Heavy Metal Adsorption Characteristics of Thiol-SAMMS
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.  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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