Sorption of heavy metal cations on rhyolitic and andesitic bentonites from Central Slovakia

Sorption of heavy metal cations on rhyolitic and andesitic bentonites from Central SlovakiaThe main purpose of this work was to determine adsorption characteristics of heavy metal cations on two Slovak bentonites. Adsorption of Pb2+, Zn2+, Cu2+and Cd2+on Jelšový Potok (JP) and Lieskovec (L) bentonites was studied by the batch equilibration technique using solutions of different concentrations. Higher smectite content (81 mass %) and higher cation exchange capacity (CEC) (105 mmol M+/100 g) of JP bentonite cause higher adsorption of all heavy metals in comparison with L bentonite. JP adsorbed heavy metals in the order Pb2+» Cd2+> Zn2+> Cu2+while sorption on L was slightly different, Pb2+» Cd2+> Cu2+≥ Zn2+. The Freundlich model of adsorption is more appropriate for adsorption of Pb2+and Cd2+while lower uptake of Cu2+and Zn2+is better described by the Langmuir model. Negative ΔG° values indicate that the adsorption process of all cations on both bentonites is feasible, spontaneous and exothermic. The decrease in thed001spacings from 14.8-14.9 Å in natural dominantly Ca2+-saturated samples to 13.2-12.6 Å for both bentonites saturated with four heavy metal cations shows the effect of less hydrated exchangeable cations on interlayer spacing. Jelšový Potok bentonite of higher montmorillonite content and greater CEC is the more effective candidate for removal of Pb2+, Zn2+, Cu2+and Cd2+from waste water than Lieskovec bentonite.

Experimental interactions of Slovak bentonites with metallic iron

Experimental interactions of Slovak bentonites with metallic ironThe experimental stability of four bentonites and one K-bentonite from Slovak deposits in the presence of iron was studied to simulate the possible reactions of clays (bentonite barrier) in the contact with Fe containers in a nuclear waste repository. The batch experiments were performed at 60 °C for 30 and 120 days in aerobic conditions. The reaction products were examined by XRD, FTIR, and Mössbauer spectroscopies and CEC (cation exchange capacities) were determined. Reaction solutions were analysed for selected elements using AAS (atomic absorption spectrometry). The results show that bentonites do not interact equally with metallic iron. Bentonites from the Jelšový Potok, Kopernica and Lieskovec deposits reacted similarly whereas the interaction between the bentonite from Lastovce and the iron was less intensive. The lower reactivity of the bentonite from Lastovce can be explained by its low content of smectite. During iron-clay interactions the iron was consumed and Fe oxides (magnetite, lepidocrocite) were formed. Decrease of the smectite diffraction peaks intensity and CEC values during the experiments show rather the rearrangement of the original smectite crystals than dissolution of smectite. In the K-bentonite from the Dolná Ves deposit where the mixed-layer illite-smectite is present instead of smectite, the dissolution of illite-smectite was observed along with the neoformation of smectite. The structure of illite-smectite deteriorated more than the structure of smectites which suggests that this mixed-layer illite-smectite is much less stable in the presence of iron than smectites.