Combined hydrous ferric oxide and quaternary ammonium surfactant tailoring of granular activated carbon for concurrent arsenate and perchlorate removal.
ABSTRACT 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).
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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; 175:298–305. DOI:10.1016/j.cej.2011.09.108 · 4.06 Impact Factor
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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 · 4.06 Impact Factor
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ABSTRACT: Studies on arsenic removal by zero-valent iron (ZVI)–based system have focused mostly on batch or small scale tests. In this research, pilot-scale studies were carried out on arsenic removal by technologies developed in rapid small-scale column tests (RSSCTs). Pilot-scale studies can provide significant information on final scale-up to full-scale operation, which RSSCT inherently was not able to provide. In addition, comparison between pilot column and RSSCT breakthrough profiles could help validate RSSCT design, especially RSSCT for arsenic. Results from pilot studies indicate that arsenic removal by a system of ZVI plus iron-tailored granular activated carbon showed significant promise for practical applications. The best performance was achieved when ZVI worked together with carbon pretailored by an iron-salt evaporation method. In addition, the similarity in arsenic breakthrough curves between RSSCTs and pilot studies serves to confirm that it is appropriate to assume proportional diffusivity for arsenic oxyanions in RSSCT design.Environmental Engineering Science 02/2012; 29(9):897-901. DOI:10.1089/ees.2011.0386 · 0.93 Impact Factor