GB 28657-2012Potassium dichromate for industrial use (English PDF)

5.1 Safety Tips

Reagents used in this test method are toxic, corrosive, the operator should be careful as splashed on the skin should be washed with water immediately Wash, severe cases should seek medical care immediately. When using flammable materials, it prohibited the use of open flame heating.

5.2 General Provisions

This standard reagent in the absence of water and other requirements stated, refer to three predetermined analytical reagents and GB/T 6682-2008 of water. The test standard titration solution, impurity standard solution, formulations and products, in the absence of other requirements specified, are by HG/T 3696.1 used, HG/T 3696.2, preparing a predetermined HG/T 3696.3 is.

5.3 Visual inspection

In natural light, the appearance was visually determined.

5.4 Determination of the content of potassium dichromate

5.4.1 Capacity Act (Arbitration Act)

5.4.1.1 Method summary

In an acidic medium, hexavalent chromium ions to divalent iron ions in the sample oxidation-reduction reaction, to phthalic acid as indicated Agent titrated solution was titrated to standard ferrous ammonium sulfate solution turned green.

5.4.1.2 Reagents

5.4.1.2.1 phosphoric acid.

5.4.1.2.2 sulfuric acid. 14.

5.4.1.2.3 standard ferrous ammonium sulfate titration solution. c [(NH4) 2Fe (SO4) 2] ~0.2mol/L.

Preparation. Weigh about 80g of ferrous ammonium sulfate [(NH4) 2Fe (SO4) · 6H2O] was dissolved in 300mL sulfuric acid solution (17), followed by addition 700mL of water, shake. This calibration solution before use.

Calibration. Weigh about 0.37g finely and at 120 °C ± 2 °C dried to a constant reference mass of potassium dichromate, accurate to 0.0001g, Placed in 500mL Erlenmeyer flask, 150mL of water was added to dissolve. Was added a solution of 15mL sulfuric acid, phosphoric acid 5 mL, dropwise with standard ferrous ammonium sulfate Given solution was titrated to yellow-green solution. O-aminobenzoic acid was added 1mL indicator solution and continue the titration to the solution from purple to green as the end point.

Concentration of ammonium ferrous sulfate standard titration solution C, the value in mol/L, calculated according to formula (1).

c = mMV × 10-3

Where.

Numerical volume standard titration solution of ammonium ferrous sulfate titration V --- consumed in milliliters (mL);

--- potassium dichromate reference value of mass m in grams (G);

M --- potassium dichromate (16K2Cr2O7 ) Molar mass values, in units of grams per mole (g/mol) (M = 49.03).

Calibration errors shall HG/T 3696.1-2002 specified in 3.6, 3.7.

5.4.1.2.4 o-aminobenzoic acid indicator solution. 1g/L.

5.4.1.3 Apparatus, equipment

5.4.1.3.1 weighing bottle. phi50mm × 30mm.

5.4.1.3.2 electric oven. temperature can be controlled at 120 °C ± 2 °C.

5.4.1.4 Analysis of step

A test solution is prepared 5.4.1.4.1 Weigh 4.99g ~ 5.01g sample, accurate to 0.0001g, was placed in a 150mL beaker, add water dissolved, transferred to 500mL volume Volumetric flask, diluted with water to the mark. This solution is a test solution A, for the content of potassium dichromate, sulfate content (visual turbidimetry) and Determination of sodium content.

5.4.1.4.2 Determination

Pipette with a pipette 25mL of test solution A, placed in 500mL Erlenmeyer flask, was added 150mL of water, 15 mL of sulfuric acid solution, 5 mL Phosphoric acid solution was titrated to titration with standard ferrous ammonium sulfate solution was yellow-green. O-aminobenzoic acid was added 1mL indicator solution and continue the titration to the solution from purple to green as the end point.

5.4.2 Potentiometric titration

5.4.2.1 Method summary

The sample was dissolved in water, in acidic medium, titrated with standard ferrous ammonium sulfate solution was titrated to the maximum rate of potential change point determination trans it should end, obtained potassium dichromate content.

5.4.2.2 Reagents

5.4.2.2.1 sulfuric acid. 11.

5.4.2.2.2 standard ferrous ammonium sulfate titration solution. c [(NH4) 2Fe (SO4) 2] ~0.2mol/L.

