Abstract
AbstractWe used potentiometric titration to study the sorption of hydrogen and cadmium ions by three sediments and the humic acid (HA) extracted from each of these sediments. The acidity constants for both sediment and HA were estimated using a discrete monoprotic acid model. Similar pK values were found for the sediments and the HAs. The pK values are 4.48, 6.10, 7.56, and 9.50 for sediment RS3; 4.03, 6.46, and 8.42 for HA(RS3); 4.00, 5.76, 7.81, and 9.90 for sediment RS4; 4.11, 6.94, and 8.69 for HA(RS4); 3.90, 5.83, 7.90, and 9.78 for sediment RS6; 3.63, 6.23, and 8.24 for HA(RS6). Cadmium binding to sediment and HA was treated as surface complexation of cadmium by ligands. A nonlinear optimization program was used to treat the sorption isotherm data at pH 4.5 and 6.5. Conditional stability constants for cadmium binding to the sediment and HA at pH 4.5 are 4.04 for sediment RS3 and 3.95 for HA(RS3), 4.71 for sediment RS4 and 4.64 for HA(RS4), and 4.56 for sediment RS6 and 4.54 for HA(RS6). At pH 6.5 the conditional constants for cadmium binding are 5.03 for sediment RS3 and 4.92 for HA(RS3), 6.08 for sediment RS4 and 6.02 for HA(RS4), and 5.92 for sediment RS6 and 5.80 for HA(RS6). We also examined the correlation between cadmium binding to sediments and to the HAs extracted from sediments. All the binding of added cadmium by these sediments can be explained by HAs.
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