Proportions Of As Research Articles

Sulphidogenic Bioprocesses for Acid Mine Water Treatment and Selective Recovery of Arsenic and Metals.

Human communities need water and mineral resources, the supply of which requires the implementation of recycling and saving strategies. Both closed and active mining sites could beneficiate of the implementation of nature-based solutions, including bioreactors involving sulphate-reducing prokaryotes (SRP), in order to separate and recover arsenic (As) and metals from aqueous stream while producing clean water. Selective precipitation strategies can be designed based on the selection of microbial communities adapted to the pH conditions, generally acidic, and to available low-cost electron donors. Laboratory batch and continuous experiments must be implemented for each type of mine water in order to determine the optimal flow-sheet in which As could be precipitated as sulphides (orpiment or realgar), inside the bioreactor or offline, through stripping of biologically produced hydrogen sulphides (H2S). The respective concentrations and proportions of As and metals and the initial acid mine drainage pH are key parameters that will influence the feasibility of efficient selective precipitation. SRP-based bioreactors could be combined with complementary treatment steps in optimised mine water management solutions that will minimise the production of As-contaminated end-solid waste.

Determination of heavy metal contamination and pollution indices of atmospheric dust in Dushanbe and Ayvaj, Tajikistan

In this paper was studied the content of heavy metals in atmospheric dust of Dushanbe and Ayvaj. Dust samples were taken and analyzed to determine the content of heavy metals (HM): Zn, Pb, Cu, Cr, V, Ni, Co, As, Sr, MnO, TiO2 and Fe2O3 using X-ray fluorescence spectrometry. The pollution levels and environmental risks of HMs were assessed using the geoaccumulation index, contamination factor, pollution load index and potential ecological risk index. The results revealed severe contamination of atmospheric dust from Ayvaj and Dushanbe with particularly hazardous HMs such as As and Pb, the proportion of As is higher in the dust of Dushanbe, and the contribution of Pb is significant in the samples of Ayvaj. The concentrations of As, Pb, Zn, MnO, Sr, TiO2, V, Co in the dust of Dushanbe and As, Pb, Zn, Sr, TiO2, Cu in the dust of Ayvaj showed high variability (CV> 35%), which indicates an intense influence of anthropogenic activity. The results of the pollution factor analysis show that As, Co, V in Ayvaj atmospheric dust samples and Pb, Cr, Ni, V, MnO in Dushanbe samples were assigned to the class of very high pollution (CF>3). According to the results of the geoaccumulation index Ayvaj is heavily polluted with the following elements: V, Pb, Cr (3< Igeo ≤4). Based on the ecological risk index method, As and Pb were found to be priority pollutants in the study areas.

Simultaneous determination and distribution analysis of eleven arsenic species in vegetables

A highly sensitive and efficient method for simultaneous determination of arsenic species in vegetables has been developed. Eleven arsenic species were separated and detected using high performance ion exchange chromatography-inductively coupled plasma mass spectrometry (HPIEC-ICP-MS). The extraction efficiency and transformation of arsenic species in vegetables was investigated using five extraction methods and eight solvents. An online background removal technique was firstly established to exclude the influence of environmental arsenic. The gradient elution conditions were optimized and the optimal collision gas velocity for mass spectrometry was determined to be 4 mL min−1 to remove interference by 75ArCl. The detection limits for the method were 0.032–0.12 μg kg−1, and the quantitative limits of the method were 0.10–0.39 μg kg−1. In order to confirm the accuracy and practicability of the method, two food matrix-type certified reference materials were analyzed. The types and concentrations of arsenic species in six different kinds of vegetable were analyzed. The proportions of As (III) and As (V), as well as total arsenic concentrations, were significantly different.

