Effects of acetate on cation exchange capacity of a Zn-containing montmorillonite: physicochemical significance and metal uptake.
Fundamental properties such as cation exchange capacity (CEC), permanent charge, pH(PZC), and metal uptake of a Zn-containing montmorillonite are modified, in a predictable manner, by a mild chemical treatment using acetate. Acetate treatment allows a controllable increase of the CEC of montmorillonite up to 180 mequiv/100 g. The CEC of the clay is increasing for decreasing Zn content, with a slope of Delta[Zn]/Delta[CEC] approximately -2. X-ray powder diffraction analysis shows that the lamellar structure of the clay remains unaltered by the acetate treatment, while XPS substantiates the removal of Zn. H(+) uptake data show that the intrinsic protonation pK values and concentration of the variable charge sites ( identical with SOH) are not modified by the acetate treatment. In contrast, the concentration of the permanent charge sites ( identical with X(-)) increased linearly with Zn removal by acetate, leading to a significant H(+) and Cd(2+) uptake enhancement. A physical model is suggested where acetate removes Zn ions strongly bound in the clay, and this in turn modulates the permanent charge and the CEC of the clay.
Department of Environmental and Natural Resources Management, University of Ioannina, Seferi 2 30100 Agrinio, Greece.
P
P
Stathi
I T
IT
Papadas
A
A
Enotiadis
R Y N
RY
Gengler
D
D
Gournis
P
P
Rudolf
Y
Y
Deligiannakis