Coulson Leaching

Question 1

Soda ash is mixed with lime and the liquor from the second of three thickeners and passed to the first thickener where separation is effected. The quantity of this caustic solution leaving the first thickener is such as to yield 10 Mg of caustic soda per day of 24 hours. The solution contains 95 kg of caustic soda/1000 kg of water, whilst the sludge leaving each of the thickeners consists of one part of solids to one of liquid.
Determine:
(a) the mass of solids in the sludge,
(b) the mass of water admitted to the third thickener and
(c) the percentages of caustic soda in the sludges leaving the respective thickeners.

Answer 1

a) 13.7 Mg/day
b) 129 Mg/day
c) thickener 1 = 4.34%
thickener 2 = 0.47%
thickener 3 = 0.05%

Question 2

Seeds, containing 20 per cent by mass of oil, are extracted in a countercurrent plant, and 90 per
cent of the oil is recovered in a solution containing 50 per cent by mass of oil. If the seeds are
extracted with fresh solvent and 1 kg of solution is removed in the underflow in association with
every 2 kg of insoluble matter, how many ideal stages are required?

Answer 2

5