Geochemical Behavior Research Articles

Chromium, tungsten and vanadium sediment-porewater geochemistry under oxic and anoxic redox conditions: Implication for their remobilization.

Global chromium (Cr), tungsten (W), and vanadium (V) cycles are emerging concerns due to their toxicities to ecosystems. However, a comprehensive understanding of their geochemical reactions and controls at the sediment-water interface remains largely unknown. This knowledge gap hinders the assessment of their potential remobilization in Earth's surface environments threatened by hypoxic conditions. We collected pore water and sediment samples from the undisturbed Castle Lake, situated in the Klamath-Siskiyou Mountains of northern California, USA, to investigate the geochemical controls responsible for the fixation and release of Cr, W, and V under redox transitions from oxia to anoxia during early diagenesis. The results show that, under oxic conditions, authigenic Cr, W, and V ratios in porewater account for approximately 4.7%, <0.1%, and<0.1%, respectively, whereas their ratios display around ten times increase under anoxic conditions with average values of 62.4% for Cr, 4.1% for W, and 1.1% for V. Our combined thermodynamic calculation and diagenetic analyses show that the sequestration and release of Cr, W, and V are intimately associated with Fe cycle under anoxic conditions. In contrast, under oxygenated conditions, only Cr and V geochemical behaviors are significantly affected by Fe cycle, while the adsorption of W to Fe minerals is probably inhibited by dissolved organic matter. Furthermore, we suggest that the Cr, W, and V pollution could become significant in coastal and inland water areas where redox conditions oscillate between oxia and anoxia, with intensified water deoxygenation, acidity, and eutrophication.

Enhancing the affinity of Pb(II) to the metastable ferrihydrite with the presence of gallic acid and anoxia condition.

Naturally widespread ferrihydrite is unstable and often coexists with complex ions, such as the heavy metal ion Pb(II). Ferrihydrite could fix Pb(II) by precipitation and hydroxyl adsorption, but release Pb(II) with mineral aging. Gallic acid plays an important role in influencing the geochemical behavior of ferrihydrite-Pb, and anoxia is one of the factors influencing the transformation of mineral. This study investigated the effects of Gallic acid and anoxia on the migration and distribution of Pb(II) in ferrihydrite-Pb co-precipitates. XRD, FT-IR, SEM, XPS were employed to explore the internal interactions. The results showed that Gallic acid could promote Pb(II) to enter the mineral and inhibit the release of Pb(II). The fixation of Pb(II) could be achieved under anoxia by passivating ferrihydrite. Gallic acid could formed ferrihydrite-gallic acid-Pb ternary complexes with ferrihydrite-Pb co-precipitates, which improved the affinity of ferrihydrite to Pb(II) and promoted the ability of ferrihydrite to fix Pb(II). The anoxia allowed the Fe(II) produced by reductive dissolution of ferrihydrite to be retained for longer time, thus catalyzed the production of goethite from ferrihydrite and passivating ferrihydrite to inhibit the aging of ferrihydrite. In addition, acid environments caused most of Pb(II) to be released into solution through competition with hydrogen ions. Pb(II) in alkaline environment led to Pb(II) immobilization by entering the interior of mineral. The findings of this study provide references for better understanding the environmental behavior of Pb(II) during ferrihydrite transformation.

Management of Acid Rock Drainage Based on Geochemical Characterisation of Waste Rock Material, Study Case: Gold Mining With High Sulfidation Ephithermal (HS) Deposits

Acid rock drainage (ARD) or Acid mine drainage (AMD) is significant challenge for the global gold mining industry, necessitating specialized treatment to prevent its occurrence. Rambajoring is deposits located at the North Sumatra Martabe gold mine, the mine is an epithermal deposit of a high sulfidation system. A crucial step in management of AMD is identifying rocks that potentially produced acid water or not if contact with water and oxygen. Static testing provides an indication of the potential acidity that can be generated by rock samples based on their composition. These rocks are classified into Potentially Acid Forming (PAF) or Non-Acid Forming (NAF). Laboratory analyses including Acid Base Accounting (ABA), Net Acid Generating (NAG) Test, and paste pH, identified all lithology with uncertain category. This uncertainty occurs impact of presence of significant non-pyritic or non-acid forming sulfide sulphur mineral in this case of Alunite (KAl3SO2OH6) minerals. Containing these minerals will result in erroneously high estimations of total sulphur (S) and increasing the calculated of NAPP. Long term implication non-pyritic sulfide may oxidize slowly, leading to delayed acid generation not reflected in static NAPP calculation. Supplementary test to validation static test result and analysis geochemical behaviour of rocks using kinetic testing with Field Column Leach Test (FCLT) method. FDCLT test confirm in eight months period monitoring, all lithology have a lag time before significant acidity is produced and classified as PAF rocks. The leaching properties of material had highest concentrations of iron (Fe), cooper (Cu) and zinc (Zn). Keyword : AMD, ABA, Geochemical Characteristics, NAF, PAF, Kinetic Test, Static Test

