CA2897950A1 - Methods and systems for treating tailing pond water - Google Patents

Abstract

Methods and systems for treating tailing pond water produced during the mining and processing of bitumen oil. The treatment methods and systems can comprise two steps. The first step primarily removes suspended solid by using a system that uses flow momentum to induce a vortex. The second step primarily removes dissolved toxic metals, organics, and other toxins and carcinogens from water by using an electrocoagulation system. The treatment methods and systems can allow for re-use of the treated water in the mining process or for return of the treated water to the Athabasca River.

Description

METHODS AND SYSTEMS FOR TREATING TAILING POND WATER
FIELD OF THE DISCLOSURE
[0001] The present disclosure is related generally to treatment methods and systems for tailing pond water produced during the mining and processing of bitumen oil.
BACKGROUND INFORMATION

[0002] Bitumen mining, often referred to as the oil sands located in northern Alberta, Canada is an unconventional petroleum deposit. Oil sand is in the form of loose sand or partially consolidated sandstone. The sand is saturated with a viscous form of petroleum often referred to as bitumen. Natural bitumen deposits are found in large quantities in Canada and are also found in smaller deposits in other countries.

[0003] Bitumen mining utilizes and produces large amounts of fluids during the mining operations and during the years of production. Mining bitumen may require 1 to 3 barrels of water per barrel of bitumen produced. During the past 40 years of mining the bitumen, large lakes or "tailing ponds" have been created to hold the water and fine tailings produced during the extraction process.

[0004] The tailing ponds in Alberta, Canada encompass over 135 sq.
kilometers. The tailing ponds are earthen dams that average 35 feet in height.

Dissolved constituents from the mining process include clay, bitumen, water and chemicals used by the mining companies.

[0005] The majority of water used during the mining process is recycled back to the mining operations but up to 15% of the fluids are sent to the tailing ponds.
These ponds are managed by the consortium of about 10 oil companies that mine the bitumen.

[0006] It is a priority concern of local, provincial and federal government agencies that tens of millions of gallons of fresh water is removed each month from the Athabasca waterway and is permanently contaminated. The methods of storing the effluent water in the earthen dams or 'tailing ponds' is an environment risk in that over time the tailing ponds are leaching and leaking into the groundwater and making its way back into the river system. These temporary dams are not built to house the contaminated water year after year without consequences. The Alberta Government is now in the process of establishing mandates and protocols to lower the environmental risk from the tailing ponds. To date none of the oil companies have met goals set forth by the governmental entities in charg- of monitoring the ponds.

[0007] Due to the concerns over the shortage and cost of water available for oil sands mining as well as the environmental risk, the need to treat and recycle the contaminated water for re-use in the mining process or for discharge into the waterways is a high priority to oil sands mining. However, finding a water treatment process that is technically and economically viable for such purposes has proven challenging, partly because of the combination of suspended solids, bitumen, and chemicals in the water.

[0008] Water treatment processes of the prior art, including a variety of water treatment technologies such as flotation, filtration, evaporation, reverse osmosis, and combinations of these technologies have not proven to be effective to adequately treat the water to meet bioassay characteristics that will enable local fisheries to survive and flourish in treated water returned to the Athabasca River system.
SUMMARY OF THE DISCLOSURE

[0009] The present disclosure provides methods and systems for treating tailing pond water in bitumen mining process. The treatment method and system can comprise two steps, which each can include a plurality of sub-steps, or be combined with additional steps (before or after). The first step can primarily remove suspended solids, and the second step can primarily remove dissolved toxic metals, organics, and other toxins and carcinogens from water. The treatment methods and systems can allow for re-use of the treated water in the mining process or for return of the treated water to the Athabasca River.

[0010] The first-step treatment process is carried out by using a system that uses flow momentum to induce a vortex. The flow-induced vortex is able to produce a centrifugal acceleration up to thousands of gravitational constant (g = 9.8 m/s2) and separate the suspended solids from water by using the centrifugal force. The separated solids include clay, sand, and other particulate suspended in water.

[0011] The second-step treatment process can be carried out through an electrocoagulation (or electropulse) technology. The equipment that carries out the electrocoagulation process can contain metal plates energized by a DC
electrical current.