Arsenic mobility and toxicity on soil acid phosphatase activity increased with added phosphorus in contaminated mine soils

AbstractSoil phosphatase activity is identified as sensitive to arsenic (As) pollution and therefore, often used as an indicator to estimate As toxicity in soil. Nevertheless, the effect of As on soil phosphatase activity after its desorption by P is not adequately studied. This study employed sequential extraction procedure and ecological dose parameters to show As mobility and its toxicity to acid phosphatase (AcP). Results indicated that P application significantly increased As desorption ratio in the As ageing process. In S1 (As 2895 mg kg−1) soil, after P addition, the water‐soluble (FWS) fraction had the highest proportion of As, while for S2 (As 645 mg kg−1) and S3 (As 39 mg kg−1) it was residual (FRES) fraction. Additionally, P addition increased the As bioavailability in all soils. Generally, P addition significantly reduced soil AcP activity under all P concentrations and increased in the soil with minimum As content. The variation partitioning analysis indicated that for S1, P concentration was the major factor, for S2 and S3 soils, it was As desorption and ageing time, respectively, that influenced the AcP activity in soils. The calculated ecological dose (ED50) showed that in most cases, As toxicity increased at the end of ageing. Thus, it is essential to control the phosphorus fertilizer applications in silty soils with acid and neutral pH, since it can lead to increased As mobility and toxicity to soil AcP.

Enhancement of heavy metals desorption from the soil by eddy deep leaching in hydrocyclone

An eddy deep leaching technology was developed in this paper to address the challenge of treating heavy metal contaminants in industrial mining areas. The desorption effect of As, Cd, Sb and Pb was investigated utilizing chemical leaching and physical eddy techniques. It was found that the heavy metals concentration increased with decreasing particle size. The highest proportion of Cd in the form distribution of soil was in the bound to iron and manganese oxides, while the maximum proportion of As, Sb and Pb were in the residual. The optimal solid-liquid ratio of the hydrocyclone was 1:20, and the corresponding separation efficiency and flow rate were 84.7% and 1.76 m3/hr, respectively. The grade efficiency of soil particle separation increases with particle size and exceeds 99% for particles above 1,000 µm. Leaching experiments have revealed that oxalic acid (OA) and a combination of oxalic acid and EDTA (OAPE) were more efficient than citric acid (CA) and a combination of citric acid and EDTA (CAPE) for the desorption of heavy metals, respectively. The comparison of OAPE and eddy leaching found that the latter improved the desorption efficiency by 9.4%, 7.5%, 7.2% and 7.8% for As, Cd, Sb and Pb compared to the former, respectively. The results demonstrated that the eddy leaching technique could further enhance the desorption efficiency of heavy metals. It is expected to provide technical support for soil remediation with reduced usage of leaching agents.

Temporal trends in incidence, prevalence, and death of aortic stenosis in Korea: a nationwide population-based study.

We aim to determine the temporal trends of incidence, prevalence, and death of aortic stenosis (AS, I35.0) in an East Asian population. Data for 3773 patients who were newly diagnosed with AS from 2006 through 2017 were extracted from the National Health Insurance Service in Korea. The age-standardized incidence rate, prevalence rate, and death rate, survival rate (SR), and death risk of AS were calculated. Overall, the mean (standard deviation) age of AS patients was 69.9 (15.3) years [66.2 (15.7) years for men and 72.7 (14.4) years for women (P=0.007)], and the proportion of men was 42.7%. The proportion of AS patients ≥60years old was 80% (71.8% in men and 86% in women, P<0.001). The proportion of patients who died of AS was 36.4% during the period from 2006 through 2017. The most common causes of death were disease of the circulatory system. The age-standardized incidence, prevalence, and death rates in 2017 were 0.85, 2.79, and 0.58 persons per 100000 persons, respectively. The 10year SR was 49.2%. The higher adjusted HRs [95% CI] for AS were observed in 70- to 79-year-old people (9.08 [1.27, 64.7], P=0.027), in individuals 80years of age or older (22.7 [3.18, 161.9], P=0.001), in men (1.46 [1.31, 1.63], P<0.001), among the middle socioeconomic group (1.19 [1.03, 1.37], P=0.016), among the lower income levels (1.32 [1.17, 1.49], P<0.001), in those with myocardial infarction (1.57 [1.16, 2.13], P=0.003), with heart failure (1.63 [1.44, 1.85], P<0.001), with ischaemic stroke (3.26 [1.20, 8.85], P=0.015), with haemorrhagic stroke (2.51 [1.94, 3.25], P=0.02), with chronic kidney disease (2.51 [1.94, 3.25], P<0.001), and with malignant neoplasm (2.33 [1.64, 3.31], P<0.001). The proportion of AS at age ≥60years was 80%. For AS, the age-standardized incidence rates were steady, prevalence rates increased, and death rates decreased by year over a decade. The 10year SR of AS was about 50%. The most common cause of death in AS was disease of the circulatory system. Given the progressively higher incidence of AS with age continued efforts are required to increase awareness regarding AS-related symptoms and potential complications in aged people.

