Shrinking-core Model
As mentioned above when leaching a solid with a liquid the desired solid goes to the liquid phase while undesired solid remains. The removal of the solid as the liquid dissolves into the particle leads to a diameter of unleached core that shrinks with time. A mathematical model can be used for this process, derived using Fick's law of diffusion taking pore diffusion as rate limiting step:
Read more about this topic: Leaching (chemistry)
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