METAL LEACHING FROM OIL SANDS FLUID PETROLEUM COKE UNDER DIFFERENT GEOCHEMICAL CONDITIONS

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

Adsorption of (Poly)vanadate onto Ferrihydrite and Hematite: An In Situ ATR–FTIR Study

Copyright © 2020 American Chemical SocietyFunding was provided by the Natural Sciences and Engineering Council of Canada (NSERC) through the Discovery Grants program (Grant no. RGPIN-2014-06589). Additional support awarded to C.J.V. was through the NSERC-Canada Graduate Scholarship-Master’s (NSERC CGS-M) Program. M.P.S. would like to acknowledge the Natural Sciences and Engineering Research Council Collaborative Research and Training Experience Sustainable Applied Fertilizer and Environmental Remediation (NSERC CREATE SAFER) program, as well as the NSERC Research and Development grant supported by Federated Cooperatives Limited for financial support.Peer ReviewedVanadium (V) has been a useful trace metal in describing Earth’s biogeochemical cycling and development of industrial processes; however, V has recently been recognized as a potential contaminant of concern. Although Fe (oxyhydr)oxides are important sinks for aqueous V in soils and sediments, our understanding of adsorption mechanisms is currently limited to mononuclear species (i.e., HxVO4(3–x)–). Here we use in situ attenuated total reflectance – Fourier transform infrared spectroscopy to examine sorption mechanisms and capacity for (poly)vanadate attenuation by ferrihydrite and hematite from pH 3 to 6. Adsorption isotherms illustrate the low affinity of polyvanadate species for ferrihydrite surfaces compared to hematite. Mononuclear V species (i.e., [HxVO4](3−x)− and VO2+) were present at all experimental conditions. At low surface loadings and pH 5 and 6, H2VO4− adsorption onto ferrihydrite and hematite surfaces results from formation of inner sphere complexes. At [V]T above 250 µM, adsorbed polynuclear V species in this study include H2V2O72− and V4O124−. Whereas, HV10O286−, H3V10O285−, and NaHV10O284− are the predominant adsorbed species at pH 3 and 4 and elevated [V]T. Surface polymers were identified on hematite at all experimental pH values, whereas polymeric adsorption onto ferrihydrite was limited to pH 3 and 4. These results suggest that hematite offers a more suitable substrate for polymer complexation compared to ferrihydrite. Our results demonstrate the pH and concentration dependant removal of (poly)vanadate species by Fe(III) (oxyhydr)oxides, which has implications for understanding V mobility, behaviour, and fate in the environment

Geochemical conditions influence vanadium, nickel, and molybdenum release from oil sands fluid petroleum coke

© 2022 Elsevier B.V. All rights reserved.Funding was provided by Syncrude Canada Ltd. and the Natural Sciences and Engineering Research Council of Canada through the Collaborative Research and Development grants program (Grant No. CRDPJ 476388) and the Industrial Research Chairs Program (Grant No. IRCPJ 428588–11).Peer ReviewedPetroleum coke is a potential source of vanadium (V), nickel (Ni), and molybdenum (Mo) to water resources in Athabasca Oil Sands Region (AOSR) of northern Alberta, Canada. Large stockpiles of this bitumen upgrading byproduct will be incorporated into mine closure landscapes and understanding the processes and conditions controlling the release and transport of these transition metals is critical for effective reclamation. We performed a series of laboratory column experiments to quantify V, Ni, and Mo release from fluid petroleum coke receiving meteoric water (MW), oil sands process-affected water (OSPW), and acid rock drainage (ARD) influents. We found that influent water chemistry strongly influences metal release, with variations among metals largely attributed to pH-dependent aqueous speciation and surface reactions. Cumulative V, Ni, and Mo mass release was greatest for columns receiving the low-pH ARD influent. Additionally, cumulative V and Mo mass release were greater in columns receiving OSPW compared to MW influent, whereas cumulative Ni mass release was greater in columns receiving MW compared to OSPW influent. Nevertheless, only a small proportion of total V, Ni, and Mo was released during the experiments, with the majority occurring during the first 10 pore volumes (PVs). This study offers insight into geochemical controls on V, Ni, and Mo release from fluid petroleum coke that supports ongoing development of oil sands mine reclamation strategies for landscapes that contain petroleum coke