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1.
Artigo em Inglês | MEDLINE | ID: mdl-33760681

RESUMO

The adsorptive removal of a pollutant from water is significantly affected by the presence of coexisting ions with various concentrations. Here, we have studied adsorption of arsenate [As(V)] by calcined Mg-Fe-(CO3)-LDH in the presence of different cations (Mg2+, Na+, K+, Ca2+, and Fe3+) and anions (CO32‒, Cl‒, PO43‒, SO42‒, and NO3‒) with their different concentrations to simulate the field condition. The experimental results indicated that Ca2+, Mg2+, and Fe3+ have a synergistic effect on removal efficiency of As(V), whereas PO43‒ and CO32‒ ions have a significant antagonistic impact. Overall, the order of inhibiting effect of coexisting anions on adsorption of As(V) was arrived as NO3-˂Cl-

Assuntos
Arseniatos/isolamento & purificação , Hidróxidos/química , Íons/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Arseniatos/análise , Arseniatos/química , Carbonatos/química , Íons/análise , Ferro/química , Cinética , Magnésio/química , Redes Neurais de Computação , Fosfatos/química , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/química , Purificação da Água/métodos
2.
Artigo em Inglês | MEDLINE | ID: mdl-33678135

RESUMO

In this study, graphene oxide and composites of graphene oxide-iron modified clinoptilolite were synthesized and used for arsenate removal from aqueous solution. All adsorbents were characterized using X-ray diffraction and specific surface area analysis. The specific surface areas of composites were found to be less than the iron modified clinoptilolite. The time required to reach equilibrium was determined as 3 hours for all adsorbents. The Box-Behnken statistical experiment design method was used to determine the effects of initial arsenate concentration, pH and the amount of adsorbent on the percent arsenate removal. Graphene oxide was not as effective as composites for arsenate adsorption from water. Arsenate adsorption on composites was showed good compatibility with the Freundlich isotherm. The maximum arsenate uptake was realized at pH 4 for graphene oxide and at pH 7 for composites. The maximum adsorption capacities obtained at the optimum points determined by using the Box-Behnken design method were calculated as 39.49, 117.98 and 124.64 µg.g-1 for graphene oxide and composites, respectively.


Assuntos
Arseniatos/isolamento & purificação , Grafite/química , Ferro/química , Poluentes Químicos da Água/isolamento & purificação , Zeolitas/química , Adsorção , Arseniatos/química , Concentração de Íons de Hidrogênio , Cinética , Propriedades de Superfície , Poluentes Químicos da Água/química , Purificação da Água/métodos
3.
J Chromatogr A ; 1609: 460459, 2020 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-31445800

RESUMO

Sulfate (SO4-sug) and sulfonate (SO3-sug) arsenosugar standard solutions were obtained using preparative liquid chromatography. Several commercial algae samples were characterized (total contents and speciation) to select the most appropriate in relation to their arsenosugar contents. Water extracts from the selected sample (Fucus vesiculosus) were fractionated using a Hamilton PRP-X100 preparative column, and the presence of arsenic species in the isolated fractions was ascertained by IC-ICP-MS. Two of the fractions successfully presented only one arsenic species corresponding to sulfate and sulfonate arsenosugars at suitable concentrations. To unequivocally confirm the presence of both compounds, high-resolution mass spectrometry (ESI-TOF/MS) was used and the exact mass determined with errors lower than 0.5 ppm. The standard solutions obtained were successfully used to identify and quantify SO4-sug and SO3-sug in several edible algae samples purchased in local market. Total arsenic content for analyzed samples ranged from 34 to 57 mg kg-1, concentration values found for SO3-sug ranged from 5 to 36 mg As kg-1 and SO4-sug was only found in fucus with a concentration of 9.3 mg As kg-1.


