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Trace metal speciation in Julia Creek oil shale
Chemical Geology., 91 ( 1991 ) 115-124 Elsevier Science Publishers B.V., A m s t e r d a m
115
Trace metal speciation in Julia Creek oil shale A.V. Hirner and Z. Xu * Mineralogisch-Petrographisches Institut, Universitgit M~inchen, Theresienstr. 41. D-8000 Miinchen 2. Federal Republic of. Germany (Accepted for publication November 13, 1990 )
ABSTRACT Hirner, A.V. and Xu, Z., 1991. Trace metal speciation in Julia Creek oil shale. In: J.F. Branthaver and R.H. Filby (GuestEditors ), Trace Metals in Petroleum Geochemistry. Chem. Geol.. 91 : 115-124. The speciation of sixteen trace elements in Julia Creek oil shale was estimated based on the comparative evaluation of three different models referring to various chemical digestion procedures. Demineralisation steps were monitored by Xray diffraction and X-ray fluorescence spectrometry, and the results discussed together with those reported in literature. While it is possible to determine some element concentrations in the carbonate (e.g. Mn, Sr ), in the silicate (e.g. Ti, V ), and in the sulfide fractions (e.g. Cu, Ga, As ), concentrations in the kerogen phase can only be estimated within a relatively broad range. Element distributions between different sedimentary phases seem to be very similar when comparing Julia Creek with other oil shales.
1. I n t r o d u c t i o n
Australia's most extensive oil shale deposits are located in Queens land (estimated reserves 4 X 109 t of shale and > 2000 billion barrels of oil ). Since 1968, the Julia Creek deposit found within the Upper Cretaceous Toolebuc Formation has been studied for commercial development. A significant contribution to modern porphyrin structural analysis was obtained by investigating Julia Creek shale oil (Fookes and Loeh. 1983; Fookes, 1983, 1985; Miller et al., 1984). Furthermore, interest in trace-element speciation in Julia Creek oil shale arose because of the desired recovery of by-products (esp. V and Mo ), as well as the possible release of toxic elements into the environment during oil shale retorting and leaching of spent shale *Present address: Box 215, Qingyang Gangsu, People's Republic of China.
dumps (Dale and Fardy, 1984; Patterson et al., 1987, 1988a). Consequently, the associations of trace elements with specific mineral phases were elucidated by applying instrumental analytical techniques (e.g. atomic absorption and emission spectroscopy, mass spectrometry, instrumental neutron activation analysis), selective leaching procedures, electron microprobe analyses, and interelement correlation techniques (Riley and Saxby, 1982; Riley, 1983; Ekstrom et al., 1983; Dale and Fardy, 1983; Dale et al., 1984a, b; Glikson et al., 1985; Glikson and Taylor, 1986; Patterson et al., 1986). Among other recent and fossil sedimentary material, Julia Creek shale samples had been subjected to bio-inorganic studies of our group, especially in respect to their soluble and insoluble organic constituents (Hirner et al., 1990). The aim of the present paper is to contribute to the evaluation of the quantitative distribution of trace elements between various organic
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116
and inorganic components by chemical methods. In particular, stepwise demineralisation of the shale samples was monitored by X-ray diffraction as well as X-ray spectrometry, and the results are discussed in the light of the relevant data gained by the Australian scientists mentioned above. 2. Geochemistry of Julia Creek oil shale The organic matter of the Toolebuc Formation is of extremely uniform composition; total organic carbon (TOC) ranges up to 20 wt.% and is probably derived from (partly modified ) marine algal matter with only minor contributions from terrestrial organic matter (Boreham and Powell, 1984, 1987). Julia Creek kerogen is largely of planktonic origin (type II), H / C = 1.1 to 1.2, O / C = 0 . 1 to 0.4, its sulfur content ranges up to 8 wt.%, and biological marker studies indicate low maturity. The kerogen shows vitrinite reflectance values (Ro) from 0.48 to 0.60% (Crisp et al., 1987), and a major portion of it (approx. 45%) is of aromatic structure with a high degree of crosslinking as well as the presence of multiple functionalised aliphatic and aromatic acids (Chaffee and McLaren, 1986). The bituminous calcareous shale (oil shale) is interbedded with coquinites and displays abundant fine, dark-brown laminae in a microcrystalline calcite and clay matrix in accordance to the characteristic morphology of algal mats (Ramsden, 1983; Glikson et al., 1985; Glikson and Taylor, 1986 ). Electron microscope studies (SEM and TEM) have shown that the shale matrix contains abundant coccolith fragments (i.e. calcareous algal plates), together with residues of Oscillatoria, and humic acids as well as associations of bacterial cell walls with Cu, of cyanobacteria with Mo, and of clay minerals with V. The dominant maceral present in Julia Creek kerogen is bituminite with associated micrinite and minor amounts of lamalginite, telalginite, liptodetrinite and inertodetrinite (Sher-
A.V. HIRNER AND Z. XU
wood and Cook, 1983, 1986). Following a modified gyttja model, bituminite is thought to have formed by lithification of an organic gel derived from bacterial attack of the original source material (algae, algal-fungal mat), anaerobically deposited below oxygenated, nutrient-rich waters (Sherwood and Cook, 1986; Boreham and Powell, 1987 ). The geology of the Julia Creek deposit is described by Exon and Senior ( 1976 ) and Senior etal. (1978). 3. Experimental techniques The analytical scheme for separation of the bulk sample into three inorganic as well as three organic fractions is presented in Fig. 1. The chemical compositions of fractions F I, F2, F3, R I and R4 were determined in a parallel study (Hirner et al., 1990). While the organic extract was received by Soxhlet extraction in dichloromethane, non-solvent extractable lipids (humic and fulvic acids) were released by reflux in alkaline solution (0.5 N KOH-methanol-benzene) followed by ether extractions. Demineralisation was accomplished by treating the samples with conc. HCI at 80°C for 2 hr. and with 52% HF at 80°C for 2 hr., respectively, each followed by intensive waterwashing until no residual halogen ions could be precipitated by silver nitrate. Finally, the residuum of HC1/HF treatment was exposed to Kiba solution (H3PO 4 + 50/oSnC12) at 270 ° C for I hr. Complete removal of pyrite by a milder agent like boiling HC1-SnClz-solutions (Chanton, 1985) could not be achieved. The individual demineralisation steps were monitored by X-ray diffraction ( X R D ) for the presence of more than a dozen minerals (carbonates, silicates, sulfates, sulfides, phosphates), and by X-ray fluorescence (XRF) for the concentrations of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Sr, Zr, Mo, Cd, and Pb. XRF procedures were those usually applied for the measurement of pressed powder pellets using the intensity of the Compton-scattered pri-
TRACEMETALSPECIATIONIN JULIACREEKOIL SHALE sample weight
I00.00
1[7
(g)
dried bulk s a m p l e organic solvent extraction
organic e x t r a c t F1
98.70
alkali 98.51
extraction
IR2
HF e x t r a c t i o n
29.29
humic
acids
and f u l v i c F2
i RCI e x t r a c t i o n - -
64.29
(lipide)
IR1
carbonates, metastable
oxides sulfides
= silicates
IR3 Klba
extraction--
stable
sulfides
heavy m i n e r a l s 11.98
IR4 Final residue
~kerogen
F3
Fig. I. Analytical scheme. Rl, R2, R3, R4: mineral and trace-element analyses by XRD and XRF. F1, F2: trace-element analysis by Hirner et al. (1990). R 1, R4, F3: trace-element analysis by R.H. Filby (pers. commun., 1989 ).
