In Situ Measurement of Thallium in Natural Waters by a Technique Based on Diffusive Gradients in Thin Films Containing a δ-MnO₂ Gel Layer

Abstract

Thallium (Tl) has been identified as a priority contaminant because of its severe toxic effects. Exact measurement of Tl is a challenge because it is difficult to avoided altering the element's chemical speciation during sampling, transport, and storage. In situ measurement may be a good choice. Based on the in situ technique of Diffusive Gradient in Thin-films (DGT), new DGT devices equipped with novel laboratory-synthesized manganese oxide (δ-MnO2) binding gels were developed and systematically validated for the measurement of Tl, including Tl(I) and Tl(III) species, in water. Comparison between Chelex binding gel and δ-MnO2 gel on the uptake kinetic of Tl demonstrated that δ-MnO2 binding gels could adsorb Tl rapidly and effectively. Removal of Tl from the δ-MnO2 gels was achieved using 1 mol L-1 oxalic acid, yielding elution efficiencies of 1.0 and 0.86 respectively for both Tl(I) and TI(III). Theoretical responses from DGT devices loaded with δ-MnO2 gel (δ-MnO2-DGT) were obtained irrespective of pH (4-9) and ionic strength (0.1-200 mmol L-1 NaNO3). δ-MnO2-DGT showed good potential for long-term monitoring of Tl due to its high adsorption capacity of 27.1 μg cm-2 and the stable performance of δ-MnO2 binding gel stored in 0.01 mol L-1 NaNO3 solution for at least 117 d. Field deployment trials confirmed that δ-MnO2-DGT can accurately measure the time-averaged concentrations of Tl in fluvial watercourses. In summary, the newly developed δ-MnO2-DGT shows potential for environmental monitoring and biogeochemical investigation of Tl in waters, sediments, and soils.

Light- and H2O2-Mediated Redox Transformation of Thallium in Acidic Solutions Containing Iron: Kinetics and Mechanistic Insights

“…11,16,19 Moreover, oxidation from Tl(I) to Tl(III) is also a critical process in water treatment since Tl is more readily removed as Tl(III) (hydr)oxides precipitate (log K sp = −45.2). 20 Therefore, a comprehensive understanding of Tl redox chemistry among species is critical for predicting both the geochemical speciation of Tl in natural aquatic systems and the removal potential in treatment processes.…”

“…As the most toxic regulated element in water, Tl is recognized to have a higher potential than lead (Pb), mercury (Hg), and arsenic (As) for causing chronic and acute poisoning in mammals. , Tl generally disperses at trace levels of <1 μg/L in nonpolluted natural waters . However, in waters affected by polluted sources of Tl, e.g., acidic mine drainages (AMDs), which are the primary sources for Tl emission into the environment, , elevated concentrations up to thousands of μg/L can be detected. , Tl mainly exists in thallous form (Tl­(I)) and thallic form (Tl­(III)). , Tl­(I) is predicted to predominate in the environment because it is more soluble, mobile, and thermodynamically stable than Tl­(III). , However, the transformation of Tl­(I) to Tl­(III) can occur due to some photochemical reactions , or microbiological activities, , resulting in considerable quantities of Tl­(III) over Tl­(I). ,− The existence of the two oxidation states allows Tl to undergo redox transformation, influencing its toxicity, reactivity, and mobility in natural waters. ,, Moreover, oxidation from Tl­(I) to Tl­(III) is also a critical process in water treatment since Tl is more readily removed as Tl­(III) (hydr)­oxides precipitate (log K sp = −45.2) . Therefore, a comprehensive understanding of Tl redox chemistry among species is critical for predicting both the geochemical speciation of Tl in natural aquatic systems and the removal potential in treatment processes.…”

In Situ Selective Measurement Based on Diffusive Gradients in Thin Films Technique with Mercapto-Functionalized Mesoporous Silica for High-Resolution Imaging of SbIII in Soil

“…The diffusive gradients in thin films (DGT) technique has been comprehensively validated for in situ measurement of inorganic species in waters , and metal fluxes in soils and sediments. − Within DGT devices, the targeted analyte diffuses through an inert filter membrane and hydrogel stack and is immobilized in a binding layer which has high affinity for the analyte of interest . The key step of the DGT technique, where the targeted species are selectively accumulated from solution, is performed in situ .…”

Kinetics of Thallium(I) Oxidation by Free Chlorine in Bromide-Containing Waters: Insights into the Reactivity with Bromine Species

“…At higher pH, however, Tl­(III) occurs as Tl­(OH) 3 and Tl­(OH) 4 – aqueous complexes. Tl­(OH) 3 exists as Tl­(OH) 3 (aq) or Tl­(OH) 3 (s) (log K sp 25°C = −45.2) in the environment, and Tl­(OH) 3 (aq) was the dominant Tl­(III) species over a wide pH range from 1.9 to 11.7 in aqueous systems . Furthermore, Tl­(III) is prone to form Tl­(III) (hydr)­oxide precipitates, that is, Tl 2 O 3 with low solubility from 10 –5.8 M at pH 7 to 10 –11.7 M at pH 9 at Eh 0.55 V .…”

“…At higher pH, however, Tl(III) occurs as Tl(OH) 3 and Tl(OH) 4 − aqueous complexes. Tl(OH) 3 exists as Tl(OH) 3 (aq) or Tl(OH) 3 (s) (log Ksp 25°C = −45.2) in the environment, 18 and Tl(OH) 3 (aq) was the dominant Tl(III) species over a wide pH range from 1.9 to 11.7 in aqueous systems. 19 Furthermore, Tl(III) is prone to form Tl(III) (hydr)oxide precipitates, that is, Tl 2 O 3 with low solubility from 10 −5.8 M at pH 7 to 10 −11.7 M at pH 9 at Eh 0.55 V. 20 Because Tl(III) is less mobile and more easily separated from aqueous solutions in the form of (hydr)oxide precipitates, 21−23 the oxidation of Tl(I) to Tl(III) is considered as a practical way for Tl removal in water and wastewater (WW) treatment.…”