We examined the uptake of Tl(I) by two hexagonal birnessites and related phase transformations in laboratory experiments over 12 sequential additions of 0.01 M Tl(I)/Mn at pH 4.0, 6.0, and 8.0. The ...Tl-reacted Mn oxides were characterized for their structure, Tl binding, and morphology using X-ray diffraction, X-ray photoelectron and X-ray absorption spectroscopies, and transmission electron microscopy. Very limited Tl oxidation was observed in contrast to previous works, where equal Tl(I)/Mn was added in a single step. Instead, both birnessites transformed into a 2 × 2 tunneled phase with dehydrated Tl(I) in its tunnels at pH 4, but only partially at pH 6, and at pH 8.0 they remained layered. The first four to nine sequential Tl(I)/Mn additions resulted in lower residual dissolved Tl
concentrations than when the same amounts of Tl(I)/Mn were added in single steps. This study thus shows that the repeated reaction of hexagonal birnessites with smaller Tl(I)/Mn at ambient temperature triggers a complete phase conversion with Tl(I) as the sole reacting cation. The novel pathway found may be more relevant for contaminated environments and may help explain the formation of minerals like thalliomelane Tl
(Mn
Cu
)O
; it also points to the possibility that other reducing species trigger similar Mn oxide transformation reactions.
Isotopically exchangeable metals in soil, also termed labile metals, are reversibly bound to soil surface and are a better index of the environmental risk of the metals than are their total ...concentrations. In this study, labile fractions of potentially toxic elements were surveyed in metal mining‐impacted soils of Mexico to test the relative importance of soil properties (pH, effective cation exchange capacity, organic matter, etc.) or attributes of the mines (ore type and lithology, metal mineralogy, etc.) on the fractions of labile elements. Mining waste‐impacted soils, corresponding uncontaminated soils and mining waste were collected around 11 metal mines in Mexico presenting contrasting ore types. Pseudo‐total concentrations and labile fractions of Cd, Ni, Zn, Pb, Cu, and As were determined by aqua regia digestion and isotope dilution, respectively. Pseudo‐total concentrations of these elements ranked: waste > contaminated soil > uncontaminated soils, and Zn and As dominated the concentrations of toxic elements. The labile fractions (% of total) in the soils ranked, with median values in brackets, Pb (22) > Cd (18) > Cu(15) > Ni∼Zn(13) > As(9). The labile fractions of waste samples were slightly higher than those of soil samples suggesting either a high weathering of mining wastes or the stabilization of heavy metals by soil. Stepwise multiple regression showed that soil properties rather than source attributes primarily explained the %E of most elements, except for Zn and As for which the ore lithology was the dominant factor. This study showed that earlier generic models explain metal lability adequately in mining waste‐impacted soils.
Thallium is the most toxic regulated metallic ion in soil and water. Previous work in soil samples contaminated by metallurgical wastes has revealed a very high correlation between extracted Tl and ...Mn in the reducible mineral fractions, which suggests a high geochemical affinity between Tl and Mn oxides, once Tl has been released from the primary minerals it is originally associated with (aluminosilicates and sulfides). The goal of the present work was to determine the behavior and mechanisms of thallium (I) sorption on Mn(IV)-birnessites, focusing on expanding the conditions previously investigated, by using two synthetic poorly-crystalline preparations of this mineral that are the closest analogs to biologically-produced Mn oxides, but differ greatly in their particle sizes; and by testing the effects of a wide range of pH values and Tl(I) concentrations, to simulate a large variability in geochemical conditions. To achieve this, we performed Tl(I) sorption isotherms on clean preparations of both birnessites at three different pH values (4, 6 and 8) and X ray Absorption Spectroscopy (XAS), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Specific Surface Area (SSA) analyses on selected samples. Thallium (I) sorption to the birnessites consists of a prevailing irreversible oxidation mechanism, with retention of the Tl(III) produced, mainly over vacant layer sites, and eventual formation of the mineral avicennite (Tl2O3) at high loadings and pH. Thallium (I) was increasingly sorbed/oxidized at all pH values, but its extent increased as pH was raised, contrary to what the redox reaction suggests, where protons contribute as reacting agents. The sorption/oxidation reaction was also independent of the birnessite initial particle size or vacancy content. This strongly suggests that the net negative electrostatic charge of the birnessite plays a major role in the reaction, and therefore, the sorption part of the mechanism is the limiting and prevailing step of the overall process; however, since Tl(I) enters into the mineral structure and may potentially access all internal Mn(IV) available, the redox reaction appears to be boundless, showing extremely high capacities for Tl(I) oxidation. Finally, at high concentrations of the Tl(III) formed, and apparently coinciding with the formation of avicennite (Tl2O3), a general delamination of the birnessite layered structure was provoked adding to its gradual dissolution.
