Determination of the As(III)/As(V) ratio in soil by X-ray absorption near-edge structure (XANES) and its application to the arsenic distribution between soil and water.

The details of a method used to determine the As(III)/As(V) ratio in soil by arsenic K-edge XANES spectroscopy are described. The spectra of mixtures of NaAs(III)O2 and NaH2As(V)O4, conducted for an As(III)/As(V) calibration, were well-fitted by combining normalized spectra of NaAsO2 and Na2HAsO4, where the coefficients multiplied by the normalized spectra were identical to the molar ratio of As(III) and As(V) in the mixtures. XANES spectra of arsenic in soil samples could also be fitted by a linear combination of the spectra of NaAsO2 and Na2HAsO4, which enabled us to estimate the As(III)/As(V) in a soil containing 10.2 mg/kg arsenic. The As(III)/As(V) ratio in the soil was compared with that of a soil solution contacted with the soil determined by HPLC-ICP-MS, showing that As(III) is distributed to water more readily than As(V). The application of the XANES method is important for a better understanding of the behavior of As(III) and As(V) independently in a natural aquifer.     

Profile distribution of As(III) and As(V) species in soil and groundwater in Bozanta area

The profile distribution of arsenic(III) and arsenic(V) species in soil and groundwater was investigated in the samples collected in 2005 from a hand-drilled well, in the Bozanta area, Baia Mare region, Romania. The total content of arsenic in the soil was in the range of 525–672 mg kg⁻¹ exceeding 21–27 times the action trigger level for sensitive soil. 0.9–11.3 % of the total content was soluble in water, 83.0–92.6 % in 10 mol dm⁻³ HCl and 2.6–13.3 % was the residual fraction. Arsenic(V) was the dominant arsenic species in the soil in the range of 405–580 mg kg⁻¹. The distribution and mobility of arsenic species was governed by soil pH and contents of Al, Fe, and Mn. The mobility of arsenic(V) decreased with depth, while that of arsenic(III) was high at the surface and in the proximity of groundwater. The total concentration of arsenic in groundwater was (43.40 ± 1.70) μg dm⁻³, which exceeded the maximum contaminant level of 10 μg dm⁻³. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Surface arsenic speciation of a drinking-water treatment residual using X-ray absorption spectroscopy

Drinking-water treatment residuals (WTRs) present a low-cost geosorbent for As-contaminated waters and soils. Previous work has demonstrated the high affinity of WTRs for As, but data pertaining to the stability of sorbed As is missing. Sorption/desorption and X-ray absorption spectroscopy (XAS), both XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) studies, were combined to determine the stability of As sorbed by an Fe-based WTR. Arsenic(V) and As(III) sorption kinetics were biphasic in nature, sorbing >90% of the initial added As (15,000 mg kg(-1)) after 48 h of reaction. Subsequent desorption experiments with a high P load (7500 mg kg(-1)) showed negligible As desorption for both As species, approximately <3.5% of sorbed As; the small amount of desorbed As was attributed to the abundance of sorption sites. XANES data showed that sorption kinetics for either As(III) or As(V) initially added to solution had no effect on the sorbed As oxidation state. EXAFS spectroscopy suggested that As added either as As(III) or as As(V) formed inner-sphere mononuclear, bidentate complexes, suggesting the stability of the sorbed As, which was further corroborated by the minimum As desorption from the Fe-WTR.     

Sorption of As(V) on aluminosilicates treated with Fe(II) nanoparticles

Adsorption of arsenic on clay surfaces is important for the natural and simulated removal of arsenic species from aqueous environments. In this investigation, three samples of clay minerals (natural metakaoline, natural clinoptilolite-rich tuff, and synthetic zeolite) in both untreated and Fe-treated forms were used for the sorption of arsenate from model aqueous solution. The treatment of minerals consisted of exposing them to concentrated solution of Fe(II). Within this process the mineral surface has been laden with Fe(III) oxi(hydroxides) whose high affinity for the As(V) adsorption is well known. In all investigated systems the sorption capacity of Fe(II)-treated sorbents increased significantly in comparison to the untreated material (from about 0.5 to >20.0 mg/g, which represented more than 95% of the total As removal). The changes of Fe-bearing particles in the course of treating process and subsequent As sorption were investigated by the diffuse reflectance spectroscopy and the voltammetry of microparticles. IR spectra of treated and As(V)-saturated solids showed characteristic bands caused by Fe(III)SO(4), Fe(III)O, and AsO vibrations. In untreated As(V)-saturated solids no significant AsO vibrations were observed due to the negligible content of sorbed arsenate.     

