Assessment of the BCR sequential extraction procedure for thallium fractionation using synthetic mineral mixtures

This work focused on the specific behavior of TI-bearing phases in the BCR (Community Bureau of Reference) sequential extraction (SE) scheme, namely TI-bearing ferrihydrite, goethite, birnessite, calcite, illite, sphalerite and feldspar in their simple model mixtures with quartz. Several significant discrepancies between the obtained and expected behaviors of these phases in the BCR SE were observed. The amount of TI released as the exchangeable/acid-extractable fraction (55-82% of the total TI content) showed a substantial W-promoted dissolution of all Fe(III) and Mn(III, IV) oxides (corresponding to up to 61% of solid Fe dissolved) and incongruent (increased) extraction of TI from ferrihydrite and goethite. Reductive conditions of the second SE step were insufficient to complete goethite dissolution with corresponding TI amount retained in the solid phase. Similarly, insufficient oxidation of sphalerite and lower TI recovery of the oxidisable fraction was identified. In contrast, the BCR SE seems to produce well predictable results of TI leaching from TI-bearing calcite and feldspar. Only 70% of total TI content was extracted from TI-modified illite in the exchangeable/acid-extractable step, while 30% was associated with the reducible and residual fractions, i.e., TI was strongly fixed to the illite matrix. (C) 2009 Elsevier B.V. All rights reserved.