CA2736675A1 - Electrokinetic process and apparatus for consolidation of oil sands tailings - Google Patents

Abstract

A method of compacting solids in situ in an oil sands extraction tailings pond. The method includes the steps of placing two or more electrodes into the tailings pond in a predetermined spacing and connecting the electrodes to a source of power, having a variable voltage. This creates at least one cathode and at least one anode and an electrical field therebetween. The electrical field is of a sufficient strength to induce flocculation of particles in the tailings and to simultaneously release water. Then the solids undergo further compaction with further water release to create a solid material having a minimum desired load bearing capacity. In a further embodiment an electrode used in carrying out the method is provided.

Description

TITLE: ELECTROKINETIC PROCESS AND APPARATUS FOR
CONSOLIDATION OF OIL SANDS TAILINGS

FIELD OF THE INVENTION

This invention relates generally to the broad field of pollution control. More particularly, this invention relates to methods and apparatus that can be used to mitigate the persistent nature of certain types of tailings ponds, such as tailings ponds filled with waste products from tar or oil sand recovery processes. Such mitigation is for, among other things, the purpose of allowing land reclamation to occur.

BACKGROUND OF THE INVENTION

Oil or tar sands are a source of bitumen, which can be reformed into a synthetic crude or syncrude. At present a large amount of hydrocarbon is recovered through surface mining. To obtain syncrude, the hydrocarbons must be first separated from the sand base in which it is found. This sand based material includes sands, clays, silts, minerals and other materials. The most common separation step used on surface mined tar sands is the hot water separation process which uses hot water to separate out the hydrocarbons. However, the separation is not perfect and a water based waste liquid is produced as a by-product which may include small amounts of hydrocarbons, heavy metals and other waste materials, but is mostly a stable colloidal mixture of water and clay, and other materials. This is waste liquid is called Mature Fine Tailings (MFT) and is collected in onsite reservoirs called tailings ponds.
Oil extraction has been carried out for many years on the vast reserves of oil that exists in Alberta, Canada. It is estimated that

-2-750,000,000 m3 of MFT have been produced. Some estimates show that 550 km2 of land has been disturbed by surface mining, yet only 267 ha (less than 0.5%) has received certification as being reclaimed. Even this small area was not mined, nor used for associated processing operations, but was only used for the storage of overburden.
The MFT ponds present three environmental and economic issues:
water management, sterilization of potentially productive ore and delays in reclamation. Although concentrations vary, MFT can typically comprise 50 to 70% water. This high water content forms, in combination with the naturally occurring clays, a thixotropic liquid. This liquid is quite stable and persistent and has been historically collected in large holding ponds.
Very little has been done to treat the MFT that has been created and so it continues to build up in ever larger holding ponds. As development of the tar sands accelerates and more and more production is brought on line, more and more MFT will be produced. What is desired is a way to deal with the MFT that has been and will be generated to permit land reclamation, a way to release captured water and to provide access to the productive ore located beneath such ponds.
MFT represent a mixture of clays (illite, montmorillonite and kaolinite), water and residual bitumen resulting from the processing of oil sands. In some cases MFT may also be undergoing intrinsic biodegradation. The biodegradation process creates a frothy mixture, further compounding the difficulty in consolidating this material. These clays, most particularly, sodium montmorillonite found in MFT are expansive; i.e., volumetric changes of as much as 30% can occur between wetting and drying. It is estimated that between 40 and 200 years are required for these clays to sufficiently consolidate to allow for reclamation of tailings ponds. Such delays will result in unacceptably large volumes of MFT, and protracted periods of time before reclamation can take place unless a way to effect disposal and reclamation is found.

