Removal of arsenic from simulated groundwater by GAC‐Fe: A modeling approach

A study on kinetics and equilibrium is presented on the adsorption of arsenic species from simulated groundwater containing arsenic (As(III):As(V)::1:1), Fe and Mn in concentrations of 0.188 mg/L, 2.8 mg/L and 0.6 mg/L, respectively, by iron impregnated granular activated charcoal (GAC‐Fe). Also presented is the interaction effect of As, Fe and Mn on the removal of arsenic species from water, which simulates contaminated groundwater. Among conventional models, pseudo second‐order kinetic model and Freundlich isotherm were adequate to explain the kinetics and equilibrium of adsorption process, respectively. However, in comparison to conventional isotherm empirical polynomial isotherm provided a more accurate prediction on equilibrium specific uptakes of arsenic species. Effects of initial concentrations of As, Fe and Mn on the removal of total arsenic (As(T)), As(V) & As(III) have been correlated within the error limit of ?0.2 to +5.64%. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Arsenic adsorption from contaminated water on Fe(III)‐coordinated amino‐functionalized poly(glycidylmethacrylate)‐grafted TiO2‐densified cellulose

BACKGROUND: The main aim of this study is to determine the sorptive potential of a novel anion exchanger, Fe(III)‐coordinated amino‐functionalized poly(glycidylmethacrylate)‐grafted TiO₂‐densified cellulose (AM‐Fe‐PGDC) for arsenic(V) removal from aqueous solutions by batch technique. RESULTS: The adsorbent was characterized using infrared spectroscopy, powder X‐ray diffraction, scanning electron microscopy, thermogravimetry and potentiometric titrations. The effective pH for removal was 6.0. The adsorption rate was influenced by initial metal ion concentration and contact time. The equilibrium was achieved within 1.5 h and follows a pseudo‐second‐order kinetic model. The adsorption capacity for As(V) calculated using the Langmuir isotherm equation was 105.47 mg g^?1. The AM‐Fe‐PGDC developed was used to remove As(V) from simulated groundwater. Regeneration experiments were attempted for four cycles using 0.1 mol L^?1 NaCl solution. CONCLUSION: It was found that AM‐Fe‐PGDC is very efficient for the removal of As(V) from aqueous solutions. © 2012 Society of Chemical Industry     

Iron Oxide-Coated on Glass Fibers for Arsenic Removal

A highly efficient adsorbent for arsenic removal from water has been prepared by impregnating high surface area iron oxides on glass fibers. Arsenic in water can easily and efficiently be removed by this adsorbent, without the need to pre-oxidize As(III) to As(V). The iron oxides coated on glass fibers (IOCGFs) can remove both arsenic species well below EPA MCL (10 ppb). IOCGFs should have the following four additional advantages: greatly improved contact efficiency; higher adsorption capacity because of high surface area; low cost and easily available adsorbent since the starting reagents (FeCl₃ and NH₃·H₂O) and glass fiber are cheap and readily available; and high adsorption efficiency of As(III) and As(V).     

Equilibrium and dynamic studies of the removal of As(III) and As(V) from contaminated aqueous systems using a functionalized biopolymer

BACKGROUND: A study of the removal of arsenic from a sample of actual groundwater using crosslinked xanthated chitosan is described. RESULTS: Removal of As(III) and As(V) was studied at pH 7.5 under equilibrium and dynamic conditions. The equilibrium data were fitted to Langmuir and Freundlich adsorption models and the various model parameters evaluated. The monolayer adsorption capacity from the Langmuir model for xanthated chitosan flakes (XCF) (As(V) 20.0 ± 0.56 mg g^?1; As(III) 33.0 ± 0.32 mg g^?1) were lower than obtained for xanthated chitosan granules (XCB) (As(V) 36.0 ± 0.52 mg g^?1; As(III) 48.0 ± 0.45 mg g^?1). Adsorption of As (V) was unaffected by the presence of other anions while in the case of As(III) the presence of sulfate and silicate caused a 26.5–50.9% decrease in adsorption. A sample (940 bed volumes) of a groundwater spiked with 200 µg L^?1 As(V) treated with XCF in column experiments reduced the arsenic concentration to < 10 µg L^?1. The adsorbent was also successfully applied for the removal of total inorganic arsenic down to < 10 µg L^?1 from real samples of arsenic‐contaminated groundwater. CONCLUSION: Xanthated chitosan was an efficient adsorbent for the removal of both forms of arsenic from groundwater under near neutral conditions. The presence of sulfur and the amino groups resulted in increased adsorption capacity of the sorbent. Copyright © 2012 Society of Chemical Industry     