mary X-ray radiation of a Mo-tube for matrix correction (Hahn-Weinheimer et al., 1984). 4. Results and discussion
4.1. Mineralogical composition of Julia Creek oil shale The weights of the individual fractions are listed in Fig. 1. For comparison, the values given in literature range from 12 to 17% for total organic carbon (TOC), 0.73% for the organic extract, and 0.6 to 3.2% for pyritic as well as 0.5 to 1.5% for organic sulfur (Riley, 1983; Dale et al., 1984a, b; Boreham and Powell, 1984; Patterson et al., 1986 ). The sample used in this study showed a TOC value of 13.47% and a vitrinite reflectance (Ro) of 0.43% (J.A. Curiale, pers. commun., 1988 ). Relatively high sulfur (7.9%) and ash contents (5.1%) are in accordance with a large sulfide-bearing heavy mineral fraction. The high-S Julia Creek kerogen leads to high-S shale oil ( S > 4 % ) with abundant alkyl substituted thiophenes and benzothiophenes.
From 35 to 45% calcite has been reported for the HCl-soluble fraction (Riley, 1983; Dale et al., 1984a). For the HF-soluble fraction, Dale et al. (1984a) cites 20% quartz, 5% mixed layer clay, 5% kaolinite and 3% albite. Crisp et al. (1987) estimate the clay mineral fraction to be composed of 50% illite, 20% montmorillonite, 20% kaolinite, and 10% chlorite. Concerning sulfides, several percent of pyrite and traces of sphalerite, chalcopyrite and galena have been observed (Dale et al., 1984a; Patterson et al., 1986). Combining these data with the results of this study, we may estimate the relative amount of accessory minerals to be pyrite: gypsum: apatite: sphalerite: chalcopyrite: g a l e n a - 7:3 : 3: 1: 1: 1.
4.2. Modelling the chemical composition of Julia Creek oil shale In Table 1, the data concerning the trace element composition of Julia Creek bulk sample and its organic components are compiled from the results of parallel studies and those given in literature. The various concentrations re-
118
A.V. H1RNER A N D Z . XU
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TRACE METAL SPECIATION IN JULIA CREEK OIL SHALE
ported for bulk sediment are within the natural spread of results reported by the investigation of core samples (Patterson et al., 1986). There is a strong increase of the organic extract metal contents when using solvents of increasing polarity, because within the organic soluble fraction (bitumen) the metals are thought to be concentrated in NOS compounds. The values in Table 1 enable, together with the matrix-corrected X-ray fluorescence intensities as described in the experimental section, to perform elemental mass balance calculations to elucidate element partitioning into the fractions R I to R4 and F1 to F3 indicated in Fig. 1. The results of these calculations are presented in Table 2 in column "model A". Under the conditions of digestion used in this study, up to 50% of the sphalerite and galena will be dissolved by hot HC1/HF, resulting in much too high concentrations for the carbonate/silicate fraction and too low ones for the sulfide fraction in the case of Zn, Cd, and Pb. Another problem arises from the observation, that Kiba solution may extract substantial amounts of metals out of the kerogen matrix. Thus, the concentrations given for the kerogen fraction in "model A" represent mini m u m values. On the contrary, traces of residual minerals may accompany the usual kerogen separation procedure. Consequently, the kerogen values obtained by usual HC1/HF digestion without applying Kiba solution are given in "model B"~ they should be taken as m a x i m u m values. Trace-element partitioning in inorganic phases was modelled on the basis of an average mineralogical composition as described above (Section 4.1 ). Eventually, in "model C", the results on the basis of leaching experiments by Patterson et al. (1986) are cited for comparison. This kind of approach was criticized by Kheboian and Bauer (1987) because of readsorption of the early dissolved metals onto surface-active solid residues. A close inspection of the numbers given in "model C" shows that these effects cannot be ruled out for about one half of the
I 19
elements studied. For the approach used in this study, we tried to overcome these difficulties by washing the solid residues after acid treatment for a very long time (approx. one day) until the filtrate was clear when reacting with silver nitrate. Whenever there is close agreement between the results given by the three models, we get a strong indication for a definite association of a trace element with particular inorganic or organic species (e.g. the fractions received by the experimental procedures given in Fig. 1 ). Summarising the results listed in Table 2, a homogeneous distribution in all phases can be recognised for V, Cr, Co, and Ni, whereas 66 to 98% of the M n - a n d 95% of the Sr-content are associated with calcites, 70 to 90% of the Ti with clays, and Fe, Cu, Zn, As, Mo, Cd and Pb are concentrated in sulfides. Significant organic affinities ( > 1% ) are observed for V, Fe, Co, Ni, Cu, Ga, As, Zr, Mo and Pb. Two-thirds of the total V is in HC1/HF-soluble forms (hydrated oxides, vanadates, silicates, mixed layer mica-montmorillonite clays), 3.2% in the organic extract, and probably up to 10% in kerogen (partly extractable by Kiba solution). Ni exhibits a similar relative distribution plus a strong affinity to pyrite. When considering the porphyrin concentrations given by Boreham and Powell (1987), just 19% of V and 7% of Ni in the organic extract are coordinated to porphyrins. Riley and Saxby (1982) recognised that the contents of vanadyl porphyrins in the shale extract are correlated with the a m o u n t of V in the shale kerogen, arguing for an organic association of V with the kerogen matrix possibly via highly fused aromatic porphyrin molecules as proposed by Yen ( 1975 ). C h r o m i u m is associated with the HCI/HFsoluble fractions (traces of magnetite or anatase?) with no significant organic combination. From 50 to 90% of the Fe is in pyrite, 2 to 10% within the kerogen matrix (micropyrite inclusions?). Cobalt is found in sphalerite (and pyrite), but also bound to humic-fulvictype substances. From 70 to 75% of the Cu is
120
A.V. HIRNER AND Z. XU
TABLE 2 Partition o f trace e l e m e n t s between inorganic a n d organic c o n s t i t u e n t s o f Julia Creek oil shale (in p e r c e n t ) El.
