1、INTERNATIONAL STANDARD IS0 925 Third edition 1997-05-01 Solid mineral fuels - Determination of carbonate carbon content - Gravimetric method Combustibles minkaux so/ides - Dosage du carbone sous forme de carbonate - Mthode gravimbtrique Reference number IS0 925: 1997(E) IS0 925:1997(E) Foreword IS0
2、(the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical comm
3、ittee has been established has the right to be represented on that committee. International organizations, governmental and non- governmental, in liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrot
4、echnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IS0 925 was prepared by
5、Technical Committee ISO/TC 27, So/id mineral fuels, Subcommittee SC 5, Methods of analysis. This third edition cancels and replaces the second edition (IS0 925:1980), which has been technically revised. Annex A of this International Standard is for information only. 0 IS0 1997 All rights reserved. U
6、nless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case postale 56 l CH-1211
7、 Geneve 20 l Switzerland Internet central iso.ch x.400 c=ch; a=400net; p=iso; o=isocs; s=central Printed in Switzerland ii INTERNATIONAL STANDARD IS0 IS0 925: 1997(E) Solid mineral fuels - Determination of carbonate carbon content - Gravimetric method 1 Scope This International Standard specifies a
8、gravimetric method of determining the carbon in the mineral carbonates associated with solid mineral fuels. NOTE - The result obtained will include any carbon from atmospheric carbon dioxide absorbed by the fuel. 2 Normative references The following standards contain provisions which, through refere
9、nce in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the m
10、ost recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IS0 331 :1983, Coal - Determination of moisture in the analysis sample - Direct gravimetric method. IS0 687:1974, Coke - Determination of moisture in the analys
11、is sample. IS0 1015:1992, Brown coals and /ignites - Determination of moisture content - Direct volumetric method. IS0 1170:1977, Coal and coke - Calculation of analyses to different bases. IS0 1988: 1975, Hard coal - Sampling. IS0 2309:1980, Coke - Sampling. IS0 5068:1983, Brown coals and /ignites
12、- Determination of moisture content - Indirect gravimetric method. IS0 5069-2:1983, Brown coals and /ignites - Principles of sampling - Part 2: Sample preparation for determination of moisture content and for genera/ analysis. IS0 941 l-l :1994, So/id mineral fuels - Mechanical sampling from moving
13、streams - Part 1: Coal. IS0 9411-2:1993, Solid mineral fuels - Mechanical sampling from moving streams - Part 2: Coke. 3 Principle A known mass of sample is treated with hydrochloric acid, which reacts with the carbonates present to liberate carbon dioxide. The carbon dioxide resulting from the deco
14、mposition of the carbonates is absorbed and weighed. 1 IS0 925: 1997(E) IS0 4 Reagents WARNING - Care should be exercised when handling reagents, many of which are toxic and corrosive. During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only distilled w
15、ater, or water of equivalent purity. NOTE - Distilled water may be freed from carbon dioxide by boiling gently for 15 min. 4.1 Hydrochloric acid, approximately 3 mol/l. 4.2 Hydrogen sulfide absorbent Any of the following: a) copper phosphate, granular, particle size 1,2 mm to 0,7 mm; NOTE 1 Copper p
16、hosphate granules may be prepared as follows: Mix copper(H) phosphate powdered reagent to a stiff paste with 1 % starch solution. Press through a sheet of metal, perforated with apertures of approximately 1 mm diameter. Dry the extruded material at 110 “C. Sieve to recover the desired size fraction.
