Lead Stabilization in Soil Amended with Lime Waste: An Extended X-ray Absorption Fine Structure (EXAFS) Investigation

초록

To determine Pb species in soils following the immobilization process, sequential extraction has been useddespite the possibility of overestimating Pb species from unintended reactions during chemical extraction. Meanwhile, the application of extended X-ray absorption fine structure (EXAFS) has been shown to providea more precise result than chemical extraction. In this study, the immobilization of Pb in contaminated soilstreated with liming materials such as oyster shell (OS) or eggshell (ES) was evaluated with thermodynamicmodelling and EXAFS analysis. Thermodynamic modelling by visual MINTEQ predicted the precipitation ofPb(OH)2 in OS and ES treated soils. In particular, the values of saturation index (SI) for Pb(OH)2 in OS(SI=0.286) and ES (SI=0.453) treated soils were greater than in the control soil (SI=0.281). Linearcombination fitting (LCF) analysis confirmed the presence of C12H10O14Pb3 (lead citrate, 44.7%) by citric acidfrom plant root, Pb-gibbsite (Pb adsorbed gibbsite, 26.4%), and Pb-kaolinite (Pb adsorbed kaolinite, 20.3%) inthe control soil. On the other hand, Pb(OH)2 (16.8%), Pb-gibbsite (39.3%), and Pb-kaolinite (25.6%) wereobserved in the OS treated soil and Pb(OH)2 (55.2%) and Pb-gibbsite (33.8%) were also confirmed in the EStreated soil. Our results indicate that the treatment with OS and ES immobilizes Pb by adsorption of Pb ontothe soil minerals as a result of the increase in soil negative charge and the formation of stable Pb(OH)2 underhigh pH condition of soils.

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