Leaching of Cd, Cu, Ni and Zn in a sewage sludge-amended soil in presence of geo- and nano-materials

Abstract

In this study, the leaching of heavy metals; cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn); from soils amended with sewage sludge (SS) in the presence of nanoparticles (NPs) (ZnO and MgO) and zeolite was studied. After spiking of soil with heavy metals and mixing with SS and adsorbents, the samples were incubated for 7 days and the column leaching experiments (18 days) were done by two leaching solutions (CaCl2 and DTPA) in glass columns. Also, the leaching curves were simulated by the PHREEQC program. The lowest and highest amounts of Cd leached by CaCl2 were attributed to control soil and soil treated with Isfahan SS in the presence of MgO NPs, respectively, while the lowest amount of Cd leached by DTPA was obtained in soil treated with Rasht SS in the presence of ZnO NPs (7.1 mg kg−1 equivalent to 21.0% of total Cd in this treatment). The lowest amount of Cu leached by CaCl2 was related to the soil treated with Isfahan SS in the presence of ZnO NPs (1.3 mg kg−1). Also, the lowest leaching of Ni (1.4 mg kg−1) and Zn (0.4 mg kg−1) by CaCl2 was related to soil treated with Isfahan SS and Rasht SS in the presence of MgO NPs, respectively. The results showed that the addition of SS decreased Cd and Cu leaching but did not affect Ni and Zn leaching and the presence of NPs and zeolite reduced the leaching of heavy metals. The use of NPs (ZnO and MgO) and zeolite is also recommended as heavy metal adsorbents in contaminated soils. The modeling results showed that the simultaneous use of ion exchange and complex surfaces in the model caused good simulation of laboratory results. Overall, the PHREEQC program demonstrated an acceptable ability to simulate heavy metal leaching in contaminated soils treated with SS in the presence of various adsorbents.