Environ. Sci. Technol. 1990, 2 4 , 258-263
Characterization of Mercury, Arsenic, and Selenium in the Product Streams of a Bench-Scale, Inert-Gas, Oil Shale Retort K. 6. Olsen," J. C. Evans, D. S. Sklarew, J. S. Fruchter, D. C. Girvin, and C. L. Nelson
Pacific Northwest Laboratory, Richland, Washington 99352 The purpose of this study was to determine the effects of heating rates and maximum temperatures on the redistribution of mercury, arsenic, and selenium into the shale oil, retort water, and offgas of a 6-kg bench-scale retort. A Green River shale (western) from Colorado and a New Albany shale (eastern) from Kentucky were heated at 1-2 OC/min to a maximum temperature of 500 "C. The eastern and western shales were also heated at 2 OC/min to 750 "C and a t 10 "C/min to 750 "C. Real-time monitoring of the offgas stream for mercury was accomplished with Zeeman atomic absorption spectroscopy or a microwave-induced helium plasma spectroscopy. Microwaveinduced helium plasma spectroscopy was also used to monitor for arsenic in the offgas stream. Raw and spent shales, retort water, and shale oil were analyzed by X-ray fluorescence, instrumental neutron activation analysis, and mercury cold vapor atomic absorption. Most of the mercury volatilized into the offgas during retorting; little or no arsenic was observed in the offgas. Mass balance calculations for arsenic and selenium accounted for essentially 100% of those elements in the spent shale, shale oil, and retort water. The mass balance calculations suggest little offgas component for arsenic and selenium. This agrees with the results of the MPD monitoring of the offgas. These results indicate the potential pathway for mercury to enter the environment is from the offgas. Arsenic and selenium preferential redistribution into the shale oil may present problems during the upgrading process. Furthermore, the tendency for arsenic and selenium to redistribute into the retort water should be considered when selecting a water treatment process to prevent the release of these elements into the environment.
Introduction Previous studies of trace element redistribution during retorting of U.S. oil shale have shown that most of the trace elements (including beryllium, chromium, cobalt, fluorine, lead, manganese, molybdenum, nickel, vanadium, and zinc) are largely retained in the retorted shale (1-3). However, several elements of environmental interest (i.e., mercury, arsenic, selenium, and cadmium) can be redistributed in significant quantities to other product streams including oil, water, and offgas. Different types of retorts affect the partitioning of these elements. For example, in the Paraho surface retort, 28% of the mercury was found in the oil, 0.01% in the water, and 23% in the offgas (4-6). The arsenic and selenium were redistributed to a lesser extent, with 5.3% and 3.8% in the oil, 0.04% and 1.9% in the water, and 0.1% and
