Electrokinetic sedimentation of mature oil sand

Electrokinetic sedimentation of mature oil sand
mine tailings
Raquibul Alam, Julie Q. Shang and Shriful Islam
Department of Civil and Environmental Engineering - Western University,
London, ON, Canada
Oil sands mines generate tailings that are a mixture of water, clay, sand and residual bitumen produced during the
extraction process. When tailings are released to tailings ponds, the coarse solids in tailings settle quickly, whereas fine
solids containing clay minerals, namely Mature Fine Tailings (MFT), remain suspended for years even decades. A study
is carried out to assess the suitability of Electrokinetic (EK) sedimentation to accelerate sedimentation of MFT. A series
of laboratory-scale column experiments are carried to examine the effects of electrophoresis during settling processes.
The investigation focuses on the effects of EK sedimentation as related to the initial solid concentration of the tailings
suspension (1%, 2%, 3% and 5%), electric field intensity (50 V/m, 100 V/m and 150 V/m), current intermittence (power
consumption coefficient 100 %, 75% and 50%), pH (8.5 and 10.5), and the use of an optimized coagulant FeCl 3 (0 and
350 mg/L). This study reveals that EK is more effective at higher electric field intensity within the range of applied
voltages tested in this study (50–150 V/m). pH has a pronounced effect on the zeta potential of oil sand tailings.
Generating an alkaline condition by adding NaOH solution in the tailings slurry increases the negative charge on tailings
particles and enhances EK sedimentation. The constant current yielded better results than intermittent current for EK
sedimentation of suspended tailings solids. It is further observed that the performance of EK is better than both chemical
coagulation and combination of coagulation and EK. The research on sedimentation of oil sand tailings has shown that
EK is a viable technology for accelerating sedimentation of fine tailings suspended solids in terms of increasing the zone
settling velocity, reducing the overall sedimentation time and increasing the final solid concentration of the tailings.
Key Words: EK Sedimentation, Mature Fine Tailings, Electric Field Intensity, Electrophoresis, Zeta Potential, Zone
Settling Velocity.