Authors: Costine, A; Benn, F; Fawell, P; Edraki, M; Baumgartl, T; Bellwood, J
Editors: Jewell, RJ; Fourie, AB
Conference: 21st International Seminar on Paste and Thickened Tailings, 11-13 April, Perth
Published: Australian Centre for Geomechanics, Proceedings of the 21st International Seminar on Paste and Thickened Tailings, pp.103-116, Perth
Tailings rehabilitation, using soil-like properties with chemical and physical stability, can be influenced by surface forces on a particle scale and microstructure. Non-homogeneous structures, manifesting as particle aggregation, alter the permeability/porosity and improve the balance of aerated and water-filled pores that then favours plant growth. Polymer flocculation in tailings thickeners yields large, weak aggregates that are sheared in beds and on pumping. While low-level residual structure may remain, sizes are small and downstream polymer impacts are minor. However, high polymer dosages added in-pipe to high-solids streams lead to further water recovery on deposition, and while this process is poorly understood, it gives aggregates that are likely denser and stronger. If such structures persist, they could potentially offer closure and rehabilitation benefits in some applications.
A high-solids (50 wt%) thickener underflow analogue (kaolin, silt, and fine sand) was treated with anionic polyacrylamide (PAM) polymers at elevated dosages (up to 1,000 g t-1) to establish if aggregate structures created during inline tailings flocculation survive or change over longer-term consolidation. Low and high molecular weight (MW) PAM polymers of fixed anionicity (30%) were tested. Focused beam reflectance measurement (FBRM) provided real-time monitoring of the aggregation state after polymer addition.
The compressibility of the inline flocculated tailings was assessed over an eight week period. Variations in the size–density relationship of aggregate structures were determined over this period using an image analysis technique, revealing that the shorter polymer chains produced denser, more compact structures immediately after deposition, whereas the longer chains resulted in a much slower re-conformation of the partially adsorbed polymer, leading to additional densification over time.
Eight weeks after deposition, inline flocculated tailings produced with the low MW polymer were characterised by a higher compressive yield stress compared with the high MW polymer, consistent with the formation of smaller, more rigid aggregate structures with the shorter chains. The potential impact of such structures on longer-term rehabilitation properties (e.g. metal/metalloid ion adsorption and surface exchange capacity) of the treated tailings is discussed.
Keywords: inline flocculated tailings, self-weight consolidation, polymer selection
Costine, A, Benn, F, Fawell, P, Edraki, M, Baumgartl, T & Bellwood, J 2018, 'Understanding factors affecting the stability of inline polymer-amended tailings', in RJ Jewell & AB Fourie (eds), Proceedings of the 21st International Seminar on Paste and Thickened Tailings
, Australian Centre for Geomechanics, Perth, pp. 103-116.
Adkins, SJ, Bellwood, J, Beveridge, A, Edgar, M & Flanagan, IA 2014, ‘Differences between secondary flocculation and rigidification via Rheomax®-enhanced tailings disposal technology', in RJ Jewell, AB Fourie, PS Wells & D van Zyl (eds), Proceedings of the 17th International Seminar on Paste and Thickened Tailings, InfoMine Inc., Vancouver, pp. 187–197.
Braunack, MV & Dexter, AR 1989 ‘Soil aggregation in the seedbed: a review. I. Properties of aggregates and beds of aggregates’, Soil and Tillage Research, vol. 14, no. 3, pp. 259–279.
Costine, A, Lester, D, Fawell, P & Chryss, A 2014, ‘Shear isn't mixing: how to build larger aggregates using chaotic advection for accelerated dewatering’, in RJ Jewell, AB Fourie, PS Wells & D van Zyl (eds), Proceedings of the 17th International Seminar on Paste and Thickened Tailings, InfoMine Inc., Vancouver, p. 644.
Costine, A, Cox, J, Travaglini, S, Lubansky, A, Fawell, P & Misslitz, H 2016 ‘Influence of polymer molecular weight in low and high solids tailings applications’, in S Barrera & RJ Jewell, (eds), Proceedings of the 19th International Seminar on Paste and Thickened Tailings, Gecamin, Santiago, chapter 4, paper 2.
Costine, A, Cox, J, Travaglini, S, Lubansky, A, Fawell, P & Misslitz, H 2017 ‘Variations in the molecular weight response of anionic polyacrylamides under different flocculation conditions’, Chemical Engineering Science, vol. 176, pp. 127–138.
