John H. Patterson

Geochemistry and mineralogical residences of trace elements in oil shales from Julia Creek, Queensland, Australia

Abstract Abundances and mineralogical residences have been determined for a comprehensive range of trace elements in Julia Creek oil shale. Many trace elements are well above normal abundances in shales. Of these elements, V and Mo are potentially useful by-products, whereas As, Se, Mo, Cd, Tl and U are of possible environmental or occupational health concern. Samples from a stratigraphic reference bore core through the Toolebuc Formation near Julia Creek in Queensland were chemically analysed using the multi-element techniques of neutron activation analysis and spark-source mass spectrometry. Inter-element correlation techniques, selective leaching procedures and electron microprobe analyses were used to establish geochemical associations and specific mineralogical residences for a full range of elements. The results provide a definitive chemical and mineralogical characterization of the oil shale and identify the major mineralogical residences of the important trace elements. V occurs mainly in a mixed-layer mica—montmorillonite clay mineral and, to a lesser extent, in kerogen, whereas most trace elements of environmental concern are resident in the sulphide minerals — pyrite and sphalerite. U is concentrated in the fluorapatite of fish debris. A sound basis is established for understanding the inorganic chemistry involved in oil shale processing and waste disposal.

Ash and slag qualities of Australian bituminous coals for use in slagging gasifiers

The suitability of Australian bituminous coals from an ash and slagging viewpoint, has been examined for use in entrained-flow slagging gasifiers which form the basis for more efficient power generation technologies based on integrated gasification-combined cycle (IGCC). Several coal deposits in both NSW and Queensland appear suitable for slag tapping without the addition of any flux. Many more thermal coals are shown to require a limestone flux addition of <3% CaCO3 by weight of coal and there could well be opportunities to reduce costs of flux addition by blending with other coals with lower ash fusion temperatures. Coal blending to yield a SiO2/Al2O3 ratio of 1.6–2.0 can minimise limestone flux requirements and avoid some limitations which arise from slag crystallisation. Limestone flux requirements can also be reduced by slag tapping at 1500°C rather than 1400°C, but this should be balanced against increased operating costs and losses in cold gas efficiency at higher gasification temperatures. Australian export coals with very low iron contents, after limestone flux addition, appear to have the potential advantage that slag viscosities (and hence slag tapping performance) are essentially independent of variability in coal ash composition. This should lower gasifier operating and maintenance costs, offsetting the costs of flux addition. Ash and slag characteristics and possible strategies for optimum coal use in entrained-flow slagging gasifiers are discussed.

A review of the effects of minerals in processing of Australian oil shales

Abstract In recent years considerable effort has been devoted to the characterization and processing of the major oil shale deposits in Queensland, with emphasis on nine deposits: Rundle, Stuart, Condor, Nagoorin, Nagoorin South, Duaringa, Lowmead, Yaamba and Julia Creek. Variations in mineralogy are important in the selection of optimum process conditions. This paper reviews the main effects of the minerals on processing and indicates how these influence the choice of process conditions. Mineralogical analyses are presented for each of the deposits, with emphasis on the significant minerals, including the clay minerals smectite and kaolinite, the carbonate minerals calcite and siderite, pyrite and buddingtonite. Of these minerals, smectite, siderite-type minerals and buddingtonite are rarely found in oil shales outside Australia and required chemical and thermal characterization. The minerals are decomposed endothermically in the retort and/or combustor. The carbonate minerals are important in limiting SO2 emissions, and the clay minerals act as catalysts in oil coking reactions. In addition, minerals are sources of trace elements which are of environmental concern or are of by-product potential. Significant mineral reactions are listed in relation to processing using an above-ground process with combusted solids recycled as a heat carrier to the retort. The importance of the minerals in processing is illustrated by example for the appropriate deposit or deposits. Examples are given of the ways in which process conditions can be modified to control mineral reactions for improved processing. Areas for future work on mineral reactions and effects are indicated.

