Decoupling the pulp and froth effect of ultrafine particles on Itabirite iron ore flotation

Abstract

The reverse flotation of Itabirite iron ore is typically performed after a desliming step in which most of the sub-10 µm particles are removed. This is done to limit processing problems such as poor flotation recovery of SiO2 due to slime coatings, increased slurry viscosities, unmanageable froths and increased losses of hematite particles due to entrainment. However, the rejection of ultrafine particles contributes to large losses in iron recovery and may contribute to the instability of tailings dams. The aim of this study is to decouple the effects of ultrafine particles in the pulp and froth phases to better understand the processing capabilities of the fines fraction. The flotation test work was performed in a special-purpose continuously operated laboratory flotation cell that has a deep froth section to simulate plant-scale froth conditions. Five conditions of fines addition were investigated at 3 different froth heights and a solids concentration of 50%. The behaviour of the pulp and the froth were decoupled using froth stability and froth recovery tests. This showed that, even though there is an exponential increase in froth stability at increasing fines quantities, the performance of the pulp has the overriding effect on the SiO2 recovery. Pulp zone, froth zone and overall SiO2 recoveries showed that recoveries increased by about 3.6% for every 1% decrease in fines content. This meant a large increase of 20% in SiO2 recovery when going from undeslimed to deslimed feed. This was driven largely by increases in the pulp zone recoveries, which were about 4% for every 1% decrease in fines content. The froth recoveries, on the other hand, decreased by between 0.75% and 2.5% for every 1% decrease in fines content, depending on froth height. This paper explores further insights into iron ore flotation processing at different slimes concentrations.