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 553.492:543BS6870-2.4:1987 This British Standard, having been prepared under the directionof the Non-ferrous Metals Standards Committee,waspublished underthe authority of the BoardofBSI and comes into effect on 28August1987 BSI 01-2000 The following BSI references relate
3、 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 issue CommentsBS6870-2.4:1987 BSI 01-2000 i Contents Page National foreword ii 1 Scope and field of application 1 2 References 1 3 Principle
4、 1 4 Reagents 1 5 Apparatus 2 6 Sampling and preparation of samples 2 7 Procedure 2 8 Expression of results 5 9 Test report 6 Table 1 Calibration solutions 5 Table 2 Precision data for silicon determinations 6 Publications referred to Inside back coverBS6870-2.4:1987 ii BSI 01-2000 National foreword
5、 This Section of BS6870 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 Organization for
6、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 drawn especi
7、ally 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 BS6870”. Addit
8、ional information. When adopting the text of the International Standard, it was noticed that in4.8 hydrochloric acid with a density of1.17 g/ml is specified, whereas in the UK hydrochloric acid with a density of1.18 g/ml is normally used. This difference, which will not affect the determination, has
9、 been brought to the attention ofISO 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 are responsible
10、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 6995:1985 BS 6870 Analysis of aluminium ores Section 2.7:1987 Method for determination of titanium c
11、ontent: spectrophotometric method (Identical) ISO 5725:1986 BS 5497 Precision of test methods Part 1:1987 Guide for the determination of repeatability andreproducibility for a standard test method by inter-laboratory tests (Identical) Summary of pages This document comprises a front cover, an inside
12、 front cover, pages i and ii, pages1 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.BS6870-2.4:1987 BSI 01-2000 1 1 Scope and field of a
13、pplication This International Standard specifies a combined gravimetric method and spectrophotometric method for the determination of the total silicon content in aluminium ores. The method is applicable to ores containing between1 and25% (m/m) of silicon dioxide. 2 References ISO 5725, Precision of
14、 test methods Determination of repeatability and reproducibility by intra-laboratory tests. ISO 6995, Aluminium ores Determination of titanium content 4,4-Diantipyrylmethane spectrophotometric method. 3 Principle Decomposition of the test portion by either a) Treatment with a mixture of hydrochloric
15、 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 portion after silica volatilization is less than1% of the mass of the test portion; or b) Sintering with sodium peroxide followed by
16、 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 for acid decomposition is greater than1% of the mass of the test portion. or c) The fusion method given in 3 c) and sub-clause 7.
17、5.1.3 of ISO6995. Dehydration of silica, dissolution of salts, filtration and ignition of the impure silica, treatment with hydrofluoric acid and sulfuric acid. Fusion of the residue with sodium carbonate/sodium tetraborate flux, dissolution of the melt with sulfuric acid and addition to the main so
18、lution. Treatment of an aliquot portion of the main solution with excess sodium hydroxide and heating to depolymerize the silica in solution. Acidification with sulfuric acid and adjustment to pH1,40, followed by addition of ammonium molybdate. Destruction of molybdophosphoric and molybdoarsenic aci
19、ds with further sulfuric acid, reduction of the -molybdosilicic acid to the blue complex and measurement of the absorbance at about810nm. 4 Reagents During the analysis, use only reagents of analytical reagent grade and only distilled water or water of equivalent purity. 4.1 Sodium peroxide NOTESodi
20、um peroxide should be protected against humidity and should not be used once it has begun to agglomerate. 4.2 Sodium carbonate/sodium tetraborate flux Mix3 parts by mass of anhydrous sodium carbonate and1 part by mass of anhydrous sodium tetraborate flux. 4.3 Hydrofluoric acid, 40% (m/m), 20= 1,13g/
21、ml. 4.4 Sulfuric acid, 20= 1,84 g/ml, diluted1+1. 4.5 Sulfuric acid, 20= 1,84 g/ml, diluted1+3. 4.6 Sulfuric acid, 20= 1,84 g/ml, diluted1+9. 4.7 Sulfuric acid, 20= 1,84 g/ml, diluted1+39. 4.8 Acid mixture Measure into a one-litre beaker225ml of water and add cautiously, with mixing,175ml of sulfuri
22、c acid ( 201,84g/ml). Cool to room temperature and add150ml of hydrochloric acid ( 20 1,17g/ml) and50ml of nitric acid ( 20 1,42g/ml). Mix. Prepare this solution fresh for each series of determinations and discard any unused solution. 4.9 Ascorbic acid, 50g/l solution. Dissolve5g of ascorbic acid in
23、100ml of water.BS6870-2.4:1987 2 BSI 01-2000 Prepare this solution daily. 4.10 Ammonium molybdate, 100g/l solution. Dissolve100g of ammonium molybdate tetrahydrate (NH 4 ) 6 Mo 7 O 24 4H 2 O in1 litre of water. Discard the solution when precipitation has commenced. 4.11 Sodium hydroxide, 160g/l solu
24、tion. Dissolve160g of sodium hydroxide in1litre of water in a plastics beaker. Store in a plastics bottle. 4.12 Silica, standard solution corresponding to 400mg of SiO 2per litre. Ignite pure silica at 1000 C for1h and cool in a desiccator. Weigh, to the nearest0,001g, 0,400g of the ignited silica i
25、nto a platinum crucible. Add4,0g of anhydrous sodium carbonate, mix thoroughly using a metal spatula and fuse carefully for10min at 1000 C. Cool and transfer to a400ml plastics beaker. Add200ml of hot water and stir to complete dissolution of the melt. Cool and transfer the solution quantitatively t
26、o a1000 ml one-mark volumetric flask. Dilute to the mark and mix thoroughly. Transfer immediately into a plastics bottle. 4.13 Silica, standard solution corresponding to4mg ofSiO 2per litre. Pipette10ml of the standard silica solution (4.12) into a1000 ml one-mark volumetric flask, dilute to the mar
27、k 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 in4.12 and4.13, but omitting the silica. 4.15 Phenolphthalein, indicator solution. Dissolve0,05g of phenolphthalein in50ml of ethano
28、l and dilute to100ml. 5 Apparatus Ordinary laboratory apparatus and scratch-free unetched glassware, and 5.1 Platinum crucible, of capacity approximately 30ml, with lid. 5.2 One-mark pipettes, 5,10,15,20and25ml, class A. 5.3 Plastics beakers, of capacity approximately150ml. 5.4 Laboratory muffle fur
29、nace, capable of being maintained at480 to1100 C, with provision for a flow of air through the heated cavity. 5.5 Zirconium crucible, of capacity approximately 40ml. 5.6 pH-meter 5.7 Spectrophotometer, for measuring absorbance at about810nm. 5.8 Desiccator, containing phosphorus(V) oxide as desiccan
30、t. 6 Sampling and preparation of samples Laboratory samples shall be taken and ground to, pass a1504m 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 independently on each ore sample.
