Adsorption Capacities Of As Research Articles

Removal of arsenic from alkaline process waters of gold cyanidation by use of γ-Fe2O3@ZrO2 nanosorbents

Arsenic is a problem in gold mining, as it can adversely affect operations and poses a health hazard. Although a number of technologies has been developed for its removal, none of them is effective under all conditions. Adsorption in particular, is a promising approach, but most methods have concentrated on the purification of water under neutral or acidic conditions. In gold mining and metallurgical processing waters, these adsorbents tend to be less effective. In this study, the removal of As(III) and As(V) from simulated mining process waters by use of composite nanoparticles is considered. The particles consisted of γ-Fe2O3 cores coated with ZrO2. The maximum Langmuir adsorption capacities of As(III) and As(V) were 62.2mg/g and 18.3mg/g, respectively, at a pH of 9. In the alkaline process waters from a gold cyanide leaching plant, adsorption of 42.3mg/g for As(III) and As(V) collectively, remained satisfactory, despite the presence of multiple competitive ions. Moreover, the particles retained their capacities well after multiple cycles of regeneration.

Redox transformation of arsenic by magnetic thin-film MnO2 nanosheet-coated flowerlike Fe3O4 nanocomposites

Inorganic arsenic cycling in the natural environment is significantly controlled by manganese/iron oxides, and studying the redox transformation of arsenic in both aqueous and solid phase is therefore essential to understand its environmental toxicity and predict its environmental behavior. Herein, the synthesized magnetic thin-film MnO2 nanosheet-coated flowerlike Fe3O4 nanocomposites have been used to simultaneously investigate the potential redox transformation of arsenic in aqueous phase and arsenic speciation on the solid phase interface. The results showed the initial Mn/Fe ratio has serious influenced the morphologies, textural properties and uptake of arsenic in aqueous solution. The maximum adsorption capacities of As(III) and As(V) by MF2 were 76.73mg/g and 120.50mg/g, respectively. After 10h reaction, the total arsenic concentration in both As(III)-MF2 system and As(V)-MF2 system far below than that of 10μg/L, which was setted the maximum guideline concentration value in drinking water by World Health Organization (WHO). HPLC-ICP-MS revealed that in aqueous solution part of As(III) was oxidized into As(V), while As(V) was not reduced into As(III). X-ray absorption near edge structure (XANES) and XPS analysis from solid phase further confirmed that the MnO2 nanosheet mainly acted as an oxidant, while flowerlike Fe3O4 only played the role as an arsenic species adsorbent. Extended X-ray absorption fine structure (EXAFS) analysis indicated that both As(III) and As(V) formed inner-sphere bidentate binuclear corner-sharing (2C) complexes with an As-Fe interatomic distance of 3.32–3.34Å on the interface of As-MF2 solid phase.

Highly efficient removal of arsenic(III) from aqueous solution by zeolitic imidazolate frameworks with different morphology

In this study, zeolitic imidazolate frameworks (ZIFs) sorbents with three different morphology (cubic ZIFs, leaf-shaped ZIFs and dodecahedral ZIFs) were successfully synthesized in aqueous solution via green methods at room temperature and tested for removal of As(III). The ZIFs are all high crystalline, and with a BET surface area of 958.4, 12.7 and 1151.2 m(2)/g for cubic ZIFs, leaf-shaped ZIFs and dodecahedral ZIFs, respectively The experiment revealed that all three adsorbents exhibited excellent adsorption capacities of As(III) despite distinct specific surface area and morphology. The adsorption isotherms of cubic ZIFs, leaf-shaped ZIFs and dodecahedral ZIFs were generally fitted by Langmuir model and the maximum adsorption capacities were 122.6, 108.1, 117.5 mg/g, respectively at pH 8.5. At initial concentration of 200 mu g/L, As(III) was rapidly decreased to below 10 mu g/L by the three ZIFs in 2 h at a adsorbent dosage of 0.2 g/L. It was found that zinc hydroxyl substitution was the main surface complexation method for As(III) adsorption onto the three ZIFs evidenced by the FTIR and XPS results. (C) 2015 Elsevier B.V. All rights reserved.

