In a Forward Osmosis Desalination Process using Ammonium sulfate as a draw solution, it was noticed that the Rejection of Cl- ion to decrease as Draw solution concentration increases. On the other hand, the Na+ ion rejection increased as DS concentration increased. Membrane used is TFC. Any possible explanation for this phenomenon?
Ya,we have to check that is there any mechanism of ion-exchange.If yes than following may be reason.
(1)In your draw solution you have monovalent NH4+ are double in molarity compare to bivalent SO4-2.In water NH4+ hydrolyzed and form H3O+ + 2NH3,while SO4-2 hydrolyzed and form H2SO4 + 2OH-+HSO4-.HSO4- and OH- is able to attract strongly to Na+ from feed solution.While NH3 ,H2SO4and H3O+ has negligible attraction to Cl- of the feed ,which decrease the rejection of Chlorine.
(2)Another reason may be lies in solubility product of that salt in water.It may be possible that Cl- ions has less solubility in ammonium sulfate solution.It is possible that Cl- is less solubilized in water due to unavailability of counter positive ions in amonium sulfate solution.While Na+ is easily solubilized by water.
Dear Sanjay Chaudhri, I need to clarify something. In an FO process where FS is NaCl and (Nh4)2SO4 is DS, if Cl- ions exhibit low rejection compared to Na+ ions, this means that high amount of Na+ and low amount of Cl- are available in feed? I think you mentioned the opposite effect in your previous explanation. Please correct me if i am wrong.
We can explain law rejection of Cl- still with same phenomenon as I explained before.If I will find time than I will write in details.
I am afraid i do not understand what you mean. Would u mind explain it in more details??
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