Envlron. Sci. Technol. 1084, 18, 887-889
NOTES Trace Element Partitioning during the Retorting of Some Australian Oil Shales Leslie S. Dale" and John J. Fardy CSIRO, Division of Energy Chemistry, Lucas Heights Research Laboratories, Sutherland NSW 2232, Australia
Oil shale samples from the Julia Creek, Condor, Rundle, and Nagoorin deposits located in Queensland were retorted under Fischer assay conditions, and the distributions of up to 19 elements detected in the shale oil and retort water were determined for each material. Although the extent of trace element partitioning varied between samples, significant amounts of arsenic, selenium, chromium, zinc, iron, aluminum, and titanium were associated with the shale oils, and arsenic, selenium, cobalt, nickel, and chlorine were transferred to the retort waters. Julia Creek shale oil also contained vanadium and antimony. Comparison of elemental mobilities demonstrates the variability in the degree of partititoning for each of the samples during retorting.
Introduction The mobilization of elements and their distribution during oil shale retorting are important in processing studies. Certain trace elements in the product oil can poison catalysts in the refining process, and those which transfer to the retort waters and are of environmental concern may lead to waste disposal problems. Their occurrence in the oil fraction may be due to the volatilization of organically associated metals present in the kerogen. Trace elements in retort waters may be due to transfer from the oil and mineral matrix decomposition at the retorting temperature. Entrained shale fines could also account for the presence of involatile elements in the products. Molecular characterization is therefore important in understanding the mechanism of mobilization of trace elements and their partitioning between the retort products. For example, organoarsenic and inorganic arsenic compounds have been identified in shale oils and retort waters (1-3). Vanadyl and nickel porphyrins have been isolated from kerogen ( 4 , 5 ) ,and although porphyrins are considered to be involatile at retorting temperatures, it has been shown that shale oil contains a complex mixture of etio-type porphyrins (6). Vanadyl porphyrins have been isolated from Julia Creek shale oil (7). A number of trace element partitioning studies have been carried out on US.oil shales (8-11). However, the results may not necessarily be applicable to other oil shale deposits. In Australia, there are a number of oil shale prospects under consideration for commercial exploitation. These include the Julia Creek, Condor, Rundle, and Nagoorin deposits in Queensland. The Julia Creek deposit is of marine origin and contains major amounts of calcite and quartz. Chemical analysis reveals that the deposit also contains substantial amounts of vanadium, arsenic, selenium, antimony, zinc, and molybdenum (12). The other deposits are of lacustrine origin and consist mainly of clay stone, limestone, and sandstone. Analysis a t these laboratories indicates that their elemental composition is similar to that of average shale (13). 0013-936X/84/09 18-0887$01.50/0
Since the genesis and geology of these deposits are different, the extent of trace element partitioning during retorting is important for oil recovery studies. No such data are available on Australian oil shales, but Bell et al. (14) have examined water from Fischer-retorted Rundle shale. An investigation was therefore undertaken to identify trace elements in retort products from samples of each of the Queensland deposits and to compare the extent of element partitioning between them. This study was done on samples which had been subjected to Fischer assay, a laboratory procedure for retorting shales. Although this procedure does not simulate conditions used in a number of commercial retorting systems, it provides products representative of direct pyrolysis which are useful for preliminary assessment of trace element partitioning. Results are reported for single Fischer assays on each material and are intended to be the basis for more extensive investigations into the partitioning of trace elements in these and other Australian deposits.