Adsorptive removal of arsenic from aqueous solution by zeolitic imidazolate framework-8 (ZIF-8) nanoparticles

In this study, zeolitic imidazolate framework-8 (ZIF-8) nanosorbent was successfully synthesized via a facile method at room temperature. The ZIF-8 nanoparticles were characterized by nitrogen sorption, powder X-ray diffraction, field emission scanning electron microscope, transmission electron microscopy and Zeta potential. The synthesized ZIF-8 nanoparticles exhibited a high surface area of 1063.5 m(2)/g and were of 200-400 nm in particle size. The kinetic and isotherm data of arsenic adsorption on ZIF-8 were well fitted by pseudo-second-order and Langmuir models, respectively. The maximal adsorption capacities of As(III) and As(V) were of 49.49 and 60.03 mg/g, respectively, at T = 25 degrees C and pH 7.0. The ZIP-8 nanoparticles were stable at neutral and basic conditions. However, large amounts of Zn2+ were released into water from the sorbent at acidic condition, which dramatically hindered the adsorption of arsenic. SO42- and NO3- had no significant effect on the arsenic adsorption while the adsorption was significantly inhibited by PO43- and CO32-. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analysis revealed that electrostatic attraction and hydroxyl and amine groups on ZIF-8 surface played vital roles in the adsorption process. (C) 2014 Elsevier B.V. All rights reserved.

Synthesis of ordered mesoporous iron manganese bimetal oxides for arsenic removal from aqueous solutions

A novel ordered mesoporous iron manganese bimetal oxides (OMIM) was synthesized via the hard template approach. The obtained OMIM sample showed excellent performance for the arsenic removal due to its large surface area and pore volume. pH affected the removal efficiency of As(III) and As(V) significantly, and the highest removal occurred in acidic solutions for both arsenic species. The adsorption isotherms were well-described by Freundlich model, and the calculated adsorption capacities of As(III) and As(V) were 67.89 and 93.54mg/g, respectively. The adsorption kinetics fitted a pseudo-second order model, and intra-particle diffusion was not the only rate-limiting step in the adsorption process. Samples were characterized using SEM-EDS, TEM, XRD and XPS, and the redox states and yields of the arsenic species in aqueous solutions after the reaction of As(III)/As(V) with OMIM were also investigated by HPLC-ICP-MS. The results showed that the changed valence of Mn in OMIM favored As(III) removal and the mechanisms removal of both As(III) and As(V) were complex. In addition, to remove As(III) in aqueous solutions, OMIM plays a dual function as an efficient oxidant of As(III) due to its MnO2 content and subsequently as an excellent adsorbent for As(V).

Adsorption characteristics of arsenic from micro-polluted water by an innovative coal-based mesoporous activated carbon

An innovative coal-based mesoporous activated carbon (NCPAC) was prepared by re-agglomeration, oxidation and two-step activation using coal-blending as precursor. Adsorption capacities of As(III) and As(V) ions (<0.5mg/L) onto NCPAC as a function of pH, adsorbent dose, initial arsenic concentrations, contact time, and adsorption isotherms at 7°C was investigated. The innovative methods promoted total pore volume (1.087cm3/g), mesoporosity (64.31%), iodine numbers (1104mg/g), methylene blue (251.8mg/g) and ash contents (15.26%). The adsorption capacities of NCPAC for As(III) and As(V) were found to be strongly dependent on pH and contact time. The optimal pH value was 6. The equilibrium time was 60min for adsorption of As(III) and As(V) by NCPAC. The Langmuir model fitted the experimental data well for both As(III) (R2=0.9980) and As(V) (R2=0.9988). Maximum adsorption capacities of As(III) and As(V) (C0=0.50mg/L) by NCPAC were 1.491 and 1.760mg/g, respectively.

