CAUSTIC DOSING FOR PRIMARY EXTRACTION IN OIL SANDS PROCESSING

Abstract

Described herein are methods and systems in which the alkaline dosage used for oil sands slurries fed into a primary separation vessel (PSV) is controlled based on a combination of clay content and process water characteristics. The dosage control can include operating within different dosage envelopes that correspond to respective combinations of clay content and dissolved solids content. Enhanced bitumen separation by the PSV and usage of alkaline compounds, such as caustic, can be facilitated by such methods.

Claims

1. A process for producing a bitumen product from oil sands, the process comprising: supplying an oil sands slurry comprising the oil sands and process water to a primary separation vessel (PSV) configured to produce a bitumen froth stream, a middlings stream, and a tailings stream; controlling a dosage of an alkaline compound for addition to the oil sands slurry, comprising: determining a clay content of the oil sands slurry; determining a dissolved solids content of the process water; and determining the dosage of the alkaline compound based on the clay content and on the dissolved solids content to achieve a target recovery level of bitumen in the bitumen froth; separating the oil sands slurry in the PSV to form the bitumen froth stream having the target recovery level; subjecting the bitumen froth stream to froth treatment to produce solvent diluted bitumen and solvent extraction tailings; and recovering solvent from the solvent diluted bitumen to produce the bitumen product.

2. The process of claim 1, wherein dosing the alkaline compound comprises: determining operating envelopes based on the clay content and the dissolved solids content; and determining the dosage of the alkaline compound for addition to the oil sands slurry according to one of the operating envelopes to achieve the target recovery level of bitumen; and adding the alkaline compound to the oil sands slurry based on the determined dosage.

3. The process of claim 2, wherein the dosage of the alkaline compound is within a low dosage interval, an intermediate dosage interval, or a high dosage interval, and each one of the low dosage interval, the intermediate dosage interval, and the high dosage interval corresponds to at least one of the operating envelopes.

4. The process of claim 3, wherein: when at least one of the clay content and the dissolved solids content is below a lower predetermined clay content threshold and a lower predetermined dissolved solids content threshold, respectively, the dosage of the alkaline compound added to the oil sands slurry is zero; and when the clay content is above the lower predetermined clay content threshold and the dissolved solids content is above the lower predetermined dissolved solids content threshold, the dosage of the alkaline compound added to the oil sands slurry is within one of the low dosage interval, the intermediate dosage interval, and the high dosage interval.

5. The process of claim 4, wherein when both the clay content and the dissolved solids content are below the lower predetermined clay content threshold and the lower predetermined dissolved solids content threshold, respectively, the dosage of the alkaline compound added to the oil sands slurry is zero.

6. The process of claim 4, wherein when: the clay content is within a first clay content range below the lower predetermined clay content threshold; or the clay content is within a second clay content range and the dissolved solids content is within a first dissolved solids content range below the lower predetermined dissolved solids content threshold; or the clay content is within a third clay content range and the dissolved solids content is within the first dissolved solids content range below the lower predetermined dissolved solids content threshold; the dosage of the alkaline compound is zero.

7. The process of claim 6, wherein when: the clay content is within the second clay content range and the dissolved solids content is within a second dissolved solids content range; or the clay content is within the second clay content range and the dissolved solids content is within a third dissolved solids content range; or the clay content is within the third clay content range and the dissolved solids content is within the second dissolved solids content range; or the clay content is within a fourth clay content range and the dissolved solids content is within the first dissolved solids content range below the lower predetermined dissolved solids content threshold; the dosage of the alkaline compound is above zero and within a low dosage interval.

8. The process of claim 7, wherein when: the clay content is within the second clay content range and the dissolved solids content is within a fourth dissolved solids content range above a higher predetermined dissolved solids content threshold; or the clay content is within the third clay content range and the dissolved solids content is within the third dissolved solids content range; or the clay content is within the fourth clay content range and the dissolved solids content is within the second dissolved solids content range; the dosage of the alkaline compound is above zero and within an intermediate dosage interval.

9. The process of claim 8, wherein when: the clay content is within the third clay content range and the dissolved solids content is within the fourth dissolved solids content range above the higher predetermined dissolved solids content threshold; or the clay content is within the fourth clay content range and the dissolved solids content is within the third dissolved solids content range; or the clay content is within a fifth clay content range above a higher predetermined clay content threshold and the dissolved solids content is within the first dissolved solids content range below the lower predetermined dissolved solids content threshold; the dosage of the alkaline compound is above zero and within a high dosage interval.

10. The process of claim 9, wherein when: the clay content is within the fourth clay content range and the dissolved solids content is within the fourth dissolved solids content range above the higher predetermined dissolved solids content threshold; the dosage of the alkaline compound is above the high dosage interval.

11. A process for producing a bitumen product from oil sands, the process comprising: mining oil sands ore to obtain mined oil sands ore; crushing the mined oil sands ore in a mixing unit to form crushed ore; subjecting the crushed ore to sizing and addition of process water to form an oil sands slurry; supplying the oil sands slurry to a primary separation vessel (PSV); dosing an alkaline compound for addition into the oil sands slurry based on: determining a clay content of the oil sands slurry; determining a dissolved solids content of the process water; adding a dosage of the alkaline compound based on the clay content and the dissolved salt content, wherein: the dosage of the alkaline compound is determined based on the clay content and the dissolved solids content; and the dosage of the alkaline compound is performed based on alkaline dosage intervals corresponding to respective determined combinations of clay content ranges and dissolved solids content ranges; and separating the oil sands slurry in the PSV to form a bitumen froth stream; subjecting the bitumen froth stream to froth treatment to produce solvent diluted bitumen and solvent extraction tailings; and recovering solvent from the solvent diluted bitumen to produce the bitumen product.

12. The process of claim 11, wherein during a start-up phase of the process, the process water comprises fresh water and the dissolved solids content is below a lower predetermined dissolved solids content threshold.

13. The process of claim 12, wherein after the start-up phase, the process water comprises recycled process water and the dissolved solids content increases over time such that during a second operating phase of the process, the dissolved solids content exceeds the lower predetermined dissolved solids content threshold.

14. The process of claim 13, wherein the recycled process water is recycled from a tailings pond.

15. The process of claim 13, wherein determining the dissolved solids content of the process water comprises determining the dissolved solids content of the recycled process water.

16. The process of claim 13, wherein during the second operating phase of the process, the process water comprises exclusively recycled process water, and the dissolved solids content of the process water is above the predetermined dissolved solids content threshold.

17. The process of claim 11, further comprising: transmitting information related to at least one of the clay content and the dissolved solids content to an analyzer operatively connected to at least one controller; and automatically dosing the alkaline compound for addition in the oil sands slurry through the at least one controller in response to the at least one of the clay content and the dissolved solids content.

