Abstract: Iron grade of fines（-15 mm） iron ore from Heigou is 37.35%.Iron mainly exists in form of hematite-limonite and the distribution rate is 85.35%.The fines iron ore was recovered by high intensity magnetic separation after ball milling in on-site process，while sliming phenomenon in grinding operation is serious，the fines iron ore can′t be recovered by high intensity magnetic separation.In order to relieve over crushing phenomenon during grinding and optimize size composition of grinding products.The fines were crushed to -2 mm，Pre-screened -120 μm size fraction with the rate of 33.30%.Rod milling experiments were implemented for +120 μm size fraction.Closed-circuit grinding was carried out with the conditions that grinding medium of rod diameter 18，20，22 mm with mass ratio of 4∶3∶3，medium filling ratio of 30%，rod to powder ratio 1.0，grinding concentration 70% and grinding for 62 s，and it can obtain qualified size fraction (38~120 μm) accounts for 57.55% of -120 μm size fraction.Decreasing classification particle size can reduce production of fine particle effectively and over grinding.It has a significant reference to reducing over grinding and optimize the size composition of grinding products by rod milling technology.

Key words: Lack grinding, Over grinding, Rod grinding, Closed circuit grinding