Assuntos
Arseniatos/química , Arseniatos/isolamento & purificação , Monossacarídeos/química , Monossacarídeos/isolamento & purificação , Phaeophyceae/química , Extratos Vegetais/química , Extratos Vegetais/isolamento & purificação , Cromatografia Líquida , Espectrometria de Massas , Água/química
4.
Molecules ; 24(13)2019 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-31277493

RESUMO

In the present research, treatment of contaminated groundwater via adsorption of As(V) with an initial concentration of 50.99 µg/L using chitosan-coated bentonite (CCB) was investigated. The effect of adsorbent mass (0.001 to 2.0 g), temperature (298 to 328 K), and contact time (1 to 180 min) on the removal efficiency was examined. Adsorption data was evaluated using isotherm models such as Langmuir, Freundlich, and Dubinin-Radushkevich. Isotherm study showed that the Langmuir (R2 > 0.9899; χ2 ≤ 0.91; RMSE ≤ 4.87) model best correlates with the experimental data. Kinetics studies revealed that pseudo-second order equation adequately describes the experimental data (R2 ≥ 0.9951; χ2 ≤ 0.8.33; RMSE ≤ 4.31) where equilibrium was attained after 60 min. Thermodynamics study shows that the As(V) adsorption is non-spontaneous (ΔG0 ≥ 0) and endothermic (ΔH0 = 8.31 J/mol) that would result in an increase in randomness (ΔS0 = 29.10 kJ/mol•K) within the CCB-solution interface. FT-IR analysis reveals that hydroxyl and amino groups are involved in the adsorption of As(V) from groundwater. Results of the present research serve as a tool to determine whether CCB is an environmentally safe and cost effective material that could be utilized in a permeable reactive barrier system for the remediation of As(V) from contaminated groundwater.


Assuntos
Arseniatos/isolamento & purificação , Bentonita/química , Quitosana/química , Água Subterrânea/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Difusão , Cinética , Temperatura , Fatores de Tempo
5.
Int J Biol Macromol ; 122: 185-194, 2019 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-30340008

RESUMO

This paper reports a simple, facile and rapid preparation of 3­mercapto­propanoic acid (MPA) modified cellulose filter paper (MPA-Cell paper) for arsenate removal from drinking water. The MPA was covalently grafted to the cellulose filter paper (Cell) by esterification process through the formation of O­acylisourea intermediate and characterized by the FTIR, SEM, EDS and XPS analyses. The arsenate adsorption efficiency was studied for batch and semi-continuous systems while exploring the adsorption kinetics, isotherm and the effect of pH for the former. The experimental data fitted well with Langmuir, Dubinin-Radushkevich (DR) and pseudo second order kinetic models. The mechanism of adsorption was studied by FTIR spectroscopy utilizing the adsorption isotherm, kinetic model and XPS results. The modified filter paper performed well at nearly neutral pH in arsenate removal through adsorption and demonstrated a significant arsenate uptake capacity of 92.59 mg/g. The DR and FTIR results indicated that the adsorption of arsenate ion occurred through ion exchange process. The MPA-Cell paper could have a potential use as low-cost but efficient commercial adsorbent for arsenate abatement from contaminated drinking water by both batch as well as semi-continuous operating systems. The MPA-Cell paper could purify ground water containing high level of arsenate.


Assuntos
Ácido 3-Mercaptopropiônico/química , Arseniatos/química , Arseniatos/isolamento & purificação , Celulose/química , Água Potável/química , Filtração , Papel , Adsorção , Água Subterrânea/química , Concentração de Íons de Hidrogênio , Cinética , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água
6.
J Environ Sci (China) ; 76: 133-141, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30528005

RESUMO

Elevated arsenic and selenium concentrations in water cause health problems to both humans and wildlife. Natural and anthropogenic activities have caused contamination of these elements in waters worldwide, making the development of efficient cost-effective methods in their removal essential. In this work, removal of arsenate and selenite from water by adsorption onto a natural goethite (α-FeOOH) sample was studied at varying conditions. The data was then compared with other arsenate, selenite/goethite adsorption systems as much of literature shows discrepancies due to varying adsorption conditions. Characterization of the goethite was completed using inductively coupled plasma mass spectrometry, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer-Emmett-Teller surface area analysis. Pseudo-first order (PFO) and pseudo-second order (PSO) kinetic models were applied; including comparisons of different regression methods. Various adsorption isotherm models were applied to determine the best fitting model and to compare adsorption capacitates with other works. Desorption/leaching of arsenate and selenite was studied though the addition of phosphate and hydroxyl ions. Langmuir isotherm modeling resulted in maximum adsorption capacities of 6.204 and 7.740 mg/g for arsenate and selenite adsorption, respectively. The PSO model applied with a non-linear regression resulted in the best kinetic fits for both adsorption and desorption of arsenate and selenite. Adsorption decreased with increasing pH. Phosphate induced desorption resulted in the highest percentage of arsenate and selenite desorbed, while hydroxide induced resulted in the fastest desorption kinetics.


