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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 3058-2008 Determination of arsenic in coal. In addition to a number of editorial changes, the following main technical changes have been made with respect to GB/T 3058-2008:
——In method summary, “dissolve the igniting matter with hydrochloric acid” is changed to “dissolve the igniting matter with sulfuric acid and hydrochloric acid" (see 3.1; 3.1 of Edition 2008);
——The requirements for zinc granular free from arsenic are modified (see 3.2.1; 3.2.1 of Edition 2008);
——The placement position of lead acetate cotton is added in the diagram of arsenic determinator (see Figure 1; Figure 1 of Edition 2008);
——The calculation method of determining the recovery rate of arsenic determinator by molybdenum blue spectrophotometric method is added (see Annex A).
This standard is redrafted by reference to but is not equivalent to ISO 11723:2016 Solid mineral fuels - Determination of arsenic and selenium - Eschka’s mixture and hydride generation method.
This standard was proposed by the China National Coal Association.
This standard is under the jurisdiction of National Technical Committee on Coal Standardization Administration of China (SAC/TC 42).
The previous editions of this standard are as follows:
——GB/T 3058-1982, GB/T 3058-1996, GB/T 3058-2008.
Determination method of arsenic in coal
1 Scope
This standard specifies the method summary, reagents and materials, apparatus, sample, test procedure, calculation and expression of result and precision of method for the determination of arsenic in coal by molybdenum blue spectrophotometric method. The molybdenum blue spectrophotometric method is the arbitration method.
This standard is applicable to lignite, soft coal and anthracite.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 483 General rules for analytical and testing methods of coal
GB/T 2304 Chemical reagent - Zinc granular free from arsenic
3 Molybdenum blue spectrophotometric method
3.1 Method summary
Mix coal sample with Eschka reagent, ignite the mixture and dissolve the igniting matter with sulfuric acid and hydrochloric acid, then add reducing agent to restore the pentavalent arsenic to trivalent arsenic, add zinc granular to make the arsenic released in the form of arsenic hydride gas, absorb and oxidize with iodine solution to generate arsenic acid, add ammonium molybdate - hydrazine sulfate solution to generate molybdenum blue, and then determine with spectrophotometer.
3.2 Reagents and materials
Unless otherwise specified, only the reagents recognized of analytical quality and distilled water or deionized water or water with equivalent purity shall be used during the analysis.
3.2.1 Zinc free from arsenic: in accordance with GB/T 2304, sift out the zinc granule with size no less than 3mm for use.
3.2.2 Eschka reagents (hereinafter referred to as aldrin): commercially available or mix two parts by mass of light magnesium oxide and one part by mass of anhydrous sodium carbonate, grind the mixture to the size of less than 0.2mm, and then store it in a closed container.
3.2.3 Hydrochloric acid: with relative density of 1.18.
3.2.4 Hydrochloric acid solution: c(HCl)=6mol/L. Mix one volume of hydrochloric acid with one volume of water uniformly.
3.2.5 Sulfuric acid solution: c(1/2H2SO4)=6mol/L. Add 167mL of sulfuric acid with relative density of 1.84 into a proper amount of water slowly, stir while adding, and then dilute it to 1L with water.
3.2.6 Sulfuric acid solution: c(1/2H2SO4)=5mol/L. Add 139mL of sulfuric acid with relative density of 1.84 into a proper amount of water slowly, stir while adding, and then dilute it to 1L with water.
3.2.7 Potassium iodide solution: 176.5g/L. Dissolve 3.0g of potassium iodide in 17mL of water, prepare it just before use.
3.2.8 Stannous chloride hydrochloric acid solution: 666.7g/L.. Dissolve 8.0g of stannous chloride in 12mL of hydrochloric acid (3.2.3), prepare it just before use.
3.2.9 Iodine solution: 1.5g/L. Dissolve 9.0g of potassium iodide and 1.5g of iodide with a small amount of water and then dilute to 1L.
3.2.10 Ammonium molybdate solution: 10g/L. Dissolve 10.0g of ammonium molybdate in 1L of sulfuric acid solution (3.2.6).
3.2.11 Hydrazine sulfate solution: 1.2g/L. Dissolve 1.2g of hydrazine sulfate in 1L of water.
3.2.12 Ammonium molybdate-hydrazine sulfate mixed solution: mix one volume of ammonium molybdate solution (3.2.10) and one volume of hydrazine sulfate solution (3.2.11) uniformly, prepare it just before use.
3.2.13 Sodium bicarbonate solution: 40g/L. Dissolve 40.0g of sodium bicarbonate in 1L of water.
3.2.14 Sodium hydroxide solution: c(NaOH)=6mol/L. Weigh 48.0g of sodium hydroxide, dissolve it with a small amount of water, and then dilute to 200mL.
