Grinding & Classification Circuits

Grinding & Classification Circuits 2017-04-04T06:57:16+00:00
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Optimum SAG Mill Discharge Density (12 replies)

Subhash-Kumar-Roy
1 year ago

In a grinding circuit, is there any relationship between SAG mill % solids and P80 (SAG mill product)? And what is the optimum % solid for sag mill?

Sudhirkumar
1 year ago
Sudhirkumar 1 year ago

P80 sag mill product is the 80 % passing particle size in sag mill discharge SAG mill solid. I am not clear about this word.

Subhash-Kumar-Roy
1 year ago

P80 sag mill product is the 80 % passing particle size in sag mill discharge is true, and about solid, I mean solid content of ore(%) in sag mill(mass of dry ore/(mass of dry ore+mass of water)

Sturmbann
1 year ago
Sturmbann 1 year ago

As % solids increases the P80 from the SAG mill decreases. You can use this to balance the load between the SAG mill and ball mill, if necessary.

Subhash-Kumar-Roy
1 year ago

Thank you for your response. I have another question, what is the optimum % solid in Sag mill. I have two suggestions from two technologist, 52 % and 60 %, which of them is better for Sag mill operation?

Sturmbann
1 year ago
Sturmbann 1 year ago

The optimum % solid depends on the material and rheology.If you want high throughput and a coarse product size you can run at <65% solids (assuming a hard rock feed with ore SG 2.7). If you want a fine product, you can run at densities approaching 75% solids, sometimes higher. For Cu porphyry we would use about 72% solids for design

Marshal Dienes
1 year ago
Marshal Dienes 1 year ago

Back to your comment on load balancing between SAG and Ball Mill in a circuit:

With SABC circuits the capability exists to ensure we are using the available power in the SAG, Ball Mill, and Pebble Crusher by controlling operating variables for each sub-circuit.

If you map the SABC circuit - showing process and variables for main process and each of the sub processes it is possible to identify response variables which can be used to monitor circuit performance and control variables which can be used in the short (real time) and longer term (e.g., SAG mill and pebble crusher liners).

% solids are a relatively easy to change variable useful for controlling this balance as ore characteristics change. Risk at higher % solids for SAG mills is packing of ore between liners.

Maya Rothman
1 year ago
Maya Rothman 1 year ago

How important and efficient really is SAG discharge density for load balancing? What if I have a single stage SAG mill? Can it be used as a reliable control tool (SSAG or not)? Or are there other better and more efficient ways to balance load? Any attempts to balance load via density control will go through a transient region and this may be seen as the ultimate balance by the operator unless enough time is allowed for the new balance to be established (if it works). If percent solids are high enough (for example high 70%s - 80%) and the ore has a lot of clay in it then there is a strong chance that packing will be an issue. But then again this depends on the spacing between lifters in a way. Therefore it is hard to make definitive calls without making generalised comments. 72% density is a good midway point around which to discover the best operating density point for your mill.

Marshal Dienes
1 year ago
Marshal Dienes 1 year ago

No worry on the 72 % as an initial point. Mill % solids provide a quick control variable. In the longer term it may be more useful to change some of the variables which are more difficult to change, e.g., SAG discharge screens, pebble ports, etc.

Your comment re generalization is spot on - some details of the circuit, ore, and process behaviour assist in setting bounds to experiment around. It's definitely critical to consider ALL the control variables we have available.

Hauptsturm
1 year ago
Hauptsturm 1 year ago

Thanks for your practical question; It was a kind of my question which was answered by other friends.But there is a point here, is there a direct relation between increasing solid% and decreasing P80%, or it has a optimum point and after a specific solid% it start to decrease? (In SAG mill)

Sandeep Bisht
1 year ago
Sandeep Bisht 1 year ago

Till now no one has talked about mineral to be ground. Are above discussions and values are same? For grinding Talk, Lime, Mica, Asbestos, etc.

Your question is for technical words and not range. You asked what is the difference between Sag mill solids and P80(Sag mill product.): You being a mineral engineer should not get this doubt. Confirm again your doubt if it is not same as above.

Marshal Meru
1 year ago
Marshal Meru 1 year ago

You will need to graph the SAG running at different densities to determine what your ore will do. P80 Vs. Grind at %solids at "X" TPH. There is a 'general' relationship. Your ore, lifter design, pebble size, pebble port size, classification in your stockpile, etc. will all have an effect, Higher densities result in longer retention, (more time to grind) prevent pooling (to a point) by allowing the pulp lifters to remove material - pooling results in low energy impacts- Low densities wash the fines and scats from the mill. Get to low and liners take a beating. To high and you get packing between the lifters, low lift, low energy grinding, etc. As noted, without all the info on the circuit and ore only general relationships can be discussed.

Sandeep Bisht
1 year ago
Sandeep Bisht 1 year ago

Relation between Sag mill solid and product P80!

Both are dependent on feed size. Dependent on Volume % solids in SAG mill. Dependent on ball charge volume. Hardness of ore. Recirculation load. Dependent on P80% size

All other parameters are secondary. In general Sag mill solids are kept at 70% by wt. Operating grinding circuit is an art. You can change several parameters to attain the targeted size. Any manual control will lead to inefficient grinding. Permutations and combinations of all above variable operating parameters play a major role. You need to experience it by yourself for your ore. Each parameter needs to be optimised. 

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