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I hope this is the right place to ask. I'm not a chemist so my question may seem obvious but it's not for me.

I work in the egg industry and we produce every hour 60 tons of dried egg shells as waste. Those shells come in small grains (few millimeters) but can be further reduced to powder (like talco or marble powder).

This powder is $97~\%\ \ce{CaCO3}$ and $3~\%$ proteins.

What I'm interested in is an idea to recycle this product in a cost-effective way. At the moment a small part is used in cultivations but the rest is just stored in abandoned mines and I don't like the environmental impact that this solution has.

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  • $\begingroup$ Hi and welcome to chemistry.stackexchange.com. Feel free to take a tour of the site. This question essentially boils down to how can we use calcium carbonate in my opinion, since the proteins are easily removed from ground egg shell. $\endgroup$ – Jan Feb 6 '16 at 13:47
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    $\begingroup$ @Jan no, it does not since the protein is a burden in most $\ce{CaCO3}$ applications $\endgroup$ – permeakra Feb 6 '16 at 13:50
  • $\begingroup$ @permeakra Naively I’m going to suggest heating it to a few hundred degrees burning the proteins to smithereens and ending up with $\ce{CaO}$ … but I could be underthinking it. $\endgroup$ – Jan Feb 6 '16 at 13:52
  • $\begingroup$ @permeakra Thank you for the edit, I wasn't sure about the tags and also I've misspelled CaCO3.. $\endgroup$ – Marco Martinelli Feb 6 '16 at 14:00
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    $\begingroup$ Out of the blue I can offer cement and lime production, but I'm unsure if organics is OK there. Both processes include heating to significant temperature, but in reducing atmosphere it won't help and I'm not aware of details. Both, however, are large-scale processes, 60 ton/hour may be too little for them. $\ce{CaCO3}$ is also used in metallurgy, again, unsure about organics and scale there. $\endgroup$ – permeakra Feb 6 '16 at 14:04
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60 tons on $\ce{CaCO3}$ per hour means half a million tons per year. That's quite some calcium carbonate.

Hens need $\ce{CaCO3}$ to produce eggs. So the most natural idea to recycle it is to produce feed lime.

Or consider producing agricultural lime. The annual consumption of agricultural lime is about 2.5 million tons in Germany, and about 25 million tons in Brazil. Your production is in this scale. The presence of 3% proteins is probably of little concern if not beneficial.

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  • $\begingroup$ Feed lime - To avoid disease problems with feed it would seem that you'd have to lime the eggshells then convert back to