Abstract: After the ultra-low-grade magnetite of micro-fine-grained disseminated in Fujian province was separated by low intensity magnetic separation. Fe grade of the concentrate was 65.30%，while the silica content was up to 8.52%,which is the major factor affecting the concentrate quality. For the concentrate of low intensity magnetic separation，technical conditions of reverse flotation for iron increasing and silicon reducing was explored. The results indicated that through the closed-circuit reverse flotation of one roughing，one cleaning and three scavengings and middles back to the flow-sheet in turn，iron concentrate with Fe grade of 68.97%，recovery of 98.25% and silica content of 3.35% was obtained，while tailings with Fe grade of just 16.39% and recovery rate of 1.75% was gained as well. A remarkable effect of iron increasing and silicon reducing is obtained in the experiment.

Key words: Primary concentrate of low intensity magnetic separation, Silica, Iron increasing and silicon reducing, Reverse flotation