Grinding & Classification Circuits

Grinding & Classification Circuits

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Cyclone or Pre-leach thickener (2 replies)

5 months ago
ManUtd67 5 months ago

Interested in opinion on whether to install a pre-leach thickener ahead of a gold leach circuit or operate cyclone at higher density.

Option 1 - Cyclone O/F at 35% solids, P80 75um.  Thicken to 65% solids and dilute with tails thickener O/F (cyanide recovery) and leach at 50% solids.

Option 2 - Cyclone O/F at 42% solids, P80 75um. Leach at 42% solids.

Both circuits have a tails thickener for cyanide recovery.  Option 1 has 2 water circuits, cyanide free (milling make-up) and cyanide water. Tails U/F at 60% solids is diluted to 50% solids with decant return ahead of detox.

Removing pre-leach thickener saves capex and opex but requires milling in cyanide, lower density leaching (larger tanks), less efficient classification in cyclones.  Will running at 42% solids O/F cause issues with achieving grind size consistently?

Comments, opinions, experiences appreciated.

5 months ago
SmartDog 5 months ago

Part of the answer is in your question, running the cyclones at a higher density will lower the cyclone efficiency, especially allowing more oversize material to the leach circuit giving a coarser grind, and a potential for higher gold losses to tails.  This will lead to greater opex (lower recovery at same expenditure).  If you can afford the gold loss and are capital poor the second option might sound good, but what is the impact on total (from mine to tails) capital costs of the first option, is it really worth a potential 5 to 10% (or higher) gold loss?

rob riggir
5 months ago
rob riggir 5 months ago


It is better to go with the preleach thickener as long as you have the project life to get payback.

You will then be able to operate your mills and cyclones at optimal densities and increase tank leach times. This will result in an improved gold recovery or the ability to increase the mill throughput with the original recovery.

I did the above in NZ a while ago and it worked a treat!



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