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It's well documented that one can reduce calcium concentrations in water by boiling the water. This is caused by CO2 being driven out of the water and the calcium precipitating out of solution. Ok, but, would calcium drop out of solution if the water was to reach its boiling point at a lower pressure atmosphere? The goal being energy-savings.

Anyone with some insight on this or ... wielding a low-pressure apparatus and a TDS meter?

Malte
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  • Could you explain the context or background of this problem? – AChem Apr 12 '20 at 01:52
  • "This is caused by CO2 being driven out..." Would CO2 also evolve at low pressure? What happens when you open a bottle of soda water? You have enough information to answer your question. – DrMoishe Pippik Apr 12 '20 at 02:34
  • It will be less efficient due better CO2 solubility at low temperatures, what would require more boiling to keep partial CO2 pressure low enough. It may be even more energy demanding, unless T is kept below Tenv and part of heat comes from the surrounding. Additionally, boiling at lower temperature requires more energy. – Poutnik Apr 12 '20 at 06:40
  • @Poutnik Thanks for your comment! So CO2 solubility is temp-dependent so I suppose I won't get around boiling the water. – Malte Apr 12 '20 at 08:19
  • Apologies for the typo-ridden previous comment.

    Additional background for this question: My tap water is very hard, with just over 100 ppm of calcium dissolved in it. This is an issue for aquarists with fish that require soft water. For a moment, I was considering using an RO filter for the water but then an friend/civil engineer recently suggested I could reduce the calcium concentration in my water as much as 50% if I boil the water. That got me thinking if there was a way to have calcium precipitate with less energy input.

     – Malte Apr 12 '20 at 11:13
  • Malte, it makes more sense now. No you will have to provide enough heat to decompose calcium bicarbonate. Generating vacuum will also cost energy. Is there a possibility of a solar still? https://en.wikipedia.org/wiki/Solar_still – AChem Apr 12 '20 at 17:16

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