Adsorption Of Arsenic Species Research Articles

The determination of oxidation rates and quantum yields during the photocatalytic oxidation of As(III) over TiO2

The determination of reaction rates for the photocatalytic oxidation (PCO) of arsenite (As(III)) using TiO2 under UV radiation is challenging due to the numerous experimental processes. This includes chemical processes running simultaneously with PCO (e.g. adsorption of arsenic species, direct UV photolysis of As(III)) and the analytical approach used (e.g. whether As(III) or As(V) are measured and used in the calculation of the PCO rate). The various experimental approaches used to date have led to oxidation rates and rate constants which vary by orders of magnitude and contradicting information on rate laws. Here we present the results of a critical examination of possible controls affecting the experimental determination of PCO rates. First, we demonstrate that the choice of analytical technique is not critical, provided that the rate constants are calculated based on the depletion of As(III) after correction of the directly adsorbed As(III). Second, we show the correction of the directly adsorbed As(III) at each time interval is best done by running two parallel experiments (one under UV and the other in dark) instead of running sequential experiment (i.e. running the experiment in the dark then turning on the UV lamp). These findings are supported by XPS analysis of the oxidation state of TiO2-sorbed As. Third, we demonstrate that photolysis by the light source itself, as well as the chemical composition of the solution (i.e. the effect of HEPES and the ionic strength), can significantly increase As(III) oxidation rates and need to be corrected. Finally, to determine the quantum yield of As(III) oxidation, we measured the photon absorption by the TiO2 photocatalyst. Our results showed that the quantum yield (Ø) for this oxidation reaction was low, and in the region of 0.1 to 0.2 %.

Competitive adsorption of As(III) and As(V) onto chitosan/diatomaceous earth adsorbent

In order to obtain a sufficient removal of heavy metal ions from water, new resources should be exploited to design more efficient and eco-friendly adsorbents. In this work, we have demonstrated an efficient, simple, and reusable adsorbent, which can be operated at the water treatment site. The simultaneous adsorption behavior and competitive interactions between As(III) and As(V) from aqueous solution onto chitosan/diatomaceous earth composite (CSD) were investigated at different solution-pH and adsorbent dosages. The adsorption mechanism was interpreted depending on the data of X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy. Results of batch equilibrium experiments indicated that the pH and adsorbent dosages have significantly influenced the adsorption process, and the adsorption of heavy metals was better fitted with Langmuir isotherm and pseudo-second-order models. The binary maximal adsorption capacities of As(III) and As(V), as determined from the Langmuir adsorption isotherms, were 87.81 mg/g and 44.07 mg/g at a pH of 6, respectively. The presence of phosphate (PO43−) as co-existing anions has an obvious impact on the adsorption of arsenic species. Based on the obtained results, the prepared adsorbent showed a great promise to be used in arsenic species adsorption from aqueous solution.

Performance Evaluation of Small Sized Powdered Ferric Hydroxide as Arsenic Adsorbent

The small sized powdered ferric oxy-hydroxide, termed Dust Ferric Hydroxide (DFH), was applied in batch adsorption experiments to remove arsenic species from water. The DFH was characterized in terms of zero point charge, zeta potential, surface charge density, particle size and moisture content. Batch adsorption isotherm experiments indicated that the Freundlich model described the isothermal adsorption behavior of arsenic species notably well. The results indicated that the adsorption capacity of DFH in deionized ultrapure water, applying a residual equilibrium concentration of 10 µg/L at the equilibrium pH value of 7.9 ± 0.1, with a contact time of 96 h (i.e., Q10), was 6.9 and 3.5 µg/mg for As(V) and As(III), respectively, whereas the measured adsorption capacity of the conventionally used Granular Ferric Hydroxide (GFH), under similar conditions, was found to be 2.1 and 1.4 µg/mg for As(V) and As(III), respectively. Furthermore, the adsorption of arsenic species onto DFH in a Hamburg tap water matrix, as well as in an NSF challenge water matrix, was found to be significantly lower. The lowest recorded adsorption capacity at the same equilibrium concentration was 3.2 µg As(V)/mg and 1.1 µg As(III)/mg for the NSF water. Batch adsorption kinetics experiments were also conducted to study the impact of a water matrix on the behavior of removal kinetics for As(V) and As(III) species by DFH, and the respective data were best fitted to the second order kinetic model. The outcomes of this study confirm that the small sized iron oxide-based material, being a by-product of the production process of GFH adsorbent, has significant potential to be used for the adsorptive removal of arsenic species from water, especially when this material can be combined with the subsequent application of low-pressure membrane filtration/separation in a hybrid water treatment process.

