Previous loop testing (Furlan et al., 2013) performed at the GIW Hydraulic Laboratory, USA, demonstrated the ability of a conventional centrifugal slurry pump (impeller diameter, 0.31 m) to transport phosphate clay slurries with Bingham yield stresses up to 600 Pa without developing an unstable, backward-sloping head curve at lower flow rates, as had been observed and reported in earlier studies of high-concentration tailings slurries. The proposed explanation for this difference focused on the utilisation of a novel tank (sump) arrangement that facilitated effective removal of entrained air and prevented the onset of pump airlock. In the current study, this test has been repeated using a slurry with a typical tailings particle size distribution, having average and maximum particle sizes of 40 and 200 μm, respectively. Once again, when using the new tank arrangement, no backward-sloping head characteristic is observed, even at concentrations up to 51% by volume. The average reductions in head at 51% concentration were 1% and 6% when pumped at 1,700 and 1,200 rpm, respectively, and the corresponding reductions in efficiency were 18% and 25%. The rheological behaviour of the phosphate clay and the tailings slurries are compared at Bingham yield stresses and plastic viscosities in the range of 200 - 300 Pa and 0.05 - 0.06 Pa.s. Both slurries show similar reductions in efficiency, while the reductions in head are larger for the clay, which also shows a stronger dependence on pump speed. In further testing, a sealed tank arrangement was used to obtain measurements of net positive suction head required (NPSHR). Results at volumetric concentrations near 50% were within 20% of the corresponding clear water results. Finally, brief comparisons with previously published models for head and efficiency reductions are discussed in light of the experimental results.
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