[0012] In some embodimenis, the electrocoagulation system can contain metal plates energized by a DC electrical current. As the contaminated water passes through the plates, charged ions are introduced into water from the plates, which neutralizes the charge on the surface of the oil and grease droplets and suspended solids. Oil and grease and suspended solids coagulate upon neutralization of the charges on their surfaces.

[0013] In some embodiments, as water passes through the plates, heavy metal ions dissolved in water may be reduced to an oxide and precipitate out of water, changing from a dissolved state to a suspended state.

[0014] In some embodiments, oxygen and hydrogen gas may form during electrocoagulation, causing the coagulated contaminants to rise to the surface of water.

[0015] In some embodiments, reactive oxygen species, broadly defined as oxygen-containing reactive chemical species, including singlet oxygen, superoxide anions, and hydroxyl radicals may be produced in the electrocoagulation step. The reactive oxygen species may oxidize the organic contaminates in water and convert them into less toxic or non-toxic species.

[0016] In some embodimen... of the present disclosure, an activated carbon filter may be used in addition to the abovementioned first- and second-step treatment processes to remove residual contaminants left from the previous two processes before water is discharged.

[0017] In another example embodiment of the present disclosure, the water treatment system is modularized. Both the vortex-induced suspended solids removal process and the electrocoagulation processes can be carried out by functional modules. The individual modules can be either (1) assembled and installed on-site near the tailing ponds, or (2) skid mounted in containers and deployed for operations in remote oil sands area.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a schematic illustration of two water treatment steps for some embodiments of the present disclosure;

[0019] FIG. 2 is a schematic illustration of the modified water treatment process shown in FIG. 1 for some embodiments of the present disclosure, with the sludge from the first-step treatment process and the second-step treatment process being processed through a dewatering unit and the water separated from the sludge being recycled to the influent.

[0020] FIG. 3 is a schematic illustration of the modified water treatment process with an optional step to process the effluent from the second-step treatment process with an activated carbon filter, for some embodiments of the present disclosure.

[0021] FIG. 4 is a schematic illustration of the liquid-solid separation system used in the first-step treatment process.

[0022] FIG. 5 is a representative simulation result of the flow pattern inside the liquid-solid separation chamber by computer software.

[0023] FIG. 6 is a schematic illustration of a configuration for the liquid-solid separation system that can be deployed in the first-step treatment process, where the effluent leaves the chamber from the top, for some embodiments of the present disclosure.

[0024] FIG. 7 is a schematic illustration of a configuration for the liquid-solid separation system that can be deployed in the first-step treatment process, where the separation system is placed horizontally.

[0025] FIG. 8 is an optical image of samples of untreated tailing pond water and treated water after the first-step treatment process.

[0026] FIG. 9 is an optical image of water sample treated by the first-step process, the second-step process, and an activated carbon filter.
DETAILED DESCRIPTION

[0027] As used herein in the specification and claims, including as used in the examples and unless otherwise expressly specified, all numbers may be read as if prefaced by the word "about", even if the term does not expressly appear, unless otherwise expressly stated. Also, any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0028] In the present description, where used or otherwise designated to apply as described above, the terms "about" and "consisting essentially of" mean 20%
of the indicated range, value, or structure, unless otherwise indicated. It should be understood that the terms "a" and "an" as used herein refer to "one or more"
of the enumerated components. The use of the alternative (e.g., "or") should be understood to mean either one, both, or any combination thereof of the alternatives, unless otherwise expressly indicated. As used herein, the terms "include" and "comprise" are used synonymously, and those terms, and variants thereof, are intended to be construed as non-limiting unless otherwise expressly stated.

[0029] In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the disclosure. However, upon reviewing this disclosure one skilled in the art will understand that the disclosure may be practiced without many of these details.

In other instances, well-known structures, systems and methods in the relevant fields have not been described in detail to avoid unnecessarily obscuring the descriptions of the embodiments of the disclosure.

[0030] Whenever the terms, "for example," "such as," or variants thereof are used herein, the provided examples are assumed to be without limitation or restriction, unless otherwise expressly indicated.

[0031] The present disclosui= relates to a water treatment process for treating contaminated water, including tailing pond water, generated from the oil sands in Alberta, Canada. The water to be treated typically contains fluids and solids and dissolved constituents from the oil sands.

