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Key performance indicators reveal the impact of demulsifier characteristics on oil sands froth treatment Ishpinder Kaur Kailey Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 03 Feb 2017 Downloaded from http://pubs.acs.org on February 3, 2017
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Key performance indicators reveal the impact of demulsifier characteristics on oil sands froth treatment Ishpinder Kailey* th
*Baker Hughes, 7020 45 Street, Leduc, Alberta, Canada T9E 7E7
ABSTRACT Demulsification with ethylene oxide (EO) -propylene oxide (PO) block copolymers is a very effective technique for treating water-in-oil emulsions in the petroleum industry. In this work, two series (A and B) of EO -PO block copolymers were synthesized and studied. The demulsifiers were defined by their relative solubility number (RSN) and interfacial tension (IFT). The performance of demulsifiers was evaluated by measuring the
percent
water
and
solids
contents
in
dilbit
product
and
hydrocarbon
(diluent/bitumen) losses to the underflow. Demulsifiers from series B showed higher performance on dilbit dehydration and demineralization as compared to demulsifiers from series A. The higher dehydration and demineralization efficiencies for series B demulsifiers were a result of the higher adsorption and lower IFT values at oil/water interface. Demulsifiers from series B also showed higher hydrocarbon losses to the underflow. These higher hydrocarbon losses were associated with higher solidsremoval efficiencies. The bi-wettable clay solids surfaces have a strong affinity for hydrocarbon components, causing increased hydrocarbon losses to the underflow.
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1. Introduction Clark hot water method under alkaline conditions is deliberated for discharge of bitumen from the ore, in which aeration causes bitumen froth to rise to the top of the flotation unit.1 The typical composition of bitumen froth is 60% bitumen, 30% water, and 10% solids by weight. Naphthenic or aliphatic diluents are added to the bitumen froth to reduce the viscosity, promoting further reduction of water and solids.2-7 A paraffinic froth treatment process uses C5-C7 alkanes as a solvent in which the asphaltenes are precipitated. Any remaining water and fines in the bitumen agglomerate with the precipitated asphaltenes, leaving behind a very clean bitumen product that meets pipeline specifications.2-6 In the naphthenic froth treatment process, the dilbit product normally includes approximately 2 to 5 % water and 0.3 to 1 % solids by weight.7,8 The remaining water in the dilbit exists as an extremely stable emulsion steadied by interfacial active constituents such as clays, asphaltenes, resins, naphthenic acids, and waxes.9-12 To meet pipeline specifications, additional removal of water and solids from the dilbit is required. Chemical demulsification is the most common process applied to break water-in-oil (W/O) emulsions in oil sands industry.13-17 Amphiphilic EO-PO block copolymers are broadly considered for demulsification applications in naphtha-based froth treatment processes.16,17 Several efforts attempted to relate demulsifier properties such as hydrophile-lypophile balance (HLB), dynamic interfacial tension, interfacial viscosity, partition coefficient, molecular weight, molecular structure, EO content, PO content, EO/PO ratio, number of EO-PO branches and relative solubility number with demulsification efficiency by measuring percent water content in a final diluted bitumen product.13-17 Few researchers studied the effect of demulsifiers structural changes such as HLB’s and molecular weights (MWs) on the disruption of W/O emulsions.18 They reported that best dewatering efficiencies were achieved with demulsifiers having high HLB’s and low MWs. Abdel-Azim et al. found that the dewatering efficiency of EO-PO block copolymers depend on percent EO, number of amino groups, HLB, number of polar 2|Page ACS Paragon Plus Environment
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groups and aromatic rings.13 Krawczyk et al. reported that best dewatering efficiency can be attained with demulsifiers with a partition coefficient close to unity.19 Wu et al. studied the effect of MWs of the demulsifiers on water removal from the diluted bitumen.20 They found that most effective demulsifiers were EO-PO copolymers and alkylphenol formaldehyde resins amended by EO/PO with MW in range 7500-15000 Da. Xu et al. reported that diethylenetriamine-based EO-PO copolymers with molar EO/PO in range 1 to 1.8 were most effective EO-PO demulsifiers in diluted bitumen dewatering.14 Kailey and Feng found that the dewatering efficiency of EO-PO copolymer influenced by number of EO-PO branches, RSN and molecular weight. They found that the effect of molecular weight of EO-PO copolymer dominates over the RSN on diluted bitumen dewatering efficiency.16 Kim et al studied the effect of the specific constituents and blends of a demulsifier formulation package on the destabilization of emulsion films.21 The results illustrated that the demulsifier components must create low interfacial tension and high diffusivity. Kailey et al. investigated the relation between crosslinking of the EO-PO demulsifiers and demulsification performance.17
They found that crosslinking of the EO-PO
demulsifier decreased the RSN value but increased the molecular weight, interfacial tension, dilational modulus and hence adsorption of the cross-linked demulsifier at the O/W interfaces.
