Geochemical Characteristics of Oil Sand Tailings and Bitumen Upgrading By-Products, Alberta, Canada

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1 Geochemical Characteristics of Oil Sand Tailings and Bitumen Upgrading By-Products, Alberta, Canada Bronwen Forsyth, Stephen Day, SRK Consulting Canada Inc. Oladipo Omotoso, Suncor Energy Inc.

2 Acknowledgements Study undertaken by Suncor Energy Inc. Geochemical analyses by Maxxam Analytics. Mineralogy by the University of British Columbia and University of Saskatchewan.

3 Oil Sands Production in Alberta, Canada Alberta has the third largest oil reserve in the world (170 billion barrels). Most oil occurs in association with three oil sand deposits. Bitumen is obtained by surface mining and in-situ extraction. Sample site Image credit Alberta Government

4 Bitumen Extraction from Mined Oil Sands Bitumen Image credit Suncor Energy Inc. Bitumen froth Froth treatment tailings (FTT) Image credit Suncor Energy Inc. Mined oil sands are crushed and bitumen is extracted using a process of gravity separation and flotation. Coarse & fine tailings

Dried MFT Fine tailings are deposited into ponds where they settle to form mature

5 Oil Sands Tailings Image credit Suncor Energy Inc. Suncor Tailings Pond 1 in 2002 Image credit Suncor Energy Inc. Dried MFT Fine tailings are deposited into ponds where they settle to form mature fine tailings (MFT) containing about 30 to 40 wt.% solids. MFT is mixed with polymer and dried in thin lifts to become dried MFT.

6 Bitumen Upgrading By-Products Bitumen is upgraded to lighter hydrocarbon products through a process of reductive coking. Some coke is utilized for heat generation resulting in bottom & fly coke ash. Image credit Suncor Energy Inc.

Overview of ARD Potential An oil sands particle Image credit Alberta Government http://www.energy.gov.ab.

7 Overview of ARD Potential An oil sands particle Image credit Alberta Government Quartz Kaolinite Mica Microcline Clinochlore Albite Pyrite Siderite Calcite Ankerite Ti oxides Zircon Tourmaline

8 Study Objective To geochemically characterize the metal leaching & acid rock drainage (ML/ARD) potential of oil sand tailings (FTT, MFT, dried MFT) and bitumen upgrading by-products (coke & coke ash) from the McMurray Formation.

9 Approach Used methodologies typically applied to coal & metal mine wastes. Included: - Mineralogy (XRD, µ-xrd) - Element composition (XRF, four-acid digestion) - Sulfur speciation (ASTM D2492) - Total inorganic carbon (by difference) - Acid-base accounting (including siderite-corrected Sobek NP) - Net acid generation (NAG) with & without Dean Stark extraction to remove residual bitumen - Humidity cell testing (minimum of 20 weeks)

10 Acid Potential Average Sulfur (wt. %) Gypsum Fe, Al sulfates Pyrite Sulfate Sulfide Insoluble Sulfur Speciation (ASTM D2492) Error bars indicate 95% confidence interval. MFT (n=57) DMFT (n=12) FTT (n=5) coke (n=8) coke ash (n=3) Sulfur associated with carbonaceous matter

11 Acid Neutralization Potential Primarily associated with calcite & ankerite dissolution. Three determinations: Inorganic C determined as the difference between total C and residual C NP associated with Ca & Mg in calcite & ankerite (CaNP) from QXRD 1 Sobek NP with siderite-correction 2 1 Day, S.J. (2009) Estimation of calcium and magnesium carbonate neutralization potential for refined acid-base accounting using electron microprobe and X-ray diffraction. 8th International Conference on Acid Rock Drainage (ICARD), Skelleftea, Sweden, June Skousen, J. (1997) Neutralization potential of overburden samples containing siderite. Journal of Environmental Quality. 26(3):

12 Acid Neutralization Potential Carbonate by XRD (% as C) :1 MFT (n=57) DMFT (n=12) FTT (n=5) CaNP (kg CaCO 3 /t) : Analytical Carbonate (% as C) Poor relationship likely attributable to high organic C content & hydrophobicity Siderite-corrected NP (kg CaCO 3 /t) More consistent relationship but differences observed

13 Acid Rock Drainage Potential CaNP (kg CaCO 3 /t) non-pag Sulfide S = 0.1% 2:1 1:1 Uncertain PAG AP (kg CaCO 3 /t) MFT (n=57) DMFT (n=12) FTT (n=5) Coke & coke ash (not shown) contained less than 0.1% sulfide & were classified as non-pag.

14 Acid Rock Drainage Potential ph ph>5 non-acidic ph 5 acidic Humidity Cell Cycle (weeks) HC-1 MFT HC-2 MFT HC-3 MFT HC-4 Dried MFT HC-5 Dried MFT HC-6 Dried MFT HC-7 MFT HC-8 MFT HC-9 MFT HC-10 Coke Ash HC-11 Coke Ash HC-12 Coke Ash HC-13 Dried MFT HC-14 FTT HC-15 MFT HC-16 MFT HC-17 Coke HC-18 Coke HC-19 FTT HC-20 FTT

15 Trace Element Leaching Potential Tailings bulk composition showed enrichment of Co, Mo, Ni, Se & U in comparison to global average values for sandstone. Coke & coke ash bulk composition showed elevated V, Ni & Mo in comparison to tailings.

16 Trace Element Leaching Potential Ni (mg/kg/week) Mo (mg/kg/week) Humidity Cell Cycle (weeks) Humidity Cell Cycle (weeks) HC-1 MFT HC-2 MFT HC-3 MFT HC-4 Dried MFT HC-5 Dried MFT HC-6 Dried MFT HC-7 MFT HC-8 MFT HC-9 MFT HC-10 Coke Ash HC-11 Coke Ash HC-12 Coke Ash HC-13 Dried MFT HC-14 FTT HC-15 MFT HC-16 MFT HC-17 Coke HC-18 Coke HC-19 FTT HC-20 FTT

17 Summary of ML/ARD Potential Tailings, coke & coke ash had low ML/ARD potential due to low sulfide content. FTT is a possible exception. Classified as potentially acid-generating by static test methods. No acidity observed in humidity cell tests. Generally low metal mobility under neutral to alkaline ph. Greater element leaching from coke ash due to soluble sulfates & oxide phases.

18 Application of ML/ARD Potential Methods to Oil Sands Sample hydrophobicity requires dispersants & sonification to allow regeants to properly react with samples. Quantitative XRD may be an alternative to wet chemistry methods for inorganic C determination. Application of siderite-corrected Sobek NP to oil sands tailings requires further investigation.

19 Application of ML/ARD Potential Methods to Oil Sands Application of humidity cell rates to site conditions requires careful consideration of: Sample hydrophobicity Scaling Likely limited oxygen diffusion due to high organic C & moisture content.

Geochemical Characteristics of Oil Sand Tailings and Bitumen Upgrading By-Products, Alberta, Canada

Geochemical Characteristics of Oil Sand Tailings and Bitumen Upgrading By-Products, Alberta, Canada Bronwen Forsyth 1, Stephen Day 1 and Oladipo Omotoso 2 1. SRK Consulting, Canada 2. Suncor Energy Inc,