This work focused on the specific behavior of Tl-bearing phases in the BCR sequential extraction (SE) scheme, namely Tl-bearing ferrihydrite, goethite, birnessite, calcite, illite, sphalerite and feldspar in their simple model mixtures with quartz. The amount of Tl released as the exchangeable/acid-extractable fraction (55–82% of the total Tl content) showed a substantial H+-promoted dissolution of all Fe(III) and Mn(III,IV) oxides (corresponding to up to 61% of solid Fe dissolved) and incongruent extraction of Tl from ferrihydrite and goethite.
Reductive conditions of the second SE step were insufficient to complete goethite dissolution. Similarly, insufficient oxidation of sphalerite and lower Tl recovery of the oxidisable fraction was identified.
In contrast, the BCR SE seems to produce well predictable results of Tl leaching from Tl-bearing calcite and feldspar. Only 70% of total Tl content was extracted from Tl-modified illite, i.e., Tl was strongly fixed to the illite matrix.