Mandate and Research Goals

Northern Alberta contains with a huge reserve of bitumen. With the ever increasing demand for sustainable development of these hydrocarbons, a major challenge remains with the management of tailings. From geotechnical perspective, matured fine tailings (MFT) are soil slurries that experience large deformation without significant change in effective stress, hence they deviate from Terzaghi’s traditional soil mechanics theory. Application of large strain consolidation theory can predict settling behavior of soil slurries, but the un‑recovered bitumen along with clay water system in MFT affects its consolidation behavior.

This study deals with understanding the consolidation and permeability characteristics of MFT from different bitumen extraction processes. Nuclear density measuring device will be used to accurately determine the density profile in settling columns. Physicochemical behavior of clay water system at low effective stress will be studied.

Foam technology has the potential to revolutionize surface tailings disposal by providing an environmentally safe alternative for reclamation of tailings. The major objective is to flow and float a pioneer sand layer on top of weak fine tailings as part of the tailings reclamation. The sand layer is going to be mixed with foam before being pumped onto the tailings pond. The role of the foam is to increase the buoyancy of the (sand/foam) mixture as well as to decrease the density. Moisture content of the sand, gradation, different properties of foaming agent as well as the physical characteristics of the tailings are among the very important parameters which must be accounted for in the tests. The body of the research involves an inclusive series of tests in order to address all different facets of the problem. Some very rudimentary tests are going to be conducted to better characterize the procedure in small scale, while more complex experiments need to be carried out later in the field to insure the feasibility of the project.

Mining and mineral processing ultimately lead to the production of waste by-products including waste rock and a finer grained slurry called “tailings”. Management of the tailings and waste rock currently results in environmental challenges and financial burdens for operators. The volume of tailings generated and associated environmental hazards depend upon the individual ore bodies and the physical/chemical extraction processes. These tailings are managed through the implementation of a tailings management system (TMS), consisting of tailings treatment/dewatering at the mill, thickening, transport to and construction of storage impoundments, natural dewatering within the impoundments, water recovery and recycle, effluent treatment, and restoration of the site. 

Evaluating all the options available to develop a sound management system or understanding the implications of modifications to an existing TMS can be time consuming and expensive. A sound, well thought out TMS will help fulfill the mining industry’s commitments to achieve sustainability and to apply the best available technologies. The objective of this study is to develop a model/tool that will guide the tailings planner/regulator through the process of tailings management to attain the most practical, economical, and environmentally sound solution. The proposed research will use an object orientated, systems dynamic modeling software called GOLDSIM to develop the “tool”. Development of the model will entail a review of the physical, chemical and natural processes experienced by the tailings and associated best management practices beginning from the initial formation through deposition and finally closure of the tailings storage facility. The goal of the review is to extract and/or to develop theoretical, empirical, process-based and qualitative formulations for each of the TMS to form the building blocks of the GOLDSIM model. Combining and linking all of the TMS components into one simulation model in a public manner has not been completed to date. 

The model will allow the tailings planner to simulate the tailings system over time, demonstrate various outcomes by alternating management practices, and conduct sensitivity analyses to determine which options have the largest impacts on the system.   

The newest operating oil sands company, Albian Sands Energy Inc., has seen a rapid development of methane emissions from their tailings pond. My research focuses on determining how methane is being produced from these tailings. Work on Syncrude Canada Ltd. tailings has revealed that methane production in tailings is due to microbial degradation of hydrocarbon compounds released into tailings from diluent. During the oil extraction process used by Syncrude, a diluent, naphtha, is added to increase the efficiency of bitumen removal from oil sands ores. Naphtha is a mixture of aliphatic and aromatic compounds. Trace amounts of diluent make their way into tailings ponds where they provide the carbon source for anaerobic methane production by microbial species in the tailings. Methanogenesis in Syncrude tailings has been observed to significantly accelerate tailings densification which is a vital process to the oil sands industry.

            Albian Sands uses a different diluent than Syncrude, consisting of a mixture of pentanes and hexanes. Albian also uses citrate as a water softening agent in their tailings ponds whereas Syncrude does not. These may be causes for the quick development of methanogenesis in Albian’s tailings pond; Syncrude’s main tailings pond, MLSB, experienced a considerable lag before methane production began.  My M.Sc. project aims to investigate the effects of Albian diluent and citrate on the microbial species in Albian tailings and also to observe the effects of gas production on densification rates of Albian tailings. Microbial species are being identified through molecular methods and methane production is being monitored in sealed cultures by gas chromatography. Densification of Albian tailings will be analyzed in small- and large-scale columns. The results of this work will be compared to Syncrude tailings to obtain important insight on the effects of different oil extraction processes on methane production from tailings ponds. A better understanding of the complex process of biogenic methane production also holds implications for options in controlling greenhouse gas emissions, tailings management, land reclamation, and water recycle and reuse. 