Assuntos
Arseniatos/química , Arseniatos/isolamento & purificação , Compostos de Ferro/química , Minerais/química , Ácido Selenioso/química , Ácido Selenioso/isolamento & purificação , Purificação da Água/métodos , Água/química , Adsorção , Cinética , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação
7.
Environ Sci Pollut Res Int ; 25(34): 34053-34062, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30280345

RESUMO

When low-cost adsorbents are being used to remove contaminant ions (e.g. arsenate, vanadate, and molybdate) from wastewater, competitive adsorption/desorption are central processes determining their removal efficiency. Competitive adsorption of As, V, and Mo was investigated using equimolar oxyanion concentrations in single, binary, and tertiary combinations in adsorption isotherm and pH envelope studies while desorption of previously adsorbed oxyanions was examined in solutions containing single and binary oxyanion combinations. The low-cost adsorbent materials used were alum water treatment sludge (amorphous hydroxy-Al) and bauxite ore (crystalline Al oxides). Adsorption isotherm and pH envelope studies showed that Mo had only a small effect in decreasing adsorption of As and V but V and As had substantial and similar effects in reducing adsorption of the other. As had a greater effect than V in reducing adsorption of Mo and it was concluded that the affinity of oxyanions for the surfaces of water treatment sludge and bauxite followed the order As > V >> Mo. In 0.3 M NaCl electrolyte, desorption of previously adsorbed oxyanions amounted to 0.3-3.4% for V and As, and 11-20% for Mo. As had approximately four times greater effect than Mo in increasing desorption of V while V had about three times the effect of Mo in increasing desorption of As. Thus, the order of oxyanions in inducing desorption of the other oxyanions (i.e. As on V and As) was the same as that for adsorption selectivity: As > V >> Mo. Water treatment sludge was a more effective adsorbent than bauxite because it had a greater adsorption capacity for all three anions and, in addition, they were held more strongly so desorption in the background electrolyte was proportionately less. It was concluded that at similar molar concentrations, arsenate would tend to reduce adsorption of vanadate as well as displace vanadate already held on adsorbent surfaces while both anions will compete effectively with molybdate. The limiting factor for simultaneous removal of As, V, and Mo from multielement solutions by adsorption will therefore be the removal of Mo.


Assuntos
Arseniatos/química , Molibdênio/química , Vanadatos/química , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água/química , Adsorção , Compostos de Alúmen/química , Óxido de Alumínio/química , Arseniatos/isolamento & purificação , Concentração de Íons de Hidrogênio , Molibdênio/isolamento & purificação , Esgotos/química , Vanadatos/isolamento & purificação , Águas Residuárias/química , Poluentes Químicos da Água/isolamento & purificação , Áreas Alagadas
8.
Environ Sci Pollut Res Int ; 25(28): 28572-28582, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30091077

RESUMO

Arsenate and phosphate have similar properties due to their electrochemical structures, but their environmental impacts are unique. The abundance and competition of arsenate and phosphate determine their bioavailability and leachability; thus, it is essential to understand their fate in the soil environment. In this study, the effects of pH and surface loading on the competitive adsorption of arsenate and phosphate on four iron (hydr)oxides were evaluated by employing the Langmuir isotherm, competitive sorption ratio (CSR), and competition effect (CE). The stability and transformation of the iron (hydr)oxides were also assessed. Various adsorption patterns were observed in the single and mixed treatments by controlling the addition of oxyanions, pH, surface loading, and type of iron (hydr)oxides. Arsenate was preferentially adsorbed at a low pH, whereas phosphate showed the opposite trend. The CEAs(V),P(V) was close to zero at low surface density (no competition) and sequentially changed to negative or positive values with increasing surface density, indirectly indicating the sequential development of promotive and competitive effects. Transformation in goethite was identified at a high pH with the presence of oxyanions, except that no transformation was observed upon the addition of oxyanions and with pH change. However, the stability of the iron (hydr)oxides decreased at a low pH and with the presence of phosphate, arsenate, or both. The hematite showed a significant promotive effect regardless of the pH. Our study revealed that the pH, surface loading, and type of iron (hydr)oxides are intercorrelated and simultaneously affect the adsorption characteristics of oxyanions and the stability of iron (hydr)oxides.