18. The process of claim 11, further comprising determining a water content of the oil sands slurry.

19. The process of claim 11, further comprising supplying dilution water to the oil sands slurry upstream of the PSV.

20. The process of claim 11, wherein the oil sands slurry is a diluted oil sands slurry, the clay content is measured on the diluted oil sands slurry, and the alkaline compound is added to at least one of the diluted oil sands slurry and the PSV.

21. The process of claim 11, wherein determining the clay content comprises obtaining a clay content indicator.

22. The process of claim 11, wherein determining the clay content of the mined ore, the crushed ore, and/or the oil sands slurry is conducted in-line.

23. A process for producing a bitumen product from oil sands, comprising: mixing oil sands ore with process water to produce an oil sands slurry; supplying the oil sands slurry to a primary separation vessel (PSV); determining a clay content of the oil sands slurry and a dissolved solids content of the process water of the slurry; adding an alkaline compound to the oil sands slurry according to an alkaline dosage, wherein: during a start-up phase, the dissolved solids content is below a lower dissolved solids content threshold and the alkaline dosage is maintained at zero; during a second operating phase, the dissolved solids content is above the lower dissolved solids content threshold and the alkaline dosage is increased above zero when the clay content is above a lower clay content threshold; separating the oil sands slurry in the PSV to produce a bitumen froth stream, a middlings stream and a tailings stream; subjecting the bitumen froth stream to froth treatment to produce solvent diluted bitumen and solvent extraction tailings; and recovering solvent from the solvent diluted bitumen to produce the bitumen product.

24. The process of claim 23, wherein the lower clay content threshold is about 0.8 mg/100 g.

25. The process of claim 23, wherein the lower dissolved solids content threshold is about 1250 mg/L.

26. The process of any claim 23, wherein measuring the clay content comprises using a methylene blue index (MBI) technique, an NIR technique or a K40 technique.

27. The process of claim 23, wherein the predetermined dissolved solids content threshold is a predetermined total dissolved salts threshold.

28. The process of claim 23, wherein during the start-up phase, the process water comprises fresh water.

29. The method of claim 23, wherein after the start-up phase, the process water comprises recycled process water and the dissolved solids content increases over time such that at the second operating phase the dissolved solids content exceeds the lower predetermined dissolved salt content threshold.

30. The method of claim 29, wherein the recycled process water is recycled from a tailings pond.

Description

DESCRIPTION OF THE DRAWINGS

[0113] FIG. 1 is a process flow diagram showing processing of a mined oil sands ore to produce a bitumen product, including a primary separation operation.

[0114] FIG. 2 is a process flow diagram showing processing of a mined oil sands ore to produce a bitumen product, including a primary separation operation, and showing various locations of clay content and water chemistry assessment and locations of caustic addition.

[0115] FIG. 3 is a portion of the process flow diagram shown in FIG. 2, showing control points of an automated process for dosing caustic addition for the primary separation operation.

[0116] FIG. 4 is a process flow diagram showing processing of a mined oil sands ore to produce a bitumen product, including a primary separation operation, wherein addition of process water is performed upstream of clay content and water chemistry assessment and caustic addition.

[0117] FIG. 5a is a graph illustrating the relationship between salinity of process water and total bitumen recovery, for various oil sands having a respective clay content.

[0118] FIG. 5b is a graph illustrating the relationship between salinity of process water and total bitumen recovery, for other various oil sands having a respective clay content.

[0119] FIG. 6 is a graph illustrating the relationship between salinity of process water and total froth quality, for various oil sands having a respective clay content.

[0120] FIG. 7 is a graph illustrating the relationship between salinity of process water and total bitumen recovery, for various oil sands having a respective clay content.

[0121] FIG. 8 is a graph illustrating the relationship between salinity of process water and total froth quality, for various oil sands having a respective clay content.

[0122] FIG. 9 is a graph illustrating the relationship between salinity of process water and total bitumen recovery, for various oil sands having a respective clay content, and when caustic soda is added.

[0123] FIG. 10 is a graph illustrating the relationship between salinity of process water and total froth quality, for various oil sands having a respective clay content, and when caustic soda is added.

DETAILED DESCRIPTION

[0124] Techniques described herein relate to methods for dosing the addition of an alkaline compound, such as caustic, in the context of primary extraction processes of oil sands ore obtained from surface mining. Enhancements described herein include the dosing of caustic in the context of hot water extraction in a primary separation vessel (PSV) that receives an oil sands slurry for separation into bitumen froth, middlings and tailings. Dosing of the caustic for addition at one or more locations of the primary extraction process can be based on certain parameters, such as the clay content, the clay-to-water ratio (CWR), and the process water chemistry of the oil sands slurry. These caustic dosing techniques can contribute to enhanced bitumen recovery, bitumen froth quality, and efficient operation of the primary separation.

[0125] The methods can include determining the clay content of the oil sands slurry and the dissolved solids content of the process water used to form the oil sands slurry, and then dosing the alkaline compound, such as caustic, based on different predetermined operating envelopes of the clay and dissolved solids contents. The caustic dosage process can be automated such that measurements regarding clay and dissolved solids content are automatically obtained and used to control the concentration or flow rate of the alkaline compound stream added to the oil sands slurry or to the PSV.

Overview of Ore Preparation and Primary Extraction of Bitumen

[0126] With reference to FIG. 1, a general example process for bitumen production through surface mining will be described. In a bitumen extraction operation, oil sands ore 10 is mined and crushed in a crushing unit 12 to obtain a crushed ore 13. The crushed ore 13 is then mixed with process water 14 (e.g., warm or hot water) in a mixing unit 16 to remove oversized clumps and form an aerated aqueous oil sands slurry 18. The mixing unit 16 can be for instance a rotary breaker that breaks up lumps of oil sands into smaller sized particles. The process water 14 and the sized oil sands material form the aqueous oil sands slurry 18, which can generally include between 5 wt % and 15 wt % bitumen, about 80 wt % solids, and between about 5 wt % and 15 wt % water.

[0127] The aqueous slurry 18 can then be shear conditioned to prepare the slurry for extraction of the bitumen from the solid minerals and water. The conditioning of the aqueous slurry 18 is typically performed through hydrotransport via a pipeline, which facilitates increased mixing, aeration and breakdown of lumps of oil sands ore in preparation for bitumen separation.

[0128] The aqueous slurry 18, which can optionally be further diluted with process water 14, is transported to a primary separation vessel (PSV) 20, which can also be referred to as a primary separation cell, sep cell, or gravity separation cell. The PSV typically uses flotation and gravity mechanisms to separate bitumen from coarse sand and other solid particles. In the primary separation process, bitumen in the aqueous slurry 18 detaches from solid particles and attaches to air bubbles that are injected into the PSV 20, thereby allowing bitumen droplets to rise and float to the top of the PSV 20, forming the primary bitumen froth 22 that is recovered typically as an overflow stream. Coarse particles contained in the aqueous slurry 18 are relatively heavy and tend to sink to the bottom of the PSV 20. The portion of the aqueous slurry 18 that is not heavy enough to sink to the bottom of the PSV 20 but not light enough to float tends to remain in the middle of the PSV 20, and can be referred to as middlings 26. The aqueous slurry 18 is thus separated into three streams withdrawn from the PSV: a primary tailings underflow stream 24 (also referred to as coarse tailings), a middlings stream 26, and a bitumen froth overflow stream 22.

