Acid generation and metal(loid) release are growing considerations for oil sands mine closure in northern Alberta, Canada. Oxidative weathering of pyrite-bearing froth treatment tailings (FTT) has potential to promote acid generation and metal(loid) release. However, the acid-neutralization reactions and their influence on pore-water pH and metal(loid) mobility have not yet been reported. Laboratory column experiments examined acid-neutralization reactions and metal(loid) release for variably weathered (i.e., non-weathered, partially weathered, highly weathered) FTT samples collected from a commercial-scale beach deposit. Solvent-washed and non-solvent-washed splits of each sample were included to assess the influence of residual hydrocarbons. Acidic influent (i.e., 0.05 M H2SO4; pH 1.5) was continuously pumped through each column, and effluent samples were collected for geochemical analysis over time. Effluent pH decreased from 7.0 to 5.5 over the first 5 pore volumes for the non-weathered and partially weathered columns, while gradual pH decreases to 4.5 were observed over the following 30 to 70 pore volumes. Subsequent decreases in effluent pH from 4.5 to < 3.0 occurred over the next 2 to 5 pore volumes for these columns. In contrast, effluent pH consistently remained below 2.0 for the highly weathered columns. We attribute these effluent pH trends to the dissolution of Ca- and Mg-bearing carbonates (pH 6.5 to 6), Fe-bearing carbonates (pH 5.6 to 4.5), Al (oxy)hydroxides (pH 4.5 to 4.0), and silicates (pH < 2). Corresponding increases in effluent concentrations of Fe (< 1 to > 500 mg L− 1), Al (< 0.1 to > 10 mg L− 1), Si (< 0.1 to > 10 mg L− 1), and additional metal(loid)s (e.g., Ni, Zn, V, As) were observed with decreasing pH. Cumulative mass releases (e.g., Ca, Mg, Fe) were greatest for the non-weathered samples and solvent-washed splits. These results offer new insights into relationships between acid neutralization reactions and metal(loid) release that can inform FTT management and reclamation.
Perfluorooctane sulfonate (PFOS) is an emerging contaminant frequently detected in subsurface environments, raising significant concern due to its environmental persistence, mobility, and potential human health impacts. This study examines PFOS adsorption onto a range of solid substrates, including pure minerals, mineral assemblages, and natural soils. Specifically, the adsorption behavior of 2-line ferrihydrite, ferrihydrite-coated sand, and soil collected from a PFOS-impacted site in Killingworth, Connecticut was investigated to evaluate their capacity to retain PFOS under varying geochemical conditions. By integrating batch adsorption experiments with surface complexation modeling (SCM) and applying the component additivity approach, this study elucidates the reactive transport mechanisms governing PFOS behavior under a range of geochemical conditions. Our findings demonstrate that PFOS adsorption occurs significantly on both ferrihydrite and quartz surfaces, with the ferrihydrite-coated sand and soil exhibiting retention behavior attributable to contributions from both mineral phases. At lower pH values, sorption is predominantly governed by outer-sphere complexation driven by the surface charge characteristics of ferrihydrite. Specifically, under acidic conditions (pH < 5.5 for ferrihydrite-coated sand and pH < 6.0 for soil), PFOS retention is primarily facilitated through an outer-sphere hydrogen-bonded complex at ferrihydrite’s surface, while a secondary outer-sphere complex involving Na+ co-adsorption contributes to a lesser extent. At elevated pH levels, however, electrostatic interactions become less favorable, and non-electrostatic hydrophobic interactions with quartz surfaces become increasingly dominant, highlighting the transition in sorption mechanisms from charge-driven to hydrophobic partitioning under neutral to alkaline conditions. A comparison with traditional partitioning coefficients (Kd) revealed that their variability closely corresponds with changes in dominant surface complexes across different pH conditions. Given the critical role of solid-phase partitioning in governing PFAS transport in the subsurface, enhanced predictive capabilities are essential for advancing site-specific risk assessments and informing management strategies aimed at protecting both public and private water resources.
