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1、BRITISH STANDARD BS 6870-2.4: 1987 ISO 6607:1985 Analysis of aluminium ores Part 2: Chemical methods Section 2.4 Method for determination of silicon content: combined gravimetric and spectrophotometric method ISO title: Aluminium ores Determination of total silicon content Combined gravimetric and s
2、pectrophotometric method UDC 553.492:543 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:48:55 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6870-2.4:1987 This British Standard, having been prepared under the direction of the Non-ferrous Metals Standards Committee, was published under the
3、authority of the Board of BSI and comes into effect on 28 August 1987 BSI 01-2000 The following BSI references relate to the work on this standard: Committee reference NFM/31 Draft for comment 83/76595 DC ISBN 0 580 16056 4 Amendments issued since publication Amd. No.Date of issueComments Licensed C
4、opy: sheffieldun sheffieldun, na, Wed Dec 06 14:48:55 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6870-2.4:1987 BSI 01-2000i Contents Page National forewordii 1Scope and field of application1 2References1 3Principle1 4Reagents1 5Apparatus2 6Sampling and preparation of samples2 7Procedure2 8Express
5、ion of results5 9Test report6 Table 1 Calibration solutions5 Table 2 Precision data for silicon determinations6 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:48:55 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6870-2.4:1987 ii BSI 01-2000 Nationa
6、l foreword This Section of BS 6870 has been prepared under the direction of the Non-ferrous Metals Standards Committee. It is identical with ISO 6607:1985 “Aluminium ores Determination of total silicon content Combined gravimetric and spectrophotometric method”, published by the International Organi
7、zation for Standardization (ISO). Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical with those used in British Standards; attention is d
8、rawn especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referring to this standard, they should be read as “Section of BS
9、6870”. Additional information. When adopting the text of the International Standard, it was noticed that in 4.8 hydrochloric acid with a density of 1.17 g/ml is specified, whereas in the UK hydrochloric acid with a density of 1.18 g/ml is normally used. This difference, which will not affect the det
10、ermination, has been brought to the attention of ISO in a proposal to amend the International Standard by specifying a wider range for the density of the hydrochloric acid required. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards
11、are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard ISO 6995:1985BS 6870 Analysis of aluminium ores Section 2.7:1987 Method for determinatio
12、n of titanium content: spectrophotometric method (Identical) ISO 5725:1986BS 5497 Precision of test methods Part 1:1987 Guide for the determination of repeatability and reproducibility for a standard test method by inter-laboratory tests (Identical) Summary of pages This document comprises a front c
13、over, an inside front cover, pages i and ii, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffiel
14、dun, na, Wed Dec 06 14:48:55 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6870-2.4:1987 BSI 01-20001 1 Scope and field of application This International Standard specifies a combined gravimetric method and spectrophotometric method for the determination of the total silicon content in aluminium ore
15、s. The method is applicable to ores containing between 1 and 25 % (m/m) of silicon dioxide. 2 References ISO 5725, Precision of test methods Determination of repeatability and reproducibility by intra-laboratory tests. ISO 6995, Aluminium ores Determination of titanium content 4,4-Diantipyrylmethane
16、 spectrophotometric method. 3 Principle Decomposition of the test portion by either a) Treatment with a mixture of hydrochloric acid, nitric acid and sulfuric acid. NOTEThis method is recommended for ores containing gibbsite and/or boehmite and when the residue from the dissolution of the test porti
17、on after silica volatilization is less than 1 % of the mass of the test portion; or b) Sintering with sodium peroxide followed by a brief fusion. Dissolution of the melt with sulfuric acid. NOTEThis method is recommended for ores containing diaspore, and when the residue after silica volatilization
18、for acid decomposition is greater than 1 % of the mass of the test portion. or c) The fusion method given in 3 c) and sub-clause 7.5.1.3 of ISO 6995. Dehydration of silica, dissolution of salts, filtration and ignition of the impure silica, treatment with hydrofluoric acid and sulfuric acid. Fusion
