Redistribution Of Arsenic Research Articles

Time-dependent redistribution of soil arsenic induced by transformation of iron species during zero-valent iron biochar composites amendment: Effects on the bioaccessibility of As in soils

Zero-valent iron biochar composites (ZVI/BC) are considered as effective amendments for arsenic (As)-contaminated soils. However, the mechanisms of transformation of various soil As species during ZVI/BC amendments remain unclear. This study investigated As transformation in four soils (namely, GX, ZJ, HB, and HN) treated with ZVI/BC for 65 days under two soil moisture conditions, unsaturated and oversaturated. Results showed that the 65-day treatment was divided into two stages based on the variation of labile As content. Within 2 days (stage 1), ZVI/BC addition quickly reduced labile As content by 5.91–90.3 % in soils under unsaturated conditions. During days 2–65 (stage 2), labile As ultimately decreased by 0.06–0.31 mg/kg in GX, ZJ, and HB while increasing by 22.1 mg/kg in HN soil, due to its lower pH value and Fe content. The variations of labile As were attributed to changes in multiple Fe minerals and associated As species. In stage 1, the corrosion of ZVI/BC generated amorphous Fe oxides to immobilize labile As, resulting in the accumulation of meta-stable As. In stage 2, amorphous Fe oxides were transformed into crystalline Fe oxides, resulting in the release and re-precipitation of As along with transformation, thus redistributing immobilized As into labile and stable As, which was evidenced by multiple methods, including chemical extraction, XRD, and TEM-EDX. The elevated soil moisture condition would enhance the corrosion of ZVI/BC in stage 1, further forming a reductive environment to facilitate the transformation of Fe minerals in stage 2. Besides, As bioaccessibility in soils was reduced by 10.8–38.7 % after ZVI/BC treatment in in-vitro gastrointestinal simulations. Overall, our study revealed the time-dependent transformation mechanism of soil As species and associated Fe minerals under different soil moisture with ZVI/BC treatments, and highlighted the effectiveness of ZVI/BC as a long-term amendment for As-contaminated soils.

Extraction of arsenic from fine dust of copper smelters by reduction roasting with natural gas

One of the current trends in the complex processing of fine dust from copper smelters is their direct leaching with sulfuric acid. As practical results show, high reliable technological parameters are not achieved due to the high content of arsenic in dust. During sulfuric acid leaching of dust, arsenic is distributed between the lead cake and the solution at a ratio of 40 and 60%, respectively. The redistribution of arsenic between leaching products significantly reduces the technological performance and leads to the accumulation of arsenic in the technological scheme. The paper presents the results of comprehensive studies of the elemental and phase composition of fine dust from one of the copper smelters in Kazakhstan. In the initial dust, along with the main phases presented in the form of lead and zinc sulfate, the following typical components were found: oxides of copper, lead, zinc and copper and zinc ferrites. Arsenic is found in two forms—As(III) and As(V). The laboratory installation and technique for conducting reduction roasting of dust with natural gas are presented. The influence of roasting duration, temperature and natural gas consumption on the extraction of arsenic from dust was studied. It has been established that almost complete, up to 99%, extraction of arsenic from dust is achieved with optimal technological roasting parameters: duration τ = 40 min.; natural gas consumption is 1.5 times higher than the stoichiometrically required amount for the reduction of As2O5, and temperature 500 °C.

Crystal phase conversion of amorphous Fe−Mn binary oxides promote the sequestration and redistribution of arsenic, cadmium, and lead in the soil: Comparison with crystalline form

Iron and manganese oxides participate in nearly all geochemical processes in soils. The crystal phase conversion of the Fe−Mn oxides is a crucial process that controls the transport and the fate of metal(loid)s (such as Pb, Cd, and As). However, this conversion and its contribution in immobilization are seldom reported. In this study, the phase transition process of amorphous Fe−Mn oxides has been investigated using TEM, HE−XRD and PDF analyses. The role of heavy metal atoms in the Fe−Mn oxides lattice has been revealed through atomic−scale structural characterization, including bond lengths and coordination numbers. In detail, Mn oxides and Fe oxides exhibit synergistic effects. Mn oxides oxidize As(III) to As(V). Meanwhile, the adsorbed As, Cd, and Pb irons were redistributed and incorporated into the lattice of the Fe−Mn oxides during the crystal phase conversion of the Fe oxides. During this process, the proportion of residual fraction of As, Cd, and Pb increased by 30 %, 25 %, and 9 %, respectively, after 28 d. 100 %, 41.8 %, and 60.7 % of decarbonate−extractable As, DTPA−extractable Cd and Pb could be immobilized, respectively. This study provides insight into the contribution of Fe−Mn oxides in controlling the cycling of metals and offers an advanced strategy in remediation of As, Cd, and Pb in contaminated soil.