Bitumen extraction from mined oil sands ore generates a large volume of fluid fines tailings (FFT) that must be incorporated into either aquatic or terrestrial reclamation landforms. Mine operators are developing various tailings technologies to accelerate FFT dewatering, including the addition of chemical coagulants and flocculants. However, the impacts of these coagulants and flocculants on biogeochemical processes in treated FFT are not fully understood. We conducted anaerobic batch experiments to examine the influence of different doses (i.e., 0, 500, 1000, and 1500 ppm) of sulfate-based coagulants, including aluminum sulfate (alum) [Al2(SO4)3∙nH2O], ferric sulfate (ferric) [Fe2(SO4)3∙nH2O], and calcium sulfate (gypsum) [CaSO4∙2H2O], on biogenic gas production and microbial communities in treated FFT. Our results show that sulfate addition stimulated microbial sulfate reduction, which inhibited methanogenesis in coagulated FFT relative to experimental controls. Sulfate depletion preceded increased methane production in the 500 ppm gypsum experiment, while larger ferric and alum doses produced higher sulfate concentrations and larger pH decreases. 16 S rRNA sequencing revealed that Comamonadaceae, Anaerolineaceae, and Desulfocapsaceae were the major bacterial families, while Methanoregulaceae and Methanosaetaceae dominated the archaeal families in all treatments. Precipitation of iron(II) sulfides limited dissolved hydrogen sulfide concentrations in experiments where Fe availability was not limited. Our results indicate that addition of sulfate-based coagulants can stimulate microbial sulfate reduction and suppress methanogenesis. However, resumption of methane production following sulfate depletion reveals complex interactions among biogeochemical reaction pathways. Overall, this study demonstrates that biogeochemical cycling of carbon, sulfur, and iron are important considerations for the development and implementation of tailings treatment technologies.
The present research work aims to understand the geochemistry of groundwater resources of the Yamuna-Hindon interfluve region of Bagpat district, Western Uttar Pradesh, India. The region is a part of Indo-Gangetic belt, one of the world's most fertile and intensely farmed areas. To investigate the geochemical processes governing groundwater quality, a total of 105 groundwater samples were collected during pre-monsoon season and analyzed for various physico-chemical parameters, namely, pH, electrical conductivity (EC), total dissolved solid (TDS), total hardness (TH), turbidity, major anions (HCO3-, SO42-, F-, Cl-, NO3-), cations (Ca2+, Mg2+, Na+, K+) following the methods outlined in the American Public Health Association (APHA). The dissolved heavy metals (Fe, Mn, Zn, Pb, Cu, Cr, Ni, As, Se, Co, Cd and Al) in groundwater were analyzed by ICP-MS following the instrument manual. The analysis results revealed that the groundwater is pre-dominantly neutral to mildly alkaline in nature. The major cation chemistry majorly followed the occurrence pattern of Na+ > Mg2+ > Ca2+ > K+, while for anions it was HCO3- > Cl- > SO42- > NO3- > F-. The data plotted on Piper triangular diagram indicated that Ca2+-Mg2+-HCO3- and Na+-K+-HCO3--Cl- were major hydrogeochemical facies. Weathering of rock-forming minerals mainly governed the groundwater geochemistry in this region, although part of the cations associated with Cl-, F- and NO3- may originate from anthropogenic sources. TDS, TH, turbidity and F- were identified as the major parameters that violated the prescribed limits for drinking water. Most of the heavy metals were found within the drinking water prescribed limits except for Fe, Mn, Al and Se. Elevated salinity, %Na, and magnesium hazard (MH) at certain sites limit its suitability for agricultural use. The assessment of selected organochlorine and organophosphorus pesticides in five samples indicated presence of lindane, β-endosulfan and DDT isomers in few samples. However, a detailed investigation of possible pesticide contamination in this intensive agriculture area is required before drawing any final conclusions.
