Xiaojiang Wang

Enhanced Transport of Low-Polarity Organic Compounds through Soil by Cyclodextrin.

The removal of low-polarity organic compounds from soils and aquifers by water flushing is often constrained by sorption interactions. There is great interest in developing systems that can enhance the transport of organic compounds through porous media, thus facilitating remediation. We investigated the potential of hydroxypropyl-[beta]-cyclodextrin (HPCD), a microbially produced compound, to reduce the sorption and to enhance the transport of several low-polarity organic compounds. The results show that cyclodextrin does not interact with the two porous media used in the study. As a result, there is no retardation of cyclodextrin during transport. The retardation of compounds such as anthracene, pyrene, and trichlorobiphenyl was significantly (orders of magnitude) reduced in the presence of cyclodextrin. The enhancement effect of the cyclodextrin was predictable with a simple equation based on three-phase partitioning. The nonreactive nature of cyclodextrin combined with its large affinity for low-polarity organic compounds makes cyclodextrin a possible candidate for use in in-situ remediation efforts. 22 refs., 6 figs., 3 tabs.

Simultaneous complexation of organic compounds and heavy metals by a modified cyclodextrin.

The cleanup of contaminated soil and groundwater at hazardous waste sites has become a major focus of research and policy debate. A major factor complicating the cleanup of many sites is the cooccurrence of organic compounds and heavy metals, the so-called mixed wastes. We investigated the ability of a modified cyclodextrin to simultaneously complex low-polarity organic compounds and heavy metals. The results of the experiments showed that carboxymethyl-{beta}-cyclodextrin could simultaneously increase the apparent aqueous solubilities of the selected organic compounds (anthracene, trichlorobenzene; biphenyl, and ODT) and complex with Cd{sup 2+}. This complexation was not significantly affected by changes in pH or by the presence of relatively high concentrations of Ca{sup 2+}. It is possible that this reagent can be used successfully to remediate hazardous waste sites contaminated by mixed wastes. 11 refs., 7 figs.

Cyclopentanol-enhanced solubilization of polycyclic aromatic hydrocarbons by cyclodextrins.

The effect of cyclopentanol on the solubilization of six polycyclic aromatic hydrocarbons (PAHs) by β-cyclodextrin (β-CD) and y-cyclodextrin (γ-CD) is reported in this paper. The addition of 0.1% v/v cyclopentanol significantly enhances the solubilization power of β-CD for pyrene, acenaphthene, phenanthrene, and fluoranthene, which form 1 :2 complexes with β-CD. However, the solubilization of acenaphthene and phenanthrene by β-CD in the presence of cyclopentanol decreases at higher β-CD concentrations following an initial increase. This phenomenon is attributed to the cyclopentanol-induced formation of insoluble β-CD aggregates. In contrast, cyclopentanol produces no pronounced effect and a marked decrease in the solubilization power of β-CD for naphthalene and anthracene, respectively. These two compounds form 1 :1 complexes with β-CD. The solubilization of all six PAHs by γ-CD is significantly enhanced by 1% v/v cyclopentanol. This result indicates that the addition of cyclopentanol increases the hydrophobicity of the γ-CD cavity and increases the solubilization power of γ-CD without inducing structure-dependent selectivity. On the basis of linearity and nonlinearity observed in the solubilization curves of the six PAHs in the presence of cyclopentanol, it is suggested that naphthalene, anthracene, acenaphthene, and phenanthrene form 1 :1 complexes with γ-CD while fluoranthene and pyrene form both 1 :1 and 2 :2 complexes.

Use of cyclodextrin and calcium chloride for enhanced removal of mercury from soil

The use of solutions containing carboxymethyl-beta-cyclodextrin (CMCD) or CaCl2 for enhancing the removal of Hg from a sandy soil was investigated using batch and column experiments. The retention of Hg appeared to be controlled by specific adsorption reactions, which greatly constrained Hg removal when using water (KNO3 solution) to flush columns packed with contaminated soil. The results showed that the two reagents did enhance the removal of Hg from the soil. For example, 81% and 60% of Hg was recovered after 50 pore volumes of flushing with 50 mM CaCl2 and 2 mM CMCD, respectively, compared to 24% recovery for a 10 mM KNO3 solution. However, significant tailing and delayed recovery of Hg during the elution process occurred in the presence of all reagents, indicating that the removal of Hg from the soil was rate limited.