EXPERIMENTAL AND COMPUTER MODELING STUDIES OF ACID LEACHING OF RUNDLE OIL-SHALE

Columns of raw and retorted oil shale from the Kerosene Ck seam of the Rundle deposit were leached with dilute H2SO4 to simulate, on an accelerated time scale, the potential effects of acidification in this system. A parallel set of control columns was leached with distilled water only so that the extent of natural in situ generation of acidity by the shale materials could be determined. The results from the controls confirmed that the raw shale has a positive acidification potential. Thermodynamic computer modelling supported the proposal that dissolution of calcite and siderite dominate the titration curve for the raw shale. There was good agreement between the observed and predicted elution profiles for Ca2+, HCO3- and Fe2+. However, the behaviour of Mn2+ was not able to be satisfactorily modelled by the simple sequential batch titration approach that was used. It is proposed that the much earlier than predicted breakthrough of Mn2+ occurred as a result of hysteresis in the solubility of MnCO3, coupled with accelerated elution caused by competition with Ca2+ for ion exchange sites in the shale matrix and depletion of available binding sites as the acid front advanced down the column.