[0129] In some implementations, the middlings 26 can be sent to a secondary separation vessel 28 to be separated into secondary bitumen froth 30 and secondary tailings 32 (which can also be referred to as a fine tailings stream herein as they contain higher fines content compared to the coarse tailings). As shown in FIG. 1, the secondary bitumen froth 30 can be fed back to the primary separation vessel 20. Alternatively, the secondary bitumen froth 30 can be added directly to the primary bitumen froth 22. It is also noted that there may be additional separation vessels downstream of the secondary separation vessel 28, which further enable separation of residual bitumen from the water and mineral solids.

[0130] Still referring to FIG. 1, bitumen froth 22 typically includes about 60 wt % bitumen, about 30 wt % water, and about 10 wt % solid materials although these percentages can vary depending on various factors. The solid materials in the bitumen froth 22 typically include hydrophilic mineral materials and heavy minerals which can include adsorbed insoluble organic material.

[0131] The primary tailings 24 and secondary tailings 32 generally include between about 45 wt % and about 55 wt % solid materials, between about 45 wt % and about 55 wt % water, and residual bitumen (typically between about 1 wt % and about 3 wt % bitumen). The solid materials in the primary and secondary tailings 24, 32 are mainly sand and other fine hydrophilic mineral materials. The primary tailings 24 and secondary tailings 32 can then be disposed of in a tailings pond 50 or further treated to extract bitumen.

[0132] The bitumen froth 22 is treated in a froth treatment process 34 in which the bitumen froth 22 is diluted with a diluent or solvent 36 to obtain a diluted bitumen froth. Froth treatment can also be referred to as secondary extraction which is performed after the froth is produced by primary extraction. The diluent 36 can be either a naphthenic type diluent or a paraffinic type diluent. The naphthenic type diluent can for example include toluene, naphtha or other light aromatic compounds. The paraffinic type diluent can for example include C4 to C8 aliphatic compounds and/or certain natural gas condensates. When a paraffinic compound is used, it can be referred to as a solvent rather than a diluent, and when used under certain conditions the paraffinic solvent induces precipitation of asphaltene aggregates that contain asphaltenes, water and fine mineral solids. The diluted bitumen froth is then separated into a bitumen product 38 (which can be further upgraded, if desired) and froth treatment tailings 40 including solid materials (hydrophilic mineral materials, heavy minerals and insoluble organic materials), water, residual diluent and residual bitumen.

[0133] Still referring to FIG. 1, in some implementations, froth treatment tailings 40 are treated in an oil sands tailings treatment process 42 in order to separate the froth treatment tailings 40 into various recovered materials 44 such as diluent and/or bitumen, and an aqueous stream 46 including process water, heavy minerals, and/or hydrophilic mineral materials. The aqueous stream 46 including process water and hydrophilic mineral materials can be disposed of in the tailings pond 50 for decantation. In the process shown, the coarse tailings stream 24 and the fine tailings stream 32 are added to the aqueous stream 46 for disposal in the tailings pond 50, but it is understood that alternatively, the coarse tailings stream 24 and/or the fine tailings stream 32 can be treated in the oil sands tailings treatment process 42.

[0134] Optionally, an overlying water phase can be pumped out of the tailings pond 50 and reused as recycled process water 52 in the mixing unit 16 to obtain the aqueous slurry 18, as well as in various other applications within the oil sands processing facility.

[0135] One or more alkaline agents, such as caustic soda (NaOH), sodium silicate, sodium bicarbonate, sodium phosphate and the like, can be added directly to the aqueous slurry 18 to chemically condition and prepare the aqueous slurry 18 for bitumen extraction and separation. Alkaline agent(s) can be added to the process water 14, to the mixing unit 16, to the aqueous slurry before, during or after hydrotransport, and/or can be added directly into the PSV 20. Features and implementations of caustic addition and dosing will be described in further detail below.

Clay Content of Oil Sands Slurry and Interactions of Clays with Bitumen

[0136] As mentioned above, the aqueous slurry 18 includes bitumen and solid particles including coarse sand and finer mineral material. Particles having a diameter larger than 44 microns are considered coarse particles, and particles having a diameter smaller than 44 microns are considered fines. Very small particulate material in the range of 2 to 4 microns and having active surface areas can be referred to as clays. Low grade ores typically have a higher clay content and can be difficult to process since clays can impair the separation process, which can result in a significant amount of bitumen being lost to the middlings and the tailings streams.

[0137] Clays can be defined in terms of their composition, activity and/or size. Clays are phyllosilicate mineral solids that have a size below 2 or 4 microns, and that have active surfaces that can interfere with the separation process of bitumen from the bitumen slurry. Due to their activity and small size, when clays are present in high concentrations in a bitumen slurry, their impact tends to dominate over other mineral solid particles, such as larger fines and coarse sand. Clays found in oil sands are mostly composed of kaolinite and illite, although oil sands can also contain fractional amounts of chlorite, smectite, feldspar and montmorillonite.

[0138] The surface chemistry of clays contributes to how they interact with bitumen. Generally, clays have surfaces that are negatively charged and edges that are positively charged. Bitumen is negatively charged, enabling attachment of bitumen to air bubbles to form a bitumen-rich froth. However, the positive charges of the clays can also attract the negative charges of the bitumen, thereby neutralizing the charge of the bitumen and resulting in loss of hydrophobicity of bitumen. Air bubbles are thus prevented from selectively attaching to bitumen droplets, impairing the floatability of bitumen and separation of bitumen from the fines, which can result in bitumen losses to the middlings and tailings streams and thus a reduced bitumen recovery. Recovery of the bitumen from the middlings can still be performed in highly aerated flotation cell, however rendering the bitumen extraction longer and more expensive.

Addition of Caustic During Separation Processes

[0139] Addition of an alkaline agent, such as caustic soda (NaOH), to a bitumen slurry can contribute to enhancing bitumen recovery and improving the quality of the bitumen-rich froth 22 during the primary extraction stage in the PSV 20. Increasing the pH of the bitumen slurry 18 is thought to charge clays negatively such that the clays tend to repel each other and that attachment of bitumen droplets to clays is prevented, which can contribute to avoiding their agglomeration and facilitate dispersion and flotation of bitumen for the separation process.

