15-20 microns by any standards is 'fine' IMO. Maybe Herald seem to think it's 'medium' and that's part of their marketing strategy. A product in this size range would require UFG (ultrafine grinding). If you are remotely interested in the cost of energy vs particle size (Fred Bond summed it up many years ago and its an approximation), but it's pretty much an exponential:
kW required = t/h * Wi * (((p80^-0.5)-(((f80^-0.5))
Work index = 16 for sphalerite (est.) t/h = tonnes per hour processed through mill f80 = 150 micron p80 = 15 micron
So for a small Zinc mine (2Mtpa @ 85% recovery with 14.5% Zn = 28 t/h of con), to regrind (i.e. Secondary grind ontop of existing primary grinding), you would need an additional ~800 kW. The Primary Mill might need ~2000 kW, so any Secondary or UFG would be 30-50% more energy.
Whichever way you look at it - Perkoa cannot be ignored as it is ready to go and it would be low op.cost compared to any other Zn mine. I knw there are other costs associated, but how many other Zn mines are there <12 months away?
Just hope someone realises it soon.
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