Processibility of Athabasca oil sand by the hot-water process when contaminated with overburden material

Fuel Processing Technology, 23 (1989) 215-231

215

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

P r o c e s s i b i l i t y of Athabasca Oil Sand by the HotWater Process w h e n Contaminated with Overburden Material RUSSELL G. SMITH and LAURIER L. SCHRAMM*

Syncrude Canada Limited, Research Department, P.O. Box 5790, Edmonton, Alberta T6C 4G3 (Canada) (Received January 18th, 1989; accepted June 9th, 1989)

ABSTRACT Marine oil sand when it occurs in the Athabasca deposit as small pockets completely surrounded by overburden clay material processes poorly when mined by commercial mining methods. The poor processibility was shown to be due to contamination of the oil sand by overburden material during the mining process. The finding rests on evidence that marine oil sand when sampled carefully to avoid contamination processes well and that the processing behavior of some of the uncontaminated samples approached that of the commercially mined material when they were deliberately contaminated by overburden material. Studies using the chelating agent tetrasodium ethylenediaminetetraacetate (EDTA) indicated that it is polyvalent metal compounds in the overburden material that cause the poor processibility of the contaminated oil sand.

INTRODUCTION

The hot-water extraction process for the recovery of bitumen from Athabasca oil sands was originally developed in the 1920's [1] and is now a commercial process used by Syncrude and Suncor in northern Alberta. Oil sand is mined, then processed by slurrying with a small amount of water and sodium hydroxide in rotating drums. The slurry is subsequently screened to remove rocks and lumps of clay, diluted with a further amount of hot water and introduced into a separation vessel where the bitumen floats, and is removed as primary froth, and the sand sinks, and is removed as primary tailings. The amount of bitumen recovered in the primary froth is referred to as primary recovery for the process. An aqueous stream known as middlings and containing water, clay and smaller quantities of bitumen is also withdrawn from (the middle of) the primary separation vessel and treated further in a secondary recovery circuit to recover more bitumen. The total recovered bitumen is pro*Present address: Petroleum Recovery Institute, 3512 - 33rd Street N.W., Calgary, Alberta, Canada.

0378-3820/89/$03.50

© 1989 Elsevier Science Publishers B.V.

216

cessed to synthetic crude oil by a series of steps involving dilution with naphtha, centrifugation to remove water and solids, distillation to remove the dilution naphtha, and fluid coking or delayed coking to convert the heavy, tarlike bitumen to a lighter oil, which is processed into synthetic crude oil by hydrotreating. The main control variable for the hot-water process is the amount of sodium hydroxide used. For any given oil sand sample there is an optimum amount of sodium hydroxide that yields maximum primary recovery, sodium hydroxide additions that are either above or below the optimum lead to reduced primary recoveries. The response of primary recovery to sodium hydroxide addition is referred to as processibility and is used to characterize specific oil sands [2]. Average grade oil sand (10 to 11 wt.% bitumen content) requires about 0.02 to 0.04 wt.% sodium hydroxide based on the mass of oil sand to yield maximum primary recovery, which for average grade oil sand is about 90%, while a lean oil sand (6 to 9 wt.% bitumen content) can require as much as 0.06 to 0.08 wt.% sodium hydroxide to yield maximum primary recovery. It is important to maximize primary recovery from the process because primary froth is of better quality (lower water and solids content) than froth recovered by secondary recovery techniques (forced air flotation) from middlings. Thus although the secondary recovery circuit can recover bitumen lost in the primary circuit, it does so at the expense of froth quality. Although most Athabasca oil sands can be efficiently processed by the hot water process, there are some incidences of samples that process poorly. In particular the Syncrude mine contains pockets of marine oil sand in the upper elevations of the mine that can present a processing problem. Designations such as marine oil sand refer to depositional environments in the deposit. They allow oil sands to be partially distinguished from one another [3,4]. The Syncrude lease contains both estuarine and marine oil sand with the current mine producing mainly the estuarine type. The marine oil sand occurs as a layer above the estuarine in portions of the lease and as relatively small pockets that are completely surrounded by overburden clays. In commercial processes, where there is an upper limit to the amount of sodium hydroxide that can be added, the total recoveries from marine oil sands can be as low as 15 to 20%. In the laboratory batch extraction unit [5 ] the same oil sand can require as much as 0.24 wt.% sodium hydroxide to yield a maximum primary recovery which is less than 10%. The batch extraction unit secondary recovery system is unable to recover all the lost bitumen and total recoveries of only about 40% result. A typical processibility curve is shown in Fig. 1. Marine oil sand has also been referred to as beach oil sand and studies concerned with the poor processibility have been reported in the literature [6,7]. The mechanism of the hot-water flotation process is not fully understood, although recent work has indicated that natural surfactants generated by reaction of the added sodium hydroxide with some oil sand components are in-

