The determinants of divalent/monovalent selectivity in anion exchangers

This research demonstrates that it is the distance of fixed-charge separation in the resin which is the primary determinant of divalent/monovalent selectivity. Anion resins, particularly acrylics and epoxies, with closely spaced N-containing (amine) functional groups are inherently divalent-ion selective. This is because the uptake of a divalent anion, e.g. sulfate, requires the presence of two closely-spaced positive charges.Results from this study of 30 commercially-available, strong- and weak-base, anion resins indicate that in order to bring positive charges into close proximity within a resin one can: (1) incorporate the amine functional groups into the polymer chains as opposed to having them pendant on the chains; (2) minimize the size and number of organic ("R") groups attached to the N atom, i.e., minimize the size of the amine; and (3) maximize the resin flexibility, i.e., its ability to reorient to satisfy divalent counterions, by minimizing the degree of crosslinking.The distance-of-charge-separation theory is not restricted to divalent anion exchangers but also applies to cation exchangers and to polyvalent ions in general.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25250/1/0000693.pd

The Efficacy of Oxidative Coupling for Promoting In-Situ Immobilization of Hydroxylated Aromatics in Contaminated Soil and Sediment Systems

Many hydroxylated aromatic compounds (HACs), particularly small molecules such as substituted phenols, are common contaminants of surface and subsurface systems. The high environmental mobility of these contaminants, due to their relatively high water solubilities, is of particular concern. Abiotic and enzymatic oxidative coupling of this class of contaminants by natural sorbents may be significant in controlling the mobility of HACs and facilitate remediation efforts. The principal objectives of this study are to investigate: (1) the role of abiotic/enzymatic coupling reactions on the sequestration of HACs by natural sorbents; (2) the effects of sorbent structure and chemical composition on such sequestration; and (3) optimal conditions for the induction of these abiotic/enzymatic coupling reactions by addition of suitable catalysts and sorbents. Information gathered from the study will be useful in quantifying the behavior of this class of organic compounds in various subsurface contamination scenarios relevant to DOE facilities, and in specifying strategies for the selection and design of remediation technologies

Modeling the sorption of hydrophobic contaminants by aquifer materials--I. Rates and equilibria

This is the first of a two-part series describing experimental studies and numerical modeling of the sorption of hydrophobic contaminants by aquifer materials. The work focuses on the evaluation of predictive modeling methods for simulating sorption processes in groundwater systems. Equilibrium behavior and rates of approach to equilibrium were investigated for two hydrophobic solutes and three aquifer materials utilizing different reactor configurations. This paper discusses investigations conducted in completely mixed batch reactors. These investigations illustrate that sorption equilibria are nonlinear for the systems studied and that sorption rates involve an initial rapid step followed by a slower continuing uptake that can persist for several days. Alternative models for description of these equilibria and rate conditions are presented and compared. The second paper evaluates the use of sorption model coefficients determined from batch-reactor systems to model column-reactor systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27364/1/0000389.pd

Modeling the sorption of hydrophobic contaminants by aquifer materials--II. Column reactor systems

This is the second of a two-part series describing laboratory investigations and mathematical modeling of the sorption of hydrophobic solutes by aquifer materials. An evaluation is made of several rate and equilibrium models for description of solute sorption as a rational basis for predicting sorption processes in groundwater systems. The first paper presents and compares sorption in completely mixed batch-reactor systems while this paper addresses column-reactor systems. The results show that accurate representation of the sorption process can be obtained with either a dual-resistance diffusion model or an equilibrium/first-order sorption rate model. Changes in velocity of the fluid phase affect the magnitude of fitted model parameters, but changes in concentration have negligible influence on these parameters.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27365/1/0000390.pd

Sorption of hydrophobic organic pollutants in saturated soil systems

Sorption equilibria and rates were characterized for a matrix of four aquifer sands and two slightly to moderately hydrophobic organic solutes (nitrobenzene and lindane), and the effects of sorption on the behavior of these solutes in saturated systems of the soils were determined. Experimental data were used to test and evaluate a variety of mathematical models for predicting contaminant fate and transport in groundwater systems.Observed equilibrium relationships between soil and solution phase solute concentrations were found to be described best by the nonlinear Freundlich isotherm model. It was further determined that the sorption process in the systems tested is rate controlled, requiring several days to approach equilibrium in completely mixed batch reactors. Subsequent modeling of solute transport in continuous flow soil column reactors was found to be most successful when rate-controlled models were used, the best results were obtained with a dual-resistance model incorporating the coupled mass transport steps of boundary-layer and intraparticle diffusion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26279/1/0000364.pd

