Date of Award

Spring 1988

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

C L Grant

Abstract

The development of western oil shale reserves will present major environmental problems due to the generation of huge quantities of mineral waste (retorted oil shale). The goals of this study are to investigate the extent of weathering within a retorted oil shale (ROS) spoil pile, in order to better understand the long term environmental impact of the material.

The U.S. Bureau of Mines operated a pilot scale retort facility in Rulison, Colorado from 1926 to 1929. Core samples from the spoil pile associated with this project were obtained by the U.S. Geological Survey, and serve as the basis for this work. The effects of over 50 years of natural weathering were investigated by using batch equilibration studies to characterize the aqueous dissolution rates of analytes from samples obtained at different depths in the spoil pile. In support of the dissolution studies, differential thermal analysis and scanning electron microscopy with energy dispersive x-ray analysis were used to examine changes in the composition and morphologies of the particles.

Dissolution rate curves, in conjunction with scanning electron microscopy, suggest the existence of different phases of an ROS particle. A highly weathered surface sample consists of two phases; the bulk silicate mineral matrix which is only very slowly soluble, and a second phase external to the bulk which consists primarily of readily soluble salts. In contrast, subsurface samples which are not highly weathered, often contain a third phase, formed from the translocation and redeposition of material at various depths. Rates of dissolution depend on the phase from which the analyte originates, although solubility and ion exchange equilibria contribute to the shapes of the dissolution curves.

Weathering processes have not significantly altered the major mineral composition of ROS as yet. The mineral matrix itself has remained largely intact. However, laboratory weathering studies and x-ray diffraction analysis suggest that accelerated weathering of the silicate mineral matrix will occur in the presence of these highly alkaline leachates.

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