217 70

60 A

,•

4O

3O

20

I 0.04

] O.O S

I 0.12

I 016

I 0.20

I 0;)4

NaOH Added (Mess % Oil Sand)

Fig. 1. The batch extraction (BEU) processibility of "as mined" marine oil sand. The curves correspond to primary recovery ( • ) and total recovery ( • ) .

volved [8,9]. The presence of surfactants in aqueous streams from the process has been known for some time [2,5,10,11] but it is only recently [9] that a connection between surfactants and process operability has been demonstrated. The early work [ 10,11 ] indicated that several surfactants were present in aqueous streams from the process and carboxylates and sulfonates were among the specific compounds suggested. In the more recent work [8,9] the field has been narrowed. It is now believed that two surfactants are produced, a carboxylate and a second surfactant that could be either a sulfate or a sulfonate. A study of several oil sand samples led to the finding (9) that maximum primary recovery occurred at the same carboxylate surfactant concentration for all the oil sands included in the study. The concentrations of both surfactants were found to increase as the amount of sodium hydroxide used in the process was increased and there was a linear relationship between the amount of surfactant produced and the amount of sodium hydroxide added. The carboxylate surfactant concentration that corresponds to maximum primary recovery has been termed the critical surfactant concentration and has a value of about 12 × 10 -5 N in the batch studies. The finding that maximum primary recovery occurred at the same carboxylate surfactant concentration for the series of oil sands studied suggests that these surfactants dominate over the sulfate/sulfonate surfactants and that the sulfate/sulfonate surfactants do not usually play a role in determining maximum primary recovery. It has, however, been found that the sulfate/sulfonate surfactants can play a role in determining maximum primary recovery in cases where carboxylate surfactants are absent or nearly absent from solution [ 12 ]. Thus, examples of

218

oil sands have been studied that produce primarily sulfste/sulfonate surfactants at low sodium hydroxide levels while producing both surfactants at higher sodium hydroxide levels. These oil sands gave two primary recovery peaks with the first peak apparently due to the sulfate/sulfonate surfactants and the second peak apparently due to the carboxylate surfactants. For the examples studied the second recovery peak occurred at the carboxylate surfactant critical concentration while the first recovery peak occurred at a sulfate/sulfonate surfactant concentration of 15 X 10 -5 N in the batch studies. This concentration has been tentatively identified as the critical concentration for the sulfate/ sulfonate surfactant. An important phenomenon, from both a practical and mechanistic point of view, is the ageing phenomenon that occurs while oil sands are in storage. We have studied ageing of several oil sands and have defined the phenomenon and determined the mechanism of ageing [13,14]. Ageing can be defined in terms of the changes which occur in the processibility behavior of an oil sand during storage. It has been shown that in some cases ageing results in the development of two peak behavior while in other cases ageing causes an increase in the amount of sodium hydroxide required for maximum primary recovery along with a decrease in the maximum obtainable recovery. In both cases ageing has been shown to cause an increase in the amount of sodium hydroxide required to generate the critical carboxylate surfactant concentration. For oil sands with high sulfate/sulfonate surfactant concentrations (above the critical concentration) this results in a shift of the recovery peak to higher sodium hydroxide levels because higher sodium hydroxide levels are required to generate the critical carboxylate surfactant concentration. For oil sands with low sulfate/sulfonate surfactant concentrations (below the critical concentration at some sodium hydroxide level) the result is an aged oil sand with a first peak due to sulfate/sulfonate surfactants and a second peak due to carboxylate surfactants. The above considerations became important in the present investigation, which was undertaken to determine the cause of the poor processing behavior of commercially mined marine oil sand. EXPERIMENTAL

