Supervisors info:
Αριάδνη Αργυράκη, Αναπληρώτρια Καθηγήτρια, Τμήματος Γεωλογίας και Γεωπεριβάλλοντος, ΕΚΠΑ
Summary:
The Fe-rich smectite clay mined in the area of Grevena, Greece, is a natural material, environmentally friendly, readily available with efficiency in environmental remediation of sοil contaminated by heavy metals. The main propose of this thesis was to study the interaction between Fe-rich smectite clays quarried at Knidi, Grevena by Geohellas S.A., and Copper (Cu) and Lead (Pb) cations in monometallic aqueous solutions by comparing the adsorption capacity of raw and thermally modified clay material.
Adequate quantity of powdered clay material was supplied by Geoellas S.A.. Separate samples were heat treated at temperatures of 130, 330, 500 and 800 oC for 4 hours in a muffle. The raw material studied is a mixture mainly of Fe-rich dioctahedral and trioctahedral smectite and palygorskite and its properties are a combination of the properties of the contained minerals. Mineralogical analysis by X-ray diffraction (XRD) before and after heat treatment showed that the crystal lattice of Fe-smectite gets destructed at temperatures higher than 130oC. Τhe comparative study of Cu and Pb adsorption efficiently of heat treated and non-treated material, was subsequently performed by using an adsorbent dose from 2 to 15 g/L, initial metal concentration of 50mg/L, shaking time between 5 minutes to 2 hours and pH 2-8. The effect of ionic strength was studied by adding NaNO3 at concentrations from 0 to 0.5 mole/L. All experiments were carried out in a thermostatic chamber set at 22oC. Metal concentrations before and after interaction, were measured by Flame Atomic Absorption Spectroscopy (F-AAS).
A decrease in the concentration of the metals in the aqueous solution was observed with increasing adsorbent dose. A clay dose of 10 g/L in the suspension was the most effective, as 90-100% of Cu and Pb was retained in the clay after interaction with all raw and heat treated materials, except the sample heated at 800 oC. The optimum pH of the standard aqueous solution was between 4 and 6 for thermally modified and raw material. In general, equilibrium was achieved after the first 30 minutes of interaction, however, a significant decrease of metal concentration was observed within the first 5 minutes indicating that adsorption is a fast process. A decrease in adsorption was observed as the concentration of NaNO3 was raised, probably due to competition between Na+ and metal ions for the available adsorption sites. The adsorption isotherm is of L-type, indicating high relation between the studied metals and the surface of the adsorbent. The samples treated at different temperatures present different adsorption capacity because of differences in their mineralogy. A difference in the physical and mechanical parameters of the material is also noticed for different temperatures of treatment. Finally, the results compared with different studies from the bibliography about materials of the same clay group like smectite, palygorskite etc. The raw as the thermally modified material was effective in the adsorption of the two metals (with small differences in their adsorption capacity) except the sample heated at 800 oC. Overall, the clay material has the potential to act as a binding agent of heavy metals from aqueous solutions in either raw or heat treated condition.
Keywords:
Fe-smectite, palygorskite, clay, heat treatment, adsorption, copper (Cu), lead (Pb)
