Supervisors info:
Αριάδνη Αργυράκη, Καθηγήτρια, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, ΕΚΠΑ (Επιβλέπουσα)
Χαράλαμπος Βασιλάτος, Επίκουρος Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, ΕΚΠΑ
Ζαχαρένια Κυπριτίδου, ΕΔΙΠ, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, ΕΚΠΑ
Summary:
In the context of this thesis, clay materials were studied as soil pollution stabilization agents and as filling materials for geosynthetic clay liners. The aim of the thesis is a) to optimize the effectiveness of palygorskite clay, as a soil additive in an industrial pollution area for the stabilization of lead (Pb), and b) to contribute to the selection of the most suitable smectite geosynthetic clay liner filler material with resistance to high temperatures.
Palygorskite clay, a commercial product of Geoellas S.A., Sanfed Powder F, was used for soil pollution stabilization. Pb-contaminated soil from an industrial area was collected and 3 treatments were created: Control (without the addition of palygorskite clay), Active_5% (adding 5% of palygorskite of clay in the active fraction of soil) and Total_5% (adding 5% of palygorskite clay to the total fraction of soil). The application of palygorskite clay to the contaminated soil did not significantly affect the soil properties (pH, TDS, SO42-). A significant reduction in the water-extractable concentration of lead was detected in the Active_5% and Total_5% treatments, with a reduction up to 54.8% and %54.1%, respectively. In addition, a reduction of 9.8% was observed for Sb in the Active_5% treatment and 11.1% in the Total_5% treatment compared to the Control. Significant Zn reduction was found equal to 75.4% in Total_5% treatment. As and Cu were not affected by the addition of palygorskite. The soil, according to Directive 33/2003, after stabilization can be categorized as inert waste for the elements Pb, As, Zn and Cu and as non-hazardous waste for Sb.
A commercial Ca-bentonite (BEN), a Mg-smectite rich clay of green color in raw form (PS1.R) and a Mg-smectite rich clay of green color, Na-converted (PS1.A) were considered as GCL fillers. The samples underwent heat treatment at temperatures of 150oC, 180oC and 210oC in a muffler furnace for 2h before the experiments. The hydraulic conductivity values of the materials have a range of 10-6-10-9cm/s. The bentonite samples thermally treated or not present the highest liquid limit (394.3-485.5%) and plasticity index (351.3-446.8%), while the highest plasticity limit (50-55%) corresponds to samples of the activated Mg-smectite. In addition, the Ca-bentonite samples maintain a high swelling index (23-26%) and low fluid loss (16.0-19.0mL). The samples of Ca-bentonite, raw Mg-smectite and activated Mg-smectite show high Pb removal with nearly 100%, 87% and 99.5% removal rate, respectively. High removal is found in Ni, with removal values of 54.3-61.2% for the Ca-bentonite samples, 50.2-53.4% for the activated Mg ¬smectite and 44-46% for the raw Mg-smectite samples. Furthermore, no difference in removal due to temperature change was observed. On the contrary, the removal of Cr(VI) was small (0-26.7%), but it is observed that the highest removal is found in the thermally modified samples.
The application of palygorskite clay to Pb-contaminated soil can be characterized as an effective method for soil stabilization, as palygorskite adsorbs soluble lead, but also helps it to transform into its stable and insoluble forms. Smectite clays tend to retain their properties despite increasing temperature. But, according to the results of the experiments and the specifications for the materials that can be used as a filler of a geosynthetic barrier, it appears that only Ca-bentonite at temperatures of 25-180oC can be used as a filler.
Keywords:
clay materials, palygorskite, stabilization, bentonite, filling materials, geosynthetic clay liner
