Process route for low grade itabirites concentration: Magnetic separation preceding flotation

Cationic reverse flotation of quartz is the standard or reference concentration route for itabirites containing at least 45% iron. Preceding the flotation stage, desliming in hydrocyclones must be conducted to remove ultrafine and colloidal particles from the flotation feed. The flotation performance assessed by weight and metallurgical recoveries and silica contamination in the concentrate is impaired by lower iron feed grades. Exploratory experiments of magnetic separation indicated that iron oxide particles in the size range <37 µm are entrained toward the non-magnetic product. This finding suggested a campaign of testing an alternative circuit consisting of magnetic separation preceding reverse flotation. Magnetic separation plays the roles of desliming and pre-concentration. The achieved content of silica in the alternative route concentrate was 1.46%, meeting the market specification for blast furnace pellet of 2%. The alternative route yielded significant gains in weight and metallurgical recoveries, reaching values 3.3% and 4.4% higher, respectively.