-3-It is known that the application of an electrical field to a dielectric material results in certain electro-kinetic phenomena, including electro-osmosis, the movement of water from an anode to a cathode;
electrophoresis, the movement of ions in the water to oppositely charged electrodes and electrostriction, a result of the application of an electrical field that results in mechanical work which deforms the dielectric material.
Electro-osmosis has been used to dewater solid or consolidated clay soils for construction projects to improve bearing capacity. Electrophoresis has been used in many industries, such as the pharmaceutical industry and ceramics industry to produce high grade separations. Electrostriction has been used on a small scale to create high density ceramics. In a electrical resistance heating treatment at Fargo, ND (Smith et al., 2006)a, where the applied electric field ranged between 0.46 to 0.8 volt/cm an electro osmotic phenomenon was observed with AC current. Examples of applications of electrical fields in various circumstances can be found in the following prior patents.
United States Patent No. 3,962,069 United States Patent No. 4,107,026 United States Patent No. 4,110,189 United States Patent No. 4,170,529 United States Patent No. 4,282,103 United States Patent No. 4,501,648 United States Patent No. 4,960,524 United States Patent No. 5,171,409 United States Patent No. 6,596,142 a Smith, G.J., J. von Hatten, and C. Thomas (2006) Monitoring Soil Consolidation during Electrical Resistivity Heating. Proceedings of the Fifth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, May 22-25, 2006, Monterey, CA,

-4-The application of electrical current to treat oil sands tailings has also been tried, as shown in U.S. Patent 4,501,648. However, this teaches a small device with a tracked moving immersed electrode onto which is deposited clay solids. The electrode is moved out of contact with the liquid and then the solids are scraped off the electrode. A chemical pre-treatment step is required to achieve the desired deposition rate on the immersed electrode. While interesting, this invention is too small to be practical for MFT treatment and requires a chemical pre-treatment step which adds to the cost. What is desired is a better way to deal with vast volumes of MFT that will need to be treated.

SUMMARY OF THE INVENTION

According to the present invention, the consolidation of solids present in MFT occurs in three phases which are initiated contemporaneously or pana-contemporaneously under the application of an electrical field. These phases include the initial consolidation under the influence of an electric field of dispersed particles in a flocculation step with an accompanying release of water, followed or contemporaneously occurring with the secondary release of pore water and pore water pressure during the residual consolidation of the solids, in turn followed or contemporaneously occurring electrostriction, whereby the flocked material is compressed under the application of electromotive forces.
MFT, in its original state being a thixotropic liquid cannot support a load, and given that the liquid is stored in large ponds, there is virtually no ability to release pore water pressure by conventional means, such as compressive loading. Therefore, the present invention provides for a reduction of the moisture content of the solids such that it is no longer a thixotropic liquid, preferably by the application of an electrical field to induce flocculation, releasing pore water and pore water pressure and then to compress the MFT to express further pore water from the solids to

-5-increase the density to increase the lithostatic loading. An aspect of the present invention is to provide a mechanism for relief of pore pressure to accelerate the consolidation of the solids.
The present invention provides the placing of equipment to allow the generation of an electrical field (AC, DC, or EM-induced) having a voltage gradient that can be varied resulting in both electrokinetic floccing of the MFT and an electrostrictive force causing the flocculated or weakly consolidated solids to further consolidate. The amount of consolidation provided by an electrostrictive force can be varied by either the duration of application and/or the magnitude of the voltage gradient to achieve a desired bearing capacity for the MFT. An appropriate magnetic force can also be applied to accomplish the same goals and is comprehended by the present invention although the electrical field is most preferred.
According to an aspect of the present invention, the electrical field neutralizes the electrostatic charges on the clay platelets, releasing water from the MFT pores during an initial flocculation step. Over time the flocculated solids will settle into a weakly consolidated mass. The electrical field also creates electro-osmotic flow to the cathodes, where water can then be pumped away to a location where it can be optionally treated and recycled. This can also assist further consolidation along with the electrostriction. Alternately, or in combination, the use of sand drains, wick drains, or the like facilitates the release of water from within the weakly consolidated MFT deposits, relieving pore pressures, further enhancing consolidation. The electrostrictive force can be applied in varying degrees to achieve the desired bearing capacity in desired zones of the MFT deposits or, to simply achieve a consolidation level sufficient to permit effective use of sand drains, wicks and the like to complete the consolidation process. Consolidation in active tailings ponds may still be desirable even if certified reclamation is not desired, because for instance, greater storage capacity can be achieved.