Comprehensive Assessment of Environmental Behavior of Mine Tailings for Sustainable Waste Management and Mitigation of Pollution Risks

The substantial volumes of tailings produced during ore beneficiation present significant challenges for sustainable management due to potential public health hazards, particularly from metal leaching. The risk associated with tailings varies greatly depending on their mineralogical composition and climatic conditions. If tailings are classified as a non-hazardous by-product, they may serve as secondary raw materials, offering a sustainable alternative to the reliance on non-renewable primary resources. In this study, the recycling feasibility of tailings from an active copper mine was assessed through mineralogical characterization, environmental tests (e.g., static, kinetic, and leaching tests), and geochemical modeling. This multi-faceted approach aimed to predict the geochemical behavior and reactivity of tailings under varying conditions. Results from the static tests indicated that the tailings were non-acid generating. Weathering cell tests revealed circumneutral pH conditions (6.5–7.8), low sulfide oxidation rates, and low instantaneous metal concentrations (&lt;1 mg/L), except for copper (0.6–3.5 mg/L) and iron (0.4–1.4 mg/L). These conditions are attributed to the low abundance of sulfide minerals, such as pyrite, chalcopyrite, bornite, covellite (&lt;0.1 wt.%), and chalcocite (0.2 wt.%), which are effectively encapsulated within gangue minerals. Additionally, the presence of neutralizing minerals, specifically dolomite (27.4 wt.%) and calcite (2.4 wt.%), further stabilizes pH and promotes metal sequestration in secondary mineral forms. The Toxicity Characteristic Leaching Procedure (TCLP) test confirmed low leachability, classifying the tailings as non-hazardous.

Effects of dimethylarsenate coprecipitation with ferrihydrite on Fe(II)-induced mineral transformation and the release of dimethylarsenate.

Organoarsenicals are toxic pollutants of global concern, and their environmental geochemical behavior might be greatly controlled by iron (Fe) (hydr)oxides through coprecipitation, which is rarely investigated. Here, the effects of the incorporation of dimethylarsenate (DMAs(V)), a typical organoarsenical, into the ferrihydrite (Fh) structure on the mineral physicochemical properties and Fe(II)-induced phase transformation of DMAs(V)-Fh coprecipitates with As/Fe molar ratios up to 0.0876±0.0036 under anoxic conditions and the accompanying DMAs(V) release were investigated. The presence of DMAs(V) during Fh formation gradually decreases the mineral crystallinity. With increasing DMAs(V) content, the specific surface areas of the coprecipitates are decreased owing to particle aggregation, while the micropore sizes are negligible changed. Fourier transformed infrared (FTIR) and As K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy show that, part of DMAs(V) binds to Fh surfaces in the coprecipitates by forming bidentate binuclear inner-sphere complexes through As-O-Fe bonds. During the reaction of the coprecipitate with 1 mM Fe(II) for 336 h, DMAs(V) inhibits the Fh transformation to goethite. No goethite forms at pH 4; at pH 7 low content of DMAs(V) hinders the further conversion of lepidocrocite to goethite, while high content of DMAs(V) completely inhibits goethite formation. DMAs(V) in the coprecipitate is continuously released into the solution, with the released proportion being generally increased with the increase of DMAs(V) content, pH and Fe(II) addition, probably owing to the desorption of weak inner- and outer-sphere DMAs(V) complexes bound on the Fh surfaces upon the Fh aging and transformation to lepidocrocite and goethite. These results provide deep insights into the fate and mobility of organoarsenical pollutants mediated by Fe (hydr)oxides in natural environments, and help design effective and ecofriendly remediation strategies for As polluted soils and sediments.

