COMPREHENSIVE INVESTIGATION OF THE LIBERATION CHARACTFXISTICS OF PYRITE AND OTHER MINERAL MATI'ER FROM COAL DE-FG22-95PC University of Utah

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1 - COMPREHENSVE NVESTGATON OF THE LBERATON CHARACTFXSTCS OF PYRTE AND OTHER MNERAL MAT'ER FROM COAL DE-FG22-95PC95220 University of Utah Reporting Date: Grant Date: Completion Date: Award 1995/1996: Program Director: Principal nvestigator: Contracting Officer's Representative: 07/30/96 07/01/95 06/30/98 $100,914 Professor R Peter King Professor R Peter King J o h C Zysk Report for Period 01/01/96-06/30/96 BiSTRBUTiON OF M1SDOCUMEhR S UNLMTED T 27 U

2 DSCLAMER This report was prepared as an awunt of work sponsored by an agency of the United States Government Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, reammendation, or favoring by the United States Government or any agency thereof The views and opinions of authors expressed herein do not neassarily state or reflect those of the United States Government or any agency thereof

3 DSCLAMER Portions of this document may be illegible in electronic image products mages are produced from the best available original document,

4 Objectives The objectives of the project are: Develop a set of laboratory techniques for the quantitative measurement of the liberation spectra in samples of coal particles in the size range 50 pm - 1 mm Threedimensional spectra will be required to account for the mineral matter and pyrite separately Establish, experimentally, the Andrews-Mika diagram for a number of typical US coals and to develop an appropriate parameterized description for the Andrews-Mika diagram so that it may be determined easily and quickly for coals of different origin and different type Establish an effective and reliable simulation technique so that liberation of both pyritic sulfur and ash during comminution operations can be modeled and the operation of coal preparation facilities-simulated These models will be incorporated into a computer simulation system for coal cleaning plants Summary of Technical Progress 1 Experimental A micron size fraction of a sample of Pittsburgh #8 coal was carefully fractionated using precise dense-liquid separation techniques The resulting washability curve is shown in Figure 1 The sample was fractionated at 125, 127, 129, 131, 133, 135, 137, 139, 150 and 160 grams per cc The fraction was then crushed in the ultrasonic miu in the Comminution Center laboratory and progeny larger than 38 microns were fractionated at 125, 127, 129, 131, 133, 135, 137, 139, 145, 150 and 160 grams per cc Each of these fractions was then screened at 500, 355, 251, 180 and 106 microns-so that the complete disposition of the progeny particle population could be established These data define what may be regarded as a coarse-grained experimental version of the Andrews-Mika diagram for parent particles at microns and g/cc The data set is recorded in Tables 1 and 2 and is shown in Figure 2 Figure 2 represents the first ever evaluation of an Andrews-Mika diagram for coal and, while it is qualitatively similar to Andrews-Mika diagrams established for other mineral systems, it illustrates that ash is liberated comparatively slowly during comminution Proximate analysis was done on each of the progeny fractions, together with sulfur and average particle density The average particle densities are particularly important in establishing the precision of the fractionation procedure The average solid densities of the air-dried coal were measured using helium pycnometry The results are shown in Figure 3 The density measured by helium pycnometry is, in all cases, slightly higher than the mid-point of the fractionation interval and this is consistent with the observation that helium pycnometry registers a higher solid density because much smaller pores are accessible to the helium and are not accessible to liquids because of capillary pressure The approximate Andrews-Mika diagram, illustrated above, does not reflect the separate 2

