ISO 5073-2021 pdf free download – Brown coals and lignites — Determination of humic acids.
5.61,10-Phenanthroline indicator.
Dissolve 1,5 g of 1,10-phenanthroline and 1 g of ammonium ferrous sulfate in 100 ml of water. Store ina dark bottle.
5.7Sulfuric acid, concentrated, P20 = 1,84 g/ml.
6 Apparatus
6.1Water bath, thermostatically controlled to (100 ± 1)°C, with four holes at least.6.2Balance, with a resolution of 0,1 mg.
7 sample
The sample shall be the general analysis test sample, prepared to a nominal top size of 212 um by thepreparation procedures specified in iso 13909-4 or ISo 18283.
The sample should be brought in moisture equilibrium with the laboratory atmosphere by exposure ina 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 withthe determination of the humic acids by the method specified in ISO 5068-2.
8Procedure
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 sodiumpyrophosphate extraction solution (5.1) and mix until the sample is thoroughly wetted. Place a smallfunnel on the flask and heat in the water bath (6.1) with the temperature of (100 ± 1) °Cfor 2 h, shakingfrequently to ensure precipitation of insoluble material.
Remove the flask from the water bath.Allow to cool to room temperature and quantitatively transferthe extract and residue to a 200 ml volumetric flask. Dilute to the mark with water and shake to ensurethorough mixing.Filter with dry medium speed qualitative filter-paper. Discard the initial 10ml andcollect the dry-filtered extract A of (50 to 100) ml for the determination of total humic acids.
Determine the total humic acids,WA,v extracted by alkaline sodium pyrophosphate as specified in8.3.1.
8.2Extraction of free humic acid
Transfer a(0,2±0,000 2) g mass of analysis sample into a conical flask.Add 150 ml of sodium hydroxideextraction solution (5.2) and mix until the sample is thoroughly wetted. Place a small funnel on theflask and heat in the water bath (6.1) with the temperature of (100± 1) °C for 2 h, shaking frequently toensure thorough mixing.
Determine the free humic acid, WHA,p extracted by sodium hydroxide as specified in 8.3.2.8.3 Determination of humic acids in extracts
8.3.1 For total humic acids
8.3.1.1 Oxidation of extracts
Pipette 5 ml of dry-filtered extract A(8.1) into a 250 ml to 300 ml conical flask. Pipette 5 ml of potassiumdichromate oxidizing solution (5.4) into the flask.Carefully add 15 ml of concentrated sulfuric acid (5.7).Place in the water bath (6.1) with the temperature of (100 ± 1) °C and heat for 30 min.Allow to cool toroom temperature. Dilute to approximately 100 ml.
8.3.1.2Titration of extracts
Add 3 drops of 1,10-phenanthroline indicator (5.6) to the solution from 8.3.1.1 and titrate with theammonium ferrous sulfate titration solution (5.5) to a brick red colour.
8.3.1.3 Blank for total humic acids
Pipette 5 ml of sodium pyrophosphate (5.1) into a 250 ml to 300 ml conical flask, add the potassiumdichromate oxidizing solution (5.4)and the concentrated sulfuric acid, heat, cool, and dilute, as specifiedin 8.3.1.1 and carry out the titration as specified in 8.3.1.2.
8.3.2 For free humic acids
8.3.2.1 Oxidation of extracts
Pipette 5 ml of dry-filtered extract B(8.2) into a 250 ml to 300 ml conical flask.Pipette 5 ml of potassiumdichromate oxidizing solution (5.4) into the flask.Carefully add 15 ml of concentrated sulfuric acid(5.7). Place in the boiling water bath (6.1) with the temperature of (100 ± 1)°C and heat for 30 min.Allow to cool to room temperature. Dilute to approximately 100 ml.
8.3.2.2 Titration of extracts
Add 3 drops of 1,10-phenanthroline indicator (5.6) to the solution from 8.3.2.1 and titrate with theammonium ferrous sulfate titration solution (5.5) to a brick red colour.
8.3.2.3 Blank for free humic acids
Pipette 5 ml of sodium hydroxide (5.2) into a 250 ml to 300 ml conical flask,add the potassiumdichromate oxidizing solution and the concentrated sulfuric acid, heat, cool, and dilute, as specified in8.3.2.1 and carry out the titration as specified in 8.3.2.2.ISO 5073 pdf download.