This study presents the first kinetic model to predict the solid and pore solution composition of Na-bentonite clay reacting with slaked lime over a period of 720 days. The model successfully accounts for most experimental data using a single kinetic rate constant. The following sequence of reactions was predicted by the model: initial rapid dissolution of portlandite within the first 7 days, leading to a decrease in pH and dissolved calcium, and concurrent formation of calcium silicate hydrates (C-S-H: jennite), calcium aluminate hydrate (C-A-H: C₄AH₁₃), calcium aluminosilicate hydrates (stratlingite) and hydrotalcite. After 7 days, jennite and stratlingite are predicted to transform into tobermorite-II, contributing to strength development up to 28 days. From 28 to 90 days, continued montmorillonite dissolution is predicted, along with minor formation of ettringite, partial tobermorite-II dissolution, and precipitation of secondary phases such as albite and talc. Experimentally, portlandite dissolution was confirmed by TGA and XRD and found to be complete within 7 days, in agreement with model predictions. However, other predicted solid-phase transformations (e.g., tobermorite-II formation and dissolution, ettringite, albite, and talc formation) could not be conclusively verified through experimental techniques. Aqueous phase measurements confirmed that the pH and Ca trends in solution, and that equilibrium was reached by 90 days.
Groundwater resources in mica mining areas of Jharkhand are vital for local communities, agriculture, and domestic utilization. The study investigates the major ion chemistry of groundwater in the mica mining regions, focusing on key physicochemical parameters such as pH, electrical conductivity (EC), total dissolved solids (TDS), and concentrations of major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) and anions (HCO₃⁻, Cl⁻, SO₄²⁻, NO₃⁻, F−). Groundwater samples from the study area were collected before the monsoon season, during the monsoon season, and after the monsoon season. The hydro-chemical analysis reveals that groundwater in the mica mining zones exhibits elevated levels of dissolved ions, with NO₃⁻, F−, Ca²⁺, Mg²⁺ and total hardness exceeding permissible limits set by Bureau of Indian Standards (BIS) for drinking purposes at some locations. Water Quality Index (WQI) assessments suggest that a significant proportion of groundwater samples fall into the “good” to “very good” category for drinking and about 29
This study investigates the trace element concentrations in the surface waters of four north-joining Himalayan tributaries of the Ganga river (Ramganga, Ghaghara, Gandak, and Kosi), highlighting the combined effects of geogenic processes and anthropogenic activities on trace element chemistry and water quality. A knowledge gap exists in understanding the sources of trace elements in these tributaries and the contribution of trace elements from these tributaries to the Gangariver. The novelty of the study lies in its assessment of sources, human health risks, and ecological impacts. The investigation was conducted by assessing trace element concentrations and comparing them with national and international standards. Various human health and ecological risk indicators, including the Heavy Metal Pollution Index (HPI), Hazard Quotient (HQ), Health Index (HI), Chronic Daily Intake (CDI), and the Potential Ecological Risk Index (PERI), were applied. The results reveal high concentrations of copper (Cu), zinc (Zn) and lead (Pb) in the Ramganga, indicating contamination from industrial activities in the catchment. Although most trace element concentrations are within safe limits, Pb concentration in the Ramganga exceeds the limit prescribed by WHO. The Ramganga shows the highest health risks, with a HItotal of 1.876 for adults and 1.616 for children. In contrast, the Ghaghara, Gandak, and Kosi exhibit lower but moderate contamination levels. HPI values for these rivers- 93.74 for the Ghaghara, 83.95 for the Kosi, 83.13 for the Gandak, and 80.43 for the Ramganga-indicate that although contamination is below critical thresholds, targeted mitigation strategies are needed. The findings provide valuable insights into trace metal sources and their implications for human health and ecological risks, and emphasize the need for frequent monitoring and pollution control measures for maintaining sustainable water quality in these tributaries.
