Removal Of Arsenic Species Research Articles

A coupled electrochemical process for schwertmannite recovery from acid mine drainage: Important roles of anodic reactive oxygen species and cathodic alkaline

The increasing need for sustainable acid mine drainage (AMD) treatment has spurred much attention to strategic development of resource recovery. Along this line, we envisage that a coupled electrochemical system involving anodic Fe(II) oxidation and cathodic alkaline production will facilitate in situ synthesis of schwertmannite from AMD. Multiple physicochemical studies showed the successful formation of electrochemistry-induced schwertmannite, with its surface structure and chemical composition closely related to the applied current. A low current (e.g., 50 mA) led to the formation of schwertmannite having a small specific surface area (SSA) of 122.8 m2 g−1 and containing small amounts of –OH groups (formula Fe8O8(OH)4.49(SO4)1.76), whereas a large current (e.g., 200 mA) led to schwertmannite high in SSA (169.5 m2 g−1) and amounts of –OH groups (formula Fe8O8(OH)5.16(SO4)1.42). Mechanistic studies revealed that the reactive oxygen species (ROS)-mediated pathway, rather than the direct oxidation pathway, plays a dominant role in accelerating Fe(II) oxidation, especially at high currents. The abundance of •OH in the bulk solution, along with the cathodic production of OH−, were the key to obtaining schwertmannite with desirable properties. It was also found to function as a powerful sorbent in removal of arsenic species from the aqueous phase.

Comparative Study Between Two Zeolitic Imidazolate Frameworks as Adsorbents for Removal of Organoarsenic, As(III) and As(V) Species from Water

Water-stable zeolitic imidazolate frameworks (ZIF) with zinc and cobalt cations were synthesized to explore the effect of metal ions on arsenic adsorption. At room temperature (25 2 ºC) and pH 7.8, maximum adsorption capacities of arsenic (As5+) on the surface of ZIF-8 and ZIF-67 were 87.03 and 86.70 mg g-1 respectively, with encouraging results up to 95% reusability of the adsorbents. The results of this study revealed that electrostatic attraction and ion exchange were the major mechanisms responsible for better efficiencies for adsorptive removal of arsenic. The evidence for the adsorption of arsenic contaminants was confirmed by FTIR analyses. The pseudo second order and Langmuir models were best suited to explain the adsorption of arsenic species on the surface of the as-synthesized metal-organic frameworks (MOFs). Based on the results, it was possible to conclude that the metal atoms in the synthesized MOFs had a minor impact on adsorption, since these MOFs presented identical results in the removal of arsenic species. This observation can be explained by the presence of a similar organic linker (2-methyl imidazole), which points to almost the same geometry and sponginess. However, there was a slight difference in the adamsite (organo-arsenic) removal achieved by the MOFs with different metal atoms.

Zirconium-organic framework as a novel adsorbent for arsenate remediation from aqueous solutions

The removal of arsenic species in water is a global challenge due to its high toxicity and carcinogenicity. In this work, a stable zirconium metal-organic framework (Zr-MOF) has been synthesized for As(V) removal. The Zr-MOF adsorbed As(V) effectively in the pH range of 4–9 with the maximum adsorption capacity of 278 mg g−1. The experimental data modelling suggested a spontaneous adsorption process involving physicochemical forces. The spectroscopic analysis confirmed the binding of As(V) on the Zr-sites via a ligand-exchange mechanism involving ZrOH. Another possible mechanism was the interaction of As(V) with the dissociation of ZrO(linker) sites. These mechanisms were further confirmed by theoretical calculations, where the Zr(μ3-O) bridges (binding energy ∼4.38 eV) bind As(V) more strongly than the ZrOC linkages (binding energy ∼4.11 eV). The material regeneration was successfully carried out with HCl solution, where the regeneration efficacy remained ∼90% for five cycles. Thus, the study provided a detailed investigation on the As(V) adsorption over Zr-MOF.

