Adsorption Behavior Of Arsenic Research Articles

Influence of Phosphate on Arsenic Adsorption Behavior of Si-Fe-Mg Mixed Hydrous Oxide.

The arsenic adsorption performance of silicon (Si), iron (Fe), and magnesium (Mg) mixed hydrous oxide containing a Si: Fe: Mg metal composition ratio of 0.05:0.9:0.05 (SFM05905) was investigated. SFM05905 was synthesized by the co-precipitation method. Batch experiments on arsenic adsorption were conducted at various temperatures and concentrations. Adsorption isotherms models were represented by a linearized equations and were insensitive to temperature change. The anion selectivity of SFM05905 at single component was high for arsenite (III), arsenate (V), and phosphate (PO4), indicating that PO4 inhibits arsenic adsorption. The adsorption amount of As (III), As (V), and PO4 were compared using a column packed with granular SFM05905, and an aqueous solution was passed by a combination of several anions that are single, binary, and ternary adsorbate systems. As (III) had the highest adsorption amount; however, As (III) and PO4 were affected by each other under the ternary mixing condition. Although the adsorption amount of As (V) was smaller than that of As (III), it was not affected by other adsorbates in the column experiments. Finally, although the adsorption of both arsenic continued, the adsorbed PO4 gradually desorbed.

Adsorption behavior of lead, cadmium, and arsenic on manganese-modified biochar: competition and promotion.

Biochar adsorption of heavy metals has been a research hotspot, yet there has been limited reports on the effect of heavy metal interactions on adsorption efficiency in complex systems. In this study, the adsorbent was prepared by pyrolysis of rice straw loaded with manganese (BC-Mn). The interactions of Pb, Cd and As adsorption on BC-Mn were systematically studied. The results of the adsorption isotherms for the binary metal system revealed a competitive adsorption between Pb and Cd, resulting in decreased Pb (from 214.38mg/g to 148.20mg/g) and Cd (from 165.73mg/g to 92.11mg/g). A notable promotion occurred between As and Cd, showing an increase from 234.93mg/g to 305.00mg/g for As and 165.73mg/g to 313.94mg/g for Cd. In the ternary metal system, Pb inhibition did not counteract the promotion of Cd and As. Furthermore, the Langmuir isotherm effectively described BC-Mn's adsorption process in monometallic, binary, and ternary metal systems (R2 > 0.9294). Zeta and FTIR analyses revealed simultaneous competition between Pb and Cd for adsorption on BC-Mn's -OH sites. XPS analysis revealed that As adsorption by BC-Mn facilitated the conversion of MnO2 and MnO to MnOOH, resulting in increased hydroxyl radical production on BC-Mn's surface. Simultaneously, Cd combined with the adsorbed As to form ternary Cd-As-Mn complexes, which expedited the removal of Cd. These results help to provide theoretical support as well as technical support for the treatment of Pb-Cd-As contaminated wastewater.

Sustainable removal of arsenic from waters by adsorption on blue crab, Portunus segnis (Forskål, 1775) chitosan-based adsorbents

Chitosan is the common name of a linear, copolymer of β-(1−4)-linked d-glucosamine and N-acetyl-d-glucosamine whose molecular structure comprises a backbone linked through glycosidic bonds. This polysaccharide has received a lot of attention due to its potential to remove heavy metals. In this context, this work was carried out with the aim of studying the efficacy of blue crab, Portunus segnis (Forskål, 1775) chitosan produced previously by the authors via a studied biological process to remove arsenic from aqueous solutions and therefore to be promoted in the environmental sector as effective ingredients for water decontamination. Batch experiments were performed to examine the effects of multiple parameters. Equilibrium isotherms were fitted using the Langmuir and Freundlich equation and finally, column experiments based on adsorption capacity were applied to better describe the adsorption process. The adsorption efficiency of powder from blue crab by-products, biological chitosan (BC) and commercially available chitosan (CC) was compared with that of magnetic chitosan (BMC) which was also prepared by a cross-linking reaction using glutaraldehyde (GTA) in the presence of magnetite. Features of each chitosan forms were analyzed by a field emission-scanning electron microscopy (FE-SEM). The BMC has been found to be effective in removing arsenic. Indeed, both BMC and CC showed improved adsorption behavior of arsenic after the addition of magnetic nanoparticles. The arsenic removal behavior of most materials can be explained by a pseudo-second-order kinetic model mechanism. The pH of the arsenic solution depends on the acid-base state of the adsorbent, which further influences the adsorption performance.