Emulsion liquid membrane separation of As(III) and As(V)

Emulsion liquid membranes (ELM) consisting of L113A (surfactant), liquid paraffin (stabilizer) and kerosene (solvent), with HCl solution acting as the external phase and KOH solution acting as the internal phase, were applied to the prior separation of arsenic(III) and arsenic(V) with subsequent spectrophotometric determination by AgDDTC. The effect of various parameters on the recovery of arsenic(III) were investigated. 8 mol/L HCl was required for 95% As(III) recovery. After reduction of As(V) to As(III) with sufficient KI, total arsenic could be determined. The RSD of As(III) and As(total) were both less than 3%. The procedure was applied to aqueous samples with a recovery of 93.5%–101%. Received: 22 March 1998 / Revised: 12 September 1998 / Accepted: 17 September 1998     

Emulsion liquid membrane separation of As(III) and As(V)

Emulsion liquid membranes (ELM) consisting of L113A (surfactant), liquid paraffin (stabilizer) and kerosene (solvent), with HCl solution acting as the external phase and KOH solution acting as the internal phase, were applied to the prior separation of arsenic(III) and arsenic(V) with subsequent spectrophotometric determination by AgDDTC. The effect of various parameters on the recovery of arsenic(III) were investigated. 8 mol/L HCl was required for 95% As(III) recovery. After reduction of As(V) to As(III) with sufficient KI, total arsenic could be determined. The RSD of As(III) and As(total) were both less than 3%. The procedure was applied to aqueous samples with a recovery of 93.5%–101%. Received: 22 March 1998 / Revised: 12 September 1998 / Accepted: 17 September 1998     

N-(2-氨乙基)-月桂酰胺浮选铝硅酸盐矿物的研究

研究了N (2 氨乙基) 月桂酰胺对高岭石、伊利石和叶腊石等铝硅酸盐矿物的浮选行为.发现该表面活性剂对叶腊石的浮选回收率最高可达97.7％，对伊利石和高岭石的回收率相对较低，一般不超过82％.矿浆pH对高岭石、伊利石和叶腊石的回收率影响较小.酸性矿浆中表面活性剂通过静电引力吸附在矿粒表面；碱性矿浆中，表面活性剂通过氢键吸附在矿粒表面.红外吸收光谱证明，三种矿物表面中均存在－OH；在一个较宽的pH范围内，三种矿物矿浆的Zeta电位均为负值，表明矿粒表面荷负电.矿粒的扫描电镜（SEM）照片（×15000）表明，叶腊石主要呈薄片状颗粒，高岭石和伊利石颗粒呈不规则形状.     

Photometric measurement of trace As(III) and As(V) in drinking water

A simple, fast and sensitive light-emitting diode (LED)-based photometric method for the differential determination of ppb-ppm levels of As(III) and As(V) in potable water in the presence of ppm levels of phosphate was developed. The detection chemistry is based on the well-known formation of arsenomolybdate, followed by reduction to heteropoly blue. The front-end of the measurement system is configured to selectively retain P(V) and As(V), based on the considerable difference of the pK(a) of the corresponding acids relative to As(III). Thus, it is As(III) that is injected into the medium, oxidized in-line with KBrO(3) to As(V) and forms Mo-blue that is detected by an LED-based detector. Only As(III) is measured if the sample is injected as such; if all As in the sample is prereduced to As(III) (by the addition of cysteine, in a provided in-line arrangement), the system measures As(V)+As(III). In the present form, limit of detection (LOD) (S/N=3) is less than 8 mug l(-1) As, and the linear range extends to 2.4 mg l(-1). Potential interference from dissolved silica and Fe(III) is eliminated by the addition of NaF to the sample.     

