Research on release of trace elements at retorting of Huadian oil shale

Oil shale is abundant in the world. Today, the industry of oil shale retorting for producing shale oil is developing owing to high price of crude oil in the world. In order to study migratory behavior of trace elements in oil shale at retorting, tests were performed in laboratory with oil shale of the Huadian deposit of China at different temperatures from 360 to 560 degrees C. Trace elements Ba, Co, Cr, Cu, Mn, Ni, P, Pb, Sr, Ti, V, Y present in oil shale and shale char were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Hg and As were determined by atomic fluorescence spectroscopy (AFS). By comparing the content of trace elements in oil shale and shale char, distribution characteristics of trace elements at retorting were studied. The analysis of trace elements indicates that in comparison with the earth crust averages, oil shale samples are richer in some elements, including Mn (more than 30x), P (more than 6x), and Ti (more than 5x). The amounts of Ti, Ba, Co, Cr, Cu, Mn, and V are increased in shale char at retorting. Pb and Hg start to volatilize at 410 degrees C. Shale char is enriched with arsenic by about 50% at temperatures from 360 degrees C to 560 degrees C. Reducing atmosphere promotes the release of trace elements. The effect of heating rate on different elements was also studied in these experiments. For most of the elements, their release from oil shale can be promoted by higher heating rate and nitrogen atmosphere.