In a previous article, Correlating Yield Stress with Pumpability of Mining Tailings, we discussed the fact that in order to understand if a (modified) tailing can be pumped with the existing pumping equipment, not just the viscosity needs to be determined but also the yield stress. The yield stress describes the amount of energy needed to overcome elastic behaviour for a given fluid and enter sustainable flow. Here is a summary of the procedure and results of a rheological test conducted to evaluate the pumpability of specific tailings:
As soft solids and slurries like tailings are often difficult to work with when using conventional parallel plate or coaxial cylinder geometries on rotational rheometers (due to possible wall slip and excessive sample disruption during sample loading into narrow gaps), vane geometries were recommended.
When a vane rotor is fully immersed in the sample, the yield stress itself can then be calculated according to Boger*: [a]
with M being the Torque and K the vane parameter that depends on the height (H) and the diameter (D) of the paddle according to:
Thus, in order to determine the yield stress the Torque (or corresponding shear stress) needs to be tracked as a function of time. The maximum value can then be calculated into the yield stress.
We recommend to rheologically test tailings with vane rotors to prevent wall slip. For this study, sand mine tailings have been tested at different solid mass fractions so that a yield stress vs. mass fraction map could be derived later.
- The test was conducted with a 0.4 solid mass fraction tailing.
- A range of sand mine tailings with different solids mass fractions ranging from 0.2 to 0.5 were tested.
With the data derived from a short series of tests, the pumpability of a specific tailing can then be easily predicted by calculating the needed pumping pressure in bar via the cross-section of the pipe and the yield stress. We concluded that the vane rotor method on the viscotester rheometer is a quick, simple and accurate approach to measure the yield stress of mining tailings. Those values can then be easily correlated with the pumpability of a specific tailing formulation with given solids mass fraction.
For more details, including references,flow curves, test charts, and product details, see Correlating Yield Stress with Pumpability of Mining Tailings. Editor’s Note: *Dzuy N.Q., Boger D.V. (1985). Direct yield stress measurement with the vane method. J Rheol 29:335-47.