Investigating the Element Geochemical Behavior and Provenance of Surface Sediments in the Offshore Area of Sierra Leone, Africa: Insights from Major and Trace Elements

The element geochemical behavior and provenance of marine sediments are of significance to understanding the oceanic material cycle. Here, we tested the grain size and major and trace elements of 35 surface sediments in the offshore area of Sierra Leone, analyzed the content characteristics and controlling factors of the elements, discussed the material source of the sediments, and made a comparative study with the sediments in the offshore area of China. The results show that sandy silt is the main sediment type in the research area, and the average sediment mean grain size (Mz) is 4.15Φ. The content of Ca in the samples is the highest among the major elements (except Si), with an average of 5.1%. The content of Sr is the highest among the trace elements (except Ti, P, and Mn), with an average of 378.2 μg/g. The results of correlation analysis and factor analysis show that there are three main sources of sediments in the research area, namely, terrigenous weathering products, ilmenite-dominated ore, and oceanic biochemical substances. Compared with the sediments in China offshore, the sediments in the study area are more affected by marine biochemistry and have special ore input characteristics.

Plants colonization accelerates galena oxidation, mineralogical transformation, and microbial community reshaping under the soil phytoremediation processes.

The ongoing weathering of metal sulfides has substantially posed threats to the eco-systems. For remediating metal sulfides-contaminated soils, phytostabilization is a promising nature-based technique that immobilizing heavy metals (HMs) that dissolved from metal sulfides in the rhizosphere, preventing their leaching and migrating into soil and groundwater. However, the underlying mechanism regarding the mineral-root interaction involving primary metal sulfides such as galena (PbS) during the remediation processes has yet been well studied. This study aims to investigate the geochemical alterations, mineralogical transformations, and microbial community reshaping of galena-added soils during plants colonization using two representative plants, ryegrass (Lolium perenne L.) and alfalfa (Medicago sativa.). After 11 weeks of plants colonization, the morphology of galena surface was altered, as massive erosion pits (ca. 200 nm) were visualized by SEM (Scanning Electron Microscope). The microspectroscopic analyses indicated that the PbS may have transformed to PbCO3 and PbSO4 during the plants colonization. Additionally, the chemical sequential extraction revealed that the plants colonization could promote the soluble Pb to be associated with carbonates and amorphous Fe/Al (oxyhydr)oxides, thus limiting their bioavailability and mobility. Moreover, the key driving factors of microbial community alteration have shifted from pH and bioavailability Pb to cation exchange capacity (CEC) during the plants colonization process. These findings have uncovered the (bio)geochemical behaviors of PbS in soils during the phytostabilization processes, which may develop an integrated mechanism of mineralogical and geochemical stabilization of HMs for non-pollution outcomes.

Mineralogical and geochemical characteristics of barium slag and ecological risks associated with heavy metals

Barium slag (BS) is a typical chemical hazardous waste, and its ecological risks cannot be ignored. Herein, the chemical composition, mineral composition and morphological characteristics of BS were investigated. In addition, the geochemical behaviour was investigated in terms of heavy-metal-leaching toxicity as well as the bioavailability, bioaccessibility and migration of these metals. The ecological risks associated with the release of heavy metals from BS driven by its geochemical behaviour were also evaluated. The BS displayed irregular particle morphologies and distinct surface structures, with heavy metal ions predominantly present in the smaller-sized BS particles. Zn, Ni, Mn and Ba exhibited a stronger potential for migration in plants than other heavy metals. This migration potential was influenced by their total amount and occurrence form as well as the pH conditions of the surrounding environment. The findings indicated that crops should not be planted around BS yards. The bioaccessible risks associated with heavy metals in BS were low. Mn, Ba, Fe and Ni primarily existed in the form of a weak-acid soluble fraction, thereby posing a high migration risk. Thus, attention should be paid to the ecological risks that may arise from Mn, Ba, Fe and Ni during storage.

