Arsenic Adsorption Capacity Research Articles

Efficient capture of arsenate from alkaline smelting wastewater by acetate modulated yttrium based metal-organic frameworks

Arsenic is worldwide recognized the first-class carcinogen. How to efficiently treat arsenic in alkaline mining smelting wastewater is an urgent technical problem. Here in, acetate modulated yttrium-based metal-organic frameworks MOF-76(Y) (MOF-76(Y)-Ac) has been exploited for investing the adsorption behavior and mechanism of arsenate in alkaline conditions. MOF-76(Y)-Ac presented smaller particle size, higher porosity and larger number of coordinatively unsaturated sites, and consequently exhibited significantly enhanced adsorption affinity and capacity toward arsenate compared with that of pristine MOF-76(Y). In the optimized operating condition (pH 9–11), the maximum Langmuir adsorption capacity of arsenate by MOF-76(Y)-Ac can be 201.46 mg g−1 within 30 min. The arsenate adsorption capacity of MOF-76(Y)-Ac remained stable with the presence of coexisting anions and natural organic matters, even in practical simulated gold smelting alkaline wastewater. The formation of Y-O-As coordination connected with Y nodes in MOF-76(Y)-Ac originating from ligand exchange between arsenate and the BTC linkers is the main adsorption mechanism, besides, the ligand change mechanism with Y-OH sites and chemical precipitation mechanism by forming YAsO4 cannot be neglected. The used MOF-76(Y)-Ac can be recycled with HCl without changing its constant crystalline phase and adsorption performance. The results show that MOF-76(Y)-Ac can be a promising dearsenification reagent for high arsenic alkaline wastewater.

Occurrence of arsenic in ultramafic rocks’ alterites from nickel mines in New Caledonia: implications for the contamination of surface waters

Arsenate As(V) and arsenite As(III) are toxic forms of arsenic in waters. The risk of As toxicity is high in small tropical islands because tap water is often provided from surface water, and As contamination of surface water is rarely studied. For instance, the risk is high in New Caledonia because 61% of the water comes from surface water, and nickel mines induce the dispersal of large quantities of ultramafic rocks’s alterites rich in iron oxide-hydroxide, which are known to be associated with arsenite and arsenate. Levels exceeding the World Health Organization standard of 10 µg L−1 have been detected in rivers downstream of Ni mines, yet there is a lack of systematic assessment. Here, we analyzed total and exchangeable As in alterites collected near three active mines. Arsenate and arsenite adsorption capacity was studied using batch experiments. The results show that alterite contains total As contents ranging from 0.20 to 5.14 mg kg−1, yet the primary mineralogical source of As remains unknown. No exchangeable arsenite was detected. Exchangeable arsenate amounted to 0.16 mg kg−1, thus meaning that 10.3% of the total As is easily mobile. The maximum adsorption capacity of arsenate and arsenite in mining sediments was 1.05 mg kg−1. Overall, our findings reveal that ultramafic rock alterites are a source of arsenic in surface water in the form of suspended particulate matter, 10.3% of which being easily soluble.

Potential use of smartly engineered red mud nanoparticles for removal of arsenate and pathogens from drinking water

The aluminum industrial waste red mud was successfully utilized as a novel adsorbent for the removal of arsenic (As) ions from water. The arsenate (As (V)) adsorption efficacy of red mud nanoparticles was also investigated. Red mud nanoparticles were prepared by ball milling raw red mud for 10 h, yielding particles’ size of 20 nm on average. The As (V) adsorption on these nanoparticles strongly depended on the size of the nanoparticles. As (V) removal increased from 58 to 83% by reducing the size of red mud particles from 200 to 20 nm. Detail kinetics and transport study confirmed the pseudo-second-order kinetic process which was governed by external mass transport. The Freundlich (and Langmuir) isotherms confirm that the arsenate adsorption capacity changes from 2.28 mg/g (1.84 mg/g) to 2.54 mg/g (1.96 mg/g) for reduction of particles from size 200 nm to 20 nm. Water filter columns made with red mud nanoparticles prepared by ball milling for 10 h showed better filtration performance than the filter packed with raw red mud. Both the hydraulic conductivity and the As (V) removal (8 mm/h and 61% respectively) of influent 1 mg/L As (V) by red mud nanoparticles were greater than the raw red mud (3.2 mm/h and 54%). The modified red mud column filters also exhibited a higher efficiency than the raw red mud filters to remove Escherichia coli and Staphylococcus aureus from the water. Overall, this research shows that nanomaterials derived from aluminum processing waste can be a promising material for water filtration.

