Abstract: The CT-0812 type permanent magnetic drum was used in the dry preconcentration of the fine crushing products with TFe grade of 23.80% in Shuichang Iron Mine. TFe grade can only be improved by 2.10 percentage points and the discarding tailing yield was only 11.32%. The mFe grade of the tailings reached 2.38%， which means unsatisfactory effect of the dry preselection. In order to improve the pre-selection effect， the comparative tests of pre-selection effect of different new dry separator were carried out， and then condition tests of the process parameters on site were conducted with the equipment which has better pre-selection effect. The industrial production indexes of the new and old dry separator were compared. The results showed that: ①In the condition of laboratory and the TFe grade of 21.45% of the Shuichang Iron Mine fine products， the tailing with yield of 16.63%， TFe grade of 6.16% and mFe grade of 1.63% was obtained after the treatment of the XDG65-50 multi-stage suction-holding combined dry pre-concentration machine. The tailing with yield of 39.83%， TFe grade of 5.45% and mFe grade of 1.02% was obtained after the preselecting of CTX0812 dry magnetic separator with rotating magnetic field， which means the ideal preselecting effect. ②In industrial test parameter range on site， the CTX0812 dry magnetic separator with rotating magnetic field is not sensitive to the running frequency of the magnetic system and the position of the distribution board， but it is sensitive to the running speed of the feeding belt. The TFe grade and mFe grade of tailings show an upward trend of first slow then fast with the running speed of the belt increasing. When the magnetic system runs at a frequency of 70 Hz， the belt runs at a speed of 3.2 m/s， and the feed with a TFe grade of 22.95% is treated with a horizontal distance of 300 mm from the center of the cylinder， dry preselected concentrate with a TFe grade of 26.93%， tailing with yield of 19.60% and mFe grade of 2.05% can be obtained. ③Under the condition of equal grade of feeding and optimum technological parameters of dry separator， the tailing with yield of 18.78%， TFe grade of 6.87% and mFe grade of 2.06%， and the concentrate with TFe grade of 28.69%， increased by 4.02 percentage points was acquired using the CTX0812 dry magnetic separator with rotating magnetic field. The tailing with yield of 14.21%， TFe grade of 7.45% and mFe grade of 2.58%， and the concentrate with TFe grade of 26.95%， only increased by 2.25 percentage points was acquired using CTX0812 permanent magnetic drum. ④The CTX0812 dry magnetic separator with rotating magnetic field can achieve efficient separation of magnetic materials and non(weak) magnetic particles through high frequency magnetic turnover， magnetic agitation and high magnetic field intensity， which is suitable for highly efficient dry discarding of fine crushing products in Shuichang Iron Mine.

Key words: Prediscarding by magnetic separation, Hang magnetic dry separator, The dry magnetic separator with rotating magnetic field, The CT type permanent magnetic drum