I can't say I have heard of a gyratory mill - do you mean crusher? For grinding potash, most plants use either a rod mill or a cage mill (cage paktor). The key is to reduce production of fines while getting the material fine enough for flotation or leaching.

No it's gyratory mill. Could you please explain more about cage mill for me? What are the products size rages?

Could you give as brief information regarding gyratory mill? I have never heard about it.

Try to make the comparison between, ball mill and rod mill, here in the past we used ball mills, but they produces more fine particles now we moved to rod mill

Instead of open circuit, if we have closed circuit with cyclone/screen for classification, may be possible to control over grinding and produce less fine size.

First what is your best size to recovery or refuse your potash on your next process from this point you need to calculate and choice how to grind and classify your potash ore.

Ball mills: They are used for coarser grinding. Mostly wet grinding. Wet process means multiple handling and more cost. Very rarely used for dry grinding. Cement, pellet feed. etc.

Gyratory:

It is used with fan above to control particle size. It can grind up to and below 2 micron. Mostly used for dry grinding for small capacities. MnO2 grinding. It develops high temperature inside and causes heavy wear on rollers used. Ball mill is for larger capacities. Small ball mills cannot do fine grinding.