3.3. Sorption capacity of the materials
3.3.1. Description of sorption isotherms
In addition to the acid buffering capacity of the materials, their sorption capacity should also be tested to suggest the appropriate materials for soil remediation. The sorption isotherm pattern varied depending on the metal + material combination. Selected Csorb vs. Ceq and Kd vs. Csorb isotherms are shown in Fig. S2 in the Supplementary material, whereas Figs. S3 to S10 of the Supplementary material show all of the Csorb vs. Ceq sorption isotherms. The sorption isotherms can be grouped in three main patterns according to the observed shape (Giles et al., 1974). Most isotherms followed the high affinity pattern, which is characterised by a decrease in the Csorb vs. Ceq slope (that is Kd) as the metal concentration increased (Fig. S2A), which is due to the material containing sites with different affinity for the metal. Constant partition isotherms, which account for linear sorption in the whole range of tested concentrations (further confirmed by the nearly constant Kd values against changes in Csorb) were only observed for a limited number of metal + material combinations (Fig. S2B) (i.e., OWH-Zn, OWH-Ni and OP-Zn). Finally, sigmoidal-shaped curves were also observed for a few cases, such as MOW-Cu, DOM-Pb, OWH-Pb and OP-Pb. These isotherms exhibited an increasing Csorb vs. Ceq slope (that is Kd) at increasing metal concentrations (Fig. S2C).
3.3. Sorption capacity of the materials3.3.1. Description of sorption isothermsIn addition to the acid buffering capacity of the materials, their sorption capacity should also be tested to suggest the appropriate materials for soil remediation. The sorption isotherm pattern varied depending on the metal + material combination. Selected Csorb vs. Ceq and Kd vs. Csorb isotherms are shown in Fig. S2 in the Supplementary material, whereas Figs. S3 to S10 of the Supplementary material show all of the Csorb vs. Ceq sorption isotherms. The sorption isotherms can be grouped in three main patterns according to the observed shape (Giles et al., 1974). Most isotherms followed the high affinity pattern, which is characterised by a decrease in the Csorb vs. Ceq slope (that is Kd) as the metal concentration increased (Fig. S2A), which is due to the material containing sites with different affinity for the metal. Constant partition isotherms, which account for linear sorption in the whole range of tested concentrations (further confirmed by the nearly constant Kd values against changes in Csorb) were only observed for a limited number of metal + material combinations (Fig. S2B) (i.e., OWH-Zn, OWH-Ni and OP-Zn). Finally, sigmoidal-shaped curves were also observed for a few cases, such as MOW-Cu, DOM-Pb, OWH-Pb and OP-Pb. These isotherms exhibited an increasing Csorb vs. Ceq slope (that is Kd) at increasing metal concentrations (Fig. S2C).
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