ISO 622:2025
(Main)Coal and coke — Determination of phosphorus — Reduced molybdophosphate photometric method
Coal and coke — Determination of phosphorus — Reduced molybdophosphate photometric method
This document specifies a reduced molybdophosphate photometric method for the determination of the total phosphorus mass fraction of hard coal, lignites and coke. Two methods for taking the phosphorus into solution are specified, namely extraction from the coal or coke ash with acid or by repeated oxidation of the coal or coke, by acid, to remove carbonaceous matter.
Charbon et coke — Détermination du phosphore — Méthode photométrique au molybdophosphate réduit
General Information
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Standards Content (Sample)
International
Standard
ISO 622
Third edition
Coal and coke — Determination
2025-06
of phosphorus — Reduced
molybdophosphate photometric
method
Charbon et coke — Détermination du phosphore — Méthode
photométrique au molybdophosphate réduit
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
4.1 Extraction .1
4.2 Determination .2
5 Reagents . 2
6 Apparatus . 3
7 Sample preparation . 4
8 Procedure . 4
8.1 Dry oxidation method .4
8.2 Wet oxidation method .5
8.3 Determination .6
9 Expression of results . 6
10 Precision of the method . 7
10.1 Repeatability .7
10.2 Reproducibility .7
11 Test report . 7
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This third edition cancels and replaces the second edition (ISO 622:2016), which has been technically
revised.
The main changes are as follows:
— the title and scope have been modified to specifically refer to coal;
— the normative references have been updated;
— Formulae (1) and (2) have been modified;
— a new Formula (3) has been added in Clause 9;
— a new test report clause (Clause 11) has been added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
International Standard ISO 622:2025(en)
Coal and coke — Determination of phosphorus — Reduced
molybdophosphate photometric method
1 Scope
This document specifies a reduced molybdophosphate photometric method for the determination of the
total phosphorus mass fraction of hard coal, lignites and coke. Two methods for taking the phosphorus into
solution are specified, namely extraction from the coal or coke ash with acid or by repeated oxidation of the
coal or coke, by acid, to remove carbonaceous matter.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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.
ISO 383, Laboratory glassware — Interchangeable conical ground joints
ISO 565, Test sieves — Metal wire cloth, perforated metal plate and electroformed sheet — Nominal sizes of
openings
ISO 1171, Coal and coke — Determination of ash
ISO 13909-2, Coal and coke — Mechanical sampling — Part 2: Sampling of coal from moving streams
ISO 13909-3, Coal and coke — Mechanical sampling — Part 3: Sampling of coal from stationary lots
ISO 13909-4, Coal and coke — Mechanical sampling — Part 4: Preparation of test samples of coal
ISO 13909-5, Coal and coke — Mechanical sampling — Part 5: Sampling of coke from moving streams
ISO 13909-6, Coal and coke — Mechanical sampling — Part 6: Preparation of test samples of coke
ISO 18283, Coal and coke — Manual sampling
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
4.1 Extraction
Method 1: Removal of carbonaceous material by ashing in a muffle furnace under specified conditions, and
extraction of phosphorus by treatment of the ash obtained with hydrofluoric and sulfuric acids.
Method 2: Removal of carbonaceous material by repeated oxidation with nitric acid in the presence of
sulfuric acid.
4.2 Determination
Addition of ammonium molybdate and ascorbic acid solution to the acid solution. Measurement of the
absorbance of the resulting blue solution by a suitable optical instrument.
5 Reagents
During the analysis, use only reagents of recognized analytical grade and only distilled water or water of
equivalent purity.
5.1 Hydrofluoric acid, approximately 400 g/l solution.
WARNING — Aqueous hydrofluoric acid is a highly corrosive liquid which attacks glass; the vapour
is irritant and toxic. Its reaction with the skin and eyes is strongly corrosive, producing severe
and painful burns which can not be immediately evident and which respond slowly to treatment.
The solution shall be handled only inside a well-ventilated fume cupboard. In the event of contact
or suspected contact, flood with water and seek immediate medical attention. The manufacturer’s
literature should be consulted for further information.
WARNING — Preparation of solutions using sulfuric acid can generate significant heat. Generation of
heat can be reduced by adding sulfuric acid as the last component of a solution mixture.
5.2 Sulfuric acid, concentrated, ρ 1,84 g/ml, approximately 98 % mass concentration solution.
5.3 Sulfuric acid, solution, prepared by diluting approximately 490 g of sulfuric acid (5.2) to a volume of
1 l with water.
5.4 Nitric acid, concentrated, ρ 1,42 g/ml, approximately 70 % mass concentration solution.
5.5 Ammonium molybdate, 60 g/l solution.
5.6 Ascorbic acid, 50 g/l solution.
Prepare the solution fresh daily.
5.7 Antimony potassium tartrate (KSbO·C H O ), 1,36 g/l solution.
4 4 6
5.8 Reagent blank solution.
Mix 25 ml of the sulfuric acid solution (5.3), 10 ml of the ammonium molybdate solution (5.5), 10 ml of
the ascorbic acid solution (5.6) and 5 ml of the antimony potassium tartrate solution (5.7). Prepare fresh
immediately before use.
5.9 Phosphorus, standard stock solution corresponding to 0,100 mg/ml.
Determine the mass by weighing, to the nearest 0,000 1 g, 0,439 2 g of potassium dihydrogen monophosphate
(KH PO ) (dried at 110 °C for 1 h) and dissolve in water. Transfer the solution quantitatively to a 1 000 ml
2 4
one-mark volumetric flask, dilute to the mark and mix.
5.10 Phosphorus, standard working solution corresponding to 1 µg/ml.
Transfer 10 ml of the standard phosphorus solution (5.9) to a 1 000 ml one-mark volumetric flask, dilute to
the mark and mix. Prepare fresh immediately before use.
6 Apparatus
Ordinary laboratory apparatus and the following.
6.1 Balance, capable of determining mass by weighing to the nearest 0,1 mg.
6.2 Muffle furnace, as specified in ISO 1171.
6.3 Dish, of silica, porcelain or platinum, as specified in ISO 1171.
6.4 Insulating plate, of silica, 6 mm thick, or its equivalent, of such size as to be an easy sliding fit into the
muffle furnace (6.2).
6.5 Platinum crucible, of capacity 25 ml to 30 ml, with lid.
6.6 Hot-air bath.
6.7 Digestion apparatus (see Figure 1), constructed of borosilicate glass, consisting of the following:
6.7.1 Flask, Kjeldahl flask, of capacity 300 ml, fitted with a 24/29 ground glass socket in accordance with
ISO 383.
6.7.2 Fume duct, of outside diameter approximately 28 mm, fitted with a dropping funnel of capacity at
least 15 ml and a 24/29 ground glass cone in accordance with ISO 383. The fume duct may be of one piece or
assembled from spate units by means of ground glass joints.
6.7.3 Fume extractor, comprising a glass tube of diameter approximately 40 mm, sealed at one end and
drawn out at the other end to form a connection to the water pump. The tube is fitted with a drain stopcock
and a series of lipped holes to accommodate a number of fume ducts.
6.8 Spectrophotometer, or photoelectric absorptiometer, of the required sensitivity.
6.9 Bunsen burner, connected to a gas supply.
6.10 Boiling water bath.
a
To pump.
Figure 1 — Apparatus for wet oxidat
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