PEO flocculation of kaolinite – Molecular weight effect

Abstract

The adsorption of poly(ethylene oxide) (PEO) of different molecular weights (MW) on kaolinite and its effects on kaolinite suspension stability were investigated. Fourier transform infrared spectroscopic and X-ray photoelectron spectroscopic analyses showed that the adsorption mechanisms of PEOs with different molecular weights appeared to be identical, i.e., through the formation of hydrogen bonds between ether‑oxygen groups of PEO and hydroxyl groups on the surface of kaolinite. Zeta potential measurements indicated that the adsorption of PEO resulted in the outward expansion of the diffuse layer on the surface of kaolinite, as evidenced by a decrease in the magnitude of zeta potential. The maximum decrease was observed to correlate to the thickness of the adsorbed layer, which in turn was proportional to the MW of PEO, indicative of the lateral extension of the “loop” and “tail” structures of adsorbed PEO. As the adsorption layer thickness increased, the likelihood of bridging flocculation increased, resulting in the formation of larger flocs with greater strength and lower density in a shorter time, observed with higher MW PEO. This conclusion was confirmed by experimental results obtained from an online monitoring system for flocculation processes composed of focused beam reflectance measurement (FBRM) particle size analyzer and confocal scanning microscopy (CSM).