1、BRITISH STANDARD BS 5072-6: 1980 ISO 3430:1976 Methods of Test for sodium fluoride for industrial use Part 6: Determination of silica content ISO title: Sodium fluoride primarily used for the production of aluminium Determination of silica content Reduced molybdosilicate spectrophotometric method UD
2、C 661.833.361:546.33161:543.42.062:546.284-31BS5072-6:1980 This British Standard, having been prepared under the directionof the Chemicals Standards Committee, was published under the authority ofthe Executive Board and comesinto effect on 30 April1980 BSI 12-1999 The following BSI references relate
3、 to the work on this standard: Committee reference CIC/24 Draft for comment 74/54500 DC ISBN 0 580 11217 9 Cooperating organizations The Chemicals Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following Government departments and
4、scientific and industrial organizations: Association of Fatty Acid Distillers British Tar Industry Association Chemical Industries Association* Chemical Society, Analytical Division* Consumer Standards Advisory Committee of BSI Department of Health and Social Security Department of Industry (Laborat
5、ory of the Government Chemist) Fertiliser Manufacturers Association Ltd Hydrocarbon Solvents Association Ministry of Agriculture, Fisheries and Food Ministry of Defence National Sulphuric Acid Association Paintmakers Association of Great Britain Ltd Royal Institute of Public Health and Hygiene Soap
6、and Detergent Industry Association Standardization of Tar Products Tests Committee The organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: Aluminium Federation Britis
7、h Ceramic Research Association Royal Institute of Chemistry Amendments issued since publication Amd. No. Date of issue CommentsBS5072-6:1980 BSI 12-1999 i Contents Page Cooperating organizations Inside front cover National foreword ii 1 Scope and field of application 1 2 Reference 1 3 Principle 1 4
8、Reagents 1 5 Apparatus 2 6 Procedure 2 7 Expression of results 4 8 Test report 4 Annex ISO Publications relating to sodium fluoride for industrial use and sodium fluoride primarily used for the production ofaluminium 5 Publications referred to Inside back coverBS5072-6:1980 ii BSI 12-1999 National f
9、oreword WARNING NOTE. Sodium fluoride is toxic and is irritant, particularly in the form of dust. Carry out operations involving its use in a fume cupboard and wear suitable protective clothing to prevent inhalation of the dust and contact with the eyes, skin and clothing. This British Standard has
10、been prepared under the direction of the Chemicals Standards Committee in order to provide methods for the analysis of sodium fluoride for industrial use. For some years the UnitedKingdom has participated in the work of preparing methods of test applicable to this material, organized by Subcommittee
11、7 (formerly WG8), Aluminium oxide and related compounds, of Technical Committee47, Chemistry, of the International Organization for Standardization (ISO). As international agreement is reached on the methods, it is proposed to publish them as Parts of this British Standard. This Part is identical wi
12、th ISO3430 “Sodium fluoride primarily used for the production of aluminium Determination of silica content Reduced molybdosilicate spectrophotometric method”. Terminology and conventions. The text of the International Standard has been approved as suitable for publication, without deviation, as a Br
13、itish Standard. Some terminology and certain conventions are not identical with those used in British Standards; attention is especially drawn to the following. The comma has been used throughout as a decimal marker. In British Standards, it is current practice to use a full point on the baseline as
14、 the decimal marker. Where the words “International Standard” appear, referring to this standard, they should be read as “British Standard”. Related British Standards for ISO2831 1) , ISO 2832 1)and ISO 2833 1)are BS5072-1, BS5072-2 and BS5072-3 respectively. NOTEThe title and clause1 of ISO3429, IS
15、O3430, ISO3431, ISO3566 and ISO4278 (seetheAnnex) state that the sodium fluoride is “primarily used for the production of aluminium”. This is incorrect, at least for the UnitedKingdom. This has been brought to the attention of ISO Technical Committee 47, in a proposal to amend the International Stan
16、dards concerned. Additional information Water. Water complying with the requirements of clause 4 is specified in BS3978“Water for laboratory use”. Cross-references International Standard Corresponding British Standard ISO 3428:1976 BS 5072 Methods of test for sodium fluoride for industrial use Part
17、4:1980 Preparation and storage of test samples (Identical) ISO 3429:1976 1) Part 5:1980 Determination of iron content (Identical) ISO 3431:1976 1) Part 7:1980 Determination of soluble sulphates content (Identical) ISO 3566:1976 1) Part 8:1980 Determination of chlorides content (Identical) ISO 4278:1
