Sorption of metal cations on suspended bentonite: effects of pH, ionic strength and complexing anions

Abstract

Abstract Batch sorption experiments have been carried out to understand the interaction of different metal cations such as Am(III), Eu(III), Sr(II), and Cs(I) with bentonite clay at varying pH (1–9). The effects of other experimental parameters such as ionic strength (0.01–1 M (NaClO4)), clay to metal ion concentration ratio, and the presence of complexing anions such as oxalic acid (ox), carbonate (CO3 2−), ethylenediaminetetraacetic acid (EDTA), and humic acid (HA) on Eu(III) sorption have also been investigated. The sorption of Eu(III) has been found to be invariant with the change in ionic strength suggesting inner-sphere complexation on the bentonite surface. Near quantitative sorption of Eu(III) and Am(III) has been observed in the entire pH range and there is marginal influence of the presence of 1 · 10 –4 M of ox and CO3 2− on the sorption profile. However, the presence of 1 · 10 –4 M EDTA suppresses the sorption of Eu(III) ion onto bentonite. Desorption studies of Eu(III) loaded onto bentonite using varying concentrations of HClO4 (0.01–1.0 M) solutions reveal that higher acidity favors the process. The sorption of Eu(III) on bentonite followed the Langmuir isotherm suggesting monolayer sorption process. The data fitting to D-R isotherm suggested that the Eu(III) sorption on bentonite follows ion exchange mechanism. The sorption capacity of bentonite clay was determined to be 3.8(± 0.1) × 10−4 moles/g using Langmuir and D-R isotherms.