Search

Thallium contamination in water can cause great danger to the environment. In this study, we synthesized manganese oxide-coated sand (MOCS) and investigated the transport and retention behaviors of Tl(I) in MOCS under different conditions. Characterization methods combined with a two-site nonequilibrium transport model were applied to explore the retention mechanisms. The results showed that Tl(I) mobility was strongly inhibited in MOCS media, and the retention capacity calculated from the fitted model was 510.41 mg/g under neutral conditions. The retention process included adsorption and oxidative precipitation by the manganese oxides coated on the sand surface. Cotransport with the same concentration of Mn(II) led to halving Tl(I) retention due to competition for reactive sites. Enhanced Tl(I) retention was observed under alkaline conditions, as increasing pH promoted electronegativity on the media surface. Moreover, the competitive cation Ca 2+ significantly weakened Tl(I) retention by occupying adsorption sites. These findings provide new insights into understanding Tl(I) transport behavior in water-saturated porous media and suggest that manganese oxide-coated sand can be a cost-effective filter media for treating Tl-contaminated water., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article., (Copyright © 2022. Published by Elsevier B.V.)

The reversibility of monovalent thallium (Tl) absorption on widely distributed iron/manganese secondary minerals may affect environmental Tl migration and global cycling. Nevertheless, quantitative and mechanistic studies on the interfacial retention and release reactions involving Tl(I) are limited. In this study, batch and stirred-flow experiments, unified kinetics modeling, spectral detection, and theoretical calculations were used to elucidate the retention behaviors of Tl(I) on goethite, hematite, and manganite with different solution pH values and Tl loading concentrations. Sustained Tl(I) retention (k d, MeOHTl =0.005∼0.018 min -1 ) was induced by hydration of the surface hydroxyl groups. Rapid Tl(I) retention (k d,MeOTlOH =1.232∼2.917 min -1 ) was enhanced by the abundant hydroxide ions and deprotonated hydroxyl groups, which increased the Tl(I) binding ability. Compared to the ambient Tl concentration, pH had a more substantial effect on the formation and distribution of surface Tl(I) binding species. In alkaline environments, the large adsorption energy for Tl(I) binding to surface species (E ads =-6.14 eV) induced fast Tl(I) binding response on the surfaces of iron/manganese secondary minerals. This study provides new insights into the heterogeneous surface complexation and retention behaviors of Tl(I) and contributes to an in-depth understanding of the environmental fate of Tl and the remediation of Tl contamination., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Understanding the transport behaviors of thallium (Tl) in porous media is of considerable interest for both natural soils and artificial filtration removal of Tl. In this context, the transport behaviors of Tl(I) in water-saturated sand columns under different conditions were systematically investigated. It was found that, in addition to the effects of pH and ionic strength (IS), the transport of Tl(I) depended on the carbonate, phosphate and macromolecular organic matter as well. Tl(I) broken the columns more difficultly under higher pH and lower IS conditions. Moreover, the adsorption of carbonate and phosphate on sand surfaces may increase the retention of Tl(I) in columns. As for macromolecular organic matter, humic acid (HA) facilitated Tl(I) transport, especially under neutral and alkaline conditions (7.0 and 9.8), which was possibly associated with Tl-complexes formation and competed adsorption between Tl(I) and HA. However, bovine serum albumin (BSA) impeded Tl(I) transport for the reason that deposited BSA might provide more adsorption sites for Tl(I), though Tl(I) had a slight effect on BSA transport. In order to evaluate the mechanisms of transport, a dual-sites non-equilibrium model was applied to fit the breakthrough curves of Tl(I). Retardation factor (R) values of individual Tl(I) transport from model calculations were found to be higher than that of Tl(I) transport with HA and lower than that of Tl(I) transport with BSA. The fraction of instantaneous sorption sites (β) was found to decrease with increasing pH, implying nonequilibrium sorption is a main sorption mechanism of Tl(I) with pH increasing. The fundamental data obtained herein demonstrated that carbonate, phosphate and macromolecular organic matter significantly influenced the Tl(I) migration and could lead to the leaking or bindings of Tl(I) at Tl-occurring sites., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Understanding the migration behavior of thallium (TI) in subsurface environments is essential for Tl pollution prevention. With the wide production and utilization of biochar, the notable ability of biochar colloids to carry environmental contaminants may make these colloids important for Tl(I) mobility. This study systematically investigated the impact of wood-derived biochar (WB) and corn straw-derived biochar (CB) colloids on Tl(I) transport in water-saturated porous media under different pH (5, 7 and 10) and ionic strengths (ISs) (1, 5 and 50 mM NaNO 3). WB colloids improved Tl(I) transport under all IS conditions at pH 7 due to the adsorption capacity of biochar and competition for adsorption sites on the sand surface. However, at IS 50 mM, CB colloids slightly impeded Tl(I) mobility due to the straining. In addition, both WB and CB colloids accelerated Tl(I) mobility under all pH conditions at IS 5 mM. At pH 10, the promotion effect was more obvious due to the deprotonation of O-containing functional groups and higher fluidity of biochar colloids. Furthermore, the two-site nonequilibrium model and two-site kinetic attachment/detachment model suitably described the breakthrough curves (BTCs) of Tl(I) and biochar colloids, respectively. The colloid-facilitated solute transport model could also describe Tl(I) transport influenced by biochar colloids reasonably well. This study provides insight into the migration and fate of Tl(I) in the presence of biochar colloids. [Display omitted] • Biochar colloids impacted Tl(I) migration through complexation with Tl(I). • WB colloids facilitated Tl(I) migration under all experimental conditions. • CB colloids slightly impeded Tl(I) migration at high IS. • The deprotonation of functional groups accelerated Tl(I) mobility at high pH. [ABSTRACT FROM AUTHOR]

