Tailings beach slopes as a dimensionless parameter of non-Newtonian flows

Abstract

The application of highly thickened tailings technologies is rapidly increasing due to the perceived benefits with respect to reduction of environmental impacts, water saving and potential reductions in dam size and impoundment footprint. Evaluation of these potential benefits requires that during design stages an understanding is developed of the range of feasible beach slopes to be achieved during deposition. A comprehensive evaluation of the operational factors influencing the beach formation process is paramount to ensure that expected performance during design stages is met throughout operations. This paper presents the derivation of a dimensionless parameter for non-Newtonian flows, associated with sheet flows on an inclined plane, which directly relates to the tailings beach slope expected to be formed due to subaerial disposal. This dimensionless parameter provides a closed expression for estimating tailings beach slopes based on rheological properties and discharge rates considering that sheet flow mechanisms occur. Conditions for sheet flow occurrence, such as level of further dewatering of the beach after deposition, active discharge times and geometry of active discharge areas, can be derived within this formulation. The dimensionless parameter and conditions found to promote sheet flow also allow to address the advantages and limitations of different discharge operation strategies, such as operating the tailings facility by sectors (allowing drying cycles) of varying geometries. Evaluation of this approach in the light of case histories is presented. Finally, discussion on how to evaluate the potential of having concave tailings beach profiles within this formulation is provided.

Integrating Site Conditions, Rate of Rise and Deposition Sequence to Beach Slope Estimations for High Thickened Tailings

“…The key concept is: Promoting a thin layer deposition scheme with drying cycles is an additional tool for having steeper beach slopes, along with increasing the tailings thickening and the discharge rate division using multiple spigots. So the integrated approach for estimating beach slope proposed is 1) first evaluate if this type of deposition scheme is possible (available area, morphology, climate) with this paper, and 2) If this is possible, you should estimate a range of beach slopes with a sheet flow based model, like Errazuriz (2018).…”

“…Each model works properly with their own assumptions, presenting consistent validation with experimental data. Li (2011) and Errazuriz (2018) assume that given a thin layer deposition scheme with drying cycles (i.e. multiple sectors for discharge), a layer by layer flow can be developed, where self-formed channel is almost plane, so called sheet flow 1 .…”

“…includes explicitly the effect of the discharge rate). The sheet flow approach by Errazuriz (2018) was verified using the data from two TMF operation (full scale) where the principle of thin layer deposition scheme with drying cycles were applied. One of them being a large production tailings operation ~100 ktpd.…”

“…In case of sheet flow ruling the tailings beach formation, it is possible to evaluate having more spigots with less separation (it is convenient having more sectors in less area, when available area for the TMF is restricted), because sheet flows should not be sensitive to coalescing processes, as the hydraulic radius is the flow height, that only needs a truly plane surface, i.e. less erodible dried tailings facing gentle tailings flow only during Top (Errazuriz, 2018, also providing equations for flow width estimation).…”

“…the rate of rise) and tailings deposition sequence (sectorized discharges and drying cycles), to the common rheological (level of thickening) and discharge rate considerations (number of multiple spigots). The sheet flow formulation for tailings and beach slope estimation model presented by Errazuriz (2018) along with a mass balance allow to develop a basic model for estimating proper TMF area, number of sectors, discharge time per sector and maximum rate of rise to implement a thin layer deposition scheme with drying cycles, promoting enough desiccation of tailings as a tool for managing the occurrence of sheet flows.…”