Moisture for comminution: the optimum moisture content in solids to be crushed or ground typically ranges within which percent band?

Introduction / Context:
Moisture content has a strong influence on size reduction. Too little moisture can increase dust and reduce nip; too much moisture causes coating, chute plugging, and reduced screening efficiency. There is an "optimum" band that aids dust control without impairing breakage.

Given Data / Assumptions:

• General-purpose crushing and dry grinding circuits.
• Moisture’s role limited to handling and nip—not slurry grinding.

Concept / Approach:
A small amount of moisture improves fines agglomeration enough to reduce airborne dust and can improve gripping (nip) in certain crushers. Beyond a few percent, materials begin to cake and adhere to liners and media, drastically reducing throughput. Standard practice cites a narrow optimum around a few percent for dry crushing/grinding.

Step-by-Step Solution:
Balance dust suppression vs. caking.Select the smallest band that represents typical optimum for dry comminution: 3–4%.

Verification / Alternative check:
Operating manuals and handbooks commonly warn that > 5–6% moisture in many ores impairs screening and promotes chute build-up; conversely < 1% can be too dusty.

Why Other Options Are Wrong:
8–20%: suitable for wet grinding/slurrying, not for dry crushing-grinding circuits.

Common Pitfalls:
Confusing optimum moisture for dry circuits with the solids content used in slurry grinding (often 60–75% solids by mass).

Final Answer:
3 to 4