Calibration. Weigh about 0.37g finely and at 120 °C ± 2 °C dried to a constant reference mass of potassium dichromate, accurate to 0.0001g, it was placed in 500mL beaker, add water to 400 mL, was added a solution of 40mL sulfuric acid. The beaker was placed on a magnetic stirrer. Insert platinum electrode Electrode and a saturated calomel electrode, and stirring, speed control solution to avoid splashing. Titration solution was titrated with standard ferrous ammonium sulfate to a yellow After the disappearance, continued microtiter. The point of maximum potential rate of change is the endpoint of the titration.

Calculation. calculated in 5.4.1.2.3.

5.4.2.3 Apparatus, equipment

5.4.2.3.1 magnetic stirrer.

5.4.2.3.2 indicator electrode. platinum electrode.

5.4.2.3.3 reference electrode. saturated calomel electrode.

5.4.2.3.4 automatic potentiometric titrator.

5.4.2.4 Analysis of step

Pipette with a pipette 25mL of test solution A, was placed in a beaker of 500mL, was added to 400 mL of water, was added a solution of 40mL sulfuric acid.

The beaker was placed on a magnetic stirrer. Insert platinum electrode and a saturated calomel electrode, and stirring, speed control solution to avoid splashing. use After standard ferrous ammonium sulfate solution was titrated to the yellow color disappeared titration, the microtiter continued, the potential of the point of maximum rate of change is the titration end point.

5.4.3 Calculation results

Potassium dichromate potassium dichromate content mass (of K2Cr2O7) fraction w1 meter, calculated according to formula (2).

w1 = cVM × 10

m × (25/500) × 100%

Where.

Numerical standard titration solution of ammonium ferrous sulfate V --- volume of the test solution consumed in the titration, in milliliters (mL);

C --- accurate value of the concentration of the solution of ferrous ammonium sulfate titration standard, in units of moles per liter (mol/L);

m --- 5.4.1.4.1 weighed mass of the sample values in grams (G);

M --- potassium dichromate (16K2Cr2O7 ) Molar mass values, in units of grams per mole (g/mol) (M = 49.03).

Parallel to the arithmetic average of the measurement results of the measurement result, the absolute difference determination results should not exceed 0.2% in parallel.

5.5 Determination of the sulfate content

5.5.1 Gravimetric method (MAL)

5.5.1.1 Method summary

In an acidic medium, with ethanol in the sample and reduction of Cr 6 Cr 3, was added a solution of barium chloride, barium sulfate ions in the raw sample to precipitate barium sulfate. The precipitate was filtered, washed, calcined and weighed to determine sulphate content was calculated.

5.5.1.2 Reagents

5.5.1.2.1 sulfuric acid.

5.5.1.2.2 95% ethanol.

5.5.1.2.3 hydrochloric acid solution. 37.

5.5.1.2.4 acetic acid solution. 11.

5.5.1.2.5 barium chloride (BaCl2 · 2H2O) solution. 100g/L.

5.5.1.2.6 silver nitrate solution. 17g/L.

5.5.1.2.7 sulfate standard solution. 1mL solution containing sulfate (SO4) 1mg.

5.5.1.2.8 diphenyl carbohydrazide azo indicator solution. 2g/L.

Azo weighed diphenyl carbohydrazide (C13H12N4O) 0.2g, was dissolved in 50mL of acetone, diluted with water to 100mL, shake, stored in Brown bottle and stored at a low temperature. After darkening can not be used.

5.5.1.3 Apparatus, equipment

Temperature furnace. temperature can be controlled at 700 °C ± 20 °C.

5.5.1.4 Analysis of step

It weighs about 10g sample to the nearest 0.01g. Was placed in 500mL beaker, 100mL of water was added to dissolve. Add 10mL pipette Sulfate standard solution was added 100mL of hydrochloric acid, heated to about 20mL95% ethanol was added dropwise with stirring, heated in a boiling water bath Paul Wen 30min. The reduction is not complete, refed with 95% ethanol (with azo-diphenyl carbohydrazide verify complete reduction 1)). Qualitative medium speed Filter paper, washed with hot water until no green filter. The filtrate and the washing water collected in a 500mL beaker, diluted with water to about 300 mL, heated boiled. In the micro-boiling state, was added slowly with stirring 50mL barium chloride solution, 20 mL acetic acid solution prepared in advance and set a little the amount of paper pulp, stir for about 2min. 30min heating on a water bath for 2h at room temperature or placed 8h. Quantitative filter with a slow A paper filter, washed thoroughly with water until no chloride ions until the (test with silver nitrate solution).

