1、BRITISH STANDARD BS 6870-2.5: 1987 ISO 6609:1985 Analysis of aluminium ores Part 2: Chemical methods Section 2.5 Method for determination ofiron content: titrimetric method ISO title: Aluminium ores Determination of iron content Titrimetric method UDC 553.492:543BS 6870-2.5:1987 This British Standar
2、d, having been prepared under the directionof the Non-ferrous Metals Standards Committee, waspublished under the authorityof the Board of BSI andcomes into effect on 28August1987 BSI 01-2000 The following BSI references relate to the work on this standard: Committee reference NFM/31 Draft for commen
3、t 83/76594 DC ISBN 0 580 16057 2 National foreword This Section of BS6870 has been prepared under the direction of the Non-ferrous Metals Standards Committee. It is identical with ISO6609:1985 “Aluminium ores Determination of iron content Titrimetric method”, published by the International Organizat
4、ion 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 draw
5、n 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 BS6870
6、”. Additional information. Attention is drawn to the toxic nature of reagent4.6, mercury (II) chloride solution, and the need to ensure the safe disposal of all test solutions containing mercury after use. When adopting the text of the International Standard, it was noticed that in4.2 hydrochloric a
7、cid with a density of1.17g/ml is specified, whereas in theUK hydrochloric acid with a density of1.18g/ml is normally used. This difference, which will not affect the determination, has been brought to the attention of ISO in a proposal to amend the International Standard by specifying a wider range
8、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 for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obl
9、igations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to4, 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
10、 inside front cover. Cross-reference International Standard Corresponding British Standard ISO 5725:1986 BS 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) Amendments issued s
11、ince publication Amd. No. Date of issue CommentsBS6870-2.5:1987 BSI 01-2000 i Contents Page National foreword Inside front cover 1 Scope and field of application 1 2 Reference 1 3 Principle 1 4 Reagents 1 5 Apparatus 2 6 Sampling and preparation of samples 2 7 Procedure 2 8 Expression of results 3 9
12、 Test report 3 Table Precision data for iron determination 3 Publication referred to Inside back coverii blankBS6870-2.5:1987 BSI 01-2000 1 1 Scope and field of application This International Standard specifies a titrimetric method for the determination of iron in aluminium ores. The method has been
13、 chosen to avoid interference from platinum which may occur with the use of platinum crucibles in the acid decomposition procedure. The method is suitable for use with ores having iron oxide contents between2 and50% (m/m). 2 Reference ISO 5725, Precision of test methods Determination of repeatabilit
14、y and reproducibility by inter-laboratory tests. 3 Principle Decomposition of the test portion by sintering with sodium peroxide followed by a brief fusion. Dissolution of the fusion mixture with water and hydrochloric acid. Determination of iron by titration with potassium dichromate after reductio
15、n with tin(II) chloride, and oxidation of excess reductant with mercury(II) chloride. 4 Reagents During the analysis, use only reagents of recognized analytical reagent grade and only distilled water or water of equivalent purity. 4.1 Sodium peroxide NOTESodium peroxide should be protected against h
16、umidity and should not be used once it has begun to agglomerate. 4.2 Hydrochloric acid, 20=1,17g/ml. 4.3 Sulfuric acid, 20=1,84g/ml, diluted1+19. 4.4 Sulfuric acid-phosphoric acid mixture Cautiously pour150ml of sulfuric acid ( 20=1,84g/ml) into about300ml of water while stirring. Cool in a water ba
17、th, add150ml ofphosphoric acid ( 20=1,70g/ml) and dilute to1 litre. 4.5 Tin(II) chloride, 100 g/l solution. Place 20 ml of the hydrochloric acid (4.2) into a100ml beaker and add10g of crystalline tin(II) chloride (SnCl 2 2H 2 O). Heat gently while stirring until the solution is clear. Cool the solut
18、ion rapidly and dilute to100ml. Store this solution in a brown glass bottle with the addition of a small quantity of granular tin metal. 4.6 Mercury(II) chloride, 40 g/l solution. Dissolve40g mercury(II) chloride in water and dilute to1 litre. 4.7 Ammonium iron(III) sulfate, standard volumetric solu
19、tion. 4.7.1 Preparation of the solution Dissolve 47,5 g of ammonium iron(III) sulfate 24 water Fe 2 (NH 4 ) 2 (SO 4 ) 4 24H 2 O in the sulfuric acid solution (4.3). Transfer to a1000ml one-mark volumetric flask and dilute to the mark with the same acid. 4.7.2 Standardization of the solution Pipette1
20、0ml of the ammonium iron(III) sulfate solution (4.7.1) into a400ml beaker and dilute toabout80ml. Add10ml of the hydrochloric acid(4.2). Boil gently and add the tin(II) chloride solution (4.5), drop by drop, whilst stirring the solution, until the yellow colour disappears. Add1 to3 drops of excess.
