Influence of ion concentration in water on the flotation response of pyrrhotite superstructures

This study investigates the intrinsic relationship between surface charge, redox properties, and collector interaction on determining the flotation performance of hexagonal and monoclinic pyrrhotite under deteriorating water conditions. Microflotation, UV-Vis spectrophotometry, zeta potential, and rest potential measurements were used under five different water chemistries with different ionic strengths at three different pH values (7, 9, and 11). The results indicated that although collector uptake is a function of ionic strength, flotation performance is controlled by the character of the surface species formed, which are a function of electrochemical conditions themselves. Zeta potential analysis indicated progressive double-layer compression at higher ionic strengths, particularly at alkaline pH, which contributed to enhanced collector adsorption but not necessarily improved flotation performance. Rest potential analysis indicated a transition from hydrophobic dixanthogen to surface-bound metal xanthate species as the condition became oxidative or chemically more complicated. These surface changes were amplified for monoclinic pyrrhotite, which consistently exhibited higher susceptibility to oxidation and electrochemical instability compared with hexagonal pyrrhotite. The correlation of the results indicated that flotation success is not only a function of collector uptake, but also of surface charge and redox potential compatibility to allow for the forming of stable hydrophobic layers. This study illustrates the need of including water as an additional factor in knowledge of flotation response of pyrrhotite, enabling most effective rejection in processing streams.