The condition of the soil environment is critical for human health and agricultural sustainability. As a result, the environmental and ecological issues impacting the soils throughout the world are ...receiving more attention. This research focuses on local site-specific studies in Cerrito Blanco, Matehuala municipality, San Luis Potosi, Mexico, and describes different types of GIS interpolation techniques, multivariate statistical analysis, and various contamination indices to investigate the relationship between predictive accuracy, levels of contamination risk, and soil toxic metal elements variation. Inductively coupled plasma optical emission spectroscopy (ICP-EOS) used to test 39 digested surface soil samples for significant toxic metals (Ag, Cd, Co, Cr, Li, and Ni) after suitable dilution with deionised water. According to the results, we found that only the mean value of cadmium (Cd) exceeded the permissible standard value. After evaluating the four types of interpolation techniques, the Inverse Distance Weighting (IDW) was determined to be the optimal interpolation model for assessing the spatial distribution patterns of toxic metal concentration in the research area. The calculated contamination risk indices showed no significant high contamination risk due to soil-borne toxic metals. These results provide a comprehensive analysis of the impact of past mining activities on toxic metal concentrations in non-cultivated surface soil.
•The study addresses the research of different approaches of contamination assessment techniques to identify the toxic metal contaminations in the surface soil.•The study exploits the estimation of the contamination risk level of toxic heavy metals.•The study discusses GIS interpolation techniques as well as multivariate statistical analysis which were used for spatial distribution.
Cation sorption on clays and on humic acids (HA) has been extensively documented in scientific literature. Both are important components of natural environments, especially in soils, and therefore, ...innate competitors in the retention of metallic cations. The aim of this work was to investigate the sorption behavior of thallium (I) on a 2:1 type clay (IMt-2 illite, from silver Hill, Montana), and to compare it with its sorption behavior on HA. For this, a total of nine sorption isotherms of thallium on illite and/or HA were conducted at different pH values (3, 7 and 9). The sorption mechanism on illite was investigated by designing a novel cation exchange sorption model that incorporates an additional surface complexation mechanism (2pKa/3CE), where selectivity coefficients for 3 different types of exchange sites and a surface complexation constant for a pH-dependent site (≡SOH) at illite particle edges were obtained. In the case of Tl complexation by HA, investigation of the mechanism involved was done using the NICA-Donnan model.
Sorption to illite showed increasing Tl+ uptake upon increasing pH from 3 to 9 by approximately one order of magnitude. Tl+ sorption on HA was also highly pH dependent, but slightly lower than on illite, although at low pH Tl+ complexation on HA was negligible.
Geochemical sorption modeling on illite suggests that at very low Tl+ concentrations cation exchange Frayed Edge Sites were dominant at all pH values, after which at pH 3 and 7 the other interlayer cation exchange sites became the major contributors to sorption; while at pH 9 surface complexation of Tl(I) on the edge sites predominated, confirming the important variable-charge nature of illite and the strong competition that protons exert for binding of Tl(I) on these sites. In the case of modeling the Tl(I) binding to HA, complexation with the phenolic groups or high affinity sites present at the HA surfaces was predicted to be dominant, although at pH 7, the electrostatic component was dominant at the higher Tl+ concentration interval. The findings in this work contribute to further the understanding of two crucial geochemical mechanisms of Tl(I) retention in contaminated soils.
