Anions In Groundwater Research Articles

The hydrochemical characteristics and quality assessment of groundwater in Shuangliao City, China

In this study, a hydrochemical investigation was conducted in Shuangliao city to identify the hydrochemical characteristics and the quality of groundwater using descriptive statistics and correlation matrices. And on that basis, combined with Analytic hierarchy process (AHP), an improved two-level fuzzy comprehensive evaluation method is used to evaluate the groundwater quality. The results indicate that the major cations and anions in groundwater are Ca2+ and HCO3-, respectively. The chemical types are mainly HCO3—Ca type water, some areas are complicated due to the influence of human activities. The evaluation results show that the water quality in the area is mostly III type water, and the groundwater quality in some areas is IV or V water due to the influence of primary geological conditions or human activities. The groundwater quality in the East Liaohe River Valley and Shuangliao urban area is relatively poor, and in the northwest part which is the saline alkali soil area is also relatively poor.

In situ bioremediation of 1,2-dibromoethane (EDB) in groundwater to part-per-trillion concentrations using cometabolism

1,2-Dibromoethane (ethylene dibromide; EDB) is a probable human carcinogen that was historically added to leaded gasoline as a scavenger to prevent the build-up of lead oxide deposits in engines. Studies indicate that EDB is present at thousands of past fuel spill sites above its stringent EPA Maximum Contaminant Level (MCL) of 0.05 μg/L. There are currently no proven in situ options to enhance EDB degradation in groundwater to meet this requirement. Based on successful laboratory studies showing that ethane can be used as a primary substrate to stimulate the aerobic, cometabolic biodegradation of EDB to <0.015 μg/L (Hatzinger et al., 2015), a groundwater recirculation system was installed at the FS-12 EDB plume on Joint Base Cape Cod (JBCC), MA to facilitate in situ treatment. Groundwater was taken from an existing extraction well, amended with ethane, oxygen, and inorganic nutrients and then recharged into the aquifer upgradient of the extraction well creating an in situ reactive zone. The concentrations of EDB, ethane, oxygen, and anions in groundwater were measured with time in a series of nested monitoring wells installed between the extraction and injection well. EDB concentrations in the six monitoring wells that were hydraulically well-connected to the pumping system declined from ~ 0.3 μg/L (the average concentration in the recirculation cell after 3 months of operation without amendment addition) to <0.02 μg/L during the 4-month amendment period, meeting both the federal MCL and the more stringent Massachusetts MCL (0.02 μg/L). The data indicate that cometabolic treatment is a promising in situ technology for EDB, and that low regulatory levels can be achieved with this biological approach.

The Use of a Polymer Inclusion Membrane for Arsenate Determination in Groundwater

A polymer inclusion membrane (PIM) containing the ionic liquid methyltrioctylammonium chloride (Aliquat 336) as the carrier has been used satisfactorily for the preconcentration of arsenate present in groundwater samples, allowing its determination by a simple colorimetric method. The optimization of different chemical and physical parameters affecting the membrane performance allowed its applicability to be broadened. The transport of As(V) was not affected by the polymer used to make the PIM (cellulose triacetate (CTA) or poly(vinyl chloride) (PVC)) nor the thickness of the membrane. Moreover, the use of a 2 M NaCl solution as a stripping phase was found to allow the effective transport of arsenate despite the presence of other major anions in groundwater. Using the PIM for the analysis of different groundwaters spiked at 100 μg L−1 resulted in recoveries from 79% to 124% after only 5 h of contact time. Finally, the validated PIM-based method was successfully applied to the analysis of waters containing naturally occurring arsenate.

