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.

Selective, Photoenhanced Trapping/Detrapping of Arsenate Anions Using Mesoporous Blobfish Head TiO2 Monoliths

“…In this pH range, oxyanions are more plentiful on the adsorbent surface. This high oxyanion content results in the electrostatic repulsion between a negative sorbent surface TiO – and anionic assist, as evidenced by ζ-potential analysis (Figure B). − Figure B exhibits that top-peak of positive charge takes place at pH 3 and then decreases to negative values with rising of pH value as a result of formation of TiO – active sites. Meanwhile, conducting similar experimental conditions under UV irradiation (λ max = 365 nm) may enhance the removal and uptake amount of As­(V) species by BHT adsorbent ≫99.8%.…”

Critical Review of Advances in Engineering Nanomaterial Adsorbents for Metal Removal and Recovery from Water: Mechanism Identification and Engineering Design

“…However, the introduction of a caustic reagent has been shown to have a beneficial effect, achieving regeneration efficiencies exceeding 90% when an ion-exchange resin was used in a full-scale configuration to remove multiple metals from groundwater . As demonstrated by Chaudray and Farrell, the addition of a strong caustic reagent also can improve the regeneration efficiency of adsorbents that form strong bonds with metals. Many metals can form mono- or multidentate inner-sphere complexes with NAs.…”

Iron oxide xerogels for improved water quality monitoring of arsenic(iii) in resource-limited environmentsviasolid-phase extraction, preservation, storage, transportation, and analysis of trace contaminants (SEPSTAT)

“…Phosphate appears to assist in desorption from these sites with lower pH dependence, presumably because it is capable of competing with arsenic for adsorption at these sites at elevated pH, similar to previous usage of higher concentrations (100-1000 mM) of chloride ions for improved regeneration of iron-oxide-based arsenic sorbents. 29…”

“…One particularly promising elution mechanism is the widely demonstrated pH dependence of arsenic adsorption onto iron oxide, with high arsenic capacity at neutral pH and decreased arsenic capacity at basic pH. 23,25 High-pH sodium hydroxide solutions have been used for regeneration of ironoxide based arsenic sorbents, 29,30 suggesting the potential for arsenic quantitation via adsorption at neutral pH and recovery under basic conditions.…”