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Chemical Industry Standard of the People's Republic of China
Realgar Ore and Orpiment Ore
Determination of Arsenic Content
1 Subject Content and Scope of Application
This standard specifies the determination of arsenic content in realgar and orpiment ore products by iodine titration. This standard is applicable to the determination of arsenic content in realgar and orpiment ore. 2 Method Summary
HG/T2275.3-92
The sample is decomposed with nitric acid saturated with potassium chlorate, and the nitric acid is driven out with sulfuric acid. In a strong acid solution, use potassium iodide to reduce pentavalent arsenic to trivalent arsenic, boil the solution to remove iodine, use sodium tartrate to mask interfering elements, and then titrate with iodine standard titration solution in a slightly alkaline solution, AsO+I+H,O=AsO+2I+2H
3 Reagents and solutions
3.1 Sodium tartrate (HG3-1101) solution: 200g/L; 3.2 Sodium hydroxide (GB629) solution: 200g/L; 3.3 Sodium hydroxide solution: 100g/L;
3.4 Sulfuric acid (GB625); 1+1 (V+V) solution; 3.5 Sulfuric acid: 1+10 (V+V) solution:
3.6 Potassium chlorate (GB645) Saturated nitric acid (GB626) solution: about 100g/L Starch solution: 5g/L.
Weigh 0.5g soluble starch, add a small amount of water to make it paste, then add 100mL boiling water while stirring, if it is turbid, heat it until clear, let it cool before use (prepare it when needed); 3.8 Sodium thiosulfate (Na2SO,5H,O) (GB637) solution: c (Na2S,O·5H,O) = 0.01mol/L. Weigh 2.5g sodium thiosulfate and dissolve it in distilled water that has just been boiled and cooled, add 0.1g anhydrous sodium carbonate (GB639), and dilute it to 1000mL with the same water , shake the hook, store in a brown reagent bottle, 3.9 Iodine standard titration solution c
3.9.1 Preparation
2)=0.08mol/L.
Weigh 10.15g iodine tablets (GB675) and about 25g potassium iodide (GB1272) and dissolve them in 50mL water. After the iodine is completely dissolved, transfer them to a 1000ml brown volumetric flask, dilute with water to the scale, shake well, store in a dark place, and calibrate after one day. 3.9.2 Calibration
3.9.2.1 Calibration method
Weigh 0.1g arsenic trioxide (GB1256) to an accuracy of 0.0002g and place it in a 250ml container. In a L conical flask, add 10mL warm sodium hydroxide solution (3.3) to dissolve, dilute with water to 150mL, add 2 drops of phenol indicator, and neutralize by adding sulfuric acid solution (3.5) until the red color disappears, add another drop in excess, and cool. Add 3g sodium bicarbonate (GB640) and 5mL starch solution (3.7), and immediately titrate with the iodine solution to be calibrated (3.9.1) to blue-purple color, which is the end point, and perform a blank test at the same time.
3.9.2.2 Calculation
The concentration of the iodine standard titration solution is calculated according to formula (1): c,
Wherein:
(VV)×0.04946
The actual concentration of the iodine standard titration solution, mol/L; the mass of arsenic trioxide, g:
VThe volume of the iodine standard titration solution consumed by the sample, mL; V. The volume of the iodine titration solution for the blank test, mL; the mass of arsenic trioxide with 1.00mL of iodine standard titration solution [c
. wwW.bzxz.Net
3.10 Phenol indicator (GB10729): 5g/L ethanol solution. 4 Instruments
-I,)=1.000mo1/LJ equivalent, 50 or 25mL acid burette expressed in grams: in accordance with QB518, Class A. And calibrated according to the provisions of Article 4, Paragraph 23 "Container Verification" of JJG196 "Basic Glass Measuring Instruments (Trial)". 5 Samples
Dry the laboratory sample (HG/T2275.2) at 80±2℃ to constant weight, cool to room temperature in a desiccator, and store in a dark place.
6 Analysis steps
6.1 Weigh 0.1~0.2g of sample by difference subtraction method, accurate to 0.0002g, place in a 250mL conical flask, moisten with a small amount of water, add 10mL nitric acid solution saturated with potassium nitrate (3.6), and heat at low temperature until the reaction stops until it is completely decomposed. 6.2 Add about 8 mL of sulfuric acid (3.4), heat until thick white smoke of sulfur trioxide is emitted, remove, cool, rinse the bottle wall with a small amount of water, and continue to heat until thick white smoke is emitted
6.3 Cool, rinse the bottle wall with water and dilute to about 50 mL, heat until soluble salts are dissolved, add 1 g of potassium iodide (GB1272), shake well, and heat to boiling. Dilute to 100 mL with hot water, continue to heat and boil to expel most of the free iodine until the solution is light yellow,
6.4 Cool quickly, add 25 mL of sodium tartrate solution (3.1), dilute with water to about 120 mL, add 5 mL of starch solution (3.7), and add sodium thiosulfate solution (3.8) until the blue-purple color just disappears. 6.5 Add 2 drops of phenolic acid indicator, neutralize with sodium hydroxide solution (3.2) until the phenolic acid turns red, add sulfuric acid solution (3.5) until the red color just disappears, add 1 drop in excess, and cool. Add 3g of sodium bicarbonate (GB640), and immediately titrate with iodine standard titration solution (3.9) until it turns blue-purple, which is the end point.
Weigh two samples each time for determination, and do a blank test at the same time. 7 Expression of analysis results:
7.1 The arsenic (As) content X expressed as mass percentage is calculated according to formula (2): 6
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c(VV.)×0.03746
Where X,
mass percentage of arsenic, %;
actual concentration of iodine standard titration solution, mol/L; V
The volume of the standard iodine titration solution consumed by the sample, mL; The volume of the standard iodine titration solution consumed by the blank test, mL The mass of the sample, g;
The mass of arsenic in grams equivalent to 1.00mL of the standard iodine titration solution [c (
=1.000mol/L) -12)
7.2 The content of realgar (As2S,) expressed in mass percentage is calculated according to formula (3): X,=X,× 1.4279
Wherein: X—mass percentage of realgar, %; X.
—mass percentage of realgar, %;
—Coefficient of converting arsenic to diastereum
7.3 The total amount of orpiment (As, S) X expressed as mass percentage is calculated according to formula (4): X,=X×1.6419
Wherein: X
—mass percentage of realgar, %;
mass percentage of arsenic , %;
- converted to the coefficient of disulphide trisulfide,
Take the arithmetic mean of the parallel determination results as the determination result. The allowable difference of the parallel determination results is shown in the following table. Arsenic (As)
>42.0~50.0
>50.0~60.0
Additional notes:
This standard is proposed by the Science and Technology Department of the Ministry of Chemical Industry of the People's Republic of China. This standard is under the jurisdiction of the Chemical Industry and Mining Design Institute of the Ministry of Chemical Industry. This standard was drafted by the Chemical Industry and Mining Design Institute of the Ministry of Chemical Industry. The main drafters of this standard are Min Yuyao, Zhao Zhiquan and Wang Hailiang. Standard allocation network mmabrca.ccm allowable difference
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