We are second year cram schoolers , we are currently working on a project tackling water desalination by reverse osmosis and are required to do an experience. During the process, we encountered some difficulties regarding applying pressure and the fabrication of membranes . Given our unfavorable circumstances (low budget , lack of material ), we were wondering if someone could give us some insights on how to proceed. Although , we have tried to diy one with accessible materials and this is what we could come up with so far .

First ,we took an unglazed flowerpot and we filled its hole with cement, we filled it with a 0.1 mol / L potassium ferrocyanide solution. Simultaneously, we soak it in a 0.1 mol / L copper sulphate solution. After waiting several hours, the two products are going to spread in the pores, one from the inside, the other from the outside. In the middle of the pores, a chemical reaction had taken place , forming a precipitate of copper ferrocyanide which closes the large pores and transforms the pottery into a semi-permeable membrane. Finally, we rinsed the pottery well with water, and left it to soak for several days so as to remove the initial reagents.

However, we didn't meet our expectations and we don't know what is it that we're doing wrong . How thick should the cement layer be ? what are the rinses so as to remove the reagents ? and how could we simulate the pressure in a compartment ? and is there any other ways to make a membrane to work with ?

  • 3
    $\begingroup$ What do you mean by "we didn't meet our expectations" ? To get a reverse osmosis you need a high pressure over the salt solution. Usually it is done by closing the flowerpot by a stopper which must be watertight and leakproof. Easy to say ! The stopper must be drilled and equipped by a long tube many meters high filled with salt water. If the salt solution is 0.5 M, the tube must be 10 meters high, and the pure water goes through drop by drop $\endgroup$
    – Maurice
    Feb 2 '20 at 22:10

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