Crushing stage identification: feed 100–300 mm reduced to product 10–50 mm corresponds to which stage of crushing?

Introduction / Context:
Comminution circuits are divided into stages according to size ranges. Correctly labeling a reduction step helps in selecting appropriate crushers and screens and in estimating power and wear.

Given Data / Assumptions:

• Feed size: 100–300 mm (typical product of primary crushers or run-of-mine with scalping).
• Product size: 10–50 mm.

Concept / Approach:
Primary crushers accept large lumps (0.5–1.5 m) and deliver products often in the 100–300 mm range. Secondary crushers then reduce this to 10–50 mm. “Fine” or “tertiary” crushing targets a few millimetres or less; “ultrafine” is in the micron range and belongs to grinding, not crushing.

Step-by-Step Solution:
Map size ranges to stages.100–300 mm → input compatible with secondary duty.10–50 mm → typical secondary product.Therefore, this step is secondary crushing.

Verification / Alternative check:
Flowsheets in aggregates and minerals show jaw (primary) → cone/roll (secondary) → screening to 10–40 mm products.

Why Other Options Are Wrong:
Primary: would start from much larger ROM sizes.Fine/ultrafine: refer to much smaller products, achieved by tertiary crushing or milling.

Common Pitfalls:
Using crusher names (e.g., “cone”) as proxies for stages; the same machine type can serve different stages at different sizes.

Final Answer:
secondary