Thallium Speciation and Extractability in a Thallium- and Arsenic-Rich Soil Developed from Mineralized Carbonate Rock

Abstract

We investigated the speciation and extractability of Tl in soil developed from mineralized carbonate rock. Total Tl concentrations in topsoil (0-20 cm) of 100-1000 mg/kg are observed in the most affected area, subsoil concentrations of up to 6000 mg/kg Tl in soil horizons containing weathered ore fragments. Using synchrotron-based microfocused X-ray fluorescence spectrometry (μ-XRF) and X-ray absorption spectroscopy (μ-XAS) at the Tl L3-edge, partly Tl(I)-substituted jarosite and avicennite (Tl2O3) were identified as Tl-bearing secondary minerals formed by the weathering of a Tl-As-Fe-sulfide mineralization hosted in the carbonate rock from which the soil developed. Further evidence was found for the sequestration of Tl(III) into Mn-oxides and the uptake of Tl(I) by illite. Quantification of the fractions of Tl(III), Tl(I)-jarosite and Tl(I)-illite in bulk samples based on XAS indicated that Tl(I) uptake by illite was the dominant retention mechanism in topsoil materials. Oxidative Tl(III)uptake into Mn-oxides was less relevant, probably because the Tl loadings of the soil exceeded the capacity of this uptake mechanism. The concentrations of Tl in 10 mM CaCl2-extracts increased with increasing soil Tl contents and decreasing soil pH, but did not exhibit drastic variations as a function of Tl speciation. With respect to Tl in contaminated soils, this study provides first direct spectroscopic evidence for Tl(I) uptake by illite and indicates the need for further studies on the sorption of Tl to clay minerals and Mn-oxides and its impact on Tl solubility in soils.

Bioaccumulation of thallium in a neutral soil as affected by solid-phase association

“…Thallium retention is generally attributed to simple exchange reactions on oxides, silicates or possibly organic matter (Tremel et al, 1997;Jović, 1999). However, the most efficient scavengers of Tl, consistent also with our findings, include Mn(III,IV) oxides (mainly birnessite, δ-MnO 2 ) and illite clays (Bidoglio et al, 1993;Jacobson et al, 2005;Gao et al, 2007;Vaněk et al, 2011;Voegelin et al, 2015). This affinity can be explained by a complex process of specific Tl adsorption and/or Tl-K replacement within the mineral structures, resulting from the same valence and similar ionic radius of Tl(I) and K(I) (Nriagu, 1998).…”

“…Taking into account the calculated Tl/Mn, Tl/Fe, and Tl/Ca ratios, compared to the initial values, similar ratios were determined only in soil B, contrary to soils A and C. An approximate two time increase was typical for soil A; the mobilization of Tl from the Mn oxide was thus incongruent, i.e., Tl and Mn were not released in the same proportion as found in the bulk "mineral", probably because the oxide surface is enriched in Tl to some extent. For example, the tendency of Tl to precipitate as Tl 2 O 3 (log K sp = −13; MINTEQA2 database) on the birnessite surface was previously documented (Bidoglio et al, 1993;Voegelin et al, 2015). We assume that a part of such associated Tl can be attacked by mild extractants more easily, including soil H 2 O, and after its mobilization, rapid Tl penetration into the soil matrix occurs (see below).…”

“…On the other hand, the role of carbonate-rich soil matrices in the complex dynamics of Tl will presumably be less pronounced in the long-term, apart from in acidic soils. However, Tl (co)precipitation with the newly formed carbonates, following CaCO 3 dissolution in the rhizosphere (Yang et al, 2005), and/or well-known stabilization behavior of illite clays (Jacobson et al, 2005;Voegelin et al, 2015) must be also taken into account. Therefore, Tl and bulk soil mineralogy, as well as the content and quality of SOM are suggested to be critical parameters controlling Tl bioaccumulation potential.…”

Constraining oceanic oxygenation during the Shuram excursion in South China using thallium isotopes

“…Therefore, it is unlikely that Tl 2 S would precipitate directly from these waters. Alternatively, Tl could also be dominantly sorbed onto the surface of clay minerals in these non‐euxinic reducing sediments, especially Na‐illite (e.g., Martin, Wissocq, Benedetti, & Latrille, ; Voegelin et al, ). Given that Tl isotope fractionation appears to be muted during sorption that is not associated with Tl oxidation (Nielsen et al, ), it would not be expected that clay minerals are fractionated relative to the water column.…”

Presence of thallium in the environment: sources of contaminations, distribution and monitoring methods

“…Determination of Tl(I) and Tl(III) species was may be carried out in soil samples (Voegelin et al 2015), wastewater samples (Ospina-Alvarez et al 2015), plant tissues (Sadowska et al 2016) and cells (Nowicka et al 2014). Several reports indicate that the use of ICP-MS allows for credible speciation of Tl.…”