Removal of Chromium(VI) from Groundwater Using Oil Shale Ash Supported Nanoscaled Zero-valent Iron

Oil shale ash(OSA) supported nanoscaled zero-valent iron(OSA-nZVI) was used as a rapid and efficient reductant for Cr(VI) reduction. The optimal mass ratio of nZVI to OSA and the optimal dosage were explored. The effects of initial pH, reaction temperature, initial Cr(VI) concentration, and common cations and anions in ground-water on Cr(VI) reduction were determined in batch experiments. The results show that the optimum initial pH is 5.0. The reaction temperature has a positive effect on Cr(VI) reduction while the real groundwater has a negative effect. Additionally, 84.22% Cr(VI) was still reduced by 3 g/L OSA-nZVI(1:2)(mass ratio of OSA to Fe0 was 1:2) within 120 min for 50 mg/L Cr(VI) under conditions of 10 oC and unadjusted pH.

Hydrochemical characteristics and quality assessment of groundwater for irrigation use in central and eastern Songnen Plain, Northeast China

The hydrochemical characteristics of groundwater in Songnen Plain's agricultural area were analyzed based on aquifer types and topography classification to evaluate irrigation suitability and factors influencing groundwater quality. Samples of different groundwater types and topographical conditions within the research area were collected and chemical indices, such as sodium adsorption ratio, %Na+, residual sodium carbonate, and magnesium hazard values, were calculated to assess the groundwater suitability for irrigation. The results indicated that groundwater was generally neutral, with low total dissolved solids and slightly high hardness; the dominant anion in groundwater was HCO3-, while Ca2+ was the relatively stable primary cation found in water samples from the high plain and river valley plain. The nitrate in groundwater significantly exceeded WHO drinking water standards, especially in the unconfined water of the high plain, which was due to the large-scale agricultural production activities in the eastern regions. The main reactions in the groundwater system were weathering and dissolution of carbonates and sulfates and ion-exchange reactions. Horizontal zoning in water chemical characteristics was prominent; from the high plain to river valley plain and low plain, the hydrochemistry gradually transitioned from HCO3-Ca-Na to HCO3-Na-Ca and HCO3-Na. Based on the chemical indices, the majority of samples were suitable for agricultural irrigation except for some in the western area with high salinity and sodium hazards. Treatment measures to groundwater and soil should be taken to reduce the possibility of soil salinization and promote crop growth in these latter regions.

An assessment of groundwater salinization in Haryana state in India using hydrochemical tools in association with GIS

Unplanned abstraction of groundwater due to various land use land cover activities and variations in monsoonal rainfall have greatly affected the availability and quality of groundwater resources in semi-arid regions of India. In the present study, a study of the hydrogeochemical characteristics of groundwater was undertaken in the Sonipat district of Haryana in India together with the use of stable isotope (δ18O and δD) measurements and GIS analysis. A total of 53 groundwater samples were collected from seven blocks of the district, and 14 water quality parameters and stable isotopes (δ18O and δD) were analysed to infer hydrogeochemical processes taking place in the area. The integration of hydrochemistry with GIS is very helpful to understand the factors governing in the area. The majority of the samples showed Na–Cl type of hydrochemical facies. The trilinear plot for major cations and anions in groundwater indicates dominance of sodium, calcium, chloride and bicarbonate ions. Nitrate plumes in the groundwater appear to be migrating in groundwater from the central and south-western parts of the area towards the urbanized areas. A total of 64% of the samples exceed the maximum permissible limit of 1.5 mg/L given by WHO for fluoride. Besides natural sources such as silicate and carbonate weathering, ion exchange, and reverse ion exchange, the leaching of surficial salts and untreated industrial wastes along with unregulated abstraction are contributing to poor groundwater quality in the study area. An assessment of saturation indices has shown that groundwater in the area is unsaturated with respect to anhydrite, halite and gypsum suggesting significant contribution of Ca2+, Mg2+ and other ions in the groundwater. A scatter plot of δ18O versus Cl also suggests mixing of saline water with fresh groundwater.