Role of As in the formation of giant Au deposits: Insights from sulfur isotope and geochemistry of pyrite from the Shuangwang Au deposit, West Qinling, central China

The Shuangwang Au deposit (SWGD), located in the Feng-Tai ore district, is one of the largest Au deposits in the West Qinling orogen, central China. Au orebodies in this deposit are mainly hosted in the Upper Devonian Xinghongpu Formation. The source of the fluids and metals, ore-forming processes and the enrichment mechanism of Au in this ore deposit remain equivocal. Here we present results from geochemical studies of pyrite from the SWGD to address these issues through the application of Scanning electron microscopy (SEM), electron probe microanalysis (EPMA), in-situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and LA-MC-ICP-MS analyses. Based on detailed petrographic studies of the mineralization and host rocks, we identify seven generations of pyrite. Among these, the pre-ore syn-sedimentary pyrite (Py0) is characterized by relatively elevated concentrations of As, Co, Ni and Au compared to the Py1 in the albite-ankerite veins and Py2 in the quartz-ankerite-pyrite veins, and has positive δ34S values of + 6.00 to + 10.48 ‰, whereas Py3 forms as veinlets or aggregates in the pyrite-tourmaline veins and is enriched in As, Co, Cu, Se and Au. Py4 occur as coarse-grained subhedral to euhedral crystals or aggregates in the ankerite-pyrite veins and exhibit oscillatory zones. Py5 comprises fined-grained subhedral to anhedral grains in the fluorite-ankerite-pyrite cements, and is relatively depleted in trace elements when compared to the other pyrite types. The δ34S values of the different types of pyrite from the SWGD have significant differences, indicating a multiple and mixed source for sulfur and, by inference, for the ore-forming fluid(s). Two periods of Au mineralization are identified in the SWGD: the early NW-trending mineralization sourced from the metamorphism of the metasedimentary sequences in a compressional environment and the late NE-trending mineralization probably exsolved from an unexposed and coeval granitoid pluton at depths in a post-collisional extensional setting. The coupled geochemical behavior of Au and As can be explained by mixing-induced cooling. Our results also indicate that arsenic might have played an important role in the enrichment of Au and the formation of this hydrothermal Au deposit.

Geochemical behaviour of biotite during interaction with aqueous and brine fluids: Constraints from hydrothermal batch experiments

Biotite plays an important role in the geochemical cycle of Li, Rb, Cs, and Ba in the upper continental crust, as it is a significant carrier of Li and large-ion lithophile elements in felsic igneous rocks and high-grade detrital metasedimentary rocks. During its interaction with meteoric and hydrothermal fluids, biotite can be transformed into various types of clay minerals (mostly, interlayer-deficient biotite, vermiculites and smectites). These transformations can cause fractionation of the alkaline trace-element ratios Rb/Li, Cs/Li and Rb/Cs between biotite and its replacement products. This study examines the mineral transformations that occur when biotite interacts with aqueous and saline fluids and the poorly understood geochemical behaviour of the resulting phyllosilicates. For this purpose, we performed batch hydrothermal experiments of the interaction of biotite + quartz ± graphite with ultrapure H2O, and 2 M NaCl, 2 M CaCl2 and 1 M NaF brine fluids at 170 °C and 10 bar using Teflon bombs, and at 550 °C and 800 to 1400 bar using autoclave apparatus. At lower-T conditions, biotite was replaced by 2:1 trioctahedral clay minerals (interlayer-deficient biotite, smectite, vermiculite, and other phyllosilicate species with higher interlayer charge) and Fe oxy-hydroxide minerals by coupled dissolution-precipitation mechanisms. At higher-T conditions, these mechanisms caused the transformation of biotite into the mineral assemblages (quartz ± graphite): diopside + anorthite + titanite (CaCl2 brine experiments), albite + ilmenite + clay minerals (NaCl brine experiments), and cryolite + alkali feldspar with albite rimmed by K-feldspar + Fe-oxides (NaF brine experiments). Therefore, a significant reduction of the clay mineral stability in the presence of NaF and CaCl2 brine fluids is inferred. The biotite replacements by phyllosilicates were mostly controlled by the ion exchange of K+ by H+ (or its hydrate state H3O+), hydrated Na+ and Ca2+, and NaF in the interlayer site. Conservation of the total mass and the Si, Al and Mg abundances occurred in most experimental phyllosilicates. However, in the products of the low-T NaF brine ± graphite experiments, the total mass may have a gain of 5.3–11 % assuming Mg conservation. Sc, V, Nb and Ta abundances were also conserved, but a significant fractionation of the Rb/Li, Cs/Li, and Ba/Li ratios occurred in the experimental phyllosilicates. The experiments predict the generation of highly fractionated Rb/Li and Cs/Li phyllosilicates by replacement of biotite during interaction with aqueous fluids and, mostly, NaCl and NaF brine fluids at high-T and low-T conditions, respectively. This demonstrates a key role of biotite in the fractionation of Rb/Li, Cs/Li and Rb/Cs during the hydrothermal alteration of felsic igneous rocks. Conversely, a reversal in the mobility of Li with respect to Rb and Cs occurred in the phyllosilicate products when biotite interacted with NaCl or CaCl2 brine fluids at relatively low-T conditions. These experimental results highlight the key role of biotite-fluid interaction processes in controlling the budget of alkaline trace elements in the continental crust.

