Mineral slurries can have very complex rheology which may not be evident in bench-scale mixing tests. On scale-up to large industrial stirred tanks, an unexpected stagnant layer sometimes forms at the surface. We hypothesize that this occurs due to build-up of yield stress when the fluid is at rest. This behavior can cause problems on scale-up, where insufficiently mixed regions of the tank contain a much larger volume of fluid and the residence time in these regions can be much longer than at the bench scale. To study this effect, a method for continuous torque measurements was developed to quantify rest time effects at the bench scale. Nickel laterite slurries (NLS) with a broad range of solids concentration (25.2–71.8 wt%) were used to test this new method. Concentric cylinder viscometry and vane rheometry were also used to measure the behavior of the test sample. Evidence for a complex mechanism of network build-up for rest times of two minutes and longer was found. Moreover, it was found that 45 wt% is the upper limit for assuming behavior which approximates Newtonian rheology in this nickel laterite slurry sample. Solids concentration greater than 60 wt% showed rapid build-up of yield stress and thixotropic behavior. The rest time experiments validated the scale-up hypothesis. The slurry concentration at which non-Newtonian behavior appears is in accordance with other rheological investigations of nickel laterite slurries.

矿物浆料可能具有非常复杂的流变性，这在实验室规模的混合测试中可能并不明显。在扩大到大型工业搅拌罐时，有时会在表面形成意想不到的停滞层。我们假设这是由于流体静止时屈服应力的累积而发生的。这种行为可能会导致放大时出现问题，其中罐中混合不充分的区域包含大量的流体，并且在这些区域的停留时间可能比实验室规模长得多。为了研究这种影响，开发了一种连续扭矩测量方法来量化工作台规模的休息时间影响。具有广泛固体浓度（25.2-71.8 wt%）的镍红土矿浆（NLS）用于测试这种新方法。同心圆柱粘度测定法和叶片流变测定法也用于测量测试样品的行为。发现了两分钟或更长时间的休息时间网络建立的复杂机制的证据。此外，发现 45 wt% 是假设在该镍红土矿浆样品中近似牛顿流变学行为的上限。大于 60 wt% 的固体浓度显示出屈服应力和触变行为的快速积累。休息时间实验验证了放大假设。出现非牛顿行为的矿浆浓度与红土镍矿浆的其他流变学研究一致。