-6-Therefore, there is provided, according to the present invention, a method of compacting solids in situ in an oil sands extraction tailings pond, the method comprising the steps of:
a) Placing at least two electrodes into the tailings pond in a predetermined spacing;
b) Connecting the electrodes to a source of electrical power having a variable voltage, wherein an electrical field of sufficient strength is established between said at least two electrodes to induce flocculation of particles in said oil sands tailings and to simultaneously release water; and c) Compacting said flocculation solids and removing further water released from said compacting solids to create a load bearing material.
In a further embodiment of the present invention, the electrical field applied during the electro-kinetic treatment can be varied at different depths. For example, by applying the electrical field to the deepest depths of the MFT deposits causes the clay particles to flocculate there first. Afterwards, the conductive zone of the electrodes which creates the electric filed can be raised to higher elevations to encourage lithostatic consolidation at a different depth. Alternatively, for especially thick MFT
deposits, the operator may wish to induce flocculation in the deeper deposits of MFT, and then electrostrictively treat a shallow zone in an amount sufficient to achieve a 5 kPa bearing capacity. This area could then be re-covered with overburden to enhance the consolidation of the non-electrostriction treated depths through the use of sand drains or wicks or the like, while re-vegetation can occur on the replaced overburden.
In a still further aspect of the present invention the flocculation step and the subsequent consolidation step both involve the release of water from the thixotropic liquid. If this free water is removed from the tailings pond for further processing and clean-up, that frees up space in the pond

-7-for additional MFT to be added. As a result the present invention provides for a way to increase the capacity of the tailings pond to accept more MFT, by the separation and removal of water content from the MFT.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to preferred embodiments of the invention, by way of example only, with reference to the following figures in which:
Figure la is a graph depicting an estimation of pressure at depth for a sample tailings pond;
Figure lb is a graph depicting an estimate of lithostatic pressures resulting from an electrostriction treatment according to the present invention at various depths;
Figure 2 is a depiction of a graph showing a change in pressure with electrical field variance according to the present invention;
Figure 3 is a layout of electrodes in a three spot treatment pattern according to the present invention;
Figure 4 is a schematic of a further electrode layout with a neutral pumping well according to a further aspect of the present invention;
Figure 5 is a tubular electrode connection according to the present invention;
Figures 5a and 5b are enlarged views of a portion of Figure 5.
Figure 6 is an enlarged view of an alternate connection;
Figure 7 is a schematic of a drain of the type that can be used in the present invention;
Figure 8 is a schematic of a first embodiment of a combined cathode well structure;
Figure 9 is a schematic of a second embodiment of a combined cathode well structure; and Figure 10 is a schematic of a variable depth electrode according to

-8-a further aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In this specification the term MFT shall mean the tailings that exist in tailings ponds that arise from the extraction of hydrocarbons, such as bitumen, from tar or oil sands. As will be appreciated by those skilled in the art, the exact composition of MET will vary, depending upon the composition of the ore being mined due to local variations in such ore.
However, as used herein the term is intended to include compositions of material that include water, clays, silts, and residual hydrocarbons and hydrocarbon by products among other things.
The present invention comprehends the application of an electromagnetic field and most preferably an electrical field to the MFT.
According to one aspect such an electric field can be used to exert a force on the solids present in the MFT due to electrostriction. Electrostrictionb is a property of dielectric materials, and is caused by the presence of randomly-aligned electrical domains (e.g., clay platelets) within the material. When an electric field is applied to a dielectric material such as clay particles, the opposite sides of the domains become differently charged and attract each other, reducing material thickness in the direction of the applied field, and simultaneously increasing thickness in orthogonal directions due to Poisson's ratio'. The resulting strain (ratio of deformation to the original dimension) is proportional to the square of the polarization (i.e., the voltage gradient). Reversal of the electric field (e.g., b A phenomenon first reported by Reuss in 1807 to the Moscow Academy of Science When a material is compressed in one direction, it usually tends to expand in the other two directions perpendicular to the direction of compression. This phenomenon is called the "Poisson effect". Poisson's ratio v is a measure of the Poisson effect.