Carb.
Sil.
Sulf./h.m.
Tot. inorg.
Tot. org.
Extr.
h+f
Ker.
Ti
< 1
>90
< 10
>99
< 1
<0.1
<0.1
< 1
20
70
V
33.9 51.1 10
34.2 32.6 60
27.8 < 5 15
5
95.9 83.7 83
93
4.1 16.3 17
7 3.2
0.2
0.7 12.~
Cr
42.9 30.3 <5
34.7 60.6 75
21.8 < 5 20
99.4 90.9 95
0.6 9.1 5
0.03
0.05
0.5 95)
Mn
66.0 98.1 85
20.3 <5 5
13.3 <5 10
99.6 98.1 > 99
0.3 1.9 < 1
0.003
0.01
0.3 1.9 2. I 10
Fe
< 1 <5 <5
49.4 <5 10
48.5 90 80
97.9 90 90
2.1 10 10
0.01
0.01.
Co
33.6 <5 30
35.3 <5 18
28.7 98 50
97.6 98 98
2.4 2 2
0.5
1.1
0.~ <2
Ni
40.7 <5 15
28.2 <5 15
28.4 91.3 60
97.3 91.3 88
2.7 8.7 12
1.7
0.5
0.5 6.5
Cu
< 1 <5 <5
26.7 <5 10
70.2 73.0 75
96.9 73.0 88
3.0 27.0 12
0.1
0.4
2.5 26.5
Zn
52.8 <5 3O
41.7 <5 l0
5.1 97.6 60
99.6 97.6 98
0.4 2.4 2
0.03
0.3
0.1 2.1
Ga
< 1
18.0
66.1
84.9
15.1
<0.01
<0.01
15.1
As
3.7 <5 10
24.8 < 5 5
61.6 69.9 80
90.1 69.9 94
8.8 30.1 6
0.6
Sr
95.7
0.8
2.8
99.3
<0.7
<0.01
<0.01
95
5
< 0.1
< 1
99
1.1
8.1 28.4 <0.7
1
Zr
63.4
27.8
7.5
98.7
1.3
< 0.1
1.3
Mo
5.1 <5 < 5
51.1 <5 30
36.5 86.1 30
92.7 86.1 60
7.3 13.9 10
0.02
6.2
1.1 7.7
Cd
10.8 <5 25
83.1 <5 <5
5.5 97.4 70
99.4 97.4 95
0.6 2.6 5
0.03
0.2
<0.4 2.4
Pb
70 < 5
14 <5
13 65
97 65
2.2 35
0.03
0.7
1.5 34.3
El. = element; carb. = carbonates; sil. = silicates; s u l f . / h . m . = sulfides + heavy minerals; tot. inorg. = total inorganic fraction; tot. org. = total organic fraction; e x t r . = organic extract; h + f = h u m i c a n d fulvic acids; ker. = kerogen. D a t a are in wt.%, a n d listed in three rows, c o r r e s p o n d i n g to m o d e l A, m o d e l B a n d m o d e l C, respectively. Calculation m o d e l A: chemical c o m p o s i t i o n o f kerogen is represented by Kiba-treated sample; mineralogical c o m p o s i t i o n according to results o f this study (Fig. 1 ). Calculation m o d e l B: kerogen isolation by u s u a l m e t h o d s ; approx, mineralogical c o m p o s i t i o n according to results o f Dale a n d Fardy ( 1983 ), Dale et al. ( 1984a, b), a n d Riley ( 1 9 8 3 ) . Calculation m o d e l C: data given in P a t t e r s o n et al. ( 1986 ).
12 1
TRACE METAL SPECIATION IN J U L I A CREEK OIL SHALE
in chalcopyrite and the remainder mainly in organic coordination. After Fischer retorting of Julia Creek oil shale, high amounts of As and lower ones for V, Cr, Co and Ni had been found in shale oil and retort waters (Dale and Fardy, 1984). According to the results of similar experiments, Patterson et al. (1987) concluded that V, Ni, Fe and Cu are derived from metalorganic compounds, while As originated by breakdown of sulfide minerals (60 to 80% of the As is in pyrite). The latter interpretation is not in accordance with the results presented in Table 2, indicating that significant amounts of As may be mobilised in organic form from kerogen; the same seems to be the case with As in Green River kerogen (Desborough et al., 1976 ). Another argument in this respect is the observation, that As may resemble the most mobile of all trace elements, and is present in retort oils of Australian oil shales, generally in concentrations of several p p m (Patterson et al., 1988a). A partition between the sulfide/or-
II.A JC ~ \
~\\
RI R2
I
Ti
R3 R4
NA'~
I
JC ~
~V
RI
R2 R3 RL
ganic phase similar to the one for As applies for Ga, but in this case there is no mobile organic carrier. Zinc and Cd are concentrated in sphalerite with no apparent organic association. 30% of the Mo is in water-soluble form (Patterson et al., 1986), the main part resides in the silicate/sulfide (pyrite) fraction, and 6.2% are combined with humic substances. From 65 to 75% of the Pb is in galena. The rest is probably associated with kerogen, and easily attacked by Kiba solution.
4.3. Comparison with other oil shales In Fig. 2, the net intensities of the X-ray emission lines of ten elements in fractions R1 to R4 are compared for several oil shales to find out whether Julia Creek oil shale displays distribution patterns similar to those of Green River, New Albany and Monterey oil shales. It can easily be recognized that Mn and Sr are lo-
,,A~
r
I!j .i
R7
R2
R3 R,~
]NA~ C u
R? R~ R5 R~ I
fie
As
M
Se
OR
M JE OR
RI
R2
R3
Rk
Ri R2 R3
JC
RI*-
,
RI
R2R3 ,
j
,
R~
IN: R1
R2 R3 R4 R1 R2 R3 R4
Fig. 2. Qualitative partition of trace elements between inorganic and organic constituents of some selected oil shales, in percent. Intensities of X-ray emission lines of the chosen elements are plotted vs. the solid digestion residues R 1 to R4 as indicated in Fig. 1. Selected oil shale samples: J C = Julia Creek; GR = Green River; NA = New Albany; M = Monterey.