Arsenic adsorption by innovative iron/calcium in-situ-impregnated mesoporous activated carbons from low-temperature water and effects of the presence of humic acids

Innovative iron/calcium in-situ-impregnated mesoporous activated carbons (GL100 and GL200) have been prepared by iron/calcium in-situ-impregnation and Multistage Depth-Activation. Arsenic adsorption kinetics, isotherms, thermodynamics, and re-usability were investigated. Effects of surface-absorbed (ST-HA) and dissolved states humic acid (DHA) on the arsenic adsorption were also determined. Results suggested in-situ iron/calcium impregnation caused the well-development of mesoporous structures during ranges of 2.0–5.0 nm in GL100 and 5.0–50 nm in GL200, respectively. The increase of iron/calcium ensured surface basicity and high ash contents on GL100/GL200, and As(III)/As(V) can be better adsorbed in neutral conditions with higher kinetics in comparison with regular mesoporous carbon XHIT. Maximum adsorption capacities of As(III)/As(V) by GL100 and GL200 were 2.985/3.385 mg/g and 2.516/2.807 mg/g, respectively. Arsenic desorption and carbon re-usability of GL100/200 was improved. As(III)(As (V)) adsorption capacities by GL100 and GL200 were 2.437(1.672) mg/g and 1.740(1.308) mg/g, respectively, after eight cycles. Arsenic adsorption capacities on GL100 were proved to be promoted with the presence of low-level of ST-HA or DHA, and be inhibited at a high-level. As(V) was bound more strongly than As(III) in the presence of ST-HA. As(III)/As(V) uptakes increased slightly and decrease gradually to 1.75/1.86 mg/g in the presence of DHA (0–10 mg DOC/L). Physisorption and chemisorption mechanisms dominant in arsenic adsorption on GL100 in presence of humic acid, forming inner-sphere complexation with metallic oxide, functional groups on carbon surface and humic acid structure, or ternary surface complexation via cationic metal ions as cation bridge.

Influence of surface chemistry of activated carbon electrodes on electro-assisted adsorption of arsenate

In this work, the influence of oxygen-containing surface groups of activated carbon electrodes on the charge efficiency of electro-assisted adsorption of As(V) was investigated. It was distinguished between activated carbons modified through acidic (oxidation) and thermal (reduction) treatments, starting with a granular pristine commercial activated carbon of bituminous origin. The textural characterization of the three materials showed that the treatments did not produce significant changes in the surface area and in the distribution of pores. The three carbon samples were used to fabricate packed electrodes with stainless-steel mesh as electric current collector. This work report that the application of anodic potentials (1.01 and 1.41 V vs. NHE) increased the adsorption capacity and rate of arsenate uptake in solutions containing only this contaminant (2.5 mg L−1) at pH 7. The oxidized carbon electrode presented the lowest capacitance and adsorption capacity during electroadsorption (0.33 mg g−1), compared to pristine material (1.77 mg g−1). On the other hand, the reduced electrode displayed the highest adsorption capacity of arsenate (3.14 mg g−1) when applying a potential of 1.01 V. The results were correlated with the potential of zero charge values. In addition, for this material, the rate of kinetics increased 26.7 % compared to experiments without applied potential.

Heterojunction of vertically aligned MoS2 layers to Hydrogenated Black TiO2 and Rutile Based Inorganic Hollow Microspheres for the highly enhanced visible light arsenic photooxidation

