Suspended solids in an end pit lake: potential mixing mechanisms

Lawrence, Gregory A.; Tedford, Edmund W.; Pieters, Roger

doi:10.1139/cjce-2015-0381

Cited by 32 publications

(36 citation statements)

References 11 publications

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“…The Reynolds number of mixing during the test was calculated to be 786, characteristic of a gentle laminar flow regime. The OSPW cap layer in oil sands tailings ponds is known to be well mixed by wind and waves [39][40][41], and NAs are furthermore constantly replenished to the interface by methanogenic bubbling in a similar process to dissolved gas flotation (estimated flux of 12 g CH 4 m −2 day −1 ) [42]. Thus, as the above photocatalytic results were observed under gentle mixing conditions, it is anticipated that the natural mixing processes provided in the tailings ponds could be sufficient for OSPW treatment, although this question will be the topic of future studies.…”

Section: Resultsmentioning

confidence: 99%

Floating Photocatalysts for Passive Solar Degradation of Naphthenic Acids in Oil Sands Process-Affected Water

Leshuk

Krishnakumar

Livera

et al. 2018

Water

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Abstract:Oil sands process-affected water (OSPW), generated from bitumen extraction in the Canadian oil sands, may require treatment to enable safe discharge to receiving watersheds, as dissolved naphthenic acids (NAs) and other acid extractable organics (AEO), identified as the primary toxic components of OSPW, are environmentally persistent and poorly biodegradable. However, conventional advanced oxidation processes (AOPs) are impractically expensive to treat the volumes of OSPW stockpiled in the Athabasca region. Here we prepared floating photocatalysts (FPCs) by immobilizing TiO 2 on glass microbubbles, such that the composite particles float at the air-water interface for passive solar photocatalysis. The FPCs were demonstrated to outperform P25 TiO 2 nanoparticles in degrading AEO in raw OSPW under natural sunlight and gentle mixing conditions. The FPCs were also found to be recyclable for multiple uses through simple flotation and skimming. This paper thus demonstrates the concept of a fully passive AOP that may be scalable to oil sands water treatment challenges, achieving efficient NA reduction solely through the energy provided by sunlight and natural mixing processes (wind and waves).

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Section: Resultsmentioning

confidence: 99%

Floating Photocatalysts for Passive Solar Degradation of Naphthenic Acids in Oil Sands Process-Affected Water

Leshuk

Krishnakumar

Livera

et al. 2018

Water

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“…The modeled scenarios with a 0.5 or 1 m disturbance generally corresponded to these field observations. Evidence of FFT disturbance was observed in the field as the water cover turbidity exhibited a rapid increase during unstable periods in the lake when the water column was completely mixed [ Lawrence et al ., ]. Disturbance within the FFT was also supported by the previous tracer study [ Dompierre and Barbour , ].…”

Section: Resultsmentioning

confidence: 99%

“…The water cover responds to seasonal temperature cycles in a similar manner as natural temperate, northern lakes [ Lawrence et al ., ; Oswald and Rouse , ; Rouse et al ., ]. During the summer months, the water cover is thermally stratified from the end of May to the beginning of September.…”

Section: Methodsmentioning

confidence: 99%

Chemical mass transport between fluid fine tailings and the overlying water cover of an oil sands end pit lake

