Tl Release Research Articles

From leaching data to release estimates: Screening and scenario assessments of electric arc furnace (EAF) slag under unencapsulated use

Electric arc furnace (EAF) slag is the non-metallic byproduct of the primary U.S. steelmaking process. Much of the slag is marked for secondary uses as aggregates. EAF slags used as construction fill or residential groundcover are directly exposed to the environment, raising concerns of potential leaching impacts. Leaching data of EAF slags as function of eluate pH (Method 1313) and liquid-to-solid ratio (Method 1314) were used to refine an initial list of constituents of potential concern to those with potential to leach at concentrations greater than project thresholds, and to estimate release from EAF slags when used as unencapsulated groundcover. Screening assessment identified 11 of over 20 constituents requiring further assessment. Scenario-based assessments results showed that constituents with high available content and low leaching concentrations (Al, Cr, Co, Mn, Se) are persistent in contacting water over the assessment period while those with limited available content (As, Ba, Mo, V) were depleted. Aging decreased the release of Se while increasing Tl release, likely through a combination of hydration, carbonation, and cracking processes. Increasing fill depth and infiltration rates did not alter leaching concentrations; however, liquid-solid ratio for each assessment interval changed thereby impacting cumulative release.

Insight into the long-term nonoxidative immobilization of thallium on birnessite

Birnessite has been considered as a potential thallium (Tl)-oxidizing mineral and Tl scavenger in natural and engineered systems. However, the birnessite aging that occurs during Tl sorption may severely limit the long-term effectiveness of Tl immobilization on birnessite. In this study, kinetic experiments were performed in batch coupled stirred-flow systems to investigate the effects of Tl(I) loading and pH on Tl(I) retention during short- and long-term Tl-birnessite interactions. Spectral analysis, microscopic observations, and theoretical calculations revealed a change in the Tl(I) binding mode to birnessite with time. In the short term, low levels of Tl(I) could be effectively immobilized through adsorption to birnessite vacancies. Structural disruption and vacancy occupation in birnessite resulted in the migration of adsorbed Tl(I) toward the edges of the mineral during a 24-d reaction period. Under acidic to neutral conditions, the migration of vacancy-bound Tl(I) induced sustained Tl(I) release (10–45%) from birnessite over the long-term. Under alkaline conditions, hydroxide ions contributed to the formation of Tl(I)–OH species with double edge sharing, which enhanced the binding ability (α ≈ 7 × 10−4 min−1) and stable retention of Tl(I) on birnessite. Understanding Tl(I) retention dynamics during long-term Tl-birnessite interactions elucidates the Tl cycle in Mn oxide-containing systems.

Release and mobility characteristics of thallium from polluted farmland in varying fertilization: Role of cation exchange

Batch and column leaching tests were used to study thallium's release and migration behaviour and evaluate its potential toxicity risks in soil. The results indicated that leaching concentrations of Tl using TCLP and SWLP were much higher than the threshold, indicating a high risk of thallium pollution in the soil. Furthermore, the intermittent leaching rate of Tl by Ca2+ and HCl reached its maximum value, demonstrating the easy release of Tl. After HCl leaching, the form of Tl in the soil has changed, and ammonium sulfate has increased its extractability. Additionally, the extensive application of calcium promoted the release of Tl, increasing its potential ecological risk. Spectral analysis showed that Tl was mainly present in minerals such as Kaolinite and Jarosite, and exhibited significant adsorption capacity for Tl. HCl and Ca2+ damaged the crystal structure of the soil, greatly enhancing the migration and mobility of Tl in the environment. More importantly, XPS analysis confirmed that the release of Tl (I) in the soil was the leading cause of increased mobility and bioavailability. Therefore, the results revealed the risk of Tl release in the soil, providing theoretical guidance for its pollution prevention and control.