•Tl + sorption on both illite and HA showed a strong dependence with pH.•A higher binding affinity occurred on illite than on HA.•Interlayer sites of illite dominated sorption at pH 3 and 7.•Variable charge sites on illite edges dominated sorption at pH 9.•Sorption on HA was dominated by phenolic sites, and the electrostatic component at pH 7.
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•As contaminates water, soils and maize crops in Matehuala, San Luis Potosi, Mexico.•High CEC, total N, P, and OM explain lower bioconcentration of As.•High soil EC explains higher ...bioconcentration of As.•Gypsum and calcite play a key and contrasting role on the mobility of As in soils.•Information on retention mechanisms of As in calcic and gypsic soils is limited.
Mobility of Arsenic (As) from metallurgical wastes in Matehuala, Mexico has been accounted for ultra-high concentration of As in water (4.8–158mg/L) that is used for recreational purposes as well as cultivation of maize. In this study, we (i) measured As concentrations in soils irrigated with this water, (ii) investigated the geochemical controls of available As, and (iii) measured bioaccumulation of As in maize. Water, soil, and maize plant samples were collected from 3 different plots to determine As in environmental matrices as well as water soluble As in soils. Soil mineralogy was determined by X-ray diffraction analysis. Bioaccumulation of As in maize plants was estimated from the bioconcentration and translocation factors. We recorded As built-up in agricultural soils to the extent of 172mg/kg, and noted that this As is highly soluble in water (30% on average). Maize crops presented high bioaccumulation, up to 2.5 times of bioconcentration and 45% of translocation. Furthermore, we found that water extractable As was higher in soils rich in calcite, while it was lower in soils containing high levels of gypsum, but As bioconcentration showed opposite trend. Results from this study show that irrigation with As rich water represents a significant risk to the population consuming contaminated crops.
In this study, we simulate the irrigation of tomato plants with arsenic (As)-contaminated water (from 0 to 3.2 mg L
−1
) and investigate the effect of the application of silicon nanoparticle (Si NPs) ...in the form of silicon dioxide (0, 250, and 1000 mg L
−1
) on As uptake and stress. Arsenic concentrations were determined in substrate and plant tissue at three different stratums. Phytotoxicity, As accumulation and translocation, photosynthetic pigments, and antioxidant activity of enzymatic and non-enzymatic compounds were also determined. Our results show that irrigation of tomato plants with As-contaminated water caused As substrate enrichment and As bioaccumulation (roots > leaves > steam), showing that the higher the concentration in irrigation water, the farther As translocated through the different tomato stratums. Additionally, phytotoxicity was observed at low concentrations of As, while tomato yield increased at high concentrations of As. We found that application of Si NPs decreased As translocation, tomato yield, and root biomass. Increased production of photosynthetic pigments and improved enzymatic activity (CAT and APX) suggested tomato plant adaptation at high As concentrations in the presence of Si NPs. Our results reveal likely impacts of As and nanoparticles on tomato production in places where As in groundwater is common and might represent a risk.
This study aims to improve the current method of studying potentially toxic elements (PTEs) in urban dust using direct chemical evidence (from dust, rock, and emission source samples) and robust ...geochemical methods. The provenance of urban dust was determined using rare earth elements (REEs) and geochemical diagrams (V–Ni–Th*10, TiO2 vs. Zr, and Zr/Ti vs. Nb/Y). The geogenic or anthropogenic source of PTEs was determined using the enrichment factor (EF) and compositional data analysis (CoDA), while a PTE's point emission source was identified using a 3.1*La–1.54*Ce–Zn diagram, mineralogy, and morphology analyses. The spatiotemporal distribution of PTEs was determined using a geographic information system, and their health risk (by inhalation) was estimated using a lung bioaccessibility test and particle size distribution. We collected urban dust (n = 38), rock (n = 4), and zinc concentrate (n = 2) samples and determined PTEs and REEs in a city of 1.25 million inhabitants in central Mexico. Results showed that urban dust derived from the San Miguelito Range. REEs, Sc, and Zr were geogenic, while Mn, Cu, Zn, As, and Pb were anthropogenic. Due to the presente of sphalerite particles, a zinc refinery was identified as the point emission source of Zn, As, and Pb. High concentrations of Zn (5000–20,008 mg/kg), As (120–284 mg/kg), and Pb (350–776 mg/kg) were found in urban dust near the zinc refinery. Additionally, particles of PM2.5 (66–84%), PM5.0 (13–27%), PM10 (3–8%), and PM20 (0–2%) and lung bioaccessibility of Sr (48.5–72.4%), Zn (9.6–28.4%), Cu (10.5–27.0%), Fe (4.5–8.6%), Mn (2.9–9.2%), Cr (38.3%) and Pb (30.6%) demonstrated a latent risk to human health. These approaches improve our understanding of the provenance of urban dust and its PTE emission sources in urban areas.