In this research, Rutile Based Inorganic Hollow Microspheres (RBIHM) and hydrogenated anatase TiO2 nanoparticles decorated with MoS2 nanosheets (HBTiO2/RBIHM-MoS2 photocatalyst) using Pulsed Laser Ablation in Liquid (PLAL) followed by microwave irradiation. Formation of vertically aligned MoS2 nanosheets, RBIHM and HBTiO2 nanoparticles were confirmed by different characterization techniques. The spectroscopic analysis revealed phase transitions in HBTiO2/RBIHM nano and microstructures along with the formation of different crystal disorders such as amorphous layers, oxygen vacancies, trivalent titanium ions and formation of molybdenum oxide (MoO3-x) in MoS2. In addition, MoS2 films in HBTiO2/RBIHM-MoS2 nanocomposite showed both Mo5+ and Mo6+ oxidation state, which indicates that these films have a p-type conductive behavior. Furthermore, the interconnected layers of MoS2 nanosheets led to the formation of a porous like 3D nanostructure in HBTiO2/RBIHM-MoS2, which could significantly improve its photocatalytic performance. Arsenite photooxidation efficiencies of 70.3% and 96.6% and arsenate adsorption capacities of 1600 and 5200 μg g−1 were obtained for HBTiO2/RBIHM and HBTiO2/RBIHM-MoS2, respectively. The synergetic effects originated from making RBIHM-HBTiO2, RBIHM-MoS2 and MoS2–HBTiO2 heterojunctions along with the surface and morphology modification in MoS2 NSs and HBTiO2/RBIHM can explain the nanocomposite superior photocatalytic performance. The present work can trigger a broad interest in the cost-effective nanoarchitecture of visible light driven heterostructured photocatalysts.

Superior arsenate adsorption and comprehensive investigation of adsorption mechanism on novel Mn-doped La2O2CO3 composites

A major challenge for effective decontamination of arsenate from aqueous solution is the development of adsorbent possessing enormous high-active sites with strong affinity to realize both high adsorption capacity and reduction of arsenate down to permissive levels. Here we demonstrate that this challenge may be overcome by doping Mn atoms into La2O2CO3 materials. The synthesized material (5.26%-MnL) achieved an arsenate capture ability superior to most other currently-reported adsorbents, with the maximum adsorption capacity of 555.6 mg/g. Additionally, this novel adsorbent could dramatically reduce the concentration of arsenate from 3775 μg/L to less than 4 μg/L, well below the acceptable value for drinking water (10 μg/L). The adsorption capacity of 5.26%-MnL was demonstrated to be >300 mg/g over a wide pH range from 4 to 9 and the efficiency was maintained >85% even after three cycles of adsorption/desorption. Through a series of characterizations, both surface complexation and ion exchange were proved to contribute to arsenate removal at low molar ratios of As(V)/5.26%-MnL while forming LaAsO4 precipitation played a greater role at higher As(V)/5.26%-MnL ratios. Density Functional Theory (DFT) calculations suggested that Mn atoms acted as active species by not only increasing lattice defects and adsorption sites, but also by activating La3+ in La2O2CO3, which lowered the adsorption energy and facilitated arsenate removal. Due to the high affinity and superior adsorption capacity towards arsenate, Mn-doped La2O2CO3 has been demonstrated to be a promising prospect for the remediation of arsenate-polluted water.

Effect of extracellular polymeric substances on arsenic accumulation in Chlorella pyrenoidosa

Inorganic arsenic (iAs) in its dominant dissolved phase in the environment is known to pose major threats to ecological and human health. While the biological effects in many arsenic-bearing freshwaters have been extensively studied, the behavior and bioaccumulation of dissolved iAS in the presence of extracellular polymeric substances (EPS) still remains to be a critical knowledge gap. In this study, the uptakes and kinetic characteristics of iAs were studied using Chlorella pyrenoidosa (a typical freshwater green algae) by addressing the different effects of EPS on arsenite (AsШ) and arsenate (AsV). The arsenic uptake capacity increased as the exposure concentration increased from 0 to 300 µmol L−1, and the uptake rate constants (Ku) in the Bio-dynamic model were greater for AsV than AsШ (0.63–11.57 L g−1 h−1 vs. 0.44–5.43 L g−1 h−1). The toxic effects as mitigated by EPS were observed through the morphological changes of algal cells by TEM and SEM. When compared with the EPS-free algal cells (EPS-F), EPS-covered cells (EPS-C) had a higher arsenic adsorption capacity through EPS-enhanced surface adsorption and reduced intracellular uptake. The overall decrease (35% and 23.3% for AsШ and AsV, respectively) in the maximum uptake capacity in intact algae cells favors cell’s tolerance to the toxic effects of iAs. These observed discrepancies between AsШ and AsV and between EPS-C and EPS-F were further elucidated through morphological images (TEM and SEM) and molecular/atomic spectroscopic data that combine three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Altogether, the spectroscopic evidence revealed the interactions of iAs with C–O–C, C–O–H and –NH2 functional groups in EPS’ tyrosine- and tryptophan-like proteins as the binding sites. Overall, this study for the first time provides comprehensive evidence on the iAs-EPS interactions. Such insights will benefit our understanding of the biogeochemical processes of iAs and the strategic development of bioremediation techniques involving microalgae in the natural and engineered systems.

