Clay Minerals (1996) 31,477-483 THE INFLUENCE OF LAYER CHARGE ON ZN 2+ AND SORPT ION BY SMECTITES

ABSTRACT: Two smectites with different layer charge localization were used to characterize the chemical and structural aspects of minerals treated with 1.9 x 10.2 M and 1 M heavy metal solutions (Zn 2 § and pb2+). Natural and treated smectites were analysed by: (1) X-ray powder diffraction first at 25 ~ and relative humidity of 60 % and then at increasing temperature up to 400 ~ (2) thermo-gravimetric and differential thermal analysis; (3) X-ray fluorescence; (4) atomic absorption and UV visible spectrophotometries. The sorption of both metals depends on 2:1 layer features and is enhanced when the total layer charge is mostly due to substitution in the octahedral sheet. The variability between Zn 2+- and pb2+-treated smectites in the interlayer water content depends both upon cation electrostatic features and upon smectite layer charge localization. The greatest water content was observed in [Zn2+]l M-treated smectite showing charge imbalance in the octahedral sheet. In smectites treated with [Zn 2+] 1 M solutions, an additional thermal reaction occurs at a temperature of ~380 ~ and the d(001) spacing, which is 10, ~ at a temperature of ~200~ gradually decreases in the temperature range 200-400 ~ In smectites treated with 1 M [Pb 2+] solutions this value is reached at a temperature of ~ 150 ~ and remains quite constant up to 400~ Cation exchange between metals from interstitia