The transformations of monovalent thallium (Tl) in an aqueous environment may be affected significantly by Tl(I) partitioning at the solid-water interface during sorption. Models used to quantify the kinetics of Tl(I) adsorption on heterogeneous adsorbents and formation of multiple complexes under a wide range of water chemistry conditions can accurately predict the environmental fate of thallium. In this study, Tl(I) sorption on representative titanium dioxide at different solution pH values and loading concentrations was investigated with two unified adsorption models, diffuse layer modeling and kinetics modeling. Three Tl(I) surface complexes, TiOTl, TiOHTl+, and TiOTlOH-, were used in the diffuse layer model and successfully described batch adsorption and the results of spectroscopic analyses. The contribution of TiOHTl+ to the adsorption capacity was much higher than those of TiOTl and TiOTlOH- under neutral and weakly alkaline conditions, while the species TiOTlOH- predominated among Tl(I) complexes in strongly alkaline environments. The adsorption and desorption rate coefficients derived from thermodynamics and kinetics coupling modeling suggested the influence of different complex characteristics on adsorption and desorption of Tl(I). Our results provide a comprehensive model for predicting the dynamic binding behavior of Tl at heterogeneous solid-water interfaces. [Display omitted] ● Thermodynamics and kinetics coupling model is proposed to predict Tl sorption behavior. ● Three complexes TiOTl, TiOHTl+, and TiOTlOH- are formed on the titanium dioxide. ● TiOHTl+ is the dominant species under neutral and weakly alkaline conditions. ● The species TiOTlOH- dominates Tl(I) complexes in strongly alkaline environments. ● The characteristics of the complexes affect the adsorption/desorption rate of Tl(I). [ABSTRACT FROM AUTHOR]

Exploring the transport behaviors of thallium (Tl) in porous media is crucial for predicting Tl pollution in natural soils and groundwater. In recent years, the misuse of plastics has led to plastic becoming an emerging pollutant in soil. In this work, the effects of plastic particles on Tl(I) transport in water-saturated sand columns were investigated under different ionic strengths (ISs), pH values, and plastic particle sizes. The two-site nonequilibrium model was selected to fit the breakthrough curves (BTCs) of Tl(I). The results demonstrated that nanoplastics (NPs) accelerated Tl(I) transport at pH 7, which might be attributed to the competitive adsorption of NPs and Tl(I) on sand surfaces. However, at pH 5, the deposited NPs might provide more adsorption sites for Tl(I), and thus enhance its retention in the columns. In addition, the "straining" process could intercept microplastics (MPs) with Tl(I) that was attached under unfavorable attachment conditions, which would result in the inhibited mobility of Tl(I). On the other hand, the migration of plastics was restrained to some extent when Tl(I) was present. Overall, the findings from this work provided a new perspective for understanding the transport of Tl(I) and plastics in subsurface environments. [Display omitted] • Cotransport of Tl(I) with NPs/MPs in water-saturated porous media was explored. • NPs facilitated Tl(I) transport in all ionic strengths (i.e.,1, 5, and 50 mM) at pH 7. • Deposited NPs provided new deposition sites and impeded Tl(I) migration at pH 5. • MPs retarded Tl(I) mobility in the column resulting from the "straining" process. • Tl(I) neutralized the surface charges of plastics and inhibited NPs/MPs mobility. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tl(I) uptake affinity decreased as: δ-MnO 2 > α-MnO 2 > γ-MnO 2 > β-MnO 2 > λ-MnO 2. • α-MnO 2 exhibited the strongest oxidation ability for Tl(I). • Tl(I) was scarcely oxidized by β-MnO 2 over a wide range of pH values. • TlOH was involved in the redox process at alkaline pH conditions. Manganese dioxides (MnO 2) with a high affinity for thallium (Tl), strongly influence its fate and toxicity in aquatic environments. The crystal structure of MnO 2 plays a critical role in their activity for the uptake of heavy metals. However, few studies have examined the differences in interactions between Tl and various crystal structured MnO 2. In this study, the fundamental data on the sorption and oxidative reactivity of Tl(I) by MnO 2 with five known crystal structures (δ-, α-, γ-, β-, λ-MnO 2) was obtained at different pH values (5, 7, 12). The results showed that the uptake of Tl followed the order of δ-MnO 2 > α-MnO 2 > γ-MnO 2 > β-MnO 2 > λ-MnO 2 , and increased with increasing pH for each MnO 2. Moreover, α-MnO 2 exhibited the strongest oxidation ability for Tl(I) at all the tested pH values, while β-MnO 2 could scarcely oxidize aqueous Tl(I). However, for δ-MnO 2, γ-MnO 2 and λ-MnO 2 , the extent of Tl(I) oxidation was much larger at pH 12 than at pH 5 or 7, which was ascribed to the active species of TlOH involved in the redox process. Besides, the sorption of Tl(I) led to a decrease in crystallinity of δ-MnO 2 and α-MnO 2 but slightly impacted the structure of γ-MnO 2 , β-MnO 2 and λ-MnO 2. These findings might contribute to understanding the immobilization processes of Tl by different crystal structured MnO 2 at various pH conditions. [ABSTRACT FROM AUTHOR]