Effects of a carbon dioxide pressure process on the solubilities of major and trace elements in oil shale solid wastes

Processing of oil shale at high temperatures produces a highly alkaline solid waste. The waste can be stabilized by a recarbonation process. In order to test a method for accelerating the recarbonation process, the authors exposed three moist oil shale solid waste (OSSW) samples to 5 psi CO{sub 2} pressure for 1 h. The treated and untreated samples were equilibrium with water for 7 days and the chemical composition of the aqueous extracts determined. Before CO{sub 2} treatment, the Ca{sup 2+} and Mg{sup 2+} concentrations appeared to be controlled by silicate phases present in the waste such as wollastonite (CaSiO{sub 3}), forsterite (Mg{sub 2}SiO{sub 4}), and talc (Mg{sub 3}Si{sub 4}O{sub 10}(OH){sub 2}), which buffered the pH at {approximately}12.0. The Co{sub 2} treatment lowered the pH from 12.0 to {approximately}9.0 through the formation of calcite. The Ca{sup 2+} concentrations from Co{sub 2}-treated samples suggested a close approach to saturation with respect to calcite (CaCO{sub 3}) whereas the Mg{sup 2+} concentrations appeared to be controlled by either magnesite (MgCO{sub 3}) or possibly a silicate. The CO{sub 2} treatment generally decreased F and Mo concentrations in aqueous extracts. The F{sup {minus}} concentration before and after Co{sub 2} treatment appeared to be controlled bymore » fluorite (CaF{sub 2}). Results demonstrate that the CO{sub 2} pressure process is an effective means of reducing the pH and the concentrations of F and Mo in aqueous extracts from alkaline solid wastes.« less