19、of the residue with sodium carbonate/sodium tetraborate flux, dissolution of the melt with sulfuric acid and addition to the main solution. Treatment of an aliquot portion of the main solution with excess sodium hydroxide and heating to depolymerize the silica in solution. Acidification with sulfuri
20、c acid and adjustment to pH 1,40, followed by addition of ammonium molybdate. Destruction of molybdophosphoric and molybdoarsenic acids with further sulfuric acid, reduction of the -molybdosilicic acid to the blue complex and measurement of the absorbance at about 810 nm. 4 Reagents During the analy
21、sis, use only reagents of analytical reagent grade and only distilled water or water of equivalent purity. 4.1 Sodium peroxide NOTESodium peroxide should be protected against humidity and should not be used once it has begun to agglomerate. 4.2 Sodium carbonate/sodium tetraborate flux Mix 3 parts by
22、 mass of anhydrous sodium carbonate and 1 part by mass of anhydrous sodium tetraborate flux. 4.3 Hydrofluoric acid, 40 % (m/m), 20 = 1,13 g/ml. 4.4 Sulfuric acid, 20 = 1,84 g/ml, diluted 1 + 1. 4.5 Sulfuric acid, 20 = 1,84 g/ml, diluted 1 + 3. 4.6 Sulfuric acid, 20 = 1,84 g/ml, diluted 1 + 9. 4.7 Su
23、lfuric acid, 20 = 1,84 g/ml, diluted 1 + 39. 4.8 Acid mixture Measure into a one-litre beaker 225 ml of water and add cautiously, with mixing, 175 ml of sulfuric acid (20 1,84 g/ml). Cool to room temperature and add 150 ml of hydrochloric acid (201,17 g/ml) and 50 ml of nitric acid (201,42 g/ml). Mi
24、x. Prepare this solution fresh for each series of determinations and discard any unused solution. 4.9 Ascorbic acid, 50 g/l solution. Dissolve 5 g of ascorbic acid in 100 ml of water. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:48:55 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6870-2
25、.4:1987 2 BSI 01-2000 Prepare this solution daily. 4.10 Ammonium molybdate, 100 g/l solution. Dissolve 100 g of ammonium molybdate tetrahydrate (NH4)6Mo7O244H2O in 1 litre of water. Discard the solution when precipitation has commenced. 4.11 Sodium hydroxide, 160 g/l solution. Dissolve 160 g of sodi
26、um hydroxide in 1 litre of water in a plastics beaker. Store in a plastics bottle. 4.12 Silica, standard solution corresponding to 400 mg of SiO2 per litre. Ignite pure silica at 1 000 C for 1 h and cool in a desiccator. Weigh, to the nearest 0,001 g, 0,400 g of the ignited silica into a platinum cr
27、ucible. Add 4,0 g of anhydrous sodium carbonate, mix thoroughly using a metal spatula and fuse carefully for 10 min at 1 000 C. Cool and transfer to a 400 ml plastics beaker. Add 200 ml of hot water and stir to complete dissolution of the melt. Cool and transfer the solution quantitatively to a 1 00
28、0 ml one-mark volumetric flask. Dilute to the mark and mix thoroughly. Transfer immediately into a plastics bottle. 4.13 Silica, standard solution corresponding to 4 mg of SiO2 per litre. Pipette 10 ml of the standard silica solution (4.12) into a 1 000 ml one-mark volumetric flask, dilute to the ma
29、rk and mix thoroughly. Prepare this solution immediately before use. 4.14 Calibration blank solution Prepare a calibration blank solution by following the steps set out in 4.12 and 4.13, but omitting the silica. 4.15 Phenolphthalein, indicator solution. Dissolve 0,05 g of phenolphthalein in 50 ml of
30、 ethanol and dilute to 100 ml. 5 Apparatus Ordinary laboratory apparatus and scratch-free unetched glassware, and 5.1 Platinum crucible, of capacity approximately 30 ml, with lid. 5.2 One-mark pipettes, 5, 10, 15, 20 and 25 ml, class A. 5.3 Plastics beakers, of capacity approximately 150 ml. 5.4 Lab
31、oratory muffle furnace, capable of being maintained at 480 to 1 100 C, with provision for a flow of air through the heated cavity. 5.5 Zirconium crucible, of capacity approximately 40 ml. 5.6 pH-meter 5.7 Spectrophotometer, for measuring absorbance at about 810 nm. 5.8 Desiccator, containing phospho
32、rus(V) oxide as desiccant. 6 Sampling and preparation of samples Laboratory samples shall be taken and ground to, pass a 150 4m test sieve, in accordance with the methods specified in the relevant standards.1) 7 Procedure 7.1 Number of determinations Carry out the analysis in duplicate and independe
33、ntly on each ore sample. 1) Where no International Standards exist, the relevant standards shall be the national standards. Two International Standards on this subject are currently in preparation: ISO 6137, Aluminium ores Method of sampling, and ISO 6140, Aluminium ores Preparation of samples. Lice
34、nsed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:48:55 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6870-2.4:1987 BSI 01-20003 NOTEThe expression “independently” implies a change of the person carrying out the analysis. If the same person has to carry out the analysis, the procedure shall be c