The quality of water can significantly affect the regional water resources due to scarcity of potable water in industrial area. The purpose of this study was to explore potentially toxic trace elements (PTEs) contamination and their seasonal variations in different water sources within the coal mining area of the Mahan River command area, Central India. To achieve this, 96 water samples were collected across two distinct seasons and analysed for PTEs. The results indicate that during the pre-monsoon season, the concentrations of Mn (18%), Cu (4%), Pb (8%), Ni (18%), Cd (2%), Al (4%), Cr (2%), and Fe (30%) exceeded permissible limits. In the post-monsoon season, Mn (15%), Pb (6%), Ni (15%), Cd (2%), Al (15%), Fe (46%) and Ba (4%) surpassed the standards. The multiple groundwater pollution indexical methods further revealed that 14% [Heavy metal pollution index (HPI)], 14% [Heavy metal evaluation index (HEI)], 18% [Contamination index (CI)], 14% [the entropy-weight based HM contamination index (EHCI)] and 20% [Heavy metal index (HMI)] of the samples exceeded permissible thresholds during the pre-monsoon season. Similarly, during the post-monsoon period, 10% (HPI), 10% (HEI), 15% (CI), 15% (EHCI) and 17% (HMI) of the samples were above acceptable limits. The relationship between the pH of water and the total load of dissolved metals is established using Caboi plot, confirming that mine water from mine water from Bhatgaon Underground (UG), Mahamaya UG, and Mahan Opencast (OC) [PR40, PR41, PR42, PR43, PR47, and PR48], surrounding rivers, and groundwater sources, exhibited an "Acid-High Metal" characteristic. This suggests significant contamination from acid mine drainage and mineral dissolution. Apart from the anthropogenic inputs, geogenic and environmental processes are responsible for the current distribution of PTEs and their seasonal variations.
In anoxic subsurface environments, low Fe(III) bioaccessibility greatly limits in situ biodegradation of petroleum hydrocarbons (PHCs). Ferric ammonium citrate is a soluble compound that has the potential to increase the bioaccessibility of Fe(III). However, in neutral to alkaline environments, Fe(III) hydrolysis can produce Fe(III) (oxyhydr)oxides that may subsequently transform or recrystallize to relatively stable and less bioaccessible phases. Accordingly, the objective of this study was to elucidate the transformation and fate of Fe(III) contributed by ferric ammonium citrate in a gasoline-contaminated subsurface environment that was undergoing in situ bioremediation. Ferric ammonium citrate, together with sodium tripolyphosphate, magnesium sulphate, and nitric acid, was continuously injected into the contaminated groundwater for about 22 weeks. Colloids in the groundwater (solid particles retained on a 0.45 μ m filter) and soil cores were collected from the site. Fe speciation in these samples was characterized using X-ray absorption near edge structure (XANES) and Fourier transform infrared (FTIR) spectroscopy. The groundwater colloids (GWCs) contained mostly octahedrally coordinated Fe(III), but the subsoils contained both octahedrally coordinated Fe(III) and Fe(II). The fraction of Fe(II) in the subsoils generally increased after about 22 weeks of continuous amendment injection. Ferric ammonium citrate did not persist in the PHC-contaminated subsurface: the Fe(III) it contained was transformed to solid phases. Fe(III)-organic-matter (Fe(III)-OM) complex/coprecipitate and sulfate green rust were the major phases present in the GWCs; akaganeite, chloride green rust, vivianite, ferrihydrite, Fe(III)-silicate, and magnetite were present as minor phases. The subsoils contained three major phases: Fe(III)-OM complex/coprecipitate, magnetite, and calcium ferric silicate. The presence of major Fe(II) phases in the subsoils strongly indicate that secondary Fe(III) phases (especially Fe(III)-OM complex/coprecipitate) served as terminal electron acceptors during the microbial degradation of PHCs in the contaminated subsurface.
