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Thursday, September 6, 2012

How to revive CaCl2 desiccant at home?

CaCl2 desiccant is usually used to dehumidify in closets and cabinets. CaCl2(calcium chloride) is a hygroscopic substance that means if you put in in the air it would absorb the water from the air. That is because calcium chloride(anhydrous) has a very high enthalpy change of solution.

 A box of used calcium chloride desiccant

 If we just put the box of used CaCl2 desiccant into a trash can that would be not environmental protection at all. So we can use a easy way to revive our CaCl2 desiccant.

Before we start to revive our desiccant , we need the tools as follow:

1. A iron pot or a pan
2. A heater (gas or electronic as you want)
3. A thermometer (~200℃ or higher)

 Calcium chloride has five hydrate state:
                772 °C   (anhydrous)
                260 °C   (monohydrate)
                176 °C   (dihydrate)
                45.5 °C  (tetrahydrate)
                30 °C     (hexahydrate)

We are going to let the CaCl2˙6H2O becomes into CaCl2˙H2O. Because it is enough to be a useful desiccant.

First, pour the calcium chloride solution(the liquid inside the box) into a iron pot and then boil it.

At first, it would look like it. 

Later on, it would become gelly liquid, and it will still boil.

When the temperature is get over 176°C, it means the liquid has become monohydrate. 

The you can take you pot away from the heater and let it cool down. While it cooling down , smashing it a the same time.

Finally, you will get a fresh powder of calcium chloride monohydrate.

 Put the powder into the box, and you can put the desiccant in to your closet again.

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