Removal of As(III) and As(V) by natural and synthetic metal oxides

The removal properties of As(III) and As(V) by the several metal oxides having different mineral type and content of metals were investigated in batch and column reactors. The used metal oxides were Fe-oxide loaded sand (ILS), Mn-oxide loaded sand (MLS), activated alumina (AA), sericite (SC) and iron sand (IS). From the pH-edge adsorption experiments with AA and ILS, maximum As(III) adsorption was observed around neutral pH while As(V) adsorption was followed an anionic-type behavior. Among five metal oxides, AA showed the greatest removal capacity for both As(III) and As(V) through adsoption process but it has little oxidation capacity for As(III). Eventhough IS had much greater content of Fe-oxides than ILS, it showed a relatively lower removal capacity for both As(III) and As(V). This result suggests that adsorption of arsenic onto metal oxides is controlled by not only the contents of Fe-oxides but also mineral type of Fe-oxides. Column tests were performed at different combinations of metal oxides in a column reactor to find the best column system, which effectively treat both As(III) and As(V) at the same time. Among several combinations, the column reactors packed with MLS-AA and MLS-ILS showed a near complete oxidation of As(III) by MLS for a long time and the greatest adsorption of total arsenic compared to the column reactor packed with MLS-IS.     

Determination of As(III) and total as in water by graphite furnace atomic absorption spectrometry after electrochemical preconcentration on a gold-plated porous glassy carbon electrode

Arsenic(III) was preconcentrated in a flow-through electrochemical cell on a gold coated porous carbon electrode. On stripping, arsenic was eluted with diluted nitric acid and determined off-line by GF AAS. The deposition and stripping steps were optimized. The limit of detection and limit of quantification were found to be 1.9 μg L⁻1 and 6.4 μg L⁻¹, respectively. The repeatability and reproducibility were found to be 5.3 % and 9.3 %, respectively. Total arsenic was determined after a microwave assisted chemical reduction of As(V) to As(III) making the procedure suitable for speciation analysis. The method was applied in analysis of water samples.     

Determination of As(III) and As(V) in soils using sequential extraction combined with flow injection hydride generation atomic fluorescence detection

An analytical procedure for determination of As(III) and As(V) in soils using sequential extraction combined with flow injection (FI) hydride generation atomic fluorescence spectrometry (HG-AFS) was presented. The soils were sequentially extracted by water, 0.6 mol l⁻¹ KH₂PO₄ solution, 1% (v/v) HCl solution and 1% (w/v) NaOH solution. The arsenite (As(III)) in extract was analyzed by HG-AFS in the medium of 0.1 mol l⁻¹ citric acid solution, then the total arsenic in extract was determined by HG-AFS using on-line reduction of arsenate with l-cysteine. The concentration of arsenate (As(V)) was calculated by the difference. The optimum conditions of extraction and determination were studied in detail. The detection limit (3σ) for As(III) and As(V) were 0.11 and 0.07 μg l⁻¹, respectively. The relative standard deviation (R.S.D.) was 1.43% (n=11) at the 10 μg l⁻¹ As level. The method was applied in the determination of As(III) and As(V) of real soils and the recoveries of As(III) and As(V) were in the range of 89.3-118 and 80.4-111%, respectively.     

The Thermal Conversion of Lepidocrocite (γ-FeOOH) Revisited

The thermal conversion of lepidocrocite (γ-FeOOH) into maghemite (γ-Fe₂O₃)and hematite (α-Fe₂O₃) has been studied by dynamic (DSC) and static heating experiments. Dynamic heating defines two main regions: conversion of lepidocrocite to maghemite (endothermal signal peaking at 255°C) and conversion of maghemite to hematite (exothermal signal peaking at 450°C). In addition, an exotherm following the lepidocrocite to maghemite endotherm is observed. The maghemite phase appears as porous aggregates of nanocrystals characterized by an extensive spin-canting. We suggest that the additional exotherm is associated with structural changes and a decreasing extent of spin-canting in the maghemite phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of As(III) and arsenic(V) in natural waters by cathodic stripping voltammetry at a hanging mercury drop electrode