Arsenic removal properties by electrolyzed and calcined manganese dioxide

As(V) removal properties of manganese dioxides which are commonly used for the removal of manganese in water treatment processes were evaluated in this paper. The following manganese dioxides were used: two types of powdered manganese dioxides powdered or electrolyzed MnO<sub>2</sub> (g-structure) and calcined MnO<sub>2</sub> (b-structure), and a granular MnO<sub>2</sub>, which was prepared by coating MnO<sub>2</sub> onto a ceramic particle. The maximum arsenate adsorption capacity of the electrolyzed and calcined MnO<sub>2</sub> was 2.22 and 2.26 mg-As g<sup>-1</sup>, respectively. The adsorption capacity of the granular MnO<sub>2</sub> was 0.543 mg-As g<sup>-1</sup> and this value corresponded to the MnO<sub>2</sub> content (23.2%) of the granular adsorbent. When an arsenate solution of 0.1 mg-As L<sup>-1</sup> was fed into the column (10 mm i.d.; 100 mm long) packed with the granular MnO<sub>2</sub> at SV = 20 h<sup>-1</sup>, the column received 28.9 L of the feed solution (3,580 times the bed volume) before the breakthrough point (0.01 mg-As L<sup>-1</sup>). The adsorption isotherms for the electrolyzed and granular MnO<sub>2</sub> were approximated by the modified Langmuir equations. On the other hand, the adsorption isotherm for the calcined MnO<sub>2</sub> was approximated by the Freundlich equation. Based on the adsorption isotherms, the As(V) adsorption amounts at 0.01 mg-As L<sup>-1</sup> of the equilibrium concentration were evaluated as follows: 1.27 mg-As g<sup>-1</sup> for the electrolyzed MnO<sub>2</sub>, 1.20 mg-As g<sup>-1</sup> for the calcined one, and 0.29 mg-As g<sup>-1</sup> for the granular one. Since granular MnO<sub>2</sub> has been commonly used for the removal of manganese from water treatment systems, the process can be also applied to arsenate removal.

Effective preparation of nitrogen-doped activated carbon by aniline thermal chemical vapor deposition for arsenate adsorption

Nitrogen-free phenol resin fiber was used to examine the effect of nitrogen-introduction via thermal chemical vapor deposition (CVD) using nitrogen-containing chemicals. In this study, a combination of heat treatment, steam activation, aniline CVD was conducted to prepare the nitrogen-doped activated carbon (AC) and the effective procedure was studied to enhance arsenic adsorption capacity. As a result, consecutive treatment of steam activation as pre-treatment, aniline CVD, steam activation for porous structure, and at least heat treatment was the best processing order for the preparation of ACs. Heat-treated samples demonstrated their robustness against steam activation; therefore heat treatment should be conducted as post treatment for effective CVD process. One of the samples which was prepared by this procedure, 8ST30-8ANL10-8ST50-9.5HT30 (sample #5) showed 0.112 mmol/g of arsenate adsorption capacity, and it was at least 70% higher than that of any other prepared samples. To inspect the high adsorption capacity of this sample, the effect of solution pH, pore structure parameters, elemental analysis, and Boehm titration was conducted comparing with the other prepared samples.