Experimental Section Fischer assay conditions used were as described in ASTM D3904-80. The feed material was raw shale (8 mesh) dried for 17 h at 110 OC. Sample weights of 100 g were taken for each retorting run. The designated heating profile was accomplished by controlling the temperature rise to 12 "C/min. After the completion of oil evolution, the receiver and adapter were transferred to a constant temperature bath and the oil and water yields determined by the prescribed method. The raw shales, spent shales, shale oils, and retort waters were first analyzed by instrumental neutron activation analysis using a procedure described elsewhere (15) and the raw shales, spent shales, and retort waters by spark source mass spectrometry using photoplate detection with lutetium as standard. To obtain data of higher precision, inductively coupled plasma atomic emission spectrometry and atomic absorption spectrometry were used where possible to reanalyze the raw shales, spent shales, oils, and waters for those elements previously detected in the oils and waters. For these solution techniques, the oil shales were fused with sodium peroxide, and the oils were acid digested with sulfuric acid-hydrogen peroxide to decompose the organic matter. All analytical methods were checked for accuracy by using the USGS Green River Shale SGR-1 and Coady Shale SCo-1 samples. Results and Discussion Details of the oil yield, water yield, and total weight loss in the Fischer assay of the samples are shown in Table I. No offgas samples were available for testing. The retort products for each samples were considered reasonably
0 1984 American Chemical Society
Environ. Sci. Technoi., Vol. 18, No. 11, 1984
887
Table I. Fischer Assays of Oil Shales
sample
wt%
retort water, mL/100 g of shale
Julia Creek Condor Rundle Nagoorin
7.62 5.38 10.64 4.95
1.60 9.73 2.68 7.98
oil yield,
weight loss, g p o o g of dried raw shale 12.0 18.7 21.7 25.7
This takes into account the variations in oil and water yields. Table I11 lists the mobilities obtained in this work and those obtained by Fox et al. (8) on Green River shale. The mobility of trace elements in the Australian oil shales is variable. However, mobilities for arsenic, selenium (except for Rundle shale where the raw shale contained less than 1pg g-l), cobalt, and nickel (except Julia Creek) were generally high, in agreement with the Green River shale results. The mobilities of chlorine and bromine were also high in the Australian shales. The mobility of vanadium was somewhat less in Julia Creek shale than in Green River shale, although the Julia Creek raw shale contained 0.21% vanadium compared to 0.017% in the Green River shale. Previous work (16)has revealed that, in Julia Creek oil shale, most of the vanadium is associated with the inorganic clay mineral fraction and only about 5% is present as organically bound material identified as a mixture of vanadium porphyrin compounds. Antimony was detected only in the Julia Creek and Nagoorin oils and, to a lesser extent, in Julia Creek water. Although the mobilities in these shales is somewhat similar to that of Green River shale, this element is more predominant in the Green River retort water than the oil (8) which is in contrast to its distribution in the Julia Creek and Nagoorin products. Antimony may therefore have an organic association in the Australian shales. It has been suggested (17) that arsenic and selenium may replace sulfur in organosulfur compounds. The observed association of antimony with oils from the Australian shales may be due to a similar mechanism.
representative since their yields were close to the average obtained for a series of runs on each material. Although a clean oil-water separation was achieved after centrifuging the sample receiver, it could not be established whether this treatment removed shale fines which may have been carried over with the oil mist. The abundances of trace elements in the oils and waters are shown in Table TI. Predominant elements in the oil fraction included aluminium, arsenic, chromium, copper, iron, selenium, titanium, and zinc. In addition, vanadium and antimony were predominant in Julia Creek oil and antimony in Nagoorin oil. Elements transferred to the retort water included arsenic, bromine, chlorine, cobalt, nickel, and selenium. The remaining elements, calcium, potassium, magnesium, manganese, and sodium, showed a random distribution. Similar associations have been obtained on retorted US. shales. Shendrikar and Faudel (9) found arsenic, chromium, copper, vanadium, and zinc in the product oil from Green River oil shale retorted under Fischer assay conditions. Differences are also evident. For example, cobalt and nickel were mainly associated with the oil from Green River oil shale yet selenium was below detectable limits. Likewise, arsenic was below detectable limits in retort water from Green River shale. Other work on Green River shale using higher temperature retorting systems @,IO) also found a similar lack of cobalt and nickel in the oil. However, in these systems, arsenic and selenium transferred to the water. A measure of the degree of partitioning of trace elements during retorting can be made by computing the element mobility. This quantity is defined as the percentage of the element distributed to the retort products relative to the quantity of feed material retorted and is expressed here as
Conclusions This study on trace element partitioning in a selection of retorted Australian oil shales reveals that a number of elements are mobilized from the raw shales during retorting. Of these, arsenic, selenium, cobalt, nickel, zinc, and iron are important in oil recovery processes and environmental aspects of processing. The variability of the mobilities for the individual elements emphasizes the need for partitioning studies to be carried out not only on a deposit-specific basis but also within deposits such as
Table 11. Elemental Abundances in Shale Oils and Retort Watersn element
analytical methodb
A1 As Br Ca c1 co Cr cu Fe K Mg Mn Na Ni Sb
A B B A B B B A A C A A C A B
Se
B A A A
Ti
v
Zn
Julia Creek oil water 37 42 0.3 60 66 0.16 1.2 0.49 17 33 9 0.4 3.6 1.9 1.8 10 13 10.2 5