The higher adsorption to the O/W interface on crosslinking the
demulsifiers increased the dehydration efficiency. Several researchers found the direct relation between demulsification efficiency and lowering of interfacial tension.19,22 Wang et al. studied the interfacial dilatational properties of demulsifiers at the oil-water interface.23 They found that the straight chain demulsifiers had strong ability for O/W interface and hence decrease the dilatational modulus.
The proficiency of a demulsifier is primarily measured by its HLB and the capability to destroy the film at O/W interface.24-25 The demulsifiers destabilize water-in-oil emulsions by two mechanisms: flocculation and/or coalescence. The coalescence should be the dominant destabilizing mechanism to attain a free water layer.26-28 Several publications 3|Page ACS Paragon Plus Environment
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supported that the demulsifiers could also link water drops and as a result promote flocculation, enhance coalescence and phase separation.29-31
The solids in W/O emulsions are hydrophobic in nature due to the adsorption of asphaltenes and resins at their surfaces. As a result they tend to stay at the W/O interface and hence stabilize the emulsion by hindering the coalescence of water droplets.32-34 The influence of EO-PO block copolymer composition on percent solids removal from the final diluted bitumen product and hydrocarbon losses to underflow/tailings have never been reported. To study the effect of EO-PO block copolymer demulsifiers on the demulsification efficiency in the naphtha-based froth treatment process, two series of EO-PO block copolymers (A and B) were synthesized and investigated. Both EO-PO copolymer demulsifier series had the same starting base, but the PO block size in series B was bigger than in series A. Within each series, the PO in the PO block was kept unchanged, but the EO was changed from 0% to 40%. Both A and B series of demulsifiers were characterized by RSN and IFT measurements. The demulsifiers’ performance was evaluated by measuring the bitumen froth treatment key performance indictors (KPIs) such as dehydration and demineralization of the diluted bitumen, and reduction in the hydrocarbon losses to underflow.
2. MATERIALS AND METHODS 2.1 Materials Bitumen froth and naphtha samples were provided in 1-gallon metal paint cans from mining producers in the Fort McMurray region. The bitumen froth was heated to 85°C for 1 hour and then homogenized using a hand-held stirrer for 15 minutes. Approximately 85 gm of homogenized bitumen froth was transferred into 180-mL graduated glass bottles that were sealed, cooled to room temperature, and stored at 4°C in a refrigerator. The froth composition was determined by a Dean Stark extraction method.
The composition of froth averaged approximately 57.16 ± 0.06 % bitumen,
33.13 ± 0.26% water and 9.71 ± 0.11% solids by weight. The fines content (≤ 45 µm) of
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each froth sample was measured by sieve analysis based on the dried solids obtained from the Dean Stark analysis. Content averaged around 27.48 ± 0.60% by weight. The naphtha was also homogenized at room temperature using a paint shaker for 5 minutes. The quantity of naphtha required to produce a naphtha-to-bitumen ratio of 0.7 was collected into another set bottles that were stored at 4°C. Before starting the tests, the froth and naphtha were removed from the refrigerator and allowed to reach room temperature. Toluene and ethylene glycol dimethyl ether (EGDME) used for IFT and RSN measurements, respectively, were obtained from Fisher Scientific.