A series of the calcium-nickel carbonate solid solutions [(Ca1−xNix)CO3] were synthesized and their dissolution in N2-degassed water (NDW) and CO2-saturated water (CSW) at 25 °C was experimentally investigated. During dissolution of the synthetic solids (Ni-bearing calcite, amorphous Ca-bearing NiCO3 and their mixtures), the Ni-calcite and the Ca-NiCO3 dissolved first followed by the formation of the Ni-bearing aragonite-structure phases. After 240–300 days of dissolution in NDW, the water solutions achieved the stable Ca and Ni concentrations of 0.592–0.665 and 0.073–0.290 mmol/L for the solids with lower Ni/(Ca + Ni) mol ratios (XNi), or 0.608–0.721 and 0.273–0.430 mmol/L for the solids with higher XNi, respectively. After 240–300 days of dissolution in CSW, the water solutions achieved the stable Ca and Ni concentrations of 1.094–3.738 and 0.831–4.300 mmol/L, respectively. For dissolution in NDW and CSW, the mean values of log IAP (Ion activity products) in the final stable state (≈ log Ksp, Solubility product constants) were determined to be − 8.65 ± 0.04 and − 8.16 ± 0.11 for calcite [CaCO3], respectively; − 8.50 ± 0.02 and − 7.69 ± 0.03 for the synthetical nickel carbonates [NiCO3], respectively. In respect to the bulk composition of the (Ca1−xNix)CO3 solid solutions, the final log IAP showed the highest value when XNi = 0.10–0.30. Mostly, the mean values of log IAP increased with the increasing XNi in respect to the Ni-calcite, the Ni-aragonite and the amorphous Ca-Ni carbonate. The plotting of the experimental data on the Lippmann diagram for the (Ca1−xNix)CO3 solid solution using the predicted Guggenheim parameters of a0 = 2.14 and a1 = − 0.128 from a miscibility gap of XNi = 0.238 to 0.690 indicated that the solids dissolved incongruently and the final Ca and Ni concentrations in the water solutions were simultaneously limited by the minimum stoichiometric saturation curves for the Ni-calcite, Ni-aragonite and the amorphous Ca-Ni carbonate. During dissolution in NDW, the Ni2+ preferred to dissolve into the water solution and Ca2+ preferred to remain in the solid, while during dissolution in CSW for the solids with higher XNi, the Ca2+ preferred to dissolve into the water solution and Ni2+ preferred to remain in the solid. These findings provide valuable insights into understanding the mechanisms governing Ni geochemical cycle in natural environments.
Green rusts (GR) are mixed-valence iron (Fe) hydroxides which form in reducing redox environments like riparian and wetland soils and shallow groundwater. In these environments, silicon (Si) can influence Fe oxides’ chemical and physical properties but its role in GR formation and subsequent oxidative transformation have not been studied starting at initial nucleation. Green rust sulfate [GR(SO4)] and green rust carbonate [GR(CO3)] were both coprecipitated from salts by base titration in increasing
The magmatic complex along the Marsa Alam-Idfu transect, Central-Eastern Desert of Egypt, represents the northern segment of the Arabian–Nubian Shield (ANS), which developed within the framework of the East African Orogen. The basement rocks of the Arabian-Nubian Shield have been developed through three distinct phases of magmatic activity: the island-arc, the syn-orogenic, and the post-orogenic phases. Transitioning of the magmatic phases from the syn-orogenic to the post-orogenic, identifies changing the tectonic regime from a compressional to an extensional setting. The scarcity of comprehensive regional geochronological data that rely on precise isochron methods, such as the zircon U-Pb technique, could limit the comprehensive understanding of this region’s geological and tectonic history. That would raise a number of uncertainties ranging from the timing of the different magmatic activities and