Assuntos
Arseniatos/química , Compostos Férricos/química , Compostos de Ferro/química , Nanopartículas de Magnetita/química , Minerais/química , Fosfatos/química , Adsorção , Arseniatos/isolamento & purificação , Concentração de Íons de Hidrogênio , Fosfatos/isolamento & purificação , Poluentes do Solo/química , Poluentes do Solo/isolamento & purificação
9.
J Environ Manage ; 224: 263-276, 2018 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-30055459

RESUMO

The modification of the fly ash (FA) by magnetite (M) was performed to obtain FAM adsorbent with improved adsorption efficiency for arsenate removal from water. The novel low cost adsorbents are characterized by liquid nitrogen porosimetry (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), Mössbauer spectroscopy (MB) and Fourier transform infrared (FTIR) spectroscopy. The optimal conditions and key factors influencing the adsorbent synthesis are assessed using the response surface method (RSM). The adsorption experiment was carried out in a batch system by varying the contact time, temperature, pH, and mass of the adsorbent. The adsorption capacity of the FAM adsorbent for As(V), calculated by Langmuir model, was 19.14 mg g-1. The thermodynamic parameters showed spontaneity of adsorption with low endothermic character. The kinetic data followed the pseudo-second-order kinetic model (PSO), and Weber-Morris model indicated intra-particle diffusion as rate limiting step. Alternative to low desorption capability of the FAM was found by five consecutive adsorption/magnetite precipitation processes which gave exhausted layered adsorbent with 65.78 mg g-1 capacity. This research also has shed light on the mechanism of As(V)-ion adsorption, presenting a promising solution for the valorization of a widely abundant industrial waste.


Assuntos
Arseniatos/isolamento & purificação , Cinza de Carvão , Óxido Ferroso-Férrico/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Arseniatos/química , Concentração de Íons de Hidrogênio , Cinética , Microscopia Eletrônica de Varredura , Espectroscopia de Infravermelho com Transformada de Fourier , Termodinâmica , Poluentes Químicos da Água/química
10.
Chemosphere ; 203: 90-95, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-29614414

RESUMO

The magnetite particles were chemically synthesized from the waste of hot rolling steel industry. The characterization of the synthesized magnetite was done by using Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The synthesized magnetite particles were used for the adsorptive removal of arsenate from the contaminated water. The maximum adsorption capacity of 7.69 mg was found on the surface of 1 g of the magnetite. The point of zero charge for magnetite is determined at the pH 6. The adsorption capacity of magnetite particles was successfully restored with alkali cleaning. Newly synthesized particles were found to be effective for arsenate removal up to 5 times with regeneration. The synthesis of magnetite from raw mill scale and its application for arsenate adsorption is a cost effective and ecofriendly process.


Assuntos
Arseniatos/isolamento & purificação , Óxido Ferroso-Férrico/metabolismo , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Adsorção , Arseniatos/química , Óxido Ferroso-Férrico/química , Concentração de Íons de Hidrogênio , Cinética , Poluentes Químicos da Água/química
11.
Artigo em Inglês | MEDLINE | ID: mdl-29278978