-9-under the application of alternating current) does not reverse the direction of the deformation. Therefore, the same phenomenon is observed under a magnetic field, DC or AC currents, and under electro-magnetically-induced current flow, again, either alternating or direct all of which are comprehended by the present invention.
The electric force density under an applied electrical field to induce electrostriction is governed by the square of the electrical gradient. From Brevik (1982)d, to determine the electric force density f', one can make use of the Helmholtz variational principle under reversible, isothermal conditions. From this, f" is defined as:

fer =- 2 ENV s+ 2 V IE2 T I
Where:
V refers to the vector in the direction of the application of the field p = mass density (kg-m-3);
= permittivity (s4 A2.m-2-kg-1);
E = electric gradient (volt-m-1); and the system is operating at constant temperature.
The second term in this equation is the electrostriction term.
According to the present invention the application of a preferred electrical field to create an electrostrictive force on the material first results in flocculation of the clay particles. This releases water that was otherwise bound to the clay particles to form the persistent gel or d Brevik, I. (1982). Fluids in electric and magnetic fields: Pressure variation and stability.
Canadian J. Physics, 60, pp 449-455.

-10-thixotropic MFT liquid. Once flocculation has occurred, the present invention provides for further water release and consolidation of the clay solids as explained in more detail below.
In one aspect of the present invention the further consolidation of the solids occurs through electrostriction. To determine the electric force required to achieve a given amount of consolidation, the change in permittivity relative to the change in mass density under a defined electric gradient (E, volt/m) is determined. Therefore, the present invention provides that it is possible to correlate changes in the permittivity and as a result density under an applied electrical field to track the progress of the electrostriction treatment of the MFT.
According Melloni, et al., (1998)e, the change in density under an applied electric field can be determined from:

z - 2 PCeo Where:
Ap = the change in density under the applied electrical field (kg-m-3) p = the density of clay (kg m-3) C = the compressibility of clay (%) ye = electrostriction coefficient (unit-less) E0 = dielectric constant (permittivity; s4-A2 m-2-kg-') for clay E = electric field (volts-m-1) Melloni, A., M. Frasca, A. Garavaglai, A. Tonini and M. Martinelli (1998).
Direct Measurement of Electrostriction in Optical Fibers. Optics Letters, Vol. 23, No. 9. p 691-693.

-11-The electrostriction coefficient used was 0.902 (Melloni, 1998).
One known dielectric constant for montmorillonite is 4.2 0.8 (Ishida, et al., 2000). The permittivity of water is 80.379. Therefore, for MFT which comprises 50% to 70% water content, the estimated permittivity for MFT
is expected to range between 43.1 and 58.7 S4 -A 2.M-2 -kg-1. IVIFT are reported to typically have between 50% and 70% water (by weight) but this is an estimated range only and the present invention can be applied to materials having either higher or lower water contents without departing from the scope of the invention. One value for the specific gravity of montmorillonite is about 2.35 g/cm3 (Webminerals.com; unknown water content) or 2,350 kg/m3. Commercial bentonite has between 5% and 8%
water by weight. The difference between soft and stiff clay can be less than 1 %. However, water content is not an accurate measure of stiffness. Solubles present in the clay, or variations in the electrolyte in the water supply can cause floccing or defloccing of clay. Typical malleable clays will have a water content of between 19.5 and 22.5%.
The desired water content for reclamation soils is in the order of 15% to 18%, based on natural water content (by weight) in clay soils.
Therefore, the desired density is between 2,107 to 2,148 kg/m3, with the flocced MFT density estimated to range between 2,046.25 to 2086.75 kg/m3. Therefore, Lp is 20.25 to 101.75 kg/m3.
The following relationship equates the applied electrical field to the electrostriction force in kPa:

4p - Y Ez p((6 - so ~o t Ishida, T., M. Tomoyuki, and C. Wang (2000) Dielectric-Relaxation Spectroscopy of Kaolinite, Montmorillonite, Allophane and Imogolite under Moist Conditions. Clays and Clay Minerals. Vol. 48, No. 1, 75-84.

g Weast, Robert, C. (ed; 1975). Handbook of Chemistry and Physics. 56th Edition, CRC Press, Cleveland, OH.