Thallium distribution in an estuary affected by acid mine drainage (AMD): The Ría de Huelva estuary (SW Spain)

This study investigates the behavior of Tl in the Ría de Huelva (SW Spain), one of the most metal polluted estuaries in the world. Dissolved Tl concentration displayed a general decrease across the estuary during the dry season (DS); from 5.0 to 0.34 μg/L in the Tinto and Odiel estuaries, respectively, to 0.02 μg/L in the channel where the rivers join. A slighter decrease was observed during the wet season (WS) (from 0.72 to 0.14 μg/L to 0.02 μg/L) due to the dilution effect of rainfalls in the watersheds. These values are 3 orders of magnitude higher than those reported in other estuaries worldwide. Different increases in Tl concentrations with salinity were observed in the upper reaches of the Tinto and Odiel estuaries, attributed to desorption processes from particulate matter. Chemical and mineralogical evidences of particulate matter, point at Fe minerals (i.e., jarosite) as main drivers of Tl particulate transport in the estuary. Unlike other estuaries worldwide, where a fast sorption process onto particulate matter commonly takes place, Tl is mainly desorbed from particulate matter in the Tinto and Odiel estuaries. Thus, Tl may be released back from jarositic particulate matter across the salinity gradient due to the increasing proportion of unreactive TlCl0 and K+ ions, which compete for adsorption sites with Tl+ at increasing salinities. A mixing model based on conservative elements revealed a 6-fold increase in Tl concentrations related to desorption processes. However, mining spills like that occurred in May 2017 may contribute to enhance dissolved and particulate Tl concentrations in the estuary as well as to magnify these desorption processes (up to around 1100% of Tl release), highlighting the impact of the mine spill on the remobilization of Tl from the suspended matter to the water column.

Effect of peat organic matter on sulfide weathering and thallium reactivity: Implications for organic environments

Weathering of Tl-containing sulfides in a model (12-week) peat pot trial was studied to better understand their geochemical stability, dissolution kinetics, alteration products and the associated release and mobility of anthropogenic Tl in organic environments. We also present the effect of industrial acid rainwater on sulfide degradation and Tl migration in naturally acidic peat. Sphalerite (ZnS) was much less stable in peat than other Tl-containing sulfides (galena and pyrite), and thus acted as a major phase responsible for Tl mobilization. Furthermore, Tl incongruently leached out over Zn from ZnS, and accumulated considerably more in the peat solutions (≤5 μg Tl/L) and the peat samples (≤0.4 mg Tl/kg) that were subjected to acid rain watering compared to a deionized H2O regime. This finding was in good agreement with the absence of secondary Tl-containing phases, which could potentially control the Tl flux into the peat. The behavior of Tl was not as conservative as Pb throughout the trial, since a higher peat mobility and migration potential of Tl was observed compared to Pb. In conclusion, industrial acid precipitations can significantly affect the stability of ZnS even in acidic peat/organic environments, making it susceptible to enhanced weathering and Tl release in the long term.

Secondary Sulfate Minerals from Thallium Mineralized Areas: Their Formation and Environmental Significance

Thallium is a highly toxic metal and is predominantly hosted by sulfides associated with low-temperature hydrothermal mineralization. Weathering and oxidation of sulfides generate acid drainage with a high concentration of thallium, posing a threat to surrounding environments. Thallium may also be incorporated into secondary sulfate minerals, which act as temporary storage for thallium. We present a state-of-the-art review on the formation mechanism of the secondary sulfate minerals from thallium mineralized areas and the varied roles these sulfate minerals play in Tl mobility. Up to 89 independent thallium minerals and four unnamed thallium minerals have been documented. These thallium minerals are dominated by Tl sulfosalts and limited to several sites. Occurrence, crystal chemistry, and Tl content of the secondary sulfate minerals indicate that Tl predominantly occurs as Tl(I) in K-bearing sulfate. Lanmuchangite acts as a transient source and sink of Tl for its water-soluble feature, whereas dorallcharite, Tl-voltaite, and Tl-jarosite act as the long term source and sink of Tl in the surface environments. Acid and/or ferric iron derived from the dissolution of sulfate minerals may increase the pyrite oxidation process and Tl release from Tl-bearing sulfides in the long term.