1) Take a drop of test solution 1 was added dropwise diphenyl carbohydrazide azo indicator solution, purple occurs if the restore completely.

The filter paper and the precipitate was placed in a pre calcined at 700 °C ± 20 °C to constant mass in a porcelain crucible, low temperature ashing in an electric furnace, removed.

After cooling 1 drop of sulfuric acid was heated on a hot plate to take the best white smoke, into 700 °C ± 20 °C high temperature burning furnace to constant mass.

At the same time a blank test without addition of the sample, the exact same amount of other reagents added to the test solution, and the same treatment and the sample.

5.5.1.5 Calculation results

Sulfate content of sulfate (SO4) w2 mass fraction basis, according to equation (3) is calculated.

w2 = 0.4116 ×

(M1-m0)

m × 100%

Where.

Numerical M1 --- barium sulphate precipitate mass in grams (G);

M0 --- mass of precipitate blank test values in grams (G);

Value m --- mass of the sample in grams (G);

0.4116 --- barium sulfate is converted to sulfate (SO4) coefficients.

Parallel to the arithmetic average of the measurement results of the measurement result, the absolute difference determination results parallel to 0.003%.

5.5.2 Visual turbidimetry

5.5.2.1 Method summary

In an acidic medium, barium sulfate and barium sulfate precipitate plasma generation poorly soluble at low sulfate ion content, within a certain time Barium sulfate suspension was, the solution was cloudy, for visual comparison with the standard turbidimetric sulfate solution.

5.5.2.2 Reagents

5.5.2.2.1 hydrochloric acid solution. 11.

5.5.2.2.2 barium chloride (BaCl2 · 2H2O) solution. 100g/L.

5.5.2.2.3 sulfate standard solution. 1mL solution containing sulfate (SO4) 0.05mg.

Pipette with a pipette 5mL sulfate standard solution according to HG/T 3696.2 formulated, a 100mL volumetric flask, dilute to Mark and shake. This solution just before use.

5.5.2.2.4 sulfate-free potassium dichromate solution. 1mL solution containing potassium dichromate (K2Cr2O7) 0.05g.

Industrial weighed 50.0g ± 0.1g potassium dichromate, was placed 500mL beaker was added 300mL of water was dissolved, heated to boiling, was added 2g Barium chloride, kept boiling for 10min, allowed to stand overnight, the crucible with glass frit (5µm ~ 15µm) suction, and the filtrate into 1000mL volumetric flask in, diluted with water to the mark.

5.5.2.3 Analysis of step

Pipette with a pipette 25mL of test solution A, a 50mL colorimetric tube, was added 3mL hydrochloric acid, barium chloride is added 5mL the solution was diluted with water to the mark. 20min ~ 30min incubation in a water bath of 30 °C ~ 40 °C, turbidity should not be greater than standard Turbid liquid.

Ratio of standard reference suspension prepared. 2 in 50mL colorimetric tube were added with a pipette 5mL sulfate-free solution of potassium dichromate, Pipetted added 1.00 mL (Excellence), 2.50 mL (first-class products, qualified) sulfate standard solution was added 3mL hydrochloric acid solution, and then Was added 5mL barium chloride solution, diluted with water to the mark. 20min ~ 30min incubation in a water bath of 30 °C ~ 40 °C.

Assay sulphate content by ion chromatography See Appendix C.

5.6 Determination of chloride content

5.6.1 Capacity Act (Arbitration Act)

5.6.1.1 Method summary

Generating an indication under slightly alkaline conditions, chloride ions in the sample solution a precipitate with silver nitrate, silver chromate micro brick red precipitate end.

5.6.1.2 Reagents

5.6.1.2.1 saturated sodium carbonate solution.

5.6.1.2.2 standard silver nitrate titration solution. c (AgNO3) ~0.05mol/L.

Pipette with a pipette 50mL formulated in HG/T 3696.1 specified standard silver nitrate titration solution, 100mL volumetric flask.

Diluted with water to the mark. This standard solution was titrated before use formulation, and stored in a brown bottle.

5.6.1.3 Instruments

Microburette.

5.6.1.4 Analysis of step

Weigh 2.00g ± 0.01g sample is placed in 250mL Erlenmeyer flask, was added 30mL of water to dissolve. Saturated sodium carbonate solution cautiously added dropwise Solution, until the solution turns yellow, then a pH of 7.5 to 8.0 (with a precision paper test). Then titrated with a standard silver nitrate solution was titrated to dissolve Liquid was slightly red brick as the end point.

