The Impact of Slurry Viscosity on Zirconia Grinding Beads

In the world of mineral processing, the choice of grinding media can significantly affect the efficiency of the grinding process. In this context, we focus on the use of zirconia grinding beads and how slurry viscosity plays a crucial role in their performance.

Introduction

The grinding beads employed in our experiments are made of zirconia, with a measured bulk density of 3600 kg/m³. These beads are utilized in all grinding tests, with a consistent fill rate of 60% and a slurry concentration of 40%. The variables under investigation include the diameter of the grinding beads and the stirring speed, as outlined in Table 1.

The Influence of Slurry Viscosity

Slurry viscosity represents the resistance encountered by the grinding beads during motion. Figure 4 illustrates the changes in slurry viscosity under different conditions of grinding bead size and stirring speed.

Overall Trends

Generally, as more energy is introduced into the system, the particle size of the ground product becomes finer, and the slurry viscosity steadily increases. This phenomenon follows a discernible pattern: as the input energy continues to rise, there is a rapid escalation in viscosity. This increase in viscosity is directly linked to the heightened resistance encountered by the grinding beads during their motion. Consequently, the grinding bead movement slows down, leading to a decrease in grinding efficiency. This decrease is likely the reason for the diminishing utilization of energy throughout the grinding process.

As more energy is introduced, the product's particle size decreases, and slurry viscosity increases. Furthermore, with sustained energy input, the trend of increasing viscosity accelerates.

Understanding the Grinding Mechanism

A stirred mill comprises a stirring shaft, impeller, and a grinding chamber. During the rotation of the stirring shaft, the impeller propels the grinding beads into active motion. Various forms of forces, including impact, shear, and friction, are responsible for breaking down the material. At an equal media fill rate, the size of the grinding beads determines their quantity within the grinding chamber. The number of grinding beads, in turn, significantly influences the effective grinding frequency within the chamber. It is generally accepted that the size of the grinding beads should be positively correlated with the particle size of the raw material. Further research suggests that zirconia bead size should be at least 20-30 times the particle size of the material or, in cases where the material contains less than 74μm particles in an 80% proportion, 2-4mm grinding beads should constitute 70%-80% of the total fill.

Stirring speed is another crucial factor affecting grinding performance. Higher speeds result in more active motion of the grinding beads, increasing the number of effective grinding events per unit time and, consequently, the grinding rate. Moreover, slurry properties such as viscosity can influence the state of motion of the grinding beads. Excessively high slurry viscosity can hinder the interactions between the grinding beads.

In conclusion, the choice of zirconia grinding beads, their size, and the stirring speed are critical factors in optimizing grinding efficiency. Understanding the impact of slurry viscosity and other variables is essential for achieving the desired grinding outcomes in mineral processing applications.

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