Coupled redox cycling of arsenic and sulfur regulates thioarsenate enrichment in groundwater

High‑arsenic groundwater is influenced by a combination of processes: reductive dissolution of iron minerals and formation of secondary minerals, metal complexation and redox reactions of organic matter (OM), and formation of more migratory thioarsenate, which together can lead to significant increases in arsenic concentration in groundwater. This study was conducted in a typical sulfur- and arsenic-rich groundwater site within the Datong Basin to explore the conditions of thioarsenate formation and its influence on arsenic enrichment in groundwater using HPLC-ICPMS, hydrogeochemical modeling, and fluorescence spectroscopy. The shallow aquifer exhibited a highly reducing environment, marked by elevated sulfide levels, low concentrations of Fe(II), and the highest proportion of thioarsenate. In the middle aquifer, an optimal ∑S/∑As led to the presence of significant quantities of thioarsenate. In contrast, the deep aquifer exhibited low sulfide and high Fe(II) concentration, with arsenic primarily originating from dissolved iron minerals. Redox fluctuations in the sediment driven by sulfur‑iron minerals generated reduced sulfur, thereby facilitating thioarsenate formation. OM played a crucial role as an electron donor for microbial activities, promoting iron and sulfate reduction processes and creating conditions conducive to thioarsenate formation in reduced and high‑sulfur environments. Understanding the process of thioarsenate formation and the influencing factors is of paramount importance for comprehending the migration and redistribution of arsenic in groundwater systems.

Arsenic redistribution associated with Fe(II)-induced jarosite transformation in the presence of polygalacturonic acid

Jarosite exists widely in acid-sulfate soil and acid mine drainage polluted areas and acts as an important host mineral for As(V). As a metastable Fe(III)-oxyhydoxysulfate mineral, its dissolution and transformation have a significant impact on the biogeochemical cycle of As. Under reducing conditions, the trajectory and degree of abiotic Fe(II)-induced jarosite transformation may be greatly influenced by coexisting dissolved organic matter (DOM), and in turn influencing the fate of As. Here, we explored the impact of polygalacturonic acid (PGA) (0–200 mg·L−1) on As(V)-coprecipitated jarosite transformation in the presence of Fe(II) (1 mM) at pH 5.5, and investigated the repartitioning of As between aqueous and solid phase. The results demonstrated that in the system without both PGA and Fe(II), jarosite gradually dissolved, and lepidocrocite was the main transformation product by 30 d; in Fe(II)-only system, lepidocrocite appeared by 1 d and also was the mainly final product; in PGA-only systems, PGA retarded jarosite dissolution and transformation, jarosite might be directly converted into goethite; in Fe(II)-PGA systems, the presence of PGA retarded Fe(II)-induced jarosite dissolution and transformation but did not alter the pathway of mineral transformation, the final product mainly still was lepidocrocite. The retarding effect on jarosite dissolution enhanced with the increase of PGA content. The impact of PGA on Fe(II)-induced jarosite transformation mainly was related to the complexation of carboxyl groups of PGA with Fe(II). The dissolution and transformation of jarosite drove pre-incorporated As transferred into the phosphate-extractable phase, the presence of PGA retarded jarosite dissolution and maintained pre-incorporated As stable in jarosite. The released As promoted by PGA was retarded again and almost no As was released into the solution by the end of reactions in all systems. In systems with Fe(II), no As(III) was detected and As(V) was still the dominant redox species.