[0032] Water treatment methods and systems for treating tailing pond water from the oil sands, according to the present disclosure, can reduce the levels of total suspended solids (also referred to herein as "TSS"), oil and grease (also referred to herein as "O&G"), chemical oxygen demand (also referred to herein as "COD"), biological oxygen demand (also referred to herein as "BOD"), total organic content (also referred to herein as "TOC"), dissolved toxic metals, and toxins and/or carcinogens from water. The treated water can be reclaimed for use in the bitumen mining process and/or returned to the Athabasca River system. In tests using the presently disclosed methods and systems as high as 99% suspended solids contained in tailing pond water were removed, and adequate removal of toxins and carcinogens harmful to aquatic and other wildlife species. It will be appreciated that in field use, the percentage of suspended solids successfully removed may not be as high.

[0033] Some embodiments of the present disclosure comprise two treatment steps, such as shown in Figure 1. The first step 100 primarily removes suspended solid by using a system that uses flow momentum to induce a vortex.
The flow-induced vortex is able to produce a centrifugal acceleration up to thousands of gravitational constant (g = 9.8 m/s2) and separate the suspended solids from water by using the centrifugal force. The separated solids include clay, sand, and other particulates suspended in water. The removed suspended solids are discharged from this process 100 in the form of sludge.

[0034] The effluent from the first-step treatment process is directed to the second-step treatment process 110 which can remove 086G, dissolved toxic metals, organics, and other toxins and carcinogens from water by an electrocoagulation technology. The second-step treatment process 110 separates the 086G, dissolved toxic metals, organics, and other toxins and carcinogens from water, which is discharged in the form of sludge.

[0035] In some embodiments, sludge from the first-step treatment process 100 and the second-step treatment process 110 will be processed through a dewatering unit, and the water separated from the sludge is recycled to the influent. The modified treatment process is illustrated in Figure 2.

[0036] In an example embodiment, the sludge from the first-step treatment process 100 is directed to a dewatering unit 200 and is separated into a liquid stream and a waste solid typically in the form of a cake. The liquid stream is recycled through a return line and mixed with the influent feed to the first-step treatment 100 unit. This dewatering unit can be chosen from various types of dewatering units including filter press, centrifuge, and electro-dewatering equipment.

[0037] In another example embodiment, the concentrate from the second-step treatment process 110 is directed to a dewatering unit 210 and separated into a liquid stream and a waste solid typically in the form of a cake. The liquid stream is recycled through a return line and mixed with the influent feed to the second-step treatment 110 unit. This dewatering unit can be chosen from various types of dewatering units including filter press, centrifuge, and electro-dewatering equipment.

[0038] Preferably, by recycling the water separated from the sludge to the influent of the treatment process in both treatment steps, the entire treatment system of the present disclosure is a zero liquid discharge system, meaning no waste is discharged in a liquid form. In tests of the technology up to 99% of water was able to be recycled and reused. The amount of water able to recycled will, of course, vary depending upon a number of factors.

[0039] In some embodiments of the present disclosure, an activated carbon filter 300 may optionally be used after the second-step treatment process to remove residual contaminants left from the previous two processes before water is discharged, as schematically shown in Figure 3.

[0040] The first-step treatment process 100 primarily removes suspended solids by using a liquid-solid separation system that uses flow momentum to induce a vortex. Figure 4 presents the design of the system 400. It comprises the following parts: an inlet 410, a stator 420, a separation chamber 430, a tube 440 placed at the center of the storage tank that directs the liquid to the outlet 450, a solid storage tank 460 for temporary storage of the sludge and the solid, and an sludge outlet 470. The stator is a ring that has grooves and/or textures on the inside surface designed to convert the axial momentum of the flow into radial momentum arl generate a vortex when the fluid flows through the stator. The flow-induced vortex is able to produce a centrifugal acceleration up to thousands of gravitational constant (g = 9.8 m/s2), depending on the flow velocity and the radius of the separation chamber. The centrifugal force separates the suspended solid particles from the fluid based on the density difference between the particles and the liquid. The liquid is pulled out of the separation chamber from the center by a tube 440, and the solid, once separated from the liquid, is directed to the temporary solid storage tank 460 and eventually removed from the sludge outlet 470.