[0140] Providing a proper dosage of caustic soda by taking into consideration characteristics of the aqueous slurry can contribute to improve bitumen recovery and bitumen froth quality. The dosage of caustic soda can take into account at least two variables, namely an amount that is sufficiently high to lead to repulsion of the clays, and an amount that is sufficiently low such that dissolved salts contained of the aqueous slurry, especially positively charged cations such as Na.sup.+ and Mg.sup.2+, do not lead to gelling, or sludging, of the fines and clays together. In addition, ion exchange, for instance between Na.sup.+ and Ca.sup.2+, can form calcium naphthenates with the naturally occurring naphthenic acids in the oil sands, which can be detrimental to bitumen froth quality. Too much caustic soda can also lead to additional Ca.sup.2+ in the bitumen froth and can be problematic with catalysts used in the refinery plant, and can cause emulsification of bitumen and smaller bitumen droplets, which can impair bitumen recovery.

Correlation of Caustic Dosage with Clay-Related Variables

[0141] It has been found that the dosage of caustic correlates with variables such as clay content of the oil sands ore and water chemistry of process water. As mentioned above, clay content is different from fines content, since clays are a subset of fines and have certain mineralogical and chemical properties.

[0142] The clay content of the oil sands ore and the water chemistry of process water can be measured at one or more locations in the separation process, and the dosage of caustic can be controlled accordingly. For instance, in some implementations, clay content can be evaluated upstream of the mixing unit 16 to obtain a clay content of the mined oil sands ore, either prior to the mined ore being broken down into lumps, or after. In other implementations, clay content can be evaluated once process water has been added to the to the mined ore to form the oil sands slurry, which is subsequently fed to the PSV, or on a sample taken directly from the PSV. In some implementations, a parameter that is indicative of clay content of the oil sands slurry or the clay's relative concentration with respect to other components of the oil sands slurry, such as CWR, can also be used for determining caustic dosage.

[0143] Clay content can be evaluated according to various measurement techniques. For instance, clay content can be measured by using a methylene blue index (MBI) test, a K40 system, or near-infrared (NIR) techniques. These different types of measurement techniques will be discussed briefly below.

[0144] MBI testing can allow obtaining an estimate of clay content based on a titration method that uses methylene blue, and is generally expressed as milliequivalents (meq) per 100 g of sample. In particular, MBI testing is an estimate of cation exchange capacity (CEC) of clays. When using this technique, the active clay particles/sheets that are negatively charged are coated with cationic MB dye molecules, resulting in a distinct dark blueish color until CEC has been reached. Excess MB that is not bound to clay remains in solution and results in a blue-green color that forms a halo around the dark blueish spot. Formation of a persistent blue-green halo indicates that the clays have reached their absorption capacity of the MB dye.

[0145] The K40 system is configured to measure emissions from a radioactive potassium isotope. The K40 system can measure isotope emissions not only from clays but also from coarser particles that include the isotope. It follows that for a slurry having a low clay content, the measured isotope emissions will not represent an accurate measure to evaluate clay content. In contrast, the K40 system provides a general trending of clay content of the oil sands slurry for oil sands slurries having high-clay levels.

[0146] NIR techniques are based on spectral measurements of an oil sands slurry or other oil sands materials and can be used to determine clay content based on predetermined correlations between clay concentration and NIR spectra. NIR-based calibration curves can be developed based on oil sands having known clay levels (e.g., clay levels measured in a laboratory using other techniques), and the resulting calibration curves can be used to determine clay content based on NIR measurements of the oil sands slurry stream or the oil sands directly.

[0147] Process water chemistry can refer to characteristics of process water in terms of electrical conductivity, pH, and/or dissolved solids, which includes dissolved metals and dissolved salts (e.g., sodium, potassium, calcium, magnesium, and iron) as well as other compounds such as dissolved organic matter. In some implementations, an indicator of water chemistry is a measure of total dissolved solids (TDS), which represents the sum of cations and anions present in the water and can be expressed for instance in mg/L or in ppm. Total dissolved salts is a subset of TDS and can also be referred to as salinity. There are various ions that can contribute to the salinity of water, such as sodium, potassium, calcium, magnesium, etc., balancing with chloride, sulfate, bicarbonate, and carbonate ions.

[0148] In some implementations, where an oil sands slurry having a high clay content is subjected to a primary extraction process, bitumen recovery and/or froth quality can decrease as salinity of the process water increases. On the other hand, in implementations where an oil sands slurry having a low clay content is subjected to a primary extraction process, process water salinity can have less of an impact on bitumen recovery and/or froth quality. This aspect will be described in further detail below.

[0149] Caustic addition is thought to mitigate the impact of salinity and thus can contribute to extend the salinity tolerant range without sacrificing bitumen recoveries at higher sodium ion concentration. For instance, when oil sands ore is mixed with process water to form an oil sands slurry, clay-cation exchange can occur and can result in variations of sodium, potassium, calcium and/or magnesium concentration in the oil sands slurry. With caustic addition to the oil sands slurry, it was found that calcium and magnesium concentrations are reduced in the middlings, a phenomenon thought to be attributed at least in part by CaCO.sub.3 and CaMg(CO.sub.3).sub.2 precipitation due to a pH increase of the process water, which in turn can contribute to an increased bitumen recovery.

[0150] In addition, OH.sup. ions of the caustic soda (NaOH) added to an oil sands slurry can attach to positively charged clays instead of to bitumen droplets, leaving hydrophobic bitumen free to attach to air bubbles, which can be beneficial for bitumen recovery.

[0151] Process water chemistry can evolve through time, from the moment a plant is put into operation and fresh water is used to start up processes, to many years later when processes have reached an equilibrium in terms of recycled process water that has gone through multiple cycles of separation processes. For instance, water from a plant's recycle pond and/or tailings pond can be reused as process water to mix with the oil sands ore and produce the oil sands slurry, and this recycled process water can have a different water chemistry compared to fresh water. After a certain number of years of a plant's operation, i.e., once the plant could be said to be mature, process water chemistry can reach an equilibrium stage. In this regard, studies that have assessed the role of water chemistry on caustic addition in the context of primary separation processes for bitumen recovery have done so based on process water having already a relatively high TDS. In contrast to a mature plant, water chemistry of process water used at a new start-up plant can change substantially in the first few years of operation, in particular with regard to TDS, which can play an important role in determining when to begin caustic addition and determining caustic dosage for primary extraction processes. It follows that as a plant is transitioning from a start-up mode using mainly fresh water having a low TDS, to a mature mode using process water having a higher TDS, tailoring the dosage of caustic may become useful to maintain a target recovery level of bitumen from the oil sands.

[0152] Provided herein are relationships between clay content and water chemistry to help guide caustic dosage requirements, for instance through a plant's lifecycle, which in turn can provide guidance to dose caustic more accurately in order to achieve enhanced bitumen recovery (e.g., by avoiding underdosing of caustic) and reduce the deleterious impact of downstream treatment and product quality (e.g., by avoiding overdosing of caustic).

