CIL carbon losses traced to the grinding circuit — a diagnostic case study

Carbon management problems in CIL circuits are rarely what they appear to be. This case study describes a plant with two persistent, seemingly unrelated problems — and the grinding circuit root cause that was hiding behind both of them.

A CIL plant I worked with had two persistent problems that nobody had managed to connect.

The first was excessive grit in the loaded carbon — a constant nuisance that was affecting elution performance and keeping the carbon handling team busy with problems that should never have existed. All efforts at solving it concentrated on the leach feed tramp screen.

The second was periodic crashes in the activated carbon inventory. Carbon was disappearing, and then slowly reappearing. Not all at once, but regularly enough to be a serious operational and financial headache. No-one had managed to figure that one out.

Two problems. Multiple investigations. No clear cause found.

When I looked at the grinding circuit, the answer was sitting there waiting.

The classification was poor — badly so. And periodically, surges of very coarse material were making their way through into the CIL circuit, causing excessive grit and a drop in slurry viscosity. The grit wasn't a carbon management problem. The vanishing carbon wasn't a carbon management problem. Both were grinding problems wearing a carbon management disguise.

The fix wasn't in the CIL circuit at all. Sort out the classification in grinding, and the carbon circuit recovers on its own.

This is a pattern worth remembering: in a processing plant, the loudest problem is rarely where the real problem lives. The CIL circuit was telling us something was wrong. The grinding circuit was the one causing it.

When a plant is misbehaving, don’t just concentrate on the apparent problem: widen the search upstream.