Chemistry and mineralogy of carbonates in Australian bituminous and subbituminous coals

Abstract The amount and chemical composition of carbonate minerals are important in relation to their influence on ash characteristics during coal utilization in conventional power stations and slagging gasifiers. Scanning electron microscopy and electron microprobe analyses have been used for in situ analysis of carbonates in Australian bituminous coals. Compositional ranges have been established for six main types of carbonates observed: calcite, dolomite-ankerite, siderite, magnesian siderite, magnesian-calcian siderite and calcian siderite. With the exception of calcite and siderite, the chemical compositions of individual carbonate grains are variable, reflecting different levels of cation substitution. Carbonate minerals strongly influence ash fusion temperatures, slagging propensity and molten slag characteristics of Australian bituminous coals.

Siderite decomposition in retorting atmospheres

Abstract This work extends the characterization of siderites found in Tertiary Australian oil shales by investigating their decomposition in atmospheres resembling retorting conditions. The decomposition of mineral siderite samples and selected oil shale samples with high siderite contents, representing the four types of siderites most commonly found, were studied by thermogravimetry in controlled carbon dioxide-nitrogen-water vapour atmospheres. The decomposition temperature of each of the siderite types increased with increasing partial pressure of carbon dioxide, and decreased with increasing partial pressure of water vapour. Both effects were non-linear: larger temperature changes were observed at lower partial pressures. This study makes it possible to predict the amount of siderite decomposition under typical retorting conditions and the consequences for both the retorting and combustion stages during oil shale processing.

Mineral reactions in the processing of Australian Tertiary oil shales

Abstract Mineralogical, mineral characterization and thermogravimetric studies were made of raw and processed shale samples from the most prospective sections of the Rundle, Stuart, Condor, Duaringa, Nagoorin South, Nagoorin, Yaamba and Lowmead oil shale deposits. The effects of processing on minerals were determined in sufficient detail to establish the relevance of the various minerals and their reactions in oil shale processing. Minerals identified as the most significant in processing were smectite, kaolinite, siderite-type minerals and pyrite. Smectite and siderite-type minerals are characteristic of the oil shales of eastern Queensland. Smectites were found to be comparable in the various deposits and to be members of the montmorillonite/nontronite series with unusually low thermal stability. Four types of siderite (siderite, manganoan siderite, magnesian siderite and high magnesian siderite) were found, with progressively increasing decomposition temperatures in the retort. The most important mineral reactions occurring in the preheater, retort and combustor have been identified. Endothermic dehydroxylation and decomposition reactions of smectite, kaolinite, siderite minerals and pyrite influence heat requirements and gaseous products from retorting and combustion. The results indicate the possibility of transferring some of these reactions from the retort to the combustor by control of partial pressures of vapour phases in the retort. A sound basis has been established for future studies of the effects of specific minerals on oil coking reactivity and oil yields in retorting.

RELEVANCE OF CARBONATE MINERALS IN THE PROCESSING OF AUSTRALIAN TERTIARY OIL SHALES

Abstract The Tertiary oil shale deposits of eastern Queensland, Australia, comprise an important future source of alternative liquid fuels. Carbonate minerals are important in relation to selection of processing conditions and in limiting sulphur dioxide emissions. This paper characterizes such minerals from the Stuart, Rundle, Condor, Nagoorin, Nagoorin South, Duaringa, Yaamba and Lowmead deposits. Composite and stratigraphically selected samples were mineralogically analysed using chemical analyses, X-ray diffractometry, thermogravimetry and scanning electron microprobe analysis. Carbonate minerals significant in processing include calcite, magnesian calcite, siderite and magnesian, calcian and manganoan siderites which occur in different amounts in the various deposits. Dolomite and ferroan dolomite were sporadically observed. Calcite and magnesian calcite are decomposed in the combustor and reduce sulphur dioxide emissions by reaction to form CaSO 4 in the combusted solids. Siderite type minerals are fully or partially decomposed depending upon siderite type and process conditions in the retort. The iron oxides produced react with hydrogen sulphide in the retort gases. Calcium replacing iron in the siderite also reacts with sulphur dioxide to form CaSO 4 and hence limits sulphur dioxide emissions from the combustor.

