1、BRITISH STANDARD BS7020-3: 1988 ISO7335:1987 Analysis of iron ores Part3: Method for the determination of combined water content ISO title: Iron ores Determination of combined water content Karl Fischer titrimetric method UDC622.341.1:620.113:543.812.4:543.24:620.1BS7020-3:1988 This British Standard
2、, having been prepared under the directionof the Iron and Steel Standards Committee, was published under the authority ofthe Board of BSI and comes intoeffect on 31 January1989 BSI07-1999 The following BSI references relate to the work on this standard: Committee reference ISM/58 Draft for comment86
3、/38438 DC ISBN 0 580 16886 7 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Iron and Steel Standards Committee (ISM/-) to Technical Committee ISM/58, upon which the following bodies were represented: British Steel Industry Institution o
4、f Mining and Metallurgy 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 of issue CommentsBS7020-3:1988 BSI 07-1999 i Contents Page Committees responsible Inside
5、front cover National foreword ii 1 Scope and field of application 1 2 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 5 Annex A Flowsheet on the procedure for the acceptance of analytical values for test samples 9 A
6、nnex B Derivation of repeatability and permissible tolerance equations 10 Annex C Graphical presentation of precision data obtained by international analytical trial 10 Figure 1 Apparatus for the Karl Fischer measurement (two-furnaces-in-series type) (Example) 6 Figure 2 Apparatus for the Karl Fisch
7、er measurement (interchangeable furnace type) (Example) 7 Figure 3 Karl Fischer absorption cell (Example) 8 Figure 4 Least-squares fit of precision against X for combined water 10 Table 1 Mass of test portion 2 Table 2 Combined water contents of test samples 10 Publications referred to Inside back c
8、overBS7020-3:1988 ii BSI 07-1999 National foreword This Part of BS7020 has been prepared under the direction of the Iron and Steel Standards Committee. It is identical with ISO7335:1987 “Iron ores Determination of combined water content Karl Fischer titrimetric method” published by the International
9、 Organization 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; attenti
10、on is drawn 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 “Part of
11、 BS7020”. The Technical Committee has reviewed the provisions of ISO385, to which reference is made in the text, and has decided that they are acceptable for use in conjunction with this standard. A related British Standard to ISO385 is BS846 “Specification for burettes”. The reference to ISO5725 is
12、 for information only. 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. Cross-references I
13、nternational standard Corresponding British Standard BS5660 Methods of sampling iron ores ISO3081:1986 Part1:1987 Manual method of increment sampling (Identical) ISO3082:1987 Part2:1987 Mechanical method of increment sampling and sample preparation (Identical) ISO3083:1986 BS5661:1987 Method for pre
14、paration 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 chemical analysis (Identical) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1
15、 to10, 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.BS7020-3:1988 BSI 07-1999 1 1 Scope and field of application This International Standard
16、 specifies a titrimetric method for the determination of the combined water content of iron ores, using Karl Fischer solution. This method is applicable to a concentration range of0,05 to10% (m/m) of combined water in natural iron ores, and iron ore concentrates and agglomerates including sinter pro
17、ducts. NOTEThe term “combined water means that part of the water content of an iron ore that can be removed only at temperatures substantially higher than100 to110 C. 2 References ISO385, Laboratory glassware Burettes. ISO3081, Iron ores Increment sampling Manual method. ISO3082, Iron ores Increment
18、 sampling and sample preparation Mechanical method. ISO3083, Iron ores Preparation of samples Manual method. ISO7764, Iron ores Preparation of predried test samples for chemical analysis. 3 Principle Liberation of adventitious hygroscopic moisture by heating the predried test portion at105 C in a fu
19、rnace in a stream of dry nitrogen. Successive heating up to950 C in another furnace and collection of the liberated combined water in ethylene glycol-methanol mixture. Measurement of combined water content by titration with Karl Fischer solution using electrometric detection of the end point. 4 Reag
