Extraction of Inorganic Chemical Constituents from Retorted Oil Shale by Complexometric Agents

摘要

Synthetic leachate solutions containing complexometric agents were used to simulate the long-term release of trace metals, carbonates, and sulfates from indirectly retorted (IH) and directly retorted (DH) oil shale. This approach was also taken to accelerate the leaching process in a lab scale/real time leach test which would approach the maximum potential release of chemical constituents. The complexometric agents examined were acetate, oxalate, and citrate ions, and EDTA and DTPA. Retorted oil shales were also extracted with distilled-deionized water. Leachate samples were analyzed for silver, arsenic, boron, barium, cadmium, chromium, copper, iron, mercury, molybdenum, nickel, lead, antimony, selenium, vanadium, zinc, fluorine, carbonate, and sulfate. For the indirectly retorted oil shale, maximum metallic element leachability was observed with EDTA and DTPA. In general, as the length of extraction period increased so did metal extractability. The DH sample, composed mineralogically of a number of high-temperature alteration products, produced higher leachate pH and electrical conductivity values. This was attributed to the instability of high-temperature mineral phases at low temperatures and pressures. Oxalate, in addition to EDTA and DTPA, was found to affect a high trace metal solubility. The extractability of trace metallic elements from DH, however, was lower than that for IH, thus illustrating the insolubility of metallic element-bearing minerals at high pH and the ability of ionic species released from DH to form sparingly soluble solids with trace metallic elements. 29 refs., 12 figs., 16 tabs. (ERA citation 11:047247)