Leaching example, calculation

The pesticide component of SWRRB takes into account the fate of the chemical applied under field conditions For example, the amount of pesticide actually reaching the ground after application over a plant canopy is calculated. Further, field dissipation of the chemical by photolysis on leaf surfaces as well as degradation in the soil is accounted for with the pesticide component of SWRRB. Leaching of the pesticide below the top 1cm of soil is also computed and runoff corrected for such losses. Further, adsorption of the pesticide to soil surfaces and sediment is taken into account by SWRRB. 

Leach rate measurements have been made on several waste forms, using the NAA technique. Some results are presented here as examples of the application of this method. Simulated wastes used in these studies consisted of two types of granules obtained from Battelle Pacific Northwest Laboratories. The differential leach rates of the bulk waste matrix were calculated with the equation ... 

The apparent diffusion coefficient, D, was determined for the particular leaching conditions of each of the thirteen experiments. This was accomplished using the measured chloride breakthrough (effluent concentration) curve and the analytical solution to Equation 7 with Kd==0. Examples of the observed and calculated chloride concentrations (determined by adjustment of D until a best fit was obtained) are presented for three different experiments (Experiments 7, 8, 11) in Figures 2-4. Values of D and the pore water velocity (v) determined for each experiment are presented in Table III. The value of D increased for cases with large v, and was different between soils for any particular v. This is consistent with the basic relationship be-... 

Triangular diagrams, such as Fig. 10.5-1, can be uned to cany am equilibrium-stage leaching calculations in the same way that analogous calculations are ceiried out for ternary liquid-liquid extractions.1 3 Other coordinate systems, for example, Janecke coordinates, can also be used for such calculations. 

EXAMPLE 12.8-1, Prediction of Time for Batch Leaching Particles having an average diameter of approximately 2.0 mm are leached in a batch-type apparatus with a large volume of solvent. The concentration of the solute A in the solvent is kept approximately constant. A time of 3.11 h is needed to leach 80% of the available solute from the solid. Assuming that diffusion in the solid is controlling and the effective diffusivity is constant, calculate the time of leaching if the particle size is reduced to 1.5 mm. 

Effective Diffusivity in Leaching Particles. In Example 12.8-1 a time ofleaching of the solid particle of 3.11 h is needed to remove 80% of the solute. Do the following calculations. 

Constant Underflow in Leaching Oil from Meal. Use the same conditions as given in Example 12.10-1, but assume constant underflow of N = 1.85 kg solid/kg solution. Calculate the exit flows and compositions and the number of stages required. Compare with Example 12.10-1. 

In this chapter, we present various equilibrium-based geochemical modeling approaches that can be used for the analysis of leaching of various species from contaminated media. We focus on two important processes that can chemically limit the concentration of the contaminant released or leached dissolution/precipitation and adsorption. We progress from a simpler approach based on aqueous speciation of chemicals to more complicated approaches that in addition require dissolution/precipitation and/or adsorption calculations. Examples for applications of the geochemical modehng approaches discussed in this chapter are provided in Table 1. 

Fig. 8 shows an example of comparison of the analysis results and actually measured results of solid-phase calcium concentration after leaching. The actually measured results are for concrete of age 30-100 years in various kinds of environments such as distribution reservoir in a water supply facility, building foundation structure in contact with groundwater, dam, and so on, similar to Fig. 3. Variation exists in actually measured results also, and although calculated accuracy cannot be discussed unconditionally, satisfactory predictions can be made depending on various conditions.

The OECD emission scenarios can be presented in a Visual Basic format and as an example. Figures 2 and 3 show the output data for a wood preservative product containing an active substance that leaches from the wood at a rate of 9.5 mg/m /day. The results of these calculations would then be used in the risk characterization stage of the risk assessment as described below. 

Time/min Absorbance Absorbance % Mn Ieached=0.839 b%Mn leached=1.38 c after 10 fold dilution Example of calculation in (b)... 

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