Adsorption of Hg²⁺ from aqueous solution onto polyacrylamide/attapulgite

Polyacrylamide/attapulgite (PAM/ATP) was prepared by the solution polymerization of acrylamide (AM) onto γ-methacryloxypropyl trimethoxy silane (KH-570)-modified attapulgite (ATP). PAM/ATP was characterized using Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The effects of contact time, adsorbent dosage, and pH of the initial solution on the adsorption capacities for Hg²⁺ were investigated. The adsorption process was rapid; 88% of adsorption occurred within 5 min and equilibrium was achieved at around 40 min. The equilibrium data fitted the Langmuir sorption isotherms well, and the maximum adsorption capacity of Hg²⁺ onto PAM/ATP was found to be 192.5 mg g^-1. The adsorption kinetics of PAM/ATP fitted a pseudo-second-order kinetic model. Our results suggest that chemisorption processes could be the rate-limiting steps in the process of Hg²⁺ adsorption. Hg²⁺ adsorbed onto PAM/ATP could be effectively desorbed in hot acetic acid solution, and the adsorption capacity of the regenerated adsorbents could still be maintained at 95% by the sixth cycle.