1、BRITISH STANDARD BS 7020-5.2: 1993 ISO 2598-2: 1992 Analysis of iron ores Part 5: Methods for the determination of silicon content Section 5.2 Reduced molybdosilicate spectrophotometric method UDC 533.31:543.42:546.28BS 7020-5.2:1993 This British Standard, having been prepared under the directionof
2、the Iron and Steel Standards Policy Committee, waspublished under the authorityof the Standards Boardand comes into effect on 15 October1993 BSI 07-1999 The following BSI references relate to the work on this standard: Committee reference ISM/58 Draft for comment90/35107DC ISBN 0 580 22292 6 Committ
3、ees responsible for this British Standard The preparation of this British Standard was entrusted by the Iron and Steel Standards Policy Committee (ISM/-) to Technical Committee ISM/58, upon which the following bodies were represented: British Steel Industry Institution of Mining and Metallurgy Coopt
4、ed members The following body was also represented in the drafting of the standard, through subcommittees and panels: British Ceramic Research Ltd. Amendments issued since publication Amd. No. Date CommentsBS7020-5.2:1993 BSI 07-1999 i Contents Page Committees responsible Inside front cover National
5、 foreword ii 1 Scope 1 2 Normative references 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Sampling and samples 2 7 Procedure 2 8 Expression of results 3 9 Test report 4 Annex A (normative) Flowsheet of the procedure for the acceptance of analytical values for test samples 5 Annex B (informative) De
6、rivation of repeatability and permissible tolerance equations 6 Annex C (informative) Precision data obtained by international analytical trials 7 Figure C.1 Least-squares fit of precision againstX for silicon 7 Table 1 Aliquots 3 Table B.1 Silicon contents of test samples 6 List of references Insid
7、e back coverBS 7020-5.2:1993 ii BSI 07-1999 National foreword This Section of BS7020 has been prepared under the direction of the Iron and Steel Standards Policy Committee and is identical with ISO2598-2:1992 Iron ores Determination of silicon content Part2: Reduced molybdosilicate spectrophotometri
8、c method published by the International Organization for Standardization (ISO). The Technical Committee has reviewed the provisions of ISO648, to which normative reference is made in the text, and has decided that they are acceptable for use in conjunction with this standard. A related British Stand
9、ard to ISO648:1977 is BS1583:1986 Specification for one-mark pipettes. 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 imm
10、unity from legal obligations. Cross-references International standard Corresponding British Standard ISO1042:1983 BS1792:1982 Specification for one-mark volumetric flasks (Identical) BS5660 Methods of sampling iron ores ISO3081:1986 Part1:1987 Manual method of increment sampling (Identical) ISO3082:
11、1987 Part2:1987 Mechanical method of increment sampling and sample preparation (Identical) ISO3083:1986 BS5661:1987 Method for preparation of samples of iron ores by manual means (Identical) ISO7764:1985 BS7020 Analysis of iron ores Part1:1988 Method for the preparation of pre-dried test samples for
12、 chemical analysis (Identical) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to8, 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 a
13、mendment table on the inside front cover.BS7020-52:1993 BSI 07-1999 1 1 Scope This part of ISO2598 specifies a reduced molybdosilicate spectrophotometric method for the determination of the silicon content of iron ores. This method is applicable to silicon contents between0,1%(m/m) and5,0%(m/m) in n
14、atural iron ores, iron ore concentrates and agglomerates, including sinter products, especially for ores containing fluorine. The fluorine content of the sample does not affect the determination. 2 Normative references The following standards contain provisions which, through reference in this text,
15、 constitute provisions of this part of ISO2598. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO2598 are encouraged to investigate the possibility of applying the most recent editions of the stan
16、dards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 648:1977, Laboratory glassware One-mark pipettes. ISO 1042:1983, Laboratory glassware One-mark volumetric flasks. ISO 3081:1986, Iron ores Increment sampling Manual method. ISO 3082:1987,
17、 Iron ores Increment sampling and sample preparation Mechanical method. ISO 3083:1986, Iron ores Preparation of samples Manual method. ISO 7764:1985, Iron ores Preparation of predried test samples for chemical analysis. 3 Principle Decomposition of the test portion by fusion with sodium tetraborate
18、or a fusion mixture (carbonate and tetraborate) and treatment with dilute nitric acid. Addition of ammonium molybdate to convert the silicate into a molybdosilicate complex and reduction to molybdenum blue with ascorbic acid. Spectrophotometric measurement of the absorbance of the molybdenum blue co
