Liming effect simulation-modeling

A large one-sixth-scale model of the unloader hopper was selected so that flow patterns in the enclosure could be evaluated.Smoke was used to simulate the behavior of the lime dust in the enclosure. The lime drop from the clamshell was simulated by releasing coarse sand, thus modeling the flow patterns caused by the volume displacement and the air entrainment. The effects of local wind speed and direction on the enclosure were also simulated. 

NPT ensemble anti used the shell-model to describe polarizability. All simulation runs were performed at atmospheric pressure and in the temperature range 10 - 1100 K. For all three surfaces at both 300 and 1100 K it was found that the surface mean square displacements are generally larger for the oxide ions than for the cations and that the out-of-plane surface motion is usually larger than the in-plane surface motion. At room temperature, the oxygen mean square displacements at the (111) surface arc a factor 1.2 larger than in the bulk, a factor 1.6 for the (Oil) surface and approximately five limes larger at the metastable (001) surface compared to the bulk. The effect of the presence of a surface on the ion dynamics (and on the structure for (011)) persists all the way to the slab centers, even for these rather thick slabs. 

In the following simulations, the other sensitivity factors (color, total-P and morphometry) were kept constant and pH varied to simulate effects of limings on the biouptake of the two test substances, Hg and Cs. It is possible to apply a given dimensionless moderator on many rates and model variables. This is schematically illustrated in Fig. 9.6 by the dotted arrow from YpH to the partition coefficient, since the water chemical conditions (pH, alkalinity, etc.) could influence the way metals are bound to carrier particles. 

Fig. 9.6. Model simulation for Hg. Curve 1 gives the values for Hg-concentration in lake water. The values do not reach a perfect steady-state level due to the fact that so much Hg has been accumulated in the catchment area during the last 50 years (initial amount in the catchment is 15 000 g in the entire catchment situated in central Sweden data for our "mean" lake), the outflow rate from the catchment is 0.0025 (1/year). Curve 5 illustrates a simulated liming during year 20 which would increase pH from 6 to 6.7. Curves 2, 3 and 4 show the effects of such a liming on Hg-concentrations in phytoplankton, prey (bottom fauna, zooplankton, small fish) and predatory fish (pike, large perch, etc.)...

Fig. 9.9. Comparison of model predicted effects of a liming (curve marked 36 and 96 for the months when pH was changed from 6 to 6.7 and back to 6) on the concentrations of 3 Cs and "Hg" in (A) prey and (B) predatory fish. These calculations are related to a peak fallout during month 24 (atmospheric load 25 units, kBq/m or g/km ). The quotation marks have been used because this is a simulation meant to illustrate a hypothetical model comparison between "Cs" and "Hg"...

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