We comparatively assessed the effect of modified clays (MCs) (zeolite and bentonite) and nanoparticles (NPs) (ZnO and MgO) on the distribution of cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) fractions in a light-textured soil amended with five sewage sludges (SSs) differed in chemical properties during a 92-day incubation experiment in the laboratory. Results indicated that presence of adsorbents and incubation time were critical parameters in stabilizing metals in SS-amended soil. The adsorbents that significantly decreased the easily soluble and exchangeable of metals in SS-amended soil (rate 2%) were bentonite, ZnO and MgO for Cd and Cu, ZnO and MgO for Ni, and bentonite and MgO for Zn. The calculated mobility factor of the metals at five incubation times (5, 15, 29, 57 and 92days) was found in the range of 34.7-51.8 for Cd, 16.7-20.0 for Cu, 15.0-27.7 for Ni, and 35.3-40.7 for Zn indicating a higher mobility of Cd. The addition of MCs and NPs decreased the available fraction of metals, and among them, we suggest bentonite and MgO as novel, promising and feasible adsorbents with the unique characteristics in ameliorating the toxic effects of metals by converting their form from labile to non-labile phases in the SS-amended soil.
Keywords: Clay minerals; Fractionation; Heavy metals; Nanoparticles; Sewage sludge.
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