Kinetic Modeling of Arsenic Removal from Water by Ferric Ion Loaded Red Mud

A laboratory study was conducted to investigate the ability of ferric ion loaded red mud (FRM) for the removal of arsenic species from water. The adsorbent material was characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. For an initial arsenic concentration lower than 0.3 mg/L, the FRM with a dosage of 1 g/L was able to reduce As(III) at pH 7 below 10 µg/L, the maximum contaminant level (MCL) of arsenic in drinking water set by the World Health Organization. In the case of As(V) removal, FRM was also particularly effective in reducing the initial arsenic concentration value of 1 mg/L at pH 2, below the MCL requirement of arsenic for drinking water. According to kinetic sorption data, the initial stage of adsorptions of As(III) and As(V) onto FRM were mainly governed by the external diffusion mechanism; however, upon saturation of the external adsorbent surface, the arsenic species were eventually adsorbed by intraparticle diffusion mechanism. The present results are promising for using the very inexpensive FRM as a low-cost material that is effective in remediating drinking waters contaminated with low concentrations of arsenic species. We report here the sorption kinetics and adsorption mechanisms of As(III) and As(V) on the FRM that has not been decsribed previously.     

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。     

Solar‐light assisted removal of arsenic from natural waters: effect of iron and citrate concentrations

The optimal conditions to remove arsenic(III) from a solution were fitted using a factorial experimental design in a reaction catalysed by visible light (black light, 360 nm) and an iron‐citrate complex. Experiments were performed by simultaneously modifying the two variables affecting the removal of arsenic, i.e. iron and citrate concentrations. The single polynomial function obtained with the factorial design methodology indicates that the iron concentration was the most critical parameter in the removal of arsenic by precipitation. Mathematically, it was determined that the optimum molar ratio for arsenic, citrate and iron was 1:4.5:18.7, respectively, over 90% of arsenic being eliminated after 4 h of irradiation. The comparison between the As(III) and As(V) co‐precipitation rates indicates that almost 80% of As(III) was removed after 1 h of irradiation with black light, while As(V) required 4 h of irradiation to reach the same value. When natural water containing approximately 1 mg L⁻¹ of arsenic, only as As(V), was irradiated with solar light under optimised conditions, approximately 95% of the arsenic was removed after 1 h of irradiation. Copyright © 2006 Society of Chemical Industry     

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.     

Synthesis of the cotton cellulose based Fe(III)-loaded adsorbent for arsenic(V) removal from drinking water

A novel macroporous bead adsorbent, Fe(III)-loaded ligand exchange cotton cellulose adsorbent [Fe(III)LECCA], is synthesized for selective adsorption of arsenate anions [As(V)] from drinking water in batch and column systems. As(V) adsorption on Fe(III)LECCA was independent of pH, especially in drinking water pH range. Film diffusive control mechanism will benefit As(V) exchange with Fe(III)LECCA whether in batch or in column experiments. When treating the tap water at 26.0 BV/h, the column still preserves 83% of the original saturation adsorption capacity of the As(V) aqueous solution. These results have indicated that Fe(III)LECCA has the potential to act as an adsorbent for the removal of As(V) from drinking water considering its availability, nontoxicity and cost-effectiveness.     

