Calcium sulfate (gypsum) is a common scalant of RO processes, especially at high recovery. It has a low water solubility

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Calcium sulfate (gypsum) is a common scalant of RO processes,
especially at high recovery. It has a low water solubility (2.4
g/L). A particular feedwater has a concentration of calcium sulfate
of 500 mg/liter (common of some waters like the Colorado river).
Ignoring concentration polarization and the presence of other
salts, at what recovery does the membrane begin to scale? What is
the recovery if concentration polarization it taken into account
(water flux is 40 liter/m^2 hr., mass transfer coefficient is 6.0 x
10^-6 m/s, assume rejection is 100%)?