1、 DEUTSCHE NORMJune 2004DIN 51725 ICS 75.160.10 Supersedes DIN 51725:1979-04 and DIN 51729-9:1963-12 Testing of solid fuels Determination of the phosphorus content Prfung fester Brennstoffe Bestimmung des Phosphorgehaltes Document comprises 9 pagesTranslation by DIN-Sprachendienst. In case of doubt,
2、the German-language original should be consulted as the authoritative text. No part of this translation may be reproduced without prior permission of DIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany, has the exclusive right of sale for German Standards (DIN-N
3、ormen). English price group 7 www.din.de www.beuth.de !,kSV“09.06 9724851DIN 51725:2004-06 2 Foreword This standard has been prepared by Technical Committee NMP 581/FABERG Prfung fester Brennstoffe of the Normenausschuss Materialprfung (Materials Testing Standards Committee) in collaboration with th
4、e Normenausschuss Bergbau (Mining Standards Committee). See Annex A for connection with International Standard ISO 622:1981 published by the International Organi-zation for Standardization (ISO). Amendments This standard differs from DIN 51725:1979-04 and DIN 51729-9:1963-12 as follows: a) The infor
5、mation on the relationship between this standard and ISO 622 has been updated. b) The test report has been included. c) The contents of these standards have been editorially revised and updated. Previous editions DIN 51725: 1955-02, 1979-04 DIN 51729-9: 1963-12 1 Scope This standard specifies a meth
6、od of determining the phosphorus content of hard coal, coke and brown coal (lignite). The method described can also be applied to ash obtained as specified in DIN 51719. 2 Normative references This standard incorporates, by dated or undated reference, provisions from other publications. These norma-
7、tive references are cited at the appropriate places in the text, and the titles of the publications are listed below. For dated references, subsequent amendments to or revisions of any of these publications apply to this standard only when incorporated in it by amendment or revision. For undated ref
8、erences, the latest edition of the publication referred to applies (including amendments). DIN 1333, Presentation of numerical data DIN 51701-2, Sampling of solid fuels Procedure DIN 51701-3, Sampling of solid fuels Sample preparation DIN 51719, Determination of ash in solid fuels DIN EN ISO 4259, P
9、etroleum products Determination and application of precision data in relation to meth-ods of test (ISO 4259:1992 + Corr 1:1993) DIN ISO 3310-1, Test sieves Technical requirements and testing Part 1: Test sieves of metal wire cloth (ISO 3310-1:2000) DIN 51725:2004-06 3 3 Designation Designation of th
10、e method of determining the phosphorus content (P) of solid fuels as specified in this standard: Method DIN 51725 P 4 Principle After the fuel sample has been burnt, its ash is digested by treatment with hydrofluoric and nitric acids. The phosphate in the resultant solution is converted into phospho
11、molybdenum blue and determined photometrically. 5 Apparatus In addition to standard laboratory equipment, the following shall be used. Spectrophotometer or filter photometer suitable for measurements above 700 nm. Hotplate or sand bath. Electrically heated muffle furnace, capable of being maintained
12、 at (815 10) C. Platinum crucible, of nominal capacity 50 ml. Test sieve (metal wire cloth sieve as in DIN ISO 3310-1, of nominal aperture size 63 m). Porcelain ashing dish, of external diameter about 40 mm. 6 Reagents Analytical grade reagents shall be used and the water used shall be distilled wat
13、er or water deionized by ion exchange. Unless otherwise stated, solutions shall be prepared with such water. The following reagents shall be used. Nitric acid, containing about 940 g of HNO3/l, density 1,40 g/ml. Approx. 38 % (m/m) hydrofluoric acid, HF. CAUTION Extreme care shall be exercised in ha
14、ndling hydrofluoric acid as specified in BGI 576 Fluorwasserstoff, Flusssure und anorganische Fluoride (Hydrogen fluoride, hydrofluoric acid and inorganic fluorides) published by BG Chemie. Sulfuric acid, containing approximately 98 g of H2SO4/l, density 1,06 g/ml. Sodium pyrosulfite solution, prepa
15、red by dissolving 20 g of Na2S2O5in 80 ml of water. The solution will be stable for one week. Ammonium molybdate solution, prepared by completely dissolving 2,5 g of (NH4)6Mo7O24 4 H2O in 500 ml of cold 0,05 mol/l sulfuric acid, H2SO4. The solution may be used for as long as no precipitation occurs.
