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

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 CaSO4 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 CaSO4 and hence limits sulphur dioxide emissions from the combustor.