Abstract:
The aim of this study is to examine the effectiveness of natural and synthetic zeolitic materials as potential soil amendments for the rehabilitation of mine degraded areas. Thus, heavily polluted soil was sampled from the Lavrion mining district in Greece. Two types of natural zeolite tuffs, clinoptilolite- and mordenite-rich, originating from Samos Island, Greece, were pulverized in the laboratory and used as low cost modifiers. Furthermore, a lignite-derived fly ash bulk sample collected from the electrostatic filters of the Meliti Lignite fired Power Station, west Macedonia, Greece, was modified by a low temperature alkaline hydrothermal treatment. The end product was the zeolite Na-P1 (Na6Al6Si10O32•12H2O), which is characterized by its high CEC capacity. Mixtures composed of 90% contaminated soil and 10% w/w of each of the three zeolitic materials were produced for analysis and tests. XRD and SEM methods were used for the characterization of the raw materials and the end-products. Estimation of water solubility and potential bioavailability with the EDTA extracting agent of heavy metals (Pb, Zn, Cu, Mn, Fe, Cd) was performed in those soil mixtures, following the with the European standard EN 12457-2. Furthermore, pot experiments that were implemented revealed that all three zeolite-bearing amendments, have successfully decrease the potentially toxic elements uptake by the Trifolium alexandrinum crop. Soil mixtures containing synthetic zeolitic materials have displayed pH regulation, higher cation exchange capacity values, excellent growth of T. alexandrinum, as well as, a decrease of heavy metals content within the plant tissue. The results of the present study demonstrated that the fly ash synthesized zeolitic material exhibited the best results not only in the regulation of pH, in the increase of CEC, in the growth of T. alexandrinum, but also in reducing of potential bioavailability and water solubility of all 6 potentially toxic elements studied.
Keywords:
Zeolites, fly ash, synthetic zeolites, contaminated soil, amendments, remediation
