Modes of Occurrence of Trace and Minor Elements in Some Australian Coals K.W. Riley*, D.H. French, O.P. Farrell, R.A. Wood and F.E. Huggins#

CSIRO Energy Technology, PO Box 52, North Ryde, NSW, 1670, Australia. # CME/CFFS, University of Kentucky, 105 Whalen Building, 533 S. Limestone Street, Lexington, KY 40506-0043, USA. * corresponding author, ken.riley@csiro.au Abstract The modes of occurrence of the trace elements in six Australian coals are reported, together with the nature and percentages of the minerals present. The trace elements studied were As, B, Be, Bi, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Th, Tl, U and Zn, as well as the minor elements S and Fe. The modes of occurrence were determined chemically by sequential extraction. For comparison, X-ray absorption fine structure (XAFS) and near edge structure (XANES) spectroscopies were used to determine the modes of occurrence of As, Pb, Ni, S and Zn in four of these six coals and 57Fe Mössbauer spectroscopy was used to estimate the Fe-species (or forms) occurring in the same four coals. The results obtained were compared with those published on coals generally in the literature. The integrated results provide the most extensive set of information published to-date on the modes of occurrence of trace elements in Australian coals. Key words: Australian coals; element speciation; trace elements; 1. Introduction Although there are numerous papers on the occurrence of trace elements in coal (see for example, Swaine, 1990, 1995), there is still some uncertainty about the assignment of some trace elements. Finkelman (1994, 1995) reports studies into the modes of occurrence of trace elements in coals and ranks the confidence (from one to a maximum of ten) in the assignment of the likely mode. Not surprisingly, the determination of the occurrence of the trace elements present at low concentrations in coal is difficult; it should be noted that the trace elements in the low-pyrite coals of Australia are frequently at very low concentrations. As well, different researchers use different techniques (Huggins, 2002). In a report on the results of an international inter-laboratory study, Davidson (2000) comments on the often poor agreement between techniques such as gravity separation and sequential leaching and the need for confirmation from techniques such as X-ray absorption near edge structure (XANES) spectrometry. This paper follows on from an earlier paper on the speciation of Se in Australian coal samples (Riley at al., 2007). This earlier paper contained information on the modes of occurrence of the environmentally important trace element, selenium, whereas this paper contains information on the occurrence of a wide ranging number of elements

in the same samples. This should provide information that will prove useful not only to geologists studying the formation and occurrence of elements in Australian coals, but also provide data that are of use to those studying the fate of these elements in the utilisation of the sampled coals. 2. Experimental 2.1 Description of the Coal Samples In total, six Australian “run of mine” coal samples from Permian and Triassic deposits were analysed (Table 1). Four of these samples were from the collection of the Cooperative Research Centre for Coal in Sustainable Development (CCSD). This Centre’s archived website can be accessed at http://pandora.nla.gov.au/index.html (accessed May, 2011). The two other samples (Cal and Tar; Table 1) were feed coals from power stations in Queensland (Narukawa et al., 2003). The locations of the samples are identified in Fig. 1. The Warkworth (War) and Great Greta (GG) samples are from the Hunter Coalfield and the Newcastle Coalfield, respectively, in the northern part of the Permo-Triassic Sydney Basin and the adjacent Cranky Corner Basin. The Great Greta sample is from the Early to Mid-Permian Greta Coal Measures and the Warkworth sample is from the Late Permian Wittingham Coal Measures. Both are bituminous coals, the Warkworth coal having a vitrinite reflectance of 0.73% and the Great Greta coal 0.52%. The Greta Coal Measures are a terrestrial coal bearing unit formed during a marine regression (Agnew et al., 1995). The high pyrite levels are indicative of marine influence and organic sulphur contents are also high, further supporting a marine influence. The vitrinite reflectance is anomalously low in relation to other rank indicators (Ward et al., 2007), again due to marine influence on the coal deposit. The Warkworth mine is a multi-seam operation within the Jerrys Plains Subgroup, a sequence of terrestrial coals. This sequence formed in an environment of prograding delta sequences interrupted by marine incursions (Sniffin and Beckett, 1995). The coal seams were deposited on the delta plain. The Curragh (Cur) and Blair Athol (BA) samples are from the Permo-Triassic Bowen Basin in central Queensland. For much of its existence, the Bowen Basin was a region of shallow-water or terrestrial sedimentation. The rank of the coals in the basin is related to Triassic thrust faulting and Cretaceous intrusions. The Blair Athol sample is from the Blair Athol Coal Measures which are considered to have formed as a raised bog intermittently cut by fluvial flood plain deposits (Mallett et al., 1995). The rank is bituminous with a vitrinite reflectance of 0.60%. The Curragh sample is from the late Permian Rangal Coal Measures, which occur in the northern and central parts of the Bowen Basin. The coal is bituminous, with vitrinite reflectance values varying from 1.22 to 1.36%. The coal measures were deposited as freshwater paludal peats on a broad shelf (Mallett et al., 1995). The Callide Basin occurs in central Queensland and is a Mesozoic intermontane basin of which the Triassic Callide Coal Measures are a significant stratigraphic unit (Biggs et al., 1995). The rank is sub-bituminous, with vitrinite reflectance varying from

0.46% to 0.53%. The sample used in this study (Cal) is from run of mine production for the nearby Callide power station. The Tarong (Tar) sample was taken from the Meandu mine in the Triassic fault-bounded Tarong Basin in southeast Queensland, and represents the coal supplied to the nearby Tarong Power Station. The coal was deposited in a complex of alluvial fans, fluvial systems and alluvial plains with lacustrine and swamp environments (Pegrem, 1995). The coal is of bituminous rank, with a vitrinite reflectance of approximately 0.68%. 2.2 Analysis of the Coal Samples The moisture contents in the coals were determined by drying at 110oC in a nitrogen-purged oven (Standards Australia, 2000). The minerals present in the coals were determined by X-ray diffraction (XRD), after ashing in an oxygen plasma instrument at approximately 100ºC -150ºC; quantification of the diffractograms was made using the Rietveld-based SIROQUANT software package (Taylor, 1991; Ward et al., 2001). The total concentrations of most of the trace elements were determined using the following procedures. After ashing of the coals at 450oC, subsamples of the ash were either fused with lithium metaborate and the fused material dissolved with nitric acid or were dissolved with a mixture of hydrochloric, nitric and hydrofluoric acids in closed vessels (prior to measurement of the analyte concentrations, the excess fluoride was complexed with boric acid). The resulting solutions were analysed using inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). The exceptions to this approach were Hg, total S and B. Mercury was determined by cold vapour/atomic fluorescence spectrometry (AFS) after extraction of the coal with aqua regia (ASTM, 2006). Both total S and B were determined by ICP-AES following ashing in the presence of Eschka’s mixture and extraction with hydrochloric acid (Standards Australia, 1997; 1998). The sulfate S and pyritic S were determined using a sequential acid leach procedure with hydrochloric and nitric acids (Standards Australia, 2002) and subsequent measurement of soluble S and Fe using ICP-AES. The modes of occurrence of the trace elements and Fe in the coals were determined by sequential extraction (and subsequent measurement using standards prepared in matrices matched to the extractants). The sequential extraction procedures and operational fractions used in the study are described below:

a) Soluble: 10g coal was extracted with 200 mL MilliQ water in a closed polypropylene bottle; this was placed in an ultrasonic bath for 10 min to mix the contents; the bottle was then rolled for 18h at ambient temperature (23o-25oC). The extract was recovered by filtration; this was acidified prior to the determinations of the soluble trace elements.

b) Exchangeable species: the washed residue was extracted (by rolling) with 200 mL of 1M ammonium acetate for 18h at ambient temperature (23o-25oC) to release “exchangeable” trace elements

c) Carbonate, oxide and monosulfide associated: the washed residue was extracted (by rolling) with 150 mL of 6M HCl for 18h at ambient temperature (23o-25oC) to dissolve the trace elements associated with the carbonates, oxides and monosulfides. This would also dissolve any Fe3+ species including

those that may have formed from Fe2+ in the previous two steps – this would include any FeSO4.

d) Pyritic: the washed residue was extracted (by rolling) with 150 mL of 2M HNO3 to dissolve pyrite; again this was done for 18 h at ambient temperature (23o-25oC).

e) Silica bound: the silicate minerals in the washed residue were extracted with 25 mL conc, HF and 2.5 mL conc. HCl at 50oC in a heated ultrasonic bath for 2 h; the extract was diluted to 150 mL with MilliQ water

f) Residual: determined by difference (total – sum of extractable phases) indicative of an organic association, shielded components, or occurrence in a resistate mineral phase.

