 0.50mg magnesium oxide in 1.00mL.
4.13 EDTA (disodium ethylenediaminetetraacetic acid) standard solution [c(EDTA)=0.01 mol/L] 4.13.1 Preparation
Weigh 3.72g disodium ethylenediaminetetraacetic acid in a 500mL beaker, add about 300mL water, heat at low temperature, stir continuously, and after the reagent is completely dissolved, cool to room temperature, transfer to a 1000mL volumetric flask, dilute to scale with water, and mix. 4.13.2 Calibration of calcium oxide titer with EDTA standard solution Take three portions of 50.00 mL of calcium oxide standard solution (4.11) and place them in 250 mL conical flasks respectively. Add 2 mL of magnesium oxide standard solution (4.12) and 50 mL of water, 5 mL of triethanolamine (4.3), 20 mL of potassium hydroxide solution (4.5) and a small amount of calcium indicator (4.8). Titrate with EDTA standard solution (4.13.1) under constant stirring until the solution changes from red to bright blue. The range of the volume of EDTA standard solution consumed by the three portions of calcium oxide standard solution should not exceed 0.05 mL. Take the average value. Calculate the titer of EDTA standard solution against calcium oxide according to formula (1): cV
wherein: Ti—the titer of EDTA standard solution against calcium oxide, g/mL; concentration of calcium oxide standard solution, g/mL; V—the volume of calcium oxide standard solution taken, mL; V—the average volume of EDTA standard solution consumed in titration, mL; Vo1—the average volume of EDTA standard solution consumed in titration of reagent blank, mL. 4.13.3 Calibration of magnesium oxide titer with EDTA standard solution (1)
Take three portions of 20.00 mL of magnesium oxide standard solution (4.12) and place them in 250 mL conical flasks respectively. Add 50 mL of water, 5 mL of triethanolamine (4.3), 10 mL of ammonia buffer solution (4.7), 2 drops of acid chrome blue K solution (4.9) and 6 to 7 drops of phenol green B solution (4.10). Titrate with EDTA standard solution until the solution changes from dark red to blue-green. The extreme difference in the number of milliliters of EDTA standard solution consumed by the three portions of magnesium oxide standard solution should not exceed 0.05 mL. Take the average value. 36
GB/T3286.1—1998
Calculate the titer of EDTA standard solution on magnesium oxide according to formula (2): ty
T, = V,- Vo2
Wherein: T2—titer of EDTA standard solution on magnesium oxide + g/mL; concentration of magnesium oxide standard solution, g/mL; V—volume of magnesium oxide standard solution taken, mL; V2—average volume of EDTA standard solution consumed in titration, mL; Vo2—average volume of EDTA standard solution consumed in titration reagent blank, mL. 4.14 EGTA (ethylene glycol diethyl ether diamine tetraacetic acid) standard solution [c(EGTA) = 0.01 mol/L] 4.14.1 Preparation
Weigh 3.90 g of ethylene glycol diethyl ether diamine tetraacetic acid and place it in a 500 mL beaker. Add about 250 ml of water and heat at low temperature. While stirring continuously, drop potassium hydroxide solution (4.5) until the reagent is dissolved. Cool to room temperature. Transfer to a 1000 mL container, dilute to the mark with water and mix.
4.14.2 Calibration of calcium oxide titer with EGTA standard solution The same as the calibration of calcium oxide titer with EDTA standard solution, operate and calculate the titer according to 4.13.2, only use EGTA standard solution (4.14.1) instead of EDTA standard solution (4.13.1). 4.15 CyDTA (cyclohexanediaminetetraacetic acid) standard solution [c(CyDTA) = D.01 mol/L] 4.15.1 Preparation
Weigh 3.70 g of cyclohexanediaminetetraacetic acid, place in a 500 mL beaker, add about 250 mL of water, heat at low temperature, and under constant stirring, drop potassium hydroxide solution (4.5) until the reagent dissolves, and cool to room temperature. Transfer to a 1000 mL volumetric flask, dilute to the scale with water, and mix well. 4.15.2 Calibration of the full titration of magnesium oxide with CyDTA standard solution Calibrate the titration of magnesium oxide with EDTA standard solution, operate and calculate the titration according to 4.13.3, and only use CyDTA standard solution (4.15.1) instead of EDTA standard solution (4.13.1). 5 Instruments
In the analysis, only common laboratory instruments and equipment are used. 6 Sample preparation
Prepare the sample according to GB/T2007.2.
