三价铁离子浓度对As(V)-Fe(II)-Fe(III)体系沉淀臭葱石的影响

在常压、95℃、初始pH=1.5的条件下,研究了As(V)–Fe(II)–Fe(III)体系中初始Fe(III)浓度对砷的去除率和臭葱石合成的影响。结果表明,溶液中初始Fe(III)/As(V)摩尔比为0时,沉淀产物为结晶度良好的臭葱石,但砷的去除率仅为24.3%,沉淀浸出砷浓度高于国标规定的浓度限值5 mg/L。溶液中初始Fe(III)/As(V)摩尔比大于0时,在升温过程中生成了无定形砷酸铁,当初始Fe(III)/As(V)摩尔比不超过1.6时,砷酸铁反应8 h后转化为臭葱石;随初始Fe(III)/As(V)摩尔比增大,砷的去除率增大,臭葱石沉淀的结晶度降低、浸出砷浓度降低;其中,初始Fe(III)/As(V)摩尔比为0.8和1.6时,臭葱石沉淀的浸出砷浓度低于5 mg/L,适合安全堆存。当初始Fe(III)/As(V)摩尔比大于1.6时,无定形砷酸铁反应8 h仍不能转化成臭葱石,砷的去除率降低,沉淀浸出砷浓度超标,不适合安全堆存。     

Arsenic adsorption on Ti‐pillared montmorillonite

BACKGROUND: Arsenic pollution in drinking water has been found in most countries. Arsenate (As(V)) and arsenite (As(III)) are two major forms of inorganic arsenic species, and the latter is the more toxic. The removal of arsenic ions from water has attracted increased attention, and therefore further understanding and development of techniques for removal of arsenic ions are required. RESULTS: Adsorption of arsenate and arsenite from aqueous solutions using Ti‐pillared montmorillonite (Ti‐MMT) was investigated as a function of contact time, pH, temperature, coexisting ions, and ionic strength. The adsorption of both arsenate and arsenite were temperature and pH dependent, indicating different adsorption mechanisms. The effect of coexisting ions on the adsorption was also studied and, among the ions investigated, only phosphate had a noticeable influence on the adsorption of arsenate, while the effect of other ions was negligible. A pseudo‐second‐order chemical reaction model was obtained for both arsenate and arsenite; adsorption isotherms of arsenate and arsenite fitted the Langmuir and Freundlich isotherm models well. X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS) were used to study the nature of surface elements before and after adsorption. CONCLUSIONS: This work demonstrates that Ti‐pillared montmorillonite is an efficient material for the removal of arsenate and arsenite from aqueous solutions. Experimental parameters such as contact time, solution pH, temperature, initial concentration, coexisting ions, and ionic strength have been optimized. Copyright © 2010 Society of Chemical Industry     

镁铝阴离子粘土对砷酸根离子的吸附作用

利用共沉淀水热法制备了镁铝阴离子粘土材料，研究了其水溶液对砷酸根离子的去除能力。结果表明：镁铝阴离子粘土对砷酸根离子具有较高的去除率和吸附容量、较快的吸附速度。砷酸根离子的吸附平衡数据很好的符合Freundlich型吸附等温方程。同时，吸附动力学数据完全符合Lagergren二级速度方程。吸附砷酸根离子后的阴离子粘土材料，用稀NazCO3溶液可以很好的洗脱再生。阴离子粘土对砷酸根离子的吸附属于层间离子交换作用。     

Exploration of As(III)/As(V) Uptake from Aqueous Solution by Synthesized Calcium Sulfate Whisker

