Question

QUESTION 3 (25 marks) One thousand kg per hour of feed containing 15% solute, 2% water and 83% inert is extracted with water in a countercurrent cascade. The rich liquor leaving the cascade is to contain 15% of the solute. No carryover of the inert in the overflow occurs. The underflow has a constant amount of 0.4 kg solution per kg inert. Also, the underflow leaving the cascade must not contain more than 0.005 kg solute per kg of inert. (a) Explain the difference between mass transfer operations in a leaching stage and a washing stage. (b) Analytically determine the number of ideal washing stages required. (c) Mention the major assumption taken in your calculations. [3 marks] [20 marks] [2 marks]

          QUESTION 3
(25 marks)
One thousand kg per hour of feed containing 15% solute, 2% water and 83% inert is extracted with
water in a countercurrent cascade. The rich liquor leaving the cascade is to contain 15% of the solute.
No carryover of the inert in the overflow occurs. The underflow has a constant amount of 0.4 kg
solution per kg inert. Also, the underflow leaving the cascade must not contain more than 0.005 kg
solute per kg of inert.
(a) Explain the difference between mass transfer operations in a leaching stage and a washing stage.
(b) Analytically determine the number of ideal washing stages required.
(c) Mention the major assumption taken in your calculations.
[3 marks]
[20 marks]
[2 marks]

QUESTION 3
(25 marks)
One thousand kg per hour of feed containing 15% solute, 2% water and 83% inert is extracted with
water in a countercurrent cascade. The rich liquor leaving the cascade is to contain 15% of the solute.
No carryover of the inert in the overflow occurs. The underflow has a constant amount of 0.4 kg
solution per kg inert. Also, the underflow leaving the cascade must not contain more than 0.005 kg
solute per kg of inert.
(a) Explain the difference between mass transfer operations in a leaching stage and a washing stage.
(b) Analytically determine the number of ideal washing stages required.
(c) Mention the major assumption taken in your calculations.
[3 marks]
[20 marks]
[2 marks]

Added by Carolyn H.

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