Wennberg, T, Stålnacke, A & Sellgren, A 2023, 'Loop pumping tests of crushed rock mixed with thickened tailings', in GW Wilson, NA Beier, DC Sego, AB Fourie & D Reid (eds), Paste 2023: 25th International Conference on Paste, Thickened and Filtered Tailings
, University of Alberta, Edmonton, and Australian Centre for Geomechanics, Perth, pp. 554-566, https://doi.org/10.36487/ACG_repo/2355_41
LKAB operates three mines in northern Sweden, where the climate is subarctic with an average temperature of about 0oC. LKAB’s long-term overall objective includes feasibility considerations of thickened or filtered tailings combined with waste rock co-disposal covering cyclic economy considerations and landscape forming. At the Kiruna underground mine, about 3.5 Mtonnes of tailings and 12 Mtonnes of waste rock are generated annually. Crushing to less than 30 mm is part of the sorting plant processing, and the rock is deposited in stockpiles while the tailings are pumped conventionally to water-holding impoundments.
The aim is to indicatively test the pipeline pumping of paste-rock mixtures at solids concentrations by weight of over 85% to limit segregation and leakage during deposition in nearby old pit holes. A test was carried out at a paste thickener with direct access to fresh paste, which was mixed in a concrete mixer with crushed rock from the processing. A 38 m long loop with a pipeline inner diameter of 0.075 m was equipped with a concrete type of pump. Unfortunately, a second test in a larger pipe could not be carried out at the planned time. LKAB then had the opportunity to test a laboratory-scale concrete industry device, the sliding pipe rheometer, Sliper, developed to simulate concrete pipeline pumping frictional resistance in a 0.126 m diameter pipeline. Initial loop results with crushed rock particles of up to 10 mm with a rock-to-paste mass ratio R:P of 1.2:1 showed a pressure requirement of about 25 kPa/m at 0.7 m/s for a total solids content of 84% by weight corresponding to 65% by volume and a water content of 19% (Solids density 3000 kg/m3).
The 10 mm product loop pressure results agreed relatively well with simulated Sliper data scaled to 0.075m from 0.126 m for Cw 85-86% and R:P of up to 2.6:1 at 0.7 m/s. The 30mm Sliper result at 89% indicated a pressure requirement of 14 to 24 kPa/m at 0.7 m/s for R:P of 2.6:1 and 3.5:1, respectively. With a 0.15 m diameter pipeline, a pumping requirement of 20 kPa/m at 84% and 0.7 m/s was also discussed regarding feeding requirements.
The results form the basis for a planned larger-diameter test. Long-term flexibility factors related to tailings availability and clarification of suitable routings and allowed water contents may necessitate that the wider diameter loop test includes a limited once-through pipeline pumping demonstration feeding arrangements. Variations in the rock-to-tailings ratio related to tailings availability and disturbances can be investigated. The system feasibility for filling depressions may cover a concentration span starting from about 75% by weight which means a more stratified flow where the coarsest particles form a sliding bed.
Keywords: paste-rock pumping, loop test, high concentration, particle stratification
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