The extraction procedure used is similar to that used by Dale et al. (1999) and also Spears et al. (1998), but it should be noted that these latter researchers destroyed the organic matter with nitric acid prior to determining the silicate bound trace elements. Dai et al. (2004) used both physical and chemical separation to determine the modes of occurrence of an extensive range of elements in a Chinese coal field. In another study, Dai et al. (2008) used a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM–EDX) used to study the characteristics of the minerals and to determine the distribution of some elements in the coal. See also comments by Davidson (2000) and the Concluding Comments of this paper. In this study, the modes of occurrence of As, Pb, Ni, and Zn in four of the coals (GG, Cur, Cal and Tar) were determined by X-ray absorption fine structure (XAFS) spectroscopy (Huggins and Huffman, 1996), although typically only the X-ray absorption near-edge structure (XANES) portion of the spectrum was utilized for the investigation. This work was completed on beam-lines 11-2 of the Stanford Synchrotron Research Laboratory (SSRL) at Stanford University, California and X-18B of the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory, NY. The modes of occurrence of S were also obtained by XAFS spectroscopy at beam-line X-19A at NSLS. The speciation of iron in the same coals was estimated using 57Fe Mössbauer spectroscopy. Both the Mössbauer and XAFS techniques were done directly on the as-received coals and not on any extract residues or ash. 3. Results and Discussion The mineral phase percentages were calculated to a coal basis from the XRD results obtained on the low temperature ashes and are reported in Table 2. Also reported in Table 2 are the low temperature ash yields; these provide an approximation of the mineral matter content of the coals. The properties (proximate and ultimate analyses and mean vitrinite reflectance) of the coals are listed in Table 3. Note that there are differences in the ash yields reported in Tables 2 and 3 (i.e. LTA and 850oC ash); these are indicative in many instances of water of hydration, structural hydroxyl groups and sulfur as sulfate being retained in the LTA. The concentrations of total, pyritic and organic sulfur by difference (air dried basis) are listed in Table 4.

The analyses of the extractant solutions (from which the modes of the occurrence of the trace elements associated with each phase in the coals, as defined by the extracting medium, can be estimated) are given in Tables 5-10. The differences between the sum of the extracted trace elements and the total concentration, i.e. the residual concentrations, are often taken as the concentrations of organically associated trace elements. It should be noted that, in a few cases, the residual concentrations are expressed as negative numbers. In these few instances, the initial total concentration is less than the sum of the concentrations determined sequentially. Either there is an error in the determination of the total concentration or the sum of the errors associated with the sequential measurements is significant relative to the total concentration of specific trace elements in the coal. Note also that the minor and trace elements seen in the residual matter may be present as compounds or in mineral matter shielded by the residual organic matter. The results from interpreting the sulfur XANES spectra are summarised in Table 11, and the results of the analyses by Mössbauer spectrometry together with the % pyritic sulfur (Huffman and Huggins, 1978) are summarised in Table 12. The wt% pyritic sulfur in the coal was estimated from the Mössbauer data for pyrite using the method of Huffman and Huggins (1978). It should be noted that this estimate is generally in good agreement with the values obtained by the chemical extraction procedure based on the methods of Standards Australia (Table 4). However, this is not particularly so for the Cal coal sample, and thus the species identified as “pyrite?” in this spectrum is in all probability not pyrite but a non-magnetic iron oxide or oxyhydroxide phase. For the GG coal sample, the difference in the pyritic sulfur determinations is possibly due to the different extents of oxidation of the pyrite to produce sulfate. The pyrite in GG may have become more oxidized at the time the Mössbauer spectrum was obtained compared to when the analyses for forms of sulfur were conducted. 4. Discussion The occurrences of the minor and trace elements are discussed below: Sulfur Pyrite is common but occurs at low concentrations in the Gondwana coals of present-day Australia (Taylor et al., 1998). Pyrite has been identified in three of the coal samples by XRD (see Tables 2 and 3). However, the results of chemical analysis indicate that pyrite is present at low levels in all of the coals. Organic sulfur is high in the GG coal but present at low levels in all of the other coals. XAFS data on the speciation of the sulfur in four of the coals, GG, Cur, Cal and Tar, were reported and discussed previously (Riley et al., 2007). Also discussed in the earlier paper were the apparent discrepancies in each coal’s mineralogy obtained by XRD (Table 2) and the speciation of sulfur results (Table 4). This is particularly so for the GG coal. It was suggested that the sulfur-rich minerals, anhydrite, bassanite and gypsum identified as being present in this coal were predominantly artefacts of the low temperature ashing process (Riley et al., 2007).

In agreement with the comments above is the relatively low %S as sulfate in the GG coal (Table 11). The XRD analysis of the low temperature ash of this coal (Table 2) indicates that this coal contains significant amounts of bassanite and gypsum; although the %S (expressed in absolute terms in Table 4) as sulfate for this coal is the highest of the six coals, it is suggested that abundant calcium sulfates are formed during the LTA procedure. Electron microprobe studies by Ward et al. (2007) have indicated significant proportions of Ca (up to 1%) in the macerals of coals from this succession; these are also consistent with such a process for bassanite and gypsum formation. It should be noted also that XAFS results are expressed as a percentage of the non-pyritic sulfur in each of the four coal samples (Table 11). The sulfur concentrations in coals from the Great Greta sample are high and are predominantly organic; thus the low relative percentage of sulfate is a consequence of this high organic sulfur concentration. The large quantity of sulfate noted for the Cur coal is consistent with the significant amounts of iron sulfate identified in the Mössbauer spectrum of the same coal, likely as a result of pyrite oxidation. The high relative percentages of elemental sulfur in the coals are intriguing. These occurrences are not readily explained unless the elemental sulfur has formed as an oxidation product (see Davidson, 1993). Iron The modes of occurrence of iron are of interest as iron-bearing minerals are likely hosts for many of the trace elements. Hydrochloric acid soluble iron is likely to include iron carbonate (e.g. siderite) and iron oxides, e.g. iron hydroxy oxides or haematite. The amount of nitric acid extractable iron provides a measure of the pyrite content. As can be seen from the data in Tables 5-10, the majority of the iron in most samples is soluble in HCl. The most likely forms of HCl-soluble iron are carbonates or oxides, some of which may have formed as a consequence of oxidation of iron sulphates during extraction (see below, the results of Mössbauer spectroscopy and Table 12). All of the coals contain some pyritic iron (HNO3 soluble), significant proportions of which (>20% of the total iron) are present in the BA and GG coals. The BA coal also contains water-soluble iron; this is presumably as Fe2+ and may be indicative of some partial oxidation of the coal. The data from the Mössbauer spectroscopy (Table12) indicate that:

a) The GG coal contains pyrite, szomolnokite (ferrous sulfate), jarosite (potasssium ferric hydroxy sulfate) and possibly melanterite (ferrous sulfate). The sulfates of iron are likely products of pyrite oxidation. Significant fractions of the iron in this coal are soluble in HCl and in HNO3. This is consistent with the Mössbauer data.