Comparative Study between Imprinted Polymer Technology and Economic Adsorption Methodologies for the Removal of Arsenic Species from Water

Among the various arsenic sources in the environment, water may pose the greatest threat to human health. Arsenic and its compounds are known to have adverse health effects on humans, including skin cancer, bladder cancer, kidney cancer, and lung cancer, as well as vascular diseases of the legs and feet. There are a few separation methods that have been studied to remove arsenic species from water. Methods to remove arsenic species such as adsorption and ion exchange, coagulation and flocculation and membrane filtration have been developed to remove arsenic species from water. However, certain separation methods require a sophisticated equipment and are too expensive. From the different possible methods, this review is based in adsorption studies using imprinted polymer technology and economic sorbents as a media to remove arsenic from water. The details of adsorption processes for imprinted polymer technology have been discussed briefly and the comparative properties for arsenic species removal using different types of sorbents has been addressed significantly for being a user-friendly, highly extended and inexpensive methodology. However, a few drawbacks for each sorbent have been determined and the details was included in this review.

Analytical study on the removal of arsenic species and its compound by applying magnetic field

Analytical study on the removal of arsenic species and its compound by applying magnetic field

The removal of arsenic species from aqueous solution by indigenous microbes: Batch bioadsorption and artificial neural network model

Arsenic contamination of groundwater is a problem that affects millions of people across the world. Biological treatment of arsenic using microorganisms is an interesting alternative to conventional methods because it is most efficient, low cost and eco-friendly. In this study, three different bacterial species were isolated from arsenic laden tailing dam sludge at gold mining and the 16S rRNA sequencing data exposed their affiliation to three different genera, Bacillus thuringiensis strain WS3, Pseudomonas stutzeri strain WS9 and Micrococcus yunnanensis strain WS11. Considering the advantage of the different structures of these bacterial cell walls in adsorption, attempts were made to use individual and mixed dried biomass of these strains to achieve highest As (III) and As (V) removal under different conditions. Mixed dried biomass of WS3, WS9 and WS11 were found to be efficient in the removal of As (III) and As (V) up to 95% and 98%, respectively. Optimal conditions for arsenic removal were found; 8 and 6 h of contact time for As (III) and As (V), respectively, 7.5 (ppm) As (III) and 9 (ppm) As (V) concentration at 37 °C, pH 7, and 0.60 mg/ml of biomass dosage. In comparison of estimated coefficient of determination (R2), Langmuir isotherm model provided the best fit to the experimental data while the adsorption kinetic model followed the pseudo-second-order. FESEM–EDX analysis established diverse cell morphological changes with significant amounts of arsenic adsorbed onto the biomass compared to original biomass. FTIR analysis showed the involvement of hydroxyl, thiol, amide and amine functional groups in arsenic removal. Comparisons between actual and model adsorption results show that the artificial neural network model can predict adsorption efficiency with high accuracy (R2 > 0.98). Consequently, mixed dried biomass of WS3, WS9 and WS11 are strongly recommended for bio-treatment of toxic arsenic from the environment.

Characterization of ZrO2 Nano Particles Prepared by Glycothermal Method and their Efficiency as Adsorbent of As(III) and As(V) from Waste Water

In this studied ZrO2 nano particles are prepared by glycothermal method. Characterization of the prepared nano particle was done using XRD, TEM and SEM. According to the obtained results, ZrO2 nano particles prepared by glycothermal method are mainly t-ZrO2 phase with tetragonal shape with an average size in the range of 30-50 nm. The formation of t-ZrO2 as the main phase of zirconium nano particles could be related to the presence of sodium hydroxide in the generation step. The removal efficiency of ZrO2 nano particles for adsorbing As(III) and As(V) from waste water is studied. The efficiency of removal is significantly increased with increasing the dose of zirconia nano particles till 0.5 g/L. This related to increasing in the active site which are available for the removal of arsenic species by increasing the dose of the nano particles. For both As(III) and As(V), the removal efficiency increased by decreasing pH value of the solution and increasing the contact time.