The Effect of Salinity on the Dielectric Permittivity of Nanoconfined Geofluids.

Nanoporosity is a characteristic feature of geological formations that provides potential pathways for geofluids to meander and interact with minerals. Confinement of water within nanopores leads to unique phenomena. The dielectric constant of water becomes anisotropic and adopts tensorial properties rather than remaining a scalar value. In such nanoconfinement, it has been found that the permittivity of water decreases perpendicularly and increases parallel to the interface. As geofluids are rarely pure water in nature, being a water-salt(-gas) mixture within the Earth, it becomes pivotal to examine how these additional constituents of water affect the permittivity of fluids confined within the nanopores of rocks. In this study, we present the calculation of the permittivity of saline water in calcite slit nanopores using molecular dynamics simulations under low-pressure-temperature conditions. The dielectric properties are weakly dependent on salinity for both the perpendicular and parallel dielectric permittivity components. We analyzed the atomic charge and polarization density of the fluid perpendicular to the nanochannel walls and the orientation of water molecules' dipole inside the nanochannel. From our analysis, most of these factors were generally not altered significantly in the presence of salinity. These findings are significant because they enable us to use well-studied pure water properties under nanoconfinement to determine the geochemical behavior of fluids within natural nanoporous systems.

K, Sr isotopes, and trace element to constrain potash origin in the Simao Basin, southwestern China, and insight into K isotope geochemical behavior in evaporite

With the advancement of emerging potassium isotope testing techniques, the characteristics of δ41K in evaporite have garnered increasing attention. Its application in constraining the genesis of potash deposits and tracing the process of potash mineralization holds significant prospects. A comprehensive analysis of the geochemical characteristics of K, Sr isotopes, and trace elements provides an opportunity to address the ongoing debate regarding the mineralization mechanism of potash in the Simao Basin. In this study, we collected 64 potash samples from the Simao and Khorat basins. The analytical results revealed that the major ions in the samples consist of Na+, K+, Mg2+, Ca2+, Cl−, and SO42-, while the trace elements Br, Sr, Rb, B, Li, V, Cr, Mn, Ba, As, and Zn are relatively enriched. The δ41K values range from −0.12 ‰ to 0.20 ‰ with an average of 0.01 ‰. The 87Sr/86Sr ratios range from 0.707553 to 0.708565 with an average of 0.708020, which is lower than that of the river water in the drainage basin. Additionally, the Br content ranges from 316.3 × 10−6 to 1709.1 × 10−6, with an average of 633.8 × 10−6. These data indicate that the Early Cretaceous Albian-Middle Jurassic Bajocian seawater serves as an important source of potassium for potash deposition in the Simao Basin. The characteristics of the ratios of the Br/Cl (mmol/mol), K/Cl (mmol/mol), Rb/Sr (mol/mol), along with the contents of the Br and Rb, indicate that the most of potash in the Simao Basin is primary origin. Moreover, we have also provided new insight into the geochemical behaviors of K isotopes during the evolution of the evaporites. The precipitation of potash may be accompanied by K isotope fractionation, as evidenced by the lighter K isotope composition of carnallite compared to that of sylvinite. K isotope fractionation occurs between the secondary sylvite and its parent source, and newly precipitated solids are characterized by relatively light K isotope. Episodic freshwater inflow into the evaporative basin stimulates microbial activity, leading to fluctuations in K isotopes in the precipitated potash during the same evaporation stage. Therefore, this work not only provided direct evidence from the K isotopes for determining the origin of the potash in the Simao Basin but also further perceived the geochemical behaviors of K isotopes during the evolution of evaporite.