6.1 The sample should be processed to a particle size of less than 0.125mm. 6.2 Before analysis, the limestone and dolomite samples should be dried at 105-110℃ for 2 hours and placed in a desiccator to cool to room temperature. 6.3 The preparation of metallurgical lime samples should be carried out quickly. After preparation, the samples should be immediately placed in a ground-mouth bottle or plastic bag and sealed, and stored in a desiccator. The samples should not be dried before analysis.
7 Analysis steps
7.1 Sample quantity
Weigh 0.50g of sample, accurate to 0.0001g. For metallurgical lime samples, the sample should be weighed quickly. 7.2 Blank test
Perform a blank test with the sample.
7.3 Sample decomposition and preparation of stock solution
7.3.1 Place the sample (7.1) in a platinum crucible pre-filled with 3.0g of mixed flux (4.1), mix well, and then cover with 1.0g of mixed flux (4.1). Place the platinum crucible in a high-temperature furnace with a furnace temperature below 300℃ and cover it with a platinum lid (leaving a gap). Then gradually increase the furnace temperature to 950-1000℃, melt for 10 min, take out, rotate the platinum crucible, and cool. 37
GB/T 3286.1-1998
7.3.2 Rinse the outer wall of the platinum crucible with water, place the platinum and the platinum lid in a 300mL beaker, add 75mL of hydrochloric acid (4.2), heat at low temperature to slowly remove the molten block, and wash out the platinum crucible and platinum lid with water. Heat at low temperature until the test solution is clear, and cool to room temperature. Transfer the test solution to a 250mL volumetric flask, dilute to the mark with water, and mix well. This test solution is used as a reserve solution for determining the amount of calcium oxide, magnesium oxide, silicon dioxide, aluminum oxide, and iron oxide. Note: GB/T3286.1 complexometric titration method for determining the amount of calcium oxide and magnesium oxide, GB/T3286.2 molybdenum blue photometric method for determining the amount of silicon dioxide, GB/T3286.3 chrome azure S photometric method for determining the amount of aluminum oxide, GB/T3286.4 o-diaza non-photometric method for determining the amount of iron oxide. The reserve solutions prepared by each analytical method are the same. If the contents of these chemical components in the sample are determined at the same time, only one reserve solution of the sample can be prepared, and then the samples can be divided and determined according to each analytical method. 7.3.3 Take two portions of 25.00 mL of the stock solution (7.3.2) (for metallurgical lime samples, take two portions of 15.00 mL), place them in 250 mL conical flasks respectively, add 25 mL of water, and determine the amount of calcium oxide and magnesium oxide according to the method specified in 7.4 or 7.5. 7.3.4 When the content of lead oxide or iron oxide in the sample is greater than 2.0% or the content of manganese oxide is greater than 0.10%, use a pot reagent to separate them: take 100.00 mL of the stock solution (7.3.2) in a 250 mL volumetric flask, add 50 mL of water, put a small piece of Congo red test paper into the solution, neutralize most of the acid with potassium hydroxide solution (4.5), rinse the bottleneck with water, add ammonia water (4.4) dropwise to neutralize until the test paper just turns red, add 10 mL of copper reagent solution (4.6), shake vigorously for 1 min, cool to room temperature, dilute to scale with water, mix well, and let stand for 30 min. Dry filter with medium-speed quantitative filter paper and discard the first 20 mL of filtrate. Take two portions of 50.00 mL of filtrate and place them in 250 mL conical flasks respectively. Determine the amount of calcium oxide and magnesium oxide according to the method specified in 7.4 or 7.5. 7.4 EDTA titration of calcium oxide and magnesium oxide 7.4.1 Titration of calcium oxide
7.4.1.1 Limestone and metallurgical lime sample
Add 5 mL of triethanolamine (4.3) to the test solution (7.3.3 or 7.3.4), mix well, add 20 mL of potassium hydroxide solution (4.5) and a small amount of calcium indicator (4.8), and mix. Titrate with EDTA standard solution (4.13) until the test solution changes from red to bright blue as the end point. For blank test and when the amount of magnesium oxide in the sample is less than 1.0%, add 1.0 mL of magnesium oxide standard solution (4.12) before titrating with EDTA standard solution. When the amount of magnesium oxide in the sample is greater than 2.5%, titrate according to the pre-set titrant method in 7.4.1.2. 7.4.1.2 Dolomite sample