timing of changes in the tectonic regime to the existence of the pre-Pan-African crust in the CED. Our study provides new insights into the aforementioned uncertainties through zircon U-Pb dating of different rock units along the Marsa Alam-Idfu transect, CED, Egypt. The resulting ages ranged from 729 ± 3 Ma to 570 ± 2 Ma, constraining the temporal evolution of the ANS in the studied region into (1) the island-arc phase, represented by a metamorphic sample with an age of 729 ± 3 Ma. (2) the syn-orogenic phase, represented by calc-alkaline and alkaline granitic samples with ages ranging from 699 ± 4 Ma to 646 ± 2 Ma. These two phases indicate initiation of the compressional subduction regime in the CED since 729 ± 3 Ma and being dominated till 646 ± 2 Ma. (3) the post-orogenic phase, represented by metavolcanics, volcanic rocks, and alkaline plutonic samples with ages ranging from 623 ± 3 Ma to 570 ± 2 Ma. This phase suggests dominance of the compressional-to-extensional tectonic transition setting from 623 ± 3 Ma to 600 ± 1 Ma along with the Dokhan volcanism and activation of post-collision tensional regime activated at 582 ± 3 Ma. Our findings discourage the proposed dominance of the island-arc and syn-orogenic phases in the CED and the classical restriction of older magmatic activity to calc-alkaline granitic rocks and younger magmatic activity to alkaline granitic rocks. Additionally, we identified evidence of local magmatic sources by dating five grains with Mesoproterozoic (pre-Arabian–Nubian Shield) xenocrysts with ages ranging from 1549 ± 4 to 1095 ± 25 Ma.
Clean river water is an essential and life-sustaining asset for all living organisms. The upper Ganga and Yamuna river system has shown signs of rejuvenation and tremendous improvement in the water quality following the nationwide lockdown due to the coronavirus pandemic. All the industrial and commercial activity was shut down, and there was negligible wastewater discharge from the industries. This article addresses the water quality assessment from the study area, which is based on the original data of physical parameters, major and trace elements, and stable isotopes (hydrogen and oxygen) systematics during the nationwide lockdown. The impact of the lockdown could be seen in terms of an increase in dissolved oxygen (DO). Water samples were collected from the Upper Ganga and Yamuna river basins (Alaknanda, Bhagirathi, and Tons rivers) during an eight-week lockdown in Uttarakhand, India. We discussed the signs of rejuvenation of riverine based on physical parameters, major ions, trace elements, isotopic ratios, and water pollution index (WPI). Results reveal that the water quality of the entire upper basins of the Ganga has significantly improved by 93 NO_3^- ), implying that they contribute little to the river water during the lockdown. Further, bicarbonate ( HCO_3^- ) is a dominant element in both river basins. The geochemical facies are mainly characterized by the ( Ca^2+ :Mg^2+ : HCO_3^- ) type of water, suggesting that silicate rock weathering dominates with little influence from carbonate weathering in the area. The positive factor loadings of some cations, like HCO_3^- , Ca^2+ , and Mg^2+ reflect their strong association with the source of origin in the lockdown phases. Stable isotopic reveals that the glaciated region contributed the most to the river basin, as evidenced by the low d-excess in riverine water compared to anthropogenic contributions. Rivers can self-rejuvenate if issues of human influence and anthropogenic activities are adequately resolved and underline our responsibility for purifying the ecosystem. We observed that this improvement in the river water quality will take a shorter time, and quality will deteriorate again when commercial and industrial activity resumes.