Arsenic removal from water by photocatalytic functional Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> porous ceramic

Fe₂O₃–TiO₂ porous ceramic (Fe/TiPC) beads with photo-catalytic performances and high adsorption capacities were prepared by a simple high temperature solid reaction and were applied for arsenic removal from drinking water. The microstructure and morphology of Fe/TiPC were characterized by X-ray diffraction and scanning electron microscopy. More than 90% removal ratio for As (III) and As (V) were respectively achieved by Fe/TiPC within 2 h under UV irradiation. The Langmuir capacity values of Fe/TiPC for As (III) and As (V) were 13.86 and 15.73 mg/g, respectively. In addition, Fe/TiPC could be reused for up to five times without significant reduction in the photocatalytic sensitivity and adsorption capacity aspects. Good catalytic oxidation performances and high adsorption capacities as well as a sample preparation for Fe/TiPC suggest that the composites may have practical prospects for the As (III) and As (V) removal from contaminated water.     

Arsenic removal through adsorption, sand filtration and ultrafiltration: In situ precipitated ferric and manganese binary oxides as adsorbents

This study proposes a process consisting of in situ precipitated ferric and manganese binary oxides (FMBO) adsorption, sand filtration, and ultra-filtration (UF) for arsenic removal. Bench scale studies indicate that the FMBO shows higher capability of removing arsenic than hydrous ferric precipitate (HFO) and hydrous manganese oxide (HMO). This is ascribed to the combined effects of oxidizing As(III) and adsorbing As(V) for FMBO. The continuous experiments indicate that this process is effective for arsenic removal. In the presence of 0.624 mg/L As(III), when the Fe(II) dosage is 3 mg/L and the KMnO₄ dosage is equivalent to the sum of As(III) and Fe(II), the residual As concentration is as low as 29.2 μg/L. The adsorption of arsenic onto FMBO is fast, and the hydraulic retention time (HRT) of 45 s is enough for the adsorption unit. Sand filtration leads to more than 90% of arsenic removal, and UF further removes the particulate arsenic that passes through the sand filter. During the backwashing of the sand filter, the maximal aqueous arsenic concentration is 0.105 mg/L (at 150 s), and the dissolution of arsenic from FMBO is neglectable. The main operating cost of this process is as low as 0.355 RMB/m³, which is acceptable in rural areas for arsenic removal in engineering.     

Modelling diffusion and adsorption of As species in Fe/GAC adsorbent beds

BACKGROUND: Arsenic decontamination of drinking water by adsorption is a simple and robust operation. When designing packed bed adsorbers for arsenic, the main problems are the slow diffusion kinetics of As in microporous media and the lack of simple equations for predicting the performance of the equipment. Commercial iron‐doped granular activated carbon adsorbents (Fe/GAC) for groundwater arsenic abatement were studied in this work. Basic parameters for arsenate (As^V) adsorption were measured and their performance at larger scale was simulated with an approximate analytical model. RESULTS: In the 0–300 µg_As L^?1 range, the As^V adsorption isotherm on Fe/GAC was found to be approximately linear. Assuming Henry's law for adsorption and homogeneous surface diffusion with constant diffusivity for intrapellet mass transfer, an approximate model for flow and adsorption of arsenate inside packed bed adsorbers was developed, and reduced to an analytic compact solution using the quasi‐lognormal distribution (Q‐LND) approximation. The use of this model with fitted and reported parameters enabled the approximate simulation of industrial adsorbers and home point‐of‐use filters. Results show that industrial adsorbers meet the breakthrough condition with incomplete utilization of the adsorbent unless convenient process configurations are used. In point‐of‐use systems with short residence times intraparticle diffusion would drastically reduce the adsorbent performance. CONCLUSION: Assuming linear adsorption of As^V over Fe/GAC, an analytical approximate solution for flow and adsorption in packed beds can be obtained. The model seems to represent correctly the main features of industrial and home filters, however, more experimental data is necessary for scale‐up purposes. Copyright © 2011 Society of Chemical Industry     

Arsenic removal from aqueous solutions with Fe-hydrotalcite supported magnetite nanoparticle