Monitoring of ion release, bioavailability and ecotoxicity of thallium in contaminated paddy soils under rice cultivation conditions

Paddy soils contaminated by thallium (Tl) have been frequently reported; however, their ecotoxicological impact in the paddy field is less known. We used a novel soil–fish exposure system with larvae of rice fish medaka (Oryzias latipes) to assess the bioavailability of Tl from soils to fish and causal toxicity under simulated conditions of rice cultivation. Two acidic soils [Pingzhen (Pc) and Sankengtzu (Sk)] spiked with monovalent Tl [Tl(I), 75–250 mg/kg] released higher Tl+ into pore or overlying waters than neutral soils [Sangkang (Su)], which resulted in higher mortality to exposed fish. The addition of K fertilizers into the system did not significantly reduce Tl release and fish mortality, but a drainage/re-flooding treatment worked effectively. The acidic Pc soil contaminated with low Tl(I) (2.5 and 15 mg/kg) caused higher sublethal toxicity in medaka than the neutral Su soil, including altered growth and swimming behavior with increased Tl body burden. These Tl-induced effects by low-Tl soils were significantly alleviated by K addition. The Tl/K ratios in aqueous phases were correlated with the mortality or Tl body burden in exposed fish. This study provides useful bio-analytical evidence that can help assess the ecological risks of Tl pollution in paddy field-related ecosystems.

Thallium cycling in pore waters of intertidal beach sediments

Pore water data of thallium (Tl) in marine environments are scarce. It has been suggested that anoxic sediments are a sink for dissolved Tl likely due to its incorporation into Fe sulfides. However, recent studies indicated that Tl is removed from solution prior to the onset of sulfidic conditions and that Tl is involved in biological cycles in coastal seawater. To assess the Tl behavior in marine sediments, pore waters of a high energy beach (Spiekeroog Island, Germany) were sampled during different seasons and on different spatial scales. The study site provides a perfect set of samples to assess trace metal behavior under various redox conditions.Samples were analyzed for the dissolved trace metals Tl, molybdenum (Mo), uranium (U), and rhenium (Re). Additionally, sediments were incubated to monitor trace metal removal or release under controlled conditions. On-site redox conditions were characterized using dissolved oxygen (O2), manganese (Mn), and iron (Fe) concentrations.Our results indicated high enrichments of Tl in pore waters concurrently to aerobic organic matter (OM) degradation, exceeding seawater concentrations up to 6-fold. In contrast, Tl was completely removed in weakly reducing pore water characterized by more than 1 µM Mn or Fe. The spatial Tl distribution in intertidal pore waters responded to the present dissolved Mn and Fe level, which varied in space and with season. We suggest, Tl release to be attributed to OM degradation, particle desorption, or reoxidation, whereas Tl removal is likely related to the presence of trace amounts of dissolved sulfide.In conclusion, the fast reaction kinetics of Tl led to fast and complete removal in comparison to Mo, U, and Re and we suggest the following order of removal: Tl > Re > U > Mo. The removal behavior as well as the high enrichments of Tl in pore waters implicate that sinks and sources in the marine environment are not yet fully understood. Although the intertidal sediments form an overall sink for Tl (U and Re), especially under mostly anoxic conditions in summer, sediments turn into a Tl net source in winter, when sediments are more oxic.For global marine Tl balances, Tl fluxes have been estimated based on pore water Tl/Mn ratios. Contrastingly, Tl removal from pore waters at low threshold concentrations of Mn at our site indicated that these Tl flux estimations may not be applicable in permeable sandy beach sediments and in many other types of sediments, which host mildly sulfidic conditions.

Emergent thallium exposure from uranium mill tailings

Thallium (Tl) pollution caused by the exploitation of uranium (U) mines has long been neglected due to its low crustal abundance. However, Tl may be enriched in minerals of U ore because Tl has both sulfurophile and lithophile properties. Herein, a semi-dynamic leaching experiment combined with statistical analysis, geochemical speciation and multi-characterization provided novel insight into the distinct features and mechanisms of Tl release from uranium mill tailings (UMT). The results showed that particle size effects prevail over the pH on Tl release, and surface dissolution is the pivotal mechanism controlling Tl release based on Fick’s diffusion model. The study revealed that long-term leaching and weathering can lead to the increased acid-extractable and oxidizable fractions of Tl in UMT, and that the exposure and dissolution of Tl-containing sulfides would largely enhance the flux of Tl release. The findings indicate that UMT containing (abundant) pyrite should be paid particular attention due to Tl exposure. Besides, critical concern over the potential Tl pollution in universal U mining and hydrometallurgical areas likewise may need to be seriously reconsidered.