21、Cool rapidly in a water bath. Add, all at once,10ml of the mercury(II) chloride solution (4.6), mix gently and allow to stand for5min. Dilute to approximately 150ml. Add30ml of the sulfuric acid-phosphoric acid mixture (4.4) and5 drops of the indicator (4.9), then titrate with the standard potassium
22、 dichromate solution (4.8) to a permanent violet end-point (30s). Record the volume of potassium dichromate solution used (V 1 ). NOTEIn the absence of iron the diphenylaminesulphonate indicator does not react with the dichromate solution. The addition of ammonium iron(III) sulfate solution is there
23、fore necessary to promote indicator response in the blank solution, and thus allow a suitable correction for the blank. 4.8 Potassium dichromate, standard solution, c(K 2 Cr 2 O 7 ) =0,01667mol/l. Dry about 6 g of finely powdered potassium dichromate in an air oven at140 to150 C for30 to60min. Cool
24、in a closed vessel. Weigh4,904g, dissolve in water, and dilute to the mark in a1000ml one-mark volumetric flask. 1 ml of 0,016 67 mol/l K 2 Cr 2 O 7 0,005585g ofFe 1 ml of 0,016 67 mol/l K 2 Cr 2 O 7 0,007985g ofFe 2 O 3 4.9 Barium diphenylaminesulfonate solution. Dissolve0,2g of barium diphenylamin
25、esulfonate (C 6 H 5 NHC 6 H 4 SO 3 ) 2 Ba in a small volume of hot water and dilute to100ml. Store in a cool, dark place. Discard when discoloured.BS 6870-2.5:1987 2 BSI 01-2000 5 Apparatus Ordinary laboratory apparatus, and 5.1 Microburette,10ml, class A. 5.2 Zirconium crucibles,40 to50 ml capacity
26、. 5.3 Balance, capable of being read to0,0001g. 5.4 Desiccator, containing phosphorus(V) oxide as desiccant. 5.5 Burette,50 ml, class A. 5.6 Muffle furnace, capable of being maintained at480 to500 C. 6 Sampling and preparation of samples Laboratory samples shall be taken and ground to pass a1504m te
27、st 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. NOTEThe expression “independently” implies a change of the person carrying out the analysis. If the same
28、 person has to carry out the analysis, the procedure shall be carried out at different times. 7.2 Test portion Weigh, to the nearest0,0001g, approximately0,40g of test sample into a zirconium crucible and record the mass (m 1 ). 7.3 Blank test In parallel with the decomposition of the test portion,
29、prepare a blank test solution according to the method of decomposition, but omitting the test portion. 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 the reagents used are from the same
30、 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. NOTEThe certified reference material should be of the same type as the sample to be analyse
31、d. 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 extent that the analytical procedure must be changed substantially. 7.5 Determination 7.5.1 D
32、ecomposition of the test portion To the test portion taken in(7.2), add5 0,1g of the sodium peroxide(4.1). Mix using a nickel spatula. Place the crucible and contents in the muffle furnace(5.6), maintained at480 to500 C for45min. Remove the crucible and contents from the furnace and heat over a burn
33、er to melt the sinter (about30s). Continue heating the melt while swirling for a total time of2min. Allow the crucible to cool to room temperature (ametal block can be used to expedite this process), and place the crucible on its side in a400ml beaker. Carefully add50ml of water and cover the beaker
34、 immediately with a watch glass. When reaction ceases add30ml of the hydrochloric acid(4.2) and cover with a watch glass until the reaction subsides. Rinse down the cover and wall of the beaker with water. 7.5.2 Determination of iron oxide Remove the crucible and rinse well with water,keeping the to
35、tal volume in the beaker to lessthan100ml. Ensure that all iron hydroxides havedissolved. Heat if necessary. Add1ml of the ammonium iron(III) sulfate solution(4.7) to the solution from the blank test. Heat to about80 C and add the tin(II) chloride solution(4.5), drop by drop, while stirring the solu
36、tion until the yellow colour disappears or ceases to fade. Then add1 to3 drops in excess. Cool rapidly in a water bath. NOTEHigh titaniferrous bauxites may give rise to a permanent yellow colouration. Add, all at once,10ml of the mercury(II) chloride solution(4.6), mix gently and allow to stand for5
