GB/T 15249.4-1994 Chemical analysis of gold alloys - EDTA titration method for determination of lead content
Some standard content:
National Standard of the People's Republic of China
Chemical analysis method for gold
Determination of lead content by EDTA titration
Crude Gold-Determinatlon of lead content-EDTA titrimetric method
1 Subject content and scope of application
This standard specifies the method for determining the lead content in gold. GB/T 15249.4-94
This standard is applicable to the determination of lead content in gold (ore gold, smelting crude gold products and recovered gold, etc.). Determination range: 1% to 15%. 2 Reference standards
GB1.4 Guidelines for standardization work Provisions for the preparation of chemical analysis method standards GB1467 General principles and general provisions for chemical analysis method standards for metallurgical products 3 Principle of the method
Weigh a certain weight of the gold sample to be tested and decompose it with dilute nitric acid and hydrochloric acid. Silver is separated by silver fluoride precipitation, gold is separated by reducing gold ions to monomer gold with sulfite, and then lead is separated from coexisting elements by lead sulfate precipitation and filtration. For example, lead sulfate is dissolved in acetic acid-sodium acetate buffer solution, and xylenol orange is used as an indicator. It is titrated with EDTA standard solution at pH 5.5-6:0, and the amount of lead is calculated by the volume of EDTA standard solution consumed.
4 Reagents
4. 1 Hydrochloric acid (p1. 19 g/mL).
4.2 Hydrochloric acid (2+98).
4.3 Nitric acid (pl.42 g/mL).
4.4 Sulfuric acid (1+1).
4.5 Sulfuric acid (1+24).
4.6 Sulfuric acid (2+98).
4.7 Sulfurous acid (p1. 03 g/mL).
4.8 Ethanol.
4. 9 Acetic acid-sodium acetate buffer solution (pH 5.5~~5. 6): Dissolve 375 g of anhydrous sodium acetate in water, add 50 mL Glacial acetic acid, diluted with water to 2.51.
4.10 Xylenol orange indicator solution (5g/L): Add 1-2 drops of ammonia water (1+1) to 50mL solution. Use within one week. 4.11 Lead standard solution: Weigh 2.0000 g of metallic lead (99.99%) in a 250 ml beaker, add 40 mL of nitric acid (1+1), cover with blood, wait for the violent reaction to stop, heat at low temperature until it is completely dissolved, boil to drive off nitrogen oxides, remove, cool to room temperature, transfer to a 1000 mL volumetric flask, dilute to scale with water, and mix well. This solution contains 2 mg/nL of lead. 4.12 EDTA (disodium ethylenediaminetetrachloride) standard titration solution [c(EDTA)～0. 01 mol/L]. Approved by the State Administration of Technology Supervision on October 7, 1994 78
Implemented on August 1, 1995
GB/T 15249.4—94
4.12.1 Preparation: Weigh 18 g of disodium ethylenediaminetetraacetate (CHN,0,Naz2H,0) in a 400 mL beaker, add 200 mL of water, heat to dissolve and dilute to 5 °C, mix well.
4.12.2 Calibration: Pipette three portions of 20.00 mL of lead standard solution and place them in 250 mL beaker, add 10ml sulfuric acid (4.4), heat at low temperature until thick sulfur trioxide smoke appears, remove and cool, wash the beaker wall with water, heat at low temperature again until the thick smoke disappears, remove and cool. The following analysis steps are the same as 5.2.4~5.2.6. .
The extreme value of the volume of EDTA standard titration solution consumed in parallel calibration should not exceed 0.10 mI., take the average value and calculate the actual concentration of EDTA standard titration solution according to the following formula: m
V×0.2072
Wherein: c——actual concentration of EDTA standard titration solution, mol/L: mass of lead in the calibrated solution, name;
V volume of EDTA standard titration solution consumed in titrating lead standard solution, mL0.2072—mass of lead equivalent to 1.00mLEDTA standard titration solution [c(EDTA)=1.000mol/L, B. 5 Analysis steps
5-1 Sample preparation
Weigh the powdered sample according to Table 1, accurate to 0.0001g. Table 1
Lead content, %
1. 00~5. 00
>5.00~15.00bzxZ.net
5.2 Determination
Sample g
5.2.1 Place the sample (5.1) in a 250 ml beaker, add 20 mL water and 5 mL nitric acid (4.3), cover the beaker, boil slightly at low temperature for 30 min, remove and cool slightly, add 20 mL hydrochloric acid (4.1), decompose the sample at low temperature until it is completely dissolved, open the beaker, evaporate at low temperature until it is nearly dry, add 5 mL hydrochloric acid (4.1), evaporate at low temperature until it is nearly dry, and remove nitrogen oxides. Remove and cool slightly, wash the surface blood and beaker with water, add 5mL hydrochloric acid (4.1), dilute the volume to about 100mL, heat and boil for several minutes, remove, slowly add 20mL sulfuric acid (4.7) while hot and stirring to reduce gold, boil and keep warm for 30min.
*5.2.2 Remove, wash the surface blood with hot hydrochloric acid (4.2), filter with medium-speed quantitative filter paper, filter the filtrate into a 250mL beaker, wash the monomer gold and silver chloride mixed precipitate in the beaker with hot hydrochloric acid (4.2) 3 times, transfer the precipitate to the filter paper with hot hydrochloric acid (4.2), wash the beaker 3 times, wash the precipitate with hot hydrochloric acid (4.2), until the filtrate volume is about 200mL. 5.2.3 Stir the filtrate with a glass rod, evaporate the filtrate to about 20mL, add 10ml sulfuric acid (4.4), continue heating until sulfur trioxide smoke appears, remove and cool, wash the cup wall with water, heat until the smoke disappears, and remove the beaker. 5.2.4 Wash the beaker with 50mL sulfuric acid (4.5), cover with table blood, slightly boil for 10min, remove and cool, add 10ml ethanol (4.8), and let stand for 1h.
5.2.5 Filter with slow quantitative filter paper by decantation method, wash the lead sulfate precipitate with sulfuric acid (4.6) 3 times, transfer the precipitate to the filter paper, wash the beaker 3 times, wash the filter paper and precipitate in batches until the filtrate volume is about 200mL, and then wash the beaker, filter paper and precipitate with water 2 times each. 5.2.6 Unfold the filter paper, wash the precipitate with water into the original beaker, add 30 mL of acetic acid-sodium acetate buffer solution (4.9), tear up the filter paper and put it into the beaker, boil slightly for 10 min, remove and cool, add water to about 100 mL, add 2 drops of xylenol orange indicator solution (4.10), and titrate with EDTA standard titration solution (4.12) until the solution turns from purple-red to bright yellow. 79
6 Calculation and expression of analysis results
Calculate the percentage of lead according to the following formula:
GB/T15249.4—94
×0.2072×100
Pb(%) =9
Wherein: — Actual concentration of EDTA standard titration solution, mol/Lt — Volume of EDTA standard titration solution consumed by titrating test solution, tnL: ml-mass of sample, g;
0.2072——Mass of lead equivalent to 1.00ml.EDTA standard titration solution Ec(EDTA)=1.000mol/L, g. 7 Allowable difference
The difference in analysis results between laboratories should not be greater than the allowable difference listed in Table 2. Table 2
1.00~5.00
>5.00~10.00
210.00~~15.00
Additional Notes:
This standard was jointly proposed by the People's Bank of China Printing Corporation and the State Gold Administration. This standard was drafted by China Gold and Silver Smelter and Changchun Gold Research Institute. This standard was drafted by Beijing Research Institute of Mining and Metallurgy. The main drafter of this standard is Liu Feng,
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