A simple, fast and quantitative method was developed for the determination of As(III) and total inorganic arsenic (As (total)) in natural spring and mineral waters using square wave cathodic stripping voltammetry (SWCSV) at a hanging mercury drop electrode (HMDE). In the determination of As(III), pre-concentration was carried out on the electrode from a solution of 1 mol/l HCl in the presence of 45 ppm of Cu(II) at a potential of −0.39 V versus Ag/AgCl, and the deposited intermetallic compound was reduced at a potential of about −0.82 V versus Ag/AgCl. In the determination of As (total) the pre-concentration was carried out in 1 mol/l HCl in the presence of 400 ppm of Cu(II) at a potential of −0.40 V versus Ag/AgCl, and the intermetallic compound deposited was reduced at a potential of about −0.76 V versus Ag/AgCl. For determination of As(III) the quantification limit was 0.2 ppb for a deposition time of 40 s, and the relative standard deviation (R.S.D.) was calculated to be 6% (n=13) for a solution with 8 ppb of As(III). For As (total), the quantification limit was 2 ppb for a deposition time of 3 min, and the R.S.D. was calculated to be 3% (n=10) for a solution with 8 ppb of As(V). The method was validated by application of recovery and duplicate tests in the measurements of As(III) and As (total) in natural spring and mineral waters. For As (total), the results of the SWCSV method were compared with the results obtained by optical emission spectrometry with ICP coupled to hydride generation (OES-ICP-HG) good correlation being observed.     

Ammonium pyrrolidinedithiocarbamate-modified activated carbon micro-column extraction for the determination of As(III) in water by graphite furnace atomic absorption spectrometry

A simple and selective method using ammonium pyrrolidinedithiocarbamate modified activated carbon (APDC-AC) as solid phase extractant has been developed for speciation of As(III) in water samples. At pH 1.8–3.0, As(III) could be adsorbed quantitatively by APDC-AC, and then eluted completely with 2.0 mL of 0.1 mol L⁻¹ HNO₃, while As(V) could almost not be retained at pH 1–7. Effects of acidity, sample flow rate, concentration of elution solution and interfering ions on the recovery of As(III) have been systematically investigated. Under the optimal conditions, the adsorption capacity of APDC-AC for As(III) is 7.3 mg g⁻¹. The detection limit (3σ) of As(III) is 0.05 ng mL⁻¹ for graphite furnace atomic absorption spectrometry (GFAAS) with enrichment factor of 50, and the relative standard deviation (RSD) is 4.1% (n = 9, C = 5 ng mL⁻¹). The method has been applied to the determination of trace As(III) in water, and the recoveries of As(III) are 100 ± 10%. Correspondence: Yiwei Wu, Department of Chemistry and Environmental Engineering, Hubei Normal University, Huangshi 435002, P.R. China     

Utilization of anion exchange resin Spectra/Gel for separation of arsenic from water

Arsenic in drinking water is one of the most challenging health hazards facing mankind today. Arsenic is a naturally occurring carcinogen and creates epidemiological problems through chronic ingestion from drinking water. Arsenic is present in water primarily as As(III) or As(V). Removal of both As(III) and As(V) from water by adsorption on strong base anion-chloride has been studied. Arsenic concentration was measured by Inductively Coupled Argon Plasma (ICP) analysis. The resin was regenerated and the adsorbed arsenic fractions were eluted by using 2 M NaCl. The effect of different parameters that influence adsorption process, such as relative arsenic and resin concentrations, retention time, and pH, were investigated. Results obtained revealed that As(III) was poorly adsorbed, whereas As(V) was successfully retained on the resin. The adsorption process was optimized by using 1 g resin for 16 ppm As(V) at pH 9 for 30 min. The removal efficiency of As(V) was 99.2%.     

Trace determination of As(III) and As(V) in natural waters by differential pulse anodic stripping voltammetry

Summary Arsenic is deposited from acid solution onto a rotating gold electrode at a potential of –0.3 V vs. NCE and then stripped anodically. The peak current is linearly dependent on the As(III) concentration. Electroinactive As(V) is first reduced to As(III) by gaseous SO₂. Trace metals in amounts as usually present in (polluted) sea water do not interfere and the destruction of dissolved organic matter is usually not necessary. For a deposition time of 4 min the determination limit is approximately 0.2 g/l As. The relative standard deviation for As contents between 2 and 5 g/l lies between 6 and 10% depending on the amount of dissolved organic matter present and a good accuracy is obtained, i. e. well within 10% of the value expected when various aqueous samples are spiked with a standard As solution.

