Coarse grinding using a lab rod mill - Grinding & Classification Circuits - Metallurgist & Mineral Processing Engineer

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Coarse grinding using a lab rod mill (3 replies and 2 comments)

tony.difeo@nrcan-rncan.gc.ca

1 year ago

I have to grind a ore sample (1 kg at -6 mesh) to 80% passing 300 microns using a lab rod mill. However, I am getting inconsistent results. For a set time to achieve 300 microns determined from the grind curve, sometimes I get finer than 300 microns and other times it is coarser. For the same grinding time I also get 80% passing 300 microns. I am puzzled. For a given grind time the mill should provide the same grind size. However, in my case, the 80% passing differs. Any thoughts?

Jorge

1 year ago

Jorge 1 year ago

1 like by David

I think, the feed material is not consistent. Is it the same ore source? A grind calibration curve is still BWI dependent and will vary based on the source.

Alternatively, You can consider a narrow grind time to build the grinding curve. The reference time could be the estimated time from the usual grinding curve.

Other thing to evaluate is the feed material, perform the PSD using different samples. Sometimes, there is an error during sample preparation.

tony.difeo@nrcan-rncan.gc.ca

1 year ago

Thank you

David

1 year ago

David 1 year ago

Hi Tony,

a fresh Grind Calibration Curve https://redesign.911metallurgist.com/blog/grind-calibration-curve is required for each "ore type". It is not generic. The Grind Calibration Curve is still related to the BWi Bond Work Index of each ore type.

tony.difeo@nrcan-rncan.gc.ca

1 year ago

Thank you. We are using charges from the same ore sample

David

1 year ago

David 1 year ago

Hi Tony,

in that case, I would review every detail:

Has sample splitting of the crushed product been done to 'perfection'.
Is the screen/sieve analysis (on the crushed and ground products) done beginning with a wet screen wash at 400 mesh? Not doing wet screening wash will introduce data variations.
There are no holes in any of the screens.
The %solids/water used in grinding is the same every time.

If the ore charge is truly the same, the procedure should be repeatable -- unless there is a hidden flaw/inconsistency.

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