Reference minerals

Fourier transform infrared (FTIR) spectroscopy of coal low-temperature ashes was applied to the determination of coal mineralogy and the prediction of ash properties during coal combustion. Analytical methods commonly applied to the mineralogy of coal are critically surveyed. Conventional least-squares analysis of spectra was used to determine coal mineralogy on the basis of forty-two reference mineral spectra. The method described showed several limitations. However, partial least-squares and principal component regression calibrations with the FTIR data permitted prediction of all eight ASTM ash fusion temperatures to within 50 to 78 F and four major elemental oxide concentrations to within 0.74 to 1.79 wt % of the ASTM ash (standard errors of prediction). Factor analysis based methods offer considerable potential in mineral-ogical and ash property applications. 

Two coal sample sets and the reference minerals are described below. 

Reference Minerals. The 42 reference minerals and the mineral classes used are listed in Table II. Most of the minerals were obtained from Ward s Natural Science Establishment, Inc., Rochester, New York. Many of the silicate minerals were American Petroleum Institute (API) standard samples or their equivalents. Numbers given in the table (e.g., kaolinite 4) refer to the API standard designation. When available, several minerals of each type were... 

All spectra were run on a Nicolet 7199 FTIR spectrometer equipped to operate in the mid-infrared (wide-band MCT detector). A leastsquares analysis program provided by Nicolet (MCOMP) was extensively modified for efficient routine use with a large number of reference minerals. The reference mineral with the lowest negative concentration in each least-squares decomposition of the LTA spectra was omitted upon each iteration, until only non-negative concentrations were obtained. Generally 12 to 18 minerals remained in the final calculation. 

In addition to spectra of the reference minerals listed in Table II, the least-squares components in each iteration included 3 "spectra" representing 1) moisture in KBr blank (obtained by subtraction of 2 KBr blank spectra), 2) a constant baseline offset (1 abs from 4000 to 400 cm" ), and 3) a sloping linear baseline (line from 1 abs at 4000 cm" to 0 abs at 400 cm" ). The final mineral component concentrations were normalized to 100%, disregarding the contributions of the three artificial components. The normalized least-squares results for each sample were combined with the ash elemental composition of each reference mineral to calculate the elemental composition of the ASTM oxidized ash corresponding to each LTA. This was done by multiplying the concentration of each reference mineral in a sample by the concentration of each elemental oxide in the reference mineral, then summing over each oxide. 

X-rav Diffraction. XRD is the most common method used for coal mineralogy (6.7.8). Its major advantage is the ability to unequivocally identify many minerals. The main disadvantages are 1) reliance on reference minerals, 2) requires careful attention to sample preparation, and 3) low sensitivity to certain minerals (especially many clays) due to poor crystallinity and to particle orientation effects. Many laboratories analyze a separate concentrated clay... 

Infrared Spectroscopy. The use of IR (9.10.11.12) and FTIR (3.4) for coal mineralogy has been reported. Painter and coworkers (3) demonstrated that FTIR can provide a virtually complete analysis. Painter, Brown and Elliott (4), and others (9.10.11) discuss sample preparation, reference minerals, and data analysis. The advantages of IR are 1) high sensitivity to molecular structure, 2) unequivocal identification of a number of minerals, 3) small sample size (a few milligrams), and 4) rapid analysis time (once LTA is available). Disadvantages include 1) reliance on reference minerals, 2) requires careful attention to sample preparation, and 3) limited selectivity (discrimination among similar minerals). 

Factor analysis extracts information from the sample data set (e.g., IR spectra) and does not rely on reference minerals. However, because abstract factors have no physical meaning, reference minerals may be needed in target transformations or other procedures to extract mineralogical information. One valuable piece of information obtainable without the use of extraneous data is the number of components required to represent the data within experimental error. Reported applications of factor analysis to mineralogy by FTIR are few (12). However, one commercial laboratory is offering routine FTIR mineral analyses to the petroleum industry, based on related methods (22). 

