Grinding & Classification Circuits

Grinding & Classification Circuits

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Ball mill feed quality variations and effect on amount of output (2 replies)

O
hovan
7 years ago
hovan 7 years ago

Greetings there,

I work at a phosphoric acid plant where we have a ball mill. Recently the mill has not been producing enough output, this is due to not being able to increase amount of ore going into the mill as air circuit temperature is dropping, vacuum not holding, and mill motor amp reduction (coating). One of the main factor has been humidity, but another major factor which I am having trouble understanding is ore softness (variation in silica content?). Kindly help me get more insight on the matter and what other factors could be included that I have not mentioned?

Also what possible ways are there to increase productivity of the ball mill, (do grinding aids have a major effect?). And is there a charge distribution effect which is leading to coating of the balls by electrostatic charges?

Would appreciate and additional info, Thank you for your time. 

Alex Doll
7 years ago
Alex Doll 7 years ago
1 like by David

It sounds like you have a dry ball mill with hot air as the fluidizing agent.  Is the mill in closed-circuit with a classifier, or is it a single-pass unit?  Also is the mill an end-grate discharge?

 

I suggest you 'benchmark' the mill two ways: First do a specific energy comparison where you determine what specific energy (or the work index) of the ore should be by laboratory testing, then measure the actual specific energy (or operating work index) of the mill. If the two are similar, then the ore isn't the problem.  Second, do a power draw calculation (such as Nordberg) where you predict what the mill power draw should be for your mill's geometry (power will be relative to the pinion).  Then compare that to your motor's actual power draw (remember to multiply the motor power by the motor's efficiency).  If the actual draw is less than the predicted, then start looking at the internals of the mill (liner configuration, discharge grates, etc.).  See here: https://www.911metallurgist.com/blog/ball-mill-design-power-example-calculation

 

I've never seen any value in grinding aids, but your application is a different chemical regime to the minerals I normally work with.

A
MineralFrothFlotation
7 years ago

Dear Hovan ,

Are you having a hot air generator  in the grinding circuit if so just try to operate it at earlier temperature when mill was running smoothly . i.e analyze the crude first .

Are you observing the variation in silica now or it is a regular phenomenon ?

what about the outer grate diaphragm slot gap ? 

you have to crash stop the mill and check the PSD at certain locations and try to co-relate with earlier results . i.e grinding media pattern and % filling/load.

if it is a close circuit mill . you have to check classifier vanes also .

above are the various reasons which use to reduce the productivity .

try to eliminate one by one .

Thanks

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