The effect of common groundwater anions on the aqueous corrosion of zero-valent iron nanoparticles and associated removal of aqueous copper and zinc

This work has investigated the influence of common groundwater anions (Cl−, NO3−, SO42− and HCO3−) on the corrosion behaviour and associated removal of copper (Cu) and zinc (Zn) ions onto nanoscale zero-valent iron particles (nZVI). After 16 week exposure to solutions containing each anion at 10mM concentrations, nZVI was observed to corrode into different iron (hydr)oxide phases (determined using XRD), depending upon the anion present: HNO3− produced goethite particles; NO3− produced predominantly magnetite/maghemite particles; both SO42− and Cl− produced a mixture of phases, including magnetite/maghemite, lepidocrocite and goethite. For solutions containing the different anions and 0.3mM concentrations of Cu or Zn, near-total metal removal onto nZVI was recorded in the initial stages of the reaction (e.g. <24h) for all systems tested. However, when Cl− and SO42− were also present significant subsequent desorption was recorded and attributed to the influence of anionic pitting corrosion. In contrast, no Cu or Zn desorption was recorded for batch systems containing NO3−, which was attributed to the enmeshment of Cu or Zn in a mixed-valent iron oxide shell. Results herein therefore demonstrate that NO3− could be utilised alongside nZVI to improve its long-term performance for in situ water treatment applications.

Hydrochemical Characteristics and Quality Assessment of Shallow Groundwater in Xincai River Basin, Northern China

In order to investigate the environmental conditions of groundwater in Xincai River Basin, and further contribute more to rational development and utilization as well as scientific management of groundwater, we analyzed hydrochemical characteristics of groundwater using descriptive statistics, correlation matrices and ion ratio coefficients, and on that basis, assessed the quality of groundwater with revised Nemerow comprehensive pollution index method. The results showed that the major cations and anions in groundwater are Ca2+ and HCO3-, respectively, and the average values and coefficient variations of groundwater parameters are relatively large (except pH), which means high concentration and large spatial variation. The average value of rCl-/rCa2+ ratios is small, indicating a good hydrodynamic condition. Strong correlation exists between NH4+ and Ca2+, implying they may have the same origin, and strong correlations also exist between TDS and the major elements, implying that the major elements contribute much to the salinity of groundwater and the tendencies among them follow a similar trend. The groundwater quality assessment results show that the shallow groundwater quality in Xincai River Basin is relatively poor, and about half of the shallow groundwater is not suitable for drinking, which may be caused by excessive use of chemical fertilizers.

Hydrochemistry for the Assessment of Groundwater Quality in Korea

Understanding of the aquifer hydraulic properties and hydrochemical characteristics of water is crucial for management plan and study skims in the target area, and flow motions and chemical species of groundwater are regarded as precious information on the geological history of the aquifers and the suitability of various usages. Cations and anions of groundwater are used to estimate the characteristics and origin of groundwater. In this study, we try to evaluate the quality of groundwater based on the comparison of the physiochemical characteristics and distribution of cations and anions in groundwater from rural areas. Therefore we focused on the evaluation of groundwater as some specific purposes such as agricultural and industrial use, general types of groundwater, lithological origin of chemical component in groundwater. In this point of view, major objectives of this study were grouped as following three categories: 1) quality assessment of groundwater as a special usage (agricultural, industrial); 2) determination of groundwater types; 3) tracing of ion sources of groundwater. The quality of agricultural water was evaluated using SAR, sodium (%), RSC, PI, SSP, MH, PS, and Kelly’s ratio, and was classified as SAR (Excellent (100%)), Sodium ((Excellent (34%), Good (55%), Permissible (9%), Doubtful (1.6%), Unsuitable (0.4%)), RSC (Good (95.7%), Medium (3.5%), Bad (0.8%)), PI((Excellent (40.6%), Good (59%), Unsuitable (0.4%)), SSP ((Excellent (26.3%), Good (59.8%), Fair (13.1%), Poor (0.8%)), MH ((Acceptable (94.4%), Non-Acceptable (5.6%)), Kelly’s Ratio ((Permissible (93%), Non-Permissible (7%)), PS ((Excellent to Good (98%), Good to Injurious (1.2%), and Injurious to Unsatisfactory (0.2%)). Evaluation based on the Wilcox diagram was classified as “excellent to good” or “good to permissible”, and the water quality evaluated using the U.S. salinity Laboratory’s Diagram was classified as C1S1 (Excellent/Excellent) and C2S1 (Good/Excellent). And, in the applications of two factors of Langelier Saturation Index (LSI) and Corrosive ratio (CR), we could get similar results for defining the suitabilities of groundwater for the industrial purpose. And the groundwater samples were also classified groundwater using the Piper diagram and estimated the origin of ions using the Gibbs and Chadah diagram, and the classifications based on the Piper diagram showed that the types of the groundwater are type and type. And, estimation of dominance type (evaporation, rock, precipitation) based on the Gibbs diagram showed that the origin of anion and cation in groundwater are from the rock-dominance, and the estimation of origin of anions using the Chadha diagram showed that the most of the ionic species was originated from the interactions between alkaline earths and alkali metals contained in the soil. And through the source-rock deduction followed by the comparison of Gibbs and Chadah diagram, it was shown that the chemical components in the groundwater were mostly induced from the water-rock deduction and major types of groundwater samples following the Chadah diagram were categorized such as following group types: dolomite type, gypsum type, alkaline and alkaline earth type.