31、1) Where no International Standards exist, the relevant standards shall be the national standards. Two International Standards on this subject are currently in preparation: ISO6137, Aluminium ores Method of sampling, and ISO6140, Aluminium ores Preparation of samples.BS6870-2.4:1987 BSI 01-2000 3 NO
32、TEThe 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 carried out at different times. 7.2 Test portion Weigh, to the nearest0,001g, approximately1g of test sample and record the mass (m 1 ).
33、 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 omission 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
34、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 reference 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. NO
35、TEThe certified reference material should be of the same type as the sample to be analysed. Such certified reference materials cannot, however, be considered as being of the same type if the properties of the sample to be analysed differ from those of the certified reference material to such an exte
36、nt that the analytical procedure must be changed substantially. 7.5 Gravimetric determination of silicon 7.5.1 Decomposition of the test portion If the decomposition is to be based on acid attack, proceed as specified in7.5.1.1. If the decomposition is to be based on alkali sintering, proceed as spe
37、cified in7.5.1.2. 7.5.1.1 Acid decomposition Transfer the test portion (7.2) to a400ml beaker. Moisten with water and add, as a freshly prepared mixture,60ml of the acid mixture (4.8). Cover the beaker and heat at80 C to decompose the sample. NOTEWith samples of high iron content 15% (m/m) of Fe 2 O
38、 3 , 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. Evaporate the uncovered solution to dense fumes of sulfuric acid. Replace the cover and heat strongly for 60min on a hot-plate set to produ
39、ce in the solution a temperature of210 10 C. NOTEDetermine the temperature setting by using a separate test beaker containing a partial-immersion thermometer in a10mm depth of sulfuric acid. 7.5.1.2 Alkali sinter decomposition Transfer the test portion (7.2) to the dry zirconium crucible (5.5), add1
40、0g 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 at480to500 C, for45min. Remove the crucible and contents from the furnace and heat over a burner to melt the sinter (about30s). Continue heating the m
41、elt while swirling for a total time of2min. Allow the crucible to cool to room temperature (ametal block may be used to expedite this process) and place it on its side in a 400ml beaker. Cover and add cautiously at the rear of the crucible 140ml of the sulfuric acid solution (4.6). Add20ml of the su
42、lfuric acid solution (4.4) and digest to leach the contents of the crucible. Remove the crucible when the contents are completely leached and 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
43、. Replace the cover and heat strongly for60min on a hot-plate set to produce in the solution a temperature of210 10 C. 7.5.2 Dissolution and filtration Cool the solution from7.5.1.1 or7.5.1.2 to room temperature, cautiously add130ml of water and heat to80to90 C for at least 40min, with stirring, to
44、completely dissolve the salts. Filter while hot through a medium-texture filter paper, collecting the filtrate in a250ml one-mark 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
45、and residue five times with5 to10ml of hot water. Reserve the filtrate and washings for use in7.5.4. Retain the filter paper containing the impure silica and continue according to7.5.3. NOTEWith high silica contents, it may be necessary to increase the volume of wash solution.BS6870-2.4:1987 4 BSI 0
46、1-2000 7.5.3 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 to600 to700 C. Cover the crucible and ignite in the muffle furnace (5.4), maintained at1
47、075 25 C, for30min and allow to cool in air for1to2min. Place in the desiccator (5.8). Allow to cool to room temperature and weigh. NOTEThe time allowed for cooling should be approximately10min. Repeat the ignition, cooling and weighing steps until the mass is constant to within0,0005g. Record the m
48、ass of the crucible and content (m 2 ). Add water, drop by drop, to the residue in the crucible until it is completely wetted. Add8 drops of the sulfuric acid solution (4.4) followed by5ml of the hydrofluoric acid (4.3). Heat cautiously and evaporate until dense white fumes cease to be evolved. Heat
49、 gently over a low flame then cover the crucible and ignite in the muffle furnace (5.4), maintained at1075 25 C, for15 2min. Allow to cool in air for1to2min. Place in the desiccator. Allow to cool to room temperature and weigh. Repeat the acid treatment, fuming and ignition steps until the mass is constant to within0,0005g. Record the mass of the crucible and contents (m 3 ). NOTEIf the mass remains constant at a value greater than0,01g more than the mass of the crucible when the acid decomposition procedure is used,
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