Activated carbon was tailored with both iron and quaternary ammonium surfactants so as to concurrently remove both arsenate and perchlorate from groundwater. The iron (hydr)oxide preferentially removed the arsenate oxyanion but not perchlorate; while the quaternary ammonium preferentially removed the perchlorate oxyanion, but not the arsenate. The co-sorption of two anionic oxyanions via distinct mechanisms has yielded intriguing phenomena. Rapid small-scale column tests (RSSCTs) with these dually prepared media employed synthetic waters that were concurrently spiked with arsenate and perchlorate; and these trial results showed that the quaternary ammonium surfactants enhanced arsenate removal bed life by 25-50% when compared to activated carbon media that had been preloaded merely with iron (hydr)oxide; and the surfactant also enhanced the diffusion rate of arsenate per the Donnan effect. The authors also employed natural groundwater from Rutland, MA which contained 60 microg/L As and traces of silica, and sulfate; and the authors spiked this with 40 microg/L perchlorate. When processing this water, activated carbon that had been tailored with iron and cationic surfactant could treat 12,500 bed volumes before 10 microg/L arsenic breakthrough, and 4500 bed volumes before 6 microg/L perchlorate breakthrough. Although the quaternary ammonium surfactants exhibited only a slight capacity for removing arsenate, these surfactants did facilitate a more favorably positively charged avenue for the arsenate to diffuse through the media to the iron sorption site (i.e. via the Donnan effect).
"Choi et al.  reported enhancement of adsorption capacity of granular activated carbon (GAC) for Cr(VI) by cationic surfactantmediated modification. Previous studies reported quaternary ammonium functional groups of cationic surfactant can serve as an effective modifier for anion exchange for perchlorate removal   . It was reported that cationic surfactant possessing trimethylammoium is more effective for Cr(VI) adsorption than pyridinium-based surfactant when used as a surface modifier of activated carbon . "
[Show abstract][Hide abstract] ABSTRACT: Modified granular activated carbon was prepared by coating quaternary ammonium-containing polymer [3-(methacryloylamino)propyl]-trimethylammonium chloride, onto granular activated carbon (GAC) to remove nitrate and Cr(VI) from aqueous solution. The removal efficiencies for nitrate and Cr(VI) increased as the concentration of the cationic polymer used for modification increased to 0.25%, but those decreased slightly when the polymer concentration further increased to 2.5%. Kinetics experiments indicated the adsorption was a fast process, reaching equilibrium in 90 and 120 min for nitrate and Cr(VI) adsorption, and the maximum equilibrium uptake of nitrate and Cr(VI) were about 26 and 81 mg g−1, respectively. The adsorption of both anions was well described by pseudo-second-order kinetics model and Langmuir isotherm model. There was a linear relationship between the amounts of desorbed chloride and adsorbed nitrate and Cr(VI), suggesting the main effect of modification was enhancement of ion exchange capacity of GAC. The thermodynamic data showed that adsorption process would be thermodynamically favorable, spontaneous, and exothermic nature. The adsorption capacity for Cr(VI) decreased continuously with an increase in initial solution pH from 3 to 8 but such an effect was less significant for nitrate. The nitrate and Cr(VI) adsorption decreased the most in the presence of sulfate, followed by chloride and phosphate. The overall results demonstrated the potential utility of a cationic polymer for enhancement of performances of GAC-based materials for anions removal from aqueous solutions.
Chemical Engineering Journal 11/2011; 175(1):298–305. DOI:10.1016/j.cej.2011.09.108 · 4.32 Impact Factor
"In the present study, the feasibility of granular ferric hydroxide (GFH) for perchlorate removal was tested as several iron-based adsorbents that require fewer chemical pretreatments and/or have longer operational lives have been intensively examined for the treatment of arsenic and perchlorate  . GFH has previously shown promising results for the removal of various anions e.g. "
[Show abstract][Hide abstract] ABSTRACT: The present research evaluates the efficacy of granular ferric hydroxide (GFH) for perchlorate removal from aqueous solutions. Laboratory scale experiments were conducted to investigate the influence of various experimental parameters such as contact time, initial perchlorate concentration, temperature, pH and competing anions on perchlorate removal by GFH. Results demonstrated that perchlorate uptake rate was rapid and maximum adsorption was completed within first 30 min and equilibrium was achieved within 60 min. Pseudo-second-order model favorably explains the sorption mechanism of perchlorate on to GFH. The maximum sorption capacity of GFH for perchlorate was ca. 20.0 mg g−1 at pH 6.0–6.5 at room temperature (25 °C). The optimum perchlorate removal was observed between pH range of 3–7. The Raman spectroscopy results revealed that perchlorate was adsorbed on GFH through electrostatic attraction between perchlorate and positively charged surface sites. Results from this study demonstrated potential utility of GFH that could be developed into a viable technology for perchlorate removal from water.
Chemical Engineering Journal 05/2010; 159(1-3-159):84-90. DOI:10.1016/j.cej.2010.02.043 · 4.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Five cationic surfactants were employed to modify activated carbon for the purpose of comparing the impacts of surfactant properties and operational parameters on modification. Surfactants under study included cetylpyridinium chloride monohydrate (CPC), hexadecyltrimethylammonium bromide (HDTMA), cetyltrimethylammonium chloride (CTAC), myristyltrimethylammonium bromide (MTAB), and decyltrimethylammonium bromide (DTAB). Results revealed that, properties of surfactants (critical micelle concentration, chemical configuration), initial loading concentration, pH of solution and carbon type all had significant impacts on surfactant loading. In general, surfactants with smaller micelle structures were more easily loaded than those with larger micelles. For all cationic surfactants tested here, loading is optimal around neutral pH. After surfactant loading, activated carbon presented a much positively charged surface and this is manifested in obvious improvement in perchlorate adsorption. Perchlorate was mainly adsorbed through ion exchange with surfactant-loaded activated carbon.
Colloids and Surfaces A Physicochemical and Engineering Aspects 10/2013; 434:236–242. DOI:10.1016/j.colsurfa.2013.05.048 · 2.75 Impact Factor
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