-12-Using the values from above, the electrostrictive force to achieve the desired reduction in moisture content and the associated degree of consolidation is estimated to be between 15.1 and 18.7 kPa. From the above relationship to achieve these forces, the applied electric field is estimated to range from 0.035 volt/m to 0.039 volt/m (within the linear range of the equations describing electrostriction). Moisture content is not always a reliable factor in clay stiffness, but provides a reasonable determination of the amount of compaction required.
The greater the applied electric field, the greater the applied force, the shorter the time period to achieve the desired degree of flocculation/compaction, or the greater the degree of compaction that can be achieved. It will be now understood by those skilled in the art that the present invention can be applied in various intensities, depending upon a balance of cost, timing and degree of compaction required. The design of the delivery system and equipment for the electrical energy can be based on the balance required between speed, cost and result required in the tailings pond being reclaimed. For example, the present invention provides that a step down transformer may be used to convert line voltages to distribute power to a network of electrodes fully penetrating the MFT to induce an electrical field resulting in a force within a predetermined appropriate range.
Turning now to the figures, Figure 1 a depicts in schematic form the pressure-depth relationship in a notional tailings pond filled with MFT. In Figure 1 a the x axis is pressure and the y axis is depth. The line 10 is hydrostatic pressure, the line 12 is the pressure at 70% water content MFT and line 14 is the pressure at 50% water content MFT. As can be seen all of the lines are straight meaning that the pressure varies linearly with depth (assuming water is a non-compressible fluid at a constant

-13-temperature and there is negligible densification of the MFT). Figure 1 b is a schematic of the pressure distribution with depth after an electro-kinetic treatment according to the present invention, where there is a 30%
reduction in MFT volume as a result of the electro-kinetic treatment of the present invention. In figure 1b, because the clay in the MFT has been flocced according to the present invention, the MFT is now denser and there has been a gravity-separation of the water from the flocked particles within the MFT. In Figure lb the line 16 is the hydrostatic pressure and the lines 18 and 20 represent the pressures at depth for reduced water content solids, such as solids having 15% water content in line 18 and 18% water content in line 20. These water contents are expressed as a percentage of the total weight.
As can now be appreciated the pressure profile of Figure 1 b results in greater lithostatic pressure with depth than is shown in 1a. Therefore the present invention provides a step-wise advance in consolidating the solids within the MFT, with these steps providing options as the treatment progresses. The invention involves a process and apparatus to create and apply an electrical (or magnetic) field with a voltage gradient that is maintained over a treatment period, and then providing for release of pore water to increase the density of the material (Figures la, and 1b) while the material consolidates.
In general there are two main aspects to the present invention.
The first part is to place the necessary equipment in position to deliver the desired electrical field to the MFT. This is explained in more detail below.
The second aspect is to identify what happens to the MFT once the electrical field is applied in a treatment process according to the present invention. The first result of the application of the electrical field according to the present treatment process is that the MFT will begin to flocculate and gravity separate. After this has occurred, the operator has the option to continue with electrostriction (described below) or allow the MFT to

-14-consolidate assisted by such techniques as sand drain, wick drains, etc.
This may be useful to the operator where the tailings pond is in operation and he wishes to increase capacity to accept additional tailings. This feature of drain-assisted consolidation further enhances and takes advantage of natural consolidation started by the application of an electrical field.
As noted above, after the flocculation step the further application of the electrical field allows for further application of an electrostriction force, which is converted to mechanical work. The relationship between the applied voltage gradient and the electromotive force is linear in the range between 0.003 to 0.04 volts/m and depicted in Figure 2. Figure 2 shows a schematic relationship between a change in the applied electrical field and the pressure. In this graph the change in pressure is plotted along the y axis and the change in electrical field is plotted on the x axis. As can be seen from the plot line 22, the greater the electrical field the greater the pressure. Of course there is a limit of how much electrical energy can be applied.
Generally, since the higher the voltage gradient, the greater the electromotive force, and as a result, the shorter the treatment time.
However, there are two negative factors in applying a higher gradient: 1) the current density around the electrodes increases, resulting in "dry-out"
and loss of electrical contact with the pore water carrying the current; and 2) the greater the gradient, the closer electrode spacing, and increased apparatus costs. The voltage gradients and number and spacing of electrodes need to be evaluated on a case-by-case basis to determine the most economical design compared against the timeframe for treatment.
Having described the action of the present invention on the MFT
the apparatus used to effect such action can now be described. The preferred embodiment of this invention involves the use of a variable voltage power supply connected to a network of electrodes. Where the

