Leaching process design

Sintering has been used to produce a porous polytetrafluoroethylene (16). Cellulose sponges are the most familiar cellular polymers produced by the leaching process (123). Sodium sulfate crystals are dispersed in the viscose symp and subsequently leached out. Polyethylene (124) or poly(vinyl chloride) can also be produced in cellular form by the leaching process. The artificial leather-tike materials used for shoe uppers are rendered porous by extraction of salts (125) or by designing the polymers in such a way that they precipitate as a gel with many holes (126). 

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

The experimental conditions influencing an ultrasound-assisted continuous leaching process were studied using an experimental design... 

Institute of Chemical Metallurgy, Division III, Staged Fluidized Leaching of Products of Chioridizing Roasting of Pyrites Cinder—Preliminary Process Design (in Chinese, unpublished), 1965-7-31 (1965). 

If a water sample contains both soluble and insoluble manganese (Mn) compounds and ions, and it is filtered to separate the dissolved and insoluble fractions, and the filtrate and insoluble residue are analyzed separately, the results can be expressed as total dissolved Mn and total suspended or insoluble Mn. Phosphorus (P) can be determined colorimet-rically as the ortho-phosphate ion, P043, in aqueous samples after a reaction that forms an intensely blue-colored derivative. However polyphosphate ions and other ions and compounds containing P do not form this derivative. Total P in a sample can be determined with the same colorimetric procedure after acid hydrolysis and oxidation of all ions and compounds containing P to P04 3. In some elemental analyses the sample is treated with reagents designed to make available for measurement some fraction of an element or elements but not the total amount. For example, a soil sample may be treated with water at pH 3 to simulate the leaching process of acid rain. A total elemental analysis of the filtrate provides information about just those elements solubilized by the mild acid treatment. This can be called the determination of total mild acid leachable elements. 

As previously stated, leaching is another extraction process in which a liquid is used to remove soluble matter from its mixture with an inert solid. With a few extra considerations, the equilibrium analysis of leaching is the same as for liquid extraction. Several assumptions are made in designing leaching processes. These can be rendered correct with the proper choice of solvent. It is assumed that the solid is insoluble in the solvent (dirt will not dissolve in water) and the flowrate of solids is essentially constant throughout the process. The solid, on the other hand, is porous and will often retain a portion of the solvent. 

Braginsky LN (1964) The study of aeration characteristics of impellers for autoclave leaching processes. Scientific Report on Research Project, Research and Design Institute NIIKhIMMASH, Leningrad, Russia, cf. Zundelevich (1979). 

Primary centrifugation process design is also affected by the method chosen to deal with the triple salt formed in the evaporators. In all cases, a leaching tank serves as a triple salt decomposer. One possible combination is to collect all the salt produced in the evaporators, recover the bulk of it in pusher centrifuges, and drop it into the leaching tank. The liquor in the tank, richer in sulfate, goes to sulfate recovery or disposal. The purified salt is reslurried and sent to a second set of centrifuges for final recovery. In other systems, the triple salt may be isolated from the pure salt formed in the other effects of the evaporator. 

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