Abstract: The iron grade of the mixed concentrate after low-intensity magnetic separation or high-in⁃tensity magnetic separation in Donganshan sintering plant is 45.48%, in which the main minerals are mag⁃ netite, hematite and siderite, along with few quartz and chlorite. In order to obtain higher grade iron concentrate, step-by-step flotation test was carried out. The results showed that under the conditions of 800 g/t for starch and 200 g/t for TD-Ⅱ in direct flotation, 500 g/t for starch and 800 g/t for calcium oxide and 800 g/t for TD-Ⅱin reverse flotation during coarsing, and 400 g/t for TD-Ⅱ in reverse flotation during cleaning, the sample is subjected to once direct flotation. A concentrate with grade of 65.58% and recovery rate of 71.97% was obtained with one roughing, one cleaning, three scavenging and middling ore return in sequence.

Key words: mixed concentrate after magnetic separation, step-by-step flotation, starch, calcium oxide