Dexter, AR 1988 ‘Advances in characterization of soil structure’, Soil and Tillage Research, vol. 11, no. 3–4, pp. 199–238.
Farrow, JB & Warren, LJ 1993, ‘Measurement of the size of aggregates in suspension’, in B Dobias (ed.), Coagulation and Flocculation – Theory and Application, Marcel Dekker, New York, pp. 391–426.
Fawell, PD, Costine, AD & Grabsch, AF 2015, ‘Why small-scale testing of reagents goes wrong’, in RJ Jewell & AB Fourie (eds), Proceedings of the 18th International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 153–165.
Finn, MD & Thiffeault, JL 2007, ‘Topological entropy of braids on the torus’, SIAM Journal on Applied Dynamical Systems, vol. 6, no. 1, pp. 79–98.
Finn, MD & Thiffeault, JL 2011, ‘Topological optimization of rod-stirring devices’, SIAM Review, vol. 53, no. 4, pp. 723–743.
Grabsch, AF, Fawell, PD, Adkins, SJ & Beveridge, A 2013, ‘The impact of achieving a higher aggregate density on polymer-bridging flocculation’, International Journal of Mineral Processing, vol. 124, pp. 83–94.
Happel, J & Brenner, H 1973, Low Reynolds Number Hydrodynamics, Noordhoff International Publishing, Leyden.
Heath, AR, Fawell, PD, Bahri, PA & Swift, JD 2002, ‘Estimating average particle size by focused beam reflectance measurement (FBRM)’, Particle & Particle Systems Characterization, vol. 19, no. 2, pp. 84–95.
Hogg, R, Lutsky, M & Suharyono, H 1995, ‘A simulation model For thickening of flocculated, fine-particle suspensions’, in JA Herbst (ed.), Proceedings of the XIX International Mineral Processing Congress – Physical & Chemical Processing, vol. 2, Society for Mining, Metallurgy & Exploration, Englewood, pp. 81–86.
Horn, R & Smucker, A 2005, ‘Structure formation and its consequences for gas and water transport in unsaturated arable and forest soils’, Soil and Tillage Research, vol. 82, no. 1, pp. 5–14.
McColl, P & Scammell, S 2004, Treatment of Aqueous Suspensions, WO 2004/060819.
Mizani, S, Soleimani, S & Simms, P 2013, ‘Effects of polymer dosage on dewaterability, rheology, and spreadability of polymeramended mature fine tailings’, in RJ Jewell, AB Fourie, J Caldwell & J Pimenta (eds), Proceedings of the 16th International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 117–131.
Owen, AT, Fawell, PD & Swift, JD 2007, ‘The preparation and ageing of acrylamide/acrylate copolymer flocculant solutions’, International Journal of Mineral Processing, vol. 84, pp. 3–14.
Poncet, F & Gaillard, N 2010, Method for Treating Mineral Sludge Above Ground Using Polymers, US Patent Application No. US2010/0105976.
Reid, D & Fourie, A 2016, ‘Laboratory assessment of the effects of polymer treatment on geotechnical properties of low-plasticity soil slurry’, Canadian Geotechnical Journal, vol. 53, pp. 1718–1730.
Thermo Haake GmbH 2017, RheoWin Pro, Thermo Haake GmbH, Karlsruhe.
Usher, SP, De Kretser, RG & Scales, PJ 2001, ‘Validation of a new filtration technique for dewaterability characterization’, AICHE Journal, vol. 49, no. 7, pp. 1561–1570.
Watson, P, Farinato, R, Fenderson, T, Hurd, M, Macy, P & Mahmoudkhani, A 2011a, ‘Novel polymeric additives to improve oil sands tailings consolidation’, Proceedings of the SPE International Symposium on Oilfield Chemistry, Society of Petroleum Engineers, Richardson, pp. 703–709.
Watson, P, Fenderson, T, Mahmoudkhani, A, Nair, M, Patel, A & Roberts, G 2011b, ‘Breakage and reformation of flocs in oil sands tailings slurries’, Proceedings of Tailings and Mine Waste 2011, InfoMine Inc., Vancouver, 10 p.
Wells, PS, Charlebois, L, Diep, J, Moyls, B, Omotoso, O, Revington, A & Weiss, M 2015, ‘In-line flocculation’, in RJ Jewell & AB Fourie (eds), Paste and Thickened Tailings – A Guide, 3rd edn, Australian Centre for Geomechanics, Perth, pp. 229–241.