Soil sorption from water temperature effect

The sorption of parathion and Lindane from a hexane solution has been studied using a Woodburn soil (fom = 0.019 68% silt 21% clay). ° An oven-dried soil gives a nonlinear isotherm (Fig. 3.14) that shows a much higher sorption capacity than that observed using water as solvent (Fig. 3.9). It is preferable to make this comparison on a relative basis since parathion, at 20°C, has a higher solubility in hexane (57 g L ) than water (12 mg L ). Thus Ce = 4 ppm C /S = 0.33) in an aqueous system corresponds to a sorption of 55 p,g g of soil. In a hexane system with Ce = 100 ppm (Ce/5h = 0.002) a sorption of 4000 p.gg of soil is observed. Sorption is decreased by water (compare the air- and oven-dried soils), and essentially no sorption is observed if the soil water content is increased to 5%. Decreased sorption at higher temperature would suggest an exothermic adsorption process. Parathion did not sorb to any extent from hexane onto a peat soil (/om = 0.51). The effect of water on the sorption of Lindane on the Woodburn soil from hexane (Fig. 3.15) was more pronounced and it was also demonstrated that parathion could compete with and reduce the sorption of Lindane. 

The vapor density of dieldrin over a Gila silt loam (0.6% om) increases with the concentration in the soil (Fig. 4.5) and at soil concentrations of only 100 ppm gives a vapor density essentially equal to that of the pure compound. As would be expected, vapor density over the soil increases with temperature. The effect of soil water content on the vapor density of dieldrin over the same sod has been reported and from Figure 4.6 it is clear that a dry sod results in a dramatic reduction in vapor density. In discussing sorption of gases on sod (see Physical chemical properties. Chapter 2) it was suggested that this effect resulted from water displacing the compound from the more polar sorption surfaces (e.g., clays) and it can be seen that this transition occurs quite abruptly. The effect of composition on the vapor density of dieldrin over soil is illustrated by the data in Table 4.7. ... 

The rate at which a chemical volatUizes from soil is controlled by simultaneous interactions between soil properties, chemical s properties and environmental conditions. Soil properties that affect volatilization include soil water content, organic matter, porosity, sorption/diffusion characteristics of the soil, etc. chemical s properties that affect volatilization include vapour pressure, solubility in water, Henry s law constant, soil adsorption coefficient, etc. and finally, environmental conditions that affect volatilization include airflow over the surface, humidity, temperature, etc. VolatUization rate from a surface deposit depends only on the rate of movement of the chemical away from the evaporating surface and its vapour pressure. In contrast, volatilization of soil-incorporated organic chemicals is controlled by their rate of movement away from the surface, their effective vapour pressure at the surface or within the soil, and their rate of movement through the soil to the vapourizing surface. 

The soil-water sorption coefficient affects only the aqueous phase transport of pollutants this coefficient will decrease in relation to the temperature. In this way, the ability of the hot fluids to remove pollutants from the soil increases significantly. The effect of the temperature is specific to the soil type, water content, and type of pollutants. 

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