Although common calcium-containing minerals such as calcite and gypsum may fix arsenic, the interaction between modified calcic minerals and arsenic has seldom been reported. The uptake behavior of As(III)/As(V) from aqueous solutions by calcium sulfate whisker (CSW, dihydrate or anhydrite) synthesized through a cooling recrystallization method was explored. A series of batch experiments were conducted to examine the effect of pH, reaction time, whisker dosage, and initial As concentration. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the samples prepared. The results showed that pH of the aqueous solution was an important parameter for As(III)/As(V) uptake, and an excellent removal efficiency could be achieved under strongly alkaline condition. The data from batch experiments for reaction of As(V) with calcium sulfate dihydrate whisker (CSDW) and calcium sulfate anhydrous whisker (CSAW) were well described with extended Langmuir EXT1 model, from which theoretic maximum adsorption capacity of 46.57 mg As(V)·(g CSDW)^− 1 and 39.18 mg As(V)·(g CSAW)^− 1 were obtained. Some calcium arsenate solids products, such as CaAsO₃(OH) (weilite, syn), Ca₃(AsO₄)₂ (calcium arsenate), CaO–As₂O₅, Ca–As–O, Ca₅(AsO₄)₃OH·xH₂O (calcium arsenate hydroxide hydrate), and CaH(AsO₄)·2H₂O (hydrogen calcium arsenic oxide hydrate), were detected at pH = 12.5 through XRD analysis. This indicates that the interaction mechanism between As(V) and CSW is a complex adsorption process combined with surface dissolution and chemical precipitation.     

Development of an Electrochemical Device for Removal of Arsenic from Drinking Water

The forthcoming introduction of lower standards for arsenic in drinking water requires new technologies for arsenic removal. We report the development of an electrochemical unit for remediating domestic water supplies for homes without municipally treated water. Electrolysis in a two‐anode system provides oxidants to convert As(III) to As(V) in situ, and a sacrificial anode to deliver iron into solution. Conditioning tanks after each electrolysis step ensure completion of the chemical reactions. At the pH of domestic water, As(V) co‐precipitates with Fe(OH)₃; subsequent filtration leaves <10 ppb of inorganic arsenic in solution.     

Treatment of simulated arsenic contaminated groundwater using GAC‐Cu in batch reactor: Optimization of process parameters

This article deals with the experimental investigation related to the removal of arsenic from a simulated contaminated groundwater by the adsorption onto Cu²⁺ impregnated granular activated carbon (GAC‐Cu) in presence of impurities like Fe and Mn. The effects of adsorbent concentration, pH, and temperature on the percentage removal of total arsenic (As(T)), As(III), and As(V) have been discussed. Under the experimental conditions, the optimum adsorbent concentration for GAC‐Cu has been found to be 6 g/L with an agitation time of 24 h, which reduces the As(T) concentration from 188 to 8.5 µg/L. Maximum removal of As(V) and As(III) has been observed in the pH range of 7–9 and 9–11, respectively. Removal of all the above said arsenic species decreases slightly with increase in temperature. Presence of Fe and Mn increases the adsorption of arsenic species. Under the experimental conditions, at 30°C, maximum % removals of As(T), As(III), As(V), Fe, and Mn are found to be 95.5%, 93%, 98%, 100%, and 40%, respectively. It has also been observed that maximum regeneration (～94%) of spent GAC‐Cu is exhibited by a 5NH₂SO₄ solution.     

Arsenic Removal from Aqueous Solution by Iron Oxide-Coated Biomass: Common Ion Effects and Thermodynamic Analysis

Abstract

A batch study showed that the presence of anions (sulfate, chloride, and nitrate) in solution did not affect the adsorption process of both As(V) and As(III) by iron oxide-coated A. niger biomass. It was found that the presence of Ca²⁺, Fe²⁺, and Mg²⁺ ions at a concentration of 200 mg/L in solution could increase the removal efficiency of As(V) by 86.5%, 95.4%, and 65.8%, respectively. Similarly, the presence of Ca²⁺, Fe²⁺, and Mg²⁺ ions at a concentration of 200 mg/L in solution could increase the removal efficiency of As(III) by 39.3%, 97%, and 8.4%, respectively. The batch adsorption-desorption study showed that the reactions between the arsenic species and the iron oxide-coated A. niger biomass were reversible. Desorption of As(V) and As(III) at neutral pH was approximately 15%. As(V) desorbed more than As(III) in acidic (pH 1.33) and alkaline (pH 12.56) solutions. At a pH of 1.33, 67% of the adsorbed As(V) desorbed, and the percentage of desorbed As(III) was only 47.1% in the same condition. At a solution pH of 12.56, 73.4% of the As(V), and 43.7% of As(III) desorbed. The thermodynamic study showed the spontaneous nature of the sorption of arsenic on IOCB. The high value of the heat of adsorption {ΔH ≈ ? 133 kJ/mol for As(V), and 88.9 k/mol for As(III)} indicated that the mechanism of arsenic sorption was chemisorption.     

