Equilibrium sorption and diffusion rate studies with halogenated organic chemical and sandy aquifer material
Concepts for rate limitation of sorptive uptake of hydrophobic organic solutes by aquifer solids are reviewed, emphasizing physical diffusion models and in the context of effects on contaminant transport. Data for the sorption of tetrachloroethene (PCE) and 1,2,4,5-tetrachlorobenzene (TeCB) on Borden sand are presented, showing that equilibrium is attained very slowly, requiring equilibration times on the order of tens of days for PCE and hundreds of days for TeCB. The rate of approach to equilibrium decreased with increasing particle size and sorption distribution coefficient, in accordance with retarded intragranular diffusion models. Pulverization of the samples significantly decreased the required time to equilibrium without changing the sorption capacity of the solids. Batch sorption methodology was refined to allow accurate measurement of long-term distribution coefficients, using purified {sup 14}C-labelled solute spikes and sealed glass ampules. Sorption isotherms for PCE and TeCB were conducted with size fractions of Borden sand over four to five orders of magnitude in aqueous concentration, and were found to be slightly nonlinear (Freundlich exponent = 0.8). A concentrated set of data in the low concentration range (<50 ug/L) revealed that sorption in this range could be equally well described by a linear isotherm. Distribution coefficients of the two solutes with seven size fractions of Borden sand, measured at low concentration and at full equilibrium, were between seven and sixty times the value predicted on the basis of recent correlations with organic carbon content. Rate results for coarse size fractions support a simple pore diffusion model, with pore diffusion coefficients estimated to be approximately 3 {times} 10{sup {minus}8} cm{sup 2}/sec, more than 200{times} lower than the aqueous diffusivities.
- Research Organization:
- Stanford Univ., CA (United States)
- OSTI ID:
- 5597636
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CHLORINATED ALIPHATIC HYDROCARBONS
SORPTION
CHLORINATED AROMATIC HYDROCARBONS
ADSORPTION ISOTHERMS
AQUIFERS
CARBON 14 COMPOUNDS
DIFFUSION
ENVIRONMENTAL TRANSPORT
PARTICLE SIZE
SOLUTES
TRACER TECHNIQUES
WATER POLLUTION
AROMATICS
CARBON COMPOUNDS
HALOGENATED ALIPHATIC HYDROCARBONS
HALOGENATED AROMATIC HYDROCARBONS
ISOTHERMS
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
MASS TRANSFER
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
POLLUTION
SIZE
540320* - Environment
Aquatic- Chemicals Monitoring & Transport- (1990-)
540311 - Environment
Aquatic- Basic Studies- Radiometric Techniques- (1990-)