Water management is critical to continued and sustainable development of the Athabasca Oil Sands resource in northern Alberta. Water treatment ptions for increased reuse and recycle leading to lower imports by replacement of raw water from the Athabasca River, as well as possible safe discharge, are needed. In this project, water treatment strategies leading to a better understanding of constraints and opportunities to manage water within an oil sands operation will be examined. They include:

• To evaluate treatment technologies to better manage water in an oil sands operation;
• To provide recommendations regarding effective treatments;
• To assess applicability, limitations and performance of various water treatment technologies for range of OSPW and natural waters associated with oil sands operations;
• To test options for treating selected oil sands source waters using lab-produced and field water samples.

As a result of this proposed research program, an innovative and advanced recipe for water treatment options for an array of deliverable water qualities will be provided.

One approach for management of oil sands tailings in northern Alberta has been
production of Non-Segregating (NST) or Composite/Consolidated Tailings (CT). Addition
of phosphogypsum to a mixture of Mature Fine Tailings (MFT) and cyclone
underflow (tailing sand) results in CT, a waste stream with an average solids
content of about 60%wt which is expected to be Non-Segregating when discharged.
However this material is not particularly robust. Partial segregation has been
observed following deposition resulting in fines release at the surface.

To overcome this challenge, NST with higher solids content is desirable.
The present research has been dealing with different methods of making a robust
NST. Two different approaches may be followed to achieve this goal:

-        
Further enhancing the solids content of CT as a
mixture, or

-        
Dewatering the components of CT (i.e. MFT, tailing
sand, or both) before preparing the NST.

In order to evaluate each of the above approaches, different methods of
solid – liquid separation including thickeners, inclined plate settlers,
hydrocyclones, sedimenting centrifuges and filtering centrifuges have been
studied. A series of tests including sedimentation in vertical and inclined
standpipes and dewatering of CT layers of different placement thicknesses on
inclined plates have been conducted to assess the dewatering characteristics of
CT. Also some standpipe, flume, slump and vane tests have been conducted to
study the dewatering and flow characteristics of the NST’s made from the
centrifuged MFT.

The results indicate that use of inclination along with dividing a thick
stream of CT to multiple thinner layers enhances dewatering of the material
significantly. Also for the CT made from thickened MFT, the initial results
indicate that this material holds higher angles upon deposition in comparison
to the CT made through the conventional method.

As a result of heightened activity in the oil sand industry, there are many challenges in dealing with the large volume of tailings. There is an urgent need to manage and reclaim these tailing ponds which requires a better understanding of the physical processes in these ponds and the physical characteristics of sand and slurry jets.

One of the proposed solutions for reclaiming these tailing ponds is to discharge sand slurries at certain locations so that these slurry jets will break up the non-settling tailings and settle to the bottom carrying some of the fine tailings and as a result the volume of fine tailings will be reduced and eventually, the ponds could be reclaimed.

The main objective of this research is to study the dynamics behind sand and slurry jets discharged into water as one phase flow and water with MFT as two phase flow.

The research is divided in two parts, the first one is studying the vertical and inclined (along beaches) slurry jets into water to recognize the characteristics of these slurries and the interaction with water.

Secondly, simulate the real tailing ponds (Water and MFT) and recognize the characteristics and the interaction of these slurries discharged into these real tailing ponds.

As a result of heightened activity in the oil sand industry, there are many challenges in dealing with the large volume of tailings. There is an urgent need to manage and reclaim these tailing ponds which requires a better understanding of the physical processes in these ponds and the physical characteristics of sand and slurry jets.

One of the proposed solutions for reclaiming these tailing ponds is to discharge sand slurries at certain locations so that these slurry jets will break up the non-settling tailings and settle to the bottom carrying some of the fine tailings and as a result the volume of fine tailings will be reduced and eventually, the ponds could be reclaimed.

The main objective of this research is to study the dynamics behind sand and slurry jets discharged into water as one phase flow and water with MFT as two phase flow.

The research is divided in two parts, the first one is studying the vertical and inclined (along beaches) slurry jets into water to recognize the characteristics of these slurries and the interaction with water.

Secondly, simulate the real tailing ponds (Water and MFT) and recognize the characteristics and the interaction of these slurries discharged into these real tailing ponds.

Oil sands generally contain between 55 and 80% mineral solids. Understanding these solids is important in understanding bitumen extraction processes, extraction waste disposal and opportunities for secondary resources from the minerals. It is the intent of this project to characterize the clay minerals and heavy minerals present in an Athabasca oil sands ore sample, as well as to provide a mineral balance around extraction. 

Work to date has included: identification and quantification of the minerals present in 5 different size fractions (<0.2 μm, 0.2-2 μm, 2-45 μm, 45-106μm and >106μm) of 5 different process streams (ore, primary froth, secondary froth, middlings and tailings), examination of heavy minerals (>2.8 g/cm3) by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and examination of middlings clay particles by high resolution TEM. 

