Study On Preconcentration Of Bayan Obo Associated Ore Using High Gradient Superconducting Magnetic Separation

The Bayan Obo deposit contains very important mineral resources in China.However,low efficiency in mineral processing,which recovers majority of the iron minerals and small portion of rare earth(RE)minerals,leads to pile up almost 200 million tons of tailings that contain 15 % iron,0.14 % niobium,23 % fluorite and 7 % rare earth during the past 50 year operation.To explore highly efficient ways in magnetic separation of Bayan Obo minerals,new magnetic method using superconducting high gradient magnetic separation(SC-HGMS)is studied with Bayan Obo raw ore containing 7.03 % of RE,27.04 % of iron.The samples were analyzed by Multi-Element Analysis,Scanning Electron Microscopy,Dissociation Degree Analysis,Mineral Composition Analysis and other methods.Analyses confirm the previous discovery that the ore contains large number of elements,and consists of variety of minerals,the useful minerals in the samples are iron,rare earth and fluorite,and the gangue is mainly quartz.The raw ore samples were crushed and grinded to particle sizes with-200 mesh counting for 95%.Firstly,strongly magnetizable minerals were separated using the BX/8000 Oe and BX/12000 Oe permanent magnetic separator,which include the magnetite,the false hematite.Secondly,the high gradient magnetic separation(HGMS)was used to separate weak magnetizable minerals such as limonite,sodium amphibole,sodium pyroxene and other relatively weak magnetic materials in the weak magnetic field tailings.Finally,high gradient SC-HGMS was employed to separate very weak magnetizable minerals such as rare earth,niobium from fluorite and gangue.The separation condition for the conventional HGMS is as follows: slurry velocity 0.035m/s,slurry concentration 18%,matrix is fabricated with iron rods,magnetic induction is0.6T.For the SC-HGMS,the slurry velocity is 0.09 m/s,slurry concentration is 10%,matrix is fabricated with iron wool of 0.12 mm diameter,filling rate is 5.8%,magnetic induction is 4.5T.The final grade of RE concentrate is 12.73%,operational recovery rate in SC-HGMS is 98.23%,and total recovery rate is 55.13%.In the tailing,RE grade is as low as 0.46%,SC-HGMS operational recovery rate is 1.77%,and total recovery rate is6.84%;iron grade is 1.7%,SC-HGMS operational recovery rate is 10.3%,and total recovery rate is 0.95%.Our experiments indicate that minerals of RE and Nb can be separated with SC-HGMS from fluorite and gangue while those minerals are considered non-magnetizable in the conventional magnetic separation.The new method reduces the RE grade in tailing to less than 1%,with fluorite concentrated in the tailing.The new method set up an advantage stage for the downstream flotation of RE and fluorite with much less chemicals.