16、 DIN 51725:2004-06 4 Reducing solution, prepared by dissolving 0,2 g of 4-(methylamino)phenol sulfate, 20 g of Na2S2O5and 1 g of Na2SO3in water and making the solution up to 100 ml. The solution will be stable for one week. Phosphate reference solution, prepared by dissolving in water 4,392 8 g of f
17、inely powdered Srensen KH2PO4previously dried over sulfuric acid in a desiccator and making the solution up to 1 000 ml. Diluting 10 ml of this solution to 1 000 ml with water results in a reference solution containing 0,010 mg/ml phosphorus. Stabilize both solutions with one to two drops of chlorof
18、orm prior to making up. 7 Sampling As specified in DIN 51701-2 and DIN 51701-3. 8 Preparation After digesting the fuel ash in hydrofluoric and nitric acids (which will require two to three hours), dissolve the residues in sulfuric acid (density 1,06 g/ml). Filter off any residue due to the presence
19、of large amounts of iron oxide. Since iron(III), arsenic(V) and vanadium(V) ions result in errors, remove them by reduction in an acidic sodium pyrosulfite solution to iron(II), arsenic(III) and vanadium(IV) ions before developing the phosphomolybdenum blue. To do this, add 10 ml of sulfuric acid (d
20、ensity 1,06 g/ml) to the test solution, followed by about 5 ml of sodium pyrosulfite. If the arsenic content of the fuel ash is greater than 0,2 % by mass, reduce for one hour in a water bath at about 100 C. Under these conditions, no interference will occur for fuel ash arsenic contents of up to 1
21、% by mass. In view of the danger of reoxidation, boil the solution to expel excess sulfur dioxide only until there is no trace of the latter in the fumes. With 12 ml of ammonium molybdate solution added, phosphorus contents of up to 0,40 mg in 100 ml of test solution can be determined. If this limit
22、 is exceeded, make the digestion solution obtained up to 100 ml and take an aliquot for the determination. In this case, however, before adding the 5 ml of sodium pyrosulfite solu-tion, add sulfuric acid (density 1,06 g/ml) to the test solution until its sulfuric acid content is 10 ml. Neglect the a
23、mount of acid used up by the elements associated with the phosphorus in the calculation. Determine the transmission (T) or the absorbance 100lgTin the red region of the spectrum (wavelength 720 nm to 800 nm). Figure 1 shows the relationship between absorbance and wavelength for the coloration produc
24、ed. Figure 1 Variation in absorbance with wavelength DIN 51725:2004-06 5 9 Plotting the phosphorus calibration graph To plot the calibration graph, measure out portions ranging from 5 ml to 40 ml of the phosphate reference solution into the volumetric flasks. After adding 10 ml of sulfuric acid (den
25、sity 1,06 g/ml) and 5 ml of sodium pyrosulfite solution, dilute each solution to about 60 ml with water. Boil the solutions until all the sulfur dioxide has been expelled, placing a bumping stick in every flask to ensure uniform boiling. After cooling to 20 C, rinse and remove the bumping stick. The
26、n add 1 ml of sodium pyrosulfite solution, 12 ml of ammonium molyb-date solution and 2 ml of reducing solution in that order to each volumetric flask, mixing well after every addi-tion. Make up to the mark with water and mix thoroughly. Prepare a blank test with the reagents in the same way. After l
27、eaving to stand for three hours at 20 C in the dark, determine the blue colorations photometrically in a cell of suitable path length using the blank as a reference. Divide the measured absorbance by the path length in centimetres and plot it against the phosphorus concen-tration of the solution. Co
28、nnecting up the measurements will result in a straight line that passes through the origin (see figure 2). Figure 2 Variation in absorbance with phosphorus concentration There will not be a linear relationship between absorbance and concentration if polychromatic light is used at the absorption edge
29、. In that case plot a calibration graph for every path length. 10 Procedure 10.1 Fuel samples Weigh, to an accuracy of 0,000 2 g, (1 0,1) g of the air-dried analytical sample, prepared as specified in DIN 51701-2 and DIN 51701-3, into the ashing dish and place the sample in a cold muffle furnace. He
30、at the furnace to (815 10) C and roast the sample at this temperature until the carbon is completely burned (about two to three hours). Use a fine animal-hair brush to transfer the ash quantitatively to a platinum crucible and moisten it with a few drops of water. Then evaporate it to dryness twice
31、on a hotplate or sand bath, adding 5 ml of hydrofluoric acid and 5 ml of nitric acid each time. To expel hydrofluoric acid residues, moisten two to three times with a few drops of nitric acid and evaporate to dryness. Take up the dry residue in 10 ml of sulfuric acid (density 1,06 g/ml), place a wat
32、ch glass on the crucible and boil for about twenty minutes. Then filter through a hardened 9 cm filter into the volumetric flask and wash the filter thoroughly with hot water until the flask contains about 50 ml to 60 ml. After adding 5 ml of sodium pyro-sulfite solution to the solution, introduce a
