ISO-5975-1983.pdf
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1、International Standard f 5975 0 N 4 d!igi INTERNATIONAL ORGANIZATION FOR STANDARDlZATION.ME#.WHAPOHAR OPTAHWAWIR IlO CTAHf.WTM3ALWWORGANlSATlON INTERNATIONALE DE NORMALISATION Chromium ores - Determination of calcium and magnesium contents - EDTA titrimetric method Minerais de chrome - Dosage du cal
2、cium et du magn Vt is the volume, in millilitres, of EDTA solution, used for the titration ; V2 is the volume, in millilitres, of EDTA solution, used for the titration of the blank test solution. The concentration, cCa, of the EDTA solution, expressed in grams of calcium per millilitre, is given by
3、the formula CC, = CMg x 1985 where 1,648 5 is the conversion factor from magnesium to calcium. 4.16 EDTA, standard volumetric solution, c(EDTA) = 0,012 5 mol/l. Transfer 250 ml of the EDTA solution (4.18) to a 500 ml one- mark volumetric flask, dilute to the mark with water and mix. 4.26 EDTA, stand
4、ard volumetric solution, c(EDTA) = 0,005 mol/l. Transfer 100 ml of the EDTA solution (4.18) to a 500 ml one- mark volumetric flask, dilute to the mark with water and mix. 4.21 Buffer solution. Dissolve 68 g of ammonium chloride in 400 ml of water, add 570 ml of the ammonia solution (4.71, dilute to
5、1 000 ml with water and mix. 4.22 Malachite green, 4-4-(dimethylamino)-a-phenyl- benzylidenel-2,5-cyclohexadienylidene dimethylammonium chloride (C23H25CIN2), C.I. 42060, 0,2 % (m/m) alcoholic solu- tion. 4.23 Fluorexon, fluorescein-2, 7-diyl-bistmethyleneni- trilolltetraacetic acid (C30H26N2013). M
6、ix 0,l g of the indicator with 10 g of the potassium chloride (4.2) and grind in a mortar. 4.24 Eriochrome black T, sodium 3-hydroxy-4-(I- hydroxy-2-naphthylazol-7-nitro-l-naphthalenesulfonate (C20H12N3Na07S), C.I. 14645. Mix 0,l g of the indicator with 10 g of the potassium chloride (4.2) and grind
7、 in a mortar. 5 Apparatus Ordinary laboratory apparatus and 5.1 Photoelectric titrimeter. 6 Procedure 6.1 Test portion Weigh 0,25 g of the sample for chemical analysis into a 250 ml beaker. 6.2 Decomposition of test portion 6.2.1 Moisten the test portion (6.1) with water, add 5 ml of the nitric acid
8、 (4.3) and 50 ml of the perchloric acid (4.41, cover with a watch glass and heat until fumes of perchloric acid appear. Maintain the solution for 10 to 15 min at a temperature of per- chloric acid fuming. Allow the contents of the beaker to cool, wash the walls of the beaker and the watch glass with
9、 water and heat again to perchloric fuming, continue heating for a further 10 to 15 min. Repeat the operation to dissolve the test portion completely. 2 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not
10、for Resale, 04/27/2007 22:11:06 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 5975-1983 (EI 8.2.2 In the case of ores difficult to decompose, add to the contents of the beaker 5 to 10 ml of the hydrochloric acid (4.5), 30 to 40 ml of water and heat to dissolve the sal
11、ts. Filter off the precipitate on the rapid paper filter containing a small amount of ashless paper pulp. Wash the precipitate on the filter 10 to 12 times with the hot hydrochloric acid (4.11) and combine the washings with the main filtrate, the filtrate being reserved as the main solution. Place t
12、he filter paper with the precipitate in a platinum crucible, dry, ash and ignite at 800 to 900 OC. Allow the crucible with the residue to cool. Moisten the residue with a few drops of water, add 3 or 4 drops of the sulfuric acid (4.121, 2 to 3 ml of the hydrofluoric acid solution (4.61, heat till th
13、e complete removal of sulfuric acid and ignite at 700 to 800 OC. Allow the contents of the crucible to cool. Fuse the residue with 1 to 2 g of the sodium carbonate (4.1) at 1 000 to 1 100 “C. Leach the melt while heating with 20 to 30 ml of the hot hydrochloric acid solution (4.1 I); combine the sol
14、ution with the main solution. 6,3 Preparation of test solution In both cases (6.2.1 and 6.2,2), evaporate the solution to fumes of perchloric acid. Remove the watch glass and carefully add, drop by drop, the hydrochloric acid (4.5) along the walls of the beaker until brown fumes of chromyl chloride
15、cease to evolve, chromium being reduced to the trivalent form. Cover the beaker with a watch glass and continue to heat the solution to oxidize chromium completely. Repeat the distillation of chromyl chloride to remove the bulk of chromium (until the solution is nearly colourless). Add 5 to 7 ml of
16、the hydrochloric acid (4.51, 30 to 40 ml of water and heat to dissolve the salts. Allow the contents of the beaker to cool. Wash the walls of the beaker and the watch glass with water. Dilute the solution with hot water to 80 to 100 ml, add 5 ml of the ammonium persulfate solution (4.13) and the amm
17、onia solution (4.7) until an ammoniacal odour persists. Add a further 2 to 3 ml. Heat the solution with the precipitate to decompose ammonium persulfate. In case an ammoniacal odour disap- pears, add ammonia solution (4.7) until the ammoniacal odour persists. Allow the precipitateto settle and filte
18、r it on a medium texture filter paper then wash with hot ammonia solution (4.8) 5 or 6 times. Reserve the filtrate with the washings as the main solution. Dissolve the precipitate on the filter with 40 to 50 ml of hot hydrochloric acid (4.10) collecting filtrate in the beaker in which the precipitat
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