Effect of a sewage sludge extract on the sorption process of cadmium and nickel by soil

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Abstract
Studies about heavy metals interactions with soils have received increasing attention due to land addition of different kinds of sewage sludge. Of particular importance in this field is the sorption process of heavy metals which influences their mobility, determining their distribution between the liquid and the solid phase of the soil. In this work, heavy metals (Ni and Cd) sorption was carried out on a sandy‐loam soil with and without a sewage sludge extract (CO2‐H2O solution at pH 3.8) to evaluate the effects of ligand species present in the sludge in the process of retaining heavy metals. The addition of sewage sludge extract, did not reduced the sorption, but rather increased the amount of heavy metals retained by the soil. The effect could be ascribable, at the pH of the experiment, to a preliminary sorption of organic ligands on to soil with the creation of new sorbing surfaces. The sewage sludge extract was, then characterized by elemental analysis, thermogravimetric, NMR and IR techniques to deepen the knowledge of the interactions with soil.