Fixation of radiocaesium traces in a weathering sequence mica → vermiculite → hydroxy interlayered vermiculite

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Abstract
Summary: Radiocaesium fixation in soils is reported to occur on frayed edge sites of micaceous minerals. The weathering of mica in acid soils may therefore influence the Cs + fixation process and thereby the mobility of the radiopollutant. We produced a laboratory weathering model biotite → trioctahedral vermiculite → oxidized vermiculite → hydroxy interlayered vermiculite (HIV) and quantified the Cs + fixation of each mineral both in a fixed K + –Ca 2+ background and in acid conditions. The transformation process was achieved through K depletion by Na‐tetraphenylboron, oxidation with Br 2 and Al‐intercalation using NaOH and AlCl 3 . In a constant K + –Ca 2+ background, vermiculite fixed 92–95% of the initial 137 Cs + contamination while biotite and HIV fixed only 18–33%. In acid conditions, the interlayer occupancy by either potassium (biotite) or hydroxy‐Al groups (HIV) strongly limited Cs + fixation to 1–4% of the initial 137 Cs + contamination. Cs + fixation occurred on vermiculitic sites associated with micaceous wedge zones. Though both oxidized and trioctahedral vermiculites fixed similar Cs + amounts in a constant K + –Ca 2+ background (92–95%), the oxidized vermiculite retained much more radiocaesium in acid conditions (78–84% against 54–59%), because of its dioctahedral character.

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