[Adsorption Cd from Solution by EDTA-modified Silicate Nanoparticles].

Silicate nanoparticles(nSiO) are a kind of widely used engineering material. In order to improve the Cd adsorption ability, the EDTA-modified nSiO nanoparticles were prepared by grafting method and characterized by TEM, N adsorption-desorption, FTIR, and TGA. The effects of solution pH, contact time, temperature and ionic strength were examined. The adsorption mechanism was further investigated by XPS. The results showed that the EDTA-nSiO nanoparticles possessed excellent stability, and were successfully prepared. Cd adsorption was mainly controlled by solution pH. The raw nSiO had limited Cd adsorption ability, while the EDTA-modified nSiO particles had significantly improved adsorption performance. At high pH, the Cd adsorption rate increased and kept balance above pH 4.0. The Cd adsorption was an endothermic spontaneous process which could be finished within 1 h. Langmuir model could be used to describe the adsorption isotherm. The temperature ranged from 293-313 K during the process, while the maximum adsorption was observed at higher temperature. Higher ionic strength could inhibit the Cd adsorption. The Cd adsorption decreased from 0.433 to 0.294 mmol·g, when NaCl concentration varied from 0 to 100 mmol·L. The desorption of Cd from the EDTA-nSiO nanoparticles was carried out with distilled water, 0.1 mol·L NaCl and 0.1 mol·L HCl. The maximum Cd desorption of 94.36% was obtained at 0.1 mol·L HCl. Based on the results of thermodynamics, pH, ionic strength, and XPS analysis, it could be concluded that Cd adsorption was a multiple process dominated by chemical chelating reaction, physical adsorption and ion exchange. This study indicated that the EDTA-nSiO is an effective engineering nanomaterial that could be used in Cd adsorption.