18、977 1) Part 9:1980 Determination of carbonate content (Identical) 1) Referred to in theAnnex, for information only.BS5072-6:1980 BSI 12-1999 iii Nitric acid, approximately 1.42g/ml, about70% (m/m) solution, which is the corresponding reagent normally obtainable in the UnitedKingdom, is suitable for
19、use in place of the approximately1.40g/ml solution specified in4.3. This standard prescribes methods of test only, and should not be used or quoted as a specification defining limits of purity. Reference to the standard should indicate that the methods of test used comply with the requirements of BS
20、5072-6. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document co
21、mprises a front cover, an inside front cover, pagesi toiv, pages1to6, 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.iv blankBS5072-6:1980 BSI
22、 12-1999 1 1 Scope and field of application This International Standard specifies a spectrophotometric method, using the reduced molybdosilicate, for determining the silica content of sodium fluoride primarily used for the production of aluminium. The method is applicable to products of which the P
23、2 O 5content does not exceed0,02% (m/m). 2 Reference ISO 3428, Sodium fluoride for industrial use Preparation and storage of test samples. 3 Principle Alkaline fusion of a test portion by means of a mixture of sodium carbonate and boric acid. Solution of the fused mass in excess nitric acid so that
24、the pH of the final solution is between0,3 and0,5 after being diluted to250ml. Formation, in a suitable aliquot portion, of the oxidized molybdosilicate (yellow) under well-defined conditions of acidity, concentration of reagents, temperature and time. Selective reduction of the complex in a high ac
25、idity sulphuric medium and in the presence of tartaric acid to eliminate interference from phosphorus. Disturbing influence of fluorine is eliminated by the presence of boric acid. Spectrophotometric measurement of the coloured complex at a wavelength of maximum absorption (about815nm). 4 Reagents D
26、uring the analysis, use only reagents of recognized analytical grade, and only redistilled water. 4.1 Sodium carbonate, anhydrous. 4.2 Boric acid (H 3 BO 3 ) 4.3 Nitric acid, approximately8N solution. Dilute 540ml of nitric acid solution, approximately 1,40g/ml, about68% (m/m) solution, with water t
27、o1000ml and mix. 4.4 Sodium molybdate, 195g/l (0,8M approximately) solution. Dissolve, in a beaker made of material free from silica, 19,5g of sodium molybdate dihydrate (Na 2 MoO 4 .2H 2 O) in hot water and, after cooling, dilute to100ml and mix. Transfer the solution to a bottle made of material f
28、ree from silica and, if necessary, filter before use. 4.5 Tartaric acid, 100g/l solution. Dissolve 10 g of tartaric acid in water, dilute to100ml and mix. Store the solution in a bottle made of material free from silica. 4.6 Sulphuric acid, approximately 16 N solution. Carefully add 450ml of sulphur
29、ic acid, approximately 1,84g/ml, about96% (m/m) solution, to about500ml of water. Cool, dilute to1000ml and mix. 4.7 Reducing solution Either of the following solutions may be used: 4.7.1 4-amino- 3-hydroxynaphthalene- 1-sulphonic acid, 1,5g/l solution. a) Dissolve 7 g of anhydrous sodium sulphite (
30、Na 2 SO 3 ) in 50ml of water. Add 1,5g of 4-amino- 3-hydroxy-naphthalene- 1-sulphonic acid (C 10 H 9 NO 4 S); b) Dissolve 90 g of sodium disulphite (Na 2 S 2 O 5 ) in900ml of water. Mix the two solutions a) and b), dilute to 1000ml and mix. Filter if necessary and store in an amber-coloured bottle m
31、ade of material free from silica, in a cool place. 4.7.2 Ascorbic acid, 20 g/l solution. Dissolve 2g of ascorbic acid in water, dilute to100ml and mix. Store the solution in a bottle made of material free from silica and protect it from light. Prepare this solution at the time of use. 4.8 Silica sta
32、ndard solution, corresponding to0,500g of SiO 2per litre. Into a platinum crucible, weigh, to the nearest0,001g: either 0,500g of SiO 2obtained from pure silicic acid (H 2 SiO 3 ), heated to constant mass at1000 C (i.e. until two consecutive weighings do not differ by more than1mg) and cooled in a d
33、esiccator; or 0,500g of finely ground pure quartz, previously heated at1000 C for1h and cooled in a desiccator. Add to the crucible5g of the sodium carbonate (4.1). Mix thoroughly using a platinum spatula, and fuse carefully until a clear, transparent melt is obtained.BS5072-6:1980 2 BSI 12-1999 All
34、ow to cool, add hot water to the crucible, heat gently to complete the dissolution and transfer the solution quantitatively into a beaker made of material free from silica. Cool, dilute to about500ml and transfer quantitatively to a1000ml one-mark volumetric flask, dilute to the mark and mix. Transf
