### TECHNICAL NOTES 8 GRINDING R. P. King

steel balls in a ball mill, or large lumps of ore in an autogenous mill or a mixture in a semi-autogenous mill, as well as the slurry that makes up the operating charge. Let Jt be the fraction of the mill volume that is occupied by the total charge, Jb the fraction of the mill volume that is occupied by steel balls and E the voidage of the balls