3.2.15 Arsenic standard stock solution: 100μg/mL. Accurately weigh 0.132 0g of GR arsenic trioxide that has been dried at 105℃~110℃ for about 2h, dissolve it in 2mL of sodium hydroxide solution (3.2.14), add about 50mL of water, after the GR arsenic trioxide is completely dissolved, add 2.5mL of sulfuric acid solution (3.2.5), dilute to 1 000mL with water. Commercially available certified arsenic standard solution may also be used as arsenic standard stock solution.
3.2.16 Arsenic standard working solution: 10μg/mL. Transfer 50mL of arsenic standard stock solution (3.2.15) into a 500mL volumetric flask accurately, dilute to the scale with water and shake well, and then transfer it into a plastic bottle for standby.
3.2.17 Lead acetate cotton: it shall be replaced in each experiment. Fully immerse the degreasing cotton in the lead acetate solution with mass concentration of 400g/L and then take out and wring out it, dry at 80℃~100℃ and store in a desiccator for standby.
3.2.18 Porcelain crucible: with capacity of 30mL. The glaze on internal surface is in good condition.
3.3 Apparatus
3.3.1 Arsenic determinator, which shall meet the provisions given in Figure 1. For newly purchased or long-term unused arsenic determinators, check whether their dimensions are qualified and whether the grinding mouths are tight before putting them into use. Select the device with recovery rate not less than 90% as daily used apparatus by reference to the recovery rate of determinator given in Annex A.
3.3.2 Spectrophotometer: with wavelength including 700nm and 830nm.
3.3.3 Muffle furnace: with temperature control device, capable of obtaining (800±10)℃ within 2h from room temperature.
3.3.4 Analytical balance: with a division of 0.1mg.
3.3.5 Balance: with a division of 0.1g.
3.3.6 Balance: with a division of 0.01g.
3.3.7 Pipette with single scale line: 1mL, 2mL, 3mL and 5mL.
Key
1——Absorber
2——Absorber sleeve
3——Lead acetate cotton
4——Round flask
Figure 1 Arsenic determinator
3.4 Sample
Coal sample for general analysis test with particle size less than 0.2mm.
3.5 Test procedure
3.5.1 Plotting of working curve
3.5.1.1 Transfer 0.00mL, 1.00mL, 2.00mL, 3.00mL, 4.00mL and 5.00mL of arsenic standard working solution (3.2.16) with the pipette with single scale line to the round flask of arsenic determinator, add 10mL of sulfuric acid solution (3.2.5) and then 20mL of sulfuric acid solution (3.2.4), dilute with water to 50mL.
3.5.1.2 Add 2mL of potassium iodide solution (3.2.7) and 1mL of stannous chloride solution (3.2.8), shake well and place for 15min at room temperature.
3.5.1.3 Pipette 3mL of iodine solution (3.2.9), 1mL of sodium bicarbonate solution (3.2.13) and 6mL of water to the absorber of arsenic determinator, insert the absorber into the absorber sleeve with lead acetate cotton (3.2.17).
3.5.1.4 Add 5.0g of zinc free from arsenic (3.2.1) to a round flask, immediately connect the absorber sleeve to the flask, and allow the process to continue for 1h after confirming that all interfaces of the apparatus are airtight.
3.5.1.5 Take out the absorber, add 5mL of ammonium molybdate-hydrazine sulfate mixed solution (3.2.12), and pump air from the side holes of absorber for about 10 times with ear wash ball to make the absorption liquid mixed fully. Heat the absorber in boiling water bath for 20min, and then take it out and cool to room temperature, which is the working curve solution.
3.5.1.6 Measure the absorbance of the working curve on a spectrophotometer with a 10mm cuvette under 700nm (or 830nm) wavelength by taking standard blank solution as reference. When the content of arsenic in coal is low, determine the absorbance under 830nm wavelength.
3.5.1.7 Plot the working curve by taking arsenic mass (μg) as the x-coordinate and corresponding absorbance as the y-coordinate, which shall be carried out simultaneously with the analysis of coal sample.
3.5.2 Sample determination
3.5.2.1 Weigh 2g (to the nearest 0.01g) of aldrin in a porcelain crucible, then weigh 0.99g~1.01g (to the nearest 0.000 2g) of coal sample for general analysis test with particle size less than 0.2mm, stir well with a glass rod carefully, and then cover the coal sample with 1g (to the nearest 0.01g) of aldrin uniformly (ensure that no black coal particle is visible). When the ash content in the coal sample is more than 40%, or the arsenic content is more than 50μg/g or the total sulfur content is more than 8%, the sample amount is 0.50g.
Foreword i
1 Scope
2 Normative references
3 Molybdenum blue spectrophotometric method
4 Hydride generation - atomic absorption method
5 Precision
6 Test report
Annex A (Informative) Recovery rate of arsenic determinator