Oil sand samples Samples were obtained in one case from a pocket of marine oil sand that had been uncovered in the overburden removal operation on the Syncrude minesite and in the other case by using an auger to drill down to a portion of the deposit containing an overlying 10-metre layer of marine oil sand. Samples were obtained from the pocket of marine oil sand by digging a large pit in the deposit to a depth of four metres, so that samples could be taken from the wall of the pit. Three samples were taken at depths of 1 m, 2 m, and 3 m. In each case the

219

surface layer of oil sand was removed from the wall of the pit to a depth of 58 cm and discarded and the samples (20 kg) were taken from behind the cleaned area. The samples were labeled samples number 1-3 and were homogenized by chopping to an average 1-2 m m size with a spatula and by mixing the chopped oil sand in a plastic bag. The samples were stored in plastic bags in a cooler at 4 ° C. The oil, water, solids and fines content of the samples were determined by standard procedures [ 15 ] and the results are given in Table 1. The second kind of samples from the deposit were obtained using a mobile auger- type of drilling rig. The drill was a 10 cm (4 inch) diameter auger which could reach a depth of about 30 m (100 feet) by adding auger sections in 1.5 m (5 foot) lengths. A count of auger sections was used to determine sample depth. Three sites, adjacent to core holes that had been drilled earlier were selected, so that the depth of the marine oil sand deposit was known. Sampling was carried out by drilling just into the deposit, removing the auger from the hole and cleaning off attached mud and clay and then lowering the auger to depth and drilling down a further 3 m (10 feet). The auger was again removed from the hole and the oil sand sample (about 20 kg) was collected from the auger flights. A further two 3 m (10 feet) sections were drilled and samples collected for a total of three samples for each hole. The samples were labeled samples number 4-12 with samples number 4-6 being from the first hole while samples number 7-9 and samples number 10-12 were from the second and third holes respectively. The samples were homogenized as above and oil, water, solids and fines content (Table 1) were determined. A sample of overburden material was taken from above the pocket of marine TABLE 1 Composition of oil sands studied Sample no.

1 2 3 4 5 6 7 8 9 10 11 12

Source of Sample

pit pit pit hole- 1 hole- 1 hole-1 hole-2 hole-2 hole-2 hole-3 hole-3 hole-3

Composition (mass %) Oil

Water

Solids

Fines a

10.9 8.1 5.0 7.0 12.5 6.2 10.5 12.0 5.8 9.3 10.6 6.5

4.4 6.0 8.0 5.0 3.5 10.2 1.5 1.8 10.8 1.8 2.7 10.8

84.7 85.9 87.1 88.1 83.9 83.6 87.9 86.6 83.4 88.7 86.8 82.7

13.7 20.0 30.8 19.4 23.8 32.0 22.6 22.7 29.0 22.4 28.6 30.9

aMass fraction of solids smaller t h a n 44 p m expressed as a percentage of total solids.

220

oil sand that was sampled to obtain samples 1-3. The overburden sample was analyzed by X-ray diffraction analysis and was found to contain by weight 58% quartz, 6% kaolinite, 16% illite, 5% smectite, 2% plagioclase, 2% potassium feldspar, 3% dolomite, 2% pyrite, 3% chlorite and 3% swelling mixed layer clays.

Batch extractions Batch extractions were carried out using a procedure that has been previously published [5]. The collected primary froth, secondary froth, primary tailings, secondary tailings and wall froth were analyzed for bitumen, water and solids by the standard analytical methods [15] and a mass balance was determined for each experiment. In cases where the secondary tailings were worked-up for surfactant analysis (see below) a secondary tailings bitumen content was obtained by recombining the bitumen in the centrifuge tubes. The recombined secondary tailings were analyzed for bitumen by standard methods [ 15]. Batch extractions with EDTA were done with the EDTA added to the batch extraction unit at the same time as the slurry water and sodium hydroxide.