2.2 Demulsifiers The EO–PO block copolymers used for this work were supplied from the Baker Hughes Research and Development Centre in Sugar Land, Texas. In this work, two series of copolymers, named A and B, were synthesized and investigated. Both A and B EO-PO copolymer demulsifier series had the same starting base, but the PO block size in series B was bigger than series A. Within each series, the PO in the PO block was unchanged, but the EO in the EO block was changed from 0% to 40%. The molecular weights of demulsifier series A and B varies from 4000 to 6700 Da and 8000 to 13500 Da, respectively. The RSNs of the demulsifiers were determined using 888 Titrando colorimeter and toluene/EGDME as the RSN solvent. The details of the RSN determination method can be found in reference [35]. Dynamic and static IFT measurements were conducted for both A and B series of EOPO demulsifiers at 23.0 ± 1.0°C and atmospheric pressure. Dynamic IFT measurements were accomplished using the pendant-drop technique with an Attension Optical Tensiometer (Biolin Scientific, Finland). The oil and aqueous phases were made up of toluene and de-ionized (DI) water. Demulsifier was added in the toluene phase. The demulsifiers were dosed into the toluene at 25 ppm, based on weight, before testing. At the beginning, a freshwater droplet was generated at the tip of a syringe needle (inner
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diameter 0.84mm) immersed in the toluene phase. Images were recorded at 12 frames per second and processed accordingly with Young-Laplace module. The static IFT was determined using the tensiometer K12, Kruss, Hamburg, Germany and Pt/Ir Du Nouy ring method. The aqueous and oil phases were DI water and 60 wt. % toluene-diluted bitumen, respectively. The diluted bitumen was dosed with 25 ppm of demulsifier on weight basis, prior to testing. 2.3 Demulsification Tests Bottle tests were used to assess the performance of EO-PO copolymers in gravity settles. The bitumen froth and naphtha samples were placed in a water bath set at 83° C. The bottles containing naphtha were dosed at 25 ppm with demulsifier based on the bitumen content in the froth. Two undosed bottle tests were kept as baseline to each set of bottle tests. After 10 minutes, the naphtha bottles were shaken for 1 minute on the horizontal shaker at high speed and then added to the particular bitumen froth bottles. The diluted samples were then mixed for 6 minutes on a horizontal shaker at a frequency of 190 shakes per minute. The bottles were placed back to a water bath at 83° C. Diluted froth samples were collected at the one third height from the surface at 10 and 30 minutes retention time, respectively, from each bottle, and the water content was determined by Karl Fischer titration. The average water content in the two control tests was used as a baseline. The water-removal efficiency of demulsifiers for each dosage was calculated from: dewatering efficiency ሺ%ሻ=
൫Wo - Wd ൯ Wo
×100
(1)
where W o is the percent water in the control test, and W d is the percent water on the addition of the EO-PO copolymer. The results stated for individual dosage are the average of three repeats. 2.4 Solids Analysis The known amount of dilbit samples collected from 1/3 height down from the surface at 30 minutes residence time from each graduated glass bottle were transferred into weighed Teflon centrifuge tubes. The tubes were then set into a titanium 50.2 Ti rotor 6|Page ACS Paragon Plus Environment
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after balancing the weights and centrifuged at 15,000 rpm for 30 minutes using a Beckman Coulter Optima L-90K ultracentrifuge. After 30 minutes, the top oil from the centrifuge tubes was carefully removed with plastic pipettes. The centrifuge tubes containing solids were filled with toluene, sonicated until the solids completely dispersed, and then centrifuged again for 30 minutes at 15,000 rpm. The sonication and centrifugation steps were reiterated till the supernatant had no black colour of the bitumen. The solids were dried at 115°C for 2 hours in an oven. The tubes containing dry solids were re-weighed to calculate the percent solids in diluted froth samples. The solids-removal efficiency of demulsifiers for each dosage was calculated from: solids-removal efficiency ሺ%ሻ=
൫So - Sd ൯ So
×100
(2)
where So is the percent solids in the control test, and Sd is the percent solids on the addition of the demulsifier. The results described for each dose are the average of three repeats. 2.5 Underflow preparation The underflow was prepared to quantify the effect of demulsifiers on hydrocarbon losses to underflow. After 30 minutes of settling, the bottles were removed from the water bath and the dilbit phase was cautiously removed above the free water at the O/W interface. The fluid left in the bottle was called the underflow. 2.6 Hydrocarbon Losses Measurement A Baker Hughes proprietary method was used to measure the diluent losses to the underflow. The Dean Stark extraction method was used to estimate the bitumen losses to the underflow.