Glass composite waste forms for iodine confined in bismuth-embedded SBA-15

The aim of this study was to stabilize bismuth-embedded SBA-15 that captured iodine gas by fabrication of monolithic waste forms. The iodine containing waste was mixed with Bi2O3 (a stabilizing additive) and low-temperature sintering glass followed by pelletizing and the sintering process to produce glass composite materials. Iodine volatility during the sintering process was significantly affected by the ratio of Bi2O3 and the glass composition. It was confirmed that BiI3, the main iodine phase within bismuth-embedded SBA-15, was effectively transformed to the mixed phases of Bi5O7I and BiOI. The initial leaching rates of iodine from the glass composite waste forms ranged 10−3–10−2 g/m2 day, showing the stability of the iodine phases encapsulated by the glassy networks. It was also observed that common groundwater anions (e.g., chloride, carbonate, sulfite, and fluoride) elevated the iodine leaching rate by anion exchange reactions. The present results suggest that the glass composite waste form of bismuth-embedded SBA-15 could be a candidate material for stable storage of 129I.

Hydrogeological and hydrogeochemical control of groundwater salinity in an arid inland basin: Dunhuang Basin, northwestern China

High groundwater salinity has become a major concern in the arid alluvial plain of the Dunhuang Basin in northwestern China because it poses a significant challenge to water resource management. Isotopic and geochemical analyses were conducted on 55 water samples from springs, boreholes and surface water to identify potential sources of groundwater salinity and analyse the processes that control increasing salinity. The total dissolved solid (TDS) content in the groundwater ranged from 400 to 41 000 mg/l, and high TDS values were commonly associated with shallow water tables and flow-through and discharge zones in unconfined aquifers. Various groundwater contributions from rainwater, agricultural irrigation, river water infiltration and lateral inflows from mountains were identified by major ions and δD and δ18O. In general, HCO3− and SO42− were the dominant anions in groundwater with a salinity of 2500 mg/l. The major ion concentrations indicated that mineral weathering, including carbonate and evaporite dissolution, primarily affected groundwater salinity in recharge areas. Evapotranspiration controlled the major ion concentration evolution and salinity distribution in the unconfined groundwaters in the flow-through and discharge areas, although it had a limited effect on groundwater in the recharge areas and confined aquifers. Agricultural irrigation increased the water table and enhanced evapotranspiration in the oasis areas of the basin. TDS and Cl became more concentrated, but H and O isotopes were not enriched in the irrigation district, indicating that transpiration dominated the increasing salinity. For other places in the basin, as indicated by TDS, Cl, δD and δ18O characteristics, evaporation, transpiration and water–rock interactions dominated at different hydrogeological zones, depending on the plant coverage and hydrogeological conditions. Groundwater ages of 3H, and δD and δ18O compositions and distributions suggest that most of the groundwaters in Dunhuang Basin have a paleometeoric origin and experienced a long residence time. These results can contribute to groundwater management and future water allocation programmes in the Dunhuang Basin. Copyright © 2015 John Wiley & Sons, Ltd.