Clarified secondary tailings The secondary tailings samples from the batch extractions were centrifuged at 23,000 g (at maximum radius) for 20 minutes and the supernatant was decanted and filtered using a 0.8 ttm nominal pore size filter paper. The clarified tailings so obtained were cloudy in most cases except for the tailings from the zero and very low sodium hydroxide experiments which were clear.

Surfactant concentration determinations The concentrations of carboxylate and sulfate/sulfonate surfactants were determined in the clarified tailings by a method that has been previously described [8].

Metallic cations Clarified tailings samples were acidified to pH 3.0 with dilute hydrochloric acid, allowed to stand at room temperature for 15 minutes and filtered using 0.45 ttm nominal pore size filter paper. The samples were analyzed by ICP flame emission spectroscopy for sodium, magnesium, aluminum, silicon, phosphorus, potassium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, molybdenum, cadmium, tin, barium and lead.

221

EDTA The EDTA used was obtained from Terochem Laboratories and was of 98% purity. R E S U L T S AND D I S C U S S I O N

The possibility exists that the poor processibility of marine oil sand samples when the small pockets of oil sand are mined by large mobile shovel is due to contamination of the oil sand with some of the surrounding clay overburden. This hypothesis was tested by obtaining samples of the oil sand free of contamination by careful hand sampling. Some uncontaminated samples were obtained from a pocket of marine oil sand that had been exposed during overburden removal operations and some uncontaminated samples were obtained from the deposit itself using a truck mounted auger. Twelve samples of uncontaminated marine oil sand were obtained from the sampling campaign with three samples, labeled samples number 1-3, obtained from the deposit of marine oil sand and nine samples, labeled samples number 4-12 obtained by auger from the deposit itself. Bitumen, water, solids and fines content of the samples are given in Table 1. Nine of the samples were processed in the batch extractor to develop processibility curves. To do this, each sample was processed at four or five sodium hydroxide levels and the primary recovery results plotted versus sodium hydroxide used. The plots were used to estimate the sodium hydroxide level needed to obtain maximum primary recovery and the maximum obtainable recovery. The results are recorded in Table 2. The data in Table 2 indicate that the uncontaminated marine oil sand samTABLE2

Processibility of marine oil sand samples Sample

Maximum primary

no.

recovery (%)

1 2 4 5 7 8 10 11 12

88 81 91 91 94 91 92 88 70

NaOH addition required for max. primary recovery (mass%) 0.03 0.04 0.06 0.03 0.02 0.02 0.03 0.04 0.10

222

ples processed very well, giving good primary recoveries at low sodium hydroxide levels. The best primary recovery obtained was 94% from sample number 7, which occurred at 0.02 wt.% sodium hydroxide. This oil sand was an average grade containing 10.5 wt. % oil and 22.6 wt. % fines. The worst primary recovery obtained was from sample number 12 which had 6.5 wt.% oil and 30.9 wt.% fines and gave 70% maximum primary recovery at 0.10 wt.% sodium hydroxide. In general the data agree with previous findings that primary recovery is to some extent related to fines content with oil sands of low fines content giving better primary recoveries than oil sands of high fines content [2,5]. A graph, showing the relationship between fines content and maximum obtainable primary recovery, taken from reference (2) is shown in Fig. 2. The data from which this figure was constructed is representative of normal Syncrude mine production and hence is representative of estuarine oil sands. Data from the nine marine oil sand samples (Table 1 ) are also shown in Fig. 2. The marine samples tended to have better primary recoveries for a given fines content than the estuarine samples but appeared to obey the same relationship with maxim u m obtainable primary recovery decreasing with increase in fines content. It may be that some of the low recoveries obtained for the estuarine samples were low due to ageing effects. The graph shows that the uncontaminated marine oil sands process at least as well as normally mined estuarine oil sand and we concluded that the processibility of marine oil sand is certainly not worse than the processibility of estuarine oil sand provided the marine oil sand is mined free of contamination. To provide some evidence that it was overburden material that was causing the poor processibility of the commercially mined marine oil sand, experiments

90 A >,

85

8 8o ~.

n

E 7o

:~ 65 60 0

-44~m

Fines In Oil Sand

Fig. 2. Relationship between maximum primary recovery (batch extractions) and oil sand fines content. The data are for estuarine oil sands ( • ) and for marine oil sands ( • ) .