17、 b) copper sulfate, deposited on a supporting base of ground pumice; NOTE 2 A suitable absorbent, based on copper sulfate, may be prepared as follows: Prepare pumice by crushing and sieving to obtain the 2,8 mm to 0,7 mm fraction. Transfer approximately 60 g of the prepared pumice to an evaporating
18、basin, covering with a saturated solution of copper sulfate, evaporate to dryness with constant stirring, and heat at 150 “C to 160 “C for 3 h to 4 h. Cool in a desiccator and store in a glass- stoppered bottle. c) silver sulfate, granular. 4.3 Magnesium perchlorate, anhydrous, particle size 1,2 mm
19、to 0,7 mm. WARNING - Due regard must be taken of local regulations when disposing of exhausted magnesium perchlorate. It is essential that regeneration of magnesium perchlorate is not attempted, owing to the risk of explosion. 4.4 Sodium hydroxide, on an inert base, preferably of coarse grading, for
20、 example 1,7 mm to 1,2 mm, and preferably of the self-indicating type. 4.5 Wetting agent, suitable for use in acid solution. NOTE - A liquid wetting agent at a concentration of 100 ml/l or ethanol 95 % (V/V) are suitable. 4.6 Check test reagent Either of the following: a) anhydrous sodium carbonate;
21、 b) anhydrous calcium carbonate. 2 0 IS0 IS0 925: 1997(E) 5 Apparatus 5.1 Analytical balance, capable of weighing to the nearest 0,i mg. 5.2 Graduated glassware, conforming to the requirements for Grade A in the International Standards prepared by lSO/TC 48, Laboratory glassware and related apparatu
22、s. 5.3 Purification tube, consisting of an absorption tube) containing sodium hydroxide on an inert base (4.4). 5.4 Reaction flask assembly, comprising a 300 ml round-bottomed flask fitted with a tap funnel, a double-surface condenser and a bulbed tube. 5.5 Absorption train, consisting of three abso
23、rption tubes a), b) and c)l) packed respectively as follows: a) magnesium perchlorate (4.3) to dry the gas; b) hydrogen sulfide absorbent (4.2) followed by a protective layer of magnesium perchlorate (4.3). The connection from this tube to tube c) shall be fitted at its outlet end with a stopcock or
24、 other means of closure; c) sodium hydroxide on an inert base (4.4) to absorb carbon dioxide generated in the reaction flask, followed by a protective layer of magnesium perchlorate (4.3) to absorb water produced in the reaction between carbon dioxide and sodium hydroxide. This tube shall be fitted
25、with stopcocks or other means of closure at the inlet and outlet ends. 5.6 Air circulation equipment A suction pump, capable of drawing air at a rate of 50 ml/min through the apparatus, connected through a flowmeter to a tee-piece fitted with a stopcock (the air vent). 5.7 Heating source, for the re
26、action flask. Either an electric heating mantle to accommodate a 300 ml flask or a small gas burner. An example of a suitable assembly of the apparatus is illustrated in figure 1. 6 Preparation of the test sample The test sample is the general analysis test sample prepared in accordance with IS0 198
27、8, IS0 2309, IS0 5069-2, IS0 9411-I or IS0 941 l-2 as appropriate. Ensure that the moisture content of the sample is in equilibrium with the laboratory atmosphere, exposing it, if necessary, in a thin layer for the minimum time required to achieve equilibrium. Before commencing the determination, th
28、oroughly mix the equilibrated test sample for at least one minute, preferably by mechanical means. If the results are to be calculated other than on an “air-dried” basis (see clause 8), then, after weighing the test portion (see 7.2), determine the moisture content using a further portion of the tes
29、t sample by the method described in IS0 331, IS0 687, IS0 1015 or IS0 5068, as appropriate. 1) Absorption tubes may be U-tubes or Midvale tubes (which reduce back-pressure and hence, risk of leakage). The tops of the reagent columns should be covered with a layer of glass wool to guard against entra
30、inment of any fine particles in the circulating air. 3 IS0 925: 1997(E) 0 IS0 Air vent perchlorate Reaction flask L Hydrogen sulfide absorbent Air inlet Sodium hydroxide - on inert base Sodium hydroxide on inert base I ” suction pump Figure 1 - A suitable assembly of the apparatus 7 Procedure 7.1 Ch
31、eck test Check the air-tightness of the apparatus and condition of the reagents by running a test according to the procedure described in 7.2, but using approximately 60 mg of the check test reagent (4.6), weighed to the nearest 0,l mg, instead of the test sample. Calculate the theoretical mass of c
32、arbon dioxide (see A.2) expected to be liberated from the check test portion, and compare it with the measured value. The test is satisfactory if the measured value is within 10 % of the theoretical value; otherwise check the apparatus carefully to seal any leaks and/or replace the reagents. Re-test
33、 until a satisfactory result is obtained. Carry out check tests after initially setting up the apparatus, after having made any changes to it or to the reagents, and before making a determination or series of determinations. 4 0 IS0 IS0 925:1997(E) 7.2 Determination 7.2.1 Preparation Weigh accuratel
