Advancing iron ore slimes magnetic separation with functionalized Nanoparticles: Molecular insights from free energy simulations

Magnetic nanoparticles have diverse scientific and technological applications, as their properties can be tuned accordingly. An example is the selective magnetic coating technique for the selective adsorption of these colloidal particles on the surface of iron minerals to improve recovery of fines by magnetic separation. Thus, fundamental physicochemical knowledge of such systems is of paramount importance. Herein, we investigate the adsorption of magnetite nanoparticles on mineral surfaces and the impact of hydrophobic coating on the adsorption process and magnetic separation. We present structural and thermodynamic characterizations from molecular dynamics and free energy simulations to rationalize the differences in association process in both native and coated particle conditions. We demonstrate that hydrophobic coating of both nanoparticle and target iron oxide surfaces is essential for selective adhesion, revealed by Delta G. Also, tuning the degree of surface coverage by oleate leads to better interactions then simply establishing a monolayer coating, because of interdigitation of adsorption layers allowing higher contact area, shorter interparticle distance and less oleate consumption. Magnetic separation experiments of ultrafine iron ore particles under different oleate and colloidal magnetite concentrations validated the molecular level analyses, thus achieving successful experiment-theory nexus based on a sound theoretical background explored beforehand by computational simulations.