Aquatic environment

Effect of background electrolytes on the adsorption of nitroaromaticcompounds onto bentonite

CHEN Baoliang , HUANG Wenhai


Received September 07, 2008,Revised December 17, 2008, Accepted , Available online

Volume 21,2009,Pages 1044-1052

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To further elucidate interaction of nitroaromatic compounds with mineral surface, the sorption of m-dinitrobenzene (m-DNB) and nitrobenzene to original bentonite in aqueous solution containing di erent electrolytes (i.e., KCl, NH4Cl, CaCl2 and Tetramethylammonium bromide (TMAB)) was studied. The sorption of m-DNB was greatly enhanced with the presence of KCl and NH4Cl, while little influence was observed with CaCl2 and TMAB, following the order of KCl > NH4Cl TMAB, CaCl2, or DI water. For nitrobenzene, sorption enhancement only occurred at high nitrobenzene concentrations in the presence of KCl, and the solute equilibrium concentration at inflexion point was lowered with increasing KCl concentration. These sorption enhancements were significantly promoted with the increase of electrolyte concentration. The salting-out e ect is insu cient to account for the sorption enhancement by original bentonite with increasing KCl or NH4Cl concentration. X-ray di raction patterns of bentonite suspensions indicated that the sorption enhancement of m-DNB was attributed to the intercalation of K+ or NH4 + into bentonite interlayer and then dehydration with m-DNB to form inner-sphere complexes, which caused previously expanded bentonite interlayers to collapse in aqueous suspension, thus further enhanced the interaction of phenyl with siloxane surface. In comparison, the sorption enhancement of NB is attributed to the formation of outer-sphere complexes with K+ at high solute-loadings (> 200–400 mg/kg). The sorption of m-DNB to initially modified TMA+-bentonite and K+-bentonite was almost the same as respective sorption to original bentonite in solution containing TMA+ and K+.

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