RESUMO

Bioremediation of arsenic using green technology via microbial enzymes has attracted scientists due to its simplicity and cost effectiveness. Statistical optimization of arsenate bioremediation was conducted by the enzyme arsenate reductase extracted from arsenic tolerant bacterium Pseudomonas alcaligenes. Response surface methodology based on Box-Behnken design matrix was performed to determine the optimal operational conditions of a multivariable system and their interactive effects on the bioremediation process. The highest biosorptive activity of 96.2 µg gm-1 of beads was achieved under optimized conditions (pH = 7.0; As (V) concentration = 1000 ppb; time = 2 h). SEM analysis showed the morphological changes on the surface of enzyme immobilized gluteraldehyde crosslinked Ca-alginate beads. The immobilized enzyme retained its activity for 8 cycles. ANOVA with a high correlation coefficient (R2 > 0.99) and lower "Prob > F"value (<0.0001) corroborated the second-order polynomial model for the biosorption process. This study on the adsorptive removal of As (V) by enzyme-loaded biosorbent revealed a possible way of its application in large scale treatment of As (V)-contaminated water bodies.


Assuntos
Alginatos/metabolismo , Arsênio/farmacocinética , Microesferas , Pseudomonas alcaligenes/enzimologia , Poluentes Químicos da Água/farmacocinética , Purificação da Água , Adsorção , Alginatos/química , Arseniatos/análise , Arseniatos/isolamento & purificação , Arseniatos/farmacocinética , Arsênio/análise , Arsênio/isolamento & purificação , Biodegradação Ambiental , Cálcio/química , Cálcio/metabolismo , Calibragem/normas , Ácido Glucurônico/química , Ácido Glucurônico/metabolismo , Ácidos Hexurônicos/química , Ácidos Hexurônicos/metabolismo , Concentração de Íons de Hidrogênio , Pseudomonas alcaligenes/metabolismo , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Purificação da Água/normas , Purificação da Água/estatística & dados numéricos
12.
Chemosphere ; 194: 117-124, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29197814

RESUMO

The mechanism of As(V) removal from the drinking water and industrial effluents by iron materials remains unclear at the molecular level. In this work, the association of Fe-based materials with As(V) species was explored using density functional theory and ab initio calculations. Solvent separated ion pair structures of [FeH2AsO4]2+aq species may be dominant in an acidic solution of FeAs complex. The association trend of H2AsO4- species by Fe3+aq is found to be quite weak in the aqueous solution, which may be attributed to the strong hydration of Fe3+aq and [FeH2AsO4]2+ species. However, the association of H2AsO4- species by colloidal clusters is quite strong, due to the weakened hydration of Fe(III) in colloidal structures. The hydrophobicity of Fe-based materials may be one of the key factors for their As(V) removal efficiency in an aqueous phase. When the number of OH- coordinated with Fe(III) increases, the association trend of As(V) by colloidal ferric hydroxides weakens accordingly. This study provides insights into understanding the coprecipitation and adsorption mechanisms of arsenate removal and revealing the high efficiency of arsenate removal by colloidal ferric hydroxides or iron salts under moderate pH conditions.


Assuntos
Arsênio/isolamento & purificação , Compostos de Ferro/química , Purificação da Água/métodos , Adsorção , Arseniatos/isolamento & purificação , Arsênio/química , Precipitação Química , Compostos Férricos , Concentração de Íons de Hidrogênio , Poluentes Químicos da Água/isolamento & purificação
13.
Environ Sci Pollut Res Int ; 24(23): 19402-19411, 2017 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-28677038

RESUMO

In present study, a novel method was developed to synthesize siderite under high temperature and high pressure (SID-HTP). SID-HTP was characterized by N2 adsorption-desorption isotherms (BET), XRD, SEM, and FTIR and utilized to remove arsenic(V) (As(V)) from aqueous solution. Results showed that, under oxic condition, pH had ignorable effect on As(V) adsorption. However, adsorption capacity increased with increasing pH from 2 to 7 and remained relatively constant at higher pH until 10 under anoxic condition. Higher adsorption was obtained in the presence of oxygen, showing oxygen-enhanced As(V) adsorption on SID-HTP. In both cases, adsorption equilibrium was achieved within 12 h and adsorption process was better described by pseudo-second-order kinetic model. The equilibrium data fitted well with Langmuir isotherm model for As(V) adsorption. The maximum adsorption capacity increased with increasing temperature, which was up to 42 mg g-1 at 55 °C in the presence of oxygen. Thermodynamic study revealed that the adsorption was a spontaneous and endothermic process. The mechanism of oxygen-enhanced adsorption was mainly ascribed to the -OH on the surface of FeOOH (goethite and lepidocrocite) in the SID-HTP. It suggested that SID-HTP would be a potentially attractive adsorbent for As(V) removal.


