Table 192

Heavy Metal Adsorption Characteristics of Thiol-SAMMS

Adsorption maximum

functionalities such as thiols (-SH groups). According to the HSAB principle, soft cations and anions possess relatively large ionic size, low electronegativity, and high polarizability (highly deformable bonding electron orbitals); therefore, they mutually form strong covalent bonds. The order of adsorption maxima observed in this experiment appears to reflect the order of softness calculated by Misono et al. [11] for these heavy metals.

The kinetics data indicated that thiol-SAMMS adsorbed ~99% of the dissolved mercury within the first 5 min of reaction (Figure 19.8). Comparatively, the resin (GT-73) adsorbed only ~18% of the dissolved mercury during the initial 5 min. These data showed that thiol-SAMMS substrate adsorbs mercury about two to three orders of magnitude faster than the commercial GT-73 ionexchange resin. After 8 h of reaction, thiol-SAMMS reduced the residual concentration of mercury to ~0.04 mg/L; the resin material was not capable of reducing mercury concentration below 1mg/L. Calculated distribution coefficients (Kd) indicated that thiol-SAMMs adsorbed mercury at about one to three orders of magnitude higher selectivity (7 x 103 - 3.6 x 105 ml/g) than the resin material (4.5 x 102 - 1.9 x 103 ml/g).

Results from the radioiodine adsorption experiments indicated that Hg-thiol, and Ag-thiol SAMMS very effectively adsorbed 125I from the groundwater matrix (Table 19.3). Both forms of SAMMS exhibited very high distribution coefficients (Kd: 2.9 x 104 to 1.2 x 105 ml/g), indicating that radioiodine was sorbed with high specificity even in the presence of anions in the groundwater that were present in significantly higher concentrations than radioiodine. Such selectivity and

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