Probing interactions between sphalerite and hydrophobic/hydrophilic surfaces: Effect of water chemistry

Due to the limited availability of fresh water sources, recycled water and sea water, generally with high salinity, have been widely used in mining industry in arid regions, which can significantly affect the interactions of mineral particles, chemical additives and air bubbles in mineral processing (e.g., flotation). In this work, the surface forces and interaction mechanism of Si3N4 tip and a model mineral (i.e. sphalerite) in various aqueous solution conditions have been studied using an atomic force microscope (AFM). The Si3N4 tip was functionalized with octadecyltrichlorosilane (OTS) to tune the surface hydrophobicity. The sphalerite substrate was either freshly cleaved or treated with conditioning solutions: activator (i.e. CuSO4) and collector (i.e. potassium amyl xanthate, PAX) in various background solutions (i.e., Milli-Q water, 0.46 M NaCl, saline water to mimic diluted sea water/industrial process water). The force-separation profiles indicate that in addition to the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions, hydration interaction plays an important role for the surface interaction in saline water (with addition of divalent cations, Ca2 + and Mg2 +) at short separation distance, while hydrophobic force dominates the interaction when Si3N4 tip and sphalerite are both hydrophobized. The surface force measurements further demonstrate that solution salinity and presence of divalent cations can significantly influence the adhesion between particles. The micro-flotation tests of sphalerite and silica mixtures of varying surface hydrophobicity can be well interpreted by the force measurements. This work provides useful insights into the fundamental interaction mechanisms of suspended particles possessing different hydrophilic and hydrophobic characteristics in complex aqueous media.