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1、INTERNATIONAL STANDARD IS0 4695 Second edition 1995-l 1-l 5 Iron ores - Determination of reducibility Minerais de fer - D re- duction in a fixed bed; reduction by means of carbon monoxide; a sample having a specified size range. The results of this test should be considered in conjunction with the r
2、e- sults of other tests, particularly those showing the physical behaviour of materials during reduction. The mathematical derivation of formulae for reducibility is included for in- formation only in annex A. III Copyright International Organization for Standardization Provided by IHS under license
3、 with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 20:46:35 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD 0 IS0 IS0 4695:1995(E) Iron ores - Determination of reducibility 1 Scope This International Standard specifies
4、 a method for determining the reducibility expressed as reduction rate of natural iron ores and agglomerates such as pellets or sinters. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At t
5、he time of publi- cation, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most re- cent editions of the standards indicated below. Members of IEC and
6、 IS0 maintain registers of cur- rently valid International Standards. IS0 2597-l :1994, Iron ores - Determination of total iron content - Part I: Titrimetric method after tin(ll) chloride reduction. IS0 331 O-l :I 990, Test sieves - Technical require- ments and testing - Part 7: Test sieves of metal
7、 wire cloth. IS0 331 O-2:1 990, Test sieves - Technical require- ments and testing - Part 2: Test sieves of perforated metal plate. IS0 9035:1989, Iron ores - Determination of acid- soluble iron content - Titrimetrk method. IS0 9507:1990, Iron ores - Determination of total iron content - TitaniumUll
8、l chloride reduction meth- ods. IS0 9508:1990, /r-on ores - Determination of total iron content - Silver reduction titrimetric method. IS0 10836:1994, Iron ores - Method of sampling and sample preparation for physical testing. 3 Definitions For the purpose of this International Standard, the followi
9、ng definition applies. 3.1 reducibility: The ease with which oxygen com- bined with iron can be removed from natural or pro- cessed ores. ISO 113231 4 Principle Isothermal reduction of the test portion at a specified size range in a fixed bed, at a temperature of 950 “C using a reducing gas consisti
10、ng of CO and N,. Weighing of the test portion at specified time inter- vals. Calculation of the degree of reduction relative to the iron(lll) state and calculation of the rate of reduction at the oxygen/iron ratio of 0,9. 5 Reducing gas Gas volumes and flow rates used in this International Standard
11、are as measured at a temperature of 0 “C and at atmospheric pressure (101,325 kPa). 5.1 Composition The reducing gas shall consist of: co 40 % (V/v) + 0,5 % (V/v) Nz 60 % (V/v) + 0,5 % (V/v) 1 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NA
12、SA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 20:46:35 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4695:1995(E) Q IS0 5.2 Purity Impurities in the reducing gas shall not exceed: H2 02 % (V/v) co2 0,2 % wvl 02 0,l % wvl H2O 0,2 % w-m Impurities in th
13、e heating gas (N,) shall not exceed 0,l % w4). 6 Apparatus 6.1 General The apparatus shall comprise: a) b) cl d) e) f) a system to supply and regulate the gases; a reduction tube; a weighing device to determine the oxygen loss at regular intervals; a frictionless connection between the gas supply an
14、d reduction tube which ensures linearity of weight loss determination; an electrically heated furnace to heat the test portion to the specified temperature; test sieves. Figure 1 shows a general arrangement of the appar- atus. Figure2 shows an arrangement of the reduction tube and the furnace. 6.2 R
15、eduction tube, made of non-scaling, heat- resistant metal to withstand temperatures of higher than 950 “C. The perforated plate is mounted in the reduction tube for supporting the test portion. The di- ameter of the reduction tube shall be 75 mm f 1 mm. Figure3 shows an example of the reduction tube
16、. 6.3 Furnace, having a heating capacity sufficient to maintain the entire test portion and the gas entering the bed at 950 “C + 10 “C. 6.4 Weighing device, capable of weighing the load to an accuracy of 1 g. The weighing device shall be checked for sensitivity at regular intervals. 6.5 Test sieves,
17、 conforming to test sieve standard specifications and having square mesh apertures of the following nominal sizes and cornforming to IS0 3310-l or IS0 3310-2: 10,O mm; 12,5 mm; 16,0 mm 7 Preparation of test sample 7.1 General In the case of a commercial test, the test sample shall be prepared accord
