Leaching screw-conveyor

Screw-Conveyor Extractors One type of continuous leaching equipment, employing the screw-conveyor principle, is strictly speaking neither a percolator nor a dispersed-solids extractor. Although it is often classed with percolators, there can be sufficient agitation of the solids during their conveyance by the screw that the action differs from an orthodox percolation. 

Screw-conveyor dryers handle solids that are too fine and too sticky for rotary dryers. They are completely enclosed and permit recovery of solvent vapors with little or no dilution by air. When provided with appropriate feeders, they can be operated under moderate vacuum. Thus they are adaptable to the continuous removal and recovery of volatile solvents from solvent-wet solids, such as spent meal from leaching operations. For this reason they are sometimes known as desolventizers. 

Figure 12.8-2. Equipment for moving-bed leaching [a) Bollman bucket-type extractor, (b) Hildebrandt screw-conveyor extractor.

Leaching of calcine. The calcine is fed by drag and screw conveyors to the first leaching stage. In this process, the zinc oxide (ZnO) is dissolved at 55 to 65"C with recycled and... 

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