Low Alloy X100 Pipeline Steel Corrosion and Passivation Behavior in Bicarbonate-Based Solutions of pH 6.7 to 8.9 with Groundwater Anions: An Electrochemical Study

This research investigates the fundamental corrosion and passivation processes occurring on API-X100 pipeline steels before, during, and after passive layer formation in bicarbonate-based simulated soil solutions of pH 6.7 to 8.9. Free corrosion potentials decrease exponentially with bicarbonate (and pH), owing to increased water and bicarbonate reduction in more alkaline conditions and the coupled iron oxidation reaction. Active corrosion rates at potentials slightly above open circuit potential increase with bicarbonate, until a concentration of 1.68 g L−1 sodium bicarbonate (plus dilute amounts of chlorides/sulfate) at which first signs of film formation appear. Thereon, increased bicarbonate concentration generally decreases current densities and resists ferrous-oxide product formations due to improved iron carbonate formation conditions precipitating more durable passive layers. Potentiodynamic polarization in the anodic regime reveals varying electrochemical processes involving interactions between hydroxide, carbonate, and oxide complexes with ferrous, with diverse pH and potential dependencies. The products of corrosion reactions were investigated by scanning electron microscopy, X-ray diffraction, and/or X-ray photoelectron spectroscopy.

Effects of nitrate on the treatment of lead contaminated groundwater by nanoscale zerovalent iron

Nanoscale zerovalent iron (nZVI) is efficient for removing Pb2+ and nitrate from water. However, the influence of nitrate, a common groundwater anion, on Pb2+ removal by nZVI is not well understood. In this study, we showed that under excess Fe0 conditions (molar ratio of Fe0/nitrate>4), Pb2+ ions were immobilized more quickly (<5min) than in nitrate-free systems (∼15min) due to increasing pH. With nitrate in excess (molar ratio of Fe0/nitrate<4), nitrate stimulated the formation of crystal PbxFe3−xO4 (ferrite), which provided additional Pb2+ removal. However, ∼7% of immobilized Pb2+ ions were released into aqueous phase within 2h due to ferrite deformation. Oxidation–reduction potential (ORP) values below −600mV correlated with excess Fe0 conditions (complete Pb2+ immobilization), while ORP values ≥−475mV characterized excess nitrate conditions (ferrite process and Pb2+ release occurrence). This study indicates that ORP monitoring is important for proper management of nZVI-based remediation in the subsurface to avoid lead remobilization in the presence of nitrate.

Effect of geochemical properties on degradation of trichloroethylene by stabilized zerovalent iron nanoparticle with Na-acrylic copolymer

Stable nanoscale zero-valent iron (NZVI) particles have been developed to remediate chlorinated compounds. The degradation kinetics and efficiency of trichloroethylene (TCE) by a commercial stabilized NZVI with Na-acrylic copolymer (acNZVI) were investigated and compared with those by laboratory-synthesized NZVI and carboxymethyl cellulose (CMC)-stabilized NZVI particles. Results show that the degradation of TCE by acNZVI was faster than that by NZVI and CMC-NZVI. Increase in temperature enhanced the degradation rate and efficiency of TCE with acNZVI. The activation energy of TCE degradation by acNZVI was estimated to be 23 kJ/mol. The degradation rate constants of TCE decreased from 0.064 to 0.026 min−1 with decrease in initial pH from 9.03 to 4.23. Common groundwater anions including NO3−, Cl−, HCO3−, and SO42− inhibited slightly the degradation efficiencies of TCE by acNZVI. The Na-acrylic copolymer-stabilized NZVI, which exhibited high degradation kinetics and efficiency, could be a good remediation agent for chlorinated organic compounds.