35、er immediately to a bottle made of material free from silica. 1 ml of this standard solution contains 0,500 mg of SiO 2 . 4.9 Silica, standard solution, corresponding to0,020g of SiO 2per litre. Take 40,0ml of the standard silica solution (4.8), place in a1000ml one-mark volumetric flask, dilute to
36、the mark and mix. 1 ml of this standard solution contains0,020mg ofSiO 2 . Prepare this solution at the time of use. 4.10 Silica, standard solution, corresponding to0,005g of SiO 2per litre. Take 50,0 ml of the standard silica solution (4.9), place in a200ml one-mark volumetric flask, dilute to the
37、mark and mix. 1 ml of this standard solution contains 0,005mg of SiO 2 . Prepare this solution at the time of use. 5 Apparatus Glassware shall be carefully washed, taking the necessary precautions, with chromic-sulphuric acid, thoroughly rinsed with water and finally with redistilled water. Do not d
38、ry either in an oven or by means of compressed air. For alkaline solutions, use only vessels made of material free from silica. Ordinary laboratory apparatus and 5.1 Platinum dish, with a flat bottom, diameter approximately70mm, height approximately35mm, fitted with a platinum lid. 5.2 Electric furn
39、ace, capable of being controlled at550 25 C. 5.3 Electric furnace, capable of being controlled at750 25 C. 5.4 pH meter, fitted with a glass measuring electrode and a calomel reference electrode, sensitivity0,05pH unit. 5.5 Spectrophotometer 6 Procedure 6.1 Test portion Weigh, to the nearest 0,001g,
40、 1g of the dried test sample (see ISO3428, sub-clause2.3). 6.2 Preparation of calibration graph 6.2.1 Preparation of the base solution Into the platinum dish (5.1), weigh 24 g of the sodium carbonate (4.1) 8 g of the boric acid (4.2) and mix carefully, using a platinum spatula. Cover the dish with i
41、ts lid and place it in the electric furnace (5.2) controlled at550 25 C, until the reaction has ceased, taking care to isolate the dish from the floor of the furnace, using a support that does not involve the risk of introducing impurities (platinum support for preference). Then transfer the dish to
42、 the electric furnace (5.3) controlled at750 25 C, isolating it, as before, from the floor of the furnace. Do not allow the dish to stay in this furnace for more than5min. Remove the dish from the furnace and allow to cool in air. Add boiling water to the dish and heat gently to complete dissolution
43、. After cooling slightly, transfer slowly the contents of the dish to a beaker made of material free from silica, of suitable capacity, containing40ml of the nitric acid solution (4.3). Carefully wash the dish and lid with36ml of the nitric acid solution, then successively with hot water, collecting
44、 the washings in the same beaker; heat gently for a few minutes at a temperature near to the boiling point. Cool somewhat and transfer quantitatively to a200ml one-mark volumetric flask. After cooling dilute to the mark and mix. Transfer the solution immediately to a bottle made of material free fro
45、m silica. 6.2.2 Preliminary test for the control and adjustment of pH Transfer 20,0 ml of the base solution (6.2.1) to a beaker of suitable capacity. Add to the beaker 15ml of water, 15ml of the standard silica solution (4.10), 5ml of the sodium molybdate solution (4.4), mix and check the pH value w
46、ith the pH meter (5.4). This value should be between0,85 and0,90, but if not, adjust the pH byslowly adding, drop by drop, the nitric acid solution (4.3) by means of a graduated pipette or burette, mixing after each drop. Dilute, if necessary, so that the final volume of the solution, after the intr
47、oduction of the nitric acid solution, is approximately 65ml and check that the pH value is between0,85 and0,90. Note the volume of nitric acid solution (4.3) used to correct the pH and discard the preliminary test solution.BS5072-6:1980 BSI 12-1999 3 6.2.3 Preparation of the standard colorimetric so
48、lutions, for spectrophotometric measurements carried out with cells of1cm optical path length. Into each of a series of six 100ml beakers made of material free from silica, place 20ml of the base solution (6.2.1) and then add the quantity of the nitric acid solution (4.3) used to correct the pH in t
49、he preliminary test (6.2.2). Then add the volumes of the standard silica solution(4.10) shown in the following table: Then dilute the solution in each beaker to approximately60ml. 6.2.4 Colour development To each beaker add 5 ml of the sodium molybdate solution (4.4), mix and allow to stand for between15 and25min at20 to25 C. Then add5ml of the tartaric acid solution (4.5), 11ml of the sulphuric acid solution (4.6) and finally2ml of the reducing solution (4.7.1 or4.7.2) and mix. Transfer the solution quantitatively to a series of100ml one
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