Kinetic modeling of AS(III) and AS(V) adsorption by a novel tetravalent manganese feroxyhyte

Magnetic nanocomposite adsorbents for abatement of arsenic species from water and wastewater

The presence of high concentrations of arsenic species in drinking water and other water bodies has become one of the most critical environmental concerns. Therefore, decontamination of arsenic-containing water is essential for improved health and environmental concern. In recent years, nano-adsorbents have been widely used for the adsorptive removal of arsenic from water. Separating existing nano-adsorbents from treated waters, on the other hand, is a critical issue for their potential applications in natural water treatment. To address these issues and to effectively remove arsenic from water, researchers looked at iron oxide-based magnetic nanocomposite adsorbents. The magnetic nanoadsorbents have the benefit of surface functionalization, making it easier to target a specific pollutant for adsorption, and magnetic separation. In addition, magnetic nanoparticles have a large surface area, high chemical inertness, superparamagnetic, high magnetic susceptibility, small particle size, and large specific surface area, and are especially easily separated in a magnetic field. Magnetic nano-adsorbents have been discovered to have a lot of potential for eliminating arsenic from water. The recent advances in magnetic nano-absorbents for the cleanup of arsenic species from water are summarized in this paper. Future perspectives and directions were also discussed in this article. This will help budding researchers for the further advancement of magnetic nanocomposites for the treatment of water and wastewater contaminated with arsenic.

Performance Evaluation of Small Sized Powdered Ferric Hydroxide as Arsenic Adsorbent

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

Cadmium, mercury, and nickel adsorption by tetravalent manganese feroxyhyte: selectivity, kinetic modeling, and thermodynamic study

This study is aiming to investigate tetravalent manganese feroxyhyte (TMFx) adsorption efficiency in removing heavy metals. The motivation of this study was the fact that TMFx is a highly negatively charged nanostructure material and that the metals Cd, Hg, and Ni were characterized as priority pollutants for drinking water. TMFx was evaluated through batch and continuous flow experiments in National Sanitation Foundation (NSF) water matrix which simulated the physicochemical characteristics of natural water. Water's pH significantly influences Cd and Ni adsorption efficiency which gradually increases when pH value rises from 5 to 9, while the corresponding one for Hg remains almost constant. Thermodynamic data showed a spontaneous and an exothermic nature weak-chemisorption (ΔΗ° = -17.5 ± 2 kJ/mol) of Cd, Ni, and Hg by TMFx. The determined ranking of adsorption affinity and selectivity (Cd > Ni > Hg) seems to be governed by the metals' speciation, as well as by hydration free energy, which is influenced, however, by their atomic radius. The lower adsorption capacity and selectivity of TMFx for Hg should be attributed both to uncharged species and to higher atomic radius. The similar Cd and Ni speciation in the NSF water matrix leads to the conclusion that the better affinity, selectivity, and adsorption kinetic of Cd versus Ni should be attributed to the lower hydration free energy of Cd which is in turn related to its higher atomic radius. The faster adsorption kinetic (Hg > Cd > Ni) of Hg may be attributed to the lower radius of its anhydrate species. Furthermore, TMFx showed high removal efficiency under continuous flow application in an adsorption bed setup. The determined uptake capacity (q _RL) at equilibrium-breakthrough concentration equal to the drinking water regulation limit (RL) of each metal were q ₁ = 2.5 μg Hg/mg TMFx, q ₅ = 5.2 μg Cd/mg TMFx, and q ₂₀ = 7.1 μg Ni/mg TMFx. Leaching tests of spent TMFx samples from the rapid small-scale column tests (RSSCTs) could be treated either as inert wastes after Cd and Ni adsorption or as non-hazardous waste after Hg adsorption.

One-Step Route to Iron Oxide Hollow Nanocuboids by Cluster Condensation: Implementation in Water Remediation Technology

The fabrication procedure of hollow iron oxide nanoparticles with a large surface to volume ratio by a single-step gas condensation process at ambient temperature is presented. Fe clusters formed during the sputtering process are progressively transformed into hollow cuboids with oxide shells by the Kirkendall mechanism at the expense of oxygen captured inside the deposition chamber. TEM and Raman spectroscopy techniques point to magnetite as the main component of the nanocuboids; however, the magnetic behavior exhibited by the samples suggests the presence of FeO as well. In addition, these particles showed strong stability after several months of exposure to ambient conditions, making them of potential interest in diverse technological applications. In particular, these hierarchical hollow particles turned out to be very efficient for both As(III) and As(V) absorption (326 and 190 mg/g, respectively), thus making them of strong interest for drinking water remediation.