Self-Competitive Adsorption Behavior of Arsenic on the TiO2 Surface.

TiO2 is a commonly used material to remove arsenic from drinking water by adsorption as well as photocatalytic oxidation (PCO). In the present paper, arsenic adsorption and PCO at different pH environments are studied on the (1 1 0) facet of rutile TiO2 (r-TiO2). A self-competitive adsorption (SCA) behavior of arsenic is observed; i.e., arsenic species compete to adsorb on the surface. Related DFT calculations are carried out to simulate adsorption. SCA behavior is the key to connecting calculation results with experimental results. Furthermore, PCO of arsenite is performed at different pH values. Of note, PCO is related to adsorption; namely, the adsorption process determines the whole PCO reaction speed. Therefore, SCA is also helpful for the PCO reaction. The SCA behavior is useful not only for arsenic on r-TiO2 but also for arsenic on anatase TiO2 (a-TiO2). It may be helpful to further study arsenic adsorption and PCO on other materials such as Fe2O3 and MnO2. The SCA behavior extends our understanding of arsenic and provides new insights into arsenic removal and its cycle in nature.

Aspartic acid derivative-based MOFs: A promising green material for simultaneous removal of phosphorus and arsenic(V) in contaminated spring water

Metal-organic frameworks (MOFs) based on amino acids and their derivatives are biocompatible and environmentally friendly and have excellent practical application value in wastewater treatment. In this work, four MOFs based on aspartic acid derivatives were synthesized using Zr(IV) as the central ions and aspartic acid, succinic acid, fumaric acid, and malic acid as organic ligands. These were used for the simultaneous removal of phosphorus and arsenic from wastewater. The results showed that the maximum adsorption capacities of the aspartic acid-based Zr-asp MOF for phosphorus and arsenic(V) were 88.30 mg P g−1, 109.75 mg As g−1, respectively, in a single system, and 32.00 mg P g−1 and 59.75 mg As g−1, respectively, in a binary system of coexisting phosphorus and arsenic; these capacities were over a broad pH range of 5.0–9.0. Also, Zr-asp can be recycled at least 4 times. The Langmuir isothermal adsorption model and pseudo-second-order model can be employed to describe the adsorption behavior of phosphorus and arsenic(V) well on the MOFs based on aspartic acid derivatives in both the single-pollutant and two-pollutant systems. The mechanism of phosphorus and arsenic(V) reaction on MOFs was mainly electrostatic attraction and coordination reaction accompanied by ligand exchange, and the hydroxyl group on the surface of the material plays a key role. All the results indicated that the synthesized MOFs based on aspartic acid derivatives are ideal eco-friendly candidates for phosphorus and arsenic(V) removal in complex actual bodies of water.

Sustainable removal of arsenic from simulated wastewater using solid waste seed pods biosorbents of Cassia fistula L.

The present investigation is focused to develop a new type of solid waste based biosorbent, derived from the Cassia fistula pod biomass. The prepared biosorbent has been characterized through different techniques including field emission scanning electron microscopy, fourier transform infrared spectroscope and X-ray diffraction to investigate the physiochemical properties which are potential for the bioadsorbent application. The experiments have been performed considering four parameters namely; pH, biosorbent dose, initial concentration of As+3 and duration in the batch reactor. The experimental results have been analyzed using the design-expert software for the optimization of different parameters. The maximum removal of arsenic could be achieved ∼91% whereas monolayer adsorption capacity is found to be 1.13 mg g−1 in 80 min at pH 6.0 and 30 °C by using 60 mg dose of bioadsorbent. The arsenic adsorption behavior of the bio-adsorbent has been well interpreted in terms of pseudo-first order and Freundlich model.