Correlation for Caustic Dosage

[0153] As mentioned above, it was found that the use of an alkaline compound such as caustic soda in the process water, in the mixing unit, in the aqueous slurry before, during or after hydrotransport, and/or directly into the PSV, can be determined according to a correlation with both clay content and water chemistry. In general terms, such a correlation can be obtained by determining a clay content, or clay indicator, of the oil sands slurry and a dissolved solids content of the process water used to form the oil sands slurry, thus obtaining different predetermined operating envelopes according to various combinations of the clay content and the dissolved solids content. The dosing of the alkaline compound can then be based on one of the predetermined operating envelopes. In other words, an operating envelop can be determined according to a combination of a given clay content, or clay indicator, and a dissolved solids content; and for each operating envelop, there can be a corresponding dosage, or dosage range, of the alkaline compound. In some implementations, the corresponding dosage or dosage range of the alkaline compound can be determined to achieve a target bitumen recovery level of bitumen.

[0154] For instance, in some implementations, there can be a first, a second, a third, a fourth and a fifth clay content range, the first clay content range being below a lower predetermined clay content threshold, and the fifth clay content range being above a higher predetermined clay content threshold, the values of the clay content increasing from the first clay content range to the fifth clay content range. There can also be there can be a first, a second, a third, and a fourth dissolved solids content range, the first dissolved solids content range being below a lower predetermined dissolved solids content threshold, and the fourth dissolved solids content range being above a higher predetermined dissolved solids content threshold, the values of the dissolved solids content increasing from the first dissolved solids content range to the fourth dissolved solids content range. Each combination of the first, the second, the third, the fourth and the fifth clay content ranges and the first, the second, the third, and the fourth dissolved solids content ranges, for a total of twenty combinations, corresponds to a corresponding operating envelop of alkaline dosage. To each operating envelop is associated a dosage or dosage range of the alkaline compound, which can be for instance a low dosage interval, an intermediate dosage interval, or a high dosage interval. By way of example, in some implementations, the low dosage range of the alkaline compound can be associated with the operating envelop corresponding to the combination of the third clay content range and the second dissolved solids content range. It is to be understood that there can be any number of clay content ranges as well as any number of dissolved solids content ranges, and that each operating envelop can have an associated alkaline compound dosing interval but that more than one operating envelop can be associated with a same alkaline compound dosing interval.

[0155] In some implementations, the correlation is determined between clay content measured according to the MBI test, and TDS of the process water. In such implementations and with reference to Table 1 below, it was found that for oil sands having a clay content according to the MBI test below 0.8 meq/100 g, no addition of caustic soda was necessary across the range of water chemistry tested, i.e., first for a TDS level below 1250 mg/L, then for a TDS level between 1250 mg/L and 2500 mg/L, then for a TDS level below 2500 mg/L, and finally for a TDS level below 3500 mg/L. In other words, it appears that for a low clay content (below 0.8 meq/100 g according to the MBI test), it is possible to achieve the target recovery level for a TDS level of up to at least 3500 mg/mL, without having to proceed with caustic soda addition. In the scenario presented in Table 1, the expression total dissolved solids refers to the total concentration of sodium, potassium, calcium, magnesium, chloride, bicarbonate, sulfate and carbonate ions etc. in the process water. Still in the scenario presented in Table 1, concentrations of sodium, potassium, calcium and magnesium ions were determined using an Inductively Coupled Plasma Mass Spectrometry (ICP-MS) method, and concentrations of HCO.sub.3, and SO.sub.4 were determined using an Ion Chromatography (IC) method. It is to be understood that other suitable methods can be used to determine concentrations of ions, as known in the art.

[0156] The target bitumen recovery level can depend on various factors, such as ore quality, for instance with regard to bitumen content and clay content. In some implementations, target bitumen recovery levels are between about 85 wt % and about 95 wt. %. In other implementations, target bitumen recovery levels are between about 90 wt % and about 95 wt. %. The target bitumen recovery level can be a single value, such as 92 wt % or 95 wt %. To determine a given target recovery level of bitumen, empirical testing can be conducted where the clay content of an oil sands slurry and/or the water chemistry of the process water are/is varied, with or without addition of given doses of caustic, and corresponding bitumen recovery levels can be compiled for the different clay-content slurries and corresponding doses of caustic, if applicable. In some implementations, the target bitumen recovery level is determined as the bitumen recovery level obtained when processing an oil sands slurry with a reference process water, for instance a process water from a given source and having a given water chemistry. For instance, in some scenarios, the target bitumen recovery level is determined when using water from the Athabasca river as process water for the recovery process of bitumen form an oil sands ore.

[0157] On the other hand, it was also found for a clay content up to about 1.2 meq/100 g according to the MBI test, no caustic soda addition was necessary to achieve a target bitumen recovery level when the TDS level was concomitantly below 1250 mg/L.

[0158] Then, still referring to Table 1, it can be observed that as clay content and TDS level of the process water increase, dosage of caustic soda should be increased as well. For instance, a relatively low dose (100 to 200 mg/L) of caustic soda would be required for addition to the process water when the clay content of the bitumen is above 1.2 meq/100 g according to the MBI test, when the TDS is below 1250 mg/L, whereas more than 500 mg/L of caustic soda would be required for a similar clay content, but for a TDS level above 3500 mg/L. The dosage of caustic soda, according to this correlation, thus ranges from less than about 100 mg/L to at least about 500 mg/L, depending on the combination of clay content and TDS level. For a clay content above 1.6 meq/100 g according to the MBI test and a TDS level above 1250 mg/L, it was found that it is not recommended to proceed with the primary extraction process, at least in part because an acceptable or target bitumen recovery level would likely not be achieved, and/or the high amount of caustic soda that would be required to achieve an acceptable bitumen recovery level could lead to an excess in Ca.sup.2+ ions, which can be detrimental to subsequent processes occurring as part of the refinery plant and to settling mechanisms when tailings are stored in a tailings pond later on. This is not to say that such high TDS and high clay materials should not be processed, but it would be recommended that such processing be adapted for such input materials.

[0159] The dosage of caustic can be expressed in various units. Table 1 shows a dosage in mg of caustic soda per tonne of oil sands slurry, which could also be expressed in ppm. Another option is to express the caustic dosage according to a given flow rate.

TABLE-US-00001 TABLE 1 Correlation between clay content (MBI) and total dissolved solids (mg/L) for determination of caustic dose (mg/tonne of ore) Total Dissolved Solids (mg/L) MBI <1250 1250-2500 >2500 >3500 <0.8 No caustic No caustic No caustic No caustic 0.8-1.0 No caustic <100 100-200 >200 1.0-1.2 No caustic 100-200 200-400 >400 >1.2 100-200 200-400 >400 >500 >1.6 >400 Not recommended to process

[0160] Table 1 offers an overview of the combined impact of clay content of an oil sands ore, tested according to MBI testing, and water chemistry of process water used to either constitute and/or dilute the oil sands slurry, expressed as a TDS level, on the caustic dosage expected to be required to achieve a target bitumen recovery level. The general concept that emerges from this overview can be viewed as caustic soda having to be added to the oil sands slurry when at least one of clay content and TDS reached a respective given threshold. This concept can be applied to various methods and techniques other than MBI and TDS used to determine clay content and water chemistry. For instance, values expressing a clay content obtained from NIR or K40 testing could be used to obtain a corresponding gradation in clay content.

