Grinding media selection when ore hardness moves
Media chosen for last year's ore body is a slow, invisible cost when the feed changes.
Media selection tends to be settled once, early in a plant's life, and then inherited. That works while the feed is stable. As a pit deepens and the ore body changes, the assumptions behind the original selection quietly stop holding.
The two costs
Media that is too soft for the feed wears fast and consumption climbs — a visible cost that shows up in the media line of the budget every month. Media that is too hard fractures rather than wearing, and the fragments contribute nothing to grinding while still occupying mill volume. That cost is invisible; it shows up as throughput that never quite recovers.
The second is the more expensive of the two and the one most operations discover last.
How to tell
- Track media consumption per tonne milled, not per month
- Screen the mill charge occasionally and look at the size distribution — a tail of fragments indicates fracture, not wear
- Re-test work index when the pit moves into a new domain, not on a calendar
Media is a consumable, which means it is treated as a purchasing decision. It behaves much more like a process variable, and it is worth reviewing on that basis whenever the feed changes materially.