In a test solution (7.3.3 or 7.3.4), add 5 mL of triethanolamine (4.3) Mix well, add EDTA standard solution (4.13) equivalent to 90%~95% of calcium oxide in the titration solution, add 20mL potassium hydroxide solution (4.5) and a small amount of calcium indicator (4.8), and mix well. Continue to titrate with EDTA standard solution (4.13) until the test solution changes from red to bright blue. Before the blank test is fully titrated, add 1.0mL of oxidation standard solution (4.12) without pre-setting titrant. Note: To determine the amount of pre-setting titrant, a pre-titration can be performed first. Take a portion of the test solution (7.3.3) and titrate according to the titration method of 7.4.1.1 to determine the pre-titration volume. During the titration, pre-add 1~~2 mL of titrant less than the pre-titration volume. 7.4.2 Titration of calcium oxide and magnesium oxide Add 5 mL triethanolamine (4.3) to another test solution (7.3.3 or 7.3.4), mix well, add 20 mL ammonia buffer solution (4.7), add 2 drops of acid chrome blue K solution (4.9), 6~~7 drops of naphthol green B solution (4.10), and titrate with EDTA standard solution (4.13) until the test solution changes from dark red to blue-green.
7.5 EGTA and CyDTA titration of calcium oxide and magnesium oxide 7.5.1 Titration of calcium oxide
7.5.1.1 Limestone and metallurgical lime sample
Add 5 mL triethanolamine (4.3) to a test solution (7.3.3 or 7.3.4), mix well, add 20 mL potassium hydroxide solution (4.5) and a small amount of calcium indicator (4.8), mix well. Titrate with EGTA standard solution (4.14) until the test solution changes from red to bright blue. For blank test and when the amount of magnesium oxide in the sample is less than 1.0%, add 1.0 mL of magnesium oxide standard solution (4.12) before titrating with EDTA standard solution. When the amount of magnesium oxide in the sample is greater than 2.5%, titrate according to the pre-setting titrant method in 7.4.1.2. 7.5.1.2 Dolomite sample
Add 5 mL of triethanolamine (4.3) to one portion of the test solution (7.3.3 or 7.3.4) and mix well. Add EGTA standard solution (4.14) equivalent to 90%~95% of the calcium oxide in the titration solution, add 20 mL of potassium hydroxide solution (4.5) and a small amount of calcium indicator (4.8) and mix well. Continue to titrate with EGTA standard solution (4.14) until the test solution changes from red to bright blue. This is the endpoint. Before the blank test titration, add 1.0 mL of magnesium oxide 38
standard solution (4.12), without pre-setting the titrant. Note: Same as Note 7, 4.1.2.
7.5.2 Titration of magnesium oxide
GB/T3286.1--1998
In another test solution (7.3.3 or 7.3.4), add 5 mL of triethanolamine (4.3) and mix well, then add EGTA standard solution (4.14), the amount of which is equal to the number of milliliters of EGTA standard solution (4.14) consumed when titrating calcium oxide, and an excess of 0.4 mL. Add 20 mL of ammonia buffer solution (4.7), 2 drops of acid chrome blue K solution (4.9), and 6-7 drops of naphthol green B solution (4.10), and titrate with CyDTA standard solution (4.15) until the test solution changes from dark red to blue-green. 8 Expression of analytical results
8.1 EDTA titration of calcium oxide and magnesium oxide 8.1.1 Calculate the mass percentage of calcium oxide according to formula (3): CaO(%) = /- Vo)T
Wherein: V,——volume of EDTA standard solution consumed in titration of calcium oxide, mL; × 100
Vo——volume of EDTA standard solution consumed in titration of blank test, mLT
-titer of EDTA standard solution on magnesium oxide, g/mL; m
is the amount of sample equivalent to the test solution in g.
8.1.2 Calculate the mass percentage of magnesium oxide according to formula (4): [(V,-Ve) -(V- Vo)T × 100www.bzxz.net
MgO(%) =-
Wherein, Vz-
the volume of EDTA standard solution consumed in titrating the total amount of calcium oxide and magnesium oxide, mL; the volume of EDTA standard solution consumed in the blank test for titrating the total amount of calcium oxide and magnesium oxide, ml. V,-the volume of EDTA standard solution consumed in titrating calcium oxide, mL; Va1-the volume of EDTA standard solution consumed in the blank test for titrating calcium oxide, mL; -the titer of EDTA standard solution on magnesium oxide, g/mL; T
the weight of the sample equivalent to the test solution, g.
