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     

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).     

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     

HG-AAS测定废水中微量As(Ⅲ)和As(Ⅴ)

在自然界水体中砷主要以无机的As(Ⅲ)和As(Ⅴ)的形态存在,而As(Ⅲ)的毒性比As(Ⅴ)大得多[1],因此必须对As(Ⅲ)和As(Ⅴ)分别测定才能可靠评价砷的毒性及其生物重要性[2-4]。目前砷的化学形态分析方法很多,萃取法、巯基棉富集分离法、离子交换法[5]等可实现砷的形态分析,但操作复     

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.     

Preservation of As(III) and As(V) in some water samples

This paper reports on the behavior of arsenite [As(III)] and arsenate [As(V)] in some water samples at storage under several conditions (pH=2/natural pH, 4°C/20°C). The investigation was carried out using⁷³As as a radiotracer for both forms and with the aid of earlier developed simple speciation methods for differentiation between arsenite and arsenate. Although arsenate is the thermodynamically stable arsenic form, it was observed that arsenate in deionized water is completely converted to the trivalent state; this phenomenon took place in about one week. By monitoring the radioactive As(III) and As(V) over a period of one month in two natural water samples, a fresh water and a sea water sample, it could be concluded that no adsorption occurs on the surface of polyethylene containers, independent of storage conditions. During that period, storage at natural pH values results for both water samples in a gradual oxidation of As(III); the oxidation rate is higher for storage at 20°C. At pH=2 As(III) is fairly stable in fresh water at both storage temperatures. However, in sea water a fast oxidation of As(III) is observed (complete oxidation within 3 d at both temperatures). As(V) is stable at all storage conditions studied.     

纳米二氧化钛对砷(Ⅲ)和砷(Ⅴ)吸附性能的研究

研究了纳米二氧化钛对As(Ⅲ)和As(Ⅴ)的吸附行为。结果表明：纳米二氧化钛在pHl—10范围内对As(Ⅲ)和As(Ⅴ)的吸附率可达99％。另外还考察了吸附时间、吸附体积、共存元素对吸附率的影响。此研究对合砷废水的处理、痕量砷的分离、分析有较高的应用价值。     

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 aqueous As(III) and As(V) by hydrous titanium dioxide

Dissolved arsenic in drinking water is a global concern as it causes serious health problems. The purpose of this research was to study the applicability of an industrial intermediate product, a mixture of titanium hydroxide and titanium dioxide for removing aqueous arsenic. The material is common, inexpensive, and non-toxic, making it an attractive choice for drinking water purification. The kinetics and equilibrium of removing both primary inorganic arsenic forms, As(III) and As(V), were studied by separate batch experiments. The tested material functioned well in removing both of these arsenic forms. The apparent values for Langmuir monolayer sorption capacities were 31.8 mg/g for As(III) and 33.4 mg/g for As(V) at pH 4. The studied TiO(2) performed the best in acidic conditions, but also reasonably well in other pH conditions.     

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.     

Surface speciation of As(III) and As(V) in relation to charge distribution

The adsorption of As(III) and As(V) on goethite has been studied as a function of pH and loading. The data can be successfully described with the charge distribution (CD) model (extended Stern layer option) using realistic species observed by EXAFS. The CD values have been derived theoretically. Therefore, the Brown bond valence approach has been applied to MO/DFT optimized geometries of a series of hydrated complexes of As(III) and As(V) with Fe(III) (hydr)oxide. The calculated ionic CD values have been corrected for the effect of dipole orientation of interfacial water, resulting in overall interfacial CD coefficients that can be used to describe the surface speciation as a function of pH and loading. For As(III), the main surface species is a bidentate complex and a minor contribution of a monodentate species is found, which is in agreement with EXAFS. The CD values have also been fitted. Such an analysis of the adsorption data resulted in the same surface species. The fitted CD values for the bidentate complex points to the presence of strong AsO bonds with the surface and a weaker AsOH bond with the free OH ligand. This agrees quantitatively with the MO/DFT optimized geometry. Interpretation of free fitted CD values for As(V) binding suggests that the main surface species is a non-protonated bidentate complex (B) with a contribution of a singly protonated surface complex (MH) at sub-neutral pH and high loading. In addition, a protonated bidentate surface complex (BH) may be present. The same species are found if the theoretical CD values are used in the data analysis. The pH dependency of surface speciation is strongly influenced by the charge attribution of adsorbed species to the electrostatic surface plane while the effect of loading is primarily controlled by the amount of charge attributed to the 1-plane, illustrating the different action of the CD value. The MO/DFT geometry optimizations furthermore suggest that for As(V) the B, MH and BH surface complexes may have very similar AsFe distances which may complicate the interpretation of EXAFS data.     

