Authors: Boshrouyeh Ghandashtani, M; Edraki, M; Costine, A; Baumgartl, T

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Boshrouyeh Ghandashtani, M, Edraki, M, Costine, A & Baumgartl, T 2021, 'Investigation of geotechnical, hydromechanical, and chemical behaviour of polymer-treated tailings', in AB Fourie & D Reid (eds), Paste 2021: 24th International Conference on Paste, Thickened and Filtered Tailings, Australian Centre for Geomechanics, Perth, pp. 79-90,

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This study investigated the properties of flocculated materials formed in a laboratory-scale inline flocculation setup at a high solid concentration of artificial tailings. Water scarcity and the willingness of using seawater in mineral processing where access to fresh water is limited highlights the importance of understanding the salinity effects on the tailings treatment processes. To better understand the inline flocculation technique for enhanced water recovery from fine-particle suspensions, this paper studied the impacts of two typical salts, NaCl and CaCl2 on the geotechnical, hydrological, hydromechanical, and chemical behaviour of polymertreated synthetic tailings slurry using a low-shear mixer for continuous flocculation under controlled conditions. A standard consolidation test was used to investigate the differences in geotechnical properties and functions between the raw and polymer-treated tailings in presence of added salt. Increasing the calcium concentration was more adversely impacted by the low molecular weight (MW) copolymers in producing aggregates with lower water recovery and turbidity and gave the greatest zeta potential compared to other polymer chemistry. Among the polyacrylamide/polyacrylate copolymers, Magnafloc® 5250 flocculant responded more effectively at the low CaCl2 salinity by producing higher zeta potential and fast realising of the less turbid water compared to that of NaCl. Greater compatibility between the high NaCl salinity with the high MW copolymer was also exhibited in terms of facilitating the polymer chains activities to create stronger aggregates. The saturated hydraulic conductivity of samples was evaluated, and the pore size distribution was analysed by determination of the water retention characteristics of the materials. Results indicated a significant difference in geotechnical and hydrological properties between the untreated and polymer-treated slurries, including: (i) a higher void ratio for the polymer-treated samples containing CaCl2; (ii) different patterns of settlement under the applied vertical stress during consolidation of the specimens; and (iii) 40% more free water drainage from samples salted with CaCl2 and treated by adding polymer. The results are discussed in light of the contribution of the polymer treatment to improved rehabilitation outcomes and the role geotechnical, hydromechanical, hydrological and chemical properties play to achieve this goal.

Keywords: inline flocculation, dewatering rate, consolidation, aggregates microstructure, water recovery, salinity

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