Adsorption of Hg(II) from an Aqueous Solution by Silica-Gel Supported Diethylenetriamine Prepared via Different Routes: Kinetics, Thermodynamics, and Isotherms

The kinetics, thermodynamics, and isotherms of Hg(II) ion adsorption onto silica-gel supported diethylenetriamine adsorbents, SG-HE-dD, SG-HO-dD, SG-HE-pD, and SG-HO-pD (where SG means silica-gel. HE, heterogeneous, HO, homogeneous, d, direct; p, protection, and D. diethylenetriamine), prepared by so-called heterogeneous-direct animation, homogeneous-direct amination, heterogeneous end-group protection, and homogeneous end-group protection methods, respectively, were investigated. The results showed that the adsorption processes of Hg(II) ions Followed well a pseudofirst-order model onto SG-HE-dD, SC-HO-dD, and SG-HE-pD, while a pseudosecond-order model was followed onto SG-HO-pD. Film diffusion might be dominated in the adsorption process of Hg(II) ions onto the four adsorbents Thermodynamic analysis revealed that the adsorption behaviors of Hg(II) ions onto the four adsorbents were endothermic processes, resulting in higher adsorption capacities at higher temperature The Langmuir, Freundlich, and Redlich Peterson models were employed to fit the isothermal adsorption The results revealed that the linear Langmuir. nonlinear Lanhmuir and nonlinear Redlich Peter son isotherm models are the best-fit models to predict the experimental data Mercury ions adsorbed on low adsorbents were desorbed effectively at about 5 % thiourea/0.1 mol . L(-1) HNO(3), and the adsorption capacity of the SG-HO-dD and SG-HO-pD adsorbents can still be maintained at the (98 and 95) % level at the fifth cycles, respectively