b) The Cur coal contains iron bound to clays, siderite, pyrite and jarosite. The large proportion of iron that is HCl-soluble and the small proportion that is HNO3-soluble are consistent with the Mössbauer data.

c) The Cal coal contains haematite, siderite and possible pyrite; the acid extraction results are in agreement with the Mössbauer data in that the major portion of the iron in HCl-soluble.

d) The Tar coal contains iron oxyhydroxides and ferrous iron bound in clays. This is consistent with the results of the chemical fractionation in that the iron oxyhydroxides would be soluble in HCl and the clay bound iron (iron in silicate structures) would be soluble in HF/HCl. However the results of chemical fractionation indicate that some pyritic iron may be present. There is also some residual iron; it is unlikely that this is organically associated. There is some uncertainty in the interpretation of the data.

Based on the results reported in the Tables 5-10, the following comments can be made on the occurrence of each of the trace elements in these Australian coals: Arsenic According to the reports in Wedepohl (1969), As “can probably” substitute for Si, Al, Fe and Ti in the rock forming minerals; it may be present in high concentrations in magnetite and ilmenite. The monosulfide, arsenopyrite (FeAsS), is the most abundant ore mineral. Finkelman (1994) reports that As is most likely present in the pyrite in coal, with a possibly minor amount organically bound (confidence level in the assignments of As is 8 out of 10). Swaine (1990) suggests that some As may also be present as arsenate ions in clays or phosphate minerals. Dale et al. (1999) report that As is associated with pyrite. Kolker et al. (2000) report that As in US coals is principally associated with pyrite, as do Ward et al. (1999) for other Australian coal samples. In a related paper, Huggins et al. (2002) used a combination of sequential leaching and XAFS to analyse a bituminous coal from Ohio. The researchers report that arsenate is the species leached by HCl and As in the pyrite is leached by HNO3 and that the arsenate in this coal is likely a product of pyrite oxidation (Kolker and Huggins, 2007). Yudovich and Ketris (2005a), in an extensive review of As in coal, suggest that there are three dominant forms, i.e. pyritic, organic, and arsenate. The results of the sequential leaching (Tables 5 – 10) do not indicate that the As in these six Australian coals is principally associated with pyrite. This may be a consequence of the low pyrite content of the coals or indicative of oxidation of some of the coals. The data from sequential leaching and XAFS spectroscopy indicate that:

a) Arsenic in the BA sample is associated with HCl-soluble minerals (probably ankerite and jarosite), with a lesser proportion present in sulfide form (note that pyrite was not identified by XRD as being present but the mineral may be present at low concentrations).

b) Arsenic in the War coal is associated with the silicates (kaolinite, illite, smectite), with a lesser proportion associated with HCl-soluble minerals (probably ankerite) and even less in sulfide form (again, pyrite was not identified by XRD).

c) Arsenic in the GG coal is associated with HCl-soluble minerals (calcite, bassanite and gypsum), with a lesser proportion associated with the clays/silicates (kaolinite) and less present in the sulfide. The data from XAFS measurements indicate that most of the As is present as oxidised forms (i.e. arsenite or arsenate), with less present in the pyrite. Both techniques give results that are in agreement.

d) Arsenic in the Cur coal is primarily associated with carbonate or monosulfide minerals. The results from the XAFS spectroscopy indicate that the As is present primarily as arsenate, with possibly some arsenite and lesser amounts of As in sulfides. Again the results are in agreement. The XAFS data indicate that the As that is soluble in HCl is more likely to be present as an oxidised species rather than associated with or as a monosulfide.

e) Arsenic in the Cal feed coal is associated with silicates and is also present in the residual (organic) matter. The results from the XAFS technique again indicate that much of the As is in an oxidised form, and this is in agreement with the evidence for silicate bound (or associated) As. The signal/noise ratio for the Cal coal is of poor quality. Thus it is reasonable to conclude that As may be in other forms, i.e. reduced species in sulfides or organically bound, as indicated by the chemical fractionation.

f) Arsenic in the Tar sample is present in the silicates and in the carbonates, with minor amounts present in the sulfides (pyrite). The XAFS data support this conclusion.

Note that the negative values for As in three of the coals indicate that the sum of As found in the six extracts is greater than the total as analysed. This is probably a consequence of the difficulty of accurately measuring the low concentrations present in the extracts. The sum of these amounts also includes the sum of all the errors associated with the measurements. There is good agreement between the results from the chemical leaching approach and the results from the XAFS spectroscopy for the four coals studied by both techniques. The XAFS data enable one to generalise that any HCl soluble As in these coals is likely associated with carbonates or oxides rather than monosulfides, or may be present as arsenate as a result of pyrite oxidation. Boron As mentioned in the earlier paper (Riley et al., 2007), the B concentrations in five of the six coals are in the range of 6 – 20 mg/kg (Tables 5-10) and are indicative of freshwater influences. The Great Greta coal, GG, contains B at a concentration of 86 mg/kg, indicative of some marine influence (Goodarzi and Swaine, 1994). Wedepohl (1969) states that with few exceptions “boron occurs in chemical combination with oxygen” i.e. as borates; the exceptions are the minerals, ferrucite, NaBF4 and avogadrite, (K, Cs)BF4. Swaine (1990) indicates that most of the B is organically associated in coal. It should be noted that B also occurs in tourmaline, a highly refractory silicate mineral with a B concentration of up to approximately 3%. Thus the “organic association” may be indicative of minor amounts of acid-resistant tourmaline present in the residual organic matter following acid extraction. Boyd

(2002) studied the volatility of B in one Australian coal and noted that B if present in tourmaline is not volatile during ashing. The researcher used this fact and leaching behaviour to identify different modes of occurrence of B in this one particular coal. Boyd (2002) also provides a comprehensive review of the literature on B in coal. It can be seen from Tables 5-10, that in all the coals, the proportion of B present in the residual “organic” matter is 40% or greater. In two of the coals, B in the residual material is approximately 100% of that present. Boron is not present in the HF-soluble silicates in any of the coals. The results of the sequential leaching indicate that:

a) Boron in the BA coal is in a water soluble form, as well as in the HCl and HNO3 leachates. The major proportion is found in the residual matter (organic, shielded, or in a resistate mineral such as tourmaline).

b) Boron in the War coal is distributed in a similar manner to that in the BA coal. There is less water-soluble B and more B occurring in the HNO3 leachate (note that pyrite was not identified by XRD of the LTA). The major proportion is found in the residual matter (organic, shielded, or in resistate minerals).

c) Boron in the GG coal is associated with HCl-soluble minerals (e.g. calcite, siderite, bassanite and gypsum, or monosulfides), and also in the HNO3 leachate. The major proportion (approx 40%) is found in the residual matter (organic, shielded or resistate minerals). A very minor proportion is water-soluble; this may be a consequence of the oxidation of pyrite.

d) Boron in the Cur coal is almost exclusively found in the residual matter (organic, shielded or resistate minerals). There is a minor proportion that is water-soluble.

e) Boron in the Cal coal is almost exclusively found in the residual matter (organic, shielded or resistate minerals). There is a minor proportion that is water-soluble.

f) Boron in the Tar coal is in a water soluble form, as well as in the HCl leachate (carbonates or monosulfides) and in the HNO3 leachate (pyrite). The major proportion is found in the residual matter (organic, shielded or resistate minerals).