20、ents During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. 4.1 Desiccant. Silica gel, self-indicating granules. 4.2 Desiccant. Anhydrous magnesium perchlorate Mg(ClO 4 ) 2 of size0,8 to1,25mm or other suitable desiccant. NOTEMag
21、nesium perchlorate is a powerful oxidant and must not be allowed to come into contact with organic materials. When exhausted, it should be washed down the sink with a copious flow of water. 4.3 Nitrogen. A supply of filtered, predried, oil-free nitrogen containing less than104l of oxygen per litre a
22、t a pressure of approximately35kPa above atmospheric pressure. 4.4 Ethylene glycol (OHCH 2 CH 2 OH)-methanol (CH 3 OH) mixture (1+1). This mixture should be tested each time before use for the amount of free moisture it contains. If it contains more than0,05% (m/m) of free moisture, it shall not be
23、used. NOTEIn place of this mixture, anhydrous ethylene glycol may be used. In this case, Karl Fischer solution must contain the appropriate amount of methanol. 4.5 Karl Fischer solution (2,5to3,0mg H 2 O/ml). This solution shall be standardized on the day of use by one of the following substances: a
24、) a standard water methanol solution; this solution shall previously be standardized by use of the following b), c) or d); b) water added by means of a microsyringe; c) citric acid monohydrate C(OH)(COOH)(CH 2 COOH) 2 H 2 O; d) disodium tartrate dihydrate (CHOHCOONa) 2 2H 2 O. 5 Apparatus A suitable
25、 apparatus for the determination is illustrated in Figure 1 (two-furnaces-in-series type) or in Figure 2 (interchangeable furnace type). 5.1 Gas flowmeter, capable of measuring a flow rate up to250ml/min. If a pressure drop over a constriction is used as a means of measuring flow rate, the manometer
26、 liquid shall be a non-volatile oil. 5.2 Drying towers (t 1and t 2 ), of250ml capacity, packed respectively with desiccant (4.1) and (4.2) to dry the stream of nitrogen entering the heating tube. 5.3 Heating furnaces (f 1and f 2 ). Electric furnaces in series as in Figure 1 or movable furnaces which
27、 can be located around, and removed from, the heating tube as in Figure 2. The furnaces shall be capable of maintaining temperatures of105 2 C and950 20 C, respectively, over a minimum tube length of about150mm, by controlling the electric current. Furnace temperatures shall be measured at the upper
28、 surface of the heating tube by means of a pyrometer or thermometer. 5.4 Heating tube. A silica tube as shown in Figure 1, of about30mm inside diameter, about800mm length, and provided with a long silica pushing rod. Another example (Figure 2) is about350mm long, closed at one end and fitted with a
29、thin inner tube of about8mm external diameter, through which gas flows towards the outlet.BS7020-3:1988 2 BSI 07-1999 5.5 Sample boats, of an inert and stable material such as quartz, platinum or porcelain. Approximate dimensions are100mm length,20mm width and5mm height, and sample loading shall not
30、 exceed1mg/mm 2for0,2 to1g test portions and1,5mg/mm 2for3g test portions. Before use, boats shall be heated at950 C, cooled and stored in a desiccator to maintain freedom from moisture. 5.6 Filter. Sintered metal, sintered glass or similar filter disc inserted in the flexible connection between the
31、 heating tube and the inlet to the absorption cell. 5.7 Flexible connections. Neoprene elastometer tubing is suitable. Some types of silicone tubing have been found to be permeable. For the gas flow lines after the drying towers, glass tubing should be used to the maximum extent possible, with the f
32、lexible tubing being used only for the connection of butt-jointed glass sections. 5.8 Flow control valve. A needle valve is placed on the outlet side of the flowmeter. 5.9 Absorption cell. A glass vessel is illustrated in Figure 3. The entries for the platinum electodes, burettes and gas inlet shall
33、 all be gas-tight to prevent moisture from entering the cell. 5.10 Platinum electrodes, either as a pair or as a dual platinum electrode. 5.11 Magnetic stirrer 5.12 Electrometric titrator, suitable for Karl Fischer titration and equipped with a microammeter(0to504A) or an equivalent means for the el
34、ectrometric indication of the end point. 5.13 Burette, of about25ml capacity, conforming to the specifications of ISO385. 6 Sampling and samples 6.1 Laboratory sample For analysis, use a laboratory sample of minus1004m particle size which has been taken in accordance with ISO3081 or ISO3082 and prep