8.2 EGTA and CyDTA titration of calcium oxide and magnesium oxide 8.2.1 Calculate the mass percentage of calcium oxide according to formula (5): Cao (%) = VV) × 100
Wherein: V.-
The volume of EGTA standard solution consumed in titrating calcium oxide, mL; Vo—the volume of EGTA standard solution consumed in titrating the blank test, mL; T; —the titer of EGTA standard solution on calcium oxide, g/mL, m: -——the amount of sample equivalent to the test solution, g. 8.2.2 Calculate the mass percentage of magnesium oxide according to formula (6): Mgo (%) --V × 100
Wherein, V--the volume of CyDTA standard solution consumed in titrating magnesium oxide, mLVo--the volume of CyDTA standard solution consumed in titrating blank test, mLT,-the titer of CyDTA standard solution on magnesium oxide, g/mL, m.--the amount of sample equivalent to the test solution, 8. · (3)
9 Allowable difference
GB/T 3286.1--1998
The difference between two independent analysis results in a laboratory and the difference between the analysis results of two laboratories should not be greater than the corresponding allowable differences listed in Table 1 and Table 2. For the sample of gold lime, no allowable difference requirement between laboratories is required. Table 1
Calcium oxide content
Limestone
Dolomite
Metallurgical lime
Magnesium oxide content
2.50~5.00
>5. 00~15.00
>15.00~～22.00
10 Method Summary
Part II
Permissible difference within the laboratory
Permissible difference within the laboratory
Flame atomic absorption spectrometry
Permissible difference between laboratories
Permissible difference between laboratories
The sample is decomposed by hydrochloric acid and hydrofluoric acid, and perchloric acid smokes. The sample solution is sprayed into an air-acetylene flame, and a magnesium hollow cathode lamp is used as the light source. The absorbance is measured at a wavelength of 285.2nm on an atomic absorption spectrometer. During measurement, add strontium chloride as an inhibitor to eliminate interference from elements such as aluminum, titanium, and silicon. 11 Reagents
11.1 Hydrochloric acid (1+1).
11.2 Hydrofluoric acid (p1.13 g/mL).
11.3 Perchloric acid (pl.67 g/mL).
11.4 Strontium chloride solution (150 g/L): Take 252 g of strontium chloride (SrCl2·6H20) in a 600 mL beaker, dissolve it in water, transfer it to a 1000 mL volumetric flask, dilute to the mark with water, and mix well. 11.5 Magnesium oxide standard solution
11.5.1 Weigh 0.1000g of high-purity magnesium oxide (not less than 99.99%) that has been burned at 950~1000℃ for 1h and cooled to room temperature, place it in a 250mL beaker, add 10mL of hydrochloric acid (11.1) to dissolve, transfer to a 1000mL volumetric flask, dilute to scale with water, and mix. 1.00mL of this solution contains 100μg of magnesium oxide.
11.5.2 Transfer 50.00ml. of magnesium oxide standard solution (11.5.1) to a 500mL volumetric flask, add 10mL of hydrochloric acid (11.1), dilute to scale with water, and mix. 1.00mL of this solution contains 10.0μg of magnesium oxide. 12 Instruments
Atomic absorption spectrometer, equipped with air-acetylene burner and magnesium hollow cathode lamp. Air and acetylene gas should be pure enough (free of water, oil and magnesium) to provide a stable and clear lean flame. According to GB/T7728's judgment on the performance of atomic absorption spectrometers, the instrument used should meet the following indicators. 40
12.1 Minimum precision requirements
GB/T 3286. 1—1998
Use the highest concentration standard solution to measure the absorbance 10 times and calculate the average value and standard deviation of the absorbance. The standard deviation should not exceed 1.5% of the average value of the absorbance.
Use the lowest concentration standard solution (not the zero concentration standard solution) to measure the absorbance 10 times and calculate the standard deviation. The standard deviation should not exceed 0.5% of the average absorbance of the highest concentration standard solution. 12.2 Characteristic concentration
The characteristic concentration of magnesium oxide should be better than 0.007μg/mL. 12.3 Detection limit
The detection limit of magnesium oxide should be better than 0.004μg/mL. 12.4 Linearity of calibration curve
Divide the calibration curve into five sections according to the concentration. The ratio of the absorbance difference of the highest section to the absorbance difference of the lowest section should not be less than 0.7.13 Sample preparation
Prepare the sample according to GB/T2007.2.