223

were done in which three of the uncontaminated samples were purposely contaminated with added overburden material. The overburden material used was material from above the pocket of marine oil sand that was sampled to obtain samples number 1-3. In general the addition of overburden to the uncontaminated samples resulted in a reduction in maximum obtainable recovery and an increase in the amount of sodium hydroxide required to obtain maximum primary recovery. Sample number 1, 10.9% wt.% oil, was processed in the batch extractor at several sodium hydroxide levels with 2 and 5 wt.% of added overburden material. Primary and total recovery are given in Table 3 and primary recovery is shown versus sodium hydroxide used for the three samples in Fig. 3. The addition of overburden material caused an increase in the amount of sodium hydroxide required to obtain maximum primary recovery and a decrease in the obtainable maximum primary recovery. At the 2 wt.% overburden TABLE 3 Processibility of oil sand with added overburden material

Oil sand sample

Overburden added (wt. % )

NaOH added (mass% oil sand)

Primary oil recovery (%)

Total oil recovery (%)

1

2

0.00 0.02 0.04 0.08 0.12

2 36 50 70 58

22.5 85.3 89.1 93.7 93.9

1

5

0.00 0.03 0.06 0.08 0.12

2 37 57 77 73

16.7 87.4 88.7 86.9 88.8

2

2

0.00 0.04 0.08 0.12 0.16

2.0 15.1 33.8 55.8 53.1

18.8 59.8 75.0 82.5 81.7

12

2

0.00 0.04 0.08 0.12 0.16 0.20 0.24

7.1 11.8 14.9 13.3 23.6 57.4 47.7

45.2 45.3 42.2 47.4 60.2 78.2 76.2

224 I00

9O

80

70 ~

v •~

60

o o

50

3O

2O

I0

I

o.o2

I

0.04

I

0.06

I

o.os

I

o, to

I

o.~2

O. 114

NeOH Added (Mess % Oil Send)

Fig. 3. Processibility of marine oil sand sample 1 by itself ( • ) and when blended with small amounts, 2 wt.% ( • ) and 5 wt.% ( • ), of overlying material.

level the amount of sodium hydroxide required for maximum primary recovery was about 0.08 wt.% while at the 5 wt.% level the sodium hydroxide requirement was about 0.11 mass%. For both cases the requirement was up considerably from the 0.03 mass% required for the uncontaminated sample. Maximum primary recovery for the sample containing 2 wt.% overburden was 70% while maximum primary recovery for the sample containing 5 wt.% overburden was 77% (compared to 88% for the uncontaminated sample). The finding of a higher maximum primary recovery at 5 wt.% overburden than at 2 wt.% overburden was surprising and in view of the little that is known about the relationship between primary recovery and overburden control worthy of some further investigation. The effect of added overburden was also investigated on sample number 2 which contained 8.1 wt.% oil to determine the effect of overburden contamination on a lean grade of oil sand. The effect of overburden was investigated at the 2 wt.% level and primary and total recovery data are given in Table 3 and primary recovery is shown as a function of sodium hydroxide added for the two samples in Fig. 4. Overburden at the 2 wt.% level caused an increase in the amount of sodium hydroxide required for maximum primary recovery from

225 IOC

~6O 40 E

L. n 20 0'02

0~)4

0.~)6

0;8

0.110

O.II2

0114

016

018

NeOH Added (Mess % Oil Send)

Fig. 4. Proeessibility of marine oil sand sample 2 by itself ( • ) and when blended with 2 wt. % ( • ) of overlying material. 7O 6O

o

4o

lO b-I

0.02

I

004

I

0.06

I

O.~)S o,o

0.112

o,.I

o16

o18

NeOH Added (Mess % Oil Send)

Fig. 5. Processibility of marine oil sand sample 12 by itself ( • ) and when blended with 2 wt.% ( I ) of overlying material.