3. RESULTS AND DISCUSSION The performance of EO-PO copolymer demulsifiers was measured by measuring the KPIs in bitumen froth treatment such as percent water and solids content in dilbit
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product and hydrocarbon losses to the underflow. A low KPI value indicates the superior performance of the froth treatment. Table 1 shows the effect of the percent EO on RSN values for both demulsifier series. The results point out that the RSN values depend on the EO and PO content of the EOPO copolymer. The EO and PO content provide hydrophilicity and hydrophobicity, respectively, to the demulsifier. The RSN value of the demulsifiers in each series increases with increasing EO content, at the fixed PO content. In contrast, at a fixed percent EO the RSN value decreases with increasing percent PO. Several researchers found that RSN value increases with increase in percent EO content at same PO content.14, 16 Kailey and Feng reported the linear relation between EO content and RSN values at a fixed PO content.16
Table 1: Information of EO-PO copolymer demulsifiers Series A
B
Demulsifier
%EO
RSN
A1
0
8.7
A2
10
10.7
A3
20
12.6
A4
30
15.8
A5
40
21.3
B1
0
7.3
B2
10
8.6
B3
20
10.6
B4
30
14.8
B5
40
20.7
Figures 1 and 2 show the dynamic IFT of EO-PO copolymers from series A and B, respectively at 25 ppm dose in toluene – DI water system. IFT values decreased with 8|Page ACS Paragon Plus Environment
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the increase of RSN values (shown in Table 1) in both A and B series of demulsifiers. In both PO-EO block copolymer series the IFT values decreased with the increase of EO content and RSN values at 25-ppm dosage in toluene – DI water system. The results reveal that B series of PO-EO block copolymers reached lower IFT values at the toluene/DI water interface than the A series of PO-EO block copolymers. In other words, the B series of demulsifiers with higher PO content and MW were more interfacially active than the A series of demulsifiers at the toluene/DI water interface.
Figure 1. Dynamic IFT of EO-PO copolymer demulsifiers for the A series at the toluenewater interface. The dosage of each demulsifier in toluene phase was 25 ppm.
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Figure 2. Dynamic IFT of EO-PO copolymer demulsifiers for the B series at the toluenewater interface. The dosage of each demulsifier in toluene phase was 25 ppm.
3.1 Correlation between RSN, IFT, and dehydration efficiency
Figures 3 and 4 show the dehydration efficiencies (calculated using equation 1) as a function of RSN values at 10 and 30 minutes retention times in the presence of 25-ppm demulsifiers from series A and B, respectively. In both demulsifier series the dehydration efficiencies improved with the increase in RSN values and the percent EO content at fixed PO content. The results disclose that the percent EO content, RSN value, and dehydration efficiency of the demulsifier in any series are directly correlated to each other at the fixed percent PO content. Earlier investigations reported a direct link between dewatering efficiency and RSN values of DETA-based EO−PO copolymers.14,16-17,36 Xu et al studied that DETA-based EO-PO demulsifiers show optimum dewatering efficiency in RSN range 18 to 22 corresponding to a PO/EO ratio of 1 to 1.8.14
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B5 B4 A5 B3
A4
B2 A3 B1 A2 A1
Figure 3. Effect of RSN on dehydration efficiency at 25-ppm dose and 10-minute retention time
The results also reveal that dehydration efficiencies for both A and B demulsifier series increased with the residence time. For instance, the demulsifiers A4 and B4 achieved dehydration efficiencies of 31.2 and 48.2%, respectively at 10-minutes retention time. However, at 30-minutes retention time the dehydration efficiencies of 41.5 and 64.3% were attained by demulsifiers A4 and B4, respectively.
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B5
B4 B3
A5
B2 B1
A4 A3 A2
A1
Figure 4. Effect of RSN on dehydration efficiency at 25-ppm dose and 30-minute retention time
The results also reveal that the EO-PO copolymers from series B achieved higher dewatering efficiencies than demulsifiers from series A. However, RSN values of demulsifier from series B were lower than series A at same percent EO content. The size of PO block in series B copolymers was bigger than series A, which increased the hydrophobicity and molecular weight of the demulsifier. The higher molecular weight of demulsifiers for series B was responsible for higher dehydration efficiencies compared to the series A demulsifiers. Several researchers identified earlier that dehydration efficiency of the demulsifier depends on its molecular weight and hydrophile-lypophile balance (HLB).16-17,
37
Kailey, et al. reported earlier that the molecular weight of the
demulsifier had a stronger influence than RSN on demulsification efficiency.16,17 Wu et al. studied the effect of MWs of demulsifiers on dewatering of O/W emulsions.20 They
found
that
low MW
sorbitan
esters,
polyoxyethylene
sorbitan
esters,
polyoxyethylene fatty alcohol ethers, and polyoxyethylene alkylphenol ethers achieve maximum 20% dewatering efficiency. However, high MW polyols, EO/PO block copolymers, and alkylphenol formaldehyde resins modified with EO/PO, assisted to remove about 90% water from O/W emulsion. They established that the demulsifiers 12 | P a g e ACS Paragon Plus Environment
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with molecular weight in range 7500-15000 Da achieved the best dewatering of O/W emulsions under gravity settling. In this work the molecular weight of series B demulsifiers is in this range.