Effects of denitrification on speciation and redistribution of arsenic in estuarine sediments

Microbially-mediated redox processes involving arsenic (As) and its host minerals significantly contribute to the mobilization of As in estuarine sediments. Despite its significance, the coupling between As dynamics and denitrification processes in these sediments is not well understood. This study employed sequential sediment extractions and simultaneous monitoring of dissolved iron (Fe), nitrogen (N), and sulfur (S) to investigate the impact of nitrate (NO3−) on the speciation and redistribution of As, alongside changes in microbial community composition. Our results indicated that NO3− additions significantly enhance anaerobic arsenite (As(III)) oxidation, facilitating its immobilization by increased adsorption onto sediment matrices in As-contaminated estuarine settings. Furthermore, NO3− promoted the conversion of As bound to troilite (FeS) and pyrite (FeS2) into forms associated with Fe oxides, challenging the previously assumed stability of FeS/FeS2-bound As in such environments. Continuous NO3− additions ensured As and Fe oxidation, thereby preventing their reductive dissolution and stabilizing the process that reduces As mobility. Changes in the abundance of bacterial communities and correlation analyses revealed that uncultured Anaerolineaceae and Thioalkalispira may be the main genus involved in these transformations. This study underscores the critical role of NO3− availability in modulating the biogeochemical cycle of As in estuarine sediments, offering profound insights for enhancing As immobilization techniques and informing environmental management and remediation strategies in As-contaminated coastal regions.

Sulfate-reducing bacteria (SRB) mediated carbonate dissolution and arsenic release: Behavior and mechanisms

Carbonate bound arsenic act as an important reservoir for arsenic (As) in nature aquifers. Sulfate-reducing bacteria (SRB), one of the dominant bacterial species in reductive groundwater, profoundly affects the biogeochemical cycling of As. However, whether and how SRB act on the migration and transformation of carbonate bound arsenic remains to be elucidated. Batch culture experiment was employed using filed collected arsenic bearing calcite to investigate the release and species transformation of As by SRB. We found that arsenic in the carbonate samples mostly exist as inorganic As(V) (93.92 %) and As(III). The present of SRB significantly facilitated arsenic release from carbonates with a maximum of 22.3 μg/L. The main release mechanisms of As by SRB include 1) calcite dissolution and the liberate of arsenic in calcite lattices, and 2) the break of H-bonds frees arsenic absorbed on carbonate surface. A redistribution of arsenic during culture incubation took place which may due to the precipitation of As2Sx or secondary FeAl minerals. To our best knowledge, it is the first experimental study focusing on the release of carbonate bound arsenic by SRB. This study provides new insights into the fate and transport of arsenic mediated by microorganism within high arsenic groundwater-sediment system.

Extraction of Pb, Cu, Zn and As from Fine Dust of Copper Smelting Industry via Leaching with Sulfuric Acid

Fine dust from copper smelting plants is an important source of raw materials for the extraction of various valuable metals. A specific feature of dust from copper smelting plants in Kazakhstan is their high arsenic content of up to 15%. This work shows the possibility of hydrometallurgical processing of fine dust from copper smelters, obtained during the converting of copper mattes through the Vanyukov process, via direct leaching with sulfuric acid. The influence of temperature, process time and the S:L (solid/liquid) ratio on the selective extraction of Pb, Zn, Cu and As into targeted products under leaching conditions is studied. The results of the test work show that with the optimal process parameters of S:L = 1.5, t = 60 °C, τ = 60 min, the extraction of copper and zinc into solution is achieved as 89% and 96%, respectively, and lead into cake by up to 97%. The relatively low extraction of copper and zinc into the solution is explained by the transition of copper and zinc ferrites that are insoluble in sulfuric acid into the lead cake. The redistribution of arsenic between the leaching products established in this case also affects the reduction in copper and zinc in the solution. The extraction of arsenic into the solution is 49.32%. More than half of the arsenic from the dust is left in the lead cake. The concentration of arsenic in lead cake will lead to its transition into circulating dust during smelting. This will increase the accumulation of arsenic in the overall process flow. Therefore, when organizing dust-processing technology, it is necessary to provide measures for the preliminary removal of arsenic.