0.04 mass% to about 0.14 mass% and a decrease in the maximum primary recovery from 81% to 58%. Overburden was also added at the 2 wt.% level to sample number 12, 6.5 wt. % oil, to study the effect of added overburden on the leanest of the uncontaminated samples. Primary and total recovery data are given in Table 3 while primary recovery is shown as a function of sodium hydroxide added for the two samples in Fig. 5. Overburden at the 2 wt.% level caused an increase in the amount of sodium hydroxide required for maximum primary recovery from 0.10 mass% to about 0.20 mass% and a decrease in the maximum obtainable recovery from 70 to 58%. The data clearly indicate that the effect of contamination of marine oil sand

226

with overburden material is to produce an oil sand sample that requires much more sodium hydroxide to obtain maximum primary recovery and that has in most cases a reduced maximum obtainable primary recovery. The behavior of the contaminated samples is very similar to that of the commercially mined samples described in the introduction which require large amounts of sodium hydroxide to obtain maximum primary recovery and have lowered maximum primary recoveries. Taken as a whole the evidence supports the theory that it is contamination by overburden materials that causes the high sodium hydroxide requirement and the low recoveries of the commercially mined product. The effect of overburden on estuarine oil sand was not investigated because estuarine oil sand is not normally mined contaminated with overburden. The effect would be expected to be similar provided the sulfate/sulfonate surfactant is above its critical concentration at all sodium hydroxide levels. In cases where the sulfate/sulfonate surfactant is below its critical concentration at some sodium hydroxide level it would be expected that the oil sand would develop two peak behavior. It is of interest to note that the effect of contamination on processibility is very similar to the effect of ageing of an oil sand [ 13,14]. Although in the case of ageing pyrite oxidation and ion exchange provide the source, polyvalent metal species are introduced (e.g., CaS04) which have the same effect of lowering processibility by reacting with the sodium hydroxide and/or surfactants. Addition of a chelating agent to remove these species from the surfactant equilibria has the same effect as in the present work. It is of interest to determine the component of overburden material that is causing the large increase in the amount of sodium hydroxide required to obtain maximum primary recovery. When the surfactant mechanism of the process as described in the introduction is considered it seems probable that the increase in sodium hydroxide requirement for maximum primary recovery must also imply an equal increase in the amount of sodium hydroxide required to generate the critical carboxylate surfactant concentration. Such an increase could be caused by reaction of either sodium hydroxide or the carboxylate surfactants with polyvalent metal compounds contained in the overburden material. If this theory is correct it should be possibly to reverse the effects of overburden material on at least sodium hydroxide consumption by the use of a chelating agent such as EDTA. Consequently the effect of added EDTA on an overburden contaminated sample was investigated. The marine oil sand sample that was used in the investigation was sample number 2 of 8.1 wt.% oil. The study was initiated after the sample of oil sand had been in storage in the homogenized state at 4 °C for 27 days. At this age the uncontaminated oil sand had a maximum primary recovery of 35% at a sodium hydroxide level of about 0.05 mass%. Ageing of this oil sand under the label Marine-Lean-1 has been previously discussed [13,14]. The primary recovery is down from the fresh primary recovery of 80% and the sodium hy-