122
cated in carbonates, Ti in silicates, whereas an appreciable portion of Ga, As and Se is found in kerogen. Furthermore, the distribution patterns are quite similar, indicating that traceelement speciation in oil shales is governed by general processes rather than by individual geochemical mechanisms within one particular sample. This is consistent with the results of Patterson (1988) and Patterson et al. (1988b) on other Australian oil shales, and with those of Desborough et al. (1976) indicating that Ti, Cr, Mn, Co, Cu, As and Sr occur in similar concentrations as well as similar speciation in Green River shale compared to Julia Creek shale. However, the Pb content is higher, and V, Ni, Zn, Mo and Cd are depleted by a factor of 5 to 20 in Green River shale. Trace element concentrations for Julia Creek bulk samples generally lie within the ranges given for bituminous shales by Wedepohl (1964). Contrary to the interpretations of the latter author, the results of this study indicate possible affinities of Cu, Ga, As, Mo and Pb to sulfidic and organic phases. 5. Conclusions An approximation of the speciation of sixteen trace elements in Julia Creek oil shale was established on the grounds of three different calculation models, based on the results of various chemical treatments of the shale sample. While most of the results could be discussed in a semi-quantitative, some in a qualitative manner only, it was possible to derive quantitative data for some inorganic (e.g. 95.4 _+0.4% and 72.6 _+2.4% of the Sr and Cu is in calcite and chalcopyrite, resp. ) as well as soluble organic fractions (e.g. 3.2% of the V and 1.7% of the Ni are in the organic extract; 1.1% of the Co and As, and 6.2% of the Mo are associated with humic and fulvic acids). There is evidence that most of the characteristic trace-element distribution patterns of Julia Creek oil shale can be found in other prominent oil shales, too.
A.V H1RNER AND Z. XU
One major draw-back concerning quantitative trace-element speciation, however, is caused by the inability to determine the a m o u n t of elements in organic coordination within the kerogen matrix. By applying various demineralisation procedures, just lower and upper limits for these concentrations can be estimated. In principle, this problem can be overcome by instrumental methods sensitive for the analysis of the chemical environment of a particular atom in solid samples (e.g. CPMAS-NMR, ESCA, E X A F S / X A N E S ) . However, the practical application of these sophisticated techniques to elements present in the ppm-range in natural samples is extremely difficult.
Acknowledgements This article has been written, while the authors were supported by fellowships funded by the Federal Republic of Germany (A.V.H.) and the People's Republic of China (Z.X.), respectively. The Julia Creek oil shale sample was supplied by CSR Ltd. (Sydney/Australia).
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TRACE METAL SPECIATION IN JULIA CREEK OIL SHALE
ization of Australian oil shales. Proc. 1st Aust. Workshop on Oil Shale, Lucas Heights, N.S.W., pp. 57-60. Dale, L.S. and Fardy, J.J., 1984. Trace element partitioning during the retorting of some Australian oil shales. Environ. Sci. Technol., 18: 887-889. Dale, L.S., Fardy, J.J., Patterson, J.H. and Ramsden, A.R., 1984a. Abundances and mineralogy of trace elements in Julia Creek oil shale. Proc. 2nd Aust. Workshop on Oil Shale, Brisbane, Qld., pp. 85-90. Dale, L.S., Fardy, J.J. and Barley, G.E., 1984b. Characterization of trace elements in Australian oil shales. ACS Prepr. Div. Fuel Chem., 29 (3): 299-306. Desborough, G.A., Pitman, J.K. and Huffmann, C., Jr., 1976. Concentration and mineralogical residence of elements in rich oil shales of the Green River Formation, Piceance Creek Basin, Colorado, and the Uinta Basin, Utah--A preliminary report. Chem. Geol., 17: 13-26. Ekstrom, A., Loeh, H. and Dale, L., 1983. Petroporphyrins found in oil shales from the Julia Creek Deposit of the Toolubuc Formation. In: F.P. Miknis and J.F. McKay (Editors), Geochemistry and Chemistry of Oil Shales. ACS Symp. Ser., 230:411-422. Exon, N.F. and Senior, B.R., 1976. The Cretaceous of the Eromanga and Surat Basins. Bur. Miner. Resour., J. Aust. Geol. Geophys., 1: 33-50. Fookes, C.J.R., 1983. Structure determination of nickel ( I1 ) deoxophyll-erythroetioporphyrin and a C3o homologue from an oil shale: Evidence that petroporphyrins are derived from chlorophyll. J. Chem. Soc. Chem. Commun., pp. 1472-1473. Fookes, C.J.R., 1985. The etioporphyrins of oil shale: Structural evidence for their derivation from chlorophyll. J. Chem. Soc. Chem. Commun., pp. 706-708. Fookes, C.J.R. and Loeh, H.J., 1983. Porphyrins in Australian oil shales: A nuclear magnetic resonance study. Proc. 1st Aust. Workshop on Oil Shale, Lucas Heights, N.S.W., pp. 65-68. Glikson, M. and Taylor, G.H., 1986. Cyanobacterial mats: Major contributors to the organic matter in Toolebuc Formation oil shales. In: D.I. Gravestock, P.S. Moore and G,M. Pitt (Editors), Contributions to the Geology and Hydrocarbon Potential of the Eromanga Basin. Geol. Soc. Aust. Spec. Publ., 12: 273-286. Glikson, M., Chappell, B.W., Freeman, R.S. and Webber, E., 1985. Trace elements in oil shales, their source and organic association with particular reference to Australian deposits. Chem. Geol., 53:155-174. Hahn-Weinheimer, P., Hirner, A.V. and Weber-Diefenbach, K., 1984. Grundlagen und praktische Anwendung der RSntgenfluoreszenzspektralanalyse. Vieweg, Wiesbaden, 253 pp. Hirner, A.V., Kritsotakis, K. and Tobschall, H.J., 1990. Metal-organic associations in sediments, I. Comparison of unpolluted recent and ancient sediments and sediments affected by anthropogenic pollution. Appl. Geochem., 5: 491-505.
