Equilibrium batch measurements were made of the adsorption of Cd(II) on 15 New Jersey soils. The soils were characterized in terms of surface properties and chemical composition, particularly organic matter and metal oxides. The adsorption of Cd(II) followed the Langmuir relation and increased with increasing pH between pH 3 and pH 10. At constant pH and metal concentration, greater adsorption was observed for soils with higher organic matter content. To better understand the mechanism of adsorption, the experimental results for the adsorption of Cd by the 15 soils were tested using a partition coefficient model that related the adsorption of the Cd(II) to the soil components: organic matter, iron oxides, aluminum oxides, and manganese oxides. This model was not successful when applied to measurements at the natural soil pH because of the competition of protons with Cd(II) for available sites. However, at constant pH, partition coefficients obtained from experimental data were highly correlated with those calculated for a partition coefficient between Cd(II) and organic matter alone. Normalization of the partition coefficients, K d , for the organic matter content of the soils, K om , greatly improved the relationship between the partition coefficient and pH (R 2 increased from 0.799 to 0.927). This suggests that the surficial adsorption sites are principally composed of organic matter. For the 24-h equilibration period employed, diffusion of Cd(II) through this superficial organic matter coating to underlying sorptive materials, including metal oxides, is unimportant in the partitioning of Cd(II).
12Cadmium (Cd) adsorption on 14 non-calcareous New Jersey soils was investigated 13 with a batch method. Both adsorption edge and isotherm experiments were conducted 14 covering a wide range of soil composition, e.g. soil organic carbon (SOC) concentration 15 ranging from 0.18% to 7.15%, and varying Cd concentrations and solution pH. by the independent data sets: adsorption isotherm data, which presumably can be used to 25 predict Cd partition equilibrium across a wide range of soil compos itions. The modeling 26 approach presented in this study helps to quantitatively predict Cd behavior in the 27 environment. 28
Environmental context. Lead is a common and persistent soil and water contaminant. This study provides a unique set of parameters for chemical models that can be used for predicting Pb adsorption by soil. The suggested modelling approach can be used to quantitatively predict Pb retention and release in soils with changing environmental conditions.Abstract. Lead (Pb II ) adsorption on 14 non-calcareous New Jersey soils was studied with a batch method. Both adsorption edge and adsorption isotherm experiments were conducted covering a wide range of soil compositions, Pb concentrations and solution pHs. Visual MINTEQ was used to calculate the Pb adsorption equilibrium by coupling the Stockholm Humic Model, the CD-MUSIC model, a diffuse layer model and a cation exchange model for Pb reactions with soil organic matter (SOM), Fe (hydr)oxides, Al hydroxides and clay minerals. For model predictions, reactive organic matter (ROM), the fraction of SOM responsible for Pb binding, and reactive Al and Fe III in soils were quantified. The models predicted Pb adsorption to soils reasonably well with varying SOM and mineral content at various pHs and Pb concentrations. For 3.0 , pH , 6.0, the log partition coefficient root mean square error was 0.34. However at higher pHs the models were less successful. Both ROM and Al competition had a significant effect on model predictions. ROM was the dominant adsorption phase at pHs between 3.0 and 5.0. For pH . 5.0, Pb adsorption to Fe (hydr)oxides became significant. The modelling approach presented in this study can be used to understand and quantitatively predict Pb adsorption on soil.
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