sion is valid. T h e red t o purple colors provide sufficient contrast t o t h e green of t h e chromic ion t o m a k e t h e color change very pronounced, although as m u c h as 1 m l of 1% indicator might be necessary when large quantities of chromous ion are used. T h e reddish cast of t h e indicator
shows u p best through t h e green color of chromic ion if t h e solutions are examined in light from a tungsten source. Received for review October 31, 1973. Accepted December 26, 1973.
Rapid and Convenient Laboratory Method for Extraction and Subsequent Spectrophotometric Determination of Bitumen Content of Bituminous Sands Mahendra S. Patel Product Research and Development Division, Research Council of Alberta, 7 7375-87
Currently, solvent extractions by toluene or carbon t e t rachloride using s t a n d a r d Soxhlet a p p a r a t u s , a n d a densit y method are t h e three analytical procedures described in t h e literature for t h e determination of b i t u m e n content of bituminous s a n d s ( I ) . T h e toluene-extraction method yields t h e most accurate results a n d is widely used in l a b oratory determinations. In t h e toluene-extraction procedure, t h e water a n d b i t u m e n are simultaneously extracted with toluene. T h e a m o u n t of silt t h a t passes through t h e extraction thimble is determined by ashing, a n d applied as a correction to t h e bitumen. Bitumen content is calculated on a dry weight basis from loss in weight. T h e procedure requires four to six hours for extraction a n d several extra hours for residual solids determination; for routine analyses, t h i s is very time-consuming a n d laborious. T h e purpose of this present investigation was t o develop a rapid a n d simple analytical procedure for determining bitumen content of bituminous sands. In t h e present method, extracting solvent (toluene) is p u m p e d through a column of bituminous s a n d of known moisture content. B i t u m e n content of t h e extract is t h e n determined by absorbance measurement a n d calculation from a per cent b i t u m e n us. absorbance plot of a s t a n d a r d bitumen.
EXPERIMENTAL The extraction column consisted of a stainless steel tube (4-in. X 5b-in. i.d.) with threaded caps at each end for inlet and outlet of the extraction fluid. The caps were fitted with metal filter disks (Yg-in. coarse-grade porous bronze) and rubber O-rings (Buna-N or Viton A). .4 Milton Roy Minipump, Model 196-47. with 240 ml per hour volume capacity and discharge pressure of 1000 psi, was used to pump the extraction solvent. Absorbance measurements were made at 530 nm. using toluene (ACS grade) as the solvent and blank, on a Bauch and Lomb Spectronic-20 colorimeter with a square silica cell of 10-mm path length. A gas chromatograph equipped with a flame ionization detector was used for toluene determination. A stainless steel column (6-in. X Yg-in. i.d.) packed with 5% SE-30 on Chromosorb G (AW 100-120 mesh) was used at a helium flow rate of 40 ml/minute and column and injection port temperatures of 60 and 75 "C, respectively. The samples used for this study were collected at the Great Canadian Oil Sands mining site in the Fort Mcxlurray, Alberta, area of the Athabasca bituminous sand deposit. Draper, A . Yates, and H. McD. Chantler, Canadian Dept. Mines & Tech. Surveys, Mines Branch, Rep. FRL-211, Fueis Division, December 1955.
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Procedure. The extraction column was assembled as shown in Figure 1. A cap was placed at the bottom end of the extraction tube. A bed of clean sand 5 - to 10-mm thick was deposited on top of the metal filter and the tube was weighed accurately to the nearest 0.01 gram. A representative sample (20-25 grams) of bituminous sand was added to the tube with light packing and the tube was reweighed. A second cap was then placed at the top end of the tube and connected to the solvent line. The extracting solvent was introduced at the top of the column and the extract was collected directly into a tared centrifuge tube. Overhead pressure was maintained at 10-20 psi by adjusting the solvent flow through the column. Complete extraction of bitumen was achieved within 10-20 minutes, with a total extract volume of 75-100 ml. Water content of the bituminous sand was simultaneously determined on another independently weighed sample (ea. 100 grams) by the Dean and Stark method. using toluene as solvent. After centrifugation of the toluene extract to remove silt, its absorbance was determined upon suitable dilution to read between 0.40 and 0.60 absorbance unit on the photometric scale. Bitumen content of the sample was then determined from a calibration curve and is reported on a dry weight basis. For calculation of bitumen content by difference, the amount of dry solids, including silt, were determined by drying the extracted column in a vacuum oven at 120 "C for 1-2 hours. Calibration Curve. A standard sample of bitumen required for the curve was prepared as follows. A bituminous sand sample (20.90 grams) of known moisture content (0.3% H20) was extracted with toluene by the extraction procedure described herein. The extract was evaporated in the cold (water bath temperature 25-30 "C) under reduced pressure on a rotary evaporator to remove the solvent. yielding crude bitumen (2.86 grams). The bitumen sample so obtained contained no detectable amount of water (IR, Karl-Fischer titration). The amount of residual toluene was quantitatively determined (15.26% w/w) by gas-liquid chromatography. using chloroform as solvent and toluene as external standard, and applied as a correction to the bitumen content. A stock solution of bitumen in toluene (0.80070 w/v) was prepared from standard bitumen accurately weighed to the nearest 0.0001 gram. Serial dilutions of bitumen in toluene, ranging in concentrations from 0.019-0.064%, were prepared and their absorbances determined. A plot of per cent bitumen rs. absorbance produced a straight line passing through the origin, corresponding to an apparent absorptivity of 6.81 f 0.02. Calculation: % bitumen = % concentration bitumen (found) x (initial volume of extract) x (final volume of diluted solution/ vol. of extract aliquot x wt. of bituminous sand sample (dry)) RESULTS AND DISCUSSION Direct determination of bitumen by t h e spectrophotometric method is based on t h e following observations. First, when measured a t 530 n m in a spectrophotometer, absorbances of t h e color of solutions of b i t u m e n in toluene
Table I. Bitumen Content of a Bituminous Sand as Determined by Two Methods B y difference (l0OYc dry solids) Bitumen, 70 (dry wt basis)
Re1 std dev, %
4 10
10.41 i 0 12a 14.14 i O . O @
1.44 0 64
4
10.24 i 0.16a
2.05
No. of determinations
Method A C o l u m n extraction with toluene (a) (b) Method B Soxhlet extraction with toluene 'I
Average deviation.