Field Experiments of Phyto-Stabilization, Biochar-Stabilization, and Their Coupled Stabilization of Soil Heavy Metal Contamination around a Copper Mine Tailing Site, Inner Mongolia

A field trial was conducted in Inner Mongolia to evaluate the stabilization effects of phyto-stabilization, biochar-stabilization, and their coupled stabilization for As, Cu, Pb, and Zn in soil. Stabilization plants (Achnatherum splendens, Puccinellia chinampoensis, and Chinese small iris) and biochar (wood charcoals and chelator-modified biochar) were introduced in the field trial. The acid-extractable fraction and residual fraction of the elements were extracted following a three-stage modified procedure to assess the stabilization effect. The results after 60 days showed that the coupled stabilization produced a better stabilization effect than biochar-/phyto- stabilization alone. Achnatherum splendens and Puccinellia chinampoensis were found to activate the target elements: the residual fraction proportion of As, Cu, Pb, and Zn decreased while the acid-extractable fraction proportion of Cu and Zn increased in the corresponding planting area. Neither type of biochar produced a notable stabilization effect. The residual fraction proportion of As (20.8–84.0%, 29.2–82%), Pb (31.6–39.3%, 32.1–48.9%), and Zn (30.0–36.2%, 30.1–41.4%) increased, while the acid-extractable fraction proportion remained nearly unchanged after treatment using Chinese small iris-straw biochar or Achnatherum splendens-straw biochar, respectively. The results indicate that phyto-stabilization or biochar-stabilization alone are not suitable, whereas the coupled stabilization approach is a more efficient choice.

Cadmium, lead and arsenic contamination in an abandoned nonferrous metal smelting site in southern China: Chemical speciation and mobility

The investigation of chemical speciation of primary toxic metal(loid)s (Cd, Pb, and As) in soil profile in nonferrous metal smelting site is a key to the assessment of their mobility characteristics and formulation of subsequent remediation strategy. In this study, 74 soil samples were collected at 12 different soil profiles; soil physio-chemical properties and total content of Cd, Pb and As and corresponding chemical speciation were also determined. The results showed that the mean total concentration followed the order of Pb > As > Cd. A large proportion of Pb, Cd and As were accumulated in upper soil profiles (depth < 3 m). Heavy pollution of Pb, Cd and As were observed in the whole soil profile at the area of fuel oil storage tank (ZY6) and lead smelting area (ZY8). The dominant fraction of Cd was exchangeable fraction (F1); Pb was dominant in Fe/Mn oxides-bound fraction (F3) in most cases; Crystallized Fe/Al hydrous oxides bound fraction (F4) generally accounted for a large proportion of As. Mobility factor (MF) followed the order Cd > As > Pb, indicating that Cd was the most mobile element in soil profiles. Pearson correlation analysis found that MFCd was significantly positively correlated to soil silt; the F4 fraction percentage of As was significantly positively correlated to soil redox potential (Eh). Additionally, MFCd/Pb was found to be positively correlated to crystalline iron (Fec), while negatively correlated to amorphous iron (Feo). The findings reported in this study, on the basis of distribution characteristics of chemical speciation could provide a new solution for future soil remediation at the site. Long-term solutions to metal(loid)s pollution might be offered by microbial-assisted soil washing technique that promotes the transformation of Fe/Mn oxides-bound fraction and organic/sulfide-bound fraction.