Significant results include indications that the swelling behavior of the oil sand clays may be due to extremely thin illite and kaolinite particles, which behave as mixed-layer swelling clays in accordance with the fundamental particle theory proposed by Nadeau et al. [1].  In addition, kaolinite tends to be enriched in the froth whereas the mixed layer clays are found in greatest abundance in the middlings fraction. The heavy mineral fraction contains a substantial fraction of TiO2 polymorphs with relatively high levels of iron contamination. This contamination, along with the presence of highly inhomogeneous leucoxene particles, indicate that the TiO2 polymorphs may be derived from the alteration of ilmenite and may explain the high level of iron contamination found in the TiO2 concentrates developed from the oil sands froth tailings. 

1. P.H. Nadeau, M.J. Wilson, W.J. McHardy and J.M. Tait, Science, 225 (1984) 923-935.

Awaiting suitable candidate

Greenhouse experiments were conducted to evaluate the suitability of using five native grass species for dewatering consolidated/composite (CT) tailings and to assess the use of direct seeding techniques and to evaluate their evapo-transpiration effect on CT. The results of germination and early plant growth of selected native grass species that were directly seeded by broadcast seeding being covered with a thin layer of CT, hydroseeding using mulch and slurry seeding indicated that native plant species: Slender Wheatgrass and Northern Wheatgrass were applicable for use in reclamation of CT deposits. The evapo-transpiration during one growing season was high for Slender Wheatgrass and Northern Wheatgrass, which indicated that these species have the ability to uptake water from CT. The average solids content of the CT mixture increased from 65% initial solids content to between 87.6 to 90.5%. 

The natural process of freeze-thaw dewatering has shown promise as a method to reclaim high moisture content mine tailings generated in Alberta’s oil sand mining industry. Dewatering of these deposits during freezing occurs due to the structural changes within the frozen soil, and from the removal of water from the underlying thawed soil during the creation of ice lenses. By determining the segregation potential of the tailings, the extent of water removal from the deposit can be predicted. Conventional freezing test methods were found to be ineffective for measuring the freezing characteristics of the compressible tailings. A method involving time-lapse photography was developed to determine the segregation potential of soft soils. Soil thermal conditions at Fort McMurray were modeled and thaw strain and frost heave were predicted for two tailings deposits.

This study investigated the feasibility of trickle freeze separation as an alternative treatment method for saline oil sands mine waste water.  Using a specially designed flume housed in a cold room, several experiments were conducted at various ambient temperatures, salt concentrations and mass flow rates.  The experiments showed the production of slush and subsequent erosion hindered the trickle freeze separation process.  Melting actually proved to be more effective at concentrating salts than the freezing process.  More than 80 % of the salts could be concentrated during melting into less than one third of the original volume.  Utilizing results from the laboratory scale experiments, a pulse-trickle freeze separation system was designed for 20 million m³/year of saline oil sands process water.  The capital investment for construction of the pulse-trickle freezing system was $127 million or $6.36/m³ capacity.  Yearly operating costs amounted to $0.13/m³ of waste water. 

The SPT and CPT are two commonly used in-situ tests to determine potential for liquefaction in sandy soils.  Results from in-situ testing at Syncrude's Aurora Tailings Dam showed conflicting results between the SPT and CPT data.  It was found from testing at the Massey Tunnel site that the discrepancy between the SPT and CPT data was likely caused by the wieght of the SPT equipment coupled with the generation of excess pore pressures due to the dynamic nature of the SPT. 

It was found that the weight of the SPT rods, sampler and hammer have a significnat impact on the blow count.  Futhermore, it was found that positive or negative excess pore pressures could be generated during the SPT depending on the relative density of the sand. 

Three ten meter high standpipe tests were initiated in 1982 to investigate the compression behaviour of oil sands tailings.  The objectives of this research are to document and analyze the compression behaviour of these tailings in ten meter standpipe tests and to use a finite strain consolidation theory to model the compression behaviour of these materials.  The mature fine tailings (MFT) standpipe has been monitored for over 22 years and although it has compressed 3 meters by self-weight, very little or no effective stresses have developed.  The MFT-sand standpipe with 82% sand content reached 100% consolidation in 8 years consolidating 1.5 m.  Modeling with the finite strain consolidation theory does not predict the compression behaviour of MFT.  The theory, however, can forecast the consolidation progress of MFT-sand mixtures which have a high percentage of sand.  A nonsegregating MFT-sand mix should result in a tailings stream that consolidates rapidly to a sufficient density in a reasonable length of time.   

Increased pore pressures and softening of dense beach above water tailings were observed at Syncrude when cyclic equipment loading was applied, resulting in stoppage of several reclamation projects and presenting challenges for future reclamation activities.  The softening was accompanied by the formation of sand boils and appeared to be a liquefaction type behaviour, although swelling and retention of static strength were also observed.

To study whether it was liquefaction that caused softening, instrumented test areas were softened by equipment and human activities that imparted cyclic loading on a Syncrude site.  Analyses of in-situ test data and subsequent laboratory test results showed that the tailings were initially dense of their critical state.  This and stress paths observed during cyclic loading are consistent with cyclic liquefaction.  Several controlling factors and potential mechanisms for the observed softening were identified, and the field data was used to develop correlations for other sites and loading conditions.