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•According to REE's fingerprints, urban dust derives from the San Miguelito Range.•The urban dust was enriched in As, Mn, Cr, Pb, V, Zn, and Cu.•The anthropogenic source of Zn, As, and Pb was a zinc refinery within the city.•High Zn, As, and Pb were mostly found in the surroundings of the zinc refinery.•Urban dust contained PM2.5 particles and bioaccessible Zn, Pb, and other PTEs.
Sponge-type nitrogen-doped multiwall carbon nanotubes (N-MWCNTs), synthesized via an aerosol-assisted catalytic chemical vapor deposition (AACCVD) method, were extensively studied. A ball-milled and ...oxidized red-leptosol (RL) was used as the catalyst precursor, and benzylamine worked as a carbon and nitrogen source. The ball-milled and oxidized RL increased their contact area and purity for the N-MWCNT synthesis. X-ray diffraction characterization revealed that raw RL contained kaolinite, quartz, graphite, hematite, and goethite. According to the electron microscopy analysis, the N-MWCNTs exhibited exotic morphologies and microstructures. The high-resolution X-ray photoelectron spectroscopy showed that the as-grown N-MWCNTs contained pyrrolic and pyridinic nitrogen species. The cyclic voltammetry studies demonstrated that the redox processes in the N-MWCNTs in 0.1 M H2SO4 were dominated by the carboxyl, pyridinic, and pyrrolic groups. Using the natural RL as a catalyst precursor in AACCVD led to a large yield of N-MWCNTs mixed with different minerals, causing the observed morphologies and influencing the electrochemical behavior, which is of interest in energy-storage and sensing applications.
Sponge-type nitrogen-doped multiwall carbon nanotubes (N-MWCNTs) synthesized by aerosol-assisted catalytic chemical vapor deposition using benzylamine as carbon and nitrogen sources and a red leptosol as a catalyst precursor. Cyclic voltammetry studies found pyrrolic-N, pyridinic-N, and oxygen groups as the leading chemical surface reactant groups for redox processes. Display omitted
•A facile route to produce sponge-type nitrogen-doped multiwall carbon nanotubes using a low-cost red-leptosol as catalyst.•Soil minerals in red-leptosol enhance the yield of N-MWCNT.•The synthesized N-MWCNTs show promising properties for electrochemical devices.•CNT morphologies exhibit unusual structures.
Toxic heavy metals in soil negatively impact soil’s physical, biological, and chemical characteristics, and also human wellbeing. The traditional approach of chemical analysis procedures for ...assessing soil toxicant element concentration is time-consuming and expensive. Due to accessibility, reliability, and rapidity at a high temporal and spatial resolution, hyperspectral remote sensing within the Vis-NIR region is an indispensable and widely used approach in today’s world for monitoring broad regions and controlling soil arsenic (As) pollution in agricultural land. This study investigates the effectiveness of hyperspectral reflectance approaches in different regions for assessing soil As pollutants, as well as a basic review of space-borne earth observation hyperspectral sensors. Multivariate and various regression models were developed to avoid collinearity and improve prediction capabilities using spectral bands with the perfect correlation coefficients to access the soil As contamination in previous studies. This review highlights some of the most significant factors to consider when developing a remote sensing approach for soil As contamination in the future, as well as the potential limits of employing spectroscopy data.
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