Distributed reactivity model

Huang W, Weber W (1997) A distributed reactivity model for sorption by soils and sediments. 10. Relationships between desorption, hysteresis, and the chemical characteristics of organic domains. Environ Sci Technol 31 2562-2569... 

Weber, W.J., P.M. McGinley, and L.E. Katz. 1992. A distributed reactivity model for sorption by soils and sediments-1 Conceptual basis and equilibrium assessments. Environ. Sci. Technol. 26 1955-1962. 

The distributed reactivity models used by Burnham and Braun [92] in the kinetic analysis of complex materials (see Section 5.5.12.) deserve further consideration, particularly in view of the results obtained by Christy et ai, [93] for the kinetics of dehydration of calcium oxalate monohydrate. Water loss proceeds at different rates from different lattice sites in this monohydrate. 

Distributed Reactivity Model. Isotherm relationships observed for natural systems may well be expected to reflect composite sorption behavior resulting from a series of different local isotherms, including linear and nonlinear adsorption reactions. For example, an observed near-linear isotherm might result from a series of linear and near-linear local sorption isotherms on m different components of soft soil organic matter and p different mineral matter surfaces. The resulting series of sorption reactions, because they are nearly linear, can be approximated in terms of a bulk linear partition coefficient, KDr that is... 

Abstract The soil as an adsorbent has various active sites leading to rather complicated adsorption mechanisms with environmental pollutants, like pesticides. According to earlier results the chloroacetani-lide type herbicides as solutes resulted in two-step isotherms on soils and quartz. This phenomenon has not been observed yet concerning trace compounds in the environment. In this case the so-called distributed reactivity model is used, suggesting that the total sorption is given as the sum of the local adsorption isotherms. The adsorption of isoproturon (urea-type herbicide) and prometryn (5-triazine type herbicide) was studied on quartz at different pH values. 

Similarly to the multisite Langmuir [9] or to the so-called distributed reactivity model which allow the addition of various isotherm equations [10] the multistep isotherm is calculated as the sum of the i steps ... 

The distributed reactivity model explanation for the biphasic rate behavior commonly observed for desorption of HOCs from soils is that the soft-carbon sorbed, or labile fraction of the contaminant desorbs readily and reversibly, whereas the hard-carbon sorbed, or resistant component is released much more slowly. The slow desorption step has been attributed to non-Fickian diffusion into a tightly-knit SOM, polymerization, or entrapment within the SOM matrix. The rate model found in comparative analyses to be the most appropriate for description of such behavior (17) is a two-phase release model which couples first-order rate equations for both the slow, resistant, and rapid, labile fractions, < >r (= 1- (j) ... 

Modified Freundlich sorption models were developed to describe sorption in heterogeneous geosorbents containing both NOM and carbonaceous materials. Composite or distributed reactivity models (DRM) were introduced [28] and applied in a manner which combines the linear partitioning (absorption) part with the nonlinear adsorption part [26, 27, 31, 32]. The overall sorption isotherm can be described in the form of ... 

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