Thermodynamic studies on the adsorption of Cu2+, Ni2+ and Cd2+ on to amine-modified bentonite

Amine-modified bentonite (TEPA-Bn) has been prepared with tetraethylenepentamine (TEPA) as a modifier. The structure of Ca-based bentonite (Ca-Bn), TEPA-Bn and TEPA-Bn after adsorbing Cu 2+ ,Ni 2+ ,Cd 2+ had been characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and simultaneous thermal gravimetric/differential thermal gravimetric (TG/DTG) analysis. The TEPA had been intercalated into Ca-Bn interlayer space but had not changed its original crystal structure. The thermal stability of TEPA-Bn was stronger than Ca-Bn while the hydrophilicity of it reduced. The adsorption ability of TEPA-Bn to Cd 2+ , Ni 2+ , Cu 2+ was much better than Ca-Bn, the saturated adsorption capacity to Cd 2+ , Ni 2+ , Cu 2+ were 14.88, 8.88 and 13.05 times as much as Ca-Bn, respectively. The adsorption behavior of Cu 2+ , Ni 2+ , Cd 2+ on to TEPA-Bn were studied by isothermal models, including Freundlich, Langmuir, Dubinin-Radushkevich Florry-Huggins, and Tempkin models. The Freundlich model simulated the experimental data best, the adsorption of Cu 2+ , Ni 2+ , Cd 2+ onto TEPA-Bn was a multilayer, heterogeneous chemical process. The variety of thermodynamic parameters (DH > 0, DS > 0, DG < 0) under different temperature indicated that the adsorption process of Cu 2+ , Ni 2+ , Cd 2+ on TEPA-Bn was endothermic and spontaneous. KEY WORDS : Amine-modified bentonite, TEPA, Heavy metal ions, Adsorption thermodynamics, Characterization Bull. Chem. Soc. Ethiop. 2016 , 30(3), 357-367 DOI: http://dx.doi.org/10.4314/bcse.v30i3.4