Laboratory Weathering of Combusted Oil Shale

Abstract

AbstractProper management of large volumes of spent oil shale requires an understanding of disposal environment chemistry and mineralogy. Laboratory weathering is one method to rapidly and inexpensively assess the long‐term potential for spent oil shales to degrade the environment. The objective of this study was to examine the mineralogy and leachate chemistry of three combusted oil shales (two Green River Formation and one New Albany) in a laboratory weathering environment using the humidity cell technique. The mineralogy of the combusted western oil shales (Green River Formation) is process dependent. In general, processing resulted in the formation of anhydrite, lime, periclase, and hematite. During the initial stages of weathering, lime, periclase, and anhydrite dissolve and ettringite precipitates. The initial leachates are highly alkaline (pH > 10.5), saline, and dominated by Na, hydroxide, and SO4. As weathering continues, ettringite dissolves, gypsum and calcite precipitate, and the leachates are dominated by Mg, SO4, and CO3. Leachate pH is rapidly reduced to between 8.5 and 9 with leaching. The combusted eastern oil shale (New Albany) is composed of quartz, illite, hematite, and orthoclase. Weathering results in the precipitation of gypsum. The combusted eastern oil shale did not display a potential to produce acid drainage. Leachate chemistry was dominated by Ca and SO4. Element concentrations continually decreased with weathering. In a western disposal environment receiving minimal atmospheric precipitation, spent oil shale will remain in the initial stages of weathering, and highly alkaline and saline conditions will dominate leachate chemistry. In an eastern disposal environment, soluble salts will be rapidly removed from the spent oil shale to potentially affect the surrounding environment.