[0041] Design of the liquid-solid separation system 400 typically involves simulation of the flow pattern inside the separation chamber by computer software based on the knowledge of the flow velocity of the fluid or the flow rate, the solid particle density, the liquid density, and the solid particle size and size distribution. The simulation can be conducted by those skilled in the relevant art by using finite element analysis and/or computational fluid dynamic simulations. Figure 5 shows the result of one such simulation where flow patterns of the fluid can be visualized after the fluid passes through the stator 420 that converts the axial flow momentum to radial momentum.

[0042] Compared to prior art of liquid-solid separators, including gravity-based settling tank or baffled bank, membrane-based filtration, air flotation, dissolved air flotation, and chemical-based flocculation and coagulation, the liquid-solid separator described in the present disclosure has the following advantages: it has no moving parts; it does not consume energy or chemicals or filtration membrane or media; it takes small footprint and is easy to maintain and operate.

[0043] It is worth noting that the liquid-solid separator described in the present disclosure is different from prior art in making liquid-solid separators that also use flow-induced vortex to separate solid from liquid, such as a hydro-cyclone. The prior art introduces the fluid to the separation chamber in a tangential direction, whereas the present disclosure introduces the fluid to the separation chamber in the axial direction. Compared to the prior art, the present disclosure is able to achieve higher separation efficiency with less pressure drop occurred inside the chamber.

[0044] The liquid-solid separator described in the present disclosure may also be constructed and deployed in different configurations. For example, in Figure 6, the liquid effluent leaves the chamber from the top, and in Figure 7, the separator is placed horizontally.

[0045] The effluent of the first-step treatment process 100 is directed to the second-step treatment process 110, where an electrocoagulation (or electropulse) technology is used to remove 086G, dissolved toxic metals, organics, and other toxins and carcinogens from water. Depending on the pH of the effluent of the first-step treatment process, the pH of the water may be adjusted by an acid or a base. An example base for adjusting pH is sodium hydroxide. An example acid for adjusting pH is hydrogen chloride. This pH
adjustment step is optional and when the pH of the feed water is satisfactory, the water can be directed into the electrocoagulation system 110 without being subjected to the pH adjustment process.

[0046] In some embodiments, the electrocoagulation system can contain metal plates energized by a DC electrical current. As the contaminated water passes through the plates, charged ions are introduced into water from the plates, which neutralizes the charge on the surface of the oil and grease droplets and suspended solids. The charge neutralization causes these contaminants to coagulate, as will be appreciated by those skilled in the art after reviewing this disclosure. Oil and grease and suspended solids coagulate upon neutralization of the charges on their surfaces. Electrocoagulation systems such as these are commercially available and will, therefore, not be further described.

[0047] In some embodiments, as water passes through the plates, heavy metal ions dissolved in water may be reduced to an oxide and precipitate out of water, changing from a dissolved state to a suspended state.

[0048] In some embodiments, oxygen and hydrogen gas may form during electrocoagulation, causing the coagulated contaminants to rise to the surface of water.

[0049] In some embodiments, as the DC electrical current passes through water in the electrocoagulation system, reactive oxygen species (ROS) broadly defined as oxygen-containing reactive chemical species, including singlet oxygen, superoxide anions, and hydroxyl radicals may be produced. The reactive oxygen species may oxidize the organic contaminates in water and convert them into less toxic or non-toxic species.

[0050] In another example embodiment of the present disclosure, the water treatment system is modularized. Both the vortex-induced suspended solids removal process and the electrocoagulation processes can be carried out by functional modules. The individual modules can be either (1) assembled and installed on-site near the tailing ponds, or (2) skid mounted in containers and deployed for operations in remote oil sands area.
WORKING EXAMPLE

[0051] The following example is intended to be illustrative and should not be construed as limiting the disclosure in any way.

[0052] This example uses a water treatment system constructed following the schemes shown in Figure 3 to treat contaminated tailing pond water obtained from Alberta, Canada.

[0053] The contaminated taiiing pond water was first treated by a liquid-solid separator constructed according to Figure 6. The liquid-solid separator was operated at a flowrate of 50 gallon per minute and the pressure drop between the inlet and the outlet of the operator was 60 psi. Optical images of the untreated tailing pond water and the water after the first-step treatment were shown in Figure 8.

