Leaching with constant flow rates

The method developed by Sparks et al. (1980b) is a good example of a continuous flow and is shown in Fig. 3.3. Samples can either be injected as suspensions or spread as dry samples on a membrane filter. The filter holder is capped securely and then is attached to a fraction collector and a peristaltic pump, which maintains a constant flow rate. Samples are leached with sorptive solutions, and effluents are collected at various time intervals. 

To determine the leaching of chemical constituents from SWMs/COMs under conditions of constant surface renewal, columns (2.5 cm in diameter, 25 cm long) filled with SWMs/COMs were leached with distilled water at three different flow rates. The column tests were used to simulate leaching of highway materials under conditions of subsurface percolation of rainwater. Effluent samples from the column were taken with time for up to 80 h. The filtered solutions were measured for TOC and/or individual compound concentrations, and for toxicity. 

Figure 2 shows the predicted, normalized cumulative mass losses based on the behaviors of silicon and sodium for three different values of the leachant renewal frequency. The physical parameters used refer to the leaching of PNL 76 68 borosilicate glass in deionized water at 90°C, (4) and reference is made to the geometric surface area, SA, of the sample. In particular, the curves corresponding to silicon and sodium tend to have the same, constant slope with increasing flow rate. In particular, the curves corresponding to = 1 day 1 practically coincide, indicative of network dissolution control. 

A schematic of a countercurrent leaching system is shown in Figure 14-4 with the appropriate nomenclature. Since leaching is quite similar to LLE, the same nomenclature is used (see Table 13-2L Even if flow rates E and R vary, it is easy to show that the differences in total and conponent flow rates for passing streams are constant. Thus, we can define the difference point from these differences. This was done in Eqs. fl3-42i and fl3-43i for the LLE cascade of Figure 13-20. Since the cascades are the same (compare Figures 13-20 and 14-4L the results for leaching are the same as for LLE. 

McCabe-Thiele diagrams can also be used for leaching if flow rates are close to constant. If flow rates are not constant, curved operating lines can be constructed on the McCabe-Thiele diagram with the... 

D12. A countercurrent leaching system is recovering oil from soybeans. The system has five stages. On a volumetric basis, liquid flow rate/solids flow rate = 1.36. 97.5% of the oil entering with the nonsoluble solids is recovered with the solvent. Solvent used is pure. Determine the effective equlibrium constant, m, where m is (kg/m of solute in solvent)/(kg m of solute in solid) and is given by the equation y = m x. 

Six grams (0.053 mole) of iron(III) fluoride is mixed thoroughly with 60 g. (0.1 mole) of purified-grade sodium meta-phosphatet in a beaker and the contents are transferred to the carbon crucible. The crucible is placed in the reaction chamber and is heated to 925°C. at the rate of 75°C./hour in a flowing argon atmosphere. The crucible is allowed to equilibrate at 925°C. for 1 hour. The center electrode is inserted to a depth of in. and a current of 250 mA. (61 mA./cm.2) is used. A constant current source is used to maintain the desired current. The electrolysis should be carried out from 12 to 24 hours to give a sufficient yield. After electrolysis the melt is cooled to room temperature at the rate of 75°C./hour. The crucible is cut to expose the reaction boule, and the excess melt is removed by leaching in hot, dilute hydrochloric acid. Free carbon is removed by flotation with methylene iodide(diiodomethane). The product is in the form of metallic needles and small crystallites with a yield of 0.5-1 g. 

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