Fast removal of Hg(II) ions from aqueous solution by amine-modified attapulgite

Natural attapulgite (ATP) was modified with an amino-terminated organosilicon (3-aminopropyltriethoxysilane, APTES) in order to develop an effective adsorbent for aqueous Hg(II) removal. The surface area of the modified ATP (M-ATP) was calculated using the Brunauer–Emmett–Teller method. The adsorbent was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FT-IR) and electrophoretic mobility. Due to complexation between mercury and the amine functional groups on the M-ATP, the adsorption capacities significantly increased from 5 mg/g (raw ATP) to 90 mg/g (M-ATP). Batch adsorption results showed that the adsorption process was rapid and over 90% of aqueous Hg(II) was removed within 1 h. The efficiency of the adsorbent was found to remain almost constant over a wide pH range (3–11). Adsorption of Hg(II) by M-ATP was proposed as the complexation between mercury and the amine functional groups on the M-ATP surface. Ionic strength and co-existing ions had a slight influence on the adsorption capacity. Hg(II) adsorbed onto M-ATP could be effectively desorbed in 1:1 (m/m) chlorohydric acid/thiourea solution. Our results suggest that the M-ATP may be used as renewable adsorbents for fast removal of Hg(II) from aqueous solutions.