227 droxide requirement for maximum primary recovery is up from the fresh case of 0.04 mass%. The small increase in sodium hydroxide requirement for maximum primary recovery is in agreement with data on other oil sands [13,14] which suggest an increase of the magnitude observed is in the normal range. Primary recovery data as a function of sodium hydroxide used is shown for the aged oil sand in Fig. 6. Surfactant concentrations were measured in clarified tailings from the batch extractions with the data recorded in Table 4 along with primary and total recovery data and with the carboxylate surfactant concentrations shown in Fig. 7 versus sodium hydroxide used. The oil sand is considered to be a case where the carboxylate surfactant is controlling because as can be seen from Table 4 the sulfate/sulfonate surfactant is above the critical concentration at all sodium hydroxide levels. The carboxylate surfactant concentration was at the critical concentration at the point of maximum primary recovery for the sample. As the next step in the study the oil sand was blended with 2 wt.% of overburden material and the processibility of the contaminated oil sand studied. The addition of 2 wt.% of overburden material increased the sodium hydroxide requirement for maximum primary recovery from 0.05 to about 0.17 mass% but did not cause a decrease in the maximum obtainable primary recovery; in fact maximum obtainable primary recovery increased from the 35% obtained from the uncontaminated sample to the 50% obtained from the contaminated sample. The carboxylate surfactant concentration reached the critical concentration also at about 0.17 mass% sodium hydroxide and hence again at the same sodium hydroxide level at which maximum recovery was obtained. The prediction that the increase in the amount of sodium hydroxide required for maximum primary recovery would be accompanied by an equal increase in the amount of sodium hydroxide required to reach the critical carboxylate surfactant concentration was confirmed. The 2% blend of sample number 2 oil sand with overburden material was next studied with added EDTA. An initial series of batch extractions was done at 0.04 mass% sodium hydroxide with the amount of EDTA used varied from 0.34 g/batch to 2.75 g/batch. This set of batch extractions was done to determine an optimum or near optimum dosage for the EDTA. Primary recovery was found to be optimum at an EDTA level of 2.24 g/batch. A second series of batch extractions was carried out, in which 2.24 g of EDTA were added per batch, and the sodium hydroxide additions varied from 0.02 to 0.06 mass%. The recovery data are plotted in Fig. 6 and it is clear the EDTA acted to restore the sodium hydroxide requirement for maximum primary recovery to that of the original uncontaminated oil sand. The maximum primary recovery was reduced from the 50% obtained with the contaminated oil sand to 40%. Surfactant concentration data were measured for the EDTA case with the data given in Table 4 along with primary and total recovery data and the carboxylate surfactant concentration data are shown in Fig. 7 as a function of

228 I00 90

so 70 > o

60

~ 50 r~ 4o

b~

30

E

"V_ 2 0 ~0

o~

oh,; o~

o~8 olo

oI~ o,14 o.'~6 o';8 o~o

NaOH Added (Mass °/o Oil Sand)

Fig. 6. Processibility of marine oil sand sample 2 at 27 days of age ( • ), w h e n blended w i t h 2 wt. % of overlying material at 35 days of age ( ~ ) , a n d w h e n blended w i t h 2 wt.% of overlying material a n d treated with E D T A at 42 days of age ( [] ). TABLE 4

Recoveries and surfactant concentrations from batch extractions on marine oil sand sample number 2 Oil sand

NaOH added Primary oil (mass% recovery (%) oil sand)

Total oil

Surfactant concentrations

recovery (%)

( 10- s N)

Carboxylate Sulfate/Sulfonate 27-days old

0.02 0.05 0.07 0.08

19 35 21 18

66 79 69 67

14.6

106 136 163

0.10 0.13 0.16 0.20

6 33 49 45

56 78 85 77

1.0 6.3 10.6 -

161 198 233 -

containing 2wt.%overburden ~ 0.02

20 39 27 16

66 78 68 50

3.9 8.5 8.7 10.3

118 119 147 152

containing 2wt.%overburden

0.04 0.05 0.06

4.8 9.1

"With added EDTA.

sodium hydroxide added. The Figure shows that the EDTA returned the carboxylate surfactant concentration curve to very nearly the same as for the uncontaminated sample. Both maximum primary recovery and the critical carboxylate surfactant concentration were reached at about 0.05 mass% sodium hydroxide. The effect of the EDTA was to restore the behavior of the contaminated oil sand back to the behavior of the uncontaminated oil sand from both a processibility and carboxylate surfactant point of view. The result supports the mechanism that suggests that the increase in the sodium hydroxide requirement for maximum primary recovery associated with contamination of

229 15 z ~

I0

J

~E5 2 =o ~.0 h(..)