The surfactants with molecular weight less than 3000 Da exhibit high interfacial activity, diffuse faster at oil/water interface and thus causing film rupture by irreversibly adsorbing at the interface, which promotes coalescence of the water droplets.38,39 The EO-PO block copolymers with molecular weight greater than 3000 Da are accountable for the separation of the O/W emulsion. These polymers alter the compressibility and rheological properties of the films at the O/W interface that stabilize the emulsion.38,39 As a result these polymers also named as water droppers favor the drainage of the thin films between approaching water droplets and so coalescence and phase separation. EO-PO amine polyols with molecular weight greater than 10000 Da act as flocculants by adsorbing at the water-oil interfaces. These polymers, also called polishers have lower diffusivities, and remove residual small water droplets after water droppers removed most of the dispersed phase.40
Figure 5. Effect of RSN on dewatering efficiency and IFT for series A EO-PO copolymers. The dose of demulsifiers was 25 ppm and dehydration efficiencies were measured at a 30-minute retention time. 13 | P a g e ACS Paragon Plus Environment
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Figure 6. Effect of RSN on dewatering efficiency and IFT for series B EO-PO copolymers. The dose of demulsifiers was 25 ppm and dehydration efficiencies were measured at a 30-minute retention time.
The relationship between dehydration efficiency and IFT as a function of RSN values of the EO-PO copolymers from series A and B is presented in Figures 5 and 6, respectively. The dehydration efficiency increased while IFT at toluene diluted bitumen/DI water interface decreased with the increase of the RSN values for both A and B demulsifier series. The A5 and B5 demulsifiers from series A and B achieved the lowest IFT and the highest dewatering efficiency at a 25-ppm dose. The lower IFT values point towards the higher adsorption of EO – PO block copolymers from series B at the toluene diluted bitumen/DI water interface with the increase of the RSN values, which resulted in higher dewatering efficiencies. The dynamic IFT values at toluene/DI water interface (Figures 1 and 2) also shows that B series of PO-EO block copolymers were more interfacially active and achieved lower IFT values than the A series of POEO block copolymers. Earlier research also reported that the fast adsorption of demulsifier at O/W interface decreased IFT and enhanced dehydration efficiency.16, 41-42 Even though the dehydration efficiency and IFT values were inversely related for both series of demulsifiers in this work, other parameters should also be considered when
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selecting a demulsifier because the IFT measurements often did not correlate well to the demulsifier performance.17,39
3.2 Correlation between RSN and demineralization efficiency
Figure 7 shows the solids-removal efficiency (calculated using equation 2) as a function of RSN value for demulsifiers. The solids-removal efficiencies in both demulsifier series improved with the RSN. However, the demulsifiers from series B achieved higher solidsremoval efficiencies than series A over the RSN range studied. Figures 3, 4 and 7 reveal that as the percent water content in diluted bitumen product decreased the percent solids contents also decreased. These results point out that the RSN values and water and solids-removal efficiencies of the demulsifiers in any series were directly related at the fixed percent PO content. The results also show that the EO-PO demulsifiers from series B achieved higher solids removal efficiencies than demulsifiers from series A. However, the RSN values of demulsifiers from series B were lower than series A at same percent EO content. The size of PO block in series B copolymers was bigger than series A, which increased the hydrophobicity and molecular weight of the demulsifier. The higher molecular weight of demulsifiers for series B was responsible for higher solids-removal efficiencies compared to the series A demulsifiers. The solids in W/O emulsions are hydrophobic in nature due to the adsorption of asphaltenes, resins and natural surfactants at their surfaces. As a result they tend to stay at the W/O interface and create a inelastic film at the water drop surfaces that prevent the coalescence and hence stabilize the W/O emulsions. Removal of water and solids from these W/O emulsions can be very complicated. In order to destabilize the solids stabilized water-in-diluted bitumen emulsions, the mineral particles must be changed back to hydrophilic nature from hydrophobic nature for effective removal from oil/water interfaces. The EO-PO block copolymers typically exhibit behavior similar to that of stabilizing agents but likely act by replacing the interfacial materials such as 15 | P a g e ACS Paragon Plus Environment
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hydrophobic/biwettable solids at the O/W interfaces, by modifying the wettability of the hydrophobic solids that stabilize the emulsions, thus favoring the thin liquid film drainage between the approaching water drops. Alternatively, demulsifier could also link water drops leading to flocculation, hence coalescence and phase separation. Few publications reported that the demulsifiers with molecular weight in range 7500-15000 Da achieved the best demulsification performance under gravity settling.20 The results showed that the EO-PO demulsifiers from series B with molecular weight in range 800013500 Da assisted to achieve higher both dehydration and demineralization efficiencies than series A EO-PO block copolymers.