35、arried out at different times. 7.2 Test portion Weigh, to the nearest 0,001 g, approximately 1 g of test sample and record the mass (m1). 7.3 Blank test In parallel with the decomposition of the test portion, prepare a blank test solution according to the method of decomposition, but with the omissi
36、on of the test portion. When the analysis is carried out on several samples at the same time, then the blank value may be represented by one test, provided that the procedure is the same and the reagents used are from the same bottles. 7.4 Check test In each run, one analysis of a certified referenc
37、e material of the same type of ore shall be carried out in parallel and under the same conditions with the analysis of one ore sample. NOTEThe certified reference material should be of the same type as the sample to be analysed. Such certified reference materials cannot, however, be considered as be
38、ing of the same type if the properties of the sample to be analysed differ from those of the certified reference material to such an extent that the analytical procedure must be changed substantially. 7.5 Gravimetric determination of silicon 7.5.1 Decomposition of the test portion If the decompositi
39、on is to be based on acid attack, proceed as specified in 7.5.1.1. If the decomposition is to be based on alkali sintering, proceed as specified in 7.5.1.2. 7.5.1.1 Acid decomposition Transfer the test portion (7.2) to a 400 ml beaker. Moisten with water and add, as a freshly prepared mixture, 60 ml
40、 of the acid mixture (4.8). Cover the beaker and heat at 80 C to decompose the sample. NOTEWith samples of high iron content 15 % (m/m) of Fe2O3, the initial heating should be conducted for an extended period. When the evolution of brown fumes ceases, carefully rinse the cover and wall of the beaker
41、. Evaporate the uncovered solution to dense fumes of sulfuric acid. Replace the cover and heat strongly for 60 min on a hot-plate set to produce in the solution a temperature of 210 10 C. NOTEDetermine the temperature setting by using a separate test beaker containing a partial-immersion thermometer
42、 in a 10 mm depth of sulfuric acid. 7.5.1.2 Alkali sinter decomposition Transfer the test portion (7.2) to the dry zirconium crucible (5.5), add 10 g of the sodium peroxide (4.1) and mix intimately using a dry metal spatula. Place the crucible and contents in the muffle furnace (5.4), maintained at
43、480 to 500 C, for 45 min. Remove the crucible and contents from the furnace and heat over a burner to melt the sinter (about 30 s). Continue heating the melt while swirling for a total time of 2 min. Allow the crucible to cool to room temperature (a metal block may be used to expedite this process)
44、and place it on its side in a 400 ml beaker. Cover and add cautiously at the rear of the crucible 140 ml of the sulfuric acid solution (4.6). Add 20 ml of the sulfuric acid solution (4.4) and digest to leach the contents of the crucible. Remove the crucible when the contents are completely leached a
45、nd rinse well into the solution in the beaker. Carefully rinse the cover and wall of the beaker. Evaporate the uncovered solution to dense fumes of sulfuric acid. Replace the cover and heat strongly for 60 min on a hot-plate set to produce in the solution a temperature of 210 10 C. 7.5.2 Dissolution
46、 and filtration Cool the solution from 7.5.1.1 or 7.5.1.2 to room temperature, cautiously add 130 ml of water and heat to 80 to 90 C for at least 40 min, with stirring, to completely dissolve the salts. Filter while hot through a medium-texture filter paper, collecting the filtrate in a 250 ml one-m
47、ark volumetric flask. Rinse the beaker with water, and using a rubber-tipped glass rod, clean the beaker and transfer the residue quantitatively to the paper. Wash the paper and residue five times with 5 to 10 ml of hot water. Reserve the filtrate and washings for use in 7.5.4. Retain the filter pap
48、er containing the impure silica and continue according to 7.5.3. NOTEWith high silica contents, it may be necessary to increase the volume of wash solution. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:48:55 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6870-2.4:1987 4 BSI 01-2000 7.5.3
49、 Treatment of impure silica Transfer the paper containing the impure silica to the pre-ignited tared platinum crucible (5.1). Dry and char slowly and then ash completely by increasing the temperature to 600 to 700 C. Cover the crucible and ignite in the muffle furnace (5.4), maintained at 1 075 25 C, for 30 min and allow to cool in air for 1 to 2 min. Place in the desiccator (5.8). Allow to cool to room temperature and weigh. NOTEThe time allowed for cooling should be approximately 10 min. Repeat the ignition, cooling and