I have monkeyed around making heat and cold packs to a small degree, long ago. I got curious about the cold packs when I fell out of a tree and had to use cold packs during my recovery. Ammonium nitrate is extremely hygroscopic. The prills pick up any moisture that is around, hard to store a bottle of it. It was my understanding (at the time) that the reaction that produces cold is not a chemical reaction, it is produced by the simple action of the water dissolving the nitrate. Although I have never tried to recover the nitrate, it would seem to be possible (in theory) to evaporate the water out and reuse the nitrate. If it were a chemical reaction this would not be practical. Well, now I have to try it as my curiosity has been aroused. Don't get ammonium nitrate near urea!!! An unpleasant reaction may occur.

 

Thanks for the info, what sort of an unpleasant reaction my occur? They do pretty much the same thing when added to water and I think urea is produced from ammonium nitrate.

 

If dry nitrate is mixed with dry urea it forms a slurry. This is also true of ammonium sulphate and urea. It just ruins everything. I actually read Material Safety Data Sheets. It is always a good idea to do this before performing chemistry to fabricate household compounds. I almost gassed myself with chlorine once so now I read up first to prevent dangerous (or disgusting)reactions. I also burned the crap out of my foot once by dumping hot grease on it when I was making soap but that is a different story.

 

Hello Guys I'm a newbie here but I have tried this and yes it does work. As all the cold packs I have ever seen around me are plain Ammonium Nitrate and simple water. Yes you can simply take a used cold pack and slowly boil off or evap the water in a glass dish like a pie plate thing and sort of reuse it. If you are going to reuse it for a cold pack please note the reaction will be much faster and colder at first but lasts not very long. However AN is the best used on your lawn makes it so your neighbors look bad.
However please note this important issue with this chemical as if you get it over 700F it CAN become unstable and explode! never seen this happen but I would not want to have to try to talk my way out why the oven and kitchen have to be remodeled to my wife.

 

You guys are killing me, Ammonium Nitrate, is the major ingreadiant in a Furtilizer Bomb, Think Oklahoma City, this stuff is hugely unstable and if mixed with other cumbustable such as kerosine or fuel renders a High Order explosion. It is also one of the toughest to acquire components of this type of explosive

 

It's not unstable. It's a standard fertilizer in fact, and as such, is pretty dang easy to get. It might require a signature now though.

 

Why not just preserve it the old fashioned way? By dehydration, canning, pickling, curing, etc.