19、mplex at a wavelength of approximately600nm. 4 Reagents During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. 4.1 Sodium tetraborate (Na 2 B 4 O 7 ), anhydrous. 4.2 Potassium nitrate (KNO 3 ). To be used as in note6 of7.4.1. 4.3
20、 Fusion mixture. Mix100g of anhydrous sodium carbonate (Na 2 CO 3 )/anhydrous potassium carbonate (K 2 CO 3 ) mixture(1+1) with30g of anhydrous sodium tetraborate(4.1) and0,5g of potassium nitrate(4.2). 4.4 Nitric acid, 1,4g/ml, diluted1+9. 4.5 Ammonium molybdate (NH 4 ) 6 Mo 7 O 24 .4H 2 O, solutio
21、n,120g/l. 4.6 Oxalic acid (C 2 H 2 O 4 .2H 2 O), solution,50 g/l. 4.7 Sulfuric acid, 1,84g/ml, diluted1+3. 4.8 Ascorbic acid (C 6 H 8 O 6 ), solution,20g/l. Prepare a fresh solution on the day of use. 4.9 Hydrogen peroxide, solution,3%(V/V). Prepare by1+9 dilution of hydrogen peroxide solution30%(V/
22、V). To be used as in note9 of7.4.1. 4.10 Silicon standard solution, 50 4g Si/ml. Calcine an appropriate quantity of silicon dioxide at1050C, cool, and weigh53,5mg 0,1mg into a platinum crucible. Add400mg of iron(III) oxide and4g of sodium tetraborate(4.1) or fusion mixture(4.3) and mix. Heat the mix
23、ture gently to a temperature of1100C (see7.4.1) until a clear melt is obtained. Cool and dissolve in200ml of nitric acid(4.4), transfer to a500ml one-mark volumetric flask, dilute to volume with water and mix. 4.11 Background solution. In parallel with the silicon standard solution(4.10), prepare a
24、background solution from4g of sodium tetraborate(4.1) or fusion mixture(4.3) and400mg of iron(III) oxide as described in4.10, but without adding silicon dioxide. 5 Apparatus Ordinary laboratory apparatus, including one-mark pipettes and one-mark volumetric flasks complying with the specifications of
25、 ISO648 and ISO1042 respectively, and 5.1 Platinum crucibles, of capacity30ml. 5.2 Muffle furnace, capable of maintaining a temperature of approximately1100C. 5.3 Spectrophotometer, suitable for measurement of absorbance at approximately600nm.BS7020-52:1993 2 BSI 07-1999 6 Sampling and samples 6.1 L
26、aboratory sample For analysis, use a laboratory sample of minus1004m particle size which has been taken in accordance with ISO3081 or ISO3082 and prepared in accordance with ISO3082 or ISO3083. In the case of ores having significant contents of combined water or oxidizable compounds, use a particle
27、size of minus1604m. NOTE 1A guideline on significant contents of combined water and oxidizable compounds is incorporated in ISO7764. 6.2 Preparation of predried test samples Thoroughly mix the laboratory sample and, taking multiple increments, extract a test sample in such a way that it is represent
28、ative of the whole contents of the container. Dry the test sample at105C 2 C, as specified in ISO7764. (This is the predried test sample.) 7 Procedure 7.1 Number of determinations Carry out the analysis at least in duplicate in accordance with Annex A, independently, on one predried test sample. NOT
29、E 2The expression “independently” means that the second and any subsequent result is not affected by the previous result(s). For this particular analytical method, this condition implies that the repetition of the procedure is carried out either by the same operator at a different time or by a diffe
30、rent operator including, in either case, appropriate recalibration. 7.2 Test portion Taking several increments, weigh, to the nearest0,0002g, approximately0,5g of the predried test sample obtained in accordance with6.2. NOTE 3The test portion should be taken and weighed quickly to avoid reabsorption
31、 of moisture. 7.3 Blank test and check test In each run, one blank test and one analysis of a certified reference material of the same type of ore shall be carried out in parallel with the analysis of the ore sample(s) under the same conditions. A predried test sample of the certified reference mate
32、rial shall be prepared as specified in6.2. NOTE 4The certified reference material should be of the same type as the sample to be analysed and the properties of the two materials should be sufficiently similar to ensure that in either case no significant changes in the analytical procedure will becom
33、e necessary. When the analysis is carried out on several samples at the same time, the blank value may be represented by one test, provided that the procedure is the same and that the reagents used are from the same reagent bottles. When the analysis is carried out on several samples of the same typ
34、e of ore at the same time, the analytical value of one certified reference material may be used. 7.4 Determination 7.4.1 Decomposition of the test portion Mix the test portion(7.2) with4g of sodium tetraborate(4.1) or fusion mixture(4.3) in a platinum crucible(5.1). (See notes5 and6.) Cover the plat