Dompierre

Barbour

North

et al. 2017

Water Resources Research

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Fluid fine tailings (FFT) are a principal by-product of the bitumen extraction process at oil sands mines. Base Mine Lake (BML)-the first full-scale demonstration oil sands end pit lake (EPL)-contains approximately 1.9 3 10 8 m 3 of FFT stored under a water cover within a decommissioned mine pit. Chemical mass transfer from the FFT to the water cover can occur via two key processes: (1) advection-dispersion driven by tailings settlement; and (2) FFT disturbance due to fluid movement in the water cover. Dissolved chloride (Cl) was used to evaluate the water cover mass balance and to track mass transport within the underlying FFT based on field sampling and numerical modeling. Results indicated that FFT was the dominant Cl source to the water cover and that the FFT is exhibiting a transient advection-dispersion mass transport regime with intermittent disturbance near the FFT-water interface. The advective pore water flux was estimated by the mass balance to be 0.002 m 3 m 22 d 21 , which represents 0.73 m of FFT settlement per year. However, the FFT pore water Cl concentrations and corresponding mass transport simulations indicated that advection rates and disturbance depths vary between sample locations. The disturbance depth was estimated to vary with location between 0.75 and 0.95 m. This investigation provides valuable insight for assessing the geochemical evolution of the water cover and performance of EPLs as an oil sands reclamation strategy. End pit lakes (EPLs) offer long-term FFT containment with relatively low initial costs [Cumulative Environmental Management Association (CEMA), 2012]. These mine closure landscapes contain FFT deposits under a water cover within decommissioned mine pits. In the future, EPLs will be incorporated into the larger mine Key Points: First study of solute release from fluid fine tailings (FFT) stored under water cover in first oil sands end pit lake Mass balance confirmed constituents in FFT pore water largest mass input to water cover Numerical models show advectiondispersion during FFT settlement controls mass transport

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“…), where ℜ ≈ ℜ δ in the numerical simulations. We predict the likelihood of forming convective rather than double‐diffusive plumes by estimating ℜ δ for three distinct studies: the laboratory measurements of Bluteau et al (), the field measurements from Tailings Lake (Pieters and Lawrence ), and those from Base Mine Lake (Lawrence et al ). To compare the laboratory and field studies with our simulations, we evaluated ℜ δ in Eq.…”

Section: Discussionmentioning

confidence: 99%

“…The estimated ℜ δ ≫ 0.25 suggests that plumes—dominated by double‐diffusive processes—transported salt throughout the water column. Measured temperature time series during the winter in another lake, Base Mine Lake, also displayed perturbations despite the presence of stable reverse‐temperature gradients (Lawrence et al ). Similar to Tailings Lake, its relatively low salinity and salt exclusion rates yield a high ℜ δ ≈ 1 (Table ).…”

Section: Discussionmentioning

confidence: 99%

Under‐ice salinity transport in low‐salinity waterbodies

Olsthoorn

Bluteau

Lawrence

2019

Limnology & Oceanography

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In cold and temperate climates, ice typically covers the surface of waterbodies during winter. Many of these systems are also weakly saline where, unlike seawater, the temperature of maximum density, Tfalse˜md, is higher than its freezing temperature, Tfalse˜f. This feature of the equation of state results in a stable temperature stratification when surface waters cool below Tfalse˜md. Conversely, salts excluded from the growing ice can destabilize the underlying water. Previous laboratory and field experiments demonstrated that excluded salts generate localized overturning and downward transport of salt, despite the persistence of a stable temperature gradient. Those experiments were not able to determine the processes responsible for this transport. Here, we use direct numerical simulations to visualize and characterize the plumes generated when ice excludes salt into a stable temperature gradient. We restrict our analysis to times much earlier than the diffusion timescale of temperature over the domain. We define a mass flux parameter ℜ that considers the strength of the reverse‐temperature stratification relative to the rate of salt exclusion. We identify two types of plumes whose characteristics depend mainly on ℜ: double‐diffusive salt‐fingering plumes and convective plumes. The former encourages transport of salt to the bottom without significantly mixing the temperature stratification, while the latter tends to mix the water column. We apply a scaled mass flux parameter to published laboratory and field observations in low‐salinity systems. These limited observations compare favorably with our numerical analysis.

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Suspended solids in an end pit lake: potential mixing mechanisms

Cited by 32 publications

References 11 publications

Floating Photocatalysts for Passive Solar Degradation of Naphthenic Acids in Oil Sands Process-Affected Water

Floating Photocatalysts for Passive Solar Degradation of Naphthenic Acids in Oil Sands Process-Affected Water

Chemical mass transport between fluid fine tailings and the overlying water cover of an oil sands end pit lake

Under‐ice salinity transport in low‐salinity waterbodies

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