GEMAS: Boron as a geochemical proxy for weathering of European agricultural soil

About a century ago, B was recognised as an essential element for the normal growth of plants and terrestrial organisms. Limitations for plant development have been recognised in agricultural systems, particularly in highly weathered soil. Boron is rarely analysed in whole rock or soil analysis, as it requires specific analytical techniques. It is often determined, after partial extraction (aqua regia or CaCl), usually on a limited number of samples. Many more questions than answers exist about the environmental behaviour of B.We present B contents in agricultural soil samples (0–10 cm) collected in 33 European countries (5.6 million km2) during the GEMAS (GEochemical Mapping of Agricultural and grazing land Soil) continental-scale project. The B content, determined by ICP-MS following hot aqua regia extraction, varies in European agricultural soil from 0.5 to 49 mg/kg (median 2.42 mg/kg, n = 2108), which is somewhat similar to total B estimates for the Upper Continental Crust (17–47 mg/kg). Its spatial distribution in agricultural soil shows a patchy pattern with low values in regions with granitic bedrock and high contents in soil formed over limestone and in volcanic areas.Boron geochemical behaviour in soil is strongly dependent on other factors such as pH, CEC, presence of organic matter, clay and secondary oxides and hydroxides. Boron geochemical mapping at the continental scale in arable soil allows investigations of plant health, i.e., the beneficial and adverse effects due to the nutritional status of boron.

Enhanced enrichment of rare earth elements during pedogenesis under subtropical climate

Rare earth elements (REEs) are crucial strategic resources, and weathering-crust rare earth deposits are one of the primary sources. To systematically understand the geochemical behaviour (e.g. enrichment and leaching) of REEs in soils (or weathering crusts) formed from diverse parent rocks under varying climatic conditions, 171 soil profiles (weathering crusts) developed from three main types of parent rocks (granite, basalt and carbonate rock) worldwide were studied. Granite shows the highest concentration of REEs at 264 [interquartile range (IQR): 278] ppm with 171 (IQR: 151) ppm and 11.9 (IQR: 36.4) ppm in basalt and carbonate rock, respectively (median test: p &lt; 0.05). The median REE values within the soil profiles were significantly different (median test: p &lt; 0.05), with the concentration of 318 (IQR: 441) ppm, 267 (IQR: 217) ppm and 207 (IQR: 417) ppm in soils derived from granite, carbonate rock and basalt, respectively. Principal component analysis and linear mixed-effects models revealed that soils developed from granite and basalt inherit the mineral characteristics of their parent rocks, with REE concentrations primarily influenced by the REE content of the parent rock and climate. In contrast, the REE concentrations in soils developed from carbonate rocks are predominantly controlled by climate. Linear mixed-effects models and correlation analysis indicate that the enrichment of REEs ( Q REE ) shows a trend of initially increasing and then decreasing with rising temperature and precipitation, due to variations in the host clay minerals. The greatest enrichment occurs in the subtropical region (mean annual temperature = 15–23°C; mean annual precipitation = 1000–2000 mm); weathering-crust type REE deposits are primarily found in the subtropics.

Geochemical behavior of riverine magnesium isotopes in the Yarlung Tsangpo River Basin, southern Tibetan Plateau

The riverine magnesium (Mg) isotope composition is generally controlled by sources and fractionation processes. However, it remains unclear in which cases these factors are predominant at the basin scale. In this study, we investigated the major elements, trace elements, and Mg and strontium (Sr) isotope ratios in the Yarlung Tsangpo River (YTR) Basin, southern Tibetan Plateau (TP), to explore the geochemical behavior of Mg isotopes and the dominant controlling factors. Riverine Mg2+ was shown to derive primarily from the weathering of silicates and carbonates. Riverine δ26Mg, which is first influenced by the mixing of different lithological sources, was detected ranging from −1.63 ‰ to −0.52 ‰. According to the saturation indexes of common Mg-bearing secondary minerals, the basin was divided into two zones. Above Shannan City (Zone I), where river waters mostly were oversaturated with minerals, positive correlations were observed between δ26Mg and the Ca/Mg and Sr/Mg ratios. This indicated that, after mixing, secondary minerals (talc and chlorite), which tend to preferentially incorporate 24Mg, may be formed in most of waters, leading to an increase in riverine δ26Mg values. The Rayleigh and batch fractionation models were fitted with factors ranging from 0.9975 to 0.9997. Below Shannan City (Zone II), where river waters mostly were unsaturated with minerals, riverine δ26Mg was positively correlated with 87Sr/86Sr and negatively correlated with the Ca/Mg, Sr/Mg, and HCO3/Na ratios. This suggested that the riverine δ26Mg were influenced by carbonate dissolution with faster kinetic rates. Our analysis of riverine δ26Mg values in the YTR Basin may be a reference for interpreting the relationships between δ26Mg and δ7Li in river systems worldwide. In minerals-oversaturated waters, secondary mineral formation was shown to lead to isotope fractionation, resulting in a positive correlation between the two parameters, whereas in minerals-unsaturated waters, the δ26Mg and δ7Li values were negatively correlated, possibly due to the predominance of mineral dissolution.

