Partitioning of trace elements during the retorting of Australian oil shales

Abstract

Samples of brown and carbonaceous oil shales from the Stuart, Condor, Yaamba and Lowmead deposits in Queensland, were retorted under Fischer assay conditions at 500 °C. The raw shales, spent shales, oils and retort waters were chemically analysed and distributions of selected trace elements to the oils and retort waters were determined. Trace element partitioning results were similar for all the Tertiary oil shales and comparable for brown and carbonaceous oil shales from the same deposit. Although the extent of partitioning varied, there are many similarities with results for the mineralogically and geologically different Green River Formation and Julia Creek oil shales. In this regard arsenic, nickel, cobalt and iron were mobilized mainly to the shale oils and arsenic, selenium, chlorine and bromine were significantly mobilized to retort waters. Porphyrins and unidentified organometallic compounds are considered to be the sources of nickel, cobalt and iron. Sources of arsenic and selenium remain uncertain. The present results appear relatively favourable for the processing of the Tertiary oil shales and show that arsenic and selenium are the most important trace elements in shale oil refining and the disposal of retort waters.