Physicochemical Characterization of Granular Ferric Hydroxide (GFH) for Arsenic(V) Sorption from Water

Abstract

Physical and chemical characterization of granular ferric hydroxide (GFH) [e.g., scanning electron micrographs (SEM), X‐ray diffraction (XRD) analysis, Brunauer‐Emmett‐Teller (BET) and Langmuir surface area measurements, pore size distribution, pH titration, and zeta potential measurements] were conducted to determine its performance as an adsorbent for trace arsenic(V) removal. Speciation diagrams for arsenate and phosphate were produced for the present system. The equilibrium adsorption isotherms were measured over initial arsenate concentrations ranging from 100–750 µg/L and the pH range of 4–9. The adsorption of arsenate was found to decrease as the pH of the solution was increased, thus giving the optimal adsorption of arsenate onto GFH at pH 4. Adherence to the Langmuir isotherm was found at all pHs for the arsenate adsorption. The competitive effect of phosphate on the uptake of arsenate at pH 4 by GFH was investigated, outlining the greater affinity of GFH for arsenate adsorption compared to phosphate. The kinetic performance of GFH was assessed and the results were analyzed by applying a particle diffusion model.     

Shewanella sp. O23S as a Driving Agent of a System Utilizing Dissimilatory Arsenate-Reducing Bacteria Responsible for Self-Cleaning of Water Contaminated with Arsenic

The purpose of this study was a detailed characterization of Shewanella sp. O23S, a strain involved in arsenic transformation in ancient gold mine waters contaminated with arsenic and other heavy metals. Physiological analysis of Shewanella sp. O23S showed that it is a facultative anaerobe, capable of growth using arsenate, thiosulfate, nitrate, iron or manganite as a terminal electron acceptor, and lactate or citrate as an electron donor. The strain can grow under anaerobic conditions and utilize arsenate in the respiratory process in a broad range of temperatures (10–37 °C), pH (4–8), salinity (0%–2%), and the presence of heavy metals (Cd, Co, Cr, Cu, Mn, Mo, Se, V and Zn). Under reductive conditions this strain can simultaneously use arsenate and thiosulfate as electron acceptors and produce yellow arsenic (III) sulfide (As₂S₃) precipitate. Simulation of As-removal from water containing arsenate (2.5 mM) and thiosulfate (5 mM) showed 82.5% efficiency after 21 days of incubation at room temperature. Based on the obtained results, we have proposed a model of a microbially mediated system for self-cleaning of mine waters contaminated with arsenic, in which Shewanella sp. O23S is the main driving agent.     

活性炭负载Fe(III)吸附剂去除饮用水中的As(V)

利用活性炭负载水合铁氧化物制备了复合吸附剂,并用于饮用水中As(V)的去除. 研究了活性炭种类、粒度、溶液pH值、Fe(III)盐浓度和干扰离子等对As(V)去除的影响. 结果表明,煤质活性炭作为基质负载水合铁氧化物比椰壳炭和果壳炭具有更好的除砷效果. 随着炭粒度降低,除砷效率显著增加. 在pH 3~9范围内,活性炭负载水合铁氧化物可有效吸附As(V). F-, Cl-, SO42-的加入对As(V)的去除效率基本无影响,而SiO32-和PO43-则明显抑制As(V)的去除. Langmuir模型比Freundlich模型能更好地描述复合吸附剂对As(V)的吸附平衡. 动力学研究表明,As(V)吸附反应可用二级速率方程描述.     

