Enhancement mechanisms of copper(II) adsorption onto kaolinite by extracellular polymeric substances of Microcystis aeruginosa (cyanobacterium)

摘要

Microcystis aeruginosa frequently forms cyanobacterial blooms in eutrophic water bodies, resulting in high concentrations of extracellular polymeric substances (EPS) in the water column. The effects of M. aeruginosa EPS (MA-EPS) on the adsorption behavior of Cu(II) onto kaolinite and the possible mechanisms were investigated in this study. The results of potentiometric titration and Fourier transform infrared (FT-IR) spectroscopy determination show that carboxyl, phosphoryl and amino/hydroxyl groups were the main adsorption groups on MA-EPS. The combination of EPS with kaolinite created new adsorption sites. MA-EPS increased the adsorption of Cu(II) by kaolinite mainly through complexation. The adsorption kinetics of Cu(II) by kaolinite or kaolinite + EPS composite (Kao + EPS) was well fitted by a pseudo-second order kinetic model. The adsorption isotherm analyses show that the incorporation of MA-EPS onto kaolinite increased its surface heterogeneity. Rather than intercalating into the kaolinite interlayers, MA-EPS and/or Cu(II) were adsorbed onto the surface of this clay.