Correlation of humic substance trihalomethane formation potential and adsorption behavior to molecular weight distribution in raw and chemically treated waters

The molecular weight distributions (MWDs) of several commercially prepared humic and fulvic acids and organic matter present in natural waters were analyzed by gel chromatography. The responses of these substances to treatment by alum coagulation, lime softening, and activated carbon adsorption were also analyzed, as were their trihalomethane formation potentials before and after each treatment. The treatability characteristics and trihalomethane formation properties of the different organic substances were then related to their respective MWDs. Differences in the MWDs were found to effect differences in the behavior of lumped parameter measures of organic matter (such as TOC) with respect to the several treatment operations. The treatments in turn were observed to alter the MWDs of the organic substances as well as their phenomenological behavior in subsequent process operations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26722/1/0000272.pd

Addendum

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22321/1/0000766.pd

Structural and behavioral characteristics of a commercial humic acid and natural dissolved aquatic organic matter

Dissolved organic matter (DOM) from two natural surface water sources and a commercial humic acid were analyzed using gel-permeation chromatography, high pressure reverse phase liquid chromatography, and 1H-NMR spectroscopy. Results from the chromatographic studies show that the DOM of two natural waters consisted primarily of relatively low molecular weight, polar organic constituents, while large and relatively nonpolar macromolecules comprised a significant fraction of the commercial humic acid. The 1H-NMR assays indicated that DOM from the two natural water samples was comprised of nonaromatic organic constituents, while the commercial humic acids tested contained both aromatic and aliphatic moieties. Based upon these composite results of the several different types of analysis employed, it is evident that the humic acid examined, and possibly others prepared in the same way, contain molecular structures which exhibit physical and chemical properties that do not reflect the true nature of DOM in real aquatic systems. Commercially available humic substances of this type may therefore not be suitable surrogates for naturally occurring DOM in laboratory investigations and analysis of geochemical and environmental transformation reactions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28942/1/0000779.pd

Impacts of dissolved oxygen on the sorption of humic substances and the subsequent inhibition of o-cresol ptake by granular activated carbon

The impacts of dissolved oxygen (DO) on the sorption of natural and model humic substances by granular activated carbon (GAC) were investigated. Among five substances tested, the sorptions of only two, polymaleic acid (PMA) and peat humic acid, were affected by the presence of DO. The uptake of the target compound o-cresol on virgin GAC and on GAC preloaded with PMA under oxic and anoxic conditions was also examined. The oxic and anoxic preloading conditions had similar effects on subsequent o-cresol reactions under both oxic and anoxic sorption conditions. A reduction of approximately 20 % in o-cresol uptake observed under anoxic conditions by GAC preloaded under each condition is attributed to a decrease in the adsorption capacity of the GAC by preloading. In the presence of oxygen, however, an observed reduction of about 45% in o-cresol uptake by preloaded GAC appears to result from a combination of decreased adsorption and inhibited o-cresol polymerization.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31488/1/0000410.pd

Determination of partition coefficients and aqueous solubilities by reverse phase chromatography--II : Evaluation of partitioning and solubility models

Part I of this series examined the chemical and thermodynamic principles underlying the solubility and partitioning characteristics of non-electrolyte organic compounds in aqueous systems. It further considered those concepts which interrelate solubility and partitioning phenomena with retentive behavior in reverse phase liquid chromatography. Conceptual and predictive models which intercorrelate solubility, octanol/water partitioning, and reverse phase retention times were developed. Part II of the series evaluates the relative predictive abilities of these models for a wide range of different classes of organic pollutants. The results reveal that the reverse phase liquid chromatography models developed in Part I provide good estimates of octanol/water coefficients and aqueous solubilities from experimentally determined chromatographic retention times. Models structured to predict aqueous solubilities from octanol/water partition coefficient data were also found to provide reasonable estimates, but require as input physical and chemical parameters which are not readily accessible.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26006/1/0000073.pd