Experimental and model studies on comparison of As(III and V) removal from synthetic acid mine drainage by bone char

AbstractAcid mine drainage (AMD) commonly contains elevated concentrations of As(III) and/or As(V) due to oxidation of arsenic-containing sulfides. Bone char has been used as a low-cost filling material for passive treatment. The breakthrough curves of As(III) and As(V) were studied in column experiments conducted at different flow rates, adsorption cycle times, and with different coexisting cations and anions to compare their transport behaviours. The experimental data were fitted by the Convection- Diffusion Equation (CDE) and Thomas model with the aim of obtaining retardation factors of As(III) and As(V) and their maximum adsorption capacities, respectively. The maximum adsorption capacities of As(III) and As(V) are 0.214 and 0.335 mg/g, respectively. Coexisting Mn2+and Al3+ions can shorten the equilibrium time of As(V) adsorption from 25 h to 8 h, but they have little effect on As(III). The retardation factors of As(III) and As(V) calculated by the CDE model decrease with adsorption cycles from 37 to 20 and 51 to 32, respectively. The Mn2+and Al3+ions could enhance retention ability with adsorption cycle time, especially Mn2+for As(V). Secondary adsorption phenomena were observed only in breakthrough curves of As(V) in the presence of Mn2+and Al3+. The competitive influences of coexisting arsenic species is As(V) &gt; As(III). Regeneration experiments using distilled water and NaOH solution were completed to quantify the degree of desorption of both As(III) and As(V). The results show that As(V) adsorbed on bone char has better desorption performance than As(III), and the average degrees of desorption of As(III) and As(V) for three desorption experiments are 75% and 31%, respectively.

Iron Mixed Ceramic Pellet for Arsenic Removal from Groundwater

In this study, an innovative media, iron mixed ceramic pellet (IMCP) has been developed for arsenic (As) removal from groundwater. A porous, solid-phase IMCP (2–3 mm) was manufactured by combining clay soil, rice bran, and Fe(0) powder at 600°C. Both the As(III) and As(V) adsorption characteristics of IMCP were studied in several batch experiments. Structural analysis of the IMCP was conducted using X-ray absorption fine structure (XAFS) analysis to understand the mechanism of As removal. The adsorption of As was found to be dependent on pH, and exhibited strong adsorption of both As(III) and As(V) at pH 5–7. The adsorption process was described to follow a pseudo-second-order reaction, and the adsorption rate of As(V) was greater than that of As(III). The adsorption data were fit well with both Freundlich and Langmuir isotherm models. The maximum adsorption capacities of As(III) and As(V) from the Langmuir isotherm were found to be 4.0 and 4.5 mg/g, respectively. Phosphorus in the water had an adverse effect on both As(III) and As(V) adsorption. Scanning electron microscopy results revealed that iron(III) oxides/hydroxides are aggregated on the surface of IMCP. XAFS analysis showed a partial oxidation of As(III) and adsorption of As(V) onto the iron oxide in the IMCP.

Comparative and competitive adsorption of Cr(VI), As(III), and Ni(II) onto coconut charcoal

This study evaluates the behavior of coconut charcoal (AC) to adsorb Cr(VI), As(III), and Ni(II) in mono- and multicomponent (binary and ternary) systems. Batch experiments were carried out for mono- and multicomponent systems with varying metal ion concentrations to investigate the competitive adsorption characteristics. The adsorption kinetics followed the mechanism of the pseudo-second-order equation in both single and binary systems, indicating chemical sorption as the rate-limiting step of adsorption mechanism. Equilibrium studies showed that the adsorption of Cr(VI), As(III), and Ni(II) followed the Langmuir model and maximum adsorption capacities were found to be 5.257, 0.042, and 1.748 mg/g, respectively. In multicomponent system, As(III) and Ni(II) adsorption competed intensely, while Cr(VI) adsorption was much less affected by competition than As(III) and Ni(II). With the presence of Cr(VI), the adsorption capacities of As(III) and Ni(II) on AC were higher than those in single system and the metal sorption followed the order of Ni(II) > As(III) > Cr(VI). The results from the sequential adsorption-desorption cycles showed that AC adsorbent held good desorption and reusability.