-15-power source is an AC source, the electrodes are arranged in a triangular (Figure 3) or hexagonal pattern (Figure 4). In figure 3 there are three electrodes denoted with the numbers 1, 2, or 3. These electrodes would be charged at 120 degrees out of phase with one another, with the phase charge varying with time. According to the present invention, the spacing between electrodes and the desire voltage gradient is determined through the conductivity of the pore water in the thixotropic liquid, the desired degree of consolidation and time to achieve, the volume and geometry of the treatment volume, and the capability of the power supply.
Figure 4 shows an embodiment of an apparatus for applying an electrical field to induce a voltage gradient across the area to be treated, or subsections of the area to be treated. There are six electrodes shown as El to E6 respectively in a regular hexagonal pattern. A source of AC
power 40, is shown and connected by electrical conductors 42, 44, 46, 48, 50 and 52 to each electrode in turn. As will be understood by those skilled in the art, each of the electrodes El through E6 will be charged at 60 degrees out of phase with the adjacent electrode, with the phased charging varying with time. This results in a maximum electrical field being generated across the long diagonals of the hexagon (e.g. El to E4), where the electrodes are 180 degrees out of phase (Note: Electrodes E2 to E5 are also 180 degrees out of phase, as are electrodes E3 to E6, and so on). The larger electrical field will have the effect of causing the greatest flocculation, at first, and then electrostriction, later, also across the longest diagonals. This phased charging is also charged sequentially with time to ensure even application of the electrical field. Thus the hexagonal pattern noted provides for a useful pattern for applying the desired electrical field across a substantial area for an AC power source 40.
The AC power source 40 will be provided with a power controller to permit the voltages being applied to be controlled. Most preferably it

-16-provides a six phase for the hexagonal geometry and a three phase time distributed and interphase synchronization power control for the three phase geometry. While the present description is with respect to an AC
power source, the present invention comprehends the use of a direct current, or electro-magnetically induced current using a variable voltage transformer as well. The voltages applied are to be determined based on the most economic use of electrodes (number and spacing) and the capabilities of the power supply, but the hexagonal pattern is believed to provide good results for illustration of an AC application where the volume of MFT to be treated has simple geometry approximating a cylinder. The desired voltage supplied by the transformer is dependent on the spacing of the electrodes, and the conductivity of the interstitial water in the MFT, which will vary during the treatment as electrophoresis causes the movement of ions in the pore water. Therefore, the present invention provides that the voltage applied may be adjusted throughout the treatment period to respond to changes in the electrical field resulting from changes in the electrical properties of the MFT as the treatment progresses. The present invention contemplates that the transformer will be kept in a safe locked housing and operatively connected to a portable computer with remote access communication features, such as for example through a cellular network communications grid. This combination permits remote monitoring and access to operate the system.
According to a further aspect of the present invention, the electrical field generating equipment will include the capability of monitoring the electrical conductivity of the pore water, both overall and throughout the treatment area. Overall, the electrical conductivity will be monitored through variations in current draw at the transformers. Throughout the treatment area, small diameter slotted CPVC tubing embedded in the MFT will allow for periodic conductivity measurements to track and optimize the application of the electrical field.

-17-Also shown is a neutral electrode 54 located at the center of the hexagonal spacing of the electrodes. According to one embodiment of the invention this electrode can also function as a water recovery device.
In this case a pump 56 is used to draw the water out of the hexagon, through a conduit 58. This water is the water that is freed from the gel by the flocculation step outlined above. The reclaimed water can then be optionally treated and recycled as desired using conventional processes.
According to the present invention, these electrodes El to E6 can be constructed using steel pipe, steel rods, sheet metal pile, electrically conductive plates suspended on electrical cable or any other electrically conductive or electro-magnetic material. The electrodes are placed in position by driving, drilling, using conventional drilling equipment, or pile driving equipment.
Figure 5 shows an electrode 58 according to one aspect of the present invention. The electrode includes an electrical connection wire 60 which connects to an electrode head connection 62. The electrode itself is in the form of hollow metal tube or pipe 64. Although the power supplied is very low and thus it might not be required, there is also shown an optional non-electrically conductive sleeve 66 to protect against accidental electrical shocks to people or the like. The sleeve 66 can be of any reasonable length but is preferred to provide enough freeboard above the level of the tailings pond that the electrodes do not become totally submerged in the pond. The electrode is most preferable driven into the MFT below the pond to ensure that it is stable during the treatment process with sufficient depth of penetration into the subsurface to be anchored in material below the 30 percent expected reduction in volume plus an appropriate factor of safety to maintain a stable installation. This installation depth is thought to provide adequate results in most cases. In figures 5a and 5b there is shown the details of the electrical head connection which can take the form of a welded flange 70 with a bolt hole