Arsenic Speciation in As(III)- and As(V)-Treated Soil Using XANES Spectroscopy

Arsenic (As) is a toxic trace element that occurs naturally in groundwater and soils. Understanding the reactions of arsenite (As(III)) and arsenate (As(V)) with soil and mineral surfaces is critical for predicting the fate and transport of As in the environment and developing better ways to remediate As-contaminated areas. This investigation uses X-ray absorption near edge spectroscopy (XANES) to evaluate the solid phase oxidation state and mineral surface binding sites in three agricultural soil samples from California, USA by fitting linear combinations of XANES spectra derived from several synthetic and well characterized As(III)- and As(V)-treated model compounds (Fe and Al metal hydroxides and aluminosilicate illite clay mineral). The results suggest that As(III) is either partially or completely oxidized to As(V) when reacted with soil in an aqueous, batch reaction. The As(III)-treated Aiken soil was composed of 60% As(III) attached to surfaces similar to lepidocrocite (γ-FeOOH)) and 40% As(V) attached to aluminosilicate (illite). The Fallbrook soil completely oxidized As(III) and the product was As(V) adsorbed on Al hydroxide (gibbsite, γ-Al(OH)₃) (62%), illite (16%), and lepidocrocite (γ-FeOOH) (22%). The reaction of As(III) with Wyo soil resulted in 42% As(III) adsorbed on surface similar to goethite and 58% As(V) adsorbed on lepidocrocite. Arsenic(V) adsorption on soil resulted in stable As(V) surface complexes that were well described by XANES spectra from As(V) adsorption complexes on gibbsite, illite, and lepidocrocite.     

Oxidant-sorbent system for potable water purification to remove As(III) and As(V) oxyanions

Sorption system based on a hydride material produced by impregnation of a fibrous polyacrylonitrile anion-exchanger with potassium permanganate was studied. Tests on purification of potable water to remove tri- and pentavalent arsenic compounds were performed and demonstrated a degree of purification to below the maximum permissible concentrations established by regulations of the World Health Organization.     

Simultaneous capillary electrophoretic separation and detection of P(V) and As(V) As heteropoly-blue complexes

A capillary electrophoretic (CE) method was developed for the simultaneous determination of P(V) and As(V). A Mo(VI)-ascorbic acid reagent reacted with a mixture of trace amounts of P(V) and As(V) to form the corresponding heteropoly-blue complexes in 0.05 M acetate buffer (pH 3.5). When 0.05 M malonate buffer was used as a migration buffer, the peaks due to their migrations were well separated in the electropherogram, and the pre-column complex-formation reaction was applied to the simultaneous CE determination of P(V) and As(V) with direct UV detection at 220 nm. With the proposed method, the calibration curves were linear in the concentration range of 5 x 10(-7) - 1 x 10(-4) M, with a detection limit of 1 x 10(-7) M (a signal-to-noise ratio of 3). Interference from foreign ions was also discussed.     