The transformation of hexabromocyclododecane using zerovalent iron nanoparticle aggregates

Hexabromocyclododecane (HBCD), an emerging contaminant, is a brominated flame retardant that has been widely detected in the environment. In this study, nanoscale zerovalent iron (NZVI) aggregates are firstly used to treat HBCD and its removal under different geochemical conditions is evaluated. HBCD is almost removed from solutions by NZVI, with a kSA of 4.22×10−3Lm−2min−1. An increase in the iron dosage and temperature increases the removal rate. The activation energy for the removal of HBCD by NZVI is 30.2kJmol−1, which suggests that a surface-chemical reaction occurs on NZVI. HBCD is adsorbed on the NZVI surface, where electrons were transferred to HBCD, and consequently forms byproducts with less bromide. Three common groundwater anions decrease the reaction kinetics and efficiency of NZVI. The kobs of HBCD in the presence of anions is in the order: pure water >Cl−>NO3−≒HCO3−. The inhibitory effect of these anions may be a result of the possible complexation of anions with the oxidized iron surface. The oxidized sites on NZVI and oxidized species of iron also contribute to the removal of HBCD by adsorption on NZVI from solutions.

Geochemical Speciation Associated to Brine and Groundwater

Chemical speciation of brine and groundwater is examined to assess the distribution of chemical stability and behaviors of their solutions. Brine and groundwater are randomly collected from Ban Muang and Wanon Niwat District, Sakon Nakhon province. Hydrochemical parameters and also chemical compositions of their major ions are examined to evaluate the hydrochemical facies. Brine is generally indicated the Na-Cl type. For major cations, groundwater expresses mainly the sodium and calcium ions. However, brine presents dominantly sodium and potassium ions. Major anions of groundwater display principally the bicarbonate and chloride, but brine shows primarily the chloride and sulphate. The salinity zone of sodium chloride is confined only in the small area. The influence of rock salts in some areas is concerned. Relationship of Na+ and Cl-proves the stoichiometric balance of them. Chemical phases from the saturation indices consist of anhydrite, calcite, dolomite and gypsum, which found most in every sample. Generally, saturation condition of groundwater indicates the under saturation. Besides, saturation indices (SI) of brine state the super saturation for anhydrite. The anhydrite saturation index is obviously presented the supersaturated condition when the total dissolved solids (TDS) are greater than 250,000 mg/L.

Heat-activated persulfate oxidation of diuron in water

Heat-activated persulfate oxidation of diuron, a commonly found herbicide in groundwater, was evaluated in this study. Sulfate radicals SO4- was the principal oxidizing agent responsible for the diuron degradation. The diuron decomposition exhibited a pseudo-first-order kinetics pattern at all the conditions tested. The observed rate constants determined at 50–70°C well fit the Arrhenius equation, yielding an activation energy of 166.7±0.8kJmol−1. Temperature, persulfate dose, initial diuron concentration, pH, and three common groundwater solutes (CO32-,HCO3-, and Cl−), to different degrees, influenced the degradation. Typically, high temperature, high persulfate dose, and low initial diuron concentration increased the decomposition rate of diuron. At the tested pH range of 5.5–8.1, the highest degradation rate (kobs=0.18min−1) occurred at pH 6.3. The three groundwater anions inhibited the diuron decomposition with the following order: CO32->HCO3->Cl-. The major oxidation products in this study were C15H15ON3Cl4 (P3, m/z=376.2), C16H16O4N3Cl4 (P4, m/z=420.3), and C17H17O7N3Cl4 (P5, m/z=465.4), different from those produced during hydroxyl radical-induced advanced oxidation. The in situ chemical oxidation (ISCO) technology can be achieved in practice through combination with in situ thermal remediation.

