Supervisors info:
Prof. Ariadne Argyraki, Section head of Economic Geology and Geochemistry, Department of Geology and Geoenvironment, National & Kapodistrian University of Athens.
Summary:
This dissertation presents the findings of the study of long-term performance of in-situ mining and metallurgical waste remediation techniques, focusing mainly on the comparison of three different elemental stabilization methods (liming, geomembrane barrier, and compacted clay barrier) that have been applied in a waste pile of pyrite tailings almost 25 years ago. Data of potential toxic element (PTE) leachability are compared with data presented in the initial remediation study held in 1998. In this way, the mobility of three PTEs (Pb, Zn, and Cd) has been assessed for each treatment technique and the spatial distribution, horizontally and vertically, of the PTEs in the waste pile has been determined.
Chemical analysis after aqua regia dissolution, a simplified bioaccessibility extraction test (SBET), and the Toxicity Characteristic Leaching Procedure (TCLP) have been utilized in this study to gather geochemical data. X-ray diffraction (XRD) with integration of scanning electron microscopy coupled with energy dispersive microanalysis (SEM-EDS) have been hired for mineralogical investigation. The X-ray energy dispersive (EDS) measurements in combination with (XRD) and total chemical analysis helped to identify the corresponding host-speciation of the trace metals and therefore the major factors controlling the environmental mobility of Pb, Zn and Cd.
The results of the present study indicate that almost 25 years after the pilot scale remediation in the Kavodokanos waste pile, the area remains polluted, posing significant risks for the health of nearby inhabitants, being exposed to very high concentrations of PTEs including Pb, Cd and As. From the geochemical data, it is deduced that liming did not reduce the PTEs infiltration to the drainage in spite of the indications for a hardpan layer formation. The compacted clay barrier showed good performance in maintaining neutral to slightly alkaline pH values along the depth profile and sustaining its water content and hence eliminating the effect of the evaporation process. The effect of the evaporation process within the pores of the waste material results in high concentrations of PTEs on the surface, especially in the control plot and the lime test plot.
Overall, the long-term performance demonstrates better effectiveness of the compacted clay barrier with the lowest TCLP leachable concentrations of PTEs in surface soil. This means that effective stabilization is better induced by this treatment in the long term. In the original study it is noted that the compacted clay has the additional advantage of low cost compared to the geomembrane barrier. Thus, the compacted clay technique can be considered as an effective sustainable remediation technique that should be considered in other areas with similar characteristics.