Arsenic transformation and redistribution in groundwater induced by the complex geochemical cycling of iron and sulfur

Iron (hydr)oxides are effective sorbents of arsenic that undergo reductive dissolution when exposed to dissolved sulfide, which significantly impacts the movement and repartition of arsenic in groundwater. This study investigated the sulfidation of As-bearing ferrihydrite and its consequences on arsenic repartitioning as well as formation and transformation of secondary minerals induced by sulfide in batch experiments. The sulfidation of As(III) and As(V) adsorbed on ferrihydrite shows very different results. In the As(V) system, sulfidation resulted in the production of significant amounts of elemental sulfur (S0) and Fe2+, and Fe2+ and sulfide combine to form mackinawite. Subsequently, Fe2+ adsorbed and catalyzed the conversion of residual ferrihydrite to lepidocrocite. However, in the As(III) system, As(III) was protonated in the presence of sulfide to produce thioarsenate, which accounted for 87.9 % of the total aqueous arsenic concentration. The formation of thioarsenate also consumed the S0 produced by the sulfidation, resulting in no detectable S0 during solid phase characterization. The adsorption of thioarsenate on iron minerals notably affected the surface charge density of ferrihydrite, hindering the further formation of secondary minerals. Studies on the influence of thiolation on As-Fe-S system are of great significance for understanding the migration and redistribution of arsenic in groundwater systems under sulfur-rich conditions.

Assessment of the Chronic Toxicity and Interactions between Arsenic and Riverbed Biofilms.

The toxic effect of exposure to arsenic, As(V), at concentrations of 0 to 30 mg L−1, for 49 days, on epipsammic biofilms, was evaluated in a microcosm experiment. The growth and composition of biofilms developed on sediments containing As concentrations of 31 mg kg−1 and 85 mg kg−1 were compared, using photosynthetic parameters and Live/Dead stains as end points. A toxic effect of arsenic could not be demonstrated; however, biofilm growth was higher over the sediment with higher arsenic concentrations, suggesting the development of pollution-induced community induced tolerance (PICT). Nevertheless, PICT was not observed after exposure to high arsenic concentration in the laboratory, as there were no differences in algal growth between the previous 0 and 30 mg L−1 systems exposed to new 30 mg As L−1 dissolution over 29 days. The algal composition was affected by the added arsenic, and brown algae were the most tolerant compared to green algae and cyanophyceae, as their percentage increased from 25 and 33% in the control samples to 57 and 47% in the samples with the highest added As concentration. In turn, the biofilm development influenced arsenic redistribution and speciation. Arsenic concentration in water decreased with time during the incubation experiment, retained by the sediment particles and the biofilm. In the biofilm, extracellular As was significantly higher (up to 11 times) than intracellular arsenic. As(V) was the predominant species in water and in the biofilm, but products of biotic transformation, namely As(III), DMA(V) and MMA(V), were also found in the solution and in the biofilm in some systems, demonstrating reduction and methylation by the organisms. As a conclusion, a toxic effect was not detected for the concentrations evaluated. Biofilms naturally exposed in the river system to high As concentrations acquire pollution-induced tolerance; however, tolerance was not acquired by exposure to 30 mg L−1 for 29 days in the laboratory.

Surficial redistribution of gold and arsenic from the Rise and Shine Shear Zone, Otago, New Zealand

ABSTRACT The historic Come-In-Time gold mine was developed in a ∼100*100 m area of the >7 km long orogenic Rise and Shine Shear Zone in Otago Schist. The oxidation of hydrothermal ankeritic and auriferous arsenopyrite and pyrite-bearing Otago Schist beneath a regional Miocene unconformity resulted in replacement of sulphides and ankerite by arsenic (As)-bearing ferric oxyhydroxide. The As-bearing ferric oxyhydroxide is mainly concentrated in and near the original mineralisation sites, especially shears, but mobilisation into post-mineralisation joints and fractures has redistributed As on a metre scale. Gold was liberated from sulphides during oxidation and aggregated by supergene oxidation processes into a smaller number of larger particles (mm scale) that are intimately intergrown with As-bearing ferric oxyhydroxide, especially in shears. Eluvial gold in proximal immature debris includes variably rounded supergene particles eroded from nearby, and some externally derived detrital flakes from previously overlying Miocene sediments. Some eluvial gold is trapped in fine sediments by lichen on outcrops. The hydrothermal As-Au relationship has therefore been broadly maintained through oxidation of rocks at the metre scale but Au concentrations have been locally enhanced in the surficial environment.