At the same time a blank test, 1.00g ± 0.01g sample is weighed, added to the other reagents identical amount of the test solution, and the sample the same treatment.

5.6.1.5 Calculation results

The chloride content by mass chlorine (Cl) w3 fraction meter, calculated according to formula (4).

w3 = c

(V-V0) M × 10-3

m-m0 ×

100% (4)

Where.

Numerical V --- standard titration solution of silver nitrate titration volume of test solution consumed, in milliliters (mL);

--- blank titration value V0 standard titration solution volume silver nitrate solution consumed in milliliters (mL);

Accurate value of the concentration of the solution c --- standard silver nitrate titration, expressed in moles per liter (mo1/L);

Value m --- mass of the sample in grams (G);

M0 --- blank test mass of the sample values in grams (G);

Numerical molar mass M --- chlorine (Cl), in units of grams per mole (g/mol) (M = 35.45).

The arithmetic average of the measurement results parallel the measurement results, the measurement result of the absolute difference is not greater than two parallel 0.002%.

5.6.2 Ion Chromatography

5.6.2.1 Method summary

After the sample is dissolved, with hydrazine hydrate reduction of hexavalent chromium to trivalent chromium, the precipitate separated was removed, ion implantation chromatograph assay.

5.6.2.2 Reagents

5.6.2.2.1 hydrazine hydrate. 110.

An amount of 10mL hydrazine hydrate (85%) was mixed with 100mL of water.

5.6.2.2.2 chloride standard solution. 1mL solution containing chloride (Cl) 0.05mg;

Pipette with a pipette 5mL chloride standard solution according to HG/T 3696.2 formulated, a 100mL volumetric flask, dilute to Mark and shake. The solution just before use.

5.6.2.2.3 a water. in line with GB/T 6682-2008 specified.

5.6.2.3 Instruments, apparatus 2)

2) The apparatus listed for reference only and configuration, the same configuration can be used, and equipment performance.

5.6.2.3.1 ion chromatography.

5.6.2.3.2 Sample before treatment column. Column hydrogen.

5.6.2.3.3 0.22µm aqueous millipore filter.

5.6.2.3.4 speed centrifuge. with 100mL centrifuge tube.

5.6.2.4 Instrument reference conditions

5.6.2.4.1 Column. IonPacAS11-HC250mm × 4mm (IonPacAG11-HC50mm × 4mm with guard column)

Or equivalent person.

5.6.2.4.2 suppressor. ASRSULTRAII, from circulation electric suppress or equivalent person.

5.6.2.4.3 Detector. electric conductivity detector, to confirm if the same function can also be used other detectors.

5.6.2.4.4 eluent. KOH gradient eluent (sparging the initial concentration of 5mmol/L, concentration of the end of 40mmol/L, leaching Wash time was 40min, elution flow rate of 1.0mL/min). Other types and varying concentrations of the eluent, to confirm if the same work top Energy can be used.

5.6.2.4.5 Eluent flow rate. 1.0mL/min.

5.6.2.4.6 Injector. 0.025mL.

5.6.2.5 Analysis of step

5.6.2.5.1 Work drawing curves

Were pipetted 0mL, 1.00mL, 2.00mL, 4.00mL, 6.00mL, 8.00mL chloride solution was placed in 100mL receiving standard Volumetric flask, add water to the mark. Solution concentrations were 0mg/mL, 0.0005mg/mL, 0.001mg/mL, 0.002mg /mL, 0.003mg/mL, 0.004mg/mL, respectively, after this series of standard solution microporous membrane filter of 0.22µm, discard the initial 10mL of the filtrate, the filtrate after the hydrogen directly into the ion chromatograph column. Chloride concentration in abscissa, the peak height or peak area of the vertical Coordinate drawing working curve.

5.6.2.5.2 Determination

Weigh about 0.5g sample to the nearest 0.01g, a 100mL beaker was added 50mL of water to dissolve. Under electromagnetic stirring dropwise After addition of 4mL of hydrazine hydrate solution, stirring was continued for 40min, all transferred to a 100mL volumetric flask, diluted with water to the mark. Put A centrifuge tube, centrifuged at high speed 10min, the supernatant through a millipore filter 0.22µm, discard the initial 10mL filtrate was Directly into the ion chromatograph column filtrate hydrogen. The peak height or peak area, isolated test solution chloride concentration on the working curve.