Removal of As(V) from aqueous solutions by waste crab shells

Waste crab shell, which has some functional groups like -NHCO or NO₂ groups, was used as an adsorbent to remove arsenate ions (As (V)). The functional groups in crab shells were confirmed by FT-IR analysis. Waste crab shell had a high uptake capacity of 35.92 mg/g-dry mass for arsenate ion at pH 4, and the regression curve using the Langmuir isotherm equation fit well with the experimental data. The effects of pH, loading of crab shells, and time on uptake capacity of arsenate ions were also investigated. The adsorption capacity of arsenate ions was increased as the pH value was increased because the amount of negative arsenic species increased as the pH value was increased. Waste crab shells could remove arsenate ions of about 45% with 0.5 g of loading amount, and adsorption of arsenate ions was almost completed in 30 min when initial concentration of arsenate ions was 100 and 9.3 mg/L, respectively. Considering recycling of crab shell, it could be an economical and promising adsorbent.     

Separation of tungstates from aqueous mixtures containing impurities (arsenate,phosphate and silicate anions) using ion flotation

Ion flotation, using dodecylamine as surfactant and magnesium ions as depressant agents, was found to be an effective method for the selective separation and recovery of tungstate from arsenate anions in dilute aqueous solutions. Arsenates represent the main impurity in tungsten-containing waste waters or leaching solutions of hydrometallurgical origin; magnesium chloride is a relatively common precipitant, used in tungsten hydrometallurgy. The main parameters affecting this process were investigated, namely concentrations of reagents (Mg²⁺ ions, dodecylamine, arsenate and tungstate), solution pH, co-existence and effective separation from other impurities, such as phosphate and/or silicate anions, and the effectiveness of the separation process in solutions of high ionic strength (using NaCl and Na₂SO₄ salts). It was found that at pH range between 2 and 5, tungstate anions can be quantitatively recovered from aqueous mixtures containing arsenates, phosphates and silicates, while the co-removal of the impurities was below 20%.     

Propylene polymerization by using TiCl4 catalyst supported on solvent‐activated Mg(OEt)2

Solvent activation of Mg(OEt)₂ in ethanol with carbon dioxide was carried out in a 1‐L three‐neck flask under nitrogen atmosphere, to investigate structural changes of Mg(OEt)₂ support. During activation of Mg(OEt)₂ by ethanol and CO₂, a suspension mixture was converted to a clear solution and CO₂ was inserted into the Mg? O bond of Mg(OEt)₂, to form magnesium ethyl carbonate. The solid supports were obtained from the removal of solvents by heating, during which CO₂ split off from the magnesium ethyl carbonate between 100 and 150°C. The structural changes of the obtained supports and the corresponding catalysts were checked by IR and TGA. The polymerization behavior of propylene with the catalyst and morphology of the obtained polymer were also examined. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 460–467, 2001     

Studies Relating to Removal of Arsenate by Electrochemical Coagulation: Optimization,Kinetics, Coagulant Characterization

The present investigation aims to remove arsenate [As(V)] by electrochemical coagulation using mild steel as anode and cathode. The results showed that the optimum removal efficiency of 98.6% was achieved at a current density of 0.2 A dm^?2, at a pH of 7.0. The effect of current density, solution pH, temperature, co-existing ions, adsorption isotherm, and kinetics has been studied. Kinetics reveals that the removal of arsenate by electrochemical coagulation is very rapid in the first 15 min and remains almost constant with the progress of reaction. The adsorption kinetics obeys the second-order rate expression. An equilibrium isotherm was measured experimentally and the results were analyzed by Langmuir, Freundlich, Dubinin- Redushkevich, and Frumkin using the linearized correlation co-efficient. The characteristics parameters for each isotherm were determined. The Langmuir adsorption isotherm was found to fit the equilibrium data for arsenate adsorption. Temperature studies showed that the adsorption was endothermic and spontaneous in nature.     