123 Kheboian, C. and Bauer, C.F., 1987. Accuracy of selective extraction procedures for metal speciation in model aquatic sediments. Anal. Chem., 59:1417-1423. McMinn, A. and Burger, D., 1986. Palynology and paleoenvironments of the Toolebuc Formation (sensn latu) in the Eromanga Basin. In: D.I. Gravestock, P.S. Moore and G.M. Pitt (Editors), Contributions to the Geology and Hydrocarbon Potential of the Eromanga Basin. Geol. Soc. Aust. Spec. Publ., 12: 139-154. Miller, S.A., Hambley, T.V. and Taylor, J.C., 1984. Crystal and molecular structure of a natural vanadyl porphyrin. Aust. J. Chem., 37: 761-766. Ozimic, S., 1986. The geology and petrophysics of the Toolebuc Formation. In: D.I. Gravestock, P.S. Moore and G.M. Pitt (Editors), Contributions to the Geology and Hydrocarbon Potential of the Eromanga Basin. Geol. Soc. Aust. Spec. PUN., 12:119-138. Patterson, J.H., 1988. Mineralogy and chemistry over a cycle ofoil shale deposition in the Brick Kiln member, Rundle deposit, Queensland, Australia. Chem, Geol., 68: 207-219. Patterson, J.H., Ramsden, A.R., Dale, F.S. and Fardy, J.J., 1986. Geochemistry and mineralogical residences of trace elements in oil shales from Julia Creek, Queensland, Australia. Chem. Geol., 55: 1-16. Patterson, J.H., Dale, L.S. and Chapman, J.F., 1987. Trace element partitioning during the retorting of Julia Creek oil shale. Environ. Sci. Technol., 21: 490-494. Patterson, J.H., Dale, L.S. and Chapman, J.F., 1988a. Partitioning of trace elements during the retorting of Australian oil shales. Fuel, 67:1353-1356. Patterson, J.H., Ramsden, A.R. and Dale, L.S., 1988b. Geochemistry and mineralogical residences of trace elements in oil shales from the Condor deposit, Queensland, Australia. Chem. Geol., 67: 327-340. Ramsden, A.R., 1983. Microscopic petrography of oil shales at Julia Creek, northwestern Queensland. J. Geol, Soc. Aust., 30:17-23. Riley, K.W., 1983. Vanadium in the Toolebuc oil shale and possibilities tbr recovery from spent shale. Proc. 1st Aust. Workshop on Oil Shale. kucas Heights, N.S.W., pp. 69-72. Riley, K.W. and Saxby, J.D., 1982. Association of organic matter and vanadium in oil shale from the Toolebuc Formation of the Eromanga Basin, Australia. Chem. Geol., 37: 265-275. Senior, B.R., Mond, A. and Harrison, P.L., 1978. Geology of the Eromanga Basin. Aust. Bur. Miner. Resour., Geol. Geophys,, Bull., 167. Sherwood, N.R. and Cook, A.C., 1983. Petrology of organic matter in the Toolebuc Formation oil shales. Proc. I st Aust. Workshop on Oil Shale, Lucas Heights, N.S.W., pp. 35-38. Sherwood, N.R. and Cook, A.C., 1986. Organic matter in the Toolebuc Formation. In: D.I. Gravestock, P.S. Moore and G.M. Pitt (Editors), Contributions to the Geology and Hydrocarbon Potential of the Eromanga Basin. Geol. Soc. Aust. Spec. Publ., 12: 255-266.
124 Wedepohl, K.H., 1964. Untersuchungen am Kupferschiefer in Nordwestdeutschland: Ein Beitrag zur Deutung der Genese bitumin6ser Sedimente. Geochim. Cosmochim. Acta, 28: 305-364.
A.V HIRNER AND Z. XU
Yen, T.F., 1975. Chemical aspects of metals in native petroleum. In: Y.F. Yen (Editor), The Role of Trace Metals in Petroleum. Ann Arbor Sci.Publ., Ann Arbor, Mich., pp. 1-30.
115
Trace metal speciation in Julia Creek oil shale A.V. Hirner and Z. Xu * Mineralogisch-Petrographisches Institut, Universitgit M~inchen, Theresienstr. 41. D-8000 Miinchen 2. Federal Republic of. Germany (Accepted for publication November 13, 1990 )
ABSTRACT Hirner, A.V. and Xu, Z., 1991. Trace metal speciation in Julia Creek oil shale. In: J.F. Branthaver and R.H. Filby (GuestEditors ), Trace Metals in Petroleum Geochemistry. Chem. Geol.. 91 : 115-124. The speciation of sixteen trace elements in Julia Creek oil shale was estimated based on the comparative evaluation of three different models referring to various chemical digestion procedures. Demineralisation steps were monitored by Xray diffraction and X-ray fluorescence spectrometry, and the results discussed together with those reported in literature. While it is possible to determine some element concentrations in the carbonate (e.g. Mn, Sr ), in the silicate (e.g. Ti, V ), and in the sulfide fractions (e.g. Cu, Ga, As ), concentrations in the kerogen phase can only be estimated within a relatively broad range. Element distributions between different sedimentary phases seem to be very similar when comparing Julia Creek with other oil shales.
1. I n t r o d u c t i o n
Australia's most extensive oil shale deposits are located in Queens land (estimated reserves 4 X 109 t of shale and > 2000 billion barrels of oil ). Since 1968, the Julia Creek deposit found within the Upper Cretaceous Toolebuc Formation has been studied for commercial development. A significant contribution to modern porphyrin structural analysis was obtained by investigating Julia Creek shale oil (Fookes and Loeh. 1983; Fookes, 1983, 1985; Miller et al., 1984). Furthermore, interest in trace-element speciation in Julia Creek oil shale arose because of the desired recovery of by-products (esp. V and Mo ), as well as the possible release of toxic elements into the environment during oil shale retorting and leaching of spent shale *Present address: Box 215, Qingyang Gangsu, People's Republic of China.
dumps (Dale and Fardy, 1984; Patterson et al., 1987, 1988a). Consequently, the associations of trace elements with specific mineral phases were elucidated by applying instrumental analytical techniques (e.g. atomic absorption and emission spectroscopy, mass spectrometry, instrumental neutron activation analysis), selective leaching procedures, electron microprobe analyses, and interelement correlation techniques (Riley and Saxby, 1982; Riley, 1983; Ekstrom et al., 1983; Dale and Fardy, 1983; Dale et al., 1984a, b; Glikson et al., 1985; Glikson and Taylor, 1986; Patterson et al., 1986). Among other recent and fossil sedimentary material, Julia Creek shale samples had been subjected to bio-inorganic studies of our group, especially in respect to their soluble and insoluble organic constituents (Hirner et al., 1990). The aim of the present paper is to contribute to the evaluation of the quantitative distribution of trace elements between various organic
0 0 0 9 - 2 5 4 1 / 9 1 / $ 0 3 . 5 0 © 1991 Elsevier Science Publishers B,V. All rights reserved.
