Thallium Sorption onto Manganese Oxides

Abstract

The sorption of thallium (Tl) onto manganese (Mn) oxides critically influences its environmental fate and geochemical cycling and is also of interest in water treatment. Combined quantitative and mechanistic understanding of Tl sorption onto Mn oxides, however, is limited. We investigated the uptake of dissolved Tl­(I) by environmentally relevant phyllo- and tectomanganates and used X-ray absorption spectroscopy to determine the oxidation state and local coordination of sorbed Tl. We show that extremely strong sorption of Tl onto vacancy-containing layered δ-MnO2 at low dissolved Tl­(I) concentrations (log K d ≥ 7.4 for ≤10–8 M Tl­(I); K d in (L/kg)) is due to oxidative uptake of Tl and that less specific nonoxidative Tl uptake only becomes dominant at very high Tl­(I) concentrations (>10–6 M). Partial reduction of δ-MnO2 induces phase changes that result in inhibited oxidative Tl uptake and lower Tl sorption affinity (log K d 6.2–6.4 at 10–8 M Tl­(I)) and capacity. Triclinic birnessite, which features no vacancy sites, and todorokite, a 3 × 3 tectomanganate, bind Tl with lower sorption affinity than δ-MnO2, mainly as hydrated Tl+ in interlayers (triclinic birnessite; log K d 5.5 at 10–8 M Tl­(I)) or tunnels (todorokite). In cryptomelane, a 2 × 2 tectomanganate, dehydrated Tl+ replaces structural K+. The new quantitative and mechanistic insights from this study contribute to an improved understanding of the uptake of Tl by key Mn oxides and its relevance in natural and engineered systems.

Thalliomelane, TIMn7.54+Cu0.52+O16, a new member of the coronadite group from the preglacial oxidation zone at Zalas, southern Poland

“…In a recent study on the sorption of Tl onto various Mn oxides (Wick et al 2019), it has been shown that hexagonal vacancy-containing birnessite can sorb Tl by oxidation and complexation.…”

“…http://www.minsocam.org/ (e.g Bidoglio et al 1993;Peacock and Moon 2012;. Voegelin et al 2015, Cruz-Hernández et al 2019Wick et al 2019) Brookins (1988). considered that under oxidizing conditions, thallium oxides: Tl O, Tl O 3 and Tl O dominate the Eh-pH space in order with increasing Eh, and only under strongly acidic oxidizing conditions Tl 3+ appears.…”

Impacts of environmental levels of hydrogen peroxide and oxyanions on the redox activity of MnO2 particles

“…Since this reaction is pH-dependent, we have measured the average oxidation state (AOS) of birnessite over the whole investigated pH range (4)(5)(6)(7)(8). The AOS of samples reacted with BPA (25 µM) alone only slightly decreased from 3.98 to 3.90 (±0.02).…”

“…2,3 As a result, birnessite-type manganese oxides play a significant role in controlling the cycles of several key nutrients as well as the fate and mobility of inorganic and organic contaminants. [4][5][6][7][8][9] Acid birnessite has been widely investigated because it is structurally similar to biogenic "natural" manganese oxides. [10][11][12][13] The birnessite reactivity is mainly affected by solution pH, surface properties and composition of MnO2 and structural characteristics of redox-active contaminants.…”

“…[10][11][12][13] The birnessite reactivity is mainly affected by solution pH, surface properties and composition of MnO2 and structural characteristics of redox-active contaminants. [4][5][6]12 It can also be influenced by the presence of naturally occurring compounds, e.g. cations, anions, natural organic matter and other redox-active compounds.…”