Variations and driving mechanism of dissolved arsenic in sediment porewater near wetland

The special hydrogeological conditions of wetland easily lead to the formation of high-arsenic (As) groundwater. However, it is unclear relative contribution of wetland water (surface water) dissolved organic matter (DOM) and sedimentary organic matter (SOM) to porewater DOM and its relations with dissolved As under the wetland. Porewater, groundwater and sediment samples were taken to monitor spatial-temporal variations in dissolved As affected by fluctuation of surface water levels near a typical wetland with high As groundwater in the arid-semiarid Hetao Basin, China. Hydrochemical data showed that As concentrations of sediment porewater (average: 17.1 μg/L) lay between As concentrations of surface water (average: 6.48 μg/L) and groundwater (average: 184 μg/L). A long-term observation showed concentrations of dissolved As, Fe, and dissolved organic carbon (DOC) of porewater obviously increased when levels of surface water rose during waterlogging period. There were positive correlations between dissolved As and Fe (r = 0.69, p < 0.01) and dissolved As and DOC (r = 0.38, p < 0.01). The sequential extraction showed that the main As form in sediment was amorphous Fe(III) oxide-coprecipitated form (averagely 45.0% of total As). It indicates that the dissolved As in porewater mainly originated from the Fe(III) oxide-bound forms in the sediment. Fluorescence indices and parallel factor analysis of the three-dimensional fluorescence spectra showed that porewater DOM mainly derived mainly from SOM during the drought period and from both surface water DOM and SOM during the waterlogging period. Higher proportions of As(III) in porewaters during waterlogging period were observed relative to those during drought period, indicating that surface water infiltration led to relatively reducing conditions. Surface water infiltration introduced DOM and stimulated the release of SOM into the porewater. DOM, acting as electron donor and electron shuttle, triggered the reductive dissolution of Fe(III) oxides, leading to the As mobilization under the wetland. This study suggests that drinking water supply near wetlands should be concerned, since high concentrations of dissolved As normally occurred in shallow aquifers near the wetland.

Determination of As species distribution and variation with time in extracted groundwater samples by on-site species separation method

It is challenging to dependably keep the native distribution of arsenic (As) species before sample analysis in the laboratory. The on-site separation method can avoid sample contamination and species change in the process of sample collection and transportation from field to laboratory. In this study, As species distribution and variation of the extracted groundwater was first analyzed by an on-site species separation method in Jianghan Plain, China. Our study illustrated that: 1) high-As groundwater generally existed under mildly reducing conditions (Eh < 200 mV), weak alkaline conditions (pH < 7.2), elevated concentrations of dissolved Fe(II) and S(-II), and high proportions of As (III); 2) As species in the groundwater changed dramatically at room temperature in 36 hours post extraction (HPE). Fe-sulfide and Fe oxides minerals, which adsorbed As (V), were the main reasons influencing the As species concentration; 3) Acidification and strong complexing agents cannot preserve As species effectively. The average proportion of As (III) in the wells, where groundwater samples from the depth of 25 m exceed 10 μg L−1 As, can be reduced by 61% and 63% after HCl and EDTA were added, respectively. Accurate assessment of concentrations and distribution variation of As species in groundwater can guide the removal of As and the safe use of water resources, especially in drought areas relying on drinking well water.

The role of agronomic factors (rice cultivation practices and soil amendments) on Arsenic fractionation: A strategy to minimise Arsenic uptake by rice, with some observations related to cadmium

Solid-phase As speciation and bioavailability during rice paddy cultivations depend on changes in cropping techniques and types of soil amendments. Field trials tested the impact of agronomic factors on As fractionation and resulting availability to rice, including aerobic (non-flooded) vs anaerobic rice cultivation (flooded); NPK, calcium silicate, ferrous sulfate, farmyard manure (FYM) and vermicompost (VC) addition. A modified sequential extraction procedure was used to determine As concentrations in the following soil fractions: exchangeable (F1); specifically sorbed (F2); amorphous iron oxide (F3); crystalline iron oxide (F4); organic matter and sulfide (F5); and residual bound (F6). Significant proportions of As were determined in F3, F4, and F6. Exchangeable fraction (F1) contained the lowest proportion of As. Aerobic cultivation practices significantly reduced soil As availability in F1 and resulted in higher retention of As in F2, F3, and F4. Application of ferrous sulfate increased As concentrations in F3 and F4 but when combined with FYM and VC, significantly lowered As concentrations in F1; a potential benefit for rice quality and consumer’s health. Linear regression analyses show that As concentrations in F1, F2, F3, and F4 are the most important factors influencing As accumulation in rice. Arsenic concentration in F1 is a good predictor of As accumulation in rice grain. The phytoavailability coefficient (PC) based on As retained in different fractional pools was determined. The addition of calcium silicate and ferrous sulfate under aerobic conditions reduced the PC in the soil, which could be responsible for reduced As accumulation in rice. There were insignificant variations in rice grain Cd concentrations between aerobic and anaerobic cultivations for monsoon trials, but significantly higher Cd concentrations were detected under aerobic cultivation than flooded cultivation for the post-monsoon trials. These data show that water management under different rice cropping practices can influence mobility and bioavailability of elements like As and Cd during rice paddy growth and can inform agricultural policy intended to attenuate element toxicity in edible crops, reducing their introduction into the food chain.

