Leaching operating line

At the heart of a leaching plant design at any level—conceptual, preliminary, firm engineering, or whatever—is unit-operations and process design of the extraction unit or line. The major aspects that are particular for the leaching operation are the selection of process and operating conditions and the sizing of the extraction equipment. 

Heap-leach operations are typically zero-discharge facilities [69]. A typical heap leach operation is shown in Figure 6.3. A weak cyanide solution is sprayed over the stacked ore and pregnant solution flows to a lined collection ditch, then to a pregnant solution pond, then to a recovery plant with carbon... 

NUMBER OF IDEAL STAGES FOR CONSTANT UNDERFLOW. When the Operating line is straight a McCabe-Thiele construction can be used to determine the number of ideal stages, but since in leaching the equilibrium line is always straight, Eq. (17.24) can be used directly for constant underflow. The use of this equation is especially simple here because yj = and — Xj. 

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... 

The leaching operation is carried out fairly rapidly in a semi-continuous manner. The vessel is first filled with 2 per cent nitric acid and then further acid and coarsely ground reaction cake are added simultaneously over a period of time. The bottom valve is opened sufficiently to allow the salt solution to drain away at the same rate as fresh acid is added, so maintaining a constant liquor level in the vessel. The titanium metal remains behind on the filter until the conclusion of the run. It is then taken away as a slurry, via an exit pipe just above the filter level. The slurry is finally dewatered in a rubber-lined batch centrifuge and dried in air at a moderate temperature. 

The use of Eq. (11.4) assumes that the amount of liquid mechanically retained with the solid (but not adsorbed) after filtration or settling is negligible. This is quite satisfactory for most adsorption, since the quantity of solid employed is ordinarily very small with respect to that of the liquid treated. If the operation under consideration is desorption and if again the quantity of liquid retained mechanically by the solid is negligible, Eq. (11.4) applies, but the operating line lies below the equilibrium curve on Fig. 11.16. In this case, however, it is much more likely that the quantity of liquid retained mechanically with the solid will be an appreciable portion of the total liquid used, and the methods of calculation described in Chap. 13 for leaching should be used. 

Another example is the palladium catalyzed allylic substitution of 3-phenyl-2-propenyl-carbonic acid methyl ester to yield iV-(3-phenyl-2-propenyl)morpho-line reported by Reetz, Kragl and co-workers. This reaction was performed in the presence of phosphino-terminated amine dendrimers [17, 18] loaded with Pd11 cations as shown in Scheme 10. For this particular dendrimer with a molecular weight of 10 212 g/mol, a retention of 0.999 per residence time [35] was estimated in a membrane reactor with a SELRO MPF-50 membrane. It must be noted that a very high retention is a prerequisite for a continuous operating system, since a small leaching of the dendrimer leads to an exponential decrease in the amount... 

It was decided to address these questions simultaneously. Several cooperating farms In Wayne County were found with similar CCCs consisting of pad, leach lines, remote water source, water storage tank, and adjacent pesticide storage. A control farm was also located. Most pesticide operations were performed by the owner-operators or regular employees, and they agreed to personally cooperate. 

Farm A (Figure 1) has a CCC which had been In operation for five years. It Is situated 86 feet away from a shallow pond bordering the orchard, and four feet upgrade from the water surface. The upper and lower leach lines extend 77 and 71 feet, respectively, between rows of apple trees parallel to the ponds edge. 

Pesticides from the CCCs were shown not to have leached Into any of the available ground water sources. In addition, the soil core analyses Indicated that disposed chemicals had traveled less than 18 Inches from the leach lines In five years of operation. Within the defined time frame, the CCCs were confining the chemicals. A long-term follow-up survey. Including test wells, would be useful to determine if migrating pesticides eventually reach the water table. The absence of any Increased risk to applicators, or of any environmental drawbacks, as measured by soil arthropod populations, was established. Consequently, the New York State Department of Environmental Conservations has regarded these Installations as normal agricultural operations and not required further documentation. 

Material balance in countercurrent leaching still is represented by Eqs. (14.14) and (14.16). Compositions Rk and Ek+1 are on a line through the operating point P, which is at the intersection of... 

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