Effect of nano-sized roughness on the flotation of magnesite particles and particle-bubble interactions

摘要

Roughness of mineral particles affects bubble-particle interactions and particle flotation separation. In this study, magnesite was ground in stainless-steel disc and ceramic ball mills to produce flotation feed material of different surface nano-roughness, which was quantified using atomic force microscopy (AFM). The effect of surface roughness on the floatability of magnesite particles was carried out by a micro-flotation kinetic test using an XFG flotation machine. The flotation results demonstrated both higher flotation recovery and larger flotation rate constant for particles having larger nano-asperities of rough particle surface. Additionally, the difference in cumulative flotation recovery between magnesite particles with different nano-roughness characteristics systematically decreased with increasing collector (sodium oleate) concentration from 25 to 150 mg/L. Contrarily, a difference in the value of flotation kinetics constant for particles with larger and smaller asperities remained at a level of 0.2-0.3 min(-1) for the entire range of collector concentration. The interaction energy between bubbles and rough magnesite particles with different nano-roughness was estimated using an extended DLVO (Derjaguin-Landau-Verwey-Overbeek) theory. The theoretical interaction energy points to lowering energy barrier when the magnesite particles are covered with 12 nm asperities as compared to 2 nm asperities. It is therefore hypothesized that the energy barrier is a primary cause for differences in flotation performance of particles decorated with nano-asperities of different dimensions.