Fabrication of α-FeOOH decorated graphene oxide-carbon nanotubes aerogel and its application in adsorption of arsenic species

Arsenic pollution has caused worldwide attention due to its mandatory toxicity. Chemical structures of the adsorbent and arsenic species greatly influence the arsenic adsorption efficiency. The goethite impregnated graphene oxide (GO)-carbon nanotubes (CNTs) aerogel (α-FeOOH@GCA) was prepared via a facile self-assembly method of GO-CNTs induced by in-situ Fe2+ reduction. α-FeOOH@GCA showed excellent adsorption capacities of 56.43, 24.43 and 102.11mgg−1 for As(V), DMA and p-ASA comparing with that of 25.71, 8.03 and 14.52mgg−1 of pristine α-FeOOH, respectively. The incorporation of GO-CNTs not only hinders the aggregation of GO-CNTs but also inhibits the growth of α-FeOOH nanoparticles greatly facilitating the diffusion and adsorption capacity of arsenic species. α-FeOOH@GCA shows wide favorable application pH for arsenic species adsorption, high adsorption kinetics and excellent reusability. The phosphate and silicate anions compete with the arsenic species for active adsorption sites due to the similar anionic structure. Based on FTIR spectra, arsenic species were proven to form inner sphere complex on the surface of α-FeOOH@GCA through different ligand exchanging mechanism greatly dependent on the molecular structures of arsenic species. The results show that α-FeOOH@GCA could be used as promising adsorbent for arsenic purification in water system.

Adsorption Kinetics and Evaluation Study of Iron Oxide Nanoparticles Impregnated in Polyurethane Matrix for Water Filtration Application

A polyurethane (PU) foam composite, loaded with iron oxide nanoparticles (IONPs), was developed for arsenic removal from drinking water at low concentrations. The effect of various synthesis parameters such as the size of IONPs and the foam shape, on the performance of the adsorbents in removing arsenic was investigated. To examine the surface adsorption of arsenic species, Energy Dispersive X-ray Microscopy (EDX) was utilized. Mercury Porosimetry was used to analyze the porosity and density of the PU-IONPs nanocomposites. Atomic Absorption Spectrometry (AAS) was conducted to measure the arsenic concentration in the treated solutions. Kinetic models were applied to determine the mechanisms which control the adsorption process. A pseudo-second-order model was found to be the best fit model for the adsorption data. Experimental results revealed that decreasing the size of IONPs from 50 - 100 nm to 15 - 20 nm yields a higher removal capacity. In addition, granular adsorbents exhibit higher removal capacity compared to cubical shaped adsorbents in the order of 20% - 100%.

Adsorption of As(III) and As(V) compounds on Fe3O4(0 0 1) surfaces: A first principle study

The adsorption of arsenic species on magnetite has been studied by first principles calculations. From the considered anionic species, a higher adsorption energy was found for the complexation of Fe3O4(001) with As(III) being 1.3eV higher than the adsorption energy for As(V). In the case of As(III), a large partial band charge density was found, which was associated to the OFe bond formation, while more delocalized electron density was found in the adsorption of As(V) subspecies, with the formation of two FeO bonds. A comparison with sorption of neutral arsenic atoms and O2 molecule was also considered. As(V) is mainly adsorbed on the surface with a double OFe bond formation, similar to the case of O2 in the most stable configuration.

Oxidation and adsorption of arsenic species by means of hybrid polymer containing manganese oxides

ABSTRACTThe aim of this work was a comprehensive study of the oxidative and sorptive properties of a hybrid polymer containing manganese oxide toward As(III) and As(V). A poly(styrene‐divinylbenzene) copolymer containing oxidative functional groups (SO2NBrNa) was used as the supporting material for MnO2. The inorganic component was deposited as a result of the oxidation reaction of Mn(II) with oxidative groups of the host polymer. The surface of the polymer matrix was evenly covered with a thin layer of manganese oxide. The obtained product (R/S/Mn) exhibited high oxidative capacity over a wide pH range (2–12); however, under acidic and neutral conditions, the reaction ran significantly faster. The studied material shows some sorption properties but its sorption capacity is much lower than its oxidation capacity. The treatment, in a column regime, of the arsenic solution containing 1 mg As(III) dm−3 and coexisting ions in concentrations similar to those in natural waters, confirmed the excellent oxidation capacity of the obtained product. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39489.

