Understanding the sorption mechanisms of aflatoxin B1 to kaolinite, illite, and smectite clays via a comparative...

In current adsorption studies of biotoxins to phyllosilicate clays, multiply weak bonding types regarding these adsorptions are not well known; the major attractive forces, especially for kaolinite and illite, are difficult to be identified as compared to smectite with exchangeable cations. Here, we discriminated the bonding types of aflatoxin B1 (AFB1) contaminant to these clays by combined batch experiment with model computation, expounded their bonding mechanisms which have been not quantitatively described by researchers. The observed adsorbent-to-solution distribution coefficients (K_d) of AFB1 presented in increasing order of 18.5-37.1, 141.6-158.3, and 354.6-484.7L/kg for kaolinite, illite, and smectite, respectively. Normalization of adsorbent-specific surface areas showed that adsorption affinity of AFB1 is mainly dependent on the outside surfaces of clay aggregates. The model computation and test of ionic effect further suggested that weakly electrostatic attractions ((Si/Al-OH)₂⋯(OC)₂) are responsible for AFB1-kaolinite adsorption (K_d, 18.5-37.1L/kg); a moderate electron-donor-acceptor attraction ((CO)₂⋯K⁺⋯(O-Al)₃) is related to AFB1-illite adsorption (K_d, 141.6-158.3L/kg); a strong calcium-bridging linkage ((CO)₂⋯Ca²⁺⋯(O-Si)₄) is involved in AFB1-smectite adsorption (K_d, 354.6-484.7L/kg). Changes in Gibbs free energy (ΔG°) suggested that the computed result is reliable, providing a good reproduction of AFB1-clay interaction.