[0054] The effluent from the first-step treatment process was fed into an electrocoagulation system, followed by treatment with activated carbon. An optical image of the treated water after the entire treatment process was shown in Figure 9.

[0055] Representative characteristics of tailing pond water before the treatment are presented in Table 1. Representative characteristics of the water after the treatment process are presented in Table 2.

Table 1. Characteristics of contaminated tailing pond water before treatment.
Water Quality Parameters Unit Value pH 7.10 Ammonia ppm <2500 Specific Conductance 1.1S/cm 2300 Oxygen Reduction Potential V +63.7 Dissolved Oxygen mg/I 10.0 Table 2. Characteristics of treated water.
Water Quality Parameters Unit Value pH 8.18 Ammonia ppm 6.0 Specific Conductance i.IS/cnn 2300 Oxygen Reduction Potential V +85.0 Dissolved Oxygen mg/I 5.81

[0056] Two parallel tests were conducted to test the survival rate of trout in treated water. 10 rainbow trout less than 2" in length were raised in treated and untreated water simultaneously. Fish were fed once per day using crushed Cichlid granules. In the untreated water, 10 fatalities were recorded within initial 2 hour test period. In the treated water, initial test was conducted for 96 hours.
No loss was observed during the 96 hour process. Test was continued for an additional 48 hours. All fish were still alive after 6 days (144 hours). Upon completion of test, fish were released into a local trout lake.

[0057] Although specific embodiments and examples of the disclosure have been described supra for illustrative purposes, various equivalent modifications can be made without departing from its spirit and scope, as will be recognized by those skilled in the relevant art after reviewing the present disclosure.
The various embodiments described can be combined to provide further embodiments. The described systems, devices and methods can omit some elements or acts, can add other elements or acts, or can combine the elements or execute the acts in a different order than that illustrated, to achieve various advantages of the invention. These and other changes can be made to the invention in light of the above detailed description.

[0058] In general, in the following claims, the terms used should not be construed to limit the disclosure to the specific embodiments disclosed in the specification.

Claims (5)

What is claimed is:

1. A method for treating tailing pond water in a bitumen oil mining process, comprising:
removing suspended solids from the pond water by using flow momentum to induce a vortex; and removing dissolved toxic metals, organics, and other toxins and carcinogens from the pond water by using an electrocoagulation process in which charged ions are introduced into the pond water to neutralize a charge on a surface of oil droplets and suspended solids, such that the oil droplets and suspended solids coagulate.

2. The method of Claim 1, wherein suspended solids are removed in a vortex induced suspended solids removal module comprising a vessel defining a separation chamber, the vessel having an inlet, an outlet and a stator ring positioned in the an axial flow path that pond water must follow through the separation chamber from the inlet to the outlet, the stator ring having an internal profile that converts axial momentum of flow through the separation chamber into radial momentum and generates a vortex, whereby suspended solids are removed by centrifugal force.

3. The method of Claim 1, wherein the dissolved toxic metals, organics and other toxins and carcinogens are removed in an electrocoagulation processing module, comprising a vessel having metal plates energized by a DC electrical current, such that as contaminated pond water passes through the plates, charged ions are introduced into the pond water from the plates.

4. A system for treating tailing pond water in a bitumen oil mining process, comprising:

a vortex induced suspended solids removal module comprising a vessel defining a separation chamber, the vessel having an inlet, an outlet and a stator ring positioned in the an axial flow path that pond water must follow through the separation chamber from the inlet to the outlet, the stator ring having an internal profile that converts axial momentum of flow through the separation chamber into radial momentum and generates a vortex, whereby suspended solids are removed by centrifugal force; and an electrocoagulation processing module, comprising a vessel having metal plates energized by a DC electrical current, such that as contaminated pond water passes through the plates, charged ions are introduced into the pond water from the plates.

5. A vortex separator, comprising:
a vessel defining a separation chamber, the vessel having an inlet, an outlet and a stator ring positioned in the an axial flow path that pond water must follow through the separation chamber from the inlet to the outlet, the stator ring having an internal profile that converts axial momentum of flow through the separation chamber into radial momentum and generates a vortex, whereby suspended solids are removed by centrifugal force.