METAL LEACHING FROM OIL SANDS FLUID PETROLEUM COKE UNDER DIFFERENT GEOCHEMICAL CONDITIONS
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The potential for metal leaching from fluid petroleum coke under different geochemical conditions was investigated, with a specific focus on metal mobility. Oil sands mine closure landscapes will contain overburden and upgrading by-products, including coke, stored permanently under varied geochemical conditions, and previous field and laboratory studies show that metal leaching is highly dependent upon the geochemical conditions within coke deposits. Therefore, this research will identify the potential for metal leaching and the relationship with water input composition with respect to the metal behavior. Petroleum coke contains elevated solid-phase concentrations of V (1380 ± 45 mg kg−1), Ni (540 ± 18 mg kg−1), Mo (75.1 ± 3.5 mg kg−1), and several other potentially hazardous metal(loid)s (e.g., Cu, Cr, Co, Se, Zn). Laboratory column experiments focused on V, Ni, and Mo, which can occur at elevated dissolved concentrations in coke deposits. Here, we examined metal leaching from fluid petroleum coke in the presence of (i) meteoric water (pH = 7.2, Ionic strength < 0.01 M), (ii) oil sands process-affected water (OSPW; pH = 8.6, I = 0.05 M), and (iii) acid rock drainage (ARD; pH = 2.0, I = 0.2 M). These solutions mimic water types that may interact with coke in closure landscapes. The input, effluent, and profile samples collected over time showed that metal leaching is strongly dependent upon input solution composition. Vanadium and Mo leaching were greatest with ARD and OSPW, whereas sorption limited V and Mo mobility in the presence of meteoric water. Also, Mo leaching was likely promoted by the high ionic strength of ARD and OSPW solutions due to the release of weakly bound MoO4−2 ions via competitive desorption, and a shift to net positive surface charge and dominance of H2MoO40 under ARD. Finally, enhanced Ni leaching in the presence of meteoric water and ARD is due to the limited potential for sorption and to the enhanced solubility of the hydroxide or carbonate phases. Although only a small proportion of total solid-phase V, Ni, and Mo was released, our results demonstrated that geochemical conditions strongly affect leaching behavior.
DegreeMaster of Science (M.Sc.)
CommitteeFerguson, Grant; Butler , Samuel; Patterson, William
Copyright DateNovember 2020
Trace Element Mobility