ISO 5073:2021 pdf download – Brown coals and lignites — Determination of humic acids.
4 Principle 4.1 Total humic acids Extraction of an analysis sample of coal is carried out with an alkaline sodium pyrophosphate solution. Carbon in the humic acid extracts is oxidized with potassium dichromate followed by titration of the excess dichromate with ammonium ferrous sulfate standard solution. 4.2 Free humic acid Extraction of an analysis sample of coal is carried out with a sodium hydroxide solution. Carbon in the humic acid extracts is oxidized with potassium dichromate followed by titration of the excess dichromate with ammonium ferrous sulfate standard solution. 5 Reagents 5.1 Sodium pyrophosphate, alkaline extraction solution. Dissolve 15 g of crystalline sodium pyrophosphate (Na 4 P 2 O 7 ·10H 2 O) and 7 g of sodium hydroxide in 1 l of water. 5.2 Sodium hydroxide solution. Dissolve 10 g of sodium hydroxide in 1 l of water. 5.3 Potassium dichromate standard solution, c(1/6 K 2 Cr 2 O 7 ) = 0,1 mol/l. Dissolve 4,903 6 g of potassium dichromate, previously dried at 130 °C, in water. Transfer to a 1 l volumetric flask and dilute to the mark with water. 5.4 Potassium dichromate oxidizing solution, c(1/6 K 2 Cr 2 O 7 ) = 0,4 mol/l. Dissolve 20 g of potassium dichromate in 1 l of water.
7 Sample The sample shall be the general analysis test sample, prepared to a nominal top size of 212 μm by the preparation procedures specified in ISO 13909-4 or ISO 18283. The sample should be brought in moisture equilibrium with the laboratory atmosphere by exposure in a thin layer on a tray. Exposure time shall be kept to a minimum. The sample shall be thoroughly mixed immediately before analysis, preferably by mechanical means. Duplicate determinations of moisture from the same test sample shall be conducted concurrently with the determination of the humic acids by the method specified in ISO 5068-2. 8 Procedure 8.1 Extraction of total humic acids Transfer a (0,2 ± 0,000 2) g mass of analysis sample into a conical flask. Add 150 ml of alkaline sodium pyrophosphate extraction solution (5.1) and mix until the sample is thoroughly wetted. Place a small funnel on the flask and heat in the water bath (6.1) with the temperature of (100 ± 1) °C for 2 h, shaking frequently to ensure precipitation of insoluble material. Remove the flask from the water bath. Allow to cool to room temperature and quantitatively transfer the extract and residue to a 200 ml volumetric flask. Dilute to the mark with water and shake to ensure thorough mixing. Filter with dry medium speed qualitative filter-paper. Discard the initial 10ml and collect the dry-filtered extract A of (50 to 100) ml for the determination of total humic acids. Determine the total humic acids, w HA,t , extracted by alkaline sodium pyrophosphate as specified in 8.3.1.