Prediction of mass-transfer coefficient for solute transport in porous media

Several previously reported laboratory studies related to transport of solu tes through packed columns were utilized to develop predictive relationship s for mass-transfer rate coefficient. The data were classified into two gro ups: those obtained under rate-limited mass transfer between mobile and imm obile water regions (physical nonequilibrium conditions), and those derived from rate-limited mass transfer between instantaneous and slow sorption si tes (sorption nonequilibrium conditions). The mass-transfer coefficient in all these studies was obtained by fitting breakthrough data to a transport model employing a first-order rate limitations with a "constant" mass-trans fer coefficient, independent of flow conditions. This study demonstrated th at the mass-transfer coefficient in these models is dependent on system par ameters including pore-water velocity, length-scale, retardation coefficien t, and particle or aggregate size. Predictive relationships were developed, through regression analysis, relating mass-transfer coefficient to residen ce time. The developed relationships adequately estimated previously report ed field mass-transfer values. Successful simulations of field desorption d ata reported by Bahr [J. Contam. Hydrol. 4 (1989) 205] further demonstrate the potential applicability of the developed relationships. (C) 2001 Publis hed by Elsevier Science B.V.