35、ared in accordance with ISO3082 or ISO3083. In the case of ores with significant contents of combined water or oxidizable compounds, use a particle size of1604m. NOTEA guideline on significant contents of combined water and oxidizable compounds is incorporated in ISO7764. 6.2 Preparation of predried
36、 test samples Thoroughly mix the laboratory sample and, taking multiple increments, extract a test sample in such a manner that it is representative of the whole contents of the container. Dry the test sample at105 2 C as specified in ISO7764. (This is the predried test sample.) 7 Procedure 7.1 Numb
37、er of determinations Carry out the analysis at least in duplicate in accordance with Annex A, independently, on one predried test sample. NOTEThe expression “independently” means that the second and any subsequent result is not affected by the previous result(s). For this particular analytical metho
38、d this condition implies that the repetition of the procedure shall be carried out either by the same operator at a different time or by a different operator, including, in either case, appropriate recalibration. 7.2 Test portion Taking several increments, weigh, to the nearest0,1mg, approximately t
39、he amount of the predried test sample (6.2) specified in Table 1. Table 1 Mass of test portion 7.3 Blank test and check test In each run, one blank test and one analysis of a certified reference material 1)of the same type of ore shall be carried out in parallel with the analysis of the ore sample(s
40、) under the same conditions. A predried test sample of the certified reference material shall be prepared as specified in6.2. NOTEThe 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
41、that in either case no significant changes in the analytical procedure become 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 the reagents used are from the same reagent bottl
42、es. Combined water content of test sample % Mass of test portion g 0,05 to0,5 0,5to2 2to5 5to10 3 1 0,5 0,2 NOTEThe test portion should be taken and weighed quickly on the day of predrying to avoid reabsorption of moisture. 1) The certified reference material should have been previously certified us
43、ing this method.BS7020-3:1988 BSI 07-1999 3 When the analysis is carried out on several samples of the same type of ore at the same time, the analytical value of one certified reference material may be used. 7.4 Determination 7.4.1 Apparatus conditioning Bring the heating tube in the furnace (f 1 )
44、to a temperature of105 2 C and maintain at this temperature through steps7.4.1 to7.4.3. Adjust the flow rate of nitrogen (4.3) to about200ml/min through the system. Momentarily close the outlet from the heating tube to check for leaks in the system. Reconnect the outlet from the heating tube to the
45、inlet of the absorption cell, and readjust the flow rate if necessary. Allow10min for the system to be purged and maintain this flow through steps7.4.1 to7.4.5. Remove the stopper from the absorption cell and transfer40ml of ethylene glycol-methanol mixture(4.4) through the absorbent inlet into the
46、absorption cell by pipette. Replace the stopper of the inlet tightly. Switch on the titrator and magnetic stirrer, adjusting the speed of the latter to ensure adequate mixing. Maintain a constant stirring speed during the titration. 7.4.2 Titration Add Karl Fischer solution (4.5) slowly to the absor
47、ption cell by burette. The approaching end point will be indicated by a rapid increase in current due to the presence of free iodine from the excess Karl Fischer solution. At this point of rapid change, select a current (30to404A) for the end point. Continue the titration until this current can be m
48、aintained for a period of30s. Make further additions of Karl Fischer solution at intervals of10min until the increment required to restore the current to the predetermined value for a period of30s is less than0,05ml. The absorbent solution shall be titrated to this end point immediately prior to the
49、 commencement of all tests and calibration. 7.4.3 Liberation of adventitious hygroscopic moisture Remove the inlet connector to the heating tube, place the sample boat containing the predried test portion (7.2) in the heating tube at the entrance to the heated zone and insert the magnetic push rod. Immediately replace the inlet connector and, using a magnet, move the boat to the centre of the heated zone of the heating tube in the low temperature furnace (f 1 ). Expel any adventitious hygroscopic moisture in the
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