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Centrifuge tailings from oil sands plants: a resource material for
titanium and zirconium
No. 1998.156
Centrifuge Tailings from Oil Sands Plants — A Resource Material for
Titanium and Zirconium
A. Majid, F. Toll, and B.D. Sparks, National Research Council of Canada, Institute for
Environmental Research and Technology, Ottawa, Ontario, Canada; and A. Turak,
TMCL Engineering, Gloucester, Ontario, Canada
Abstract
In the hot water process (HWP) for the extraction of bitumen from the Athabasca oil sands, enriched concentrations of tita-nium and zircotita-nium minerals have been observed in the dilu-tion centrifuge tailings. These minerals are hydrophobic and are preferentially wetted by bitumen. Consequently, they may be beneficiated by oil phase agglomeration with low grade coal, refinery coke as hydrophobic collectors and heavy oil as a binder. This study presents the results of a bench scale feasi-bility study to evaluate liquid phase agglomeration (spherical agglomeration) as an option for the recovery of titanium and zirconium minerals from dilution centrifuge tailings.
The overall objective of the Mineral Development Author-ity program on heavy minerals was to conduct laboratory and pilot studies to develop a technically feasible and economical scheme for the concentration and subsequent separation of Ti and Zr from various HWP tailings streams. The results obtained demonstrated the potential for beneficiation of the specified tailings streams and separation into zirconium and titanium minerals concentrates.
Introduction
The production of refinery grade oil from the Alberta oil sands deposits as currently practiced by Syncrude and Suncor, gen-erates a substantial amount of waste including, coke, fly ash, coarse sand and fine tailings. Under current production condi-tions, a plant producing 15,900m3/day (100,000 bbl/day) of
synthetic crude oil requires the processing of 100,000 m3/day
ore which results in a tailings stream consisting of 100,000 m3
of coarse sand, 2,000 m3 of coke, 100 m3 of fly ash and 20,000
m3 of Mature Fine Tailings (30% solids)1-2. As a result, a large
inventory of process-affected materials are accumulating. The major concern regarding these wastes is a question of the vol-umes involved and the lack of an acceptable reclamation option.
The recognition and exploitation of the useful intrinsic
has been limited to the use of sulphur and the burning of small amounts of coke. Recently, however, there has been extensive investigation of heavy metal recovery from centrifuge rejects and aluminum production from clay3. It is anticipated that
high disposal costs and increased regulatory pressures to min-imize landfill disposal options will increase the incentives for recycling byproducts from these oil sands industry wastes.
Heavy minerals, especially those of titanium and zirco-nium, present in the oilsands are discarded in various tailings streams during the bitumen extraction process. Centrifuge tailings, produced during the treatment of bitumen froth for the removal of water and solids, by solvent dilution and cen-trifugation, are significantly enriched with titanium and zirco-nium minerals4. Concentration of these minerals in the
centrifuge plant tailings is attributed to the effects of bitumen-flotation and froth treatment on the oil-wet surfaces5 of part or
most of the heavy minerals in oil sands. The volume of tail-ings is sufficient to provide feed for a large-scale titanium pig-ment plant with enough zircon to satisfy Canadian demand for metallic zirconium6.
The oil sands coproducts evaluation project, carried out by a consortium of oil and oil sands companies and R&D organi-zations in Canada, is aimed at determining the technical and economical viability of a Ti/Zr extraction operation in North-ern Alberta. Financial support was provided by the Canada-Alberta Minerals Program. The initial focus of this project was on the utilization of centrifuge plant tailings from both the Syncrude and Suncor oil sands operations. Part of the pro-cess development efforts in the current MDA Project was focused on further concentration of heavy minerals in the tail-ings, before dry beneficiation, in order to produce separate titanium and zirconium concentrates for marketing and/or subsequent chemical processing.
Test work, carried out by various partners in the project, utilized either a combination of hydrocyclone and froth flota-tion or froth flotaflota-tion alone. Preliminary results raised con-cerns about the loss of ultrafine particles of Ti and Zr min-erals during recovery by the methods tested. In earlier work
tion tests utilizing fine coke from the oilsands operations to concentrate the heavy minerals in the centrifuge tailings streams. Bitumen in the tailings would also contribute to the bridging liquid requirements for this coagglomeration pro-cess. This processing approach was expected to result in the capture of all ultra-fine particles of Ti and Zr bearing minerals. This report is a summary of the results of the preliminary lab-oratory testing carried out by TMCL Engineering and the National Research Council of Canada, using NRCC's spheri-cal agglomeration process11.
Materials
A 5 gallon sample of Syncrude centrifuge plant tailings was received from the University of Alberta. The crude tailings contained 2.5w/w% bitumen and 19.3w/w% water with the balance being solids; approximately 20% of the solids were finer than 60 mm. Average Ti and Zr content of the bitumen free, ashed dry solids was 5.9 w/w% and 0.34 w/w% respec-tively. Distribution of Ti and Zr in various size fractions is shown in Table 1.
Syncrude fluid coke was used for coagglomeration of cen-trifuge tailings. The coke particles, as received, ranged in size from 200 to 600 mm; size reduction was accomplished in a Brinkman Grinding Mill ZM-1 to provide a size fraction of 100-150 mm.
