Solid-liquid leaching immersion

Whatever the scale of the extraction, leaching is performed in one of two ways. In the first, the raw material is placed in a vessel, forming a permeable bed through which the solvent or menstrum percolates. The wanted constituents are dissolved, and the solution issues from the bottom of the bed. This liquid is sometimes called the miscella and the exhausted solids, the marc. The process is called leaching by percolation. The second process employs immersion and consists of immersing the solid in the solvent and stirring. After a suitable period of time, solid and liquid are separated. 

Percolation leach particle diameter >700 pm hquid concentration 0.8 to 20% relatively fragile solid (e.g., seeds). Immersion leach particle diameter <700 pm liquid concentration <20% relatively robust solids (e.g., minerals). Combo leach high feed concentration of solute, relatively robust solid. Supercritical solvent usually CO2 for small capacity of high value products, especially for temperature sensitive foods, cosmetics, and pharmaceuticals. 

Immersion leach low solute leach rate. Product of residence time x concentration of leachant for acid leach = constant for a given particles diameter. Tends to have a separate leacher followed by system to separate and wash sohds. Pachuca plus CCD, settler particle diameter <70 pm sohds 30 to 60% w/w agitator 0.07 to 0.2 kW/m for CCD 1.5 to 2 kg liquid solvent carryover/kg inert solid. Autoclaves plus CCD particle diameter <70 pm solids 30 to 60% w/w 0.7 to 1.3 kW/m. ... 

Immersion leach particle diameter < 700 pm liquid concentration < 20% relatively robust solids (e.g. minerals)... 

---