Thallium and co-genetic trace elements in hydrothermal Fe-Mn deposits of Central Spain

Thallium (Tl) is a hazardous trace metal that can harm human and environmental health. Tl pollution can result from the mining and smelting of Tl-bearing minerals, but also the natural weathering of Tl-bearing sulfide minerals may induce Tl release to the environment. In this study, hydrothermal deposits hosted in dolostone rocks sited along fossil thermal springs in the Lodares region (Soria province, central Spain) were studied. In this hydrothermal mineralization zone, Tl association with primary minerals, identified Tl-bearing secondary products resulting from natural weathering of primary minerals, as well as the dispersion from its natural source along a seasonal small streambed were explored. Samples were analyzed by chemical, microscopic and spectroscopic techniques and epithermal pyrite, sphalerite, galena and barite and secondary gypsum, jarosite, scorodite, anglesite, goethite, epsomite and elemental sulfur produced by both inorganic and bacterial processes were found. The highest Tl contents were found in hydrothermal pyrite (188 mg kg−1), jarosite (142 mg kg−1), Mn-oxides (27 mg kg−1) or kerogen (13 mg kg−1). Feldspar was identified by electron probe microanalysis as potential host phase of Tl. XANES results confirmed the association of Tl(I) with metal sulfides in pyrite-rich samples and highlighted the role of jarosite-like minerals for Tl(I) sequestration upon pyrite oxidation, even in carbonate-rich samples at near-neutral pH. In addition to micaceous minerals, jarosite-group minerals and K-feldspars may contribute to the natural attenuation of Tl in soils and sediments.

Distribution, fractions, and potential release of thallium in acidic soils nearby a waste copper mining site from southern China.

Although thallium (Tl) is a highly toxic element, little information is available on the environmental risks of Tl in agricultural soils with intensive practices, particularly nearby mining sites. Therefore, we investigated the potential release of Tl in acidic soils with intensive cultivation nearby a waste copper mining site from southern China based on its level and chemical fractions as well as simulated release under artificial acid rain. Results showed that the average Tl content was 1.31mg/kg in the studied area, which significantly exceeds the permissible thallium value of 1mg/kg for agricultural soil in China. Some vertical increases of soil Tl from different land uses indicate the potential transport of Tl downward to groundwater. High positive correlations between surficial soil Tl and rubidium (Rb) and copper (Cu) indicated that Tl has the lithophile and chalcophile behavior. Tl in soils is mainly entrapped in residual fraction. The exchangeable fraction of Tl in agricultural soils was less than undisturbed natural soils and copper mined soils. Additionally, the percentage of Tl release from undisturbed natural soils and soils of copper ore area was more than that from agricultural soils in simulated acid rain. Furthermore, the releases of Tl from the soils increased with the acidity of artificial acid rain. Thus, more attention must be paid to land management of this similar area to avoid the risk of Tl impact on human health.

Thallium transformation and partitioning during Pb–Zn smelting and environmental implications

Thallium (Tl) is a toxic and non-essential heavy metal. Raw Pb–Zn ores and solid smelting wastes from a large Pb–Zn smelting plant – a typical thallium (Tl) pollution source in South China, were investigated in terms of Tl distribution and fractionation. A modified IRMM (Institute for Reference Materials and Measurement, Europe) sequential extraction scheme was applied on the samples, in order to uncover the geochemical behavior and transformation of Tl during Pb–Zn smelting and to assess the potential environmental risk of Tl arising from this plant. Results showed that the Pb–Zn ore materials were relatively enriched with Tl (15.1–87.7 mg kg−1), while even higher accumulation existed in the electrostatic dust (3280–4050 mg kg−1) and acidic waste (13,300 mg kg−1). A comparison of Tl concentration and fraction distribution in different samples clearly demonstrated the significant role of the ore roasting in Tl transformation and mobilization, probably as a result of alteration/decomposition of related minerals followed by Tl release and subsequent deposition/co-precipitation on fine surface particles of the electrostatic dust and acidic waste. While only 10–30% of total Tl amounts was associated with the exchangeable/acid-extractable fraction of the Pb–Zn ore materials, up to 90% of total Tl was found in this fraction of the electrostatic dust and acidic waste. Taking into account the mobility and bioavailability of this fraction, these waste forms may pose significant environmental risk.