AML-278: Examination of Optimal Administration of Arsenic Trioxide in Continuous Renal Replacement Therapy During Acute Promyelocytic Leukemia Treatment

<h3>Background and Aim:</h3> Arsenic trioxide (ATO), a safe and effective treatment for acute promyelocytic leukemia (APL), has an effective plasma arsenic concentration (PAC) of 37.6–150 ng/mL. According to current recommendations, the ATO dosage should be reduced for patients receiving intermittent hemodialysis. However, there are no reports on proper ATO administration in patients receiving continuous renal replacement therapy (CRRT); the PAC during CRRT is unknown, and the optimal dosage for patients on CRRT has not been established. We evaluated the appropriate ATO dosage for patients on CRRT. <h3>Patients and Methods:</h3> We enrolled two APL patients undergoing CRRT during ATO therapy. We measured PAC over time to determine the optimal timing of administration required to achieve the therapeutic range for ATO. <h3>Results:</h3> Prior to APL treatment, both patients had normal renal function. The first case was a woman in her 30s with a recurrence of APL. She developed acute kidney injury owing to severe differentiation syndrome and disseminated intravascular coagulation, and she suffered from uncontrolled uremia and fluid volume. Thus, continuous hemodialysis (CHD) was initiated. Because of previous therapy, her PAC was 68 ng/mL at the start of CHD. We administered ATO (0.15 mg/kg) 18 hours after the start of CHD. Her PAC before ATO administration was 60 ng/mL. Immediately after ATO administration, her PAC was 80 ng/mL. However, owing to the redistribution of arsenic, the PAC gradually rose to 100 ng/mL. The second case was a male patient in his 30s who had untreated APL. He also developed acute kidney injury owing to differentiation syndrome. He initially received dialysis but soon required CHD. We administered ATO (0.15 mg/kg) before initiating CHD and at 13 and 39 hours after the start of CHD. His PAC was 110 ng/mL immediately prior to CHD; thereafter, ATO was administered, and his PAC ranged between 130 and 190 ng/mL. At 117 hours after the start of CHD, his PAC was 114 ng/mL, which was within the optimal range. <h3>Conclusions:</h3> PACs exceeded the effective range, even in the presence of CHD. Therefore, we suggest that patients undergoing CHD receive ATO every 48 to 72 hours.

The redistribution of arsenic during the interaction between high-temperature flue gas and ash

Transformation of As in the post-combustion zone has a significant effect on its emission characteristics. In this study, redistribution of As that occurs during the interaction between flue gas and ash has been elucidated using a double-layer fixed-bed reactor at 800–1000 °C. Herein, flue gas and ash samples with different As contents and inorganic components were produced by two varieties of coals. The As content in the ash with high Ca and Al contents increased after interacting with the flue gas with a high As content, indicating gaseous As adsorption. However, the As content in the ash decreased by up to 67% for other cases. The blank experiments showed that the As occurrences in ash were thermally stable, suggesting that the decrease was caused by the action of flue gas. Accordingly, the effect of flue gas components on the release of As from the ash was investigated. It was found that a significant amount of As release was primarily caused by the reaction of gaseous Na in the flue gas with the residual As in ash. A bi-directional interaction was observed between the high-temperature flue gas and ash, which led to the redistribution of As.

Arsenic redistribution and transformation during Fe(II)-catalyzed recrystallization of As-adsorbed ferrihydrite under anaerobic conditions

The redistribution and transformation of arsenic (As) during the Fe(II)-catalyzed transformation of As-adsorbed ferrihydrite remains unclear. This study investigated the re-crystallization process and products of As-adsorbed ferrihydrite accelerated by Fe(II) and the fate of arsenate and arsenite at pH 7 under anaerobic condition. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and synchrotron based X-ray absorption near edge structure (XANES) were utilized for the As and Fe speciation analysis. Results showed that both As(V) and As(III) can retard the transformation of ferrihydrite. The concentration and speciation of As strongly influenced the mineralogy and morphology of produced crystalline Fe oxyhydroxides. The higher As(V) loading (Fe/As = 40–100) resulted in the conversion of most ferrihydrite to lepidocrocite instead of goethite. The adsorbed As(III) showed weak effect on the re-crystallization of ferrihydrite at the early stage. A considerable fraction of As(III) (70–80%) was oxidized to As(V) during the Fe(II) catalyzed transformation of As(III)-adsorbed ferrihydrite. The oxidation of As(III) to As(V) in turn retarded the transformation of the remaining ferrihydrite to goethite and induced the production of a small amount of lepidocrocite. A temporary release of As(V) was observed during the first 5 days and the released As(V) was re-adsorbed back to the crystalline products, whereas no As was released to the aqueous phase in the As(III)-ferrihydrite systems. During the re-crystallization of ferrihydrite, 1 M phosphate-extractable As decreased quickly by up to 90% in the solid phase, indicating that partial As transformed to more stable phase. Our results suggested that Fe(II)-catalytic transformation of As-adsorbed ferrihydrite could help reducing the mobility and toxicity of As in anoxic aquifers.