Beryllium According to Wedepohl (1969), Be is “widely distributed in low concentration in rock-forming minerals in which it replaces Si. In minerals the coordination number is always four”. Both Swaine (1990) and Finkelman (1994) suggest (level of confidence 4) that Be is associated with the organic matter with some present in clays. According to Finkelman (1994), there is “abundant evidence in the literature” that “indicates an organic affinity for Be. Few other elements are so consistently concentrated in the float fraction in laboratory float-sink experiments. Moreover, the Be content of coal varies inversely with ash yield”. Dale et al. (1999) report that Be is present in the silicates in the Australian coals studied by that group. It can be seen from the data in Tables 5-10 that:

a) Beryllium in the BA coal is associated primarily with the silicates (quartz and clays) and the carbonates/monosulfides (probably siderite). There does appear to be some Be associated with the pyrite and the hematite.

b) Beryllium in the War coal is primarily associated with the silicates.

c) Beryllium in the GG coal is present in the residual organic matter or in a shielded or resistate mineral (possibly beryl).

d) Beryllium in the Cur coal is probably associated with calcite, the silicates and either the residual organic matter, or a shielded or resistate mineral (possibly beryl).

e) Beryllium in the Cal coal is present in phases soluble in HCl (possibly bassanite and gypsum) and also HF (i.e. silicates). There appears to be some Be associated with sulfides.

f) Beryllium in the Tar coal is primarily in the silicates, with smaller proportions associated with carbonates/monosulfides, sulfides, and in the residual material (organic or shielded or resistate mineral).

The association of Be with organic matter is not generally seen in the results for these coals. Nor is there any relationship between the ash yield and the concentrations of Be (see Table 2). Of course, this survey is limited. If Be was associated with the organic matter, then an inverse relationship between ash yield and Be content is possible. The presence of the acid resistant mineral beryl, Al2Be3Si6O18, may partly explain the “organic” association reported by some researchers. This mineral would only have to be present at very low levels.

Bismuth There does not appear to be any work published on the direct speciation of Bi in coal. Spears and Tewalt (2009) used indirect measurements (i.e. regression analysis) to suggest that Bi is associated with the clays in a Late Carboniferous coal from the UK. Bismuth occurs at very low concentrations in the Australian coals of the present study, i.e. 0.13 – 0.32 mg/kg, and this in itself can lead to analytical errors. However, it can be seen from the data in Tables 5-10 that:

a) Bismuth in all the coals is present in the HCl extracts; this is indicative of Bi being present as oxides or carbonates, or perhaps present associated with monosulfides.

b) Bismuth is also present in the residual material in all of the coals. Significant amounts relative to those present in the HCl extract are present in the War, Cur, Cal and Tar samples. In fact, the Tar sample contains equal amounts of Bi in both forms (Table 10).

Cadmium

Finkelman (1994) reports (level of confidence 8) that Cd is predominantly associated with sphalerite, ZnS, although it may be found in other sulfides. This is in agreement with the summation of Swaine (1990). Goodarzi (2002) reports that Cd is associated with sphalerite in Canadian feed coals. Dale et al. (1999) report Cd as being present in the monosulfides, pyrite and also in the silicates. Although Finkelman (1994) rates the level of confidence at 8 for the assertion that Cd is predominantly associated with ZnS, there appears to be some uncertainty about the modes of occurrence of Cd in coal. The data reported here (Tables 5-10) indicate that Cd is present in many modes. However, Cd is present at extremely low concentrations, and there is the possibility of error in the measurement itself or from contamination. In fact, all the coal samples in the present study contain Cd at less than 0.2 mg/kg and the residual concentration is negative (i.e. total is less than the sum of the concentrations in all the extracts). Although the data set is limited, there is no obvious relationship between the Cd and Zn concentrations in the coal samples, apart from the fact that the two coals with the highest concentrations of Cd also have the highest concentrations of Zn. This does not exclude the possibility of Cd being present in sphalerite, as there is no reason to expect that the sphalerite in coals from different locations would contain similar concentrations of Cd. Obviously, for there to be a relationship between Cd and sphalerite, there is also a supposition that Zn is predominantly present as sphalerite. The XAFS data for Zn obtained on the GG, Cur, Cal and Tar coals indicate that sphalerite is the major form of Zn in only the latter two samples, and that Zn may be present as other species (see below). Cobalt Cobalt is most likely associated with sulfide minerals, but also in clays and in the organic matter (level of confidence 4, Finkelman, 1994). Dale et al. (1999) found that Co was associated with the silicates in the Australian coals studied by that group. Cobalt in the present series of samples (Tables 5-10) is distributed across all the modes of occurrence as defined by the analytical scheme. In all coals, Co is associated with silicates and with the residual matter (organic, shielded or resistate minerals). It is also present in the oxide/carbonate/monosulfide group, and also to a lesser extent in pyrite. Chromium Finkelman (1994) states that there “are insufficient data to specify the modes of occurrence of chromium in coal”. Some organic association is suspected (see also Swaine, 1990). Dale et al. (1999) report that Cr is present in the oxide/carbonate/monosulfide group, but that it may be present in the silicates and associated with the organic matter. Huggins et al. (1999) used XAFS spectroscopy to determine the valency of the Cr present in both coal and coal ash (see also Huffman et al., 1994). Those researchers concluded that Cr was present as Cr3+ in the coal. In a more recent paper, Huggins and Huffman (2004), state that “chromium appears to occur in most bituminous coals in only two major forms: as Cr3+ in organic

association and as Cr3+ in illite (although these conclusions were based principally on the findings of studies on coals from the USA). The data from the sequential leaching (Tables 5-10) indicate that:

a) Chromium in the BA coal is principally associated with the silicates. Minor proportions are found in the carbonate/monosulfide group and in the residual matter (organic shielded, or a resistate mineral).

b) Chromium in the War coal is distributed in a similar manner to that in the BA coal. The major proportion is found in the silicates and a significant proportion in the residual matter (organic, shielded or resistate minerals). A minor proportion is found in the oxide/carbonate/monosulfide group

c) The distribution of Cr in the GG coal is similar to that in the BA coal and very similar to the War sample, i.e. the major proportion is found in the silicates and significant proportions in the residual matter (organic, shielded or resistate minerals) and the oxide/carbonate/monosulfide group.

d) Chromium in the Cur coal is found principally associated with the silicates. A significant proportion is found in the oxide/carbonate/monosulfide group.

e) The distribution of Cr in the Cal sample is similar to that in the War coal, i.e. the major proportion is found in the silicates and a significant proportion in the residual matter (organic, shielded or resistate minerals). A very minor proportion is found in the oxide/carbonate/monosulfide group.

f) The distribution of Cr in the Tar coal is again similar to that in the War coal (and thus to that in the Cal).

