Effect of solution salinity on settling of mineral tailings by polymer flocculants

Abstract

Understanding the interaction mechanism between polymeric flocculants and solid particles in solutions of high salinity and the associated flocculation mechanism is of great practical and fundamental importance in mineral processing and colloid and interface science. In this work, the effects of three polymers, polyacrylamide (PAM), Magnafloc 1011 (MF) and Al(OH)3-polyacrylamide (Al-PAM), on the settling of mineral tailings in freshwater and in saline solution were investigated. The settling of tailings significantly depends on solution salinity, type and dosage of polymer flocculants. MF showed the best settling performance among the three polymers in both freshwater and saline solutions. The tailings settling was found to be largely dependent on the various interactions among negatively charged clay particles and polymers including van der Waals attractions, electrostatic repulsion, and polymer bridging. The increased solution salinity significantly reduces the electrostatic repulsion among the negatively charged solid particles and negatively charged polymer flocculants (i.e. for MF, but not for PAM and Al-PAM), leading to more effective polymer bridging interactions, which enhances the settling of mineral tailings. Our results provide some new insight into the understanding of the effects of solution salinity on the settling of mineral tailings and the development of novel polymer flocculants.