5 liberation characteristics of pyritic sulfur and the other ash-forming minerals n order to construct separate diagrams for these two components, it is necessary to separate, at least approximately, mineral matter excluding pyrite and pyrite n order to do so, a simple model for the three-component system has been constructed based on the following assumptions: a constant ratio, y, relates mineral matter in the coal to measured ash; and the coal contains a fraction constant, s, of organic sulfur and constant fraction, c, of inherent mineral matter n addition, all pyrite is assumed to convert to Fe203 on ashing, and pyrite contains 494 percent of sulfur A simple mass balance allows the calculation of the fraction of pyrite and mineral matter-free coal in any sample in which ash and sulfur are determined The model is described by: A S w1 +w,+w3 = 072 w2 + $cwl + w;) = 0494 W Z + S W ~ = 1 where A and S are measured ash and sulfur fractions respectively and wl,w 2 and w 3 are the calculated mass fractions of koal," pyrite and mineral matter The efficacy of this simple model can be tested by comparing the calculated density of the separated fractions to the mid-point of the separted fraction using where pc, p and pmare the densities of the "coal," the pyrite and the mineral matter respectively p The data usmg pc = 125, pp = 502, pm = 31, y = 09, S = 0015 and c = are shown in Figure 4 The effectiveness of this simple model can be established by noting that the specific volume of the sample is related to these quantities by Equation 2 The predicted specific volumes are compared to the mid-point of the separation densities in Figure 4 A mounting, polishing and imaging technique has been developed to examine particles of coal using scanning-electron microscopy A typical image is shown in Figure 5 The mounting technique was adapted from one developed in Australia and the images show good, clear discrimination between the particles of coal and the mounting medium Pyrite is easily identified in the images and areas of high mineral content also show clearly Suitable image processing and image analysis techniques will be developed to characterize the geometrical structure of the various component regions in the coal Very careful calibration will obviously be required 2 Theoretical Two approaches are available to model the Andrews-Mika diagram The first establishes the characteristics of the entire three-dimensional surface of the diagram including the constraint envelope This approach has been successfully used to characterize the liberation characteristics of sphalerite from a dolomitehphalerite ore in a previous study n essence, the model assumes that the distribution of progeny at any size across the composition coordinate is described by a beta distribution When the range of the beta distribution extends beyond the liberated boundaries, the extended area is concentrated at the appropriate boundary A good model that 3

6 uses a minimum of parameters is available for this description and will be applied to the coal data A second method, which has been developed by Professor L G Austin, regards the Andrews-Mika diagram as resulting from a two-stage process First, the parent particle' distributes across the size coordinate of the progeny spectrum according to the conventional breakage functions with a separate breakage function determined for each component The threecomponent breakage functions for the one parent that has been investigated are shown in Figure 6 These data show clearly that both ash,and sulfur-bearing constituents generate finer progeny than the less brittle coal components The next step in the development of a quantitative description of the Andrews-Mika diagram is to determine how each component is distributed within the three-dimensional coal, mineral-matter, pyrite space at each progeny size Calculated distribution curves are not yet available for the first sample data set Personnel Personnel who have contributed to this project during the reporting period are: Professor R P King Professor L G Austin Dr C L Schneider Mr D fitzgerald Mrs K Haynes Principal nvestigator Visiting Professor (June 1 - July 31, 1996) Postdoctoral Associate Technician Program Administrator Mr Kerning Wu, currently at the University of Concepcion Chile, has been offered a post on the project team so that he can undertake work toward a PhD degree He has not yet been formally admitted to the University of Utah because some of his personal information is not yet available in documented form An offer was made to Mr Naiyang Ma, currently at the University of Birmingham, England He has satisfied all of the requirements for entry to the University of Utah but he has been refused a visa by NS because he has not been able to return to his home country to make the visa application Negotiations are currently underway with additional students who have been admitted for graduate study at the University of Utah n particular, Mr Suraj Jain, who is presently in ndia, appears to be particularly suitable for this project Mr Kendall Oliphant, an undergraduate student at the University of Utah, will rejoin the project at the end of summer Mr Oliphant is particularly suited because he is already well-trained in all of the experimental techniques that are being used in this project Activities Planned for Next Six Months 1 Each of the parent samples will be crushed using ultrasonic milling and the progeny fractionated and analyzed according to the methods that are now being developed 2 Three-component Andrews-Mika diagrams will be constructed for each parent particle type using both modeling techniques 3 The image-analysis procedure wiu be further developed and calibrated against the samples prepared by density fractionation 4

7 ,-, Table Measured data for parent particles weight % Carbon % 56n Volatile % Sulfur %

8 Table Measured data for progeny Analysis of Progeny after Fracture 1

9 Table Measured data for progeny -

10 v) v)!i Density g/cc Figure 1 Measured washability in the Pittsburgh #8 coal used to produce parent particles for the determination of the Andrews-Mika diagram 8

11 Y Figure 2 Approximate Andrews-Mika diagram for Pittsburgh #8 coal 9

12 Midpoint of separation density interval, g/cc Figure 3 Confirmation of fraction densities 10

13 Mid point of separation interval g/cc Figure 4 Confirmation of the three-component density model for Pittsburgh #8 coal 11

14 Figure 5 SEM image of s e c t i o n e d c o a l p a r t i c l e s 12

15 Component breakage functions O' : : :/ ;:: 1: 1: ::;1: :: : - : 'd' :: : i i i ii, "", -,,,,,, ::,, L Z, ~~ L 1 :, \ 4 5 i % i 1 3, 100 1,,, ' :z, i, i, \\, a i Zi 5 6 Sieve size microns Figure 6 Breakage functions for three separate components with ultrasonic mill 13 : J,