Assuntos
Arseniatos/química , Carbonatos/síntese química , Compostos Férricos/síntese química , Temperatura Alta , Pressão , Poluentes Químicos da Água/química , Purificação da Água/métodos , Adsorção , Arseniatos/isolamento & purificação , Carbonatos/química , Compostos Férricos/química , Concentração de Íons de Hidrogênio , Oxigênio , Termodinâmica , Poluentes Químicos da Água/isolamento & purificação
14.
Chem Asian J ; 12(15): 1952-1964, 2017 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-28544414

RESUMO

Because of the devastating impact of arsenic on terrestrial and aquatic organisms, the recovery, removal, disposal, and management of arsenic-contaminated water is a considerable challenge and has become an urgent necessity in the field of water treatment. This study reports the controlled fabrication of a low-cost adsorbent based on microscopic C-,N-doped NiO hollow spheres with geode shells composed of poly-CN nanospherical nodules (100 nm) that were intrinsically stacked and wrapped around the hollow spheres to form a shell with a thickness of 500-700 nm. This C-,N-doped NiO hollow-sphere adsorbent (termed CNN) with multiple diffusion routes through open pores and caves with connected open macro/meso windows over the entire surface and well-dispersed hollow-sphere particles that create vesicle traps for the capture, extraction, and separation of arsenate (AsO43- ) species from aqueous solution. The CNN structures are considered to be a potentially attractive adsorbent for AsO43- species due to 1) superior removal and trapping capacity from water samples and 2) selective trapping of AsO43- from real water samples that mainly contained chloride and nitrate anions and Fe2+ , and Mn2+ , Ca2+ , and Mg2+ cations. The structural stability of the hierarchal geodes was evident after 20 cycles without any significant decrease in the recovery efficiency of AsO43- species. To achieve low-cost adsorbents and toxic-waste management, this superior CNN AsO43- dead-end trapping and recovery system evidently enabled the continuous control of AsO43- disposal in water-scarce environments, presents a low-cost and eco-friendly adsorbent for AsO43- species, and selectively produced water-free arsenate species. These CNN geode traps show potential as excellent adsorbent candidates in environment remediation tools and human healthcare.


Assuntos
Arseniatos/isolamento & purificação , Técnicas de Química Analítica/métodos , Poluentes Químicos da Água/isolamento & purificação , Água/química , Ânions/isolamento & purificação , Arseniatos/química , Técnicas de Química Analítica/economia , Limite de Detecção , Nanopartículas/química , Porosidade , Poluentes Químicos da Água/química
15.
J Chromatogr A ; 1479: 129-136, 2017 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-27939600

RESUMO

A new rapid monitoring method by means of high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) following the heat-assisted extraction was developed for measurement of total inorganic arsenic species in rice flour. As(III) and As(V) eluted at the same retention time and completely separated from organoarsenic species by an isocratic elution program on a reversed phase column. Therefore, neither ambiguous oxidation of arsenite to arsenate nor the integration of two peaks were necessary to determine directly the target analyte inorganic arsenic. Rapid injection allowed measuring 3 replicates within 6min and this combined with a quantitative extraction of all arsenic species from rice flour by a 15min HNO3-H2O2 extraction makes this the fastest laboratory based method for inorganic arsenic in rice flour.


Assuntos
Arsênio/análise , Espectrometria de Massas , Oryza/química , Arseniatos/análise , Arseniatos/isolamento & purificação , Arsênio/isolamento & purificação , Arsenitos/análise , Arsenitos/isolamento & purificação , Cromatografia Líquida de Alta Pressão , Cromatografia de Fase Reversa , Peróxido de Hidrogênio/química , Ácido Nítrico/química
16.
Chemosphere ; 168: 539-548, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-27839879