116
and inorganic components by chemical methods. In particular, stepwise demineralisation of the shale samples was monitored by X-ray diffraction as well as X-ray spectrometry, and the results are discussed in the light of the relevant data gained by the Australian scientists mentioned above. 2. Geochemistry of Julia Creek oil shale The organic matter of the Toolebuc Formation is of extremely uniform composition; total organic carbon (TOC) ranges up to 20 wt.% and is probably derived from (partly modified ) marine algal matter with only minor contributions from terrestrial organic matter (Boreham and Powell, 1984, 1987). Julia Creek kerogen is largely of planktonic origin (type II), H / C = 1.1 to 1.2, O / C = 0 . 1 to 0.4, its sulfur content ranges up to 8 wt.%, and biological marker studies indicate low maturity. The kerogen shows vitrinite reflectance values (Ro) from 0.48 to 0.60% (Crisp et al., 1987), and a major portion of it (approx. 45%) is of aromatic structure with a high degree of crosslinking as well as the presence of multiple functionalised aliphatic and aromatic acids (Chaffee and McLaren, 1986). The bituminous calcareous shale (oil shale) is interbedded with coquinites and displays abundant fine, dark-brown laminae in a microcrystalline calcite and clay matrix in accordance to the characteristic morphology of algal mats (Ramsden, 1983; Glikson et al., 1985; Glikson and Taylor, 1986 ). Electron microscope studies (SEM and TEM) have shown that the shale matrix contains abundant coccolith fragments (i.e. calcareous algal plates), together with residues of Oscillatoria, and humic acids as well as associations of bacterial cell walls with Cu, of cyanobacteria with Mo, and of clay minerals with V. The dominant maceral present in Julia Creek kerogen is bituminite with associated micrinite and minor amounts of lamalginite, telalginite, liptodetrinite and inertodetrinite (Sher-
A.V. HIRNER AND Z. XU
wood and Cook, 1983, 1986). Following a modified gyttja model, bituminite is thought to have formed by lithification of an organic gel derived from bacterial attack of the original source material (algae, algal-fungal mat), anaerobically deposited below oxygenated, nutrient-rich waters (Sherwood and Cook, 1986; Boreham and Powell, 1987 ). The geology of the Julia Creek deposit is described by Exon and Senior ( 1976 ) and Senior etal. (1978). 3. Experimental techniques The analytical scheme for separation of the bulk sample into three inorganic as well as three organic fractions is presented in Fig. 1. The chemical compositions of fractions F I, F2, F3, R I and R4 were determined in a parallel study (Hirner et al., 1990). While the organic extract was received by Soxhlet extraction in dichloromethane, non-solvent extractable lipids (humic and fulvic acids) were released by reflux in alkaline solution (0.5 N KOH-methanol-benzene) followed by ether extractions. Demineralisation was accomplished by treating the samples with conc. HCI at 80°C for 2 hr. and with 52% HF at 80°C for 2 hr., respectively, each followed by intensive waterwashing until no residual halogen ions could be precipitated by silver nitrate. Finally, the residuum of HC1/HF treatment was exposed to Kiba solution (H3PO 4 + 50/oSnC12) at 270 ° C for I hr. Complete removal of pyrite by a milder agent like boiling HC1-SnClz-solutions (Chanton, 1985) could not be achieved. The individual demineralisation steps were monitored by X-ray diffraction ( X R D ) for the presence of more than a dozen minerals (carbonates, silicates, sulfates, sulfides, phosphates), and by X-ray fluorescence (XRF) for the concentrations of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Sr, Zr, Mo, Cd, and Pb. XRF procedures were those usually applied for the measurement of pressed powder pellets using the intensity of the Compton-scattered pri-
TRACEMETALSPECIATIONIN JULIACREEKOIL SHALE sample weight
I00.00
1[7
(g)
dried bulk s a m p l e organic solvent extraction
organic e x t r a c t F1
98.70
alkali 98.51
extraction
IR2
HF e x t r a c t i o n
29.29
humic
acids
and f u l v i c F2
i RCI e x t r a c t i o n - -
64.29
(lipide)
IR1
carbonates, metastable
oxides sulfides
= silicates
IR3 Klba
extraction--
stable
sulfides
heavy m i n e r a l s 11.98
IR4 Final residue
~kerogen
F3
Fig. I. Analytical scheme. Rl, R2, R3, R4: mineral and trace-element analyses by XRD and XRF. F1, F2: trace-element analysis by Hirner et al. (1990). R 1, R4, F3: trace-element analysis by R.H. Filby (pers. commun., 1989 ).
mary X-ray radiation of a Mo-tube for matrix correction (Hahn-Weinheimer et al., 1984). 4. Results and discussion
4.1. Mineralogical composition of Julia Creek oil shale The weights of the individual fractions are listed in Fig. 1. For comparison, the values given in literature range from 12 to 17% for total organic carbon (TOC), 0.73% for the organic extract, and 0.6 to 3.2% for pyritic as well as 0.5 to 1.5% for organic sulfur (Riley, 1983; Dale et al., 1984a, b; Boreham and Powell, 1984; Patterson et al., 1986 ). The sample used in this study showed a TOC value of 13.47% and a vitrinite reflectance (Ro) of 0.43% (J.A. Curiale, pers. commun., 1988 ). Relatively high sulfur (7.9%) and ash contents (5.1%) are in accordance with a large sulfide-bearing heavy mineral fraction. The high-S Julia Creek kerogen leads to high-S shale oil ( S > 4 % ) with abundant alkyl substituted thiophenes and benzothiophenes.
From 35 to 45% calcite has been reported for the HCl-soluble fraction (Riley, 1983; Dale et al., 1984a). For the HF-soluble fraction, Dale et al. (1984a) cites 20% quartz, 5% mixed layer clay, 5% kaolinite and 3% albite. Crisp et al. (1987) estimate the clay mineral fraction to be composed of 50% illite, 20% montmorillonite, 20% kaolinite, and 10% chlorite. Concerning sulfides, several percent of pyrite and traces of sphalerite, chalcopyrite and galena have been observed (Dale et al., 1984a; Patterson et al., 1986). Combining these data with the results of this study, we may estimate the relative amount of accessory minerals to be pyrite: gypsum: apatite: sphalerite: chalcopyrite: g a l e n a - 7:3 : 3: 1: 1: 1.
