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Petit, J. A.; LaFargue, P.; Porte, L.; Duc, T. M. Electrochim. Acta 1979,24, 1023-1028. Cotton, F. A.; W i n , G. Advanced Inorganic Chemistry; John Wiley & Sons: New York, 1980. Brown, G. N. Ph.D. Dissertation, University of Colorado a t Boulder, 1991. Cooper, G.; Newell, D. A.; Sczechowski, J. Elucidation of Photocatalytic Purification Processes for the Removal of Trichloroethylene and Metal Ions from Water at Superfund Sites; USEPA Final Report No. 68D80059, 1990.
(32) Prairie, M. R.; Pacheco, J.; Evans, L. R. Proceedings of the A S M E International Solar Energy Conference, 1992. (33) Buxton, G. V.; Greenstock, C. L.; Helman, W. P.; Ross, A. B. J . Phys. Chem. Ref. Data 1988, 17, 513-886.
Received for review June 22,1992. Revised manuscript received October 13,1992. Accepted October 28,1992. This research was supported through a subcontract (XC-1-10105-1) from the National Renewable Energy Laboratory.
Transport of Aminonaphthalene with a Site-Limited Transformation Reaction Jlm E. Szecsody," Gary P. Streile, and Wayne J. Pavalko Paciflc Northwest Laboratory, P.O. Box 999, Richland, Washington 99352
It is proposed that aminonaphthalene transport in groundwater systems that contain clay can be altered by two slow reactions on the clay surface: an ion-exchange reaction followed by an irreversible transformation reaction with a limited number of sites. Results of this study support the proposed reaction sequence and provide estimates of the reaction rates. Evidence that the initial ion exchange has occurred includes decreasing sorption at higher pH. Evidence that a transformation has occurred includes a lack of desorption even after 660 h and the presence of a transformation product on the surface. Solute breakthrough in columns shows that both reactions are slow and rates are needed to quantify transport. Reaction rates indicate that the ion-exchange reaction occurs within 0.05-2 h whereas the transformation reaction occurs in 50->lo00 h. This reaction sequence is limited by the number of transformation sites, and for the clay-coated alumina particles used, the number of sites is directly correlated to -1/140 of the cation-exchangesites. Because the transformation product is irreversibly sorbed, the number of ion-exchange sites decreases, and the sorption of other solutes is affected. Thus, increased aminonaphthalene sorption was shown to decrease the sorption of another ion exchanger (quinoline), but had no effect on a hydrophobic sorbing compound (naphthalene).
Introduction Aminonaphthalene is an environmentally important subsurface contaminant from the production of energy (1, 2 ) that is being studied in order to accurately predict its movement in groundwater systems and its effect on the movement of other solutes. Because aminonaphthalene undergoes a transformation reaction on a clay surface (3), the ability to predict its movement in a system with clay requires accurate knowledge of the reaction(s), the pass in different forms, and the reaction rates. In addition, because the transformation product appears to be strongly held on the surface, the sorption of other compounds may be affected. Further laboratory-scaleexperimentation and modeling was undertaken in this study, as there are not currently data or reactive transport models to answer these questions. The systems used to quantify the reactive transport consist of batch and column experiments, because both batch ( 4 , 5 )and column (6)systems have limitations. An understanding of processes at the field scale also involves larger-scale experiments, to account for interactions of small-scale processes with physical heterogeneities (7,8). Because this study involves only small-scale laboratory columns, only processes and interactions at a 356
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particle scale or smaller can be quantified. Given that the sorption and transformation reactions of aminonaphthalene can be defined, accurate masstransfer or reaction rates are also important for accurate predictions because the approach to equilibrium appears to be relatively slow. At the particle size, both physical and chemical processes can control the rate of aminonaphthalene sorption, desorption, and transformation. Slow chemical reactions can be caused by steric hindrance or high activation energy, whereas slow physical processes can result from ordinary diffusion in immobile pore water, ordinary diffusion in near-surface pore water, and nonordinary diffusion between clay interlayers or other small pores. Slow diffusion through soil organic matter has also been reported as a probable slow physical process (4). This process was not considered in this study because the surface studied has no organic matter. Both chemical mechanisms cannot be ruled out, as slow chemical sorption of bulky molecules with few functional groups is reported caused by steric hindrance (9) or high activation energy (10). Ordinary diffusion through immobile pore water is unlikely for the
