Partitioning of inorganic contaminants between fluid fine tailings and cap water under end pit lake scenario: Biological, Chemical and Mineralogical processes

• Author / Creator

  Samadi,Najmeh

• Fluid fine tailings (FFT) are generated during bitumen extraction from surface mined oil sands ore (in Alberta, Canada) and comprised of oil sands process-affected water (OSPW), fine particles, unrecovered bitumen and residual diluent. For reclaiming huge volumes of FFT, a viable remediation option is to place FFT in open pit covered by a mix layer of OSPW and fresh water to form an end pit lake (EPL). A potential concern is the flux of constituents of concern (COCs) from underlying FFT to overlying cap water that could affect the quality and sustainability of EPLs. In this research, chemical, mineralogical and microbiological approaches were used to investigate how biogeochemical processes in underlying FFT would affect COCs transport to cap water. For this study, 10 L columns were filled with FFT (7 L) and cap water (1.4L), sealed anaerobically and incubated at room temperature in the dark. Labile hydrocarbons (a mixture of short chain n-and iso-alkanes and monoaromatics compound representing extraction diluent) endogenous to FFT were added to FFT (amended columns) to accelerate methanogenesis for the enhancement of biogeochemical processes in FFT. Some hydrocarbon-amended columns also received nutrients such as nitrogen (N) and phosphorus (P) at C: N: P ratio of 100:10:1 for optimal microbial growth, whereas others that did not receive any amendment as served as control (unamended) columns. The results demonstrated that hydrocarbon addition increased methane (CH4) and carbon dioxide (CO2) production in the FFT and N addition exhibited incremental effect on methanogenesis and all other subsequent biogeochemical processes. Molecular analysis (16S rRNA gene) revealed that Syntrophaceae and Peptococcaceae (Bacteria) syntrophically worked with acetoclastic (Methanosaetaceae) and hydrogenotrophic (Methanoregulaceae) methanogens (Archaea) to metabolize hydrocarbons into CH4 and CO2 under methanogenic conditions.Methanogenesis in amended columns increased dewatering and consolidation of FFT by altering porewater chemistry and transforming iron (Fe) minerals. Biogenic CO2 productioniiidecreased pH that dissolved carbonate minerals in FFT and increased concentrations of Ca2+, Mg2+, HCO3- in the porewater. Some trace metals such as strontium (Sr) and barium (Ba) also increased significantly in the porewater of amended columns. These soluble ions/metals were transported to cap water via porewater expression and CH4 ebullition Iron fractionation in FFT revealed that methanogenesis also transformed crystalline FeIII minerals to amorphous FeII minerals decreasing the concentrations of certain metals such as arsenic (As), antimony (Sb), chromium (Cr), vanadium (V) and molybdenum (Mo) in porewater and cap water probably through reduction and precipitation with newly formed amorphous Fe minerals. Sequential metal extraction from FFT showed that carbonate, Fe, and manganese (Mn) oxide minerals in FFT were the major source of Sr and Ba in the porewater. Naphthenic acids (NAs) concentrations were also decreased in the porewater and capwater of amended columns. These results can help assess the water quality in EPL and understand the role of indigenous microbial communities in the sustenance of methanogenesis and partitioning of COCs from underlying FFT to overlying cap water.

• Subjects / Keywords

  • EPL
  • Contaminants movement
  • Trace metals
  • NAs
  • Sr
  • Ba
  • Capwater
  • Porewater
  • Methanogenesis
  • Nutrients

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-8730-4k32

• License

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