34、y, to the nearest 0,Oi g, 5 g of the sample into the reaction flask and add 5 drops of the wetting agent (4.5) and 100 ml of water. Close the flask by means of a rubber stopper and shake vigorously to wet the sample. Remove the stopper and wash any sample adhering to it back into the flask. Assemble
35、 the apparatus as shown in figure 1, with the air vent closed. NOTE - For fuels containing more than 03 % carbonate carbon, the sample mass may be reduced pro-rata, to a minimum of 095 g. 7.2.2 Conditioning Draw air through the apparatus at a rate of 50 ml/min for 10 min. Stop the circulation of air
36、 and close the ends of the carbon dioxide absorption tube and the outlet end of the hydrogen sulfide absorption tube connected to it. Remove the carbon dioxide absorption tube and wipe it with a clean, dry, lint-free cloth. NOTE 1 Under certain conditions of humidity, wiping the absorbers with a clo
37、th may induce a static charge, which, if significant, could affect the weighing. Consideration should therefore be given to employing static eliminators. Allow the tube to cool to the balance room temperature and weigh it at 10 min intervals until constant weight is obtained, i.e. two successive wei
38、ghings do not differ by more than 1 mg. NOTE 2 Tubes used for the absorption of carbon dioxide, particularly Midvale tubes, cool slowly and up to 60 min should be allowed before weighing. When not connected to the apparatus, the tubes should be protected from atmospheric contamination by closing the
39、 taps and fitting guard seals of plugged rubber tubing to the open limbs. It is usual to weigh the absorption tubes without guard seals, after wiping. 7.2.3 Reaction and completion Reconnect the absorption tube to the apparatus and open the stopcocks or otherclosures in the absorption train. Place 2
40、5 ml of the hydrochloric acid (4.1) in the tap funnel, open the air vent and admit the acid to the reaction flask. Close the air vent and draw air through the system at a rate of about 50 ml/min. Raise the temperature of the liquid in the reaction flask slowly so that it boils after about 15 min. Co
41、ntinue boiling for a further 30 min, the rate of boiling being adjusted so that the condenser is not overloaded. Turn off the heating source, stop the circulation of air, remove the absorption tube, wipe clean and weigh as before (see 7.2.2). 8 Expression of results Results may be expressed in terms
42、 of carbonate carbon content or carbon dioxide content, as appropriate, as follows. The carbonate carbon content of the sample WC, as analyzed, expressed as a percentage by mass, is given by the formula w, = 27,29 X m2 ml and the carbon dioxide content of the sample, Wco2, as analyzed, expressed as
43、a percentage by mass, is given by the formula wco, = 100xm2 ml where ml is the mass, in grams, of the test portion; m2 is the increase in mass, in grams, of the absorption tube. 5 IS0 925: 1997(E) IS0 Report the results as the mean of duplicate determinations, to the nearest 0,Ol %. The results of t
44、he determination described in this International Standard are reported on the “air-dried” basis. Calculation of results to other bases is dealt with in IS0 1170. 9 Precision 9.1 Repeatability limit The results of duplicate determinations, carried out at different times within a short interval, in th
45、e same laboratory, by the same operator, with the same apparatus, on representative portions taken from the same analysis sample, should not differ by more than the values shown in table 1 or table 2, as appropriate. 9.2 Reproducibility critical difference The means of the results of duplicate deter
46、minations, carried out in each of two laboratories, on representative portions taken from the same sample after the last stage of sample preparation, should not differ by more than the values shown in table 1 or table 2, as appropriate. Table 1 - Precision as carbonate carbon content Carbonate carbo
47、n up to 0,4 % 0,4 % and over Maximum acceptable differences between results (calculated to the same moisture content) Same laboratory Different laboratories (repeatability) (reproducibility) 0,02 % absolute 0,04 % absolute 5 % relative 10 % relative Table 2 - Precision as carbon dioxide content Carb
48、on dioxide up to 1 % 1 % and over Maximum acceptable differences between results (calculated to the same moisture content) Same laboratory Different laboratories (repeatability) (reproducibility) 0,05 % absolute 0,l % absolute 5 % relative 10 % relative 10 Test report The test report shall include t
49、he following particulars: a) reference to this International Standard; b) an identification of the sample tested; c) the results and the method of expression used; d) any unusual features noted during the determination; e) any operation not included in this International Standard, or regarded as optional; f) the date of the test. 6 IS0 IS0 925:1997(E) Annex A (informative) Derivation of factors used in calculations in this International Standard A.1 General In this annex, relative atomic masses and relative molecular masses are represented by the chemical formulae in square bra