The interaction between organic acids and green rust-Co(II): Mineralogical changes of green rust and redistribution of Co(II)

Green rust (GR), as a vital intermediate product during the formation of various iron oxides, exists with organic matters and metals contaminants in natural environments. Understanding the effects of these natural factors on the transformation process of GR into iron oxides and the environmental behaviors of heavy metals and organic matters during process are critical for environmental quality management, but the fundamental identification of the interaction mechanisms between them and GR is still challenging. In this study, the transformation mechanisms of Co-bearing green rust (GR-Co) synthesized by co-precipitation, and the redistribution behaviors of Co(II) in an environment containing oxalic acid (OA) and citric acid (CA) were clarified. The findings indicated that OA promoted the Fe(II) dissolution and the transformation of GR-Co to goethite, while CA decreased the Fe(II) dissolution and the proportion of non-extractable Co. Furthermore, in the presence of CA, the transformation products of GR-Co were ferrihydrite, magnetite, lepidocrocite and goethite instead of only lepidocrocite and goethite. Meanwhile, CA prohibited ferrihydrite from transforming into more highly crystalline iron minerals. The finding of this study improves the understanding of the interaction mechanisms between GR-Co and organic matter, and the environmental geochemical behaviors of Co and organic carbon during the transformation processes in nature.

Physico-thermal and geochemical behavior and alteration of the Au indicator gangue hydrothermal quartz at the Kubi Gold ore deposits

Altered and gangue quartz in hydrothermal veins from the Kubi Gold deposit in Dunkwa on Offin in the central region of Ghana are investigated for possible Au-associated indicator minerals and to provide the understanding and increase the knowledge of the mineral hosting and alteration processes in quartz. X-ray diffraction, air annealing furnace, differential scanning calorimetry, energy dispersive X-ray spectroscopy, and transmission electron microscopy have been applied on different quartz types outcropping from surface and bedrocks at the Kubi Gold Mining to reveal the material properties at different temperatures. From the diffraction results of the fresh and annealed quartz samples, we find that the samples contain indicator and the impurity minerals iron disulfide, biotite, titanium oxide, and magnetite. These minerals, under oxidation process between 574 and 1400 °C temperatures experienced hematite alterations and a transformation from α-quartz to β-quartz and further to cristobalite as observed from the calorimetry scans for hydrothermally exposed materials. The energy dispersive spectroscopy revealed elemental components of Fe, S, Mg, K, Al, Ti, Na, Si, O, and Ca contained in the samples, and these are attributed to the impurity phase minerals observed in the diffraction. The findings also suggest that during the hydrothermal flow regime, impurity minerals and metals can be trapped by voids and faults. Under favorable temperature conditions, the trapped minerals can be altered to change color at different depositional stages by oxidation and reduction processes leading to hematite alteration which is a useful indicator minerals in mineral exploration.

