? i) (a) In studying the rate of leaching of a substance A from solid particles by

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i) (a) In studying the rate of leaching of a substance A from solid particles by a solvent B, we may postulate that the rate-controlling step is the diffusion of A from the particle surface through a liquid film out into the main liquid stream as shown in Figure Q1a. The solubility of A in B is C A0 gm moles/cm³ and the concentration in the main stream beyond the liquid film of thickness & is CAS Assume steady state and one-dimensional constant area molecular diffusion through a stagnant liquid film (ii) Obtain a differential and concentration profile equation for CA as a function of Z by making a mass balance on A over a thin slab of thickness AZ (Figure Qla). Assume that DAB is constant and that A is only slightly soluble in B. Take NAZ=-D AB NAZ dC₁ A dZ Neglect the curvature of the particles. Show that the rate of leaching is given by = [4 marks] DAB (CAO - CAS) 8 Continued Q1 (a) Solid particle containing A Z=0 CAO AZ HE Liquid film Z=6 CAS L Figure Q1a: Diffusion through a stagnant liquid film i) (a) In studying the rate of leaching of a substance A from solid particles by a solvent B, we may postulate that the rate-controlling step is the diffusion of A from the particle surface through a liquid film out into the main liquid stream as shown in Figure Q1a. The solubility of A in B is C A0 gm moles/cm³ and the concentration in the main stream beyond the liquid film of thickness & is CAS Assume steady state and one-dimensional constant area molecular diffusion through a stagnant liquid film (ii) Obtain a differential and concentration profile equation for CA as a function of Z by making a mass balance on A over a thin slab of thickness AZ (Figure Qla). Assume that DAB is constant and that A is only slightly soluble in B. Take NAZ=-D AB NAZ dC₁ A dZ Neglect the curvature of the particles. Show that the rate of leaching is given by = [4 marks] DAB (CAO - CAS) 8 Continued Q1 (a) Solid particle containing A Z=0 CAO AZ HE Liquid film Z=6 CAS L Figure Q1a: Diffusion through a stagnant liquid film