The sorptive removal of arsenic from water by synthetically-prepared magnetic Fe-hydrotalcite (M-FeHT) seeding by nano magnetite was investigated. The synthesis of M-FeHT was achieved by a co-precipitation method. M-FeHT was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and magnetic susceptibility analysis. Batch tests were conducted to investigate the removal mechanism of As(III) and As(V) by M-FeHT. Kinetic studies revealed that uptake of As(V) (95% removal) and As(III) ions occurs rapidly within the first 15 min, and slows thereafter. The adsorption data follow a pseudo-second-order kinetic model and fit the Langmuir isotherm well. The experimental results show that stable arsenic removal efficiency, and the capability to reduce As levels, make M-FeHT a suitable adsorbent for the treatment of As-polluted waters. After adsorption, tests were conducted with magnetic separation to determine the separability of M-FeHT from solution. At magnetic field intensity of 2 T, the efficiency of M-FeHT separation was 91%. Finally, after adsorption by M-FeHT, residual arsenic concentration decreased to less than 10 μg/L (i.e., below the threshold specified by the WHO). Fe-hydrotalcite-supported magnetite nanoparticles were not only more efficient in the removal of As but also in recovery by the magnetic separator.     

Removal of Arsenic(III), Chromium(III) and Iron(III) Traces from Hydrofluoric Acid Solutions by Specialty Anion Exchangers

The removal of As(III), Fe(III), and Cr(III) at trace levels from HF solutions by means of specialty ion exchange resins has been investigated. These impurities are usually found in technical‐grade HF, and they need to be removed to prepare metal‐free HF for the semiconductor industry. It was assumed that Fe(III) and As(III) species in dilute HF were present in anionic form, while Cr(III) was probably in neutral form, CrF₃. First, a selection of specialty ion exchangers was performed. Then, fixed‐bed experiments were carried out to check the ability of selected resins to reach the impurity levels required in SEMI C29 for 5 wt.% HF (5 ppb of As, and 10 ppb of Cr and Fe). The effect of the flow rate and the HF concentration on the metal removal was studied with Purolite D‐3777 and Fuji PEI‐CS‐07 resins respectively. Fuji PEI‐CS‐07 showed the best performance for Fe(III) removal, even at high HF concentration (25 wt.%). A strong decrease in the Cr(III) and As(III) removal capacity with increasing concentration of HF was observed.     

超声对铁锰氧化物吸附废水中无机砷的强化效应

快速吸附去除废水中无机砷的技术,由于其高效性成为污水处理领域亟需的一种技术。采用草酸沉淀法制备了不同铁锰比（物质的量比）的铁锰复合草酸盐,以铁锰复合草酸盐为前驱体通过热分解得到铁锰元素均匀分布的复合氧化物,以铁锰复合氧化物为吸附剂吸附去除废水中的无机砷。在超声波辅助下,铁锰复合氧化物对废水中无机砷的去除效果显著。实验结果表明,铁锰物质的量比为6:4的铁锰复合氧化物,因具有较高的比表面积（396.6 m²/g）和独特的形貌,超声辅助1 min对废水中无机砷的吸附率可达95%以上。吸附动力学研究表明,该吸附过程符合准二级动力学模型,吸附速率常数为1.11 g/（mg·s）。吸附剂再生实验表明,将吸附砷的吸附剂采用碳酸氢钠溶液洗脱重复用于吸附实验,吸附剂重复使用3次对砷的吸附率仍可达到83.6%。     

Nanofiltration Membrane Process for the Removal of Arsenic from Drinking Water

The removal of arsenic from drinking water by nanofiltration membranes was investigated. Experiments were conducted with tap water to which arsenate and arsenite were added. Two types of nanofiltration membranes, i.e., NF‐90 and NF‐200, have been tested. The effect of various operating conditions, e.g., applied pressure, feed concentration, pH and temperature, were also investigated. The pH and arsenic concentration in the feed and the operating temperature are found to be decisive factors in determining the arsenic concentration remaining in the permeate. The level of removal of As(V) was higher than 98 % for both membranes, but that of As(III) was much lower. It can be concluded that by controlling the operating parameters, source water containing As(V) may be recovered as drinking water to EPA maximum contaminant level quality standards, but that water containing As(III) must undergo a pre‐oxidation treatment before passing through the nanofiltration membrane in order to maintain drinking water quality.     