Effectiveness of various sorbents and biological oxidation in the removal of arsenic species from groundwater

Environmental context Arsenic contamination of aquifers is a worldwide public health concern and several technologies have been developed to reduce the arsenic content of groundwater. We investigated the efficiency of various materials for arsenic removal from groundwater and found that iron-based sorbents have great affinity for arsenic even if groundwater composition can depress their ability to bind arsenic. Moreover, we showed that the use of microorganisms can enhance the removal of arsenic from groundwater. Abstract The AsIII and AsV adsorption capacity of biochar, chabazite, ferritin-based material, goethite and nano zero-valent iron was evaluated in artificial systems at autoequilibrium pH (i.e. MilliQ water without adjusting the pH) and at approximately neutral pH (i.e. TRIS-HCl, pH 7.2). At autoequilibrium pH, iron-based sorbents removed 200μgL–1 As highly efficiently whereas biochar and chabazite were ineffective. At approximately neutral pH, sorbents were capable of removing between 17 and 100% of AsIII and between 3 and 100% of AsV in the following order: biochar<chabazite<ferritin-based material<goethite<nano zero-valent iron. Chabazite, ferritin-based material and nano zero-valent iron oxidised AsIII to AsV and ferritin-based material was able to reduce AsV to AsIII. When tested in naturally As-contaminated groundwater, a marked decrease in the removal effectiveness occurred, due to possible competition with phosphate and manganese. A biological oxidation step was then introduced in a one-phase process (AsIII bio-oxidation in conjunction with AsV adsorption) and in a two-phase process (AsIII bio-oxidation followed by AsV adsorption). Arsenite oxidation was performed by resting cells of Aliihoeflea sp. strain 2WW, and arsenic adsorption by goethite. The one-phase process decreased As in groundwater to 85%, whereas the two-phase process removed up to 95% As, leaving in solution 6μgL–1 As, thus meeting the World Health Organization limit (10μgL–1). These results can be used in the scaling up of a two-phase treatment, with bacterial oxidation of As combined to goethite adsorption.

Effect of pH and Treatment Time on the Removal of Arsenic Species from Simulated Groundwater by Using Fe<SUP>3+</SUP> and Ca<SUP>2+</SUP> Impregnated Granular Activated Charcoals

This paper deals with the removal of arsenic species from simulated groundwater containing arsenic (As(III):As(V): 1:1), Fe and Mn in concentrations of 0.188mg/l, 2.8mg/l and 0.6mg/l respectively, by surface modified granular activated charcoals produced by impregnating Fe3+ and Ca2+ on GAC surface. Effects of pH and treatment time on the removal of arsenic species by using these adsorbents have been compared. The phenomenon has been explained on the basis of individual pHzpc of oxides and metal complexes present in the adsorbents. The present approach clearly explains the adsorption of negatively charged arsenic species at high pH (>11). Under optimum process conditions at neutral pH, Fe3+ impregnated granular activated charcoal (GAC-Fe) has been found more efficient for the treatment of contaminated groundwater than Ca2+ impregnated granular activated charcoal (GAC-Ca). Treatment time for equilibrium adsorption of arsenic species on GAC-Ca is found to be less than that of GAC-Fe.

Removal of Arsenic from Simulated Groundwater Using GAC‐Ca in Batch Reactor: Kinetics and Equilibrium Studies

AbstractThis paper deals with kinetics and equilibrium studies 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, 2.8, and 0.6 mg/L, respectively, by Ca2+ impregnated granular activated charcoal (GAC‐Ca). Effects of agitation period and initial arsenic concentration on the removal of arsenic species have also been described. Although, most of the arsenic species are adsorbed within 10 h of agitation, equilibrium reaches after ∼24 h. Amongst various kinetic models investigated, the pseudo second order model is more adequate to explain the adsorption kinetics and film diffusion is found to be the rate controlling step for the adsorption of arsenic species on GAC‐Ca. Freundlich isotherm is adequate to explain the adsorption equilibrium. However, empirical polynomial isotherm gives more accurate prediction on equilibrium specific uptakes of arsenic species. Maximum specific uptake (qmax) for the adsorption of As(T) as obtained from Langmuir isotherm is 135 µg/g.

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.

