Reverse Floc-Flotation of Talc from Chalcopyrite Using Polyvinyl Acetate as a Flocculant: Adsorption and Bubble Capture Studies

Abstract

Chalcopyrite is often intergrown with talc, which, after grinding, forms ultrafine particles (<10 μm) that readily coat chalcopyrite surfaces, hindering flotation and causing significant losses in tailings. This study evaluates polyvinyl acetate (PVAc), a thermoplastic polymer, as a selective flocculant to enhance reverse flotation separation of chalcopyrite from ultrafine talc. Flotation tests showed that at a PVAc dosage of 40 mg/L, talc can be effectively and selectively removed, enabling efficient separation. Laser particle size analysis and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) confirmed that PVAc promotes selective talc aggregation without affecting chalcopyrite. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations revealed that hydrogen bonding between PVAc ester groups and surface hydroxyls on talc drives the flocculation, while chalcopyrite lacks suitable binding sites. PVAc adsorption also enhances talc hydrophobicity. Furthermore, particle-bubble coverage angle measurements and extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory theoretical calculations demonstrated that PVAc-induced flocculation increases attractive interactions between talc and bubbles, shifting the total interaction energy from repulsive to attractive and promoting bubble-particle attachment. This study clarifies the selective adsorption and flocculation mechanisms of PVAc and reveals the coupling of flocculation and flotation of ultrafine talc from a particle-bubble capture perspective, while expanding the potential of ester-based polymers for ultrafine mineral recovery.

1. Introduction

Ultrafine mineral particles, typically defined as those with particle sizes smaller than about 10 μm, are difficult to effectively recover and utilize during mineral processing and separation due to their small sizes. These particles cannot be efficiently recovered by froth flotation and are often discarded to tailings [1]. Tailings are the leftover waste materials after ore beneficiation and commonly contain pollutants such as heavy metals, acid-generating sulfide gangue, and chemical reagents. Long-term accumulation of wet fluid tailings poses severe environmental threats, including water pollution, air pollution, soil contamination, ecological damage, and potential geological hazards. The abandonment and storage of ultrafine minerals constitute latent pollution sources, posing a threat to human life.

In terms of the separation of ultrafine minerals, traditional methods such as gravity separation, magnetic separation, and conventional froth flotation are generally not effective. In contrast, floc-flotation has emerged as one of the most efficient approaches for recovering ultrafine minerals. This technique relies on the adsorption of polymeric flocculants to the mineral surface, where the polymers' bridging action promotes the aggregation of ultrafine particles into larger flocs, thus enhancing flotation performance [2]. Floc-flotation not only enhances the separation of ultrafine minerals, but also mitigates their environmental impact and contributes to resource recovery. By optimizing the choice of flocculants and flotation conditions, it is possible to improve mineral separation efficiency, reduce environmental contamination, and achieve more sustainable mineral resource recovery and tailings management.