Rod mills: identify the correct set of characteristics that describe common rod mill geometry, handling capability, and media configuration in industrial grinding circuits.

Introduction / Context:
Rod mills provide selective grinding with reduced fines relative to ball mills, making them useful ahead of classification or when minimizing slimes is critical. Understanding their geometry and operating niche guides appropriate equipment selection for ores prone to overgrinding or stickiness.

Given Data / Assumptions:

• L/D for rod mills typically falls between about 1.5 and 3.
• Rod charge consists of long steel rods, usually 2–12 cm in diameter.
• Line contact between rods can help process feeds that would foul in ball mills, aiding sticky material handling.

Concept / Approach:
Rod mills grind primarily by line contact and cascading, producing a more uniform product with fewer fines for a given top size. Their geometry favors axial mixing and mitigates tangling when properly charged and operated. This makes statements (a), (b), and (c) simultaneously correct.

Step-by-Step Solution:
Check geometry: L/D ~1.5–3 is consistent with design practice.Check application: rod mills are often used where slimes are undesirable and where some stickiness exists.Check media: long rods extending near shell length is standard loading practice.

Verification / Alternative check:
Design manuals and OEM sheets depict rod mills with these characteristics, especially in AG/SAG-ball-rod flowsheets or as tertiary regrind units where fines control is critical.

Why Other Options Are Wrong:
Each single statement is correct but incomplete. Only the combination “All (a), (b) & (c)” captures the full description of common rod mill features and use cases.

Common Pitfalls:
Overfilling rod mills can cause rod tangling; maintaining correct % filling and rod length distribution is necessary for stable operation.

Final Answer:
All (a), (b) & (c)