Exploring the role of time-dependency in tailings deposition flows

Authors: Talmon, AM; Nabi, M; Meshkati, E Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2455_21

Cite As:
Talmon, AM, Nabi, M & Meshkati, E 2024, 'Exploring the role of time-dependency in tailings deposition flows', in AB Fourie & D Reid (eds), Paste 2024: Proceedings of the 26th International Conference on Paste, Thickened and Filtered Tailings, Australian Centre for Geomechanics, Perth, pp. 257-270, https://doi.org/10.36487/ACG_repo/2455_21



Abstract:
In the field of fluid dynamics, initial focus is often placed on steady flow conditions. However, an intriguing phenomenon emerges when we observe that flow behaviour in deposits can be time dependent. While the deposition of coarse particles might seem an obvious contributor to this phenomenon, it’s important to note that time-dependent flow also occurs in flocculated or coagulated, fine, non-settling materials. This prompts us to explore the possibility of time-dependency in homogeneous non-Newtonian fluids, considering two key aspects: changes in rheological properties and variations in fluid flow characteristics over time. An initial comparison by Talmon et al. (2023) of two different time-dependent rheology models revealed similar behaviour but also showed intriguing differences in numerical calculation of beach deposition’s straight channel flow, which demanded further investigation. We reveal the origin of differences, recalculate and converge results. These two models concerned reversible time-dependency, e.g. thixotropy. Rheomalaxis, e.g. irreversible time-dependency of rheological properties, will be addressed too. With shear thinning of tailings, deposition conditions appear prone to the development of surface waves. The flow conditions in open channel flow experiments and a tailings flume deposition trial are analysed by means of numerical fluid flow simulation (time-independent rheology) and indeed, surface level variations are calculated. This corresponds qualitatively with observed variation of plunge pool level and irregular flow. Tailings are flocculated to speed up dewatering. Our studies show that it is also necessary to quantify associated time-dependent rheological properties because flocculation highly influences deposition flow. Our calculations show that flocculation affects both the depth of streams as well as their velocity. In 3D, relating to earlier devised analytical channel formation theory (Talmon 2023), it may initiate pattern formation and affect run-out distances. Dedicated flocculation might be a way to influence and manage deposition; when we better understand the flow path of the material.

Keywords: tailings storage facility, rheology, thixotropy, rheomalaxis, computational fluid dynamics, free surface waves, validation

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