Question

4- Certain solid substances, known as hydrated compounds, have well-defined molecular ratios of water to some other species. For example, calcium sulfate dihydrate (commonly known as gypsum, CaSO4 2H30), has 2 moles of water per mole of calcium sulfate; alternatively, it may be said that I mole of gypsum consists of 1 mole of calcium sulfate and 2 moles of water. The water in such substances is called water of hydration. In order to eliminate the discharge of sulfuric acid into the environment, a process has been developed in which the acid is reacted with aragonite (Cacos) to produce calcium sulfate. The calcium sulfate then comes out of solution in a crystallizer to form a slurry (a suspension of solid particles in a liquid) of solid gypsum particles suspended in an aqueous Casos solution. The slurry flows from the crystallizer to a filter in which the particles are collected as a filter cake. The filter cake, which is 95.0 wt% solid gypsum and the remainder Caso solution, is fed to a dryer in which all water (including the water of hydration in the crystals) is driven off to yield anhydrous (water-free) Caso, as product. A flowchart and relevant process data are given below. Solids content of slurry leaving crystallizer: 0.35 kg Caso 21:0/L slurryCaso content of slurry liquid: 0.209 g CaSO/100 g H:0. Specific gravities: CaSO4-2H2O(s), 2.32; liquid solutions, 1.05). 125 marks] OSO Slamy CRYSTALLER DRYER (a) Briefly explain in your own words the functions of the three units (crystallizer, filter, and dryer). (b) Take a basis of one liter of solution leaving the crystallizer and calculate the mass (kg) and volume (L) of solid gypsum, the mass of CaSO4 in the gypsum, and the mass of CaSO4 in the liquid solution. (c) Calculate the percentage recovery of CaSO4 that is, the percentage of the total CaSO4 (precipitated plus dissolved) leaving the crystallizer recovered as solid anhydrous CaSO4.

Answer 1

a) Crystallizer : This processing step is done to actually obtain crystals from the saturation solution entering the crystallizer. Thi will result in hydrated crystals in a solution which will require further processing
Filter: This unit operation is used to separate solid particles from a slurry . In this case we have used this unit operation to separate crystals from the solution .
Dryer: This unit operation is used to remove the moisture conetent of the stream. in this case after filtration little amount of water will still be present in the filter cake which is removed with the help of drying

b) Bais: 1 liter & skersy Douby, solids sentent on the ser trys 0.35 kg Caboy - 24,01 sady Ebolid contest =0-35 kg (aļ04.2H3O. Howy Ind laboy, Jond labou - 240 Melo Mass Colo42 136.14 glod Daler Bass 2, 0.06042 134-14+2013): 172.14 g/mol Inol labou a Imol Cobou. 24, a Weason 0:35 136.14 172.14 3 Weight of Cobbų > 0:35x134430-1768 kg Ca304 172.14 massal labo4in gupsum 2 0-9763_kg. now we need to evaluate Mole fractico pitst 0.209 g Cosol per loog of ho is presen! wt praction of (05042 204FD0 20:002086 Wt fraction of Wates 2.0-993914

Seiquid Belutio = 1.05xlad beglos? Volume 212 2133m3 Mass of solution : 1.05 Xilo? Rexholm? los by m3 Wt praction of Caboy = 0.00) 088. massol Cobou in soluticn : 0.00 3086X/:05 = 0.0021903 kg °2-19039 mass of solid gypsum 20:31 kg. Sgypsune Mgypsum Vaypsum = Mgypsum 20-35 Voupsur 2328162 Vay psum 1.5086x10m 30.15086 liter fgypsum

c) ft is said that all of the casou is kemeved os anhydroes Casou anhydrous 0.2768 kg 02 03 Total Caboy in stroom exiting krystallizer 2 (abou as Crystal + labou in bole ton 2 0.2768 + 2.1903x10² 20.23.89903 04 05. ..recovery 20.2769_xloo 294-25.70 0-2789963 06 07

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