Removal of arsenate from ionic mixture by anion exchanger water-soluble polymers combined with ultrafiltration membranes

This study shows the influence of Cl^?, SO₄ ^2?, NO₃ ^?, SiO₃ ^2?, Na⁺, and Ca²⁺ on arsenate removal by anion exchanger polymers using the liquid-phase polymer-based retention (LPR) technique. The LPR was carried out in the presence of anion exchanger soluble polymers containing quaternary ammonium salts. These polymers were characterized by NMR. Compared with As(V) removal from deionized water, the results showed that in the presence of ionic mixture, the As(V) removal capacity decreased. However, P(ClVBTA) showed As(V) removal ability of 91?% when the ionic mixture was used. Polymers with chloride exchanger groups showed a higher ability to remove arsenate than the polymer that contains methyl sulfate as anion exchanger group. At higher arsenate concentration (47.6?mg L^?1), arsenate retention by the water-soluble polymers ranged between 58 and 91?%. This removal capacity increased gradually reaching 100?% retention when the arsenate concentration in the cell was minimum (5.5?mg?L^?1). The values of maximum retention capacity were 264?mg?g^?1 for P(ClMPTA), 260?mg?g^?1 for P(ClVBTA), and 200?mg?g^?1 for P(ClAPTA) at the total filtrate volume of 300?mL. The charge–discharge process found to be suitable for saturate the polymer with As(V) and then eluting As(V) for regenerating the extracting capacity of polymer.     

沉淀法制备氢氧化镁及其对砷溶液的吸附特性

以蛇纹石制备的硫酸镁为镁源,以氨气为沉淀剂,常压下采用一步法制备氢氧化镁。对氢氧化镁吸附处理含砷(Ⅴ)废水进行了研究,考察了氢氧化镁用量、pH值、吸附时间及砷初始浓度等因素对砷(Ⅴ)去除效果的影响,并探讨了吸附作用机理。结果表明:氢氧化镁对废水中砷(Ⅴ)的去除率为76.45%,氢氧化镁对水溶液中砷(Ⅴ)的吸附量随吸附时间的变化规律符合Langmuir吸附等温模式,而吸附量随砷起始浓度的变化则符合Freundlich吸附等温模式。     

One step preparation of ZnFe2O4/Zn5(OH)6(CO3)2 nanocomposite with improved As(V) removal capacity

Novel adsorbents consisting of ZnFe₂O₄/Zn₅(OH)₆(CO₃)₂ (hydrozincite) nanocomposite materials were studied for efficient As(V) removal from water. Nanocomposites were synthesized by the co-precipitation of Zn and Fe salts in alkaline conditions. Depending on the Zn/Fe molar ratio, a variety of materials was produced with different ZnFe₂O₄/Zn₅(OH)₆(CO₃)₂ contents. The adsorbent’s efficiency for As(V) removal was enhanced proportionally to the percentage of Zn₅(OH)₆(CO₃)₂ content. The nanocomposite with 74 ± 7 wt% of Zn₅(OH)₆(CO₃)₂ provided a capacity of 18.4 μg As(V)/mg for residual concentration of 10 μg/L (pH 7) which is over twice that of an iron oxy-hydroxide prepared under similar conditions.     