33、 bumping stick and heat slowly to boiling point on the hotplate or DIN 51725:2004-06 6 sand bath to expel the excess sulfur dioxide. Cool the solution to 20 C and make it up to 100 ml, then pro-ceed as described in clause 9. Use the same amounts of hydrofluoric and nitric acids for the blank test. 1
34、0.2 Fuel ash samples Burn the air-dried fuel sample, prepared as specified in DIN 51701-2 and DIN 51701-3, at (815 10) C. Grind the ash until it passes without residue through a sieve (as in DIN ISO 3310-1) having a nominal aperture size of 63 m, mix and continue roasting for two hours at (815 10) C
35、. Weigh, to an accuracy of 0,000 1 g, (0,1 0,02) g of the fuel ash into a platinum crucible and moisten it with a few drops of water. Evaporate to dryness twice on the hotplate or sand bath, adding 5 ml of hydrofluoric acid and 5 ml of nitric acid each time. Then proceed as described in subclause 10
36、.1. 11 Evaluation Either read off the phosphorus content of the test solution corresponding to the absorbance from the calibre-tion graph or, if the calibration curve is a straight line, calculate it using the proportionality factor. Calculate the phosphorus content, w(P), as a percentage by mass, o
37、f the sample with the moisture content at analysis or of the anhydrous fuel sample using equations (1) and (2), respectively, for fuels and using equa-tions (3) and (4), respectively, for fuel ash: ()bmoist10 mPw=a(1) ()()AMmPw=10010banha(2) ()aanhmoist0001 mAPw=a(3) ()()aanhanh10100 mAMAPw=a(4where
38、 a is the amount of phosphorus in the digestion solution, in mg; mbis the initial sample mass of fuel with the moisture content at analysis, in g; mais the initial sample mass of the fuel ash, in g; Aanhis the ash content of the analytically moist fuel, as a percentage by mass; AM is the moisture co
39、ntent of the fuel at analysis, as a percentage by mass. 12 Expression of result The test report shall refer to this standard and report the total phosphorus content of the anhydrous fuel, w(Panh), to the nearest 0,001 % by mass. DIN 51725:2004-06 7 DIN 1333 shall be taken into account when rounding
40、to the last significant place. 13 Precision (Cf. DIN EN ISO 4259) Repeatability limit (same operator, same equipment) If two results are obtained under repeatability conditions, both results shall be considered as acceptable and in conformity with this standard if they differ by no more than the num
41、erical value given in column 2 of table 1 or their difference does not exceed the numerical value given in column 3 of that table. Reproducibility limit (different operators, different equipment) If two separate laboratories each obtain a result under reproducibility conditions, both results shall b
42、e considered acceptable and in conformity with this standard if their means differ by no more than the numerical value given in column 4 of table 1 or if the difference in their means does not exceed the numerical value given in column 5 of that table. NOTE When comparing results, greater difference
43、s may be expected if the samples examined originate from the same bulk sample but have been obtained by division in a state other than analytically fine and the subsequent sample preparation has been performed separately, or if the samples have been obtained by separately sampling the same batch. Ta
44、ble 1 Precision data Repeatability limit (difference between the results of two determinations) Reproducibility limit (difference between the means of two determinations in each case) Phosphorus content, w(Panh), as a percentage % Percentage of mean % Percentage of mean 0,02 0,002 0,004 0,02 10 20 1
45、4 Test report The test report shall include the following details as a minimum: a) Designation as specified in this standard (i.e. Method DIN 51725 P). b) Complete characterization of sample. c) The result expressed as specified in clause 12. d) Any unusual observations during the determination. DIN
46、 51725:2004-06 8 Annex A (informative) Explanatory notes This standard is equivalent in substance to ISO 622:1981 except in the following respects. a) 4-(methylamino)phenol sulfate has been used instead of ascorbic acid. b) 4-(methylamino)phenol sulfate has been given preference because the time int
47、erval between the coloration of the test solution and the determination is long enough for series analyses to be performed more easily. If ascorbic acid is used, the time interval of 15 minutes has to be maintained very precisely. c) The initial sample mass of ash is 100 mg instead of 50 mg as in IS
48、O 622. However, the procedure for an analytically fine fuel sample has also been described and the analytical result then applies to the anhy-drous fuel. Re clause 8 It has been found by experience that fairly small amounts of undissolved digestion residues do not affect the result of the determinat
49、ion. If necessary the initial sample mass may be reduced. Re subclause 10.1 The initial sample mass of ash-rich fuel samples may be reduced so that about 0,1 g of fuel ash is obtained. DIN 51725:2004-06 9 Bibliography BGI 576, Fluorwasserstoff, Flusssure und anorganische Fluoride. 1)(Hydrogen fluoride, hydrofluoric acid and inorganic fluorides) ISO 622:1981, Solid mineral fuels Determination of phosphorus content Reduced molybdophosphate photometric method 1) Obtainable from Carl