Assessing the Removal of Arsenite and Arsenate Mixtures from the Synthetic Bangladesh Groundwater (SBGW) Using Combined Fe(VI)/Fe(III) Treatments and Local Regression Analysis

Arsenic is an inorganic pollutant that, depending on oxidation–reduction and pH level conditions, may be found in natural waters in two variants: As(III) and As(V). Any treatment to effectively remove arsenic from water will be conditioned by the presence of one or both variants. In this context, this study assesses using electrochemically produced Fe(VI) with Fe(III) to remove As(III), As(V), and their combinations from the Synthetic Bangladesh Groundwater (SBGW) containing anions that interfere with iron-based arsenic removal processes. The combined use of Fe(VI) and Fe(III) allowed us to remove the total arsenic below the 10 mg L−1 threshold established by the World Health Organization and Peruvian regulations for drinking water. An optimum combination of 1 mg L−1 of Fe(VI) and 30 mg L−1 of Fe(III) was identified and tested on the removal of four different proportions of As(III):As(V) for two total concentrations: 500 and 250 mg L−1. There were no significant differences in the final removal values under the different proportions of As(III):As(V) for each total concentration, with a final removal average of 99.0% and 96.9% for the 500 and 250 µg L−1 concentrations, respectively.

Bioaccumulation and biotransformation of inorganic arsenic in zhikong scallop (Chlamys farreri) after waterborne exposure

Arsenic (As) and As speciation in marine bivalves have been widely investigated. However, little is known about the bioaccumulation and biotransformation of inorganic As in different tissues of scallops. Therefore, the tissue-specific accumulation, biotransformation and subcellular partitioning of As were investigated in Chlamys farreri following 12 d inorganic As [arsenite (AsⅢ) and arsenate (AsⅤ)] exposure and 30 d depuration. Total As levels were highest in the kidneys and lowest in the adductor muscle after 12 d exposure for both As (Ⅲ) and As (Ⅴ) treatment groups, and the bioavailability of As (Ⅲ) was significantly higher than that of As (Ⅴ) for C. farreri. After 30 d elimination, total As levels were significantly decreased to the control levels. The subcellular fate of As in five different tissues was similar for different inorganic As treatment groups. The greatest proportion of As was found in the metallothionein-like protein fraction (MTLP) and the second was the cellular debris (CD). A little part of As (Ⅲ) could be oxidized to As (Ⅴ) in the gill and digestive gland for As (Ⅲ) treatment groups, and the reduction of As (Ⅴ) to As (Ⅲ) happened in the gill and kidney under As (Ⅴ) exposure. Although a high methylation activity was found in C. farreri, it varied in different tissues with different inorganic As species exposure. The present results indicated that exposure to As (Ⅲ) and As (Ⅴ) could induce different responses in bioaccumulation and biotransformation in five tissues of C. farreri.

Epiphytic bacterial community enhances arsenic uptake and reduction by Myriophyllum verticillatum.