Effect of operating conditions on iron corrosion rates in zero-valent iron systems for arsenic removal

Owing to newly established water quality standards, the use of the zero-valent iron (ZVI) method for arsenic removal is gaining attention. The spontaneous chemical oxidation of ZVI by dissolved oxygen, a complex process involving a variety of metastable ferrous–ferric intermediate species, was studied in short-term batch experiments using two different commercially available ZVI materials. Differences in corrosion rates may be attributed to the different specific reactivity of these materials. The effects of pH, ZVI loading, initial conductivity and dissolved oxygen concentration on both Fe(II) and Fe(III) kinetic profiles were investigated. ZVI corrosion rates in the presence of As(III) and As(V) were also studied. Depending on the pH, the concentrations of Fe(II) and Fe(III) are significantly influenced by the presence of As(III) and As(V). Our results may be important from a technological point of view, since it is well known that iron corrosion rates govern the generation of sites for arsenic removal.     

Experimental and Numerical Modeling Studies of Arsenic Removal with Wood Ash from Aqueous Streams

Most of the arsenic removal processes are not cost‐effective and/or not efficient in removing As (III). In this research, it was found that Maple wood ash has the potential to adsorb both As (III) and As (V) from contaminated aqueous streams at low concentration levels without any chemical treatment. Static tests showed up to 80% arsenic removal and in various dynamic column tests the arsenic concentration was reduced from 500 ppb to lower than 5ppb. Finally, the ash column was modeled using the surface excess theory. The identified model significantly facilitates practical design of arsenic adsorption system.     

Is the Coagulation-Filtration Process with Fe(III) Efficient for As(III) Removal from Groundwaters?

The coagulation–filtration process using Fe(III) salts is the most frequently practiced technology for As(V) removal in full scale water treatment plants. The co-existing As(III) is usually oxidized to As(V) prior to removal. Nonetheless, research studies applying high As(III) initial concentrations showed significant As(III) removal capacities, however, the efficiency of the process for initial As(III) concentrations commonly encountered in drinking water, i.e., 10-100 μg/L is not sufficiently investigated. The experimental results of this study indicated that the coagulation–filtration process using Fe(III) can safely meet the drinking water regulation limit of 10 μg/L, only when the initial As(III) concentration is < 25 μg/L and the Fe(III) dose ≥ 5 mg/L, for experiments performed with NSF challenge water. The limitations for efficient As(III) removal are attributed to the fact that As(III), under circumneutral pH values is mostly present with the uncharged H₃AsO₃ form, which is not efficiently adsorbed onto iron oxy hydroxides (FeOOH), the product of Fe(III) hydrolysis. Adsorption isotherms data were best fitted to BET model, indicating multi-layer adsorption and low affinity of As(III) for Fe(III) hydroxides.     

Polyvinyl Pyrrolidone K25 Modified Fungal Biomass as Biosorbent for As(V) Removal from Aqueous Solution

Abstract

Biosorption experiments were carried out in batch and column mode for the removal of As(V) from aqueous solution using native, autoclaved and PVP treated Aspergillus clavatus biomass. The influence of process parameters such as contact time, As(V) concentration, adsorbent dosage, and pH have been investigated for As(V) adsorption. Maximum As(V) removal was observed with PVP K25 modified biomass (PVPAB) (80.25%) when compared to native (57%) and autoclaved (71.63%) biomass. PVPAB biomass required less time to reach equilibrium (90 min) whereas autoclaved and native biomass required 105 and 125 min to attain saturation respectively. The PVPAB showed maximum As(V) removal (Q₀ = 2.06 mg/g) and was used as adsorbent for column studies. Equilibrium isotherms were analyzed by Langmuir and Dubinin and Radushkevich isotherms. Kinetics of the adsorption process was studied using pseudo-first-order and second-order models and it was found to obey pseudo-second-order kinetic model. Desorption studies showed that PVPAB could be reused after regeneration and could lead to the development of viable and cost-effective technology for arsenic removal from ground water.