Arsenic Removal from Water by Adsorption onto Iron Oxide/Nano-Porous Carbon Magnetic Composite

This study aimed to develop magnetic Fe3O4/sugarcane bagasse activated carbon composite for the adsorption of arsenic (III) from aqueous solutions. Activated carbon (AC) was prepared from sugarcane bagasse by chemical activation using H3PO4 as an activating agent at 400 °C. To enhance adsorption capacity for arsenic, the resultant AC was composited with Fe3O4 particles by facile one-pot hydrothermal treatment. This method involves mixing the AC with aqueous solution of iron (II) chloride tetrahydrate, polyvinyl pyrrolidone (PVP), and ethanol. Batch adsorption experiments were conducted for the adsorption of As (III) onto the composite. The effects of pH, adsorbent dosage, and contact time on the arsenic adsorption were studied. The result showed that the composite could remove the arsenic from the water far more effectively than the plain AC. The highest percentage of arsenic removal was found at pH at 8, adsorbent dose of 1.8 g/L, and contact time of 60 min. Langmuir and Freundlich adsorption isotherm was used to analyze the equilibrium experimental data. Langmuir model showed the best fit compared to the Freundlich model with a maximal capacity of 6.69 mg/g. These findings indicated that magnetic Fe3O4/sugarcane bagasse AC composite could be potentially applied for adsorptive removal of arsenic (III) from aqueous solutions.

In-Furnace Control of Arsenic Vapor Emissions Using Kaolinite during Low-Rank Coal Combustion: Influence of Gaseous Sodium Compounds.

Using additives in the in-furnace control of arsenic emissions is promising for reducing the impact on the downstream selective catalytic reduction system and blocking the spread of arsenic pollutants into the environment. The study quantifies the arsenic adsorption capacity of kaolinite at high temperature and clarifies its fixation pathway with and without the existence of sodium vapor, which is easily adsorbed by kaolinite. Experiments about Al-coordination and acid sites of products, as well as calculations of thermodynamic equilibrium and the adsorption energy based on density functional theory were performed. During separated arsenic adsorption, nearly 40% of trivalent arsenic [As(III)] is oxidized to pentavalent arsenic [As(V)] and bonded to kaolinite, forming an As-O-Al structure. In this respect, the arsenic adsorption capacity of kaolinite is 200 μg g-1, with 24% of arsenic shown to be well-crystallized Al-bound. During the co-adsorption process, 82% of As(III) is oxidized to As(V) and connected to the Al surface of kaolinite, and the O-Na groups bond to As around the As-O-Al structure, thereby forming Na-O-As-O-Al. The arsenic adsorption capacity increased to 878 μg g-1 with well-crystallized Al-bound arsenic accounting for 56%. This study demonstrates the potential for the application of kaolinite as an arsenic adsorbent in the actual furnace.

Efficient arsenic(V) removal from contaminated water using natural clay and clay composite adsorbents.

The natural clay is an abundant, accessible, and low-cost material that has the potential for use in the water and wastewater industry. In this paper, Iranian natural clay and clay/Fe-Mn composite were used to remove toxic arsenic from the liquid environment. The natural clay and clay/Fe-Mn composite were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray (EDX), X-ray diffractometry (XRD), thermo-gravimetric analysis (TGA), and atomic force microscopy (AFM) techniques. The effects of parameters (initial pH, temperature, sorption dose, and contact time) on the efficiency and behavior of the arsenic(V) adsorption process were studied. Freundlich (R2 = 0.945 and 0.989), Langmuir (R2 = 0.922 and 0.931), modified Langmuir (R2 = 0.921 and 0.929), and Dubinin-Radushkevich (R2 = 0.706 and 0.723) models were fitted to evaluate the equilibrium data of arsenic(V) adsorption process by natural clay and clay/Fe-Mn composite, respectively. The Langmuir adsorption capacity of arsenic(V) by the natural clay and clay/Fe-Mn composite was determined to be 86.86 mg/g and 120.70 mg/g, respectively. The arsenic(V) adsorption process followed the pseudo-second-order model. Negative values of ΔG° and ΔH° showed that the arsenic(V) sorption by the studied materials is thermodynamically spontaneous and exothermic. According to the findings, the natural clay and clay/Fe-Mn are suitable and recyclable sorbents for arsenic(V) adsorption from aqueous solutions. Also, the composite of clay with iron and manganese can improve the efficiency of clay in the removal of arsenic.

