| Summary: | PPy-Fe<sub>3</sub>O<sub>4</sub>/Kaolin was prepared with polypyrrole functionalized magnetic Kaolin by a simple, green, and low cost method to improve the agglomeration and low adsorption capacity of Kaolin. PPy-Fe<sub>3</sub>O<sub>4</sub>/Kaolin was employed to remove Hg<sup>2+</sup> and the results were characterized by various methods. Relevant factors, including solution pH, dosage of adsorbent, concentration (<i>C</i><sub>0</sub>), and temperature (<i>T</i>), were optimized by Response Surface Methodology (RSM) and Central Composite Designs (CCD). The optimal results show that the importance for adsorption factors is pH > <i>T</i> > <i>C</i><sub>0</sub> > dosage, and the optimal adsorption conditions of PPy-Fe<sub>3</sub>O<sub>4</sub>/Kaolin are pH = 7.2, <i>T</i> = 315 K, <i>C</i><sub>0</sub> = 50 mg/L, dosage of 0.05 g/L, and the capacity is 317.1 mg/g. The adsorption process conforms to the pseudo-second-order and Langmuir models. Dubinin–Radushkevich model shows that adsorption process is spontaneous and endothermic. Moreover, the adsorption of mercury by PPy-Fe<sub>3</sub>O<sub>4</sub>/Kaolin was achieved mainly through electrostatic attraction, pore diffusion, and chelation between amino functional groups and Hg<sup>2+</sup>. PPy-Fe<sub>3</sub>O<sub>4</sub>/Kaolin has excellent reproducibility, dispersity, and chemical stability, and it is easy to be separated from solution through an external magnetic field. The experiments show that PPy-Fe<sub>3</sub>O<sub>4</sub>/Kaolin is an efficient and economical adsorbent towards mercury.
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