Overview
ISO 925:2019 - Solid mineral fuels - Determination of carbonate carbon content - Gravimetric method specifies a laboratory gravimetric procedure to measure carbonate carbon associated with solid mineral fuels (coal, coke, lignite). The method decomposes mineral carbonates with hydrochloric acid, captures the liberated carbon dioxide (CO2) in an absorption tube, and determines carbonate carbon gravimetrically by weighing the absorber. Note: results include any carbon from atmospheric CO2 absorbed by the fuel.
Key topics and technical requirements
- Principle: Acid decomposition of carbonates → CO2 liberated → CO2 absorbed on sodium hydroxide on an inert base → increase in absorber mass is measured.
- Reagents: ~3 mol/L hydrochloric acid; magnesium perchlorate (drying); hydrogen sulfide absorbents (copper(II) phosphate or copper(II) sulfate on pumice, or silver sulfate); sodium hydroxide on inert base; wetting agent; check-test reagents (anhydrous sodium or calcium carbonate).
- Apparatus: analytical balance (0.1 mg), reaction flask assembly (300 ml round-bottom, tap funnel, condenser, bulbed tube), absorption train (Mg(ClO4) drying tube; H2S absorbent + Mg(ClO4); CO2 absorber tube with NaOH + Mg(ClO4)), suction pump/flowmeter.
- Sample and preparation: analysis sample prepared to nominal top size 212 μm; equilibrate moisture to laboratory atmosphere; typical test portion 5.00 g (weighed to 0.01 g). For fuels >0.5% carbonate carbon, sample mass may be reduced pro rata to a minimum of 0.5 g.
- Operating conditions: air flow ~50 ml/min; condition apparatus 10 min; add 25 ml HCl, heat to boil after ~15 min, continue boiling ~30 min; cool and weigh CO2 absorption tube to constant mass.
- Calculations: carbonate carbon (%) Wc = 27.29 × (m2 / m1); CO2 (%) WCO2 = 100 × (m2 / m1), where m1 = mass of test portion (g) and m2 = increase in mass of the absorption tube (g). Report mean of duplicate determinations to 0.01%.
- Quality checks: perform airtightness/reagent check using ~60 mg of check reagent; acceptable result within ±10% of theoretical CO2.
Applications and users
ISO 925:2019 is suited for:
- Laboratories performing fuel analysis, carbon accounting and compositional testing of coal, coke and lignite.
- Quality control and QA/QC in mining, power generation, and coke production.
- Research groups studying mineral carbonate content or CO2 uptake in solid fuels.
- Regulatory and compliance testing where standardized carbonate carbon data are required.
Keywords: ISO 925:2019, carbonate carbon, solid mineral fuels, gravimetric method, CO2 content, absorption tube, hydrochloric acid, magnesium perchlorate.
Related standards
Normative references cited in ISO 925:2019 include:
These relate to sample preparation, moisture determination and calculation bases used together with ISO 925 analyses.
Open preview (PDF)Solid mineral fuels — Determination of carbonate carbon content — Gravimetric method