LC-ICPMS speciation of arsenite and arsenate oxyanion mixtures during their adsorption with dried sludge

This report describes the speciation of arsenic oxyanion mixtures using a liquid chromatography coupled with inductively coupled plasma mass spectrometry (LC-ICPMS) technique. The proposed method allowed a fast, sensitive and environmentally friendly determination of arsenic inorganic species in water. The speciation was carried out during adsorption experiments using dried sludge as an adsorbent. The dried used sludge was generated as discarded material from a water plant after coagulation and sedimentation stages and was selected due to its chemical and mineralogical composition. The sludge composition includes high proportions of silica, aluminium and iron minerals, which are known to be responsible for the adsorption of arsenic species. The As speciation results demonstrated a low limit of detection (LOD) of 5.26 ppb for arsenite and 9.85 ppb for arsenate species. The arsenate species was removed faster compared to the arsenite species when both are present as mixtures. These findings confirm that electrostatic interactions between the sludge components and charged H2AsO4−, arsenate predominant species at pH 6.0, result in a faster equilibrium than H3AsO3 (arsenite, a predominantly neutral species at pH 6.0). The adsorption was fitted by Langmuir and Freundlich models; the second one being the one which better represented the adsorption process. The Freundlich parameter k, the relative uptake capacity of the adsorbent, was 0.221 (mg g−1) (L mg−1)n for arsenite and 0.101 (mg g−1) (L mg−1)n for arsenate. The data from competitive adsorption tests suggested that the removal mechanism for arsenic species is due to the formation of an outer sphere complex via electrostatic or van der Waals attractions. The results show the capability of the dried sludge as a green alternative to remove trace levels of both arsenic oxyanions from contaminated or wastewaters. Also, the developed speciation protocol allowed a better understanding of the adsorption mechanism of arsenic species by Fe-rich sludge.

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

Improvement of Arsenic Electro-Removal from Underground Water by Lowering the Interference of other Ions

Electrocoagulation (EC) has been evaluated as a treatment technology for arsenic (As) removal. Experiments were developed in an electrochemical reactor with three parallel iron plates. Current densities of 15, 30, and 45 A m−2 were used to treat model water and 45 A m−2 to treat underground water (GW). For both types of water, the EC process was able to decrease the residual arsenic concentration to less than 10 μg L−1. However, the treatment time for As removal from GW was higher. This phenomenon was attributed to the competition of dissolved species present in GW such as silica and calcium with arsenic for the adsorption sites on the ferric oxyhydroxides flocs generated during the EC process. A procedure is proposed to reduce such interference by the addition of a silica adsorption inhibitor compound into the GW achieving a reduction in the process time. The adsorption of arsenic species over adsorbent was found to follow Lagergren adsorption model.

Adsorption of arsenic species from water using activated siderite–hematite column filters

Arsenic is present at relatively high concentrations in surface water and groundwater as a result of both natural impacts and anthropogenic discharge, which requires proper treatment before use. The present study describes As adsorption on a siderite–hematite filter as a function of activating condition, empty bed contact time, and As species. Hydrogen peroxide activating increased As adsorption on siderite by 16.2 μg/g, and on hematite by 13.0 μg/g. The H 2O 2 conditioning enhanced adsorption efficiency of activated siderite–hematite filters up to throughput of 500 pore volumes of 500 μg/L As water. At values greater than 47 min, the empty bed contact time (EBCT) had only a weak influence on the removal capacity of pristine siderite–hematite filters. Due to the formation of fresh Fe(III)-oxide layer in the H 2O 2-conditioned filter and the pristine hematite–siderite filter, both of them may be utilized as a cost-effective reactor for treating As water. A toxicity characteristic leaching procedure (TCLP) test showed that the spent minerals were not hazardous and could be safely landfilled.

The Sorption of Arsenic onto Activated Carbon Impregnated with Metallic Silver and Copper

Abstract The adsorption of arsenic species in aqueous solutions onto activated carbon with and without chemical impregnation has been studied. The ability of activated carbon to adsorb arsenic depends on the arsenic oxidation state, the pH of the water, and the activity of the metal used for the activated carbon impregnation. The results of the investigations have shown that physical adsorption is effective only for the arsenic(V) species in water. Activated carbon adsorbs arsenic(V) with a saturation adsorption capacity of 0.27 mmol/g. The chemisorption process is effective for both arsenic species. By impregnation of activated carbon by copper, the sorption process for the arsenic(III) species is significantly improved. The saturation adsorption capacity of the activated carbon impregnated by copper is 0.41 and 0.23 mmol/g for the arsenic(III) and arsenic(V) species, respectively. The pH values of the water are important for both sorption processes because of the change in the ionic forms of both arseni...