RESUMO

Layered double hydroxides have been proposed as effective sorbents for As(V), but studies investigating adsorption mechanisms usually lack a comprehensive mechanistic/modeling approach. In this work, we propose coupling surface complexation modeling with various spectroscopic techniques. To this end, a series of batch experiments at different pH values were performed. Kinetic data were well fitted by a pseudo-second order kinetic model, and the equilibrium data were fitted by the Freundlich model. Moreover, the pH-dependent As(V) sorption data were satisfactorily fitted by a diffuse layer model, which described the formation of >SOAsO3H- monodentate and >(SO)2AsO2- bidentate inner-sphere complexes (">S" represents a crystallographically-bound group on the surface). Additionally, XPS analyses confirmed the adsorption mechanisms. The sorption mechanisms were affected by anion exchange, which was responsible for the formation of outer sphere complexes, as identified by XRD and FTIR analyses. Furthermore, a homogenous distribution of As(V) was determined by HR-TEM with elemental mapping. Using low-temperature Mössbauer spectroscopy on isotope 57Fe, a slight shift of the hyperfine parameters towards higher values following As(V) sorption was measured, indicating a higher degree of structural disorder. In general, mechanistic adsorption modeling coupled with solid state analyses presents a powerful approach for investigating the adsorption mechanism of As(V) on Mg-Fe LDH or other sorbents.


Assuntos
Arseniatos/química , Compostos Férricos/química , Hidróxido de Magnésio/química , Modelos Teóricos , Adsorção , Arseniatos/isolamento & purificação , Concentração de Íons de Hidrogênio , Cinética , Soluções , Espectroscopia de Infravermelho com Transformada de Fourier , Propriedades de Superfície , Difração de Raios X
17.
J Environ Manage ; 181: 856-862, 2016 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-27397845

RESUMO

The aim of this research was to investigate sulphate removal from mine water by precipitation as ettringite (Ca6Al2(SO4)3(OH)12·26H2O) and the utilisation of the precipitate as a sorbent for arsenate removal. The mine water sulphate concentration was reduced by 85-90% from the initial 1400 mg/L during ettringite precipitation depending on the treatment method. The precipitation conditions were also simulated with MINEQL + software, and the computational results were compared with the experimental results. The precipitated solids were characterised with X-ray diffraction and a scanning electron microscope. The precipitated solids were tested as sorbents for arsenate removal from the model solution. The arsenic(V) model solution concentration reduced 86-96% from the initial 1.5 mg/L with a 1 g/L sorbent dosage. The effect of initial arsenate concentration on the sorption of arsenate on the precipitate was studied and Langmuir, Freundlich, and Langmuir-Freundlich sorption isotherm models were fitted to the experimental data. The maximum arsenate sorption capacity (qm = 11.2 ± 4.7 mg/g) of the precipitate was obtained from the Langmuir-Freundlich isotherm. The results indicate that the precipitate produced during sulphate removal from mine water by precipitation as ettringite could be further used as a sorbent for arsenate removal.


Assuntos
Arseniatos/isolamento & purificação , Minerais/química , Sulfatos/isolamento & purificação , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Adsorção , Arseniatos/química , Precipitação Química , Microanálise por Sonda Eletrônica , Concentração de Íons de Hidrogênio , Mineração , Espectrometria por Raios X , Sulfatos/química , Poluentes Químicos da Água/química , Difração de Raios X
18.
Environ Pollut ; 216: 575-583, 2016 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-27376988

RESUMO

Magnetic biochars (MW) prepared by chemical co-precipitation of Fe(2+)/Fe(3+) on water hyacinth biomass followed by pyrolysis exhibited important potential in aqueous As(V) elimination. In comparison, MW2501 outperformed other MWs and exhibited the highest As(V) sorption capacity which was estimated to be 7.4 mg g(-1) based on Langmuir-Freundlic model. With solution pH ranging from 3 to 10, As(V) removal efficiency by MW2501 kept stable and consistently higher than 90%. Besides, ∼100% removal of 0.5 mM As(V) can be obtained in the presence of P ≤ 0.1 mM or Cr/Sb ≤ 0.5 mM, indicating a wide applicability of MW2501 for treatment of As-containing water. The predominance of Fe3O4 on MW2501 surface was evidenced by XRD. Ligand exchange between As(V) anion and the hydroxylated surface of Fe3O4 as well as H bond was largely responsible for As(V) sorption as suggested by FTIR. XPS analysis further revealed the dominance of As(V) in the sorbed As on MW2501 surface with co-occurrence of a minor proportion of As(III) (11.45%). In parallel, oxidative transformation of Fe3O4 to Fe2O3 was also suggested by XPS. By a lab-scale column test, the potential and suitability of MW2501 in As-containing water treatment was further confirmed, which could also provide an alternative way to manage and utilize this highly problematic invasive species.


