Overview
ISO 622:2025 - "Coal and coke - Determination of phosphorus - Reduced molybdophosphate photometric method" specifies a laboratory method for measuring the total phosphorus mass fraction in hard coal, lignite and coke. The standard defines two validated extraction routes to take phosphorus into solution (ash acid extraction or repeated wet oxidation) and a photometric determination based on the formation of reduced molybdophosphate (blue complex) whose absorbance is measured by a spectrophotometer.
This third edition updates scope, normative references and calculation formulae, and adds a detailed test report requirement.
Key topics and requirements
- Scope and samples: Analysis sample prepared and ground to pass a 212 µm sieve, taken and prepared per ISO sampling standards. Ash is prepared per ISO 1171 when using the dry-ash extraction route.
- Two extraction methods:
- Dry oxidation (ash extraction): ash the sample, grind to pass 63 µm, extract with hydrofluoric acid (HF) and sulfuric acid (H2SO4).
- Wet oxidation: repeated oxidation of the coal/coke with nitric acid (HNO3) in the presence of sulfuric acid to remove carbonaceous matter.
- Photometric determination: add ammonium molybdate and ascorbic acid (with antimony potassium tartrate as accelerator) to produce the reduced molybdophosphate blue; measure absorbance with a spectrophotometer or photoelectric absorptiometer.
- Reagents and apparatus: lists analytical-grade reagents (HF, H2SO4, HNO3, molybdate, ascorbic acid, standards) and apparatus (muffle furnace, platinum crucible, Kjeldahl flask assembly for wet digestion, spectrophotometer).
- Safety notes: strong warnings for handling hydrofluoric acid (highly corrosive and toxic) and heat generation when preparing sulfuric acid dilutions.
- Quality and performance: clauses on precision (repeatability and reproducibility) and requirements for reagent blanks, calibration (standard phosphorus solutions) and expression of results.
- Reporting: updated Clause 11 specifies required information in the test report.
Applications and users
ISO 622:2025 is used for:
- Quality control in coal and coke production and trading
- Laboratory analysis in power generation, metallurgical coke plants, and coal research
- Environmental monitoring and regulatory compliance where phosphorus content affects ash behavior, slagging or emissions
- Instrument and reagent suppliers for method validation and product guidance
Typical users: analytical chemists, coal testing laboratories, QA/QC managers, plant technical teams, environmental laboratories and standards bodies.
Related standards
Normative references include ISO 1171 (ash), ISO 565 (sieves), ISO 18283 and ISO 13909 series (sampling and sample preparation), and ISO 383 (lab glassware). Reference ISO 622:2016 for prior edition comparisons.
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