No abstract

No abstract

Listwaenitization processes have significantly altered the mantle section of the West Chalkidiki ophiolites, generating the second largest magnesite deposit in Greece. Although research studies have been conducted in the region, the post-magmatic processes, and especially the geotectonic settings under which listwaenitization took place, remain unclear. In this study, minerals and rocks were studied applying XRD, clay fraction, SEM, EMPA, ICP-MS, INAA, LA-ICP-MS, and thermodynamic modeling. The results revealed that alteration processes significantly affected the mantle wedge peridotite protoliths leading to the following chemical changes (a) SiO2 increase with decreasing MgO, (b) Cs, Pb, As, and V enrichments, (c) limited alteration of magnesiochromite hosted within listwaenitized chromitites and (d) enrichment in PPGE and Au in listwaenitized chromitites and desulfurized laurite. Alteration was induced by fluids deriving from subducted Mesozoic sediments, represented by the Prinochori Formation or chemically similar formations. The final product of completely silicified peridotite (silica listwaenite) is thermodynamically stable in Earth-surface conditions, with dolomite and phyllosilicates transforming into clay minerals. Based on detailed petrographical observations, peridotites were subjected to serpentinization, and subsequently, serpentine interacted with CO2, silica and calcium-bearing fluids, leading to its transformation into amorphous rusty-silica mass and/or tremolite.

Raw and modified fibrous clay minerals palygorskite (Pal) and sepiolite (Sep) were tested for their ability to remove ammonium from ammonium polluted water. Palygorskite and sepiolite underwent thermal treatment at 400 o C (T-Pal and T-Sep respectively). Raw and thermally treated samples were characterized using XRD, SEM, BET, FT-IR, TGA, zeta potential and XRF. The techniques verified the effect of thermal treatment on samples structures and the enhancement of negative charge. Both raw and thermally-activated materials applied in batch kinetic experiments, and found to be efficient adsorbents in their raw forms, since Pal and Sep achieved 60 and 80% NH4 + -N removal respectively within 20 min of contact for initial NH4 + -N concentration of 4 mg/L. Similar removal rates were gained for other concentrations representative of contaminated aquifers that were examined, ranging from 1 mg/L to 8 mg/L. Results for the modified T-Pal and T-Sep minerals showed up to 20% higher removal rate. Saturation tests indicated the positive effect of thermal treatment on the minerals since T-Pal and T-Sep removal efficiency reached 85% and remained stable for 24 h. However, competitive ions in real water samples can influence the NH4 + -N removal efficiency of the examined samples. In all cases, the Freundlich isotherm and pseudo-second kinetic models showed better fitted all examined samples thus indicating heterogeneous chemisorption.

No abstract