Quarrying of rock aggregates generates produced water that, if not handled properly will be a source of pollution for nearby water bodies, thus affecting the chemistry of the water. This study examined the chemistry, impact of quarrying activities on water resources and the health consequences/risks posed by ingestion of the water by humans in the Akamkpa quarry region in southeastern Nigeria. Thirty (30) water samples consisting of pond water, stream water, hand dug wells, and borehole samples were collected and analyzed for their physicochemical parameters using standard methods. The results obtained from the analyses indicated that the water was moderately acidic, fresh, and not salty, with many parameters below the recommended standards with Ca2+, and HCO3- being the dominant ions present in the water resources. Rock weathering processes including silicate weathering as illustrated by hydrochemical facies, cross plots, and Gibbs diagrams are the dominant mechanisms influencing the quality and major ions chemistry of the water resources with minor contributions from dissolution, anthropogenic activities, and ion exchange. Ca-Mg-SO4-Cl and Na-K-HCO3- are the most important water types. Although the water quality index shows that the water is suitable for human use and irrigation, the mean values of As, Cd, Pb, and Se are above the acceptable limits. Additionally, the calculated contamination factor revealed the water resources are moderate to highly contaminated by As, Cd, Cr, Mo, Pb, Sb, and Se, and are therefore unsuitable for consumption with regards to these parameters. However, the residual sodium carbonate and water hazard index (WHI) values showed that 38% to 90% of sites in the quarry area were unsuitable for cultivation, 10-30% were in the low to medium impact category, and 60% were classified as risky and are from high to very high impact category. A non-cancer study of inhabitants living in the vicinity of the quarry area indicated that 6.7% of the sites have values greater than one, indicating that it may endanger the health of the people. Therefore, constant monitoring of the water quality is recommended as long-term use of contaminated water can harm humans, plants, and soils.
The South Eastern Desert (SED) of Egypt is one of the most promising areas in Egypt; it is widely explored for exploring the rare earth elements (REEs) and uranium-bearing ores. It is a main part of the Arabian-Nubian Shield (ANS). Therefore, the present study concerns with Sikait-Nugrus area as one of the most prolific sites in this region. The study provides a detailed geological, structural, and mineralogical investigation of the monzogranites to describe and characterize the various alteration types and sequence. For this purpose, remote sensing, geochemical and petrographical techniques were applied. The remote sensing technique helped in constructing a detailed geologic map of the study area to follow up strictly the alteration zone of the Sikait-Nugrus area. Petrographically, the granites predominates in the study area, they are described as slightly and highly altered monzogranites. The slightly altered one is composed mainly of quartz ( 20–35
δMnO2 is an important component of environmental minerals and is among the strongest sorbents and oxidants. The crystalline morphology of δ-MnO2 is one of the key factors affecting its reactivity. In this work, δ-MnO2 was initially synthesized and placed in an acidic environment to react with Mn2+ and undergo a crystalline transformation. During the transformation of crystalline δ-MnO2, kinetic sampling was conducted, followed by analyses of the structures and morphologies of the samples. The results showed that at pH 2.5 and 4, δ-MnO2 nanoflakes spontaneously self-assembled into nanoribbons via edge-to-edge assembly in the initial stage. Subsequently, these nanoribbons attached to each other to form primary nanorods through a face-to-face assembly along the c-axis. These primary nanorods then assembled along the (001) planes and lateral surfaces, achieving further growth and thickening. Since a lower pH is more favorable for the formation of vacancies in δ-MnO2, δ-MnO2 can rapidly adsorb Mn2+ directly onto the vacancies to form tunnel walls. At the same time, the rapid formation of the tunnel walls leads to a quick establishment of hydrogen bonding between adjacent nanoribbons, enabling the assembly of these nanoribbons into primary nanorods. Therefore, in a solution with the same concentration of Mn2+, the structure transformation and morphology evolution of δ-MnO2 to α-MnO2 occur faster at pH 2.5 than at pH 4. These findings provide insights into the mechanism for crystal growth from layer-based to tunnel-based nanorods and methods for efficient and controlled syntheses of nanomaterials.