Process Implementations

[0161] FIGS. 2 and 3 illustrate different process implementations for control of caustic addition in the context of primary extraction operations. These process implementations are described in further detail below.

Clay Content and Water Chemistry Measurements

[0162] With reference to FIG. 2, the general process for bitumen production through surface mining described above is presented to illustrate clay content data acquisition locations 17. Assessment of clay content can be performed on a sample of mined ore 10 or crushed mined ore 13, taken prior to process water 14 being added to the crushed mined ore 13 for mixing in the mixing unit 16. In some implementations, a geology ore model can be obtained based on a previous drilling program before ore is actually processed, and the geology ore model can be used to determine clay content of the ore. Assessment of clay content can also be performed on the oil sands slurry once process water 14 has been added thereto, i.e., prior to the conditioned slurry 18 being fed to the PSV 20, or on a sample taken directly from the PSV 20. In some implementations, clay content can also be measured for the middlings stream 26. The general idea is that clay content can be monitored at any location deemed relevant in order to obtain information to adjust the caustic soda accordingly, either as a standalone variable or taking into consideration other input variables such as water chemistry of process water, if applicable. In some implementations, the value representative of clay content that is obtained can be used directly to contribute to the determination of caustic dosage. In other implementations and as mentioned above, the clay data obtained can be used to construct a clay content indicator, such as CWR.

[0163] Still referring to FIG. 2, assessment of water chemistry 19 can also be performed at various locations throughout the bitumen production process. For instance, as illustrated on FIG. 2, water chemistry 19 can be assessed on the process water 14 upstream of the process water 14 being introduced into the PSV 20. In some implementations, the process water 14 can be obtained by the combination of various recycled water streams. The process water 14 can include water recycled from a tailings pond, from a separation unit used for separation of a froth concentrate, from a recycle pond, or any water stream deemed suitable for recycle as process water in other portions of the process such as for the operation of the PSV 20. Process water can also be obtained from a tailings ponds 50 to be introduced into the PSV 20, and assessment of water chemistry 19 can thus be performed on recycled process water stream 52.

[0164] In the context of the present disclosure, when referring to water chemistry assessment, it is to be understood that different variables can be obtained in accordance with the information that can be useful for subsequent contribution to the determination of an enhanced dosage of caustic soda to reach a predetermined target recovery level of bitumen.

Caustic Addition

[0165] FIG. 2 also illustrates locations at which caustic soda 21 can be added from a caustic soda supply 23 in preparation and during the primary separation process. In some implementations, caustic addition is based on mg/tonne of ore. Caustic soda can be added in a solid form, such as a powder, to process water, or can be already in solution when addition to process water occurs. In some implementations, caustic soda is in solution at a concentration of about 50% w/w, although other compositions are also possible. Referring to FIG. 2, caustic soda 21 can be added to process water 14, recycled process water 52 or to another stream of recycle water not shown, and/or can be added directly to the mixing unit 16. Caustic soda 21 can also be added downstream of the mixing unit 16, to the aqueous slurry 18, i.e., to the feedstock of the PSV 20. Caustic soda 21 can also be added directly into the PSV 20. It is to be noted that in some implementations, there can be a single location for caustic addition, while in other implementations, caustic can be added at more than one location. For instance, in some cases, caustic addition can be performed in a single location, i.e., by direct addition into the mixing unit 16.

Real-Time Caustic Dosage Adjustments Based on Measured Characteristics

[0166] In some implementations, clay content and/or water chemistry can be monitored continuously, in contrast to an offline monitoring performed once a day for instance, to facilitate enhanced dosing of caustic soda for enhanced bitumen recovery performance. In some scenarios, the continuous monitoring can be an advantageous strategy for determining the amount of caustic soda required for achieving a target recovery level of bitumen as a processing plant evolves from a startup plant to a mature plan. In particular, as the processing plant evolves from a start up to a mature plant, water chemistry can change as fresh water is progressively replaced by recycled water to be used as process water, and/or characteristics of oil sands ore can change, particularly in terms of clay content, which can influence caustic soda dosing requirements.

[0167] There are various methods described herein for performing automated real-time, or online, control of caustic addition in response to continuous monitoring of clay content and water chemistry of process water in order to facilitate bitumen recovery and separation performance.

[0168] There may be an interest in monitoring the transition from a very low caustic dosage, even no caustic addition at all, to a higher caustic dosage to mitigate the effects of water chemistry changes as a plant evolves from a startup phase to a mature phase, particularly as the salinity of the process water increases with recycle water having gone through many process cycles. On the other hand, real-time caustic dosage adjustments based on measured characteristics may not be as beneficial in the first few years of operation of a process plant, especially as long as mainly fresh water is used as process water. Indeed, in accordance with the correlation described above, for a total dissolved salt level below 1250 mg/L and clay content of up to 1.2 meq/100 g according to the MBI testing, no caustic addition is expected to be required to achieve a target bitumen recovery level. However, when using recycled water as process water, which is expected to have a higher salinity than fresh water, it can be advantageous to monitor the water chemistry to adjust caustic dosage addition within a desirable operating dosing range, taking into account the clay content of the oil sands slurry as well. When low-grade oil sands ore is mined and supplied to a mixing unit to produce an oil sands slurry, the oil sands slurry can have a high clay content that is consistently above a determined threshold level, for instance above 1.0 meq/100 g when MBI testing is used, and thus continuous caustic dosage determination can be advantageously implemented. It is also noted that the water properties and clay content of the ore can fluctuate, e.g., when changing from one water source or another or when mining a new section of the formation, and thus a rapid adjustment of caustic dosage can facilitate adapting to variable characteristics in the slurry feed to the PSV.

[0169] With reference to FIG. 3, in some implementations, clay content of the oil sands slurry can be measured at one or more of the clay content data acquisition locations 17, and when the measured clay content is above a clay content threshold or setpoint, caustic soda can be added at one or more of the caustic soda addition location 21 at a dose such that the pH of the oil sands slurry introduced into the PSV 20, or already in the PSV 20 depending of where the caustic soda is added, reaches a desired value within a suitable range for facilitating a target bitumen recovery level. In addition, water chemistry 19 can be concomitantly analyzed such that the dosage of caustic soda 21 can take into account the joint impact of both the clay content 17 and the water chemistry 19. Automated dosing of caustic soda in response to a measured predetermined clay content threshold in the oil sands slurry and a measured predetermined TDS threshold in the process water can notably enhance bitumen recovery from the oil sands, in particular at high clay levels and/or at high TDS levels. In some implementations, the automated control of caustic soda dosing can be based on clay content directly or on a clay content indicator.

