Experimental and Molecular Dynamics Study of Pyrite Effects on the Flocculation of Clayey Tailings in Seawater

This study investigates the effect of pyrite content on the flocculation and sedimentation of clay-based tailings composed of kaolin, quartz, and pyrite in seawater at pH 8. A high-molecular-weight anionic hydrolyzed polyacrylamide (SNF 704) was used in batch settling tests, supported by floc characterization with FBRM, zeta potential measurements, and molecular dynamics (MD) simulations. Results showed that increasing pyrite content reduced the maximum floc size and increased the fraction of unflocculated fines, particularly at 10 g/t dosage. Although the fractal dimension remained nearly constant (1.92-1.97 at 10 g/t and 2.05-2.08 at 30 g/t), floc density increased linearly with pyrite proportion due to its higher specific gravity. Zeta potential analysis confirmed strong polymer-pyrite interactions, with charge inversion from +5.3 to -4.5 mV, while MD simulations indicated that adsorption occurs mainly through aliphatic chain segments, in contrast to hydrogen bonding observed for quartz and kaolinite. These findings demonstrate that pyrite affects flocculation dynamics both by its density and by specific polymer-surface interactions, directly influencing floc size, density, and sedimentation performance in seawater thickening systems.