Although, the data set is limited, the evidence is that Cr is generally present in the silicates and in the residual organic matter. These findings are in agreement with the observation of Huggins and Huffman (2004) and also the comments on an organic association by Swaine (1990). However, it is reasonable to consider that Cr may be present in resistate minerals. It is well known that Cr3+ can replace cations (isomorphous replacement) in highly resistate minerals such beryl, corundum, rutile, spinel and tourmaline (Wedepohl, 1969). Copper Copper is likely to be present in coal as chalcopyrite or other sulfides, and possibly as organically bound species (Swaine, 1990). Dale et al. (1999) report that Cu is present in the oxide/carbonate/monosulfide group, in the pyrite, and in the silicates. The data from the sequential leaching (Tables 5-10) indicate that Cu occurs in many modes in the coals of the present study:

a) Copper in the BA coal is principally found in the residual matter (organic, shielded or resistate minerals). There is some associated with the silicates and

also minor proportions in the carbonate/monosulfide group and in the sulfide (pyrite) fraction. There is a very small portion that is water-soluble.

b) Similarly, Cu in the War coal is in the residual matter (organic, shielded or resistate minerals). Copper is also found in the silicates, the sulfide and the carbonate/monosulfide group.

c) Copper in the GG coal is distributed “evenly” between the sulfide and the carbonates. Significant proportions are also found in the silicates, and the carbonate/monosulfide group. A lesser fraction is found in the residual matter (organic, shielded or resistate minerals), and as an ion-exchangeable form (possibly bound to clays).

d) Copper in the Cur coal is evenly distributed in the silicates, the sulfide and the residual matter (organic, shielded or resistate minerals).

e) Copper in the Cal coal is principally in the carbonates, the residual matter (organic, shielded or resistate minerals), the silicates and also in the oxide/carbonate/monosulfide group and the sulfide fraction.

f) The distribution of Cu in the Tar sample is similar to that in the Cal coal, i.e. principally in the oxide/carbonate/monosulfide group, the silicates and in the residual matter (organically bound, shielded or in resistate minerals).

Mercury In coal, it seems that much of the Hg is associated with pyrite (Finkelman, 1994, level of confidence 6). Swaine (1990) states that Hg is “probably associated with pyrite and sometimes sphalerite, with organically bound Hg still an uncertainty”. Dale et al. (1999) report that Hg is associated with the pyrite and that there is residual Hg present after acid extractions; this could be organically bound, or more likely Hg associated with finely dispersed pyrite, which is protected by coaly matter during acid leaching. The occurrence of Hg in US coals has been studied by the US Geological Survey (Tewalt et al., 2001), and the point is made that, because of the element's low concentration, "it is particularly difficult to determine the modes of mercury occurrence in coal". It is further stated that researchers suggest much of Hg in coal is associated with pyrite, although other forms in coal have been reported including organically bound, elemental, and in sulfide and selenide minerals (see Tewalt et al., 2001). Hower and Robertson (2003) report the presence of Hg in lead selenide in coal. Yodovich and Ketris (2005b) review the geochemistry of Hg in coal worldwide and suggest that Hg may be associated with the clays (silicates), organic matter and sulfides. The data in Tables 5-10 indicate that, in most of the coals of the present study, the Hg is predominantly associated with pyrite, but that other forms, including organically bound (or associated or shielded) and elemental Hg, as well as sulfides and selenides, are also possible. Manganese

Swaine (1990) states that Mn in coal is associated with carbonate minerals and clays. Finkelman (1994; confidence level 8) indicates that most of the Mn is in carbonates, especially siderite and ankerite. Consistent with this, Dale et al. (1999) found Mn present in the oxide/carbonate/monosulfide group. The data in Tables 5-10 indicate that, in most of the coals for the present study, the Mn is predominantly in an HCl-soluble form (oxide/carbonate/monosulfide group). However some of the Mn is present in association with other phases. There appears to be some associated with the silicates and sulfides. Some water-soluble Mn is also present in the BA and GG coals. Molybdenum Swaine (1990) states that “the mode of occurrence of molybdenum in coals ranges from mostly inorganic to mostly organic”. Dale et al. (1999) report that Mo is present in the monosulfides, pyrite and possibly associated with organic matter. The data for the present study (Tables 5-10) indicate that in most of the coals the Mo is found in the residual material (organically associated, shielded or present in resistate minerals). Nickel According to Finkelman (1994), there is a lack of any direct evidence for the modes of occurrence of Ni in coal; it may be either organically bound or associated with sulfides (level of confidence 2). The results of Dale et al. (1999) indicate that Ni is present in both the monosulfides and the organic matter. The results of chemical fractionation in the present study indicate that:

a) Nickel in the BA coal is associated with the silicates and also the residual matter (organic, shielded or in resistate minerals), with a lesser proportion present in the sulfide (pyrite was not identified by XRD but the mineral may be present at low concentrations).

b) Nickel in the War coal is associated with the residual matter (organic, shielded or in resistate minerals), with a lesser proportion associated with the silicates (kaolinite, illite, smectite).

c) Nickel in the GG coal is distributed over a number of modes, i.e. water soluble, extractable in the oxide/carbonate/monosulfide group, pyrite and the silicates. It is not obvious why the Ni is so widely distributed. It may be a result of some oxidation.

d) Nickel in the Cur coal is primary associated with the residual matter (organic, shielded or in resistate minerals), with lesser proportions in the oxide/carbonate/monosulfide group and the silicates.

e) Nickel in the Cal sample is distributed over a number of modes i.e. in the residual matter (organic, shielded or in resistate minerals), the silicates, pyrite and also in the oxide/carbonate/monosulfide group.

f) Nickel in the Tar coal is present in the oxide/carbonate/monosulfide group, the silicates and pyrite. Some contamination has apparently occurred with this sample during extraction, as the sum of the Ni in these modes is greater than the analytical result for the “total” Ni concentration.

Lead Lead in coal occurs as sulfides (galena) or associated with sulfide minerals (Finkelman, 1994; level of confidence 8). The presence of lead selenide has been reported in coals (Hower and Robertson, 2003), and Dale et al. (1999) report that some of the Pb is present in the silicates. As can be seen in Tables 5-10, Pb is predominantly in an HCl-soluble form in all the coals in the present study. This is consistent with it being present as a monosulfide (e.g. galena). There also appears to be some (minor) Pb in the silicates and in the sulfides (e.g. pyrite) in all of the coals. The XAFS spectroscopic data indicate that Pb is present primarily as lead sulfide in the Cur and Tar coals, and this is consistent with the Pb being soluble in HCl. Antimony According to Wedepohl (1969), Sb can probably substitute for Fe in many minerals. It is possibly found in ilmenite; there are also numbers of Sb-bearing sulfide minerals e.g. stibnite Sb2S3. It is possible for Sb to occur as a substitute for iron in sulfides such as pyrite. Swaine (1990) states that “It is not clear how Sb occurs in coals, but it is likely that an organic association prevails in many coals, together with a sulfide association.” According to Finkelman (1994), Sb may be present in pyrite and as accessory sulfides (e.g. stibnite) dispersed through the organic matter. Finkelman (1994) also states that some Sb “may be organically” bound; the level of confidence, however, is low (4 out of a possible 10). It is apparent (Tables 5-10) that Sb is primarily in two forms within the coals of the present study, a species soluble in HF (i.e. in the silicates) and an insoluble form (e.g. organically bound, shielded or in acid resistate minerals such as ilmenite). Thorium The scarcity of Th, its ability to substitute for other elements in crystal lattices, and the absence of a geochemical method of concentration of the element all combine to render Th a highly dispersed material (Wedepohl, 1969). It is adsorbed into clays and retained in “heavy resistate” minerals. According to Swaine (1990), Th is unlikely to be organically bound. It is also found in minerals such as monazite and zircon. Finkelman (1995) agrees that Th is likely to be “associated with monazite with minor amounts in xenotime, zircon, and perhaps some clays”. The presence of Th in “resistate” minerals such as monazite and zircon is a likely explanation for its occurrence in the residual organic matter of the coals studied