Effects of common dissolved anions on the reduction of para-chloronitrobenzene by zero-valent iron in groundwater

Batch tests were conducted to evaluate the influences of several common dissolved anions in groundwater on the reduction of para-chloronitrobenzene (p-CNB) by zero-valent iron (ZVI). The results showed that p-CNB reduction was enhanced by both Cl(-) and SO(4)(2-). HCO(3)(-) could either improve or inhibit p-CNB reduction, depending on whether the mixing speed was intense enough to rapidly eliminate Fe-carbonate complex deposited on ZVI surface. Above a concentration of 100 mg L(-1), NO(3)(-) increased the p-CNB reduction rate. The reduction rate by ClO(4)(-) decreased because the ClO(4)(-) competed with p-CNB for electrons. The p-CNB reduction was inhibited by PO(4)(3-), SiO(3)(2-) and humic acid, in the order humic acid < PO(4)(3-) < SiO(3)(2-), since these ions could form inner-sphere complexes on iron surface. The reaction even ceased when the ion concentrations were greater than 4, 0.5, and 30 mg L(-1), respectively. The results indicated that common dissolved anions in groundwater should be taken into account when ZVI is applied for contaminated groundwater remediation.

An ATR–FTIR study of carbonate sorption onto magnetite

AbstractCarbonate is one of the most abundant anions in ground water. It also appears as saturated concentration in the process water at LKAB, a mining company in the northern part of Sweden. Sorption of carbonate on magnetite (the major source of iron ore in this company) may affect the surface chemistry of the iron oxide by forming a carbonate surface instead of an oxide surface. This would affect the interactions between magnetite particles and other species dissolved in the process water. Attenuated total reflection Fourier transform infrared spectroscopy (ATR–FTIR) has proved to be a useful technique in the study of adsorption/desorption properties of ions in mineral processing and environmental science. Magnetite was synthesized by coprecipitation of Fe II and Fe III in alkaline solution and deposited on a ZnS internal reflection element. Adsorption of carbonate on magnetite, and the effect of pH, Na, Ca, and silicate ions on the amount and speciation of adsorbed carbonate was monitored in situ. Adsorption of carbonate onto magnetite was found to increase with the acidity of the solution from pH 8.5 to pH 6.5 and also increased with increasing calcium concentration from 0 to 1.0 mM. The spectroscopy results were discussed and compared with previous findings in the literature. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Chemical Transformations during Aging of Zerovalent Iron Nanoparticles in the Presence of Common Groundwater Dissolved Constituents

Nanoscale zerovalent iron (NZVI) that was aged in simulated groundwater was evaluated for alterations in composition and speciation over 6 months to understand the possible transformations NZVI could undergo in natural waters. NZVI was exposed to 10 mN of various common groundwater anions (Cl(-), NO(3)(-), SO(4)(2-), HPO(4)(2-), and HCO(3)(-)) or to dissolved oxygen (saturated, approximately 9 mg/L). Fresh and exposed NZVI samples, along with Fe-oxide model compounds, were then analyzed using synchrotron radiation X-ray absorption spectroscopy (XAS) to yield both relative oxidation state, using the X-ray absorption near edge structure (XANES), and quantitative speciation information regarding the types and proportions of mineral species present, from analysis of the extended X-ray absorption fine structure (EXAFS). Over 1 month of aging the dissolved anions inhibited the oxidation of the NZVI to varying degrees. Aging for 6 months, however, resulted in average oxidation states that were similar to each other regardless of the anion used, except for nitrate. Nitrate passivated the NZVI surface such that even after 6 months of aging the particles retained nearly the same mineral and Fe(0) content as fresh NZVI. Linear least-squares combination fitting (LCF) of the EXAFS spectra for 1 month-aged samples indicated that the oxidized particles remain predominantly a binary phase system containing Fe(0) and Fe(3)O(4), while the 6 month aged samples contained additional mineral phases such as vivianite (Fe(3)(PO(4))(2).8H(2)O) and iron sulfate species, possibly schwertmannite (Fe(3+)(16)O(16)(OH,SO(4))(12-13).10-12H(2)O). The presence of these additional mineral species was confirmed using synchrotron-based X-ray diffraction (XRD). NZVI exposed to water saturated with dissolved oxygen showed a rapid (<24 h) loss of Fe(0) and evolved both magnetite and maghemite (gamma-Fe(2)O(3)) within the oxide layer. These findings have implications toward the eventual fate, transport, and toxicity of NZVI used for groundwater remediation.