TiO2 pillared montmorillonite as a photoactive adsorbent of arsenic under UV irradiation

A TiO2 pillared montmorillonite (TiO2/MMT) adsorbent was used to remove As(III) and As(V) from aqueous solution with or without UV irradiation. The adsorption kinetics, role of pH, effect of UV, and column experiments are discussed herein. The Ti-polyoxocations in pillared montmorillonite (MMT) were crystallised to anatase in the interlayer and on the external surface with hydrothermal treatment. The anatase TiO2 exhibited not only an improved arsenic adsorption capacity, but also enhanced photocatalytic efficiency. The TiO2/MMT adsorbent was characterised by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photo-electron spectroscopy (XPS) and nitrogen adsorption–desorption techniques. The interlayer d-spacing and BET-specific surface area increased after intercalation of TiO2 in montmorillonite. Without UV irradiation, the adsorption capacities of As(III) and As(V) were 4.58 and 4.86mgg−1. With UV irradiation, the adsorption capacities of As(III) and As(V) were 5.19 and 5.16mgg−1, respectively, and the equilibrium concentrations of both As(III) and As(V) were below 10μgL−1. In addition, column experiments of arsenic-contaminated groundwater removal were conducted using granular TiO2/MMT packed in a 10-cm-ID column with initial arsenic concentrations of 120, 220 and 410μgL−1. The results indicated that TiO2/MMT is a promising adsorbent for As(III) and As(V) removal from arsenic-contaminated water.

Removal of As(III) and As(V) in Groundwater Using Ferrite Adsorbents

Ferrite adsorbents containing magnesium, cobalt, nickel, zinc were prepared in order to remove As (III) and As (V) . They are adsorbents with large specific surface area. The ferrite adsorbents could effectively adsorb As (III) and As (V) at neutral pH. The adsorption percentage of As (III) and As (V) onto cobalt ferrite was larger than the other ferrite adsorbents. The adsorption capacity of cobalt ferrite for As (III) and As (V) was 0.83 and 0.52 mmol/g, respectively. The adsorption capacities of As (III) and As (V) on magnesium ferrites increased with increasing their specific surface area, suggesting that functional groups on the surface participate in the adsorption.

Adsorption Behavior of Arsenic (III) and Arsenic (V) Using Magnetite

In order to investigate the adsorptive properties for As(III) and As(V) at 303 K, the magnetite was prepared by adding the aqueous sodium hydroxide solution to the mixture solution of Fe 2+ :Fe 3+ = 1:2 using iron chloride. The adsorption ofAs(III) and As(V) was dependent on equilibrium pH and showed a maximum value at pH 6 and 5, respectively. From their chemical species existing at each pH and the pH of the zero point of charge of the magnetite surface, As(V) was probably adsorbed on the surface of the magnetite through the electrostatic force, while the adsorption ofAs(III) was different from that of As(V). It is probable that As(III) was absorbed through an ester reaction on the magnetite. The adsorption capacities of As(III) and As(V) were 2.77 x 10 -1 mmol.g -1 and 2.28 x 10 -1 mmol.g -1 , respectively. The adsorption equilibrium constants for As(III) and As(V) were 4.74 dm 3 .mmol -1 and 12.1 dm 3 .mmol -1 , respectively, suggesting that the magnetite has higher affinity to As(V). An aqueous sodium hydroxide solution was useful as an eluent for desorption of As(III) and As(V).

Geochemistry of inorganic arsenic and selenium in a tropical soil: effect of reaction time, pH, and competitive anions on arsenic and selenium adsorption

Factors that can affect As and Se adsorption by soils influence the bioavailability and mobility of these elements in the subsurface. This research attempted to compare the adsorption capacities of As(III), As(V), Se(IV), and Se(VI) on a tropical soil commonly found in Singapore in a single-species system. The effect of reaction time, pH, and competitive anions at different concentrations on the adsorption of both As and Se species were investigated. The As and Se adsorption isotherm were also obtained under different background electrolytes. The batch adsorption experiments showed that the sequence of the As and Se adsorption capacities in the soil was As(V) > Se(IV) > As(III) > Se(VI). The adsorption kinetics could be best described by the Elovich equation. The adsorption of As(V), Se(IV), and Se(VI) appeared to be influenced by the variable pH-dependent charges developed on the soil particle surfaces. Phosphate had more profound effect than SO 4 2− on As and Se adsorption in the soil. The competition between PO 4 3− and As or Se oxyanions on adsorption sites was presumably due to the formation of surface complexes and the surface accumulation or precipitation involving PO 4 3−. The thermodynamic adsorption data for As(V) and Se(IV) adsorption followed the Langmuir equation, while the As(III) and Se(VI) adsorption data appeared to be best-represented by the Freundlich equation.