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Understanding Regeneration of Arsenate-Loaded Ferric Hydroxide-Based Adsorbents.

ABSTRACT: Adsorbents comprising ferric hydroxide loaded on a variety of support materials are commonly used to remove arsenic from potable water. Although several studies have investigated the effects of support properties on arsenic adsorption, there have been no investigations of their effects on adsorbent regeneration. Furthermore, the effect of regenerant solution composition and the kinetics of regeneration have not been investigated. This research investigated the effects of adsorbent and regenerant solution properties on the kinetics and efficiency of regeneration of arsenate-loaded ferric hydroxide-based adsorbents. Solutions containing only 0.10-5.0?M NaOH or 0.10-1.0?M NaCl, as well as solutions containing both compounds, were used as regenerants. On all media, >99% of arsenate was adsorbed through complexation with ferric hydroxide. Arsenate recovery was controlled by both equilibrium and kinetic limitations. Adsorbents containing support material with weak base anion-exchange functionality or no anion-exchange functionality could be regenerated with NaOH solutions alone. Regeneration of media containing strong base anion (SBA)-exchange functionality was greatly enhanced by addition of 0.10?M NaCl to the NaOH regenerant solutions. Adsorbed silica had a significant effect on NaOH regeneration of media containing type I SBA-exchange functionality, but on other media, adsorbed silica had little impact on regeneration. On all media, 5-25% of arsenate was resistant to desorption in 1.0?M NaOH solutions. However, the use of 2.5-5.0?M NaOH solutions significantly reduced the desorption-resistant fraction.

SUBMITTER: Chaudhary BK

PROVIDER: S-EPMC4378614 | biostudies-literature | 2015 Apr

REPOSITORIES: biostudies-literature

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Understanding Regeneration of Arsenate-Loaded Ferric Hydroxide-Based Adsorbents.

Chaudhary Binod Kumar BK Farrell James J

Environmental engineering science 20150401 4

Adsorbents comprising ferric hydroxide loaded on a variety of support materials are commonly used to remove arsenic from potable water. Although several studies have investigated the effects of support properties on arsenic adsorption, there have been no investigations of their effects on adsorbent regeneration. Furthermore, the effect of regenerant solution composition and the kinetics of regeneration have not been investigated. This research investigated the effects of adsorbent and regenerant ...[more]

PMID: 25873779

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Project description:Understanding arsenic reactions with ferric hydroxides is important in understanding arsenic transport in the environment and in designing systems for removing arsenic from potable water. Many experimental studies have shown that the kinetics of arsenic adsorption on ferric hydroxides is biphasic, where a fraction of the arsenic adsorption occurs on a time scale of seconds while full equilibrium may require weeks to attain. This research employed density functional theory modeling in order to understand the mechanisms contributing to biphasic arsenic adsorption kinetics. The reaction energies and activation barriers for three modes of arsenate adsorption to ferric hydroxides were calculated. Gibbs free energies of reaction depended on the net charge of the complexes, which is a function of the system pH value. Physical adsorption of arsenate to ferric hydroxide proceeded with no activation barrier, with Gibbs free energies of reaction ranging from -21 to -58 kJ/mol. The highest Gibbs free energies of reaction for physical adsorption resulted from negative charge assisted hydrogen bonding between H atoms on the ferric hydroxide and O atoms in arsenate. The conversion of physically adsorbed arsenate into monodentate surface complexes had Gibbs free energies of activation ranging from 62 to 73 kJ/mol, and Gibbs free energies of reaction ranging from -23 to -38 kJ/mol. The conversion of monodentate surface complexes to bidentate, binuclear complexes had Gibbs free energies of activation ranging from 79 to 112 kJ/mol and Gibbs free energies of reaction ranging from -11 to -55 kJ/mol. For release of arsenate from uncharged bidentate complexes, energies of activation as high as 167 kJ/mol were encountered. Increasingly negative charges on the complexes lowered the activation barriers for desorption of arsenate, and in complexes with -2 charges, the highest activation barrier was 65 kJ/mol. This study shows that the slow kinetics associated with arsenic adsorption and desorption can be attributed to the high Gibbs free energies of activation for forming and breaking bonds with the ferric hydroxide.

Project description:In this research article, wood based microfibrillated cellulose (MFC) was studied to gain a better understanding of the process of dependent network formation. Networking potential and obtained properties of the produced dimensional structures could be controlled using opted processing routes. The fabricated dimensional structure, using freeze-drying (FD) is a highly open and porous network (98% porosity) compared to slightly tight, dense and less porous network produced after pressing at 200kN (96% porosity), followed by vacuum-filtered (VF) networks (33% porosity). The porosity (17%) was further decreased when the casting (CS) method was used, further producing a highly dense and compressed network. High water flux (180.8?±?11?L/m2h) of pressed freeze-dried (PFD) followed by vacuum-filtered (VF) (11.4?±?1.9?L/m2h) and casting CS (0.7?±?0.01?L/m2h) were calculated using device. Furthermore, increased water flux (1.4 fold) of Experimental Paper Machine (XPM) based structures was reported in comparison with CS structures. Pore-sized distribution and surface area were measured using Hg porosimetry; they showed an average pore size of 16.5 ?m for FD, followed by PFD (8.2 ?m) structures. A 27-fold decrease in average pore-size was observed for CS structure in comparison with the FD structures. Highest tensile strength (87?±?21?MPa) was recorded for CS structures, indicating a more highly compacted network formation compared to VF (82?±?19?MPa) and PFD (1.6?±?0.06?MPa). Furthermore, an attempt was made to upscale the VF structures using traditional paper making approach on XMP. Improved tensile strength (73?±?11?MPa) in machine produced structures is due to alignment of fibers towards machine direction compared to cross directional (43?±?9?MPa) fractured structures as shown in our Scanning Electron Microscopy (SEM) analysis. Surface functionalization of MFC using enzyme (hexokinase) was performed to increase the adsorption efficiency towards ferric ions removal. All fabricated structures were further evaluated for Fe(iii) removal and it was summarized that charge densities of functional groups, produced ?-potential and networking potential were dominating influential factors for adsorption fluctuation of ferric ions.

Dataset Information

Understanding Regeneration of Arsenate-Loaded Ferric Hydroxide-Based Adsorbents.

Publications

Understanding Regeneration of Arsenate-Loaded Ferric Hydroxide-Based Adsorbents.

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