4.2. Modelling the chemical composition of Julia Creek oil shale In Table 1, the data concerning the trace element composition of Julia Creek bulk sample and its organic components are compiled from the results of parallel studies and those given in literature. The various concentrations re-
118
A.V. H1RNER A N D Z . XU
r--- , . ~
0
e-
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_
~
u,5
~
V
Z
E ~
~
vv
m.
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c
e..
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o
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.-2
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TRACE METAL SPECIATION IN JULIA CREEK OIL SHALE
ported for bulk sediment are within the natural spread of results reported by the investigation of core samples (Patterson et al., 1986). There is a strong increase of the organic extract metal contents when using solvents of increasing polarity, because within the organic soluble fraction (bitumen) the metals are thought to be concentrated in NOS compounds. The values in Table 1 enable, together with the matrix-corrected X-ray fluorescence intensities as described in the experimental section, to perform elemental mass balance calculations to elucidate element partitioning into the fractions R I to R4 and F1 to F3 indicated in Fig. 1. The results of these calculations are presented in Table 2 in column "model A". Under the conditions of digestion used in this study, up to 50% of the sphalerite and galena will be dissolved by hot HC1/HF, resulting in much too high concentrations for the carbonate/silicate fraction and too low ones for the sulfide fraction in the case of Zn, Cd, and Pb. Another problem arises from the observation, that Kiba solution may extract substantial amounts of metals out of the kerogen matrix. Thus, the concentrations given for the kerogen fraction in "model A" represent mini m u m values. On the contrary, traces of residual minerals may accompany the usual kerogen separation procedure. Consequently, the kerogen values obtained by usual HC1/HF digestion without applying Kiba solution are given in "model B"~ they should be taken as m a x i m u m values. Trace-element partitioning in inorganic phases was modelled on the basis of an average mineralogical composition as described above (Section 4.1 ). Eventually, in "model C", the results on the basis of leaching experiments by Patterson et al. (1986) are cited for comparison. This kind of approach was criticized by Kheboian and Bauer (1987) because of readsorption of the early dissolved metals onto surface-active solid residues. A close inspection of the numbers given in "model C" shows that these effects cannot be ruled out for about one half of the
I 19
elements studied. For the approach used in this study, we tried to overcome these difficulties by washing the solid residues after acid treatment for a very long time (approx. one day) until the filtrate was clear when reacting with silver nitrate. Whenever there is close agreement between the results given by the three models, we get a strong indication for a definite association of a trace element with particular inorganic or organic species (e.g. the fractions received by the experimental procedures given in Fig. 1 ). Summarising the results listed in Table 2, a homogeneous distribution in all phases can be recognised for V, Cr, Co, and Ni, whereas 66 to 98% of the M n - a n d 95% of the Sr-content are associated with calcites, 70 to 90% of the Ti with clays, and Fe, Cu, Zn, As, Mo, Cd and Pb are concentrated in sulfides. Significant organic affinities ( > 1% ) are observed for V, Fe, Co, Ni, Cu, Ga, As, Zr, Mo and Pb. Two-thirds of the total V is in HC1/HF-soluble forms (hydrated oxides, vanadates, silicates, mixed layer mica-montmorillonite clays), 3.2% in the organic extract, and probably up to 10% in kerogen (partly extractable by Kiba solution). Ni exhibits a similar relative distribution plus a strong affinity to pyrite. When considering the porphyrin concentrations given by Boreham and Powell (1987), just 19% of V and 7% of Ni in the organic extract are coordinated to porphyrins. Riley and Saxby (1982) recognised that the contents of vanadyl porphyrins in the shale extract are correlated with the a m o u n t of V in the shale kerogen, arguing for an organic association of V with the kerogen matrix possibly via highly fused aromatic porphyrin molecules as proposed by Yen ( 1975 ). C h r o m i u m is associated with the HCI/HFsoluble fractions (traces of magnetite or anatase?) with no significant organic combination. From 50 to 90% of the Fe is in pyrite, 2 to 10% within the kerogen matrix (micropyrite inclusions?). Cobalt is found in sphalerite (and pyrite), but also bound to humic-fulvictype substances. From 70 to 75% of the Cu is
120
A.V. HIRNER AND Z. XU
TABLE 2 Partition o f trace e l e m e n t s between inorganic a n d organic c o n s t i t u e n t s o f Julia Creek oil shale (in p e r c e n t ) El.
Carb.
Sil.
Sulf./h.m.
Tot. inorg.
Tot. org.
Extr.
h+f
Ker.
Ti
< 1
>90
< 10
>99
< 1
<0.1
<0.1
< 1
20
70
V
33.9 51.1 10
34.2 32.6 60
27.8 < 5 15
5
95.9 83.7 83
93
4.1 16.3 17
7 3.2
0.2
0.7 12.~
Cr
42.9 30.3 <5
34.7 60.6 75
21.8 < 5 20
99.4 90.9 95
0.6 9.1 5
0.03
0.05
0.5 95)
Mn
66.0 98.1 85
20.3 <5 5
13.3 <5 10
99.6 98.1 > 99
0.3 1.9 < 1
0.003
0.01
0.3 1.9 2. I 10
Fe
< 1 <5 <5
49.4 <5 10
48.5 90 80
97.9 90 90
2.1 10 10
0.01
0.01.