Thallium contamination of soils/vegetation as affected by sphalerite weathering: A model rhizospheric experiment

The environmental stability of Tl-rich sphalerite in two contrasting soils was studied. Rhizospheric conditions were simulated to assess the risk associated with sulfide microparticles entering agricultural (top)soils. The data presented here clearly demonstrate a significant effect of 500μM citric acid, a model rhizospheric solution, on ZnS alteration followed by enhanced Tl and Zn release. The relative ZnS mass loss after 28 days of citrate incubation reached 0.05 and 0.03wt.% in Cambisol and Leptosol samples respectively, and was up to 4 times higher, compared to H2O treatments. Incongruent (i.e., substantially increased) mobilization of Tl from ZnS was observed during the incubation time. Generally higher (long-term) stability of ZnS with lower Tl release is predicted for soils enriched in carbonates. Furthermore, the important role of silicates (mainly illite) in the stabilization of mobilized Tl, linked with structural (inter)layer Tl–K exchange, is suggested. Thallium was highly bioavailable, as indicated by its uptake by white mustard; maximum Tl amounts were detected in biomass grown on the acidic Cambisol. Despite the fact that sulfides are thought as relatively stable phases in soil environments, enhanced sulfide dissolution and Tl/trace element release (and bioaccumulation) can be assumed in rhizosphere systems.

Phase-dependent phytoavailability of thallium – A synthetic soil experiment

The study deals with the environmental stability of Tl-modified phases (ferrihydrite, goethite, birnessite, calcite and illite) and phytoavailability of Tl in synthetically prepared soils used in a model vegetation experiment. The data presented here clearly demonstrate a strong relationship between the mineralogical position of Tl in the model soil and its uptake by the plant (Sinapis alba L.). The maximum rate of Tl uptake was observed for plants grown on soil containing Tl-modified illite. In contrast, soil enriched in Ksat-birnessite had the lowest potential for Tl release and phytoaccumulation. Root-induced dissolution of synthetic calcite and ferrihydrite in the rhizosphere followed by Tl mobilization was detected. Highly crystalline goethite was more stable in the rhizosphere, compared to ferrihydrite, leading to reduced biological uptake of Tl. Based on the results obtained, the mineralogical aspect must be taken into account prior to general environmental recommendations in areas affected by Tl.

Geochemical position of thallium in soils from a smelter-impacted area

The study complements our previous research, focused on metal contamination of soils in the area historically affected by Zn smelting near Olkusz (Silesia–Krakow region, southern Poland) and provides complex data on the geochemistry of anthropogenic Tl in soils with contrasting land use. Significant differences in Tl concentrations and chemical fractionation were observed between forest and grassland soil profiles, indicating the effect of land use on Tl behavior. Our findings proved the ability of forest soils to concentrate high amounts of Tl, particularly within the organic layers. A comparison of Tl concentrations in the upper (O or A) and the bottom horizons (C) of forest and grassland soils clearly demonstrates vertical mobility of Tl. The results of the sequential extraction procedure indicated the important role of soil organic matter in Tl mobilization, probably as a result of long-term alteration/dissolution of smelter-derived particles followed with Tl release; up to ~20% of total Tl amount was associated with the exchangeable/acid-extractable fraction in forest soils. The Tl concentrations detected in grassland soils were up to an order of magnitude lower than in forest soils. Taking into account the dominant bonding of Tl to the residual fraction, Tl present in grassland soils poses lower environmental hazard with respect to the potential mobilization or uptake by plants. Nevertheless, further research on Tl dynamics with emphasis to the environmental stability of Tl-bearing phases is essential for precise understanding of Tl behavior in such polluted (agro)systems.