-18-72 for electrical connection. In these figures the flange 70 is welded to the side of the pipe 64 and the pipe 64 has closed capped top. In an alternate embodiment of Figure 6 the welded bolt connection 74 is placed centrally on a cap 76 which covers the open top of the pipe 64.
The present invention comprehends that it may be desirable to remove supernatant water and or water being electro-osmotically drawn towards the cathode in certain circumstances. In some cases it may be desirable to leave the water in place, above the flocculated solids, as a means to provide access to the treatment area by floating barge or the like, but in other cases, where it is desired to create more room in the pond for fresh tailings the water may be removed. In addition the present invention contemplates the use of a wick or drain to help remove additional pore water from consolidating solids within the pond. An example of such a drain 88 is depicted in Figure 7, in which the hollow skeleton 90 supports a water permeable mesh 92. Essentially this drain provides a leak path for pore water to be expressed through the consolidation process. A Mebradrain, as sold by Cofra, Kwadrantweg 9, 1042 AG Amsterdam, P.O. Box 20694, 1001 NR Amsterdam, The Netherlands, would produce adequate results.
In a further embodiment the present invention provides as shown in Figure 8 a dual purpose electrode and well. In this example, of a cathode, the cathode tubing 100 includes an upper section 102 and a lower section 104. The lower section is made water permeable, such as by being formed from a wire wound screen. A submersible pump 106 is located within the lower section 104 to pump the water collecting at the cathode out of the tubing 100 through a riser pipe 108. As noted the tubing 100 is provided with a centralizer 110 to keep the pump located within the middle of the tubing 100 and would electrically isolate the pump from the wall of the tubing 100. In figure 8a there is shown a top view of the cathode of figure 8 in which the top 112 is shown with the riser pipe 108, which is

-19-protected by an insulator 114. Figure 9 shows an alternate embodiment in which the wire screen has been replaced with a perforated pipe section 116.
The present invention also comprehends being able to selectively treat sections of the tailings pond as local requirements demand. In the first instance the tailings ponds tend to be vast in area and to facilitate the treatment the present invention contemplates creating smaller treatment areas by means of sheet piling or the like. This can be used to divide the area of the pond up into smaller areas or cells to facilitate treatment. The sheet pile can also be used as an electrode in some cases. The use of the sheet pile wall is used to hydraulically and hydrologically isolate the treatment cell from the rest of the pond to also allow the supernatant water to be removed to the extent desirable prior to or during treatment within the treatment cell.
In addition to dividing the pond into smaller areas for treatment through the use of cells, the present invention comprehends treating the pond at various depths to achieve certain desired results. Figure 10 shows a cable electrode 200 which includes an electric cable 202 connected to a source of power and at the free end is an electrode 204.
The electrode 204 can be an electrically conductive plate, bar, tube, or other electrically conductive element and can be made of any desired length depending upon the depth of the zone which is to be treated. Most preferable the cable electrode is inserted within a driven borehole 206 which when it collapses will provide good electrical contact with the electrode 204, which is further maintained as the pore water is released during treatment. As can now be appreciated the electrode 204 can be positioned at any depth within the tailings pond to permit the flocculation and/or electrostriction to occur at such depth.
As will be appreciated by those skilled in the art, it may be desirable to control the generation and/or release of methane during

-20-treatment. One method to do so is to add gypsum to the MFT being treated.
As will further be appreciated, the present invention provides a low voltage electrical field in the MFT. Higher voltage ranges may lead to heating up of the near electrode area, and the drying out of this area.
Heating and drying are not desirable according to the present invention, especially in light of the presence of residual hydrocarbons. Thus, the present invention comprehends using a voltage that is small enough, having regard to the properties of the MFT, to avoid such heating and drying out of the MFT. As well, the supernatant water is desirable as an additional safety factor. Most preferably the current is being applied to the MFT below the surface of any such supernatant water.
Although the foregoing description has been made with respect to preferred embodiments of the present invention it will be understood by those skilled in the art that many variations and alterations are possible without departing from the broad spirit of the claims attached. Some of these variations have been discussed above and others will be apparent to those skilled in the art.

