Removal of Hg²⁺ with Polypyrrole-Functionalized Fe₃O₄/Kaolin: Synthesis, Performance and Optimization with Response...

PPy-Fe₃O₄/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-Fe₃O₄/Kaolin was employed to remove Hg²⁺ and the results were characterized by various methods. Relevant factors, including solution pH, dosage of adsorbent, concentration (C₀), and temperature (T), were optimized by Response Surface Methodology (RSM) and Central Composite Designs (CCD). The optimal results show that the importance for adsorption factors is pH > T > C₀ > dosage, and the optimal adsorption conditions of PPy-Fe₃O₄/Kaolin are pH = 7.2, T = 315 K, C₀ = 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-Fe₃O₄/Kaolin was achieved mainly through electrostatic attraction, pore diffusion, and chelation between amino functional groups and Hg²⁺. PPy-Fe₃O₄/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-Fe₃O₄/Kaolin is an efficient and economical adsorbent towards mercury.