Mobile anion concept

The SMART model (De Vries et al., 1989) estimates long-term chemical changes in soil and soil water in response to changes in atmospheric deposition. The model structure is based on the mobile anion concept, incorporating the charge balance principle. SMART 2 adds forest growth and biocycling processes, which allow soil... 

Stern layer are not completely immobilized but show a relatively high mobility. This concept of diffusion in the adsorbed state is well established in the older colloid literature and obviously has a firm experimental basis. The correlation between binding and the parameters of anions and anion-exchange resins is shown in Figure 4. 

A concept of anion mobility may be considered a useful paradigm for explaining the net retention and loss of cations from soils, and thus exposure pathways. This paradigm relies on the simple fact that total cations must balance total anions in soil solution (or any other solution), and, therefore, total cation leaching can be thought of as a function of total anion leaching. The net production of anions within the soil (e.g., by oxidation or hydrolysis reactions) must result in the net production of cations (normally H+), whereas the net retention of anions (by either absorption or biological uptake) must result in the net retention of cations. 

A further point of great interest that emerges from the work of Curtis and from the mechanism depicted in Fig. 4.14 is the concept of latent vacancies and sulfur mobility . This can be related to some recent important considerations on the existence of real anionic vacancies on Co-Mo-S surfaces, a frequently encountered key feature of HDS mechanisms. Tlie Co atom, which is known to be the primary site of attack of thiols in this case, is electronically saturated, but the empty site required for... 

Thus the mobility must increase considerably to an extent dependent on the ratio of charge and radius. These considerations lead Me BaiN to attribute the fall of the conductivity to the formation of undissociated soap molecules, while Lotter-moSer thinks that neutral colloid is produced in these circumstances. This conception by Me Bain is very improbable according to Hartley, since the considerable increase of the solubility of the soap above the critical concentration is then inexplicable (see Fig. 3). Also it is not clear to what the considerable solvent power for organic compounds could be attributed. Everythii indicates that micelles are, in fact produced at the critical concentration. Such a micelle of many fatty acid anions may however be considered more or less as a polyvalent ion and this makes it probable that deviations from the classical laws of ions occur. In the first place large Debye-Huckel effects can be expected, while on the other hand, a large part of the counter ions will be bound. This latter must be found by a comparison of the conductivity and the transport numbers (Hartley ). From such an investigation it I... 

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