Effect of low-molecular-weight organic acids on the leaching of thallium and accompanying cations from soil – A model rhizosphere solution approach

The kinetic batch leaching of Tl-bearing mineral soil in 500 μM solutions of citric, oxalic and acetic acid was performed to simulate the release of Tl and main cations (Al, Fe, Si, K, Ca, Mn) in the rhizosphere-like environment. The obtained data demonstrate that low-molecular-weight organic acids (LMWOAs) significantly contribute to soil alteration accompanied by the release of lithogenic Tl (if present). The highest mobilization rates for Tl were observed after 0.5 h of leaching (with maximal values obtained for oxalate) followed by a substantial decrease. Thallium extractability in the organic acid solutions was up to 2.8-fold higher compared to water. Based on the experimental and speciation modeling data, Tl release is mainly pH-driven and can be attributed to acid ion exchange and/or acid leaching, as the formation of Tl-LMWOA complexes is negligible. The main Tl solubility-controlling phases predicted include illite and the identified Mn(III,IV) oxide due to their ability to efficiently sorb Tl + on the mineral surfaces from which Tl can be potentially mobilized. The role of primary silicates (i.e., orthoclase and muscovite) in the total process of Tl mobilization seems to be of lesser importance because the supposed alteration/dissolution of these phases during LWMOA leaching was limited.

Thallium uptake by white mustard ( Sinapis alba L.) grown on moderately contaminated soils—Agro-environmental implications

The work focused on Tl uptake by white mustard ( Sinapis alba L.) grown on moderately contaminated soils with different characteristics. The data presented here clearly demonstrate the ability of white mustard to (hyper)accumulate Tl. Substantially higher Tl levels were was found in mustard grown on the Arenosol as compared to the carbonate-rich Leptosol; a relationship between the content of labile Tl (adsorbed, bound to carbonates etc.) in soil and its uptake by the plant is suggested. Approximately 3-fold lower concentrations of Tl in roots and stems of the mature mustard (compared to the young plant) indicate a decreasing trend of Tl uptake with the age of the plant. The exchangeable/acid-extractable and reducible Tl fractions were evaluated as the dominant fractions controlling Tl transfer from both contrasting soils. Thallium associated with the residual fraction (e.g., incorporated into silicates) was rather stable in the rhizosphere, proving a negligible influence of root exudates on Tl release from such an operationally defined fraction, despite the anthropogenic origin of Tl. Regarding our results, when mustard is cultivated for nutrition purposes and/or as green manure, it may pose an important source of Tl introduction into the food chain.

Thallium dynamics in contrasting light sandy soils—Soil vulnerability assessment to anthropogenic contamination

The influence of different soil conditions and the presence of LMWOA (Low Molecular Weight Organic Acids) on anthropogenic Tl dynamics were discussed in this study. A shift from the “labile” to the residual fraction during the ageing was identified, indicating Tl incorporation into stable phases (e.g., illite and/or amorphous silicates). The increased water-soluble Tl concentration (1.8-fold, in maximum) after the split application of LMWOA (simulating root exudation) was observed in all soils; partial dissolution of relatively “insoluble” Tl-bearing phases (silicates and eventually oxides) in the presence of LMWOA is suggested. Thermodynamic modeling showed that Tl mobilization in the presence of citric and oxalic acids was indirect and could be attributed to complexation of major elements (Ca, Mg, Al) originating from the dissolution of various soil phases. On the contrary, H +-promoted dissolution by acetic acid was assumed as the predominant mechanism of Tl mobilization. Manganese(III,IV) oxides, illite and probably amorphous silicates were evaluated as the dominant phases responsible for Tl retention in the soils. In carbonate-rich soils, Tl coprecipitation with the newly formed carbonates seems to be an important factor influencing Tl release. Therefore, we suggest data on CEC, pH ZPC and soil mineralogy to be critical for assessment of Tl behavior in soil systems.

PARAMETRIC STUDY OF THE RESIDUAL GAS IN SPARK IGNITION ENGINES

ABSTRACT The residual gas xr affects the number of moles of unburned mixture. Consequently it affects the mixture's molecular mass, specific heats, gas constant, internal energy and enthalpy of formation and entropy. Its magnitude affects volumetric efficiency and engine torque and power directly, whereas thermal efficiency and emissions are affected by the change in thermodynamic properties of the working fluid. A parametric study covers the variables which affect xr namely compression ratio,equivalence ratio φ, inlet air temperature Ti, ratio of exhaust and intake pressures pc/pi, and fuel. A computer program was devised to calculate xr,Tr, Tl and specific heat release, and the consequent performance namely power, ηth and bmep. Results show the relative importance of the parameters such as rc,φ, pc/pi and fuel type on residual gas particulars, and fuel on power and ηth whereas for bmep the pc/pi acquires additional importance.