Abstract: To increase the adaptability of air dense medium fluidized bed with different external moisture selected coal, surface hydrophobic modification of magnetite powder is a effective way. Influence of surface modification to fluidization characteristics of magnetite powder was studied, the results indicated, surface modification increased the minimum fluidization velocity of magnetite powder, but no apparent influence to distribution of pressure drop; density of bed was more uniform and stable compared with before modification, in favor of formation of fluidized state with high quality; as gradually increase of external moisture of selected coal, had influence to fluidization characteristics of magnetite powder of both unmodified and modified, surface modification made the external moisture limit of selected coal increased from 2% to 4%, and still keep good fluidized state when moisture content 4%.Using modified magnetite powder as medium solid, formed fluidized bed had good separating properties, result of screening test showed, possible deviations E value was all 0.075 when external moisture of selected coal was 3% and density of separation was 1.55 g/cm3 or 1.82 g/cm³.

Key words: Hydrophobic, Medium solid, Fluidization characteristics, Separation properties