Binders tested included, Bunker Fuel 4 and a mixture of Athabasca oil sands bitumen and Varsol.
Testing Procedure and Equipment
Agglomeration tests were carried out on a laboratory shaker, with 100 and 250 mL glass containers used as a reactor vessel. Preconditioned fine coke and bitumen were added to a sample of centrifuge tailings diluted with water to the desired pulp density. After shaking the jar for a preset time, the contents were screened and washed over a 60 mesh Tyler screen to recover the agglomerates.
Sub-samples of air dried agglomerates were further dried in an oven to determine the water content and then ashed at 500 °C to remove the organic matter in order to prepare the sam-ples for heavy metals analysis by ICP. In a few selected tests the slurry, remaining after the screening of coke-heavy metal concentrates, was centrifuged and dried in preparation for heavy metal analysis. These results were used to check mass balance closure.
A flow-diagram for the test procedure is presented in Fig-ure 1.
Test Results
A total of 10 standard agglomeration tests were conducted to agglomerate heavy metal minerals with coke and bitumen. Conditions were varied to determine conditions to produce a beneficiated, bulk mineral concentrate with high recoveries of the targeted minerals. Rejection of gangue materials in the centrifuge tailings was expected to increase the efficiency of subsequent separation of Ti and Zr by carbo-chlorination.
Test results indicated that both minerals agglomerated with coke and bitumen to produce concentrates with acceptable recoveries. A summary of these tests is shown in Table 2. Test 4 represents the best result obtained under nonoptimized agglomeration conditions. In this test a concentrate containing 25.5% TiO2 (15.3% Ti) and 1.2 % ZrO2 (0.9% Zr) was obtained. Recovery of Ti was over 90% and for Zr virtually 100%.
Conclusions
A series of agglomeration tests were carried out by NRCC and TMCL Engineering to determine the technical viability of using coke/bitumen agglomeration to collect Ti and Zr from oil sands centrifuge tailings to produce a concentrate suitable as feedstock for metal refining by direct carbo-chlorination. Based on the results of these preliminary tests it is concluded that:
1. In non-optimized tests, the Ti minerals in the oil sands centrifuge tailings were beneficiated by a factor of 2.5 to produce a concentrate containing approximately 25% TiO2 in the ashed product,.
2. It was also possible to beneficiate the Zr bearing minerals under tthe same conditions by a factor of nearly 4 to pro-duce a concentrate of approximately 1.9% ZrO2 in the ashed concentrate.
3. The recovery of both minerals was very high, being 91% for Ti and virtually 100% for Zr.
4. Only coke and bitumen addition levels were tested. It is expected that by optimizing other parameters, such as: pulp density, binder oil viscosity, agitation intensity and time and carbon type, higher concentration ratios for both metals and better recovery for titanium could be achieved. These tests clearly showed the technical viability of the agglomeration process. Optimized process conditions com-bined with a continuously operating multi-stage counter-cur-rent agglomeration system, should produce high concentra-tions of Ti and Zr minerals, in a hydrocarbon matrix. This mixture will be an ideal feedstock for a subsequent carbo-chlorination process for metal recovery.
Acknowledgement
The authors are grateful to V. Boyko for the analytical work.
References
1. Morgenstern, N.R., Fair, A.E., and McRoberts, E.C., Canadian Geochemical Journal, 1988, 25:637-661 2. George, Z. M.; Kessick, M.A., preprints 32nd Can Chem.
Eng. Conf. 1982, 712.
3. Koch G., Oil Week, August 21, 1995, page 14
4. Trevoy, L.W. proc. First Int. Conf. The future of heavy crude oils and tar sands, Edmonton Alberta, 1979, 698-702, R.F. Meyer and C.T. Steele Editors
5. Ityokumbul, M.T., Kosaric, N., Bulani, W. and Cairns, W. L., AOSTRA J. Research, 1985, 2, 59-66.
6. Kramers, J. W. and Brown, R.A.S., CIM Bull.1976, 92-99.
7. Majid, A., Sirianni, F.A. and Ripmeester, J.A., Canadian Patent No. 1,200, 778 (1985)
8. Majid, A. and Ripmeester, J.A., 3rd UNITAR/UNDP
Con-ference Proceedings, 1985, 1425-1438. Richard F. Meyer, Editor
9. Majid, A., Sirianni, F. A. and Ripmeester, J.A., Proc. 2nd
World Congress of Chem. Eng. 1981, 11, 434-437. 10. Majid, A., Ripmeester, J.A. and Kodama, H., Fuel, 1988,
67, 443-444.
11. Puddington, I.E., and Sparks, B.D.; Minerals Sci. Engng., 1975, 7(3), 282.
Abbreviations
ND Not Detected
ICP Inductively Coupled Plasma R&D Research and Development MDA Mineral Development Authority NRCC National Research Council of Canada
Table 1: Distribution of Ti and Zr in Various Size Fractions of Syncrude Centrifuge Tailings
Table 2: Summary Results for Agglomeration Tests