Assuntos
Arseniatos/isolamento & purificação , Carvão Vegetal/química , Eichhornia , Óxido Ferroso-Férrico/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Biomassa , Compostos Férricos/química , Espécies Introduzidas , Análise Espectral , Purificação da Água
19.
J Environ Manage ; 172: 71-6, 2016 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-26921567

RESUMO

A novel bioflocculant (MBF-79) prepared using formaldehyde wastewater as carbon resource was investigated in the study. The optimal conditions for bioflocculant production were determined to be an inoculum size of 7.0%, initial pH of 6.0, and formaldehyde concentration of 350 mg/L. An MBF-79 of 8.97 g/L was achieved as the maximum yield. Three main elements, namely C, H, and O, were present in MBF-79 with relative weigh percentages of 39.17%, 6.74%, and 34.55%, respectively. The Gel permeation chromatography analysis indicated that the approximate molecular weight (MW) of MBF-79 was 230 kDa. MBF-79 primarily comprised polysaccharide (71.2%) and protein (27.9%). Additionally, conditions for the removal of arsenic by MBF-79 were found to be MBF-79 at 120 mg/L, an initial pH 7.0, and a contact time 60 min. Under the optimal conditions, the removal efficiencies of arsenate (0.5 mg/L) and arsenite (0.5 mg/L) were 98.9% and 84.6%, respectively. Overall, these findings indicate bioflocculation offers an effective alternative method of decreasing arsenic during water treatment.


Assuntos
Arsênio/isolamento & purificação , Formaldeído/química , Águas Residuárias/microbiologia , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Arseniatos/isolamento & purificação , Arsênio/química , Arsenitos/isolamento & purificação , Carbono/metabolismo , Floculação , Concentração de Íons de Hidrogênio , Esgotos/microbiologia , Águas Residuárias/química
20.
Chemosphere ; 138: 682-90, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26247411

RESUMO

Blue green algae Anabaena sp. was cultivated in synthetic arsenite solution to investigate its bio-oxidation potential for arsenic species. Response surface methodology (RSM) was employed based on a 3-level full factorial design considering four factors, viz. initial arsenic (III) concentration, algal dose, temperature and time. Bio-oxidation (%) of arsenic (III) was considered as response for the design. The study revealed that about 100% conversion of As (III) to As (V) was obtained for initial As (III) concentration of 2.5-7.5 mg/L at 30 °C for 72 h of exposure using 3 g/L of algal dose signifying a unique bio-oxidation potential of Anabaena sp. The dissolved CO2 (DCO2) and oxygen (DO) concentration in solution was monitored during the process and based on the data, a probable mechanism was proposed wherein algal cell acts like a catalytic membrane surface and expedites the bio-oxidation process. Bioaccumulation of arsenic, as well as, surface adsorption on algal cell was found considerably low. Lipid content of algal biomass grown in arsenite solution was found slightly lower than that of algae grown in synthetic media. Toxicity effects on algal cells due to arsenic exposure were evaluated in terms of comet assay and chlorophyll a content which indicated DNA damage to some extent along with very little decrease in chlorophyll a content. In summary, the present study explored the potential application of Anabaena sp. as an ecofriendly and sustainable option for detoxification of arsenic contaminated natural water with value-added product generation.


Assuntos
Anabaena/metabolismo , Arseniatos/metabolismo , Arsênio/química , Arsenitos/metabolismo , Poluentes Ambientais/metabolismo , Adsorção , Arseniatos/isolamento & purificação , Arsenitos/isolamento & purificação , Clorofila/análogos & derivados , Clorofila/metabolismo , Clorofila A , Poluentes Ambientais/isolamento & purificação , Oxirredução , Soluções
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