13.1 The sample should be processed to a particle size of less than 0.125mm. 13.2 Before analysis, the limestone and dolomite samples should be dried at 105-110℃ for 2h and placed in a desiccator to cool to room temperature. 13.3 The preparation of metallurgical lime samples should be carried out quickly. After preparation, the samples should be immediately placed in a ground-mouth bottle or plastic bag and sealed, and stored in a desiccator. The samples should not be dried before analysis.
14 Analysis steps
14.1 Sample quantity
Weigh 0.20g of sample, accurate to 0.0001g. For metallurgical lime samples, the sample should be weighed quickly. 14.2 Blank test
Carry out a blank test with the sample.
14.3 Sample decomposition and test solution preparation
14.3.1 Place the sample (14.1) in a platinum or polytetrafluoroethylene beaker, moisten with a small amount of water, carefully add hydrochloric acid (11.1) until the violent reaction stops, and then add 5mL in excess. Add 2mL hydrofluoric acid (11.2) and 2mL perchloric acid (11.3), heat at low temperature, evaporate the perchloric acid white smoke until it is almost dry, cool,
14.3.2 Add 10mL hydrochloric acid (11.1), heat at low temperature to dissolve the salts, and cool. Transfer the test solution to a 100ml volumetric flask, dilute to the mark with water, and mix.
Note: This test solution is the same as the test solution (14.3.2) prepared in the analytical method for the determination of iron oxide content by flame atomic absorption spectrometry in Part II of GB/T3286.4, and can be used for the determination of iron oxide content at the same time.
14.3.3 Measurement of test solution
14.3.3.1 Transfer 10.00 mL of the test solution (14.3.2) to a 250 mL volumetric flask, add 5 mL of hydrochloric acid (11.1), 5.0 mL of strontium chloride solution (11.4), dilute to the mark with water, and mix. This test solution is used for the determination of 0.10% to 1.00% magnesium oxide content. 14.3.3.2 Transfer 25.00 mL of the test solution (14.3.3.1) to a 100 mL volumetric flask, add 1.5 mL of hydrochloric acid (11.1), 1.5 mL of strontium chloride solution (11.4), dilute to the mark with water, and mix. This test solution is used to determine the amount of magnesium oxide above 1.00%. 14.4 Measurement
According to the requirements and operation of GB/T7728, adjust the atomic absorption spectrometer to the optimal working conditions, use air acetylene flame at a wavelength of 285.2nm, adjust the zero point with water, measure the absorbance of magnesium in the test solution, and find the corresponding magnesium oxide concentration on the calibration curve. 14.5 Calibration curve drawing
Pipette 0, 1.00, 2.00, 4.00, 6.00, 8.00, 10.00mL of magnesium oxide standard solution (11.5.2) into a group of 100mL volumetric flasks, add 2mL of hydrochloric acid (11.1) and 2.0mL of strontium chloride solution (11.4) respectively, dilute to the scale with water, and mix well. At the wavelength of 285.2nm of the atomic absorption spectrometer, adjust the zero point with water and measure the absorbance. Draw a calibration curve with the concentration of magnesium oxide as the horizontal axis and the absorbance of the zero concentration solution minus the vertical axis.
15Description of the analysis results
Calculate the mass percentage of magnesium oxide according to formula (7): MgO (%) =
Where: ci—
(c) - c2)f .V
m×106
The concentration of magnesium oxide in the test solution is obtained from the self-calibration curve, μg/mL; × 100
The concentration of magnesium oxide in the blank test solution is obtained from the self-calibration curve, μg/mL at a dilution multiple;
VThe final volume of the sample solution is measured, mL, m—sample volume, g.
16 Allowable error
(7)
The difference between two independent analysis results in a laboratory and the difference between the analysis results in two laboratories shall not be greater than the corresponding allowable error listed in Table 3. For the sample of metallurgical lime, no allowable error requirement is required between laboratories. Table 3
Magnesium oxide content
0.10~~0. 50
>0.50~1.00
>1. 00 ~2. 50
Allowable error within the laboratory
Allowable error between laboratories
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