Superior removal of As(III) and As(V) from water with Mn-doped β-FeOOH nanospindles on carbon foam

Arsenic pollution of water is one of the severest environmental challenges threatening human health. Iron-based nanomaterials have been demonstrated effective in arsenic removal. However, they generally suffer from low removal efficiency towards highly toxic As(III), loss of active sites owing to agglomeration, and poor reusability. Herein, we report a carbonized melamine foam supported Mn(IV)-doped β-FeOOH nanospindles(CF@Mn-FeOOH NSp) for tackling the technical hurdles. The designed CF@Mn-FeOOH NSp appears as a free-standing monolith through a low-cost and straightforward hydrothermal method. The atomic-scale integration of Mn(IV) into β-FeOOH enables an oxidation-adsorption bifunctionality, where Mn(IV) serves as oxidizer for As(III) and Fe(III) acts as adsorber for As(V). The maximal adsorption capacity for As(V) and As(III) can reach 152 and 107 mg g−1, respectively. Meanwhile, As in simulated high arsenic groundwater can be decreased to below 10 μg L−1 within 24 h. By simple “filtrating-washing”, 85% and 82% of its initial adsorption capacity for As(V) and As(III) can be easily recovered even after 5-cycles reuse. Kinetics and isotherm adsorption study indicate that the arsenic adsorption behavior is mainly through chemical bonding during single-layer adsorbing process. The as-prepared CF@Mn-FeOOH offers a scalable, efficient, and recyclable solution for arsenic removal in groundwater and wastewater from mines and industry.

Arsenic Adsorption on Modified Clay Minerals in Contaminated Soil and Water: Impact of pH and Competitive Anions

AbstractThis study evaluates the arsenic adsorption behavior of Fe‐exchanged smectite and phosphate‐bound kaolinite, in soil, tap water and double distilled water in the presence of competing anions such as silicate, phosphate, and sulfate, and at variable pH values. The maximum amounts of As adsorbed in soil are 620.6 and 607.6 µg g–1 at pH 5 by Fe‐exchanged smectite and phosphate‐bound kaolinite, respectively. The pH‐modified Freundlich equation fits well (R2 > 0.96) to the adsorption data, distinguishing the effect of pH on adsorption. The coefficients of pH‐value are 0.04 and 0.05 for phosphate‐bound kaolinite and Fe‐exchanged smectite, suggesting that low pH is suitable for the adsorption. The As adsorption is decreased in tap water at low pH compared to the soil due to the presence of iron (Fe2+/3+), sulfate, and bicarbonate in tap water. Among the competing anions in distilled water, phosphate is the most interfering anion for As adsorption. The competition coefficients of As‐phosphate binary adsorption derived from the Sheindorf equation are 3.93 and 0.56 for Fe‐exchanged smectite and phosphate‐bound kaolinite at pH 5. The Fe‐exchanged smectite can be used more effectively than phosphate‐bound kaolinite for As remediation in systems having low pH (pH ≈5) and high phosphate concentration.

Effect of solution chemistry on aqueous As(III) removal by titanium salts coagulation.

Solution chemistry is of great importance to the removal of arsenic by coagulation through influencing the speciation of arsenic, the in situ precipitation of metal salts coupled with the adsorption and coprecipitation behavior of arsenic during coagulation. While the researches on the influence of solution chemistry in As(III) removal by titanium salts, a promising candidate for drinking water treatment was still deficient. Batch tests were performed to evaluate the removal of As(III) by titanium salts coagulation under solution chemistry influences. The results indicated that As(III) removal by Ti(SO4)2 and TiCl4 increased first and then decreased with the rising of solution pH from 4 to 10. TiCl4 preformed better in As(III) removal than Ti(SO4)2 at pH4-8, but the opposite trends were observed at pH9-10. XPS analysis indicated that the involvement of surface hydroxyl groups was primarily responsible for As(III) adsorption on Ti(IV) precipitates. As(III) removal was inhibited in the presence of SO42- mainly by competitive adsorption, especially at elevated SO42- concentration under acidic and alkaline conditions. F- exerted a greater suppressive effect than SO42- via indirectly hindering Ti(IV) precipitate formation, and through direct competitive adsorption with H3AsO3, the inhibitive effect increased as F- concentration increased and depended highly on solution pH. As(III) removal was promoted by co-existing Fe(II) primarily through the facilitation of Ti(IV) precipitation, especially under neutral and alkaline conditions, while it was inhibited to a different extent by the presence of high-concentration Mn(II) possibly via competitive adsorption. The presence of Ca2+ and Mg2+ enhanced the removal of As(III), but the positive effect did not increase as ionic concentration elevated.