AbstractThis study aimed to assess the influence of pollution on the quality of sediments and the risks associated with El-Qusier and Safaga Cities, Red Sea, Egypt, during 2021, divided into four sectors, using multiple pollution indices. To achieve that, we evaluated the metal pollution index (MPI), contamination factor (Cf), pollution load index (PLI), contamination security index (CSI), and anthropogenicity (Anp%). Moreover, carcinogenic and non-carcinogenic risks are used for human health hazards. Results indicated that Mn and Fe recorded the highest concentrations, whereas Cd had the lowest. El-Quseir City sediments were found the following metal ions: Fe > Mn > Ni > Zn > Cu > Co > Pb > Cd, where the order in the Safaga City was: Fe > Mn > Zn > Ni > Cu > Pb > Co > Cd. MPI > 1, this is alarming in the study area due to heavy metal pollution. In addition, Cf < 1 in all metals except Cd with contamination degree CD ranged from low to considerable contamination in El-Qusier city. In contrast, contamination ranged from significant to very high in Safaga city. PLI < 1 is lower than the reference at all monitored stations. CSI values ranged from relatively low to moderate. Besides Cd, data reflect each element's low environmental danger (EriMe40). This study's risk index (RI) is low to moderate in Sector 1 and high to extremely high in Sector 2. HQ and HI index < 1 means it is safe for human health in order: HI ingestion > HI dermal. CSR for different pathways was recorded as dermal > ingestion, in which total CSR for all paths is considered harmful, and the cancer risk is troublesome and higher than the reference ranges of 1 × 10–6–1 × 10–4. In conclusion, the examined heavy metals provide environmental hazards across the assessed locations.
Thioamide bonds are important intermediates in prebiotic chemistry. In cyanosulfidic prebiotic chemistry, they serve as crucial intermediates in the pathways that lead to the formation of many important biomolecules (e.g., amino acids). They can also serve as purine and pyrimidine precursors, the two classes of heterocycle employed in genetic molecules. Despite their importance, the formation of thioamide bonds from nitriles under prebiotic conditions has required large excesses of sulfide or compounds with unknown prebiotic sources. Here, we describe the thiol-catalyzed formation of thioamide bonds from nitriles. We show that the formation of the simplest of these compounds, thioformamide, forms readily in spark-discharge experiments from hydrogen cyanide, sulfide, and a methanethiol catalyst, suggesting potential accumulation on early Earth. Lastly, we demonstrate that thioformamide has a Gibbs energy of hydrolysis ( Δ G^∘_r ) comparable to other energy-currencies on early Earth such as pyrophosphate and thioester bonds. Overall, our findings imply that thioamides might have been abundant on early Earth and served a variety of functions during chemical evolution.
AbstractToday, carbon dioxide removal from the atmosphere is the most ambitious challenge to mitigate climate changes. Basalt rocks are abundant on the Earth’s surface (≈ 10%) and very abundant in the ocean floors and subaerial environments. Glassy matrix and minerals constituting these rocks contain metals (Ca2+, Mg2+, Fe2+) that can react with carbonic acid to form metal carbonates (CaCO3, MgO3 and FeCO3). Here, we present a data compilation of the chemical composition of waters circulating in basalt aquifers worldwide and the results of simple basalt-water-CO2 experiments. Induced or naturally occurring weathering of basalts rocks release elements in waters and elemental concentration is closely dependent on water CO2 concentration (and hence on water pH). We also performed two series of experiments where basaltic rock powder interacts with CO2-charged waters for one month at room temperature. Laboratory experiments evidenced that in the first stages of water-rock interaction, the high content of CO2 dissolved in water accelerates the basalt weathering process, releasing in the water not only elements that can form carbonate minerals but also other elements, which depending on their concentration can be essential or toxic for life. Relative mobility of elements such as Fe and Al, together with rare earth elements, increases at low pH conditions, while it decreases notably at neutral pH conditions. The comparison between experimental findings and natural evidence allowed to better understand the geochemical processes in basaltic aquifers hosted in active and inactive volcanic systems and to discuss these findings in light of the potential environmental impact of CO2 storage in mafic and ultramafic rocks.