18、ing to IS0 10836. The test sample shall be oven dried at 105 “C + 5 “C to constant mass and cooled to room temperature before testing. A quantity of test sample sufficient to provide at least five 500 g test portions shall be prepared. 7.2 Sample for reducibility test The gross sample taken for test
19、ing is repeatedly div- ided, extracting masses for the reserve sample, the tumble test sample etc., until a stage is reached where the mass retained just exceeds the minimum required for the preparation of the test sample for reducibility. 7.2.1 Pellets The division of the gross sample by riffle sha
20、ll proceed until the mass retained just exceeds 30 kg. This sample shall be sieved on 12,5 mm and IO,0 mm test sieves, discarding the + 12,5 mm - IO,0 mm frac- tions and retaining the - 12,5 mm + IO,0 mm frac- tion. A minimum of 2,5 kg shall be used for the reducibility test sample. From the test sa
21、mple, four test portions and one chemical analysis sample, each having a mass of 0,5 kg shall be obtained. 7.2.2 Sinters and ores A test sample in the size range - 12,5 mm + 10.0 mm and of mass 30 kg shall be used. This shall be prepared by first sieving on a 12,5 mm sieve then carefully crushing th
22、e + 12,5 mm material until it all passes the 16,0 mm sieve. All fractions are combined and removed by sieving the + 12,5 mm - 10.0 mm material from the sample. From the test sample, four test portions and one chemical analysis sample, each having a mass of 0,5 kg shall be ob- tained. 7.3 Sample for
23、chemical analysis A 500 g test portion shall be reserved for the deter- mination of total iron content and Fe(ll) content. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 20:46:3
24、5 MDTNo reproduction or networking permitted without license from IHS -,-,- 8 Test conditions 8.1 Flow rate of reducing gas The reducing gas (clause 5) flow rate shall, during the test period, be maintained at 50 I/min + 0,5 I/min. 8.2 Temperature of test The test portion shall be reduced at a tempe
25、rature of 950 “C. The reducing gas shall be preheated before entering the test portion to maintain the test portion at 950 “C + 10 “C during the entire test period. 9 Procedure 9.1 Number of determinations Carry out the test in duplicate on one ore sample. 9.2 Other determinations Simultaneously wit
26、h the test, determine the total iron content k-r accordance with IS0 2597, IS0 9507 or IS0 9508 and the Fe(ll) content in accordance with IS0 9035. 9.3 Test portion Weigh, to the nearest 1 g, approximately 500 g (_+ 1 particle) of the test sample (mass %I. 9.4 Reduction Place the test portion (9.3)
27、in the reduction tube (6.2) so that the surface is even. In order to achieve a more uniform gas flow, a two-layer bed of porcelain pellets having a size range of IO,0 mm to 12,5 mm may be placed between the perforated plate and the test portion. Place the thermocouple in the centre of the test sampl
28、e. Close the top of the reduction tube. Insert the re- duction tube into the furnace (6.3) and suspend it centrally from the weighing device (6.4) ensuring that there is no contact with the furnace or heating el- ements. Connect the gas supply. Pass a flow of N, through the reduction tube at a flow
29、rate of approximately 25 l/min and commence the 1) The derivation of the equation is given in annex A. heating. When the temperature of the test portion approaches 950 “C increase the flow rate of the N, to 50 I/min. Continue the heating whilst maintaining the flow of the N, until the mass of the te
30、st portion is constant (mass nt,) and the temperature is constant at950”CA 10C. CAUTION - Carbon monoxide and the reducing gas, which contains carbon monoxide, are toxic and therefore hazardous. During the following procedure, the testing shall be carried out in a well ventilated area or under a hoo
31、d. Precautions, according to the safety codes of each country, should be taken for the safety of the operator. Introduce the reducing gas to replace the N, at a flow rate of 50 I/min. Record the mass of the test portion at least every three minutes for the first 15 min and thereafter at 10 min inter
32、vals. Terminate the reduction when the oxygen loss re- aches 65 %. If, after 4 hours, this has not been achieved, the test may be stopped. NOTE 1 If so desired, the test portion may then be cooled under a flow of N, to enable sample examination to be carried out. 10 Expression of results 10.1 Calcul
