Removal of arsenic, selenium, and chromium(VI) from wastewater using Fe(III)-doped alginate gel sorbent

Of the many toxic metals that may be present as contaminants in natural waters and wastewaters, a few (specifically arsenic, selenium, and chromium(VI)) occur as oxygen containing, negatively-charged ions (i.e., oxyanions). Removal of arsenic is, in particular, an issue of increasing concern. Re-evaluation of the current Maximum Contaminant Level for arsenic is mandated under the 1996 re-authorization of the Safe Drinking Water Act. A decrease in the current standard (50 {dollar}mu{dollar}g/L) would impact the required levels of treatment not only for potable water, but also for hazardous wastewaters and effluents under Resource Conservation and Recovery Act.; The study was designed to investigate a remediation strategy for selective removal of oxyanions by employing a negatively-charged biopolymer pretreated with cations. Charged polysaccharides, such as sodium alginate, often form hydrogels in the presence of cations, and this property was used in developing spherical gel sorbents (2 mm in diameter) by dispensing the biopolymer solution dropwise into calcium solution; Ca gel beads were further doped with Fe(III) to optimize both sorptive capacity for oxyanions and the physical properties of the gel beads.; Bench scale tests were conducted to study the fundamental aspects of oxyanion removal from contaminated water by investigating the effect of parameters such as pH, total Fe content, initial oxyanion concentration, ionic strength, and presence of anions and cations. Kinetics aspects of oxyanion sorption and desorption were also studied. The batch experiments demonstrated the effectiveness of Fe(III)-doped gels at removing As(V) and Se(IV) from solution over a wide concentration range (from {dollar}mu{dollar}g/L to mg/L); Cr(VI) removal was much less effective and the rate of sorption was much slower than that of As(V) and Se(IV). The column study ascertained that Fe(III)-doped gel sorbents were effective in removing oxyanion contaminants at concentrations and under conditions similar to those found in actual treatment systems.; The research demonstrated a possible remediation alternative for oxyanion contaminated wastewater by employing Fe(III)-doped biopolymeric gel sorbents, which are selective for oxyanions, economical compared to commercial anion-exchange resins, and environmentally benign.