Figure 7. Effect of RSN on demineralization efficiency at 25-ppm dose and 30-minute retention time
3.3 Correlation between RSN and hydrocarbon losses to underflow The naphtha losses to underflow were measured using a Baker Hughes proprietary method. The naphtha losses were quantified as a percentage of the naphtha collected by the Baker Hughes method to the initial amount of naphtha added to the test sample. 16 | P a g e ACS Paragon Plus Environment
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The values presented in this section are indications only and cannot be correlated to the actual system because the test system cannot simulate the downstream processing equipment used by mining operators, such as hydrocyclones and the naphtha recovery units that further reduce the hydrocarbon losses to underflow. Therefore, the data presented shows higher losses than would be expected in the commercial plant. The key point to consider is that relative comparisons can be made between the different demulsifiers to confirm the same, better, or worse performance on naphtha losses to the underflow.
Figure 8: Effect of RSN on percent naphtha loss to the underflow at 25-ppm dose and 30-minute retention time
The naphtha losses to the underflow as a function of RSN values of the demulsifiers are shown in Figure 8. Naphtha loss to underflow augmented with the RSN value in the presence of demulsifiers from both A and B series. In addition, the demulsifiers from series B showed higher naphtha losses to the underflow as compared to EO-PO copolymers from series A at 25-ppm dose and 30-minutes settling time. The increase of naphtha losses with RSN value was due to increase of demineralization efficiencies in
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both demulsifier series. The demineralization efficiencies of demulsifiers from series B were higher than series A, resulting in the naphtha losses to the underflow. Numerous publications pointed out that adsorption of hydrocarbon components, mainly on surfaces of clay minerals have been linked with hydrocarbon losses during oil sands processing.43-44 The bitumen loss to the underflow was assessed by Dean Stark extraction method. The bitumen losses to the underflow with RSN values of the demulsifiers are shown in Figure 9. Bitumen loss to underflow augmented with the RSN value for demulsifiers from both A and B series, which point towards direct relation between RSN and bitumen losses to the underflow. Kailey and Feng also reported direct correlation between RSN and bitumen losses to the underflow.16 The increase of bitumen losses to the underflow with RSN values was due to higher solids removal content from diluted bitumen product to the underflow. The solids-removal efficiencies of demulsifiers from series B were higher than series A, resulting in the bitumen losses to the underflow.
Figure 9: Effect of RSN on percent bitumen loss to the underflow at 25-ppm dose and 30-minute retention time
18 | P a g e ACS Paragon Plus Environment
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Energy & Fuels
The greater bitumen losses to the underflow were observed for demulsifiers from series B as compared to EO-PO copolymers from series A at 25-ppm dosage and 30-minute settling time. The higher demineralization efficiencies of demulsifiers from series B justify the higher bitumen losses to the underflow. Sparks, et al. reported that in naphtha-based froth treatment processes certain solids are connected with substantial quantities of toluene insoluble organic material that adsorbed onto surfaces of the particles.44 The particle size of these organic-rich solids can vary from less than 44 µm to greater than 100 µm. The particles of size >100 µm typically occur as aggregates of smaller particles bound together by humic material and precipitated minerals. During the oil sands processing, the hefty aggregates carry any allied bitumen into the aqueous tailings, plummeting total bitumen recovery. The particles of size
