phendrol
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Separating calcium hypochlorite from CaCl2 and Ca(OH)2
Hello!
Commercially available bleaching powder is a mixture of calcium hypochlorite along with CaCl2 and Ca(OH)2. Is there a fairly easy way to separate
Ca(ClO)2 from bleaching powder?
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weiming1998
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I have found a way to get quite pure calcium hypochlorite.
First, add bleaching powder to water. Then, heat the mix and let it sit. A pink solution would be sitting on top of some white precipitate. The white
precipitate is Ca(OH)2, CaCO3, etc. Decant off the pink solution and keep it. Then, as CaCl2 is much more soluble than Ca(ClO)2, (http://en.wikipedia.org/wiki/Calcium_chloride) (http://en.wikipedia.org/wiki/Calcium_hypochlorite) boil the mix down until crystals starts to form. These crystals are relatively pure, hydrated
(?) Ca(ClO)2. You can test it by adding a strong acid like HCl on the crystals. Green Cl2 gas should result. Discard the remainder of the solution and
keep the crystals for later use. Don't use paper to filter, as hypochlorites attack them to a pulp.
Anyway, for most purposes, like generating Cl2, untreated bleaching powder works just fine. What is your purpose for the Ca(ClO)2?
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woelen
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Purifying a mix of CaCl2/Ca(OCl)2 in this way does not seem very good to me. Hypochlorites are not very stable and the boiling down results in big
loss of hypochlorite.
Modern swimming pool calcium hypochlorite is not a mix of CaCl2 and Ca(OCl)2, but is relatively pure hypochlorite. The main impurities are Ca(OH)2 and
CaCO3, but I think well over 80% of the solid is calcium hypochlorite.
In earlier times there was the mixed chloride/hypochlorite, which was made by reacting Cl2 with Ca(OH)2 and the disproportionation reaction indeed
gives a mix of chloride and hypochlorite. Newer processes are used nowadays and the resulting powder is (more or less) pure hypochlorite. Available
chlorine content of modern powders is around 70%, while old-fashioned powders had available chlorine of 30 ... 40%.
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