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

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.