(Tables 5-10). However, Th is also present in an HCl-soluble phase (oxide/carbonate/monosulfide), and also appears to be associated with the silicates (e.g. clays). Thallium Finkelman (1995) suggests that Tl in coal is most likely associated with pyrite (although the level of confidence is low, 4 out of 10). Thallium is distributed across most phases in all the coals covered by the present study (Tables 5-10). Relatively high residual Tl is found in the Cur and Tar coals. There is no indication from the results that Tl is predominantly in the HNO3 extract (associated with pyrite) in any of the Australian coals studied. Uranium According to Wedepohl (1969), oxidation of U minerals results in the formation of carbonates, phosphates, vanadates, silicates and sulfates of U. Swaine (1990, pp 170-171) states that in coal “U may be in the mineral matter but also organically bound to the coal. In the latter form, it would presumably be volatile”. In the present series of coals (Tables 5-10), U is present at trace levels, generally in or associated with oxide/carbonate/monosulfides and in the silicates (quartz and feldspars); it is also apparent that a high percentage of the U is present in the residual matter of all the coals after extraction. It may be present in association with organic matter as suggested by Swaine (1990). However, Finkelman (1995) states that “Much of the U in coal appears to be organically bound. However, a substantial proportion of the U in high-rank coals may be associated with accessory minerals such as zircon and rare-earth phosphates”. It is thus also conceivable that U is present in the resistate mineral, monazite, in the coals of the present study. It is also apparent from examination of the data in Tables 5-10, that both U and Th often have a similar distribution, i.e. in the HCl-soluble and HF-soluble fractions and also in the residual matter. The one exception to this is the distributions in the Cur sample, in which there is a significant amount of U in the residual matter but little or no Th in the same fraction. It is a matter of conjecture, but this could indicate that the U is associated with the organic phase in this coal rather than being present in a resistate Th/U mineral phase. If U but not Th was organically bound then it is to be expected that the ratio of Th to U would vary significantly in those coals where U was “organically bound”. Zinc Although there are significant errors in the estimation of residual Zn (often the value is negative, and it well established in analytical chemistry that Zn may be a notorious contaminant), it is obvious that predominant occurrence of Zn in all of the coals is in the HCl-soluble phase. Zinc is most likely to occur as sphalerite, ZnS in coal (Swaine, 1990). The results of Dale et al. (1999) are consistent with this observation.

Finkelman (1994 and1995) gives a confidence level of 8 (out of 10) to the probability of Zn occurring as sphalerite. The chemical fractionation data (Tables 5-10) indicate that Zn in the coals studied is generally present in a phase soluble in HCl. This is consistent with it being present as sphalerite. It is also possible that the HCl-soluble Zn is associated with carbonates or oxides or adsorbed on to clays (such as illite). Unfortunately, there is evidence that contamination has occurred in some samples during extraction; the sums of the amounts extracted are significantly greater than the totals as analysed directly on the coals (e.g. War, GG and Cur). The data from XANES spectroscopy indicate that:

a) The spectrum from the Zn in the GG coal is quite unlike that from any coal examined by the authors previously. The Zn in the GG coal is predominantly present as ZnO, with a lesser fraction in the clays (illite) and possibly as other forms (unidentified). Any Zn as the oxide is soluble in HCl and the chemical fractionation results indicate that the bulk of the Zn is HCl-soluble. Zinc adsorbed on to illite would also be extracted with HCl.

b) The Zn in the Cur coal is predominantly present as Zn bound to illite, with possibly some Zn in the silicates or other species. Again, the chemical fractionation indicates that most of the Zn is extractable with HCl (as is possible if the Zn is in chlorite which is present in this coal).

c) The Zn in the Cal coal is predominantly present as ZnS (sphalerite), with a lesser proportion of Zn bound to illite. It is possible that Zn as sulfate or silicate may be present. These results are consistent with the Zn being extractable with HCl.

d) The Zn in the Tar coal is also predominantly ZnS, with possibly some bound to illite and present as other unidentified forms.

In the case of Zn, the data from XANES enable identification of Zn species that are soluble in HCl. It is apparent that it is simplistic to assume that all the Zn soluble in HCl is predominantly ZnS (sphalerite). 5. Concluding Remarks It is possible to criticise most (if not all) results obtained from studies of speciation or modes of occurrence of trace elements in coal based on selective extraction techniques. It may be simply that some of the extraction or separation techniques used do not obtain a “pure” extract of the species of interest. Some of the physical separation techniques may depend on particle size, i.e. some species may be shielded by organic matter; this also may be a factor during chemical separation. As well, species may change during chemical extraction (e.g. precipitate or oxidise). In this study, the chemical extraction techniques were used to obtain data on speciation/occurrence of trace elements (often at very low concentrations) in Australian coal samples. However, such data, if generated with care and interpreted with the same care, do provide a very good indication of the speciation/occurrence. There is obviously one significant limitation in the technique used, and that is the residual concentration of a trace element being used to indicate that the trace element

is organically associated. Such an occurrence could equally be interpreted as being indicative of an association with residual mineral matter (either shielded by organic matter or in an acid resistant mineral) or simply an analytical error. The certainty of any designation is obviously increased by the use of sophisticated techniques such as XANES/XAFS, although even these techniques may lack the required sensitivity (detection limits) or may not be applicable to some trace elements. Nevertheless, this compilation of speciation data is the most comprehensive ever reported on a suite of Australian coals. These data provide information on the modes of occurrence of a range of elements. Such data provide information on the likely residences of these elements within the coals and, apart from being of interest to geologists who are studying the occurrence of these elements in coals, the data may be of use in providing information of the behaviour and impact of these elements when the sampled coals are utilised. 6. Acknowledgements

The authors wish to acknowledge the comprehensive work completed by the two anonymous reviewers and to Colin Ward and Shifeng Dai, and also the financial support provided by the Cooperative Research Centre for Coal in Sustainable Development, which was funded in part by the Cooperative Research Centres Program of the Commonwealth Government of Australia. The XAFS/XANES investigations were performed at the National Synchrotron Light Source, Brookhaven National Laboratory, NY, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

7. References

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Table 1. Description of coal samples Ident. Coal (location) Description BA Blair Athol Bituminous; blend of Nos 1, 3 and 4 seams

from the Permian Blair Athol Basin, Queensland.

War Warkworth Bituminous; blend of six seams (Vaux, Mt. Arthur, Piercefield, Glen Munro, Woodlands Hill and Blakefield ) from the Permian Wittingham Coal Measures of the Sydney Basin, Hunter Valley, NSW.

GG Great Greta Bituminous; from the Great Greta Colliery; early Permian Tangorin seam (marine influenced), Cranky Corner Basin, Hunter Valley, NSW

Cur Curragh Bituminous; from the Cancer, Aries, Castor, Pollux and Pisces seams within the late Permian Rangal Coal Measures of the Bowen Basin, Queensland.

Cal Feed to Callide Power Station Sub-bituminous; blend of several seams from the Late Triassic Callide Basin, Queensland

Tar Feed to Tarong Power Station Bituminous; blend of three seams from the Triassic Tarong Basin, Meandu, Queensland.

