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 different electrolytes (i.e., KCl, NH4Cl, CaCl2 and Tetramethy- lammonium 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 effect is insufficient to account for the sorption enhancement by original bentonite with increasing KCl or NH4Cl concentration. X-ray diffraction 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+.
CHEN Baoliang, HUANG Wenhai Department of Environmental Science, Zhejiang University, Hangzhou 310028, Zhejiang, China.
A series of carbonaceous biosorbents was prepared by pyrolyzing pine needles,a model biomass,at various temperatures (100-700℃) under an oxygen-limited condition for 6h. The elemental composi-tions and the specific surface areas (BET-N2) of the biosorbents were analyzed. Sorption properties of 4-nitrotoluene to the biosorbents and their mechanisms were investigated,and then correlated with the structures of the biosorbents. The result shows that with the increase of the pyrolytic temperature,the aromaticity of the carbonaceous biosorbents increases dramatically and the polarity (the (N+O)/C atomic ratio) decreases sharply. Correspondingly,conformations of the organic matter in the biosor-bents transform gradually from a "soft-state" to a "hard-state" and the specific surface areas of the resultant biosorbents extend rapidly. The sorption isotherms fit well with the Freundlich equation. The regression parameters (i.e.,N and lgKf) are linearly related to the aromaticity indices (the H/C atomic ratio). Contributions of adsorption and partition to total sorption of the carbonaceous biosorbents are quantified. The adsorption of the carbonaceous biosorbents increases quickly with the increase of the pyrolytic temperature. The saturated adsorption amounts (Qmax) increase linearly with the increase of the specific surface areas (SA) of the biosorbents. For the carbonaceous biosorbents with hard-state carbon,the calculated normalized-Qmax values by SA are comparable to the theoretical estimation (2.45 μmol/m2). In comparison,for the carbonaceous sorbents with soft-state carbon,the calculated nor-malized-Qmax values by SA are much higher than the theoretical estimation. The partition coefficients (Kom) increase with the decrease of the polarity of the biosorbents,reaching a maximum,and then de-crease sharply with further decreasing the polarity,suggesting that partition mechanism be dominated by the compatibility and accessibility of the sorbent medium with organic pollutant. These observations will provide a theoretica