Results of classical least-squares analysis of FTIR spectra of ten coals using forty-two reference minerals were evaluated with regard to reproducibility and accuracy as described below. 

The third method for assessing accuracy is to calculate an elemental composition for each LTA s corresponding oxidized ash, based on the reference mineral elemental compositions. Reasonably close agreement between the actual (obtained by ICP-AES) and calculated elemental compositions would substantiate (but not prove) the mineral analysis. The standard error of prediction (SEP) for... 

Adsorption of NOM onto mineral surfaces produces a composite that possesses physical and chemical properties distinct from either of its constituent components. The ill-defined, heterogeneous nature of NOM makes the interpretation of data from the characterization of naturally occurring OMN complexes problematic. In this respect, studies involving NOM- component classes (e.g., lipids, proteins, etc.) and reference minerals may offer insights. The characterization of model NOM-mineral composites provides the opportunity to employ techniques specific to the interaction of interest. 

Reference Mineral pH Thickness of the leached layer (10—8 cm) Diffusion coefficient, log D (cm2 s 1)... 

EXAFS Parameters for Zn Reference Minerals and Sorption Samples... 

Keller, W., Pickett, E. E., and Reesman, A. L. Elevated dehydroxylation temperature of the Keokuk geode kaolinite— a possible reference mineral, Jai Proceedings Internat. Clay Conf. 1, 75-85 (1966). 

In 1812, German geologist Frierich Mohs (1773-1839) devised a scale with specimen minerals that offered comparison of hardness qualities that allows the assignment of a Mohs hardness number to a mineral. Mohs scale utilizes ten specific representative materials that are arranged numerically from the softest (1) to the hardest (10). The reference minerals are (1) talc, (2) gypsum, (3) calcite, (4) fluorite, (5) apatite, (6) orthoclase feldspar, (7) quartz, (8) topaz, (9) corundum, and (10) diamond. 

Goldberg, S., Forster. H.S., and Heick, E.L., Temperature effects on boron adsorption by reference minerals and soils. Soil Sci., 156, 316, 1993. 

The hardness of a mineral is an immediately accessible character, useful in its identification. One can say that A is harder than B, if A scratches B. The hardness is defined in comparison to reference minerals. 

Nevertheless, this scale can be improved by means of smoothing, i.e., taking the absolute determinations into account. The hardness of reference minerals is weakly modified Table 21 gives the classical Mohs values and the smoothed values H. In this lecture, we use only the H scale. 

Addison J, Davies LST, McIntosh C, and Porteous RH (1992) Bulk Asbestos Reference Minerals for Optical Microscope Identification Preparation, Evaluation and Validation, lOM report to client, HSE contract no. R2490/ R48.44. Edinburgh Institute of Occupational Medicine. 

Goldberg, S., and N. J. Kabengi. 2010. Bromide adsorption by reference minerals and soils. Vadose Zone Journal 9, no. 3 780. doi 10.2136/vzj2010.0028. 

Hardness tests are at best semi-empirical, and comparisons between different scales unreliable, as the test conditions differ. Some indications of comparative values for materials of ceramic interest can be gleaned from the following tables. The Mohs reference minerals are in bold type. 

Mohs hardness scale Empirical scale by which the hardness of solids can be determined by comparison with 10 reference minerals ranked from 1 to 10 1, talc 2, gypsum 3, calcite 4, fluorite 5, apatite 6, orthoclase 7, quartz 8, topaz 9, corundum and 10, diamond. 

Boron oxide particles were incorporated to silicone rubber-based mixes containing fumed silica (reinforcing filler) and reference mineral fillers - aluminum hydroxide, wollastonite, calcined kaolin, mica (phlogipite) and surface modified montmorillonite with dimethyl-dihydrogenatedtal-low quaternary ammonium salt. Acidic character of boron oxide, which can disturb the peroxide curing process, was compensated by addition of magnesium oxide. The influence of boron oxide particles on properties of composites was determined and mechanism of their ceramization process studied. 

APPENDIX REFERENCES MINERAL NAME INDEX FORMULA INDEX... 

---