0.'02

J 0.04

0.~)6

O.~)S

1 O.lO

I 0,12

Co cs

O.il4

o'le

Oil8

0.20

NaOH Added (Mass % Oil Sand)

Fig. 7. Free carboxylate surfactant concentrations generated during the processing of marine oil sample 2 at 27 days of age ( • ), when blended with 2 wt.% of overlying material at 35 days of age ( ~ ) , and when blended with 2 wt.% of overlying material and treated with EDTA at 42 days of age ([~). TABLE 5 Metal ion content of clarified tailings from batch extractions of sample no. 2 with 2 wt.% overburden using EDTA NaOH added (mass % oil sand)

EDTA added ( 10- 5 mol/Bx ) ~

Metal ion (10 -5 mol/Bx) a

Total polyvalent metal ions Iron Calcium Manganese Magnesium (10-Smol/Bx) a

0.02 0.04 0.05 0.06

538 538 538 538

92 72 42 29

442 488 466 471

2 3 2 2

129 135 137 135

665 698 647 637

"Moles per batch. TABLE 6 Metal ion content of clarified tailings from batch extractions of sample no. 2 with 2wt.%overburden NaOH added (mass% oil sand)

EDTA added ( 10- 5 mol/Bx) ~

Metal ion (10 -5 mol/Bx)a

Total polyvalent metal ions Iron Calcium Manganese Magnesium (10-Smol/Bx) ~

0.10 0.13 0.16

0 0 0

0 0 1

16 12 11

0 0 0

5 3 2

21 15 14

"Moles per batch.

marine oil sands with overburden is due to reaction of sodium hydroxide or carboxylate surfactants with polyvalent metal compounds contained in the overburden material. Since it was expected that the polyvalent metal compounds would be solu-

230

bilized by reaction with EDTA the clarified tailings samples from the batch extractions were analyzed for metals content. The analysis included the metals as listed in the experimental section. For purposes of comparison the clarified tailings from the contaminated oil sand as run without the use of EDTA were also analyzed for metals. The polyvalent metals that were found to be present in more then trace quantities in the experiments using EDTA included iron, calcium, manganese and magnesium and the quantities of these metals found in moles per batch extraction experiment are listed in Table 5. The most abundant metal found was calcium, with significant quantities of magnesium and iron also present. There was only a minor amount of manganese present. The polyvalent metals found in the experiments without EDTA are listed in Table 6. There were only minor amounts of calcium and magnesium present. For the experiments using 2.24 g of EDTA per batch agreement between the amount of EDTA used (538× 10 -s mol) and the amount of polyvalent metal ion solubilized (637 to 698× 10 -s mol) was fairly good. The excess found over the amount of EDTA used indicates some soluble but non-chelated metal, which we have not subtracted from the Table 6 metals, since the solution pH values differ from the with-EDTA case, changing the solubilities of the metals. The finding of solubilized polyvalent metal ions in tailings from the batch extractions using EDTA serves to confirm that the EDTA is acting to bind polyvalent metal compounds removing them from competition with surfactant producing reactions. CONCLUSIONS

The major conclusion of the present work is that the processibility of marine oil sand, when it is commercially mined on a large scale from the small pockets of this oil sand that exist in the Athabasca deposit, is due to contamination by overburden material. The contamination is probably sometimes unavoidable given the size of the mining equipment involved and the small size of the pockets of oil sand. It is also a conclusion of the work that marine oil sand when it occurs in significant quantity in the deposit such that it can be mined without overburden contamination will process well. The study using EDTA indicated that it is polyvalent metal compounds in the overburden material that cause the processing problem. The results of the study with EDTA indicate that the polyvalent metal compounds interfere with carboxylate surfactant production which in turn leads to poor processibility. It seems probable that the polyvalent metal compounds interfere with carboxylate surfactant production either by reacting with sodium hydroxide, thus rendering it unavailable for production of carboxylate surfactants, or by reacting with the carboxylate surfactants themselves, thus rendering them unavailable to promote the flotation. This is similar to the effect ageing has on a "pure" oil sand sample.

231 ACKNOWLEDGEMENTS

The authors thank Drs. J.M. Cooley and J.K. Liu for valuable discussions and advice regarding the manuscript. The experimental assistance of A. Lemke, J.B. Turnbull, and J.M. Severyn are gratefully acknowledged. The authors thank Syncrude Canada Ltd. for permission to publish this work.

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