37、min. Dilute to approximately250ml. Add30ml of the sulfuric acid-phosphoric acid mixture(4.4) and5 drops of the indicator(4.9) and titrate with the potassium dichromate solution(4.8) to a permanent violet end-point(30s). Record the volumes for the test solution (V 2 ) and for the blank test solution
38、(V 3 ). NOTEFor samples having an Fe 2 O 3content greater than20% (m/m), use a50ml burette. 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 s
39、ampling, andISO6140, Aluminium ores Preparation of samples.BS6870-2.5:1987 BSI 01-2000 3 8 Expression of results 8.1 Calculation of total iron (asironoxideFe 2 O 3 ) The total iron content (as iron oxide, Fe 2 O 3 ), expressed as a percentage by mass, is given by the formula where V 1 is the volume,
40、 in millilitres, of standard potassium dichromate solution(4.8) used to titrate10ml of the ammonium iron(III) sulfate solution(4.7); V 2 is the volume, in millilitres, of standard potassium dichromate solution(4.8) used for titration of the analytical sample; V 3 is the volume, in millilitres, of st
41、andard potassium dichromate solution(4.8) used for titration in the blank test; m is the mass, in grams, of the test portion. 8.2 General treatment of results 8.2.1 Precision The precision of this method, as determined in an international test programme, is expressed in terms of repeatability, repro
42、ducibility and reproducibility index in theTable. Table Precision data for iron determination where r is the repeatability; R is the reproducibility. 8.2.2 Acceptance of analytical values (seeISO5725) The analytical value for the test sample shall be accepted when the analytical value obtained for t
43、he corresponding certified reference material agrees with the certified value within the limit of the reproducibility index contained in theTable, and when the difference between the two values for the test sample does not exceed2,77r, as calculated from the appropriate value of r given in theTable.
44、 When the analytical value obtained for the certifiedreference material is outside the reproducibility index, an analysis shall be carried out simultaneously on one test sample and one certified reference material, with one blank test. The analytical value obtained for the certified reference materi
45、al shall be examined for the acceptance of the value for the test sample, as above.If the value obtained for the certified reference material is again outside the limits, theprocedure shall be repeated with a different reference material of the same type of ore until two acceptable values for the te
46、st sample are obtained. 8.2.3 Calculation of final result The final result is the arithmetical mean of the acceptable analytical values calculated to four decimal places and rounded off to the second decimal place as follows: a) when the figure in the third decimal place is less than5, it is discard
47、ed and the figure in the second decimal place is kept unchanged; b) when the figure in the third decimal place is5 and there are figures other than0 in the fourth decimal place, or when the figure in the third decimal place is greater than5, the figure in the second decimal place is increased by one
48、; c) when the figure in the third decimal place is5and there are no figures other than0 in thefourth decimal place, the5 is discarded and the figure in the second decimal place is kept unchanged if it is0,2,4,6 or8, and increased byone if it is1,3,5,7 or9. 9 Test report The test report shall include
49、 the following information: a) details necessary for the identification of the sample; b) reference to this International Standard; c) results of the analysis; d) reference number of the results; e) any characteristics noticed during the determination and any operations not specified in this International Standard which may have had influence on the results. Sample Mean Fe 2 O 3content Components of standard deviation Reproducibility index % (m/m) r R 2s MT/12/3 MT/12/1 MT/12/5 MT/12/2 5,63 17,41 19,50 43,30 0,06 0,14 0,09 0,13 0,08 0,14 0,
