Sepiolite functionalized with N-[3-(trimethoxysilyl)propyl]ethylenediamine triacetic acid trisodium salt. Part II: Sorption of Ni2+ ions from water

The sorption of Ni2+ on sepiolite functionalized by covalent grafting of N-[3-(trimethoxysilyl) propyl] ethylenediamine triacetic acid trisodium salt, MSEAS, was studied in batch experiments as a function of the initial metal concentration, the equilibration time, the pH value and the temperature. The modification of sepiolite resulted in enhanced Ni2+ retention with a capacity of 0.261 mmol g(-1) at 298 K. The retention of Ni2+ occurred dominantly by specific sorption and exchange of Mg2+ from the sepiolite structure. The sorption process followed pseudo-second-order kinetics. The sorption equilibrium results were best described by the non-linear form of the Langmuir sorption equation. The values of the thermodynamic parameters (changes of enthalpy, free energy and entropy) were calculated from temperature dependent sorption isotherms and their values showed that the sorption of Ni2+ onto modified sepiolite was endothermic.