Certain solid substances, known as hydrated compounds, have well-defined molecular ratios of water to some other species,

Question:

Certain solid substances, known as hydrated compounds, have well-defined molecular ratios of water to some other species, which often is a slat. For example, calcium sulfate dehydrate (commonly known as gypsum, CaSO₄ ? 2H₂O), has 2 moles of water per mole of calcium sulfate; alternatively, it may be said that 1 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. Solid gypsum is formed in a crystallizer and leaves that unit as a slurry (a suspension of solid particles in a liquid) of solid gypsum particles suspended in an aqueous CaSO₄ 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 CaSO₄ 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) CaSO₄ as product. A flowchart and relevant process data are given below.

Solids content of slurry leaving crystallizer: 0.35 kg CaSO₄ ? 2H₂O/L slurry

CaSO₄ content of slurry liquid: 0.209g CaSO₄/100g H₂O

Specific gravities: CaSO₄ ? 2H₂O(s) 2.32; liquid solution, 1.05

(a) Briefly explain in your own words the fu8nctions 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.