Sorption of selected inorganic materials on raw and retorted oil shales

Abstract

Shale oil is an attractive, alternative fuel source for a world in which there is an increasing demand for energy. However, it is necessary to assess the environmental impacts of the shale oil industry before widescale production is begun. Diversity of retorting processes, the subsequent variability in waste products and the possible waste management schemes makes assessment of these impacts complicated. Waste treatment and disposal are areas which must be researched thoroughly. To properly evaluate the environmental risks associated with the disposal of processed shales and process wastewaters, an appreciation for the sorption/desorption (S/D) characteristics of oil shales is required.

The overall objective of this research was to evaluate the S/D capacity of four types of shale: Antrim (spent, eastern shale), Anvil (raw, western shale), Oxy 6 and Run 16 (spent, western shales). Batch and continuous-flow, column experiments were performed in which the S/D behavior of five cations (As, Ca, Cd, Fe, and K) and three anions (F, SO₄, and HCO₃/CO₃) was monitored. The conductivity, redox potential, and pH of the eluent fluids were also determined.

This study showed that retort temperature and porosity of the various shales had a significant effect an their S/D characteristics. Batch elution trials with spent shales produced eluents having a characteristic pH in the range 8.5 to 11.5. In these experiments, the shales retorted at lower temperatures (660°C and 793°C) released higher levels of Ca, K, and SO₄ than did a higher temperature, retorted shale (800 to 1000°C) and raw shale. The shales retorted at lower temperatures also had the highest porosities of the four shales and exhibited a greater capacity for sorption of As and F than did the other shales. Continuous-flow, elution trials showed that most inorganics monitored were flushed from the columns of shale in the first 5 to 8 pore volumes of effluent.