Trommel screens separate a mixed particulate feed primarily on the basis of which material property?

Introduction / Context:
Trommels are rotating cylindrical screens widely used in mineral processing, waste sorting, and aggregates. Understanding the separation criterion is essential for selecting screen aperture and rotational parameters.

Given Data / Assumptions:

• Trommel comprises perforated or meshed cylinders.
• Particles are classified as they pass through openings.
• No dense media or fields are applied.

Concept / Approach:
Screening devices, including trommels, perform size classification. Particles smaller than the aperture size pass through; oversize advance with the drum. Density, wettability, and electrical/magnetic properties are relevant to other separation methods (e.g., gravity, flotation, electrostatic/magnetic), not trommel screening.

Step-by-Step Solution:
Identify trommel as a screen (rotating).Recall screening criterion: geometric size relative to aperture.Select “Size.”

Verification / Alternative check:
Process flow diagrams annotate trommels as classifying screens; design equations relate capacity to aperture, length, and inclination—reinforcing size as the basis.

Why Other Options Are Wrong:
Density: gravity separators.Wettability: flotation.Electrical/magnetic: specialty separators.

Common Pitfalls:
Assuming rotating equipment implies centrifugal separation; in trommels the rotation primarily advances material and promotes screening.

Final Answer:
Size