Thallium (Tl) sorption onto illite and smectite: Implications for Tl mobility in the environment

Abstract

Clay minerals play a relevant role in the transport and fate of trace elements in the environment. Though illite has been referred as an important Thallium (Tl) bearing phase in soils, mechanisms and affinity of thallium for clay minerals remain poorly known. This study investigated the sorption behavior of thallium as Tl(I) onto illite and smectite, two clay minerals occurring mainly in soils and sediments. Different sorption experiments were carried out under various pH conditions and Tl concentrations, in competition with sodium and calcium at a constant ionic strength of 0.01 mol L À1. Our results showed that illite displayed more affinity than smectite for thallium. With illite, the distribution coefficients (K d in L kg À1) varied between 10 2.75 ± 0.17 and 10 4.0 ± 0.17 in Na solutions versus between 10 2.25 ± 0.17 and 10 3.0 ± 0.17 in Ca solutions, depending on pH. With smectite, K d (in L kg À1) ranged between 10 2.50 ± 0.16 and 10 3.20 ± 0.16 and between 10 1.25 ± 0.16 and 10 1.95 ± 0.16 in Na and Ca solutions, respectively. Sorption behavior was described with the Multi-Site Ion Exchanger model and selectivity coefficients with respect to protons were calculated for the first time. In all cases, independently of clay mineral and background electrolyte, low capacity but highly reactive sites were dominant in thallium uptake, highlighting Tl affinity for those sites. Moreover, the exchangeable and reversible interactions between Tl + and clays reactive sites suggested that in changing conditions, thallium could be released in solution. The role of clay minerals in thallium environmental cycle is evident and confirmed illite to be a dominant Tl bearing phase, in some environment competing with manganese oxides. Compared to others Tl bearing mineral phases, clays are ranked as follows: MnO 2 > illite > smectite $ ferrihydrite ! Al 2 O 3 $ goethite > SiO 2. Finally, over the three monovalent cations (Tl, Rb, Cs) Tl is the one less sorbed on illite independently of the background cations.

Geochemical Alteration and Mineralogy of Coals under the Influence of Fault Motion: A Case Study of Qi’nan Colliery, China

“…HREE, MREE and related elements that migrated into the coal seam in a dissolved form could be mostly adsorbed by clay minerals, which has been reported by previous studies and confirmed by relevant experimental studies [78,86,[109][110][111][112][113][114]. Experimental studies have shown that the sorption of REE and related elements mainly depended on adsorption sites of clay minerals, namely, hydroxyl units on Al-O hexahedron or Si-O tetrahedron sheets [115][116][117]. An increase in the three types of hydroxyl groups supplied more edge and basal adsorption sites for trace elements in sample 3, which resulted in the accumulation of HREE, MREE and related elements in zone I.…”

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.…”

Sorption of Heavy Metals on Clay Minerals and Oxides: A Review

“…The sorption data was successfully modelled with 1-pK Diffuse layer model [73]. In another study, thallium is found to associate with illite in natural environment and sorption studies reveal that TI(I) sorbs more onto illite than smectite [74]. The affinity for TI follows this sequence: MnO 2 > illite > smectite = ferrihydrite > = Al 2 O 3 = goethite > SiO 2 .…”

“…The affinity for TI follows this sequence: MnO 2 > illite > smectite = ferrihydrite > = Al 2 O 3 = goethite > SiO 2 . However, in presence of Rb, Cs, Ti adsorption to illite is less [74].…”