FINALLY, I came across someone confirming what I suspected already.
O2 absorber is a simple chemical reaction. Rusting Iron absorbs oxygen as it rusts.

> snip< http://www.offthegridnews.com/letters-to-the-editor/...If you choose to make your own absorbers:
It will take about 6 grams of iron filings and 6 grams of sea salt for a 5/6 gal bucket. Mix the two elements together and place in a small paper envelope. Put 2 to 4 drops of water on the envelope just before it is placed in the grain. There is enough moisture in the grain to keep this process going for a long time if the bucket isn’t perfectly sealed.

This process is perfectly safe. The salt rapidly converts the Iron (Fe) to Iron Oxide (FeO, or Fe2O3). The oxygen is all tied up with the iron, thus leaving a near oxygen-free environment so the grain won’t oxidize. It is almost the same as nitrogen-packed; 78% of the air is nitrogen and that is about the only thing left when the oxygen is gone...
> snip <
Not just the COST of o2 absorbers, but the HASSLE and limited shelf life of trying to use just a few at a time.
And what do you do when tshtf and no more mail-order survival suppliers?

Iron filings/ $7.00 USD - One pound http://secure.sciencecompany.com/Iro...1lb-P6370.aspx
One pound should be enough to do 75 5 gal. buckets

I remember in a magnet book I had as a young scientist, they showed how to MAKE iron filings/dust.
Put STEEL WOOL in a glass jar with some bleach. cover and let sit a day or 2. The steel wool will rust into dust.
To remove the oxygen that's combined with the iron, you heat it in a sturdy spoon, cast iron pan, etc. over a gas flame until it turns black.

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If you add some powdered charcoal and sawdust to the iron & salt, you have the ingredients for those chemical pocket/hand warmers.