At the same time a blank test without addition of the sample, the exact same amount of other reagents added to the test solution, and at the same time with the same sample deal with.

5.6.2.6 Calculation results

The chloride content by mass chlorine (Cl) w3 fraction meter, calculated according to formula (5).

(rho1-rho0) × 100 × 10-3 m × 100% (5) where.

Numerical rho] 1 --- chloride by Richard working curve of the test solution concentration, in milligrams per milliliter (mg/mL);

--- concentration value p0 blank test solution obtained by the search on the working curve of chloride, in milligrams per milliliter (mg/mL);

Value m --- mass of the sample in grams (g).

Parallel to the arithmetic average of the measurement results of the measurement result, the absolute difference determination results should not exceed 0.002% parallel.

5.7 Determination of sodium content

5.7.1 Method summary

The sample was dissolved, were determined by flame atomic absorption spectrophotometer at a wavelength of 589.0nm sodium content by standard addition method.

5.7.2 Reagents

5.7.2.1 hydrochloric acid solution. 11.

5.7.2.2 sodium standard solution. 1mL solution of sodium (Na) 0.01mg.

Pipette with sodium standard solution of 10mL press HG/T 3696.2 prepared, placed in 1000mL volumetric flask, dilute to the mark with water Degree, shake. The solution just before use.

5.7.2.3 two Water. 6682-2008 compliance with the provisions of GB/T .

5.7.3 Instruments and equipment

Atomic absorption spectrophotometer. with sodium hollow cathode lamp.

5.7.4 Analysis of step

Pipette with a pipette 20mL test solution A, diluted with water to a 100mL volumetric flask to the mark.

Pipette 2.00 mL of each (Excellence) or 1.00 mL (first-class products, qualified) of the above test solution was placed 100mL capacity four Flask, each flask were transferred 0mL, 2.00mL, 4.00mL, 6.00mL sodium standard solution, 5mL each was added a solution of hydrochloric acid, Diluted with water to the mark. Sodium content concentration in the solution were 0mg/L, 0.2mg/L, 0.4mg/L, 0.6mg/L. In the original Sub absorption spectrophotometer, at a wavelength of 589.0nm, the air - acetylene flame zero, water transfer, the absorbance was measured.

In the test concentration was added sodium as abscissa corresponding to the ordinate is absorbance, drawing working curve, the reverse curve extended cross-the coordinates of the intersection, is the test concentration of sodium solution.

5.7.5 Calculation results

Sodium content by mass sodium (Na) fraction w4 meter, calculated according to formula (6).

w4 = rho1 × 0.1 × 10-3 m × (20/500) × (V/100) × 100% (6) where.

Sodium rho] 1 --- isolated from the working curve of the test solution concentration value in milligrams per liter (mg/L);

m --- 5.4.1.4.1 weighed mass of the sample values in grams (G);

V --- pipetting volume after the secondary dilution test solution, in milliliters (mL).

Parallel to the arithmetic average of the measurement results of the measurement result, the absolute difference determination results should not exceed 0.04% in parallel.

5.8 Determination of Moisture

5.8.1 Method summary

At 105 °C ± 2 °C, the sample was dried to constant mass. Sample mass difference before and after drying to determine water content according.

5.8.2 Instruments and equipment

5.8.2.1 weighing bottle. phi50mm × 30mm.

5.8.2.2 Electric oven. temperature can be controlled at 105 °C ± 2 °C.

5.8.3 Analysis of step

It weighs about 10g sample accurately to 0.0001g. That is placed in advance at 105 °C ± 2 °C dried to constant mass in the weighing bottle, in ± 2 °C 105 °C the electric oven dried to constant mass.

5.8.4 Calculation results

W5 water mass fraction basis, calculated according to formula (7).

w5 = m-m1m × 100%

Where.

M1 --- dried sample material mass value in grams (G);

Value m --- mass of the sample in grams (g).

The arithmetic average of the measurement results parallel the measurement results, the measurement result of the absolute difference is not greater than two parallel 0.005%.

5.9 Determination of the water insoluble content

5.9.1 Method summary

After the sample is dissolved by suction filtration, washed, dried, weighed and determined the content of the water-insoluble substance.

5.9.2 Instruments and equipment

Sand core glass crucible. filter plate aperture 5µm ~ 15µm.

5.9.3 Analysis of step

Weigh about 50g sample to the nearest 0.01g, was placed 500mL beaker was added 300mL of water, covered with a watch glass and heated to boiling in Boiling water bath incubated 1h, with a ...