Arsenic Adsorption by Some Iron Oxide Minerals: Influence of Interfacial Chemistry

The dramatic increase in hydrometallurgical extraction of gold from arsenic bearing gold ores has inevitably resulted in the release of arsenic into the environment worldwide. Residual arsenic minerals in tailings storage facilities can be oxidised and mobilise arsenic into the environment. This can contaminate soils, ground and surface waters and eventually biota. In spite of well-established technologies and recent advances in arsenic remediation, there are limited knowledge and understanding of the iron oxide substrate (goethite, hematite and magnetite) mineralogy and the fate of arsenic on the surface charge of these iron oxide substrates in an aqueous media during adsorption. The aim of the present study was to investigate the influence of interfacial chemistry on arsenic adsorption onto selected iron oxide particles to assist in developing a better understanding and new knowledge in arsenic removal from contaminated waters. Bulk mineralogy and partial chemical composition of selected iron oxide minerals were obtained using quantitative x-ray diffractometry (QXRD) and acid digestion followed by metal determination using inductively coupled plasma optical emission spectrometry (ICP-OES) respectively. Zeta Potential measurements involving iron oxide particles as arsenic adsorbents were carried out to elucidate the influence of interfacial chemistry on the adsorption behavior of arsenic from solution. The study confirmed that the iron oxide minerals were predominantly hematite, magnetite and goethite with goethite containing significant amounts of quartz. Arsenic adsorption was pH dependent and strongly influenced the zeta potential and isoelectric point (IEP) of the iron oxide particles. The zeta potential of all substrates studied was strongly positive at pH 2 but indicated a reversal at pH ~ > 9. The interaction between substrates, arsenic and its hydrolysable products resulted in significant decrease in the magnitude of zeta potential and change in IEP indicating specific adsorption.
 
 Keywords: Arsenic, Adsorption, Iron Oxide Minerals, Zeta Potential

Synthesis of uniform-sized and microporous MIL-125(Ti) to boost arsenic removal by chemical adsorption

The adsorption behavior of arsenic on adsorbent have been researched widely, but chemical adsorption of arsenic is uncommon. In this work, a kind of microporous metal-organic framework (MIL-125(Ti)) with columnar morphology and uniform size was solvothermally synthesized, and its chemical adsorption behavior and mechanism of arsenic were firstly investigated by experimental and simulation study. Remarkably, ultra-fast adsorption behavior and excellent arsenic removal capability was achieved. It takes only 20 min to rapidly remove 5 mg L−1 arsenic with 0.2 g L−1 MIL-125(Ti), which is far superior to the previously reported materials. Both experimental and simulation study results show that the adsorption of arsenic obeys a new chemical adsorption mechanism. Both As(III) and As(V) can easily replace the terephthalic acid ligand via competitive coordination and bind to the Ti active site of MIL-125(Ti). In addition, the reaction energy barriers for ligand substitution by H2O, As(III) and As(V) are 0.46, 0.33 and 0.15 eV, respectively, which further confirming that structure reforming of MIL-125(Ti) plays a key role for chemical adsorption. The study solves the difficulty of removing low concentration of arsenic and provides molecular-level understanding of the chemical adsorption mechanism of arsenic on MIL-125(Ti).

