Enhanced floatability of low rank coal using surface functionalized polystyrene nanoparticles as collectors

Abstract

Low rank coal (LRC) is difficult to be upgraded by flotation due to the rich oxygen-containing functional groups on its surface. The main objective of this study was to identify the feasibility of surface functionalized polystyrene nanoparticles as LRC flotation collectors. Tetrahydrofurfuryl-functionalized polystyrene nanoparticles (TFPNs) and hydroxyl-functionalized polystyrene nanoparticles (HFPNs) were prepared by emulsion polymerization, and their properties were characterized by X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), Zeta potential and particle size measurement. The effect of nanoparticles properties on the LRC flotation was investigated and the performance between TFPNs, HFPNs, polystyrene nanoparticles (PNs) and diesel oil (DO), was compared. The results show that the LRC flotation recovery of PNs was 2.82%–16.86% higher than that of DO, while that of TFPNs and HFPNs exceeded 28.30%–34.33% and 3.58%–18.92%, respectively, which indicated that the performance of PNs was improved by immobilizing tetrahydrofurfuryl or hydroxyl onto the surface. But surface functionalization degree (SFD) should be kept in an appropriate range, i.e. 5.78%–6.56% for TFPNs, 3.94%–5.62% for HFPNs. TFPNs and HFPNs can specifically deposit onto the LRC with the hydrogen bonding function. By improving the hydrophobicity and roughness with deposited nanoparticles, the flotation performance of LRC was significantly enhanced. The performance of TFPNs was superior to that of HFPNs, which resulted from the strong ability to form hydrogen bond for hydroxyl that reduced nanoparticle hydrophobicity. Effective nanoparticle collectors for LRC flotation were likely to be TFPNs with ∼50 nm diameter, positive Zeta potential and SFD around 6.56%. The balance among colloidal stability, hydrophobicity and selectivity of nanoparticles was an effective way to reduce the dosage of nanoparticle collector and promote its industrial application. The results of this study introduce a new class of special collectors for enhancing LRC flotation and put forward its path to commercial utilization.