Treatment of Arsenic Contaminated Groundwater Using Calcium Impregnated Granular Activated Carbon in a Batch Reactor: Optimization of Process Parameters

AbstractThis paper is an experimental investigation into the removal of arsenic species from simulated groundwater by adsorption onto Ca2+ impregnated granular activated carbon (GAC‐Ca) in the 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 of GAC‐Ca was found to be 8 g/L with an agitation time of 24 h, which reduced As(T) concentration from 188 to 10 μg/L. Maximum removal of As(V) and As(III) was observed in a pH range of 7–11 and 9–11, respectively. Removal of all the above arsenic species decreased slightly with increasing temperature. The presence of Fe and Mn increased the adsorption of arsenic species. Under the experimental conditions at 30°C, the maximum percentage removals of As(T), As(III), As(V), Fe, and Mn were found to be ca. 94.3, 90.6, 98.0, 100 and 63%, respectively. It was also observed that amongst the various regenerating liquids used, a 5 N H2SO4 solution exhibited maximum regeneration (ca. 91%) of the spent GAC‐Ca.

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

AbstractA 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

As(III) Removal by Palladium-Modified Nitrogen-Doped Titanium Oxide Nanoparticle Photocatalyst

Removal of arsenic species from water by palladium-modified nitrogen-doped titanium oxide (TiON/PdO) nanoparticles was investigated with and without visible light. For the first time, a high degree of As(III) removal undervisible light illumination was demonstrated on oxide photocatalysts. Over 2 orders of magnitude decrease of As(III) concentration in waterwas observed in 1 h as the As(III) concentration was reduced below the U.S. Environmental Protection Agency standard (10 microg/L) by TiON/PdO photocatalyst Such an efficient removal of As(III) was shown to result from the combined effects of strong adsorption and photooxidation by TiON/PdO, where an enhanced photocatalytic activity undervisible light illumination than nitrogen-doped titanium oxide (TiON) was derived from the strong optoelectronic coupling between PdO and TiON.

Arsenic reduction and precipitation by shewanella sp.: Batch and column tests

The effect of bio-geochemical processes on speciation, fate, and transport of arsenic was investigated through the laboratory tests. Shewanella sp., iron-reducing bacteria, was used for batch and column tests. In contrast to the control batch test, the bio-active batch test indicated that Shewanella sp. reduced As(V) to As(III) with concurrent oxidation of lactate to acetate and the decrease of Eh. As time went, a significant amount of the precipitates were formed, and the removal of arsenic species from the solution was attributed to precipitates. SEM-EDX and chemical analyses of the precipitates suggested that As(III) and As(V) were precipitated with sulfides. The reduction and subsequent precipitation of arsenic species were also observed in the column tests. The batch and column tests suggest that in natural groundwater system, Shewanella sp. participates in the reduction of As(V) and sulfate, and sulfides produced by the microbial activity precipitate As(V) and As(III).

Arsenic(III) Oxidation by Iron(VI) (Ferrate) and Subsequent Removal of Arsenic(V) by Iron(III) Coagulation

We investigated the stoichiometry, kinetics, and mechanism of arsenite [As(III)] oxidation by ferrate [Fe(VI)] and performed arsenic removal tests using Fe(VI) as both an oxidant and a coagulant. As(III) was oxidized to As(V) (arsenate) by Fe(VI), with a stoichiometry of 3:2 [As(III):Fe(VI)]. Kinetic studies showed that the reaction of As(III) with Fe(VI) was first-order with respect to both reactants, and its observed second-order rate constant at 25 degrees C decreased nonlinearly from (3.54 +/- 0.24) x 10(5) to (1.23 +/- 0.01) x 10(3) M(-1) s(-1) with an increase of pH from 8.4 to 12.9. A reaction mechanism by oxygen transfer has been proposed for the oxidation of As(III) by Fe(VI). Arsenic removal tests with river water showed that, with minimum 2.0 mg L(-1) Fe(VI), the arsenic concentration can be lowered from an initial 517 to below 50 microg L(-1), which is the regulation level for As in Bangladesh. From this result, Fe(VI) was demonstrated to be very effective in the removal of arsenic species from water at a relatively low dose level (2.0 mg L(-1)). In addition, the combined use of a small amount of Fe(VI) (below 0.5 mg L(-1)) and Fe(III) as a major coagulant was found to be a practical and effective method for arsenic removal.