Theoretical Investigation of Arsenic and Selenium Species Adsorption Behavior on Different Mineral Adsorbents

CaO and Fe₂O₃ are effective mineral sorbents to inhibit the damage of arsenic and selenium release into the atmospheric environment. Density functional theory was applied to explore the adsorption mechanism of different arsenic and selenium species (atom, hydride, oxide, and chloride) on CaO and Fe₂O₃ surfaces. The effect of the As₄O₆ cluster on the adsorption behavior of CaO and Fe₂O₃ surfaces was also examined. The results show that the O top sites serve as the active sites for arsenic and selenium atom adsorption on the CaO(001) surface. For the Fe₂O₃(001) surface, the adsorption energy of the As atom at the Fe top and O bridge site can reach −381.38 and −439.55 kJ/mol, respectively. The results show that the Fe top site and O bridge site are both effective chemical adsorption sites. CaO and Fe₂O₃ also exhibit a good performance to adsorb atomic arsenic and selenium under the condition of multicoverage. In addition, the interactions between two adsorbents and complex arsenic/selenium species are weakened in different degrees, but still belong to chemical adsorption. The adsorption of the As₄O₆ cluster on the CaO surface is mainly attributed to the interaction between As atoms and O atoms on the CaO surface. The As₄O₆ adsorption on the Fe₂O₃ surface depends on the interaction between O atoms of As₄O₆ and Fe atoms on the Fe₂O₃ surface. However, the interactions can both lead to the formation of more stable arsenate, which contributes to the reduction of detrimental arsenic release.

Adsorption behavior and mechanism of arsenic on mesoporous silica modified by iron-manganese binary oxide (FeMnOx/SBA-15) from aqueous systems

Iron-manganese binary oxides (FeMnOx) can remove contaminants from aqueous solutions with high efficiency, and mesoporous silica (SBA-15) is widely used as a supporting material due to its large specific surface area and good stability. In this study, SBA-15 was used to support FeMnOx in the synthesis of a novel arsenic (As) adsorbent (FeMnOx/SBA-15), and its characteristics under different reaction conditions, such as pH, temperature, presence of competing ions, and humic acid, were tested. The results showed that the contaminant adsorption efficiency of the novel adsorbent was better than that of bare FeMnOx, as the addition of SBA-15 decreased the agglomeration effect of FeMnOx. Additionally, FeMnOx/SBA-15 underwent calcination to further enhance its performance. The state of iron and manganese in FeMnOx/SBA-15 and the corresponding arsenic removal efficiency were improved by calcination at 350 °C with an FeMnOx/SBA-15 mass fraction of approximately 45%. Almost 90% of As (50 mL, 5.0 mg L−1) could be removed by 0.2 g L−1 of FeMnOx/SBA-15 (mass ratio of 45% and calcination temperature of 350 °C). The FeMnOx/SBA-15 could regenerate and still be used after four consecutive cycles. The high As sorption capacity, ability to regenerate, and reusability of FeMnOx/SBA-15 confirmed that this adsorbent is promising for treating As-contaminated drinking water.

Co-adsorption of arsenite and arsenate on mixed-valence Fe(II,III) (hydr)oxides under reducing conditions

The reduction of Fe(III) in iron hydroxides plays a significant role in the geochemical cycling of arsenic. However, the adsorption behavior of arsenic (As) at mixed-valence Fe(II,III) (hydr)oxides/water interface remains unclear. This work presents the kinetics, isotherms, and pH edge of arsenite (As(III)) and arsenate (As(V)) co-adsorption on the surface of Fe(II,III) (hydr)oxides as a function of Fe(II)/Fe(III) molar ratio and pH under anoxic environment. The XRD and Raman results indicated that by using Fe(II) and Fe(III) mixed solution as precursors, the coprecipitated products at pH 9 possibly were the mixture of ferrihydrite, goethite, magnetite and green rust, leading to a significantly smaller surface area than ferrihydrite. The adsorption of both As(III) and As(V) decreased significantly as the Fe(II)/Fe(III) molar ratio in the synthetic Fe(II,III) (hydr)oxides increased from 0 to 4. The adsorption of both As(III) and As(V) on the Fe(II,III) (hydr)oxides was strongly pH-dependent and showed completely opposite trends. As(V) was more easily adsorbed on the Fe(II,III) (hydr)oxides under acidic conditions, whereas an increasing amount of As (III) was adsorbed on Fe (hydr)oxides under alkaline conditions, possibly due to the competitive adsorption. Our findings may contribute to the understanding of the interfacial behavior of arsenic in the reducing environments.