Microbes play an important role in the biotransformation of arsenic (As) speciation in various environments. Nevertheless, whether epiphytic bacteria that attached on submerged macrophytes have the potential to influence As speciation still remains unclear. In this study, sterile or nonsterile Myriophyllum verticillatum was cultured with arsenite (As(III)) or arsenate (As(V)) to investigate the impact of epiphytic bacterial community on As uptake, transformation, and efflux. Results showed that both sterile and nonsterile M. verticillatum did not display substantial As(III) oxidation, suggesting that neither M. verticillatum nor epiphytic bacterial community has the capacities of As(III) oxidation. However, sterile M. verticillatum exhibited capacity for As(V) reduction, and the presence of epiphytic bacterial community substantially enhanced the proportions of As(III) in the medium (from 39.91 to 98.44%), indicating that epiphytic bacterial community contributes significantly to As(V) reduction in the medium. The presence of epiphytic bacterial community elevated As accumulation (by up to 2.06-fold) in plants when exposed to As(V). Results also showed that epiphytic bacterial community contributed little to As(III) efflux. Quantitative PCR of As metabolism genes revealed the dominance of the respiratory As(V) reductase genes (arrA) in epiphytic bacterial community, which might play a significant role in As(V) reduction in aquatic environments. Phylogenetic analysis of the arrA genes revealed the widely distribution and diversity of As(V)-respiring bacteria. These results highlighted the substantial impact of the epiphytic bacterial community associated with submerged aquatic macrophytes on As biogeochemistry in wetland and water environments.

Immobilization and release risk of arsenic associated with partitioning and reactivity of iron oxide minerals in paddy soils.

The consumption of agricultural products grown on paddy soils contaminated with toxic element has a detrimental effect on human health. However, the processes and mechanisms of iron (Fe) mineral-associated arsenic (As) availability and As reactivity in different paddy soil profiles are not well understood. In this study, the fractions, immobilization, and release risk of As in eleven soil profiles from the Changzhutan urban agglomeration in China were investigated; these studied soils were markedly contaminated with As. Sequential extraction experiments were used to analyze fractions of As and Fe oxide minerals, and kinetic experiments were used to characterize the reactivity of Fe oxide minerals. The results showed that concentrations of total As and As fractions had a downward trend with depth, but the average proportions of As fractions only showed relatively small changes, which implied that the decrease in the total As concentrations influenced the changes in fraction concentrations along the sampling depth. Moreover, we found that easily reducible Fe (Feox1) mainly controlled the reductive dissolution of the Fe oxides, which suggest that the reductive dissolution process could potentially release As during the flooded period of rice production. In addition, a high proportion of As was specifically absorbed As (As-F2) (average 20.4%) in paddy soils, higher than that in other soils. The total organic carbon (TOC) content had a positive correlation with the amount of non-specifically bound As (As-F1) (R = 0.56), which means that TOC was one factor that affected the As extractability in the As-F1. Consequently, high inputs of organic fertilizers may elevate the release of As and accelerate the diffusion of As. Graphical abstract.

Distribution of trace elements between carbonaceous matter and sulfides in a sediment-hosted orogenic gold system

Carbonaceous matter (CM) plays a critical role in the formation of sediment-hosted ore deposits, but metal partitioning between CM and associated sulfides remains unclear. Here we use synchrotron X-ray fluorescence microscopy (SXRF), laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS), and nanoscale secondary ion mass spectrometry (NanoSIMS) to characterize the distribution and deportment of trace elements between CM and sulfides from the Daqiao orogenic gold deposit, China. Four types of CM co-existing with different generations of sulfides are recognized: sedimentary CM1 with pyrite polyframboids in black shale host; indigenous CM2 with early- to main-ore pyrite and marcasite; CM3 with main-ore pyrite; CM4 with pyrite porphyroblasts in underlying graphitic schists.The SXRF results reveal that As, Se, Ni, Pb, and Cu are enriched in pyrite polyframboids relative to CM1 in black shales, although a small proportion of As, Pb, Bi, and U is accommodated in the latter. NanoSIMS images show that Au and As are associated with the CM1 matrix within pyrite framboids that are overgrown by recrystallized pyrite rims. Most trace elements are enriched in the newly-formed aggregates of pyrite and marcasite relative to the CM2 rims that formed via the interactions between ore fluids and pre-existing CM2 cores. Gold, As, Tl, Se, and Hg are highly enriched in the main-ore pyrite relative to co-precipitated CM3 veinlets, and this deportment might reflect changes in fluid redox conditions in response to hydraulic fracturing that is the main mechanism of gold deposition. The pyrite porphyroblasts in the schists are enriched in As, Se, Ni, and Cu relative to CM4, but have lower Au, As, Co, Ni, and Pb than sedimentary pyrite framboids. Taken together, we suggest that biological activity causes accumulation of As and Au within CM interstitial to the framboidal pyrite, and that these elements are released during metamorphic recrystallization and hydrothermal replacement. Trace element deportment in hydrothermal CM and sulfides is controlled by a variety of factors such as the fluid chemistry and interaction between indigenous CM and fluids. Our quantitative results provide significant new insights into the complex processes that formed carbonaceous sediment-hosted ore systems worldwide.