Co
33.6 <5 30
35.3 <5 18
28.7 98 50
97.6 98 98
2.4 2 2
0.5
1.1
0.~ <2
Ni
40.7 <5 15
28.2 <5 15
28.4 91.3 60
97.3 91.3 88
2.7 8.7 12
1.7
0.5
0.5 6.5
Cu
< 1 <5 <5
26.7 <5 10
70.2 73.0 75
96.9 73.0 88
3.0 27.0 12
0.1
0.4
2.5 26.5
Zn
52.8 <5 3O
41.7 <5 l0
5.1 97.6 60
99.6 97.6 98
0.4 2.4 2
0.03
0.3
0.1 2.1
Ga
< 1
18.0
66.1
84.9
15.1
<0.01
<0.01
15.1
As
3.7 <5 10
24.8 < 5 5
61.6 69.9 80
90.1 69.9 94
8.8 30.1 6
0.6
Sr
95.7
0.8
2.8
99.3
<0.7
<0.01
<0.01
95
5
< 0.1
< 1
99
1.1
8.1 28.4 <0.7
1
Zr
63.4
27.8
7.5
98.7
1.3
< 0.1
1.3
Mo
5.1 <5 < 5
51.1 <5 30
36.5 86.1 30
92.7 86.1 60
7.3 13.9 10
0.02
6.2
1.1 7.7
Cd
10.8 <5 25
83.1 <5 <5
5.5 97.4 70
99.4 97.4 95
0.6 2.6 5
0.03
0.2
<0.4 2.4
Pb
70 < 5
14 <5
13 65
97 65
2.2 35
0.03
0.7
1.5 34.3
El. = element; carb. = carbonates; sil. = silicates; s u l f . / h . m . = sulfides + heavy minerals; tot. inorg. = total inorganic fraction; tot. org. = total organic fraction; e x t r . = organic extract; h + f = h u m i c a n d fulvic acids; ker. = kerogen. D a t a are in wt.%, a n d listed in three rows, c o r r e s p o n d i n g to m o d e l A, m o d e l B a n d m o d e l C, respectively. Calculation m o d e l A: chemical c o m p o s i t i o n o f kerogen is represented by Kiba-treated sample; mineralogical c o m p o s i t i o n according to results o f this study (Fig. 1 ). Calculation m o d e l B: kerogen isolation by u s u a l m e t h o d s ; approx, mineralogical c o m p o s i t i o n according to results o f Dale a n d Fardy ( 1983 ), Dale et al. ( 1984a, b), a n d Riley ( 1 9 8 3 ) . Calculation m o d e l C: data given in P a t t e r s o n et al. ( 1986 ).
12 1
TRACE METAL SPECIATION IN J U L I A CREEK OIL SHALE
in chalcopyrite and the remainder mainly in organic coordination. After Fischer retorting of Julia Creek oil shale, high amounts of As and lower ones for V, Cr, Co and Ni had been found in shale oil and retort waters (Dale and Fardy, 1984). According to the results of similar experiments, Patterson et al. (1987) concluded that V, Ni, Fe and Cu are derived from metalorganic compounds, while As originated by breakdown of sulfide minerals (60 to 80% of the As is in pyrite). The latter interpretation is not in accordance with the results presented in Table 2, indicating that significant amounts of As may be mobilised in organic form from kerogen; the same seems to be the case with As in Green River kerogen (Desborough et al., 1976 ). Another argument in this respect is the observation, that As may resemble the most mobile of all trace elements, and is present in retort oils of Australian oil shales, generally in concentrations of several p p m (Patterson et al., 1988a). A partition between the sulfide/or-
II.A JC ~ \
~\\
RI R2
I
Ti
R3 R4
NA'~
I
JC ~
~V
RI
R2 R3 RL
ganic phase similar to the one for As applies for Ga, but in this case there is no mobile organic carrier. Zinc and Cd are concentrated in sphalerite with no apparent organic association. 30% of the Mo is in water-soluble form (Patterson et al., 1986), the main part resides in the silicate/sulfide (pyrite) fraction, and 6.2% are combined with humic substances. From 65 to 75% of the Pb is in galena. The rest is probably associated with kerogen, and easily attacked by Kiba solution.
4.3. Comparison with other oil shales In Fig. 2, the net intensities of the X-ray emission lines of ten elements in fractions R1 to R4 are compared for several oil shales to find out whether Julia Creek oil shale displays distribution patterns similar to those of Green River, New Albany and Monterey oil shales. It can easily be recognized that Mn and Sr are lo-
,,A~
r
I!j .i
R7
R2
R3 R,~
]NA~ C u
R? R~ R5 R~ I
fie
As
M
Se
OR
M JE OR
RI
R2
R3
Rk
Ri R2 R3
JC
RI*-
,
RI
R2R3 ,
j
,
R~
IN: R1
R2 R3 R4 R1 R2 R3 R4
Fig. 2. Qualitative partition of trace elements between inorganic and organic constituents of some selected oil shales, in percent. Intensities of X-ray emission lines of the chosen elements are plotted vs. the solid digestion residues R 1 to R4 as indicated in Fig. 1. Selected oil shale samples: J C = Julia Creek; GR = Green River; NA = New Albany; M = Monterey.
122
cated in carbonates, Ti in silicates, whereas an appreciable portion of Ga, As and Se is found in kerogen. Furthermore, the distribution patterns are quite similar, indicating that traceelement speciation in oil shales is governed by general processes rather than by individual geochemical mechanisms within one particular sample. This is consistent with the results of Patterson (1988) and Patterson et al. (1988b) on other Australian oil shales, and with those of Desborough et al. (1976) indicating that Ti, Cr, Mn, Co, Cu, As and Sr occur in similar concentrations as well as similar speciation in Green River shale compared to Julia Creek shale. However, the Pb content is higher, and V, Ni, Zn, Mo and Cd are depleted by a factor of 5 to 20 in Green River shale. Trace element concentrations for Julia Creek bulk samples generally lie within the ranges given for bituminous shales by Wedepohl (1964). Contrary to the interpretations of the latter author, the results of this study indicate possible affinities of Cu, Ga, As, Mo and Pb to sulfidic and organic phases. 5. Conclusions An approximation of the speciation of sixteen trace elements in Julia Creek oil shale was established on the grounds of three different calculation models, based on the results of various chemical treatments of the shale sample. While most of the results could be discussed in a semi-quantitative, some in a qualitative manner only, it was possible to derive quantitative data for some inorganic (e.g. 95.4 _+0.4% and 72.6 _+2.4% of the Sr and Cu is in calcite and chalcopyrite, resp. ) as well as soluble organic fractions (e.g. 3.2% of the V and 1.7% of the Ni are in the organic extract; 1.1% of the Co and As, and 6.2% of the Mo are associated with humic and fulvic acids). There is evidence that most of the characteristic trace-element distribution patterns of Julia Creek oil shale can be found in other prominent oil shales, too.
A.V H1RNER AND Z. XU
One major draw-back concerning quantitative trace-element speciation, however, is caused by the inability to determine the a m o u n t of elements in organic coordination within the kerogen matrix. By applying various demineralisation procedures, just lower and upper limits for these concentrations can be estimated. In principle, this problem can be overcome by instrumental methods sensitive for the analysis of the chemical environment of a particular atom in solid samples (e.g. CPMAS-NMR, ESCA, E X A F S / X A N E S ) . However, the practical application of these sophisticated techniques to elements present in the ppm-range in natural samples is extremely difficult.
Acknowledgements This article has been written, while the authors were supported by fellowships funded by the Federal Republic of Germany (A.V.H.) and the People's Republic of China (Z.X.), respectively. The Julia Creek oil shale sample was supplied by CSR Ltd. (Sydney/Australia).
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