Facile Synthesis of Magnetic Activated Carbon Composite for Arsenic Adsorption

Porous activated carbon (AC) and magnetic iron oxide nanoparticles (NPs) are widely used for the removal of arsenic from water body. Fabrication of composite material of iron oxide NPs on the surface of porous AC can further enhance this activity for commercial application. In this research, a magnetic AC composite for arsenic adsorption was prepared by facile hydrothermal treatment of aqueous solution containing activated carbon obtained from lapsi seed stone, iron(II) chloride, polyvinylpyrrolidone (PVP) and ethanol. Several analytical techniques such as scanning electron microscopy (SEM), energy dispersive x-ray (EDX), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) confirmed the formation of magnetite (Fe3O4) nanoparticles on the surface of porous AC. The prepared materials were accessed for their arsenic adsorption capacity using arsenic (III) trioxide solution and found that composite Fe2O3/AC can remove the arsenic from water far more effectively than activated carbon alone. For 0.5 g/ltr loading of composite sample with contract time of 5 hours, the arsenic content was significantly reduced, which shows that as-fabricated composite can be used potentially for water treatment.

Assessing the Brazilian prevention value for soil arsenic: Effects on emergence and growth of plant species relevant to tropical agroecosystems

One of the entry routes of arsenic (As) into the food chain is through the consumption of edible parts of crops contaminated by this element. Different plant species present distinctive As accumulation and tolerance capacities. These differences are also influenced by As availability and speciation in soils. This study assessed the effect of As contamination on plant emergence and initial growth, as well as on accumulated As contents in different crops grown in tropical soils. In addition, it was intended to verify the protection level of the current soil As prevention value adopted in Brazil, which should be applicable for conceivably other tropical soils in Latin America. Plants of maize, rice, sorghum, common bean, sunflower, and radish were cultivated in two different tropical soils (Oxisol and Inceptisol) and in a standard substrate (tropical artificial soil - TAS) dosed with As (0; 8; 14.5; 26; 46.5; 84; 150; 270 mg kg−1). Early germination, total dry mass, As content, and bioconcentration factor were evaluated. The EC20 and EC50 values (the As concentration for 20% or 50% of effect relative to control treatment) based on total As concentration were more variable among different soils than the corresponding EC20 and EC50 values based on extractable (phytoavailable) As concentration. From the studied species, common bean was the most sensitive and maize was the least sensitive to As. Those species were the ones that accumulated the lowest As levels in shoot tissues. Arsenic concentrations measured in plant tissues and estimated bioaccumulation factors were not related to relative As toxicity among species. Data obtained suggest that the current Brazilian prevention value for arsenic is adequate for soils with high arsenic adsorption capacity.

Adsorption of hydrogen arsenate and dihydrogen arsenate ions from neutral water by UiO-66-NH2

The metal-organic framework (MOF) UiO-66-NH2 was synthesized with different substrate to solvent ratios and its morphology, surface area, pore distributions, and NMR, XRD, and TGA-FTIR patterns were obtained. Adsorption tests at pH 7 and 25 °C showed that the produced UiO-66-NH2 has a hydrogen arsenate adsorption capacity of 76.9 mg/g. With the affinity onto Zr clusters, this MOF also can adsorb phosphate ions from water. Treatment with 1–4 M hydrochloric acid (HCl) protonated the amine groups in the MOF. Treatment with 1 M HCl at 25 °C for 6 h maximized the adsorption capacity of UiO-66-NH2 to 161.3 mg/g, such that the protonated amine groups accounted for 53.7% of the adsorption of arsenate from the water. The use of excessively strong acid at elevated temperature reduced the adsorption capacity.

Arsenic adsorption and removal by a new starch stabilized ferromanganese binary oxide in water

A new starch stabilized ferromanganese binary oxide (starch-FMBO) with an Fe/Mn ratio of 1.00–2.00 and a synthetic pH of 2 was prepared using an organic polymer (starch) as the stabilizing dispersant. The maximum arsenic adsorption capacity of starch-FMBO was 161.29 mg/g. Adsorption optimization was also conducted, which revealed that starch-FMBO had a high adsorption capacity over a wide pH range (pH 3.0 to pH 11.0) and in the presence of some common anions (HCO3−, SO42−, Cl−, and NO3−). Arsenic removal by FMBO and starch-FMBO followed pseudo-second-order dynamics (R2 ≥ 0.99), indicating that the adsorption rate depended on the chemical adsorption process. Through the analysis of X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR), it was shown that hydroxyl was continuously produced and complexated with As(III) and As(V) during the adsorption process. Thus, the reaction of iron oxide and manganese oxide with arsenic was inferred and explained. The developed starch-FMBO shows promise for its application in the treatment of arsenic-contaminated water.