Reinforcement of peroxide‐cured styrene–butadiene rubber vulcanizates by mathacrylic acid and magnesium oxide

Through the neutralization of magnesium oxide (MgO) and methacrylic acid (MAA), magnesium methacrylate [Mg(MAA)₂] was in situ prepared in styrene–butadiene rubber (SBR) and used to reinforce the SBR vulcanizates cured by dicumyl peroxide (DCP). The experimental results show that the mechanical properties, dynamic mechanical properties, optical properties, and crosslink structure of the Mg(MAA)₂‐reinforced SBR vulcanizates depend on the DCP content, Mg(MAA)₂ content, and the mole ratio of MgO/MAA. The formulation containing DCP 0.6–0.9 phr, Mg(MAA)₂ 30–40 phr, and MgO/MAA mole ratio 0.50–0.75 is recommended for good mechanical properties of the SBR vulcanizates. The tensile strength of the SBR vulcanizates is up to 31.4 MPa when the DCP content is 0.6 phr and the Mg(MAA)₂ content is 30 phr. The SBR vulcanizate have good aging resistance and limited retention of tensile strength at 100°C. The SBR vulcanizates are semitransparent, and have a good combination of high hardness, high tensile strength, and elongation at break. The T_g values of the SBR vulcanizates depend largely on the DCP content, but depend less on the Mg(MAA)₂ content and the MgO/MAA mole ratio. The contents of DCP, Mg(MAA)₂, and the MgO/MAA mole ratio have also great effects on the E′ values of the vulcanizates. The salt crosslink density is greatly affected by the Mg(MAA)₂ content and MgO/MAA mole ratio, but less affected by the DCP content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2667–2676, 2002     

Oxidized and Ethylenediamine-Functionalized Multi-Walled Carbon Nanotubes for the Separation of Low Concentration Arsenate from Water

In this work multiwalled carbon nanotubes (MWCNTs) modified by oxidation (o-MWCNTs) and by aminofunctionalization (e-MWCNTs) were examined as potential adsorbents for arsenate removal from water. Adsorption characteristics of raw and modified MWCNTs were investigated in batch adsorption experiments. The influence of solution pH (pH range 3–10), contact time, and temperature (25, 35, and 45°C) were studied. Ethylenediamine-functionalized MWCNTs have the greatest affinity for arsenate ions, followed by o-MWCNTs and raw-MWCNTs. The obtained experimental data for raw- and o-MWCNTs fitted Sips isotherm model, while for the e-MWCNTs, the Freundlich model provided the best fit to the experimental points. The maximum adsorption capacity for arsenate ions was achieved using e-MWCNTs, 12.18 mg g^?1. The presence of the arsenate on the adsorbent is confirmed by FTIR spectroscopy. Thermodynamic studies indicated the spontaneity and endothermic nature of the adsorption. Sodium hydroxide solution (0.1 M) was found to desorb about 70% of arsenate from e-MWCNTs. The results with spiked drinking water samples demonstrated that e-MWCNTs, due to the present basic and acidic groups, were very efficient for the removal of arsenate ions, as well as of some cations, at pH 4.     

Water‐soluble polymer and photocatalysis for arsenic removal

In this study, the photocatalytic oxidation of hazardous arsenite (As(III)) to arsenate (As(V)) and the sequential removal of arsenate from aqueous solution by liquid‐phase polymer‐based retention (LPR) were investigated. The photocatalytic oxidation of arsenite was performed using TiO₂ (P25 Degussa, Germany) under UV‐A light. The optimal photocatalytic conditions to oxidize 10 mg L^?1 of arsenite solution were achieved using a 0.5 g L^?1 of catalyst at a pH value of 2. The As(III) oxidation reached 100% after 30 min of illumination with UV‐A light. A water‐soluble polymer containing quaternary ammonium groups, poly(3‐acrylamidopropyl)trimethylammonium chloride (P(ClAPTA)), was used as an extracting reagent in the LPR process. To obtain the optimized conditions, the removal experiments were performed at various polymer : As(V) molar ratios using 10 mg L^?1 of arsenate solutions. After the oxidation of As(III) to As(V), the removal of arsenate by P(ClAPTA) was obtained in a 99% yield using a 20 : 1 polymer : As(V) molar ratio at a pH value of 9. The results demonstrate that the combination of these methods is highly useful for potential applications related to the treatment of wastewater contaminated with As(III). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40871.