2. LEACHING
• Leaching is solid-liquid extraction
• In order to separate a desired solute component from a
solid phase, the solid is contacted with a liquid phase
• The two phases are in intimate contact and the solute
diffuses from solid to liquid phase resulting in separation
• This is called LEACHING
3. SOLUTES AND SOLVENTS
SOLUTES EXTRACTED BY LEACHING
Vegetable seeds like cotton seeds, soybeans, linseeds,
peanuts, rice bran, castor beans
Metal processing industries like copper, nickel, gold
and cobalt
SOLVENTS USED FOR LEACHING
Petroleum napthals, Hexane, chlorinated hydrocarbons
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4. EQUIPMENTS FOR LEACHING
• Fixed bed leaching
- uses typical fixed bed diffuser or extracter
• Moving bed leaching
- uses Bollman extractor, Hildebrandt extractor
• Agitated solid leaching
- counter current leaching using thickeners
Other extractors used include ROTOCEL, FRENCH
STATIONARY BASKET EXTRACTOR, KENNEDY EXTRACTOR,
CONTINUOUS HORIZONTAL EXTRACTOR
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7. Description
• Bollman extractor – one of basket type machine
• It consists of a vapor tight vertical chamber in which a
series of baskets are attached to a chain conveyor
• The baskets are provided with perforations at the
bottom
• Dry flakes or solids are added at the upper right side to a
perforated basket or bucket in a closed casing
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8. Continued…….
• As the baskets on the right descend they are leached by a
dilute solution of oil in solvent called half
miscella*
• The liquid percolates downward through the moving
baskets and is collected at the bottom as a strong solution
or full miscella*
• The baskets moving upward on the left are leached counter
currently by fresh solvent sprayed on the top basket
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9. Continued………
• The wet flakes are dumped as shown in the figure and
are removed continuously using a screw conveyor
• Usually the conveyor speed is one revolution per hour
and solvent to fresh meal(seeds) ratio is 1
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10. Recovery of solvent
• The recovery of solvent from both the miscella and the
leached seeds or beans is an essential part of the
vegetable oil leaching process
• In a typical arrangement, the filtered miscella is passed
to an evaporator for removal of solvent followed by final
stripping in a tray column to produce solvent-free oil
• The wet seeds are streamed to remove residual solvent
and air-cooled
• Ventilated gases from condenser can be to an absorber
to recover any solvent
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