GB/T 15555.8-1995 Determination of total chromium in solid wastes - Ammonium ferrous sulfate titration method
Some standard content:
National Standard of the People's Republic of China
Solid waste
Determination of total chromium
Ammonium ferrous sulfate titration method
Solid waste-Determination of total chromium-Titrimetric method
1 Subject content and scope of application
1.1 This standard specifies the ammonium ferrous sulfate titration method for determining total chromium in solid waste leachate. GB/T15555.8--1995
1.2 This standard method is applicable to the determination of total chromium in solid waste leachate. The method can also determine the total chromium in water and wastewater. 1.2.1 The lower limit of quantification of the method is 1 mg/mL. 1.2.2 Interference
Vanadium interferes with the determination. Except for vanadium slag leachate, the vanadium content in the general leachate will not affect the determination. Trivalent iron interferes with the determination. When the concentration of trivalent iron (m/L) is 175 times that of chromium, a relative error of 2.8% can be introduced. 2 Principle
In an acidic solution, silver salt is used as a catalyst and ammonium persulfate is used to oxidize trivalent chromium to hexavalent chromium. A small amount of sodium chloride is added and boiled to remove excess ammonium persulfate and chlorine and other oxidants produced in the reaction. Phenyl-anthranilic acid is used as an indicator and hexavalent chromium is titrated with ammonium ferrous sulfate solution. Excess ammonium ferrous sulfate reacts with the indicator and the solution turns bright green as the end point. The total chromium content in the solid waste leachate is calculated based on the amount of ammonium ferrous sulfate standard solution used. The reaction equation is as follows: 3(NH,)2S:O:+Cr2(SO,) +7H,0 Ag3(NH.),SO, +H,Cr20,+6H,SO.6Fe(NH,)2(SO,)2+H,Cr20,+6H,SO, =----3Fe2(SO)3+Cr2(SO,);+6(NH),SO,+7H,03 Reagents
Unless otherwise specified, reagents that meet national or professional standards, deionized water or water of equivalent purity are used. 3.1 Ammonia water: (1+1).
3.2 Sulfuric acid-phosphoric acid mixed solution: Slowly add 150mL concentrated sulfuric acid to 700mL water, cool and add 150mL concentrated phosphoric acid solution, mix well.
3.3 Silver nitrate solution 5g/L: Dissolve 0.5g of silver nitrate (AgNO3) in water and dilute to 100mL. 3.4 Manganese sulfate solution 10g/L: Dissolve 1g of manganese sulfate in water and dilute to 100mL. 3.5 Ammonium persulfate solution 250g/L: Dissolve 25g of ammonium persulfate [(NH,)S,Og in 100mL of water. 3.6 Sodium chloride solution 10g/L: Dissolve 1g of sodium chloride in water and dilute to 100mL. 3.7 N-phenyl-o-aminobenzyl indicator 0.2% (abbreviated as chromium indicator, C13HnNOz): Weigh 0.2g of chromium indicator, dissolve in 100mL of 0.2% sodium carbonate solution, shake well, store in a brown bottle, and store at low temperature. 3.8 Hexavalent chromium standard solution (0.40 mg/mL): Weigh 1.1316 g potassium dichromate (K,Cr20, high-grade pure) dried at 120°C for 2 hours, dissolve it in distilled water, transfer it to a 1000 mL volumetric flask, dilute it to the mark with distilled water, and shake it well. Approved by the State Environmental Protection Administration on March 28, 1995, implemented on January 1, 1996, GB/T15555.8—1995 3.9 Ammonium ferrous sulfate standard solution: Weigh 25 g of analytically pure ammonium ferrous sulfate [Fe(NH)2(SO. 6HO] and dissolve it in 1000 mL sulfuric acid-phosphoric acid mixed solution (3.2), filter it, and calibrate it using the following method. Take 10.00ml of hexavalent chromium standard solution (3.8), place it in a 150ml conical flask, add 50ml of water, add 5ml of sulfuric acid-phosphoric acid mixed solution (3.2) and 5 drops of N-phenyl-anthranilic acid indicator (3.7), and titrate with ammonium ferrous sulfate solution (3.9) until the solution changes from purple-red to yellow-green, which is the end point. The titration degree of ammonium ferrous sulfate solution on hexavalent chromium is calculated as follows: T = 10.00 × 0.40
·(1)
Where: T—1.00ml of ammonium ferrous sulfate solution is equivalent to the number of milligrams of hexavalent chromium; V is the consumption of ammonium ferrous sulfate solution, mL, 0.40—the number of milligrams of hexavalent chromium contained in each milliliter of potassium dichromate solution (3.5). Note: Ammonium ferrous sulfate solution is unstable and needs to be recalibrated before use. 4 Instruments
