Experimental interactions of Slovak bentonites with metallic iron

Abstract

Abstract:The 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.

About the Corrosion Mechanism of Metal Iron in Contact with Bentonite

“…The correlation of the LCD presented in the presented study, however, is insignificant because of the small number of samples, different cation populations in the interlayer (natural state), and variable amounts of reactive silica. Based on more defined systems and based on a significant sample set, this correlation was established before in different corrosion test series (e.g., variable dominating exchangeable cation).…”

“…Under oxic conditions, Fe oxides/hydroxides form. 3 In real HLRW systems, however, oxygen will soon be consumed and corrosion will proceed anaerobically (as indicated by an intense green color, e.g., Figure 1 published by Kaufhold et al 4 ). Corrosion products formed under anaerobic conditions are magnetite 5 and/or different Felayered silicates 4,6,7 depending on the temperature.…”

“…Laboratory tests as well as large-scale tests proved the formation of new Fe phases caused by corrosion of the metal Fe. Under oxic conditions, Fe oxides/hydroxides form . In real HLRW systems, however, oxygen will soon be consumed and corrosion will proceed anaerobically (as indicated by an intense green color, e.g., Figure published by Kaufhold et al).…”

Mineralogical and physico–chemical properties of bentonites from the Jastrabá Formation (Kremnické vrchy Mts., Western Carpathians)

“…1). Bentonites consist predominantly of montmorillonite, accompanied by variable amounts of opal-C/CT, quartz, feldspars, mica, zeolites and kaolinite (Šamajová et al 1992;Kraus et al 1994;Osacký et al 2009;Uhlík et al 2012;Górniak et al 2016Górniak et al , 2017. The thickness of bentonite beds ranges from a few metres up to 50 m (Šamajová et al 1992).…”

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

“…Smectite content in the blends was the dominant factor affecting their properties. Osacký et al (2009) investigated in batch experiments stability of four bentonites and one K-bentonite from Slovak deposits in the presence of iron to simulate possible reactions of a bentonite barrier in the contact with a Fe container in a nuclear waste repository. The structure of illite-smectite deteriorated more than the structure of smectites.…”