Claims (28)

1. A method of compacting solids in situ in an oil sands extraction tailings pond, the method comprising the steps of:
a. Placing at least two electrodes into the tailings pond in a predetermined spacing;
b. Connecting the electrodes to a source of electrical power having a variable voltage to create at least one cathode and at least one anode, wherein an electrical field of sufficient strength is established between said at least two electrodes to induce flocculation of particles in said oil sands tailings and to simultaneously release water; and c. Compacting said flocculation solids and removing further water released from said compacting solids to create a compacted material having a minimum desired load bearing capacity.

2. The method of claim 1 wherein said compaction step includes using electrostriction to compact said flocculated solids.

3. The method of claim 1 or 2 wherein said compaction step includes using gravity loading to further compact said flocculated solids.

4. The method of claims 2 or 3 further including the step of inserting a drain or wick into said flocculated solids to permit pore water to be expressed from said compacting solids.

5. The method as claimed in claim 1 further including the step of removing water from said tailings pond as said solids are compacted.

6. The method as claimed in claim 5 wherein said water is pumped out of said tailings pond.

7. The method as claimed in claim 6 wherein said electrode includes an associated pump, electrically isolated from said electrode, to remove said water.

8. The method of claim 7 wherein the pump is located within a hollow cathode.

9. The method of claim 1 further including the step of partitioning said tailings pond to create at least one cell, and wherein said step of placing said at least two electrodes comprises placing said electrodes within said cell.

10. The method of claim 9 further including the step of partitioning said tailings pond into a plurality of cells.

11. The method of claim 10 wherein said cells are formed by sheet metal pilings.

12. The method of claim 11 wherein said sheet metal pilings are electrically connected to said source of power and thereby become one of said electrodes.

13. The method of claim 1 further including the step of sampling said tailings pond to determine one or more electrical properties, and using said measured electrical properties to control the output from the source of power.

14. The method of claim 1 further including the step of measuring the electrical properties of said tailings pond over time and adjusting said variable voltage across said electrodes in response to changes detected in said measured electrical properties.

15. The method of claim 13 wherein said electrical properties vary as said solids compaction process progresses, and said voltage is varied as said compaction progresses.

16. The method of claim 1 wherein said source of power is at least one transformer.

17. The method of claim 16 wherein said at least one transformer is operatively connected to a computer to permit the power from said transformer to be controlled.

18. The method of claim 17 wherein said controller includes a remote access controller.

19. The method of claim 1 wherein said predetermined load bearing capacity of said compacted solids is about 5kPa or more.

20. The method of claim 1 wherein the flocculation of the solids within the MFT is induced by one or more of an AC, DC or EM-induced electrical field.

21. The method of claim 1 wherein said electrical field gradient can have any range, but the preferred embodiment ranges from about 0.3 volt per centimeter to about 4 volt per centimeter.

22. The method of claim 12 wherein said electrical field gradient is a substantially uniform field between said electrodes.

23. An electrode for use in a method of compacting solids in an oil sands extraction tailings pond, the electrode comprising:
a. A connector to electrically connect said electrode to a source of power;
b. An electrically conductive body having a size and shape to permit said body to be inserted into said tailings pond and to extend below and above said tailings; and c. A means to electrically isolate a portion of said electrode which extends above said tailings pond.

24. The electrode of claim 23 wherein said body is hollow and includes openings to permit water to pass into said electrode.

25. The electrode of claim 24 wherein said openings are screened to prevent solids from passing into said hollow electrode.

26. The electrode of claim 25 further including a pump located with said electrode to remove said water from within said hollow body.

27. The electrode of claim 26 wherein said pump is electrically isolated from said electrode.

28. A method of treating a layer of a tailings pond comprising the steps of: providing a cable electrode which can be submerged to a desired depth; positioning the electrode within the tailings pond at the depth of the layer to be treated; positioning at least one other electrode at the same depth at a location remote from the first electrode; connecting the electrodes to a source of power and encouraging flocculation to occur at the depth that the electrodes are submerged within the tailings pond.