4.1 Pipette: 10mL, 25mL.
4.2 Erlenmeyer flask: 500mL.
4.3 Burette (divided into 0.1mL): 25mL, 50mL. 5 Samples
5.1 Sample storage: The leachate should be placed in a hard glass bottle or a high-density polyethylene bottle, and concentrated nitric acid should be added to adjust the sample pH value to less than 2, and the sample should be analyzed as soon as possible. If it is left for more than 24 hours, it should not be left for more than 24 hours. 5.2 Sample treatment
Put an appropriate amount of leachate in a 500mL Erlenmeyer flask, and adjust the pH of the solution to 1~2 with ammonia solution (3.1). Add 20mL of sulfuric acid-phosphoric acid mixed solution (3.2), 1~3 drops of silver nitrate solution (3.3), 0.5mL of manganese sulfate solution (3.4), and 25mL of ammonium persulfate solution (3.5), shake well, and add a few glass beads. Heat until the purple-red color of permanganate appears, and boil for 10 minutes. Remove and cool slightly, add 5 ml of sodium chloride solution (3.6), heat to a slight boil for 10 to 15 minutes, and remove all chlorine. Remove and cool rapidly, wash the bottle wall with water and dilute to about 220 ml. 6 Titration
Add 5 drops of N-phenyl anthranilic acid indicator (3.7) to the treated sample, and titrate with ammonium ferrous sulfate standard solution (3.9) until the solution changes from purple-red to yellow-green, which is the end point. Record the amount of standard solution used. Replace the test solution with water, prepare a blank solution and titrate it in the same way. Deduct the amount of blank test sample from the amount of standard solution used in the test solution.
7 Expression of resultsWww.bzxZ.net
The total chromium concentration c in the leachate is calculated as follows: TXV
c(mg/L) = 1
X 1 000
Wherein: T-titration degree of ammonium ferrous sulfate, mg/mL; V, the amount of ammonium ferrous sulfate standard solution consumed in titration, mL; V——volume of leachate absorbed in titration, mL. 8 Precision and accuracy:
Indoor, for the chromium slag leachate with a total chromium concentration of 196.5 mg/L, the relative standard deviation of 6 parallel determinations was 0.34%; for the double sample of leachate with a total chromium content of 5.895g, 5.00μg of standard sample was added, and the recovery rates were 99.8% and 100.4%. 555
A1 Blood should not be washed with chromium-containing solutions. GB/T15555.8—1995
Appendix A
Notes
(reference)
A2 If the solution does not turn red after adding ammonium persulfate and boiling, it means that divalent manganese has not been oxidized to heptavalent manganese, indicating that trivalent chromium has not been completely oxidized to hexavalent chromium (because manganese has a higher oxidation potential than chromium), which makes the result low. If this phenomenon occurs, remove the conical flask and cool it slightly before adding a little ammonium persulfate and boiling it until it turns red. When the amount of ammonium persulfate added is insufficient, the solution cannot change from green to red, indicating that trivalent chromium has not been oxidized. A3 Sodium chloride is added to the boiling solution to reduce the generated HMnO4, which does not decompose chromic acid. The amount of sodium chloride added should not be too much. The boiling time should be properly controlled. If the time is too short, the oxidant is not completely removed, which makes the result high. If the time is too long, the solution volume is small and the acidity is high, so that part of the hexavalent chromium is reduced, which makes the result low.
A4 Chromium indicator has reducing properties, so it is not advisable to add more during titration. The amount of blank and each test solution added should be consistent. A5 When vanadium coexists, the determination result can be converted using the coefficient (1% vanadium is equivalent to 0.34% chromium) to deduct the amount of vanadium. Note: For the preparation method of the leaching solution, see Appendix B of GB/T15555.11995 "Determination of total mercury in solid waste by cold atomic absorption spectrophotometry". Additional notes:
This standard was proposed by the Science and Technology Standards Department of the State Environmental Protection Administration. This standard is interpreted by the China National Environmental Monitoring Center. The main drafters of this standard are Wang Sufang, Su Huaqing, and Xing Shucai. This standard was commissioned to the China National Environmental Monitoring Center for drafting. 556
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