[0170] Still referring to FIG. 3, when a clay content indicator is used, it may be necessary to retrieve additional data to complete the relationship between the different variables making up the indicator. For example, when using CWR as a clay content indicator, data regarding water content of the oil sands slurry may be obtained to be combined with data regarding clay content 17 of the oil sands slurry, and thus arrive at the CWR. As mentioned above, water content of the oil sands slurry can be determined, measured or estimated in various ways. For instance, in some implementations, data regarding added water to the crushed oil sands can be monitored at given locations, for instance by a flowmeter 25 installed on the process water 14 pipeline or on the recycled water from the tailings pond 50 pipeline 52, and used as an input variable transmitted to an analyzer 27 to derive a CWR value when combined with data regarding clay content 17. Alternatively, CWR can be estimated based on the clay content alone using a predeveloped formula depending on how the clay content is measured. Automation of data acquisition and conversion to a clay content indicator can facilitate enhanced caustic soda dosage and enhance bitumen recovery and separation performance.

[0171] Regarding automated or inline implementations, controller(s) 29 can be used and can be operatively connected to the analyzer 27 to control the dosage of caustic soda 21 for addition to the mixing unit 16, the conditioned slurry 18, and/or to the PSV 20, according to the data related to clay content 17 and water chemistry 19 that has been obtained. As schematically represented on FIG. 3, information punctually or continuously transmitted to the analyzer 27 can be clay content 17, water added to the mixing unit 16 through flowmeter 25, and/or water chemistry 19. This information can then be processed by the analyzer 27 to automatically adjust the dosage of caustic soda 21 added to the different possible locations, i.e., to the mixing unit 16, to the conditioned slurry 18, and/or to the PSV 20, through a respective controller 29. It is to be noted that FIG. 3 shows two analyzers 27 for schematization purposes. It is to be understood that in some implementations, one analyzer 27 can be used to gather data, while in other implementations, two or more analyzers 27 can be used. When two or more analyzers 27 are used, they can be operatively connected to each other to compile various acquired data, such that necessary information can be transmitter to the controller 29 to adjust caustic soda dosage, or they can each be individually operatively connected to a corresponding controller 29.

[0172] The output values of the analyzer 27 may be sent to the controller 29, which can compare a target bitumen recovery level to a real-time bitumen recovery level. The controller 29, operatively connected to respective caustic dosing valve(s), can then control the amount of caustic to be added in response to the output values to achieve the target bitumen recovery level. The bitumen recovery level can be expressed either as the primary recovery, the secondary recovery, or the total recovery, according to the following formulas:

[00001]$\mathrm{Total}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{quality}.Math.\left[\left(B.Math.\text{/}.Math.S\right)\right]=\frac{\left(\begin{array}{c}\mathrm{mass}.Math..Math.\mathrm{primary}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{bitumen}+\\ \mathrm{mass}.Math..Math.\mathrm{toluene}.Math..Math.\mathrm{wash}.Math..Math.\mathrm{bitumen}+\\ \mathrm{mass}.Math..Math.\mathrm{of}.Math..Math.\mathrm{secondary}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{bitumen}\end{array}\right)}{\left(\begin{array}{c}\mathrm{mass}.Math..Math.\mathrm{primary}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{solids}+\\ \mathrm{mass}.Math..Math.\mathrm{secondary}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{solids}\end{array}\right)}$$\mathrm{Secondary}.Math..Math.\mathrm{recovery}=\frac{100*\left(\mathrm{mass}.Math..Math.\mathrm{of}.Math..Math.\mathrm{secondary}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{bitumen}\right)}{\mathrm{mass}.Math..Math.\mathrm{of}.Math..Math.\mathrm{oil}.Math..Math.\mathrm{sands}.Math..Math.\mathrm{bitumen}}$$\mathrm{Total}.Math..Math.\mathrm{recovery}=\mathrm{primary}.Math..Math.\mathrm{recovery}+\mathrm{secondary}.Math..Math.\mathrm{recovery}$

[0173] The above formulas are typically used when assessing recovery levels in a laboratory setting. It is important to note that when a total recovery level is calculated in a so-called real plant setting, the total recovery level can be calculated differently, and can include for instance bitumen recovered from scavenger froth, e.g., tertiary froth. As noted above, clay content may be a single input variable provided to the controller 29, but additional variables can also be measured and provided to enhance the control strategy, such as the amount of water added to the oil sands slurry. Thus, the analyzer 27 can be configured to receive multiple input variables and to provide an output variable related to the dosage of caustic soda that can be added at various locations in the process. The multiple variables may be different clay-based measurements taken from different streams or locations in the facility, and/or various variables related to the water chemistry of the process water. For example, clay content measurements can be made on oil sands ore, oil sands slurry, tailings streams, bitumen enriched streams, middlings streams, and so on. Multiple clay measurements can facilitate redundancy and higher accuracy for the caustic addition control techniques described herein. In some situations, clay can be tracked through the overall facility and various units can be controlled to enhance separation of clay from bitumen and promote high bitumen recovery levels.

[0174] In some implementations and with reference to FIG. 4, process water 14 can be added to the oil sands slurry 18 exiting the mixing unit 16, to obtain a diluted oil sands slurry feedstream for the PSV 20. In such implementations, a flowmeter 25 can be provided on the process water 14 pipeline to control the flowrate of process water 14 being added to the aqueous slurry, and to produce a diluted oil sands slurry having desired properties, for instance having a clay content and/or a clay content indicator within a certain range. Information about how much process water is added to the aqueous slurry 18 can be transmitted to the analyzer 27 for processing. The clay content 19 of the diluted slurry can be measured following addition of process water 14. Measurements related to water chemistry 19, such as TDS or total dissolved salts, can also be performed, either directly on the process water that is fed to the oil sands slurry, or the diluted oil sands slurry. The data related to clay content 17 and water chemistry 19 can be transmitted to the analyzer 27. Proper processing of the acquired data can provide information to the controller 29 that is operatively connected to a valve that can be actuated to provide a given dosage of caustic, either inline or directly into the PSV 20.

[0175] In some implementations, the clay content of the oil sands ore can be based on an online analysis. K40 and near infrared (NIR) methods can perform in-line measurements and provide clay content in real-time, although other clay measurement methods can be used. In other implementations, an automated MBI analysis can be performed.

Experimentation

[0176] Various experiments were conducted to illustrate some aspects of the processes and systems described herein.

