Heavy Metals in Colorado and Chinese Oil Shale Semicoke: Disposal Issues, Impediments to Byproduct Conversion

Abstract

Oil shale, a fine-grained sedimentary rock, contains a proportionally large amount of kerogen, which can be converted into oil by thermal degradation of the compacted rock. The primary byproduct of current oil shale oil extraction processes is semicoke. Its landfill deposition presents a possible threat to the environment and represents a waste of a potentially useable byproduct. In this work, we explore the heavy metal content of oil shale semicoke pyrolyzed at 500 and 1000 °C to better understand the risks posed by disposal of oil shale processing waste on the nearby environment, as well as impediments to potential byproduct conversion. The greatest potential obstruction to byproduct conversion and the greatest environmental risk posed by open air disposal of oil shale semicoke is likely due to relatively high arsenic concentrations; using X-ray fluorescence spectroscopy, we find arsenic concentrations in semicoke (pyrolyzed at 500 °C) ranging from 25 ppm for Chinese oil shale from the Huadian mine (class C) to 79 ppm for Green River, Colorado, 50 gallons per ton (GPT) of oil shale. Other heavy metal elements analyzed, including barium, copper, lead, manganese, and iron, are well below the United States Environmental Protection Agency (U.S. EPA) regional screening limits.

Identifying the reaction mechanism of oil-shale self-heating retorting by thermal analysis techniques

“…The thermal decomposition of kerogen is an extremely complex process consisting of a series of chemical reactions, and thus it's usually represented by a global kinetic analysis [8,27,37]. TG has been extensively used as an effective method to determine the global kinetic parameters of thermal decomposition [22].…”

“…The primary byproduct of ex-situ retorting is semicoke waste, a solid carbonaceous residue containing minerals and heavy metals [8]. Because OS has much high mineral contents as compared to coal, the yield of semicoke is usually as high as 70-90% by mass of the original OS [5].…”

Leachability of Trace Elements From the Aged and Fresh Spent Shale Deposit – A Field Study

“…Oil shale, commonly defined as a fine-grained sedimentary rock containing significant amounts of organic matter, is widely distributed around the world [1]. Increased attention has been lately paid to the use of oil shale for oil and energy production, as well as related environmental problems [2][3][4][5][6].…”

Experimental and Computational Demonstration of a Low-Temperature Waste to By-Product Conversion of U.S. Oil Shale Semi-Coke to a Flue Gas Sorbent

“…Heavy metals, polycyclic aromatic hydrocarbons, and phenols present in the semi-coke can leach into groundwater and contaminate the surrounding areas. Semi-coke mountains created after oil shale extraction present a physical environmental danger [3][4][5][6][7][8]. Mountains of semi-coke dot the Estonian landscape where oil shale is used to generate a majority of the country's electricity.…”