Arsenate retention mechanisms on hematite with different morphologies evaluated using AFM, TEM measurements and vibrational spectroscopy

Lenticular, ellipsoidal and flat tubular hematite particles were precipitated from ferric nitrate solutions in presence of minor amounts of Al, Si, Mg and organic acids (oxalic, citric and tartaric). Particle shape identification was performed using Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). Arsenate adsorption onto hematite with different morphologies was studied in batch experiments and through vibrational spectroscopy. Three bands assigned to As(V)–O–Fe at, respectively, 920, 895 and 820 cm−1 were in agreement with sorption data indicating inner-sphere complexes. As(V) adsorption kinetics was well described by a general model for diffusion into microporous surface sites showing large difference among the studied hematite samples. The maximum As(V) adsorption occurred near pH 4.0 while at alkaline pH there was a significant decrease of adsorption as confirmed by the shift of infrared As–O stretching bands of arsenate group. A change from tetrahedral Td symmetry to more stable symmetric groups such as C3v (monodentate complex), C2v (bidentate binuclear) or C1v (edge-sharing, bidentate binuclear) was deduced for As(V) sorbed on hematite. Fast arsenate adsorption was higher on ellipsoidal hematite particle with a dominant non basal (1 1 0) face. On the contrary, electrostatic attraction interaction could explain the fast As(V) adsorption on platy morphology characterized by basal face (0 0 1). Despite the discrepancy between theoretical considerations and experimental observations, the present contribution could lead to better understanding of the role played by hematite morphology on surface complexation model to describe arsenic adsorption behavior. Diffusional mass transport models applied to As sorption systems can explain such divergence due to: (i) external mass transport across the boundary layer surrounding the particle; (ii) diffusional mass transfer within the internal structure of the adsorbent particle by a nanopore, (iii) heterogeneity of the surface site. These findings are relevant to understanding the rates of interfacial processes involving arsenate sorption that can be take into account in mass transport models used for the removal of arsenic from contaminated water or wastewaters.

Arsenic adsorption on α-MnO2 nanofibers and the significance of (1 0 0) facet as compared with (1 1 0)

The adsorption behavior of arsenic (As) on specific crystalline phases of manganese dioxide (MnO2) remains unclear. In this study, we evaluated the ability of α-MnO2 nanofibers (MO-2) to remove both arsenite (As(III)) and arsenate (As(V)), using experimental and computational methods. The maximum adsorption capacity values of As(III) and As(V) on MO-2 were 117.72 and 60.19mg/g, respectively, which is higher than values reported for α-MnO2, β-MnO2 and γ-MnO2. In particular, because MO-2 has much higher adsorption capacity for As(III) than As(V), it can be effectively applied in removal of As(III) from groundwater, and a pre-oxidation process is not required. Fixed-bed tests showed that about 800mL As(III)- or 480mL As(V)-contaminated water could be treated before breakthrough, and MO-2 can be effectively regenerated using only 12mL of eluent. This means we can concentrate the As(III) and As(V) by factors of 66.6 and 40.0, respectively. According to density functional theory (DFT) calculations, As(III) and As(V) form stable complexes on (100) and (110) of α-MnO2. Moreover, the surface complexes of As(III) and As(V) on (100) are more stable than (110). Electron transfer from As(III) on (100) is greater than (110). These phenomenon are may due to the fact that (100) has lower surface energy than (110). Partial density of state (PDOS) analysis further confirmed that As(III, V) are chemisorbed on MO-2, which agreed with the Dubinin-Radushkevich model.

Graphene-Supported Spinel CuFe₂O₄ Composites: Novel Adsorbents for Arsenic Removal in Aqueous Media.