Redox synergistic Mn-Al-Fe and Cu-Al-Fe ternary metal oxide nano adsorbents for arsenic remediation with environmentally stable As(0) formation.

Arsenic mitigation behavior in aqueous systems is being evaluated for Mn-Al-Fe, Cu-Al-Fe nano adsorbents. Morphological, and vibrational spectroscopy analysis are observed with As-OH, and As-O surface complexes. XPS study of individual As(3d) spectra at different parameters is observed with multiplet peak behavior attributed to redox behavior of Mn-Al-Fe, Cu-Al-Fe. Significant proportions of As(0) signal (∼25 at.% in pH 7, ∼78 at.% in pH 2, ∼58 at.% in pH 12) implicate an environmentally stable behavior of these adsorbents to address the arsenic leaching issue. Adsorption kinetics are observed with Pseudo Second Order (PSO) model, and Freundlich model supported multilayer adsorption behavior is observed for adsorption isotherms. Trace metal voltammetry studies are observed with 75-90 % of As(III) mitigation in aliquot samples. Detailed study of Mn(2p), Cu(2p), Fe(2p), and O(1 s) spectra explains redox active, and surface ligand exchange synergism in arsenic adsorption. Low equilibrium concentrations (Ce < 10 ppb) in As(V) systems (Ci ∼ 100 and 500 ppb) indicate the drinking water application of these systems. Cyclic-voltammetry (CV) studies implicate the mitigation and immobilization of arsenic species onto adsorbent by both reduction, and sorption phenomenon.

Textural and trace element evolution of pyrite during greenschist facies metamorphic recrystallization in the southern Apuan Alps (Tuscany, Italy): Influence on the formation of Tl-rich sulfosalt melt

Several small pyrite ± baryte ± iron-oxide orebodies (Buca della Vena, Canale della Radice, Fornovolasco, Monte Arsiccio and Pollone) are hosted in the metamorphic rocks of the southern Apuan Alps, northern Tuscany, Italy. These deposits are exceptionally thallium-rich, expressed in part by assemblages comprising rare Tl-sulfosalts. Using a variety of techniques including laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on fifty-four samples, the textural and trace element evolution of pyrite during greenschist facies metamorphism has been described. Five generations of pyrite have been recognised. Pyrite-1 (py1) and pyrite-2 (py2) (framboidal and colloform pyrite, respectively) likely represent pristine generations and are rich in trace elements. Pyrite-3 (py3) forms fine-grained disseminations often aligned with the metamorphic fabric and likely formed during the earliest stages of deformation associated with metamorphism. Pyrite-4 (py4) forms coarse, euhedral, inclusion-rich crystal clusters and likely formed as pristine pyrite generations began to recrystallize. Pyrite-5 (py5) is typically coarse, relatively ‘clean’ and often euhedral. It is interpreted to be the end-product of pyrite recrystallization, with grain size increasing and micro-inclusions being expelled late on the prograde path, then granoblastic annealed textures forming during retrograde cooling. Pyrite (especially primary pyrites; py1 and py2) is particularly rich in As (up to 17,400 ppm), Sb (up to 5100 ppm) and Tl (up to 4200 ppm), while Ni, Pb and Mn may be present above 1000 ppm, and Hg, Co, Cu, Zn, Mo, Bi and Ag may all be present above 100 ppm. Some trace elements, particularly As, Ni and Co, are commonly zoned in late metamorphic pyrite overgrowths. The incorporation of some trace elements into pyrite seems to have been facilitated by the presence of Sb in a similar way that As generally facilitates Au incorporation. Concentrations of most trace elements decrease from py3 to py4 at Fornovolasco and Monte Arsiccio, while in the other deposits the opposite trend is observed. Concentrations of most trace elements drop significantly from py4 to py5, where recrystallization of pyrite liberates a large proportion of As, Sb, Tl, Pb, Hg, Cu, Zn, Ag and Mn, likely during retrograde cooling and annealing. The release of these elements from pyrite during metamorphic recrystallization has directly facilitated the formation of late-stage sulfosalts, especially at Monte Arsiccio, where textural evidence suggests sulfosalt assemblages intimately associated with py5 were mobilised as melts during greenschist facies metamorphism. At Monte Arsiccio, around 75% of Tl hosted in early recrystallized pyrite is released upon complete recrystallization. As such, mass balance calculations show that all Tl contained in Tl-sulfosalts could be supplied from locally recrystallizing pyrite, and that in total, more than 250 tons of Tl could potentially have been liberated from the pyrite orebody at Monte Arsiccio during metamorphism. This study highlights the significant quantities of Tl and other metals that may be hosted in pyrite, and also the potential role that metamorphic recrystallization may play in mobilising and (re)-concentrating (or indeed dispersing) metals in a pyrite-dominant ore system.