Direct determination by photometric method
- ~ . _ _ _ _ _ _
Bitumen, yo (dry wt basis)
10.50 i 0.15a 14.14 i 0.14a
Re1 std dev,
1.81 1.20
For statistical purposes, precision of bitumen was obtained for 10 determinations, using a different tar sand sample.
exhibit a linear relationship with concentrations over a range of a b o u t 0.02-0.08% b i t u m e n . T h e silica cell used for optical measurements exhibits o p t i m u m transparency a t t h e analytical wavelength, a n d there is no interference from porphyrin absorption (porphyrin pigments in A t h a basca b i t u m e n have absorption m a x i m a a t 410 a n d 575 n m ) . Second, t h e absorbance determinations of several samples of b i t u m e n representing t h e s a m e general area of t h e mining site indicate t h a t there is very little or no lateral variation in color characteristics of b i t u m e n within t h e s a n d deposit (relative s t a n d a r d deviation, 0.48%). T h u s , it is possible to use a calibration curve prepared for one particular site of a s a n d deposit for all subsequent determinations of b i t u m e n content for samples from t h a t area. However, t h e color densities of b i t u m e n m a y vary layerwise-z.e , depthwise-within a s a n d deposit, a s well as from deposit t o deposit, a n d s e p a r a t e calibration curves m a y be required. T h e present extraction procedure h a s been effectively applied t o bituminous s a n d s containing varying proportions of bitumen, sand, a n d clay, a n d containing from 0.2-15% moisture. T h e silt content of t h e extract ranged from 0.1-0.5% (based on s a m p l e weight). T h e efficiency of b i t u m e n extraction was equal t o or better t h a n t h a t a t t a i n e d with toluene extraction by t h e Soxhlet method. Loss of light boilers was tested by gas chromatography a n d found to be negligible; therefore, t h e composition of t h e s t a n d a r d b i t u m e n used for t h e calibration curve closely resembled virgin bitumen. T h e spectrophotometric method is suitable for only virgin bituminous sands. Comparison of t h e per cent relative s t a n d a r d deviations indicated a n o p t i m u m concentration range of 0.05-0.0'i% b i t u m e n in toluene over which t h e precision a n d sensitivit y of t h e photometric measurements were good. T h e relative s t a n d a r d deviations in absorbances a t 0.048 a n d 0.064% concentrations were 1.21 a n d 1.26%, respectively. T h e precision a n d sensitivity of photometric measurem e n t s can be considerably increased by t h e use of a spectrophotometer with provision for scale expansion. Bitumen content of a representative sample of b i t u m i nous s a n d was determined in quadruplicate by t h e present procedure, a n d compared to t h a t obtained by a s t a n d a r d Soxhlet extraction. Results are summarized in T a b l e I. Differences in t h e b i t u m e n content of t h e sample as determined by t h e two methods c a n be a t t r i b u t e d partly to sampling error a n d partly to t h e m a n n e r in which t h e bi-
IU"ST**LESS TUBE
STEEL
Figure 1. Extraction assembly
t u m e n contents are calculated. I n t h e absence of other direct methods, t h e Soxhlet method h a s been used a s a guide to b i t u m e n content of t h e sample. T h e method present'ed here c a n be very useful in rout i n e analysis of b i t u m e n where knowledge of t h e water content of t h e sample is u n i m p o r t a n t . T i m e required for one complete analysis is a b o u t 30 minutes; however, when b i t u m e n content is t o be reported on a dry basis, t h e method requires separate water determination a n d complete analysis t i m e is a b o u t 1-2 hours. Applicability of a calibration curve c a n easily be checked since t h i s method lends itself t o determination of b i t u m e n content both directly a n d by difference.
ACKNOWLEDGMENT T h e a u t h o r wishes t o express his sincere t h a n k s to H. W. Habgood a n d D. L. Mitchell of t h e Research Council of Alberta for their valuable comments during preparation of this manuscript. Received for review September 4, 1973. Accepted December 17, 1973. Contribution No. 655 from t h e Research Council of Alberta, 11315-87 Ave., E d m o n t o n , Alberta, C a n a d a T 6 G 2C2
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