Table 2. Calculated percentages of mineral phases in coals (from XRD analyses of

low temperature ashes)

Coal: BA War GG Cur Cal Tar % Quartz 2.58 4.67 1.00 5.93 4.22 17.90 Kaolinite 5.62 5.27 6.05 4.77 19.27 18.30 Illite 0.15 2.96 1.37 Smectite 0.05 0.17 0.19 0.13 Chamosite 4.08 Anatase 0.23 0.37 Brookite 0.28 Boehmite 0.14 Hematite 0.17 0.04 0.85 Calcite 3.50 2.27 Ankerite 0.59 Siderite 0.11 0.79 2.72 Bassanite 1.92 1.79 0.91 Gypsum 2.18 Anhydrite 2.61 Jarosite Pyrite 0.22 1.05 0.57 Total ash yield

8.9 13.9 18.5 21.8 28.3 36.6

(low temperature)

Table 3. Coal Analyses – Proximate, Ultimate and Vitrinite Reflectance

Coal BA War GG Cal Cur Tar

Proximate Analysis (ad)# Air-dried moisture 7.9 2.8 1.4 8.0 1.3 1.8 Ash 8.1 11.9 14.1 21.4 19.9 nd* Volatile Matter 27.0 31.4 43.2 24.5 19.1 nd* Fixed Carbon 57.0 53.9 41.3 46.1 59.7 nd*

Ultimate Analysis (daf)## Carbon 83.5 83.7 81.6 78.1 88.1 79.0 Hydrogen 4.84 5.45 6.09 4.30 4.57 5.5 Nitrogen 1.84 1.81 1.25 1.12 1.70 1.4 Sulphur 0.35 0.47 6.29 0.30 0.90 0.7 Oxygen 9.50 8.60 4.80 16.20 4.70 13.4

Mean Maximum Vitrinite Reflectance % 0.60 0.73 0.52 0.46 1.31 0.64

nd*: not determined ad#: air dried basis daf##: dry ash free basis Table 4. Concentrations of the Sulfur Species in the Coals

Coal Sulfur Species (% air dried)

Total Pyritic Sulfate Organic

BA 0.29 0.12 0.02 0.15 War 0.40 0.07 <0.01 0.33 GG 5.32 0.53 0.12 4.67

Cur 0.71 0.36 0.08 0.27 Cal 0.19 0.02 0.02 0.15 Tar 0.23 0.06 0.02 0.15

Table 5. Distribution of trace elements (mg/kg, on an air-dried basis) in leachates and residue (by difference) of BA Total as

analysed MilliQ 1M

acetate 6M HCl 2M

HNO3 HF/HCl Residual As 2.3 0.01 <0.01 1.22 0.51 <0.01 0.6 B 20 2.3 0. 6 3.5 3.0 <0.1 10.6 Be 0.73 0.02 <0.01 0.33 0.085 0.23 0.07 Bi 0.15 <0.01 <0.01 0.14 0.002 <0.01 0.01 Cd 0.07 0.02 0.01 0.02 0.01 0.02 -0.01 Co 1.9 0.10 0.02 0.70 0.05 0.56 0.5 Cr 5.0 0.01 <0.2 0.84 0.150 3.8 0.2 Cu 6.2 0.16 <0.04 0.76 0.5 1.20 3.6 Fe 2392 253 0.17 1345 620 124 50 Hg 0.058 <0.005 <0.005 <0.005 0.024 <0.005 0.034 Mn 9.3 2.06 0.90 6.91 0.03 0.4 -0.7 Mo 0.87 <0.01 0.009 0.02 0.18 0.05 0.61 Ni 4.30 0.12 <0.01 0.49 0.59 1.60 1.50 Pb 5.0 0.01 0.05 4.56 0.23 0.69 -0.5 Sb 0.14 <0.01 <0.01 <0.01 0.02 0.07 0.05 Th 3.5 <0.01 <0.01 0.81 0.051 1.80 0.8 Tl 0.07 0.01 0.01 <0.01 0.01 0.01 0.03 U 0.71 <0.01 0.003 0.15 0.05 0.27 0.23 V 6.7 <0.01 <0.01 2.48 1.20 2.81 0.2 Zn 20 2.65 0.16 14.73 2.46 1.15 -1

Table 6. Distribution of trace elements (mg/kg, on an air-dried basis) in leachates and residue (by difference) of War. Total as

analysed MilliQ 1M

acetate 6M HCl 2M

HNO3 HF/HCl Residual As 0.43 <0.01 <0.01 0.17 0.04 0.30 -0.08 B 15 0.6 <0.1 2.5 4.0 <0.1 7.9 Be 1.8 <0.01 <0.01 0.26 0.10 1.12 0.3 Bi 0.19 <0.01 <0.01 0.13 <0.01 <0.01 0.06 Cd 0.09 <0.01 <0.01 0.03 <0.01 0.09 -0.03 Co 6.4 <0.01 0.06 0.72 0.07 2.3 3.3 Cr 6.9 <0.01 <0.01 0.87 0.10 4.2 1.7 Cu 7.60 <0.01 0.10 1.7 1.4 1.7 2.7 Fe 3140 <0.2 <0.2 2294 283 572 -9 Hg 0.015 <0.005 <0.005 <0.005 0.013 <0.005 0.002 Mn 25 0.31 1.27 20.8 0.82 3.4 -2 Mo 0.64 0.02 <0.01 0.04 0.09 0.03 0.46 Ni 7.1 0.02 0.09 0.55 0.32 1.80 4.3 Pb 6.8 <0.01 0.39 4.86 0.48 0.87 0.2 Sb 0.59 <0.01 <0.01 0.02 0.02 0.24 0.31 Th 3.0 <0.01 <0.01 1.57 0.031 0.65 0.8 Tl 0.11 <0.01 0.01 <0.01 0.02 0.04 0.04 U 1.02 <0.01 0.01 0.25 0.03 0.18 0.54 V 29 <0.01 <0.01 2.4 2.2 19.2 5 Zn 15 <0.01 2.0 13.1 2.3 3.5 -6

Table 7. Distribution of trace elements (mg/kg, on an air-dried basis) in leachates and residue (by difference) of GG Total as

analysed MilliQ 1M

acetate 6M HCl 2M

HNO3 HF/HCl Residual As 1.7 <0.01 <0.01 1.42 0.22 0.30 -0.2 B 86 5.3 1.8 25 17 1.4 35 Be 0.95 <0.01 <0.01 0.10 0.04 0.20 0.62 Bi 0.22 <0.01 <0.01 0.19 0.01 <0.01 0.02 Cd 0.10 <0.01 0.025 0.05 0.01 0.03 -0.02 Co 1.9 0.057 0.070 0.50 0.08 0.59 0.6 Cr 9.4 <0.01 <0.01 2.09 0.16 5.1 2.1 Cu 13 0.06 0.71 5.6 4.0 1.8 1 Fe 6613 <0.2 <0.2 5119 1750 112 -368 Hg 0.16 <0.005 <0.005 0.02 0.059 <0.005 0.08 Mn 160 29.9 32 82.66 6.2 16.2 -7 Mo 0.73 0.014 0.009 0.10 0.12 0.09 0.4 Ni 4.0 0.54 0.66 1.42 0.45 0.90 0 Pb 5.0 <0.01 0.019 4.86 0.70 0.33 -0.9 Sb 0.25 <0.01 <0.01 0.08 0.02 0.06 0.09 Th 1.2 <0.01 <0.01 0.40 0.04 0.35 0.41 Tl 0.15 <0.01 0.03 0.05 0.03 0.04 <0.01 U 0.57 <0.01 <0.01 0.05 0.03 0.13 0.35 V 20 0.01 0.02 2.3 2.3 11 5 Zn 7.7 <0.01 <0.01 8.6 1.1 0.68 -2.3

