LIQUID-SOLID LEACHING PROCESS

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1 LIQUID-SOLID LEACHING PROCESS

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4 Leaching Processes Use to separate the desired solute constituent or remove an undesired solute component from the solid phase. The solid is contacted with a liquid phase in which the two phases are in intimate contact. This allow the solute diffuses from the solid to the liquid phase resulting separation.

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6 Leaching Process for Biological Substances Leaching of sugar from sugar beets with hot water. Production of vegetable oil, where organic solvent, e.g. hexane, acetone and ether, are used to extract oil from peanuts, soybens, sunflower seeds, cotton seeds, and halibut liver. Pharmaceutical products are obtained by leaching plant roots, leaves, and stems. Production of soluble instant coffee where ground roasted coffee is leached with fresh water. Soluble tea is produced by water leaching of tea leaves.

7 Leaching Process for Inorganic and Organic Materials Extensively used in the metals processing industries. Leaching is used to remove metals as soluble salt. Copper salts are dissolved or leached from its ore by sulfuric acid or ammoniacal solutions. Gold is leached from its ore using aqueous sodium cyanide solution. Cobalt and nickel salts are leached using sulfuric acid-ammonia-oxygen mixtures.

8 Preparation of Solid Leaching Crushing and grinding of solid to allow soluble portions are made more accessible to the solvent thus increasing rate of leaching. Simple washing can be applied if the soluble substance is widely distributed throughout the whole solid. For biological material, i.e. sugar beet, they are cut into wedge-shape slices for leaching. For soybeans and many vegetable seeds they are ruptures by rolling and flaking in such a way that the vegetable oil is easily accessible to the solvent. For pharmaceutical product e.g. leaves, stems and roots, drying of the material before extraction help to rupture the cell wall and hence solvent can directly dissolved the solute.

9 Equilibrium Relations and Single-Stage Leaching Assumptions: 1. Solute-free solid is insoluble in the solvent. 2. Solvent present in sufficient amount so all solute can be completely leached out from solid. 3. Equilibrium is reached when solute is dissolved. 4. No absorption of solute by the solid. UNDERFLOW/SLURRY STREAM the settled solid leaving a stage that contains some liquid containing dissolved solid. OVERFLOW STREAM Concentration in the liquid solution accompanying the slurry stream.

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12 Single-Stage Leaching Process flow Material balance

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15 COUNTERCURRENT MULTISTAGE LEACHING However, the Ln (the liquid retained in the underflow) will vary and the slope of ( ) will vary from stage to stage.

16 Variable Underflow in Countercurrent Multistage Leaching

17 Estimation of the operating point Δ,

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24 Assignment Answer: L N =175.8, yan=0.073, V 1 =348.8 kg/hr, N 0 =2.89, 6.1 stages needed

25 FIXED-BED LEACHING It has been used in beet sugar industry, extraction of tanning extracts from tanbark, extraction of pharmaceuticals from barks and seeds. The cover is removable for solid loading. Heated water flows into the bed to leach out sugar. About 95% of sugar in the beets to yield outlet solution containing 12 wt% sugar.

26 BOLLMAN EXTRACTOR Filling and emptying of basket

27 M0VING BED LEACHING BOLLMAN BUCKET-TYPE EXTRACTOR HILDE-BRANDT SCREW-CONVEYOR EXTRACTOR Dry flakes/solids are added at the upper right side to a perforated basket/bucket. As the bucket moving downward clockwise, half miscella (oil+solvent) is sprayed. The liquid percolate through the solid and finally collected at the bottom as full miscella (strong solution). As bucket move to the final stage, it is contacted by the fresh solvent. The final spent flakes are dumped that continuously remove out of the extractor. For the Hilde-Brandt extractor, three screws are arranged in a U shape where solid fed coveyed downward, cross the bottom and up to other leg Solvent flows countercurrently.

28 AGITATED SOLID LEACHING Handles fine solids to about 200 mesh (0.074 mm). Fine particles have tendency to suspend. This particular continuous countercurrent leaching may consists of a number of agitators in series that combines contactor-agitator and settlers. The overflow liquid flows from stage to stage countercurrently with solid-liquid slurry. The solids together with some liquid are pump as slurry to the next tank. Mixer may be incorporated between each tank to provide sufficient contact.