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Spurenbestimmung von As(III) und As(V) in natürlichen Wässern durch Differentialpuls-Anodic Stripping-Voltammetrie

Zusammenfassung Arsen wird aus saurer Lösung bei einem Potential von –0,3 V vs. NKE auf einer rotierenden Goldelektrode abgeschieden und anschließend anodisch wieder aufgelöst, wobei die Höhe des Strompeaks linear von der As(III)-Konzentration abhängig ist. As(V) ist nicht elektroaktiv und muß deshalb zuerst mit SO₂-Gas zu As(III) reduziert werden. Die normalerweise in belastetem Meerwasser vorliegenden Metallspuren und gelösten organischen Stoffe stören bei der Bestimmung nicht. Bei einer Anreicherungszeit von 4 min liegt die Bestimmungsgrenze bei ungefähr 0,2 g/l As. Die relative Standardabweichung für As-Gehalte zwischen 2 und 5 g/l liegt zwischen 6 und 10%, in Abhängigkeit vom Gehalt an gelösten organischen Stoffen. Die Richtigkeit der Methode ist gut, d. h. der Fehler lag unter 10%, wenn verschiedene, mit As-Standard aufgestockte Lösungen analysiert wurden.

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Dedicated to Prof. Dr. H. Weisz, University of Freiburg, on occasion of his 60th birthday     

Efficient polymers in conjunction with membranes to remove As(V) generated in situ by electrocatalytic oxidation

Electrochemistry and ultrafiltration membrane methods (electro‐oxidation and liquid phase polymer based retention technique LPR, respectively) were coupled to remove As(III) inorganic species from aqueous solutions. Our main objective was to achieve an efficient extraction of arsenic species by associating a polymer‐assisted liquid phase retention procedure, based on the As(V) adsorption properties of cationic water‐soluble polymers, with the electrocatalytic oxidation process of As(III) into its more easily removable analog As(V). The exhaustive oxidation of As(III)–As(V) was readily performed in high yield at iridium oxide film modified carbon felt electrodes in the presence of different water‐soluble poly(quaternary ammonium) salts acting also as supporting electrolyte. The progress of the macro‐scale oxidation of As(III)–As(V) was followed using iridium oxide film modified glassy carbon electrodes. Finally, a study on arsenic retention by LPR‐technique performed on fully oxidized solutions of arsenic, showing that complete (100%) retention of the arsenic could be achieved using a 20:1 polyammonium:As(III) mole ratio. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of As(III) and As(V) ions by chemiluminescence method

A new chemiluminescence (CL) method for the selective determination of As(III) and As(V) ions in aqueous solution has been studied using a FIA system. The method is based on the increased CL intensity with the addition of As(V) ion into a solution of lucigenin and hydrogen peroxide. The addition of As(III) ion into the solution did not change the CL intensity. Total concentration of As ions was determined after pre-oxidation of As(III) to As(V) with hydrogen peroxide in basic solution. The As(III) content was estimated by subtracting the content of As(V) ion from total As concentration. The effects of concentrations of KOH and H₂O₂, and flow rates of reagents on CL intensity have been investigated. The calibration curve for As(V) ion was linear over the range from 1.0×10^-2 to 10 μg/g, the coefficient of correlation was 0.997 and the detection limit was 5.0×10^-3 μg/g under the optimal experimental conditions.     

The successive polarographic determination of As(III) and As(V)

A method has been described for the successive polarographic determination of As(III) and As(V)in a sulphuric acid solution.A directly recorded polarogram shows a limiting current corresponding to the As(III) concentration, another polarogram, recorded with a second sample after reduction of As(V) to As(III) by hydrazine sulphate, gives a limiting current corresponding to the concentration As(II) + As(V).     

Differential preconcentration of arsenic(III) and arsenic(V) with thionalide loaded on silica gel

2-Mercapto-N-2-naphtylacetamide (thionalide) on silica gel is used for differential preconcentration of μg l^?1 levels of arsenic(III) and arsenic(V) from aqueous solution. In batch experiments, arsenic(III) was quantitatively retained on the gel from solutions of pH 6.5–8.5, but arsenic(V) and organic arsenic compounds were not retained. The chelating capacity of the gel was 5.6 μmol g^?1 As(III) at pH 7.0. Arsenic retained on teh column was completely eluted with 25 ml of 0.01 M sodium borate in 0.01 M sodium hydroxide containing 10 mg l^?1 iodine (pH 10). The arsenic was determined by silver diethyldithiocarbamate spectrophotometry. Arsenic(V) was subsequently determined after reduction to arsenic(III) with sulphite and iodide. Arsenic(III) and arsenic(V) in sea water are shown to be < 0.12 and 1.6 μg l^?1, respectively.