Surficial arsenic redistribution above gold-mineralised zones in East Otago, New Zealand

ABSTRACTGroundwater-driven clay alteration of gold-mineralised Otago Schist has caused leaching and redistribution of arsenic (As). At Macraes mine in East Otago, there is a zone of alteration up to 50 m thick beneath a Cretaceous-Cenozoic regional unconformity where hydrothermal As concentrations >1000 ppm have decreased to <150 ppm. Where periglacial aeolian silt (loess) overlies mineralised Otago Schist, As has migrated in near-surface groundwater to form geochemical enrichment anomalies in loess and colluvium, with As concentrations locally as high as 500 ppm. Most As in the clay-altered basement and Pleistocene cover is closely associated with iron oxyhydroxide (HFO) and occurs as adsorbed As(V) on the HFO or as ferric arsenate minerals. However, initial As mobility was most effective as more soluble As(III) during oxidative transition from original sulphides to arsenate. Upward As migration into Pleistocene debris on the metre scale can facilitate location of gold-mineralised rocks that have been obscured by the young cover.

The behavior of chromium and arsenic associated with redox transformation of schwertmannite in AMD environment

Schwertmannites are metastable and often contaminated by chromium and arsenic. However, when schwertmannite is subjected to reducing conditions, the effect of reductive dissolution of schwertmannite coupled to the potential reduction of Cr(VI) or As(V) on the behavior of chromium and arsenic are less known. The present study systematically explored Fe(II)-induced transformation of schwertmannite with adsorbed CrO2-4 or AsO3-4 at pH 6.5, and the consequent redistribution of chromium and arsenic. The results show that adsorption of oxyanions obviously facilitated the release of schwertmannite-bound SO42− from both the mineral surface and the lattice structure via SO42--exchange. Adsorbed chromate and arsenate both inhibited the Fe(II)-induced transformation of schwertmannite. CrO2-4 -schwertmannite persisted as the dominant mineral phase for up to 30 d as a consequence of Fe(II) consumption and coverage of Cr(III)-Fe(III) hydroxide. In contrast, AsO3-4-schwertmannite transformed to poorly crystalline goethite via an intermediate lepidocrocite in 4 mM Fe(II) treatment. Both sorption and redox processes of Cr(VI) imprisoned chromium on schwertmannite. Transformation of AsO3-4-schwertmannite caused no re-mobilization of arsenic into solution, indicating the repartition to secondary minerals. Reduction of Cr(VI) to Cr(III) by Fe(II) would greatly lower the environmental hazard of chromium, and the persistence of As(V) would limit the toxicity of arsenic. These findings will help to understand the geochemical behavior of the important toxic Cr(VI) and As(V) specifically in the environmental systems with cyclic redox conditions.

Effect of iron reduction by enolic hydroxyl groups on the stability of scorodite in hydrometallurgical industries and arsenic mobilization.

