The interaction mechanism of Th(IV) on sepiolite investigated by batch and modeling techniques

The effect of Paecilomyces cateniannulatus (P. cateniannulatus) on Th(IV) adsorption by sepiolite were investigated by batch techniques. The batch adsorption showed that the adsorption of Th(IV) on sepiolite and sepiolite + P. catenlannulatus significantly increased with increasing of pH from 3.0 to 6.0, then remained the high-level adsorption. P. cateniannulatus significantly facilitated the adsorption of Th(IV) on sepiolite at pH 2.0-5.0, whereas inhibited adsorption was observed at pH > 6.0. The adsorption of Th(IV) on sepiolite + P. catenlannulatus was independent of ionic strength at pH from 3.0 to 9.0. The adsorption kinetics of Th(IV) on sepiolite and sepiolite + P. catenlannulatus can be satisfactorily simulated by pseudo-second-order kinetic model. The maximum adsorption capacities of sepiolite and sepiolite + P. catenlannulatus for Th(IV) calculated Langmuir model at pH 3.0 and 293 K were 50.76 and 57.80 mg/g, respectively. Based on surface complexation modeling, the adsorption mechanism of Th(IV) on sepiocite + P. catenlannulatus was cation exchange/outer-sphere surface complexation at low pH, whereas inner-sphere surface complexation dominated the Th(IV) adsorption at high pH conditions. The findings presented in this study are of great importance towards understanding of fate and transport of heavy metals under natural aquatic environments.