Nanomineralogy of thorite in the supergiant Huayangchuan uranium ore deposit: Revealing a new geochemical behavior of actinide in environment

Thorium (Th) is a naturally occurring radioactive element found in the environment, and recent advancements have been made in identifying and characterizing Th-bearing nanoparticles (NPs). However, the main focus is still on synthesized Th-bearing NPs and knowledge about natural Th-bearing NPs remains limited. Here, high-resolution transmission electron microscopy (HRTEM) observations of thorite from the Huayangchuan uranium ore deposit in Shaanxi Province, Central China, have revealed the nanoscale mineral characteristics of thorite. In this study, thorite NPs ranging from 5–10 nm in size were identified within the uranium ore. A combination of transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) elemental mapping and corresponding HRTEM images alongside Selected Area Electron Diffraction (SAED) and Fast Fourier Transform (FFT) patterns revealed a complex nanoscale structure in the thorite NPs, consisting of both amorphous and crystalline nanodomains with abundant defects. These nanostructures are associated with a metamictization mechanism in micrometer-sized thorite. Our findings indicate that the metamictization process can generate numerous thorite nanoparticles. Given the high penetrability and mobility of these NPs, the metamictization of thorite poses new challenges for the long-term stability of radioactive substances and the storage containers for radioactive waste. Furthermore, considering the likelihood of environmental release and the chemical toxicity, radioactivity, and nanotoxicity of natural Th-bearing NPs, increased attention should be given to the presence of natural thorite NPs in the ore deposit.

Synergistic release of Cd(II) and As(V) from ternary sorption systems containing ferrihydrite nanoparticles: The role of binary and ternary surface complexes

Cadmium (Cd) and arsenic (As) generally exhibit mutually beneficial co-sorption behavior on iron oxyhydroxides through multiple mechanisms, including surface precipitation, ternary surface complexes, and electrostatic interactions. However, the numerous factors that control the immobilization of Cd and As in turn complicated the processes and mechanisms involved in their co-desorption from iron minerals, which hindered the full understanding of their geochemical behaviors. Here, the simultaneous release of Cd(II) and As(V) from newly precipitated ferrihydrite nanoparticles by either Ca or P was investigated through kinetics and isothermal desorption experiments. We showed that the Cd(II) and As(V) present two-phase desorption processes (rapid desorption and slow desorption) in both binary (Fe–Cd or Fe–As alone) and ternary systems (Fe–Cd–As co-presence). Compared to their binary counterparts, Cd(II) and As(V) in the ternary systems are more prone to detachment from ferrihydrite. Further desorption of Cd(II) and As(V) at different co-presence scenarios (different initial concentrations) demonstrated mutual promotion behaviour towards their counterparts; the co-presence of Cd(II) facilitates the desorption of As(V), while the co-presence of As(V) also promotes the desorption of Cd(II). XPS and FTIR results demonstrated that either Ca or P showed minor effects on the binding environment of Cd and As. Further results from the in-situ ATR-FTIR experiment and second derivative peak fitting analysis indicate that the enhanced detachment of Cd(II) and As(V) from the ternary system may be due to the synergistic desorption of the ternary surface complexes and other surface complex species. Our results provide new insights into the prediction of the environmental behaviour of the coexistence of Cd(II) and As(V) in iron-rich geological settings. The potential environmental risks of iron-based remediation methods should be considered due to the enhanced bioavailability of Cd(II) and As(V) in co-presence circumstances.

Geochemical Constraints on Arsenic and Rare Earth Elements in Groundwater of Ganges Delta, Nadia District, West Bengal

ABSTRACT Geochemical studies of groundwater from 302 tubewells and aquifer sediments of the Ganges delta plain of Quaternary age are conducted. The geochemical behaviour of Fe, Mn, SO42-, arsenic (As), REEs, and Eu parameters in groundwater indicates two contrasting environments: (i) a more oxic condition in the fluvial environment of the Jalangi River in the northern part, and (ii) a less oxidizing/reducing environment in the palaeo-lacustrine environment towards south of the study area. Arsenic concentration in groundwater is more in palaeo-lacustrine environment due to (i) reductive desorption from Fe-oxyhydroxide in the high pH reducing environment and (ii) mobilization by ion exchange with the help of fertilizer used in agricultural activities. Both these phenomena are attributed to the strong spatial correlation of arsenic (As) with pH, PO4, and SO4. However, the dissimilar nature of REE pattern in groundwater and aquifer sediment indicates that REE geochemistry of groundwater is being modified by the “reductive dissolution of Fe-oxyhydroxides” in sediment which releases REE into the groundwater. We conclude that desorption and “reductive dissolution of Fe-oxyhydroxide” controls release of As and REE into the groundwater in both oxic and reducing aquifer conditions in the Ganges delta.