Comparison of the mineralogy and geochemistry of the Kerosene Creek member, Rundle and Stuart oil shale deposits, Queensland, Australia

Abstract The contiguous Rundle and Stuart oil shale deposits of Queensland, Australia, contain resources equivalent to more than 5·10 9 bbl of shale oil. Characterisation of these Tertiary oil shales is important in selecting suitable processing technology. Detailed stratigraphic analysis at two locations revealed significant variations in ore type over the most prospective Kerosene Creek Member in both the Rundle and Stuart deposits. The stratigraphy, geochemistry and mineralogy are comparable with differences mainly attributed to location relative to the edge of the lake during deposition. Ore-type samples were analysed for major and trace elements relevant to processing. Mineralogical compositions were determined by chemical analyses, X-ray diffractometry and electron microprobe analysis. The major ore types were not clearly discriminated by chemical composition or mineralogy. Minerals which most effect processing of the oil shales included smectite, kaolinite, calcite, pyrite and siderite-type minerals. Carbonate mineralogy proved particularly variable and dependent upon depositional environment. Calcite, magnesian calcite, dolomite and a wide range of manganoan and magnesian siderites are observed. Siderite appears to be formed under very shallow lacustrine conditions.

Dissolution of lime into synthetic coal ash slags

Abstract One of the alternate processes presently being investigated to produce electrical power from coal is Integrated Gasification Combined Cycle (IGCC). The ash, which remains when the coal is gasified in this process, is removed by tapping the molten ash at 1400–1500°C. To ensure that the coal ash is molten at 1400–1500°C, the melting temperature of the coal ash may need to be reduced by addition of a flux, usually limestone, which is added with the coal to the gasifier. The rate of dissolution of the flux is uncertain. This paper reports the investigation of the rate of lime dissolution into synthetic coal ashes, consisting of SiO 2 , Al 2 O 3 and CaO. Results previously reported have shown that the free dissolution of fine particles (50–200 μ m) is mass-transfer controlled [S.M. Wang, T.F. Wall, J.A. Lucas, L. Elliott, A.C. Beath, Experimental studies and computer simulation of dissolution of lime particles into coal ash slags. Australian Symposium on Combustion and the Fourth Flame Days, Univ. of Adelaide, South Australia, November 9–10, 1995]. To investigate forced dissolution, a high-temperature viscometer was used to rotate a cylinder of lime in the molten slag for a given period. At temperatures between 1450°C and 1650°C, reaction products of 3CaO·SiO 2 /3CaO·Al 2 O 3 , 2CaO·SiO 2 /3CaO·Al 2 O 3 form around the lime cylinder. The concentration gradient involved in the mass transfer and the diffusion coefficient are currently being investigated.

Geochemistry and mineralogical residences of trace elements in oil shales from the Condor deposit, Queensland, Australia

Abstract Stratigraphically selected samples from several bore cores were chemically analysed for trace elements using neutron activation analysis and X-ray fluorescence spectrometry. Inter-element correlation techniques, selective leaching procedures, X-ray diffraction and electron microprobe analyses were used to establish geochemical associations and specific mineralogical residences for a comprehensive range of elements. Abundances and mineralogical residences have been determined for a comprehensive range of trace elements in Condor oil shale. Trace-element abundances are generally similar to or less than those reported for an average shale. The exceptions are pyritic S, inorganic N and Mn which are often above normal abundances and together with As, are of possible environmental concern during processing. The results provide a definitive chemical and mineralogical characterization of the oil shale and identify the major mineralogical residences of the important trace elements. S, As, Ni and Co occur mainly in the mineral pyrite, while Mn is resident in siderite and magnesian siderite. S, Ni and Co also occur, to a lesser extent in the kerogen. Inorganic N occurs in the ammonium feldspar, buddingtonite, which formed by diagenetic replacement of K-feldspar. A sound basis is established for studies of mineral reactions during retorting, spent shale combustion and waste disposal.