New Solids in As-O-Mo,As(P)-O-Mo(W) and As(P)-O-Nb(W) Systems That Exhibit Nonlinear Optical Properties

Interactions between well-mixed fine powders of As₂O₃, P₂O₅, MoO₃, WO₃ and Nb₂O₅ at different stoichiometry in quartz ampoules under vacuum at ~1000 °C in the presence of metallic molybdenum (or niobium), over several weeks, led to shiny dichroic crystalline materials being formed in cooler parts of the reaction vessel. An addition of small quantities of metals-Mo or Nb-was made with the aim of partially reducing their highly oxidized Mo(VI), W(VI) or Nb(V) species to corresponding Mo(V), W(V) and Nb(IV) centers, in order to form mixed valence solids. Sublimed crystals of four new compounds were investigated using a variety of techniques, with prime emphasis on the X-ray analysis, followed by spectroscopy (diffusion reflectance, IR, Raman and EPR), second harmonic generation (SHG), thermal analysis under N₂ and air atmosphere, and single crystals electrical conductivity studies. The results evidenced the formation of new complex solids of previously unknown compositions and structures. Three out of four compounds crystallized in non-centrosymmetric space groups and represent layered 2D polymeric puckered structures that being stacked on each other form 3D lattices. All new solids exhibit strong second-harmonic-generation (SHG effect; based on YAG 1064 nm tests with detection of 532 nm photons), and a rare photosalient effect when crystals physically move in the laser beam. Single crystals’ electrical conductivity of the four new synthesized compounds was measured, and the results showed their semiconductor behavior. Values of band gaps of these new solids were determined using diffusion reflectance spectroscopy in the visible region. Aspects of new solids’ practical usefulness are discussed.     

氢化物发生-原子荧光光谱法测定环境水样中的砷(Ⅲ)、砷(Ⅴ)

用氢化物发生-原子荧光光谱法测定环境水样中的砷(Ⅲ)和砷(Ⅴ),在0～100μg/L范围内砷的浓度与荧光强度呈线性关系,相关系数r=0.9999.测定结果的相对标准偏差为0.7%,检出限为0.08μg/L.与二乙氨基二硫代甲酸银光度法进行比对,经F检验和t检验,两种方法无显著性差异.     

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.     

氢化物发生-原子荧光光谱法测定环境水样中的砷（Ⅲ）、砷（V）

用氢化物发生-原子荧光光谱法测定环境水样中的砷(Ⅲ)和砷(V)，在0～100μg／L范围内砷的浓度与荧光强度呈线性关系，相关系数r=0．9999。测定结果的相对标准偏差为0．7％，检出限为0．08μg／L。与二乙氨基二硫代甲酸银光度法进行比对，经F检验和t检验，两种方法无显著性差异。     

Polarographic studies of catalytic reduction of hydrogen in Cr(VI)−As(III) and Cr(III)—As(III) systems

In the presence of traces of Cr(VI) or Cr(III) ions in ammonia or borate buffers containing the As(III) ions a catalytic hydrogen wave arises in the dc polarogram. It was established that the complex Cr(H₂AsO₃)_n^+3?n is formed in the solution, and that its reduced form adsorbed at DME is of catalytic activity. The wave can be employed for the determination of low concentrations (2×10^?8×10^?7M) of Cr(VI) and Cr(III) ions.     

Potentiometric determination of the standard potential of the As(V)/As(III) couple

The potential of the As(V)/As(III) half-cell was measured at 25 degrees with a glass electrode as reference electrode in order to eliminate the liquid-junction potential. Rapid and reproducible values could be obtained only in the presence of iodide, which increases the rate of electron-exchange between the two oxidation states of arsenic, but only at hydrogen-ion concentrations higher than about 0.5M. Extrapolation to zero ionic strength was therefore required to obtain the standard potential. A value of 573 +/- 2 mV was calculated for the half-reaction AsO(OH)(3) + 2e(-) + 2H(+) right harpoon over left harpoon As(OH)(3) + H(2)O.