A graphene nanoplate-supported spinel CuFe2O4 composite (GNPs/CuFe2O4) was successfully synthesized by using a facile thermal decomposition route. Scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Electron Dispersive Spectroscopy (EDS), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) were employed to characterize the prepared composite. The arsenic adsorption behavior of the GNPs/CuFe2O4 composite was investigated by carrying out batch experiments. Both the Langmuir and Freundlich models were employed to describe the adsorption isotherm, where the sorption kinetics of arsenic adsorption by the composite were found to be pseudo-second order. The selectivity of the adsorbent toward arsenic over common metal ions in water was also demonstrated. Furthermore, the reusability and regeneration of the adsorbent were investigated by an assembled column filter test. The GNPs/CuFe2O4 composite exhibited significant, fast adsorption of arsenic over a wide range of solution pHs with exceptional durability, selectivity, and recyclability, which could make this composite a very promising candidate for effective removal of arsenic from aqueous solution. The highly sensitive adsorption of the material toward arsenic could be potentially employed for arsenic sensing.

Arsenic removal from aqueous solutions and the impact of humic and fulvic acids

This work studied the impact of humic and fulvic acids on the removal kinetics of arsenic (V) by granular ferric hydroxide (GFH) and the adsorption capacity of arsenic (V) onto GFH at equilibrium. The Freundlich and DubininRadushkevich models describe the arsenic (V) adsorption behavior onto GFH reasonably well (r2>0.905). The removal kinetics were studied by fitting the experimental data to both first-order and second-order models. The lowest adsorption capacity was observed in the presence of fulvic acids (FA), and conversely, the adsorption capacity in the presence of humic acids (HA) was lower than that without humic substances (WHS). The removal kinetics of arsenic (V) were well defined for the second-order model, with correlation coefficients ranging from 0.951 to 0.977. This study suggests that the presence of humic substances negatively impacts the removal of arsenic from water.

Aluminum Substituted Cobalt Ferrite (Co-Al-Fe) Nano Adsorbent for Arsenic Adsorption in Aqueous Systems and Detailed Redox Behavior Study with XPS.

Arsenic [As(III) and As(V)] adsorption on aluminum substituted cobalt ferrite (Co-Al-Fe) ternary metal oxide adsorbent is reported by means of qualitative and quantitative spectroscopy tools. IR and Raman active signals were observed around 810-920 cm-1 band indicate different As-OHcomplexed and As-Ouncomplexed stretching vibrations on to the adsorbent. The adsorption behavior of arsenic (III and V) onto these adsorbents is studied as a function of contact time, different concentrations, and pH conditions. The kinetics study on adsorption were performed to understand nature of adsorption which supports the Pseudo Second Order (PSO) model. The adsorption isotherms study indicates Freundlich type of adsorption. The maximum adsorption capacity of Co-Al-Fe adsorbent is observed around 130 and 76 mg g-1 for As(III) and As(V) systems, respectively. Detailed XPS study of As 3d, Fe 2p, Co 2p, and O 1s spectra has been reported in explaining the redox behavior and ligand exchange reactions in supporting arsenic adsorption mechanism.

Fabrication of a GNP/Fe-Mg Binary Oxide Composite for Effective Removal of Arsenic from Aqueous Solution.

Graphene nanoplates (GNPs) can be used as a platform for homogeneous distribution of adsorbent nanoparticles to improve electron exchange and ion transport for heavy-metal adsorption. In this study, we report a facile thermal decomposition route to fabricate a graphene-supported Fe–Mg oxide composite. The prepared composite was characterized using scanning electron microscopy, transmission electron microscopy, energy-dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. Batch experiments were carried out to evaluate the arsenic adsorption behavior of the GNP/Fe–Mg oxide composite. Both the Langmuir and Freundlich models were employed to describe the adsorption isotherm, in which the sorption kinetics of the arsenic adsorption process by the composite was found to be pseudo-second-order. Furthermore, the reusability and regeneration of the adsorbent were investigated by an assembled-column filter test. The GNP/Fe–Mg oxide composite exhibited significant fast adsorption of arsenic over a wide range of solution pHs, with exceptional durability and recyclability, which could make this composite a very promising candidate for effective removal of arsenic from aqueous solutions.