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chief
National Hazard
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Right. What then about the really available and cheap sulfate: CaSO4 aka gypsum: This is soluble in water (0.2 g/100 ml), and maybe used for
diaphragma at the same time too . Only the conductivity will be lower than with other electrolytes ...
The most simply-thinkable cell of this would have it for diaphragma in the middle of the cell, as some sort of a wall. Then on the one side of it
H2SO4 would accumulate, and on the other Ca(OH)2 would make the water milky ...
To tune up the efficiency of this one might have to make the surface big enough and put the electrodes close enough together to limit the
current-losses.
Besides the mentioned pyrosulfate is a big-scale industrial product ; used everywhere in the food-industry .
[Edited on 21-2-2009 by chief]
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DerAlte
National Hazard
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Instead of calcium, magnesium is better. The sulphate is quite soluble and cheap (fairly pure too, as fertilizer). This requires a divided cell, the
Sulphate being converted to Mg(OH)2 and precipitated at the cathode.
Simplest of all, any platable metal sulphate could be used in an undivided cell, the metal ion being plated on the cathode . Fe, Cu Ni etc. could be
used. Iron(II) sulphate is also a cheap fertilizer. The rest are more expensive.
Regards, Der Alte
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not_important
International Hazard
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In the divide cell the increasing concentration of OH(-1), H(+1), HSO4(-1) and SO4(-2) will also result in increasing pressure driving those ions
across the membrane. This is why most attempts at commercialising this sort of process use ion-selective membranes in various arrangements.
When plating out a metal the hydrogen ion concentration rises until the production of H2 rivals that rate of plating out the metal, and then exceeds
it. In electro-analytic chemistry almost all the metal can be plated out, but this frequently requires additives that would run the acid produced as
a reagent.
So those are effects that will compete with the production of useful grades of acid and base. It can be done, I've read of a plant that split a waste
(NH4)2SO4 stream into H2SO4 and "NH4OH" using a multistage electro-dialysis process with ion-selective membranes.
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mysteriusbhoice
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what if you add CaSO4 in the cathode area of the cell
make sure its hydrated first or you will end up with a solid block!!
it should continue to pull out the SO4 ions from the CaSO4 and regenerate the small amount of NaOH used
while keeping the sodium concentration low in the anode side!!
Ca(OH)2 is not soluble in water just make sure no CO2 enters the cathode are or else ..... Cement
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