33、ation of degree of reduction Calculate the degree of reduction after time I, R, relative to the iron (Ill) state, as a percentage, by the following equation! R, = 0,111 Wl 0,430 Iv2 + ml - mt mo x 0,430 w2 x 100 xl00 where m, ml 4 WI 2) is the mass, in grams, of the test portion; is the mass, in gra
34、ms, of the test portion immediately before starting the reduction; is the mass, in grams, of the test portion after reduction time t; is the iron (II) oxide content, as a percent- age by mass, of the test sample prior to the test and is calculated from the iron (II) content by multiplying it by a fa
35、ctor of 1, 2863; 2) In the case of a commercial test, it is preferable to adopt w, and w, not for the 500 g test portion (7.3). but for consignment. 3) Oxide conversion factor FeO/Fe(li) = 1,286. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee
36、=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 20:46:35 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4695:1995(E) Q IS0 w2 21 is the total iron content, as a percentage 10.3 Permissible tolerance and acceptance by mass, of the test sample prior to
37、the of test results test, determined in accordance with IS0 2597, IS0 9507 or IS0 9508. Prepare the reduction curve by plotting the degree of reduction R, against time t. 10.2 Calculation of reducibility index 10.3.1 Pellets For a paired result, the two individual results shall be within f 3,5 % of
38、the mean value of the pair of re- sults. Read off from the reduction curve the time in minutes to attain degrees of reduction of 30 % and 60 %. 10.3.2 Sinters and ores The reducibility index, expressed as the rate of re- duction at the atomic ratio of O/Fe of 0,g4, in %/min, is calculated from the f
39、ollowing formula: For a paired result, the two individual results shall be within ) 0,085 % for sinters and + 0,05 % for ores. The reducibility index reported shall be the a,rithmetic mean of a paired result rounded off to the nearest where 0,Ol %/min. 40 is the time to attain a degree of reduction
40、If the difference between the paired results does not of 30 % (min); meet the permissible tolerance, another duplicate test shall be carried out. The reducibility index reoorted SO is the time to attain a degree of reduction shall be the arithmetic mean of the four results of 60 % (min); rounded off
41、 to the nearest 0.01 %jmin. 33,6 is a constant. Express the result to two decimal places. 11 Test report NOTE 2 in certain instances, a degree of reduction of 60 % is not attained in the test. In such cases, lower values may be accommodated by the following formula: % (O/Fe = 0.9) = K is constant de
42、pending on y; The test report shall include the following information: a1 reference to this International Standard; b) description of the test sample; c) reducibifity index; d) total iron content and iron in the sample before reduction; If y = 50 % then the value of K = 20,2; if y = 55 % then the e)
43、 loss in mass-versus-time data, if specified at the value of K = 26.5. time of order. 4) The atomic ratio O/Fe = 0,9 means a 40 % degree of reduction 4 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not f
44、or Resale, 04/22/2007 20:46:35 MDTNo reproduction or networking permitted without license from IHS -,-,- i- I I I I I co 1 t-42 1 Key 1 Gas cylinders with manometer and reduction valve 2 Gas flowmeters 3 Mixing vessel 4 Electrically heated furnace 5 Test portion 6 Thermocouple 7 Gas inlet 8 Layer of
45、 porcelain pellets 9 Double wall retort with perforated plate as sample holder 10 Digital balance 11 Load 12 Plotter for recording temperature and weight loss 13 Beam Figure 1 - Example of arrangement of a test unit for determination of reducibility 5 Copyright International Organization for Standar
46、dization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 20:46:35 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4695:1995(E) 2 3 5 6 4 1 Key 1 Furnace (10 kV.A) (6.3) 2 Reduction tube (6.2) 3 Heating ele
47、ment 4 Perforated plate 5 Test portion a NOTE - Dimensions are for information only. - - 6 Layer of porcelain pellets 7 Gas inlet 8 Gas outlet 9 Thermocouple -I Q tso Dimensions in millimetres - Figure 2 - Example of test apparatus 6 Copyright International Organization for Standardization Provided
48、by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 20:46:35 MDTNo reproduction or networking permitted without license from IHS -,-,- 6 IS0 IS0 4695:1995(E) Dimensions In millimetres 075 Perforated plate Hole diameter : 2.5 mm Pitch between holes : 4 mm Number of holes : 241 Total hole area : 1180 mm2 Thickness of plate : 4 mm NOTE - The dimensions not specified in clause 6 are shown for information only. Figure 3 - Example of reduction tube (6.2) 7 Copyright International Organization for Standardization Provided by