35、inum crucible and heat gently in a muffle furnace(5.2) up to a temperature of1100C. Maintain this temperature until the test portion is completely dissolved. (See note7.) Cool the platinum crucible (see note8), place it in a600ml glass beaker containing200ml of nitric acid(4.4), and dissolve the coo
36、led melt at a temperature below90C. (See note9.) Cool the solution, wash into a500 ml one-mark volumetric flask, dilute to volume with water and mix. (This is the test solution.) NOTE 5To minimize corrosive attack on the platinum crucible, it is recommended that2g of sodium tetraborate(4.1) or fusio
37、n mixture(4.3) be pre-melted in the crucible and swirled while cooling to cover the lower walls of the crucible. The remaining2g of sodium tetraborate or fusion mixture is mixed with the test portion on the surface of the cooled melt and then fused. NOTE 6When fusing with sodium tetraborate(4.1),0,1
38、g of potassium nitrate(4.2) should be added to samples containing reducing elements or sulfides, to accelerate the decomposition and to prevent any attack on the crucible. NOTE 7Swirling the melt during the heating period greatly helps dissolution of the test portion. In general,15 min will be suffi
39、cient; however, the fusion should be continued until the test portion is completely dissolved. NOTE 8To accelerate the subsequent dissolution of the cooled melt, it is recommended that the melt be gently swirled during cooling, to enable it to solidify as a thin uniform film on the inner wall of the
40、 crucible. Slight heating during the swirling may help this process. NOTE 9High manganese contents of the sample may cause cloudiness. In this case, add a few drops of hydrogen peroxide solution(4.9) and heat to boiling for the minimum time required to decompose the excess hydrogen peroxide. 7.4.2 P
41、reparation of the blank test solution In parallel with the fusion of the test portion, make a second fusion using all the reagents and following the procedure described in7.4.1, but omitting the test portion. Dissolve the cooled melt, treat it in the same way as the test solution, dilute it in a vol
42、umetric flask to500ml with water and mix. 7.4.3 Spectrophotometric determination Transfer5,0ml of the test solution to a100ml volumetric flask. Add2ml of nitric acid(4.4) and5,0ml of ammonium molybdate solution(4.5). Mix the solution thoroughly and allow to stand for5min.BS7020-52:1993 BSI 07-1999 3
43、 Add the following reagents, in quick succession, shaking well after each addition:10,0ml of oxalic acid solution(4.6),5,0ml of sulfuric acid(4.7) and5,0ml of ascorbic acid solution(4.8). The maximum time allowed for the complete addition shall not exceed3 min. After the final thorough mixing, allow
44、 the solution to stand for1min, dilute to volume with water and mix. After a further5 min, measure, in cells of10mm optical pathlength, the absorbances of the test solution and the blank test solution, against water as a reference. The portion of the absorption curve suitable for measurement is loca
45、ted at approximately600nm. Correct the absorbance of the test solution with the absorbance of the blank test solution. NOTE 10As an indication of the sensitivity of the method, the following information is provided: 0,250mg Si/100ml determined with a mercury vapour lamp and an Hg578 filter results i
46、n an absorbance of0,55 for an optical pathlength of1cm. 7.5 Calibration To plot the calibration graph, measure aliquots of the silicon standard solution(4.10) and make up to5,0ml with appropriate quantities of the background solution(4.11) in accordance with Table 1. NOTE 11During the preparation of
47、 the test solution and calibration solutions, the same fusion reagents should be used. Table 1 Aliquots Treat these solutions as indicated in7.4.3, correcting the absorbances with the absorbance obtained for the zero calibration solution. Plot the absorbance calculated for an optical pathlength of1c
48、m on the abscissa, against the known mass of silicon on the ordinate. Use the slope Z of the graph to calculate the silicon content as a percentage by mass. 8 Expression of results 8.1 Calculation of silicon content The silicon content, w Si , as a percentage by mass, is calculated to four decimal p
49、laces, using the equation 8.2 General treatment of result 8.2.1 Repeatability and permissible tolerance The precision of this analytical method is expressed by the following regression equations 1) : Silicon standard solution (4.10) ml Background solution (4.11) ml Mass of Si in 5 ml aliquot mg Content of Si in 0,50g sample % (m/m) 0,00 0,10 0,20 0,50 1,00 3,00 5,00 5,0 4,9 4,8 4,5 4,0 2,0 0,0 0,00 0,0050 0,010 0,025 0,050 0,150 0,25 0,0 0,10 0,20 0,50 1,00 3,00 5,00 . (1) where A is the absorbance of the test solution, corrected w
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