Impact of Clay Content and Salinity

[0177] With reference to FIGS. 5a, 5b and 6, various oil sands having different characteristics were subjected to a separation process. The oil sands slurry streams were characterized in terms of ore composition (% bitumen, % solids and % water), ore solids analysis (fines, clays and D.sub.50) and clay content determined by the MBI test. Total recovery (FIGS. 5a and 5b) and bitumen froth quality (FIG. 6) were assessed at various salinity levels. To vary the salinity levels, sodium chloride was added to Edmonton tap water, to obtain a sodium ion concentration range of from 0 to 1500 ppm. The tests were designed to study the impact of the salinity of process water on bitumen recovery and froth quality (B/S), when the oil sands subjected to separation have different compositions, especially in terms of clay content. In FIGS. 5a and 5b, the y axis of graph represents the total recovery of bitumen, determined using the relation described in the above paragraph on primary, secondary and total recovery. In FIG. 6, the y axis represents the bitumen froth quality (B/S) expressed as:

[00002]$\mathrm{Total}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{quality}.Math.\left[\left(B.Math.\text{/}.Math.S\right)\right]=\frac{\left(\begin{array}{c}\mathrm{mass}.Math..Math.\mathrm{primary}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{bitumen}+\\ \mathrm{mass}.Math..Math.\mathrm{toluene}.Math..Math.\mathrm{wash}.Math..Math.\mathrm{bitumen}+\\ \mathrm{mass}.Math..Math.\mathrm{of}.Math..Math.\mathrm{secondary}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{bitumen}\end{array}\right)}{\left(\begin{array}{c}\mathrm{mass}.Math..Math.\mathrm{primary}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{solids}+\\ \mathrm{mass}.Math..Math.\mathrm{secondary}.Math..Math.\mathrm{froth}.Math..Math.\mathrm{solids}\end{array}\right)}$

[0178] With reference to FIGS. 5a and 5b, it can be observed that the total recovery for some of the oil sands was not particularly influenced by the increase in salinity in the process water, i.e., the oil sands having a relatively low clay content, i.e., a clay content 1.3 meq/100 g. In contrast, the oil sands having a higher clay content, i.e., 2.4 meq/100 g, showed a substantial decrease in bitumen recovery as the salinity increased. For the oil sands having a clay content 2.4 meq/100 g, the total bitumen recovery was between 55% and 85% when no sodium chloride was added to the fresh water. The total bitumen recovery was reduced to between 18% to 30% for a sodium ion concentration of approximately 900 ppm, and plateaued at around 20% as the sodium ion concentration continued to increase up to 1500 ppm. FIGS. 5a and 5b therefore illustrates that for an oil sands having a higher clay content, total bitumen recovery is influenced by salinity of process water.

[0179] Turning to FIG. 6, various sands having different characteristics were subjected to a separation process, which included primary separation and secondary separation of a middlings stream in a secondary separation vessel, and the quality of the total bitumen froth obtained was assessed. The oil sands were also characterized in terms of ore composition (% bitumen, % solids and % water), ore solids analysis (fines, clays and D.sub.50) and clay content as determined by the MBI test. FIG. 6 illustrates that for the oil sands having a clay content between 0.2 and 0.4 meq/100 g, the total froth quality (B/S) was above about 3.5. In contrast, for the oil sands having a clay content between 2.4 and 4.1 meq/100 g, the total froth quality was below about 1.0. FIG. 6 shows that as the clay content of an oil sands increases, the quality of the froth recovered decreases. The impact of salinity is observable with the oil sands having a clay content of 1.3 meq/100 g, for which it can be seen that when tap water is used as process water, the total froth quality is about 2.5, and as the salinity of the process water increases, up to a sodium ion concentration of 1500 ppm, the total froth quality (B/S) is decreased to about 1.25.

[0180] With reference now to FIG. 7, nine oil sands having different characteristics were subjected to a separation process, which included primary separation and secondary separation of a middlings stream in a secondary separation vessel. Three of the oil sands slurry streams were single facies, and the six other streams were blends of the facies in different proportions. The oil sands slurry streams were also characterized in terms of ore composition (% bitumen, % solids and % water), ore solids analysis (fines, clays and D.sub.50) and clay content determined by the MBI test. Primary separation tests were performed at various salinity levels. To obtain the different salinity levels, sodium chloride was added to Edmonton tap water, to obtain a sodium ion concentration range of from 0 to 1500 ppm. In this study, total recovery of bitumen was assessed.

[0181] FIG. 7 shows that for an oil sands having a clay content between about 1.3 and 1.7 meq/100 g, total recovery of bitumen started to decrease substantially for a sodium ion concentration of 300 ppm in the process water following addition of sodium chloride in tap water. For the oil sands having a clay content of 4.1 meq/100 g, the change in total bitumen recovery was even more stark, decreasing from about 65% to about 40% for a sodium ion concentration of 300 ppm.

[0182] With regard to total froth quality for these nine oil sands, FIG. 8 illustrates that there is a decrease in total froth quality (B/S) as the clay content of the oil sands increases, similarly to what is shown in FIG. 6. However, FIG. 8 shows more clearly the decreases in total froth quality (B/S) as the salinity of process water increases. In particular, it can be observed that for an oil sands having a clay content below about 1.1 meq/100 g, the decreases in total froth quality (B/S) is observable for a sodium ion concentration of 300 ppm in process water. On the other hand, when the clay content of the oil sands is below about 0.9 meq/100 g, the decrease in total froth quality (B/S) appears to occur at a higher salinity level, i.e., for a sodium ion concentration of 600 ppm in process water. Impact of caustic soda addition

[0183] Experiments were conducted to assess the impact of caustic soda (NaOH) addition and salinity levels on total bitumen recovery and total froth quality (B/S) for oil sands having different characteristics, especially in terms of clay content. The impact of caustic soda addition on total bitumen recovery and froth quality (B/S) can be observed as the salinity of the process water is increased.

[0184] FIG. 9 shows that for an oil sands having a clay content above 1.5 meq/100 g, when NaOH is added to the process water and for a same sodium ion concentration, total bitumen recovery was generally improved. This effect is mitigated when the clay content is high, i.e., above 4 meq/100 g, in which scenario it was observed that addition of NaOH did not result in an improved total bitumen recovery. This observation is an accordance with the correlation presented in FIG. 1, where an MBI above 1.6 meq/100 g and a TDS level between 1250 and 2500 mg/L are conditions for which it can be not recommendable to proceed. In these experiments, NaOH was added in an amount ranging from about 30 ppm to about 550 ppm, based proportionally on bitumen content of the oil sands ore.

[0185] FIG. 10 illustrates that in general, addition of NaOH improved total froth quality (B/S) compared to when there was no addition of NaOH, up to a threshold of about 600 ppm for the sodium ion concentration. For a sodium ion concentration above 600 ppm, the addition of NaOH generally resulted in an improved total froth quality (B/S) compared to when no NaOH soda was added, although the total froth quality (B/S) generally decreased as the salinity level kept on increasing, especially for oil sands having a higher clay content, i.e., 1.3 mwq/100 g or higher.