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Has anyone tried using rock salt as a dehumidifier? Ive read a few DIY bits on it. I live in Georgia and its swampy and humid. I have a couple small dehumidifiers but I'm looking for some green and non-electrical dehumidifier options for my closets and storage spaces. Mold grows everywhere. Thanks!

https://byemould.com/2017/09/04/homemade-dehumidifier/

https://dengarden.com/cleaning/Ways-to-Dehumidify-Your-Greenhouse-andor-Home-Environment

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    $\begingroup$ Once the salt is wet / went into aqueous solution, the effect passes away. And your options then? At best getting new salt, but on this way you open the door to the porch and humidity enters again. Assuming you already took measures for thermal insulation, you now look for a more efficient method based on physics like an heat engine (which heat pumps are) to freeze the humidity out of the air (like a fridge does) before humidity condenses at your walls. Thus, the question might be better suited for physics.se. $\endgroup$
    – Buttonwood
    Jun 30, 2021 at 18:25
  • $\begingroup$ Same can be said about other hygroscopic salts. Problem like effectiveness and disposal apart, it would be better to look for CaCl2. It is a cheap side product (though I guess that in that form is already hydrated, so it would absorb less). Commercial cartridges do exist, but I don't think that they are greener if a total energy and CO2 balance is considered. $\endgroup$
    – Alchimista
    Jul 2, 2021 at 11:13

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Your suggested use is impractical to dehumidify a living space, though it might help keep humidity down to ~75% in an enclosure.

The issue is that air holds a fair amount of water. At 30°C, 100% humidity (i.e., dewpoint of 30°C), not untypical for a "mild" Georgia (US, not Republic thereof) day, that's 30 g/m3. If you were to buy a 22 kg block of salt for ~US$8, it might last a few days, never dropping the humidity much below 80%, and leaving you with perhaps 28 kg of saturated brine.

Disposing of concentrated brine is hardly ecologically sound -- misquoting Cato, "Ceterum autem censeo Georgia esse delendam." Regenerating it to solid salt by heating will take copious energy, releasing a lot of heat, and likely putting more $\ce{CO2}$ into the atmosphere from your heat source..

[If someone wishes to edit the spelling of Georgia (accusative?), please do so, since I declined to do so, in this case.]

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  • $\begingroup$ This way may not be much useful for a house of a flat with extensive air exchange, but could be applicable for a small, mostly closed space with limited air exchange. $\endgroup$
    – Poutnik
    Jul 2, 2021 at 8:42
  • $\begingroup$ It might work, if the goal is ~75% humidity. Libraries aim for ~30-50% humidity, but 70% is listed as good for cigar storage. But cigars are not good for us. $\endgroup$
    – DrMoishe Pippik
    Jul 2, 2021 at 18:07

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