Chemical speciation and bioavailability concentration of arsenic and heavy metals in sediment and soil cores in estuarine ecosystem, Vietnam

The first investigation of arsenic (As) contamination in soil cores in the biggest estuarine ecosystem in northern Vietnam was conducted using FE-EPMA, ICP-MS and XRD techniques. Concentrations of arsenic and five heavy metals were measured and mineralogical characteristic of soils and sediments in different land uses were analyzed. Most of the soils contained high proportions of As and heavy metals in the potential mobility fractions and silicate minerals. High concentrations of As and heavy metals were observed in river sediments and top-layers of mangrove forest soil cores. Qualitative analyses using WDS technique on FE-EPMA found As on the iron (hydro)oxides and framboidal pyrite surfaces in the samples. The principal component analysis indicated the enrichment of As and heavy metals in the upper soil layers, suggesting that intensive human activities in upstream of the Red river in recent decades could be the cause of elevated levels of these toxic elements in the estuarine ecosystem.

Groundwater co-contaminant behavior of arsenic and selenium at a lead and zinc smelting facility

Co-contaminant behavior of arsenic (As) and selenium (Se) in groundwater is examined in this study at a former lead and zinc smelting facility. We collected water quality data, including concentrations of trace metals, major ions, and metalloid speciation, over a 15-year period to document long-term trends and relationships between As, Se, geochemical parameters, and other redox-sensitive trace metals. Concentrations of dissolved As and Se were negatively correlated (Kendall's Tau B correlation coefficient, r = −0.72) and showed a distinctive L-shaped relationship. High-concentration arsenic wells (>5 mg L−1) were characterized by intermediate oxidation-reduction conditions (75 < Eh < 275 mV), near-neutral pH (6.1–7.9), low Ca/Na ratios, elevated Fe and Mn concentrations, and high proportions of As(III) relative to total dissolved As. High-concentration Se wells (>500 μg L−1) were characterized by more positive Eh (305–500 mV), low Fe concentrations, and high proportions of As(V). Batch micocosm experiments showed that aquifer solids contain mineral surfaces and/or microbial communities capable of removing selenate from groundwater. Electron microprobe and Se K-edge X-ray absorption near-edge spectroscopic analyses demonstrated that Se was predominantly associated with elemental Se in the reduced aquifer solids. Factor analysis revealed three discernible groupings of trace metals. Group I includes U, Se, and nitrate-N, all of which are mobile under oxygenated to moderately oxygenated conditions. Group II includes elements that are mobile under Fe(III)-reducing conditions: Fe, total dissolved As, As(III), and ammonium-N. Group III elements (Mo, Sb, and V) showed mobility across the entire range of redox conditions encountered in site groundwater; As(V) clustered with this group of elements. Geochemical modeling suggests that As and Se species were in a state of disequilibrium with respect to measured parameters indicative of redox conditions, although predicted patterns of redox-controlled mobility and attenuation were confirmed. This analysis is important to better understand groundwater contaminant behavior in response to redox conditions ranging from oxic/suboxic to Fe(III)-reducing, but excluding sulfate-reducing conditions.