Table 8. Distribution of trace elements (mg/kg, on an air-dried basis) in leachates and residue (by difference) of Cur. Total as

analysed MilliQ 1M

acetate 6M HCl

2M HNO3 HF/HCl Residual

As 0.93 <0.01 <0.01 0.58 0.10 <0.01 0.25 B 5.3 0.2 <0.1 < 0.1 < 0.1 <0.1 5.1 Be 0.70 <0.01 <0.01 0.16 <0.01 0.21 0.33 Bi 0.13 <0.01 <0.01 0.09 <0.01 <0.01 0.04 Cd 0.05 <0.01 0.021 0.02 <0.01 <0.01 0.01 Co 5.7 0.01 0.07 2.3 0.15 0.68 2.5 Cr 8.3 <0.01 <0.01 3.0 0.06 4.9 0.4 Cu 13 0.01 0.68 1.0 4.1 3.8 3.4 Fe 18473 <0.2 <0.2 15192 1940 485 856 Hg 0.022 <0.005 <0.005 <0.005 0.009 <0.005 0.013 Mn 150 0.6 24 131 2.4 1.1 -9 Mo 0.25 0.01 <0.01 0.10 0.05 <0.01 0.09 Ni 10 0.11 0.56 2.6 0.45 1.7 4.6 Pb 3.9 <0.01 <0.01 2.7 0.47 0.92 -0.2 Sb 0.19 <0.01 <0.01 0.03 0.01 0.06 0.09 Th 1.4 <0.01 <0.01 0.71 0.01 0.77 -0.1 Tl 0.04 <0.01 <0.01 <0.01 <0.01 <0.01 0.04 U 0.47 <0.01 0.02 0.16 <0.01 0.12 0.17 V 32 <0.01 0.05 11 0.30 16 5 Zn 8.7 <0.01 0.18 11 1.5 0.85 -5.3

Table 9. Distribution of trace elements (mg/kg, on an air-dried basis) in leachates and residue (by difference) of Cal. Total as

analysed MilliQ 1M

acetate 6M HCl 2M

HNO3 HF/HCl Residual As 1.7 <0.01 <0.01 0.19 0.11 0.60 0.8 B 18 2.8 0.6 3.5 3 <1 8.1 Be 0.82 <0.01 <0.01 0.37 0.13 0.28 0.05 Bi 0.28 <0.01 <0.01 0.17 <0.01 <0.01 0.11 Cd 0.15 <0.01 <0.01 0.06 0.02 0.11 -0.04 Co 6.6 <0.01 0.09 1.8 0.38 1.10 3.2 Cr 12 <0.01 <0.2 0.76 0.45 6.4 4.4 Cu 19 <0.01 <0.04 10 1.6 3.1 4 Fe 22839 <0.2 <0.2 19492 630 765 1952 Hg 0.022 <0.005 <0.005 0.011 0.020 0.007 -0.016 Mn 439 0.89 29 371 0.26 3.5 34 Mo 0.81 <0.01 <0.01 0.02 0.05 0.14 0.6 Ni 13 <0.01 0.09 1.7 1.9 3.8 5.5 Pb 8.8 <0.01 0.03 6.2 0.61 1.4 0.6 Sb 0.21 <0.01 <0.01 0.01 0.02 0.08 0.1 Th 3.9 <0.01 <0.01 2.2 0.11 0.66 0.9 Tl 0.15 <0.01 0.02 0.01 0.08 0.01 0.03 U 1.06 <0.01 <0.01 0.33 0.06 0.22 0.45 V 33 <0.01 0.02 13 4.6 13 3 Zn 33 0.03 0.22 24 2.0 2.4 5

Table 10. Distribution of trace elements (mg/kg, on an air-dried basis) in leachates and residue (by difference) of Tar Total as

analysed MilliQ 1M

acetate 6M HCl 2M

HNO3 HF/HCl Residual As 1.7 0.11 <0.01 0.62 0.14 1.3 -0.5 B 12 1.0 <0.1 2.6 3.0 <0.1 5.4 Be 1.5 <0.01 <0.01 0.27 0.19 0.78 0.3 Bi 0.32 <0.01 <0.01 0.16 <0.01 <0.01 0.16 Cd 0.16 <0.01 0.03 0.09 0.01 0.12 -0.1 Co 7.2 0.14 0.56 2.7 0.50 1.3 2.0 Cr 7.5 <0.01 <0.01 0.55 0.14 4.6 2.2 Cu 21 0.04 <0.04 11 2.8 4.1 3.0 Fe 646 <0.2 <0.2 214 57 234 141 Hg 0.022 <0.005 <0.005 <0.005 0.014 <0.005 0.008 Mn 5.5 0.25 1.5 2.7 0.02 0.9 0.2 Mo 1.7 0.10 0.33 0.10 0.08 0.12 0.97 Ni 4.4 0.09 0.32 3.2 1.2 2.1 -2.5 Pb 10 <0.01 0.25 6.9 0.75 1.3 0.8 Sb 0.31 <0.01 <0.01 0.02 0.01 0.08 0.2 Th 4.6 <0.01 <0.01 1.9 0.04 0.77 1.9 Tl 0.28 <0.01 0.04 <0.01 0.05 0.02 0.17 U 1.4 <0.01 <0.01 0.20 0.03 0.29 0.88 V 65 0.34 0.30 8.9 11 31 14 Zn 62 0.78 5.1 51 2.4 1.6 1

Table 11. Distribution of sulfur among the major sulfur forms in four coals (excluding pyrite and other metal sulfides) as determined by XANES spectrometry .

Coal Relative % of the S Forms Present (other than as sulfides)

Elemental. S

Organic sulfide Thiophenic Sulfone Sulfate

GG <3 21 73 <2 6 Cur 10 <5 49 3 38 Cal 29 <5 48 2 21 Tar 5 7 74 <2 14

Table 12. 57Fe Mössbauer results including % Pyritic S on four Australian coals (note that % Fe is relative to total Fe and pyritic sulfur is on an air-dried basis)

Coal Mössbauer Component IS QS H0 Width %Fe Mineral Pyritic

S

Cal 1Q 1.21 1.80 0.26 27 Siderite 2Q 0.32 0.63 0.60 16 Pyrite? 0.41 1M 0.40 -0.07 489 0.44 17 Hematite 2M 0.40 -0.07 459 1.20 39 Hematite

Cur 1Q 0.31 0.59 0.28 13 Pyrite 0.30 2Q 1.23 1.78 0.40 27 Siderite 3Q 0.29 1.19 0.29 10 Jarosite 4Q 1.15 2.67 0.30 50 Clay/Fe2+

GG 1Q 0.32 0.59 0.31 40 Pyrite 0.28 2Q 1.27 2.72 0.26 34 Szomolnokite 3Q 0.35 1.06 0.34 24 Jarosite 4Q 1.27 3.52 0.31 2 Melanterite?

Tar 1Q 0.37 0.78 0.73 74 FeOOH? <0.04 2Q 1.13 2.64 0.54 26 Clay/Fe2+

Note that “Pyrite?”, “Melanterite?” and “FeOOH?” are probable species in the relevant coal samples. Note also the Components: Q – Quadrupole doublet; M – Magnetic sextet. Mössbauer parameters: IS – isomer shift, relative to metallic iron; QS – quadrupole splitting; H0 – Magnetic hyperfine splitting in kGauss. Width – full peak width at half maximum height. % Fe is the percentage of the total iron in the coal present in the iron-bearing mineral; it is derived from the relative areas under the Mossbauer peaks attributed to each mineral.

Figure 1. Location of samples in relation to coalfield areas of eastern Australia