Scorodite (FeAsO4·2H2O) is an important arsenic-bearing solid waste in hydrometallurgical industries, but its stability in reducing environments is not well understood. This study investigated the effect of Fe(III) reduction by enolic hydroxyl groups on the stability of scorodite and arsenic mobilization at various pH values and ascorbic acid/scorodite molar ratios (AH2/Sc). The results showed that 47-89% Fe(III) reduction by ascorbic acid caused approximately 10-69% (~37-260mgL-1) arsenic release and 4.5-63% (~13-176mgL-1) Fe(II) release at pH 5-8. The releases of arsenic and Fe(II) increased with increasing AH2/Sc, whereas they decreased as pH increased. The results of the solid characterization and chemical analysis indicated that the mixture of poorly crystalline parasymplesite and probably amorphous FeHAsO4⋅xH2O was the new arsenic sink. The high solubility of this ferrous arsenate with the Fe(II)/As(V) molar ratio >1 was deemed to be a major contributor to the relatively high arsenic release. This work differed from our previous finding that almost all arsenic was retained in the solid phase after similar Fe(III) reduction in scorodite with hydroquinone. Phenolic hydroxyl groups complexed with aqueous Fe(II), unlike enolic hydroxyl groups, was possibly the dominant reason for the formation of different secondary minerals, which strongly influenced arsenic redistribution between aqueous and solid phases.

Fixation and redistribution of arsenic during early and late diagenesis in the organic matter-rich members of the Lockatong Formation, Newark basin, USA: implication for the quality of groundwater

The Byram and Walls Island members in the lower and upper sections, respectively, of the Lockatong Formation in the Newark basin near the border between Pennsylvania and New Jersey were chosen to assess (i) the role of euxinic/anoxic conditions in sequestering arsenic (As) and other trace elements and (ii) the redistribution of these elements during catagenetic transformations. ἀese members are rich in organic matter and host pyrite which occurs as disseminations, small patches, and subparallel veins. ἀe sulfur isotope values of pyrite samples range between -7.5 and 0.5 ‰CDT (average = -3.5‰CDT). ἀe negative δ34S values are indicative of Bacterial Sulfate Reduction (BSR) under low temperature and euxinic/anoxic conditions. ἀe total organic carbon (TOC) values in this member ᴀuctuate between 0.5 and 2.1%. ἀese euxinic/anoxic conditions enhanced the incorporation of As and other trace elements in both organic matter and pyrite. ἀe As concentrations range from 13 to 800 mg/kg and from 1.4 to 34 mg/kg in pyrite and black shale samples, respectively. Rock Eval analyses reveal that organic matter is over-mature which altered the correlation between TOC and As. ἀe thermal cracking of organic matter resulted in the removal of these elements from organic matter and their subsequent incorporation in pyrite and bitumen. Organic matter- and pyrite-rich anoxic black shale layers and bitumen veins are potential sources of arsenic in groundwater in the Newark basin, with arsenic values that reach up to 215 μg/L.

Effect of ash composition on the partitioning of arsenic during fluidized bed combustion

The effect of the ash composition on the redistribution of arsenic in a coal combustion system was determined via both experimental laboratory simulations and thermodynamic equilibrium calculations. The experimental study was performed in a fluidized bed reactor in combustion temperature range of 500–1000°C. The results show that arsenic redistribution is strongly related to the chemical composition of coal in a combustion system. The presence of Fe, Ca, Mg, Al, Na and K favour arsenic retention, while Si causes an opposing effect. The arsenic retention on ash compositions is both temperature and amount dependent. With rising combustion temperature, the arsenic retention efficiency of Fe, Ca and Mg oxides augmented up to a maximum and then decreased, while those of Al, Na and K compounds continued expanding in the range of 500–1000°C. Chemical adsorption may be the primary mechanism for Fe, Ca, Mg, K and Na, while the adsorption of arsenic by Al may be ascribed to both physical and chemical adsorption. Arsenic is captured in ashes as a result of the formation of stable arsenate compounds arising from interactions with the inorganic matrix. The negative arsenic retention effect by silica is attributed to reactions with ash compositions which promote arsenic capture and the reduction of the solid arsenic compounds.

Atomic scale investigation of arsenic segregation in high-k metal gate stacks

The redistribution of arsenic in high-k metal gate stacks on fully depleted silicon was investigated. Both gates corresponding to n and p-type devices were analysed by atom probe tomography. Reconstruction shows the presence of arsenic at various interfaces. The most important accumulation is between the silicon and titanium nitride. This is confirmed by energy dispersive X-ray spectroscopy. The maximum concentration is in the order of 10%, with a thickness around 1nm. Interaction energies between dopants and interface have been estimated to be approximately 0.4eV. The arsenic is shown by X-ray photo-electron spectroscopy to be bonded to silicon throughout.