La ruta de trimetilsililación para preparar sílice modificada con grupos mercapto y su empleo como adsorbente de arsénico de fuentes de agua

La trimetilsililación (TMS) es una reacción que ha sido empleada, entre otros usos, para la obtención de oligosiloxanos a partir de silicatos naturales. La modificación de las condiciones de reacción puede permitir la obtención de sílice con propiedades texturales interesantes (área superficial, tamaño y volumen de poro) -y lo que ha sido poco explorado y se propone en este estudio-, la obtención de sílice modificada con grupos orgánicos por una ruta relativamente simple en función de los reactivos usados y de las condiciones de la reacción. La sílice a modificar es obtenida in situ y modificada en el mismo medio de reacción, ahorrando varias etapas. En este estudio, se sintetizó sílice modificada con grupos mercapto. La caracterización del material se realizó por FT-IR, resonancia magnética nuclear (RMN) en estado sólido de 29Si y 13C, análisis térmico (DTG/DTA) y fisisorción de nitrógeno. El material se valoró como adsorbente para la remoción de arsénico de soluciones acuosas estándar (hasta de 1 ppm de arsénico), usando un sistema de adsorción por lotes, variando la temperatura en un intervalo entre 20 °C y 30 °C. Se encontró que la mayor capacidad de remoción se favorece a la menor temperatura, logrando hasta un 68% de remoción, valores similares a otros reportados.

Application of Response Surface Methodology and Desirability Function in the Optimization of Adsorptive Remediation of Arsenic from Acid Mine Drainage Using Magnetic Nanocomposite: Equilibrium Studies and Application to Real Samples.

A magnetic multi-walled carbon nanotube/zeolite nanocomposite was applied for the adsorption and removal of arsenic ions in simulated and real acid mine drainage samples. The adsorption mechanism was investigated using two-parameter (Langmuir, Freundlich, Temkin) and three-parameter (Redlich–Peterson, and Sips) isotherm models. This was done in order to determine the characteristic parameters of the adsorptive removal process. The results showed that the removal process was described by both mono- and multilayer adsorptions. Adsorption studies demonstrated that a multi-walled carbon nanotube/zeolite nanocomposite could efficiently remove arsenic in simulated samples within 35 min. Based on the Langmuir isotherm, the adsorption capacity for arsenic was found to be 28 mg g−1. The nanocomposite was easily separated from the sample solution using an external magnet and the regeneration was achieved by washing the adsorbent with 0.05 mol L−1 hydrochloric acid solution. Moreover, the nanoadsorbent was reusable for at least 10 cycles of adsorption-desorption with no significant decrease in the adsorption capacity. The nanoadsorbent was also used for the arsenic removal from acid mine drainage. Overall, the adsorbent displayed excellent reusability and stability; thus, they are promising nanoadsorbents for the removal of arsenic from acid mine drainage.

Characterization of magnetite nanoparticles synthetized from Fe(II)/nitrate solutions for arsenic removal from water

Magnetite nanoparticles (NPs) were synthetized by partial oxidation of hot Fe(II) sulfate aqueous solutions upon addition of variable amounts of alkali/nitrate ions in a N2 atmosphere. The resulting NPs were extensively characterized by Scanning Electron Microscopy (SEM), X-Ray Powder Diffraction (XRPD), Dynamic Light Scattering (DLS) and Brunauer-Emmett-Teller (BET) analysis. Depending on the final pH after synthesis, partially oxidized magnetite NPs were obtained with average crystallite size ranging from 29 to 116 nm. The potential of NPs as arsenic adsorbents was investigated through batch adsorption experiments. The analysis of the adsorption isotherms performed on the basis of both Freundlich and Langmuir models, revealed that arsenic adsorption capacity was more efficient for magnetite NPs synthetized at final pH ≤ 6.56, characterized by polydisperse submicrometric aggregates with coarse macro- and mesopore distributions.