Evaluation of thiol-modified vermiculite for removal of Hg(II) from aqueous solutions

Aiming the removal of Hg(II) from waters, Na+ exchanged vermiculite (Na-VT) was modified with l -cysteine (CYS-VT), cysteamine hydrochloride (CTA-VT) and (3-mercaptopropyl) trimethoxysilane (3-MPS-VT). Modification with CTA and CYS was made at pH 6.0 ± 0.1 to facilitate ion exchange of Na+ in the interlayer with the protonated amines. Modification with 3-MPS was made by silylation, covalently binding the modifier to the silanols. Initial adsorption rate (μmol g− 1 min− 1) on Na-VT and 3-MPS-VT was very fast and obeyed a pseudo second order kinetics. Intraparticle diffusion controlled the initial adsorption rate in CTA-VT and CYS-VT. Adsorption isotherms constructed at pH 6.0 ± 0.1 and 25.0 ± 0.5 °C fitted to Langmuir and Freundlich equations. The adsorption capacities of CTA-VT, CYS-VT, 3-MPS-VT and Na-VT were 83 ± 30, 57 ± 4, 21 ± 2 and 18 ± 1 μmol g− 1 (n = 3), respectively. The adsorption capacity in columns followed the order: 3-MPS-VT > CTA-VT > CYS-VT > Na-VT, which is consistent with the instantaneous adsorption on 3-MPS-VT and the intraparticle diffusion control in CTA-VT and CYS-VT. The modifications afforded materials with adsorption capacities less affected by variation of ionic strength and pH as a consequence of the strong binding of Hg(II) to the incorporated thiols.