Particle Aggregation and Dispersion Effect on Mineral Slurry Yield Stress
Mineral slurry yield stress is an extremely important parameter used in pumping calculations. The slurry mineral particles aggregation and dispersion states alter the yield stress values. In mineral slurry pumping the state of aggregation and dispersion can be modified by two agents:
A) Chemical and Biochemical Agent
- By dispersing or coagulating reagent addition
- By system chemical reactions
- By biological agents means
Dispersing reagents break down agglomeration of particles containing entrapped water, this water becomes part of the carrier by decreasing the flow stress, on the other hand, the coagulating reagents act to form new agglomeration of particles, imprisoning water and increasing the yield stress as shown in Figure 2.
Figure 2 - Coagulant effect on the dispersed slurry yield stress
B) Physical Agent
- Slurry shearing is an intrinsic process to coagulated slurries pumping. It causes particle agglomerate ruptures that releases imprisoned water to the vehicle, thus reducing the yield stress, as shown in figure 3. Shearing occurs more sharply in localized points than centrifugal pumps and orifice, as shown in figure 4A and less strongly along of the duct, as shown in Figure 4B.Figure 4 - Shearing effect - (A) Intensive shearing in Pumps and Valves, (B) Moderate shearing along the pipe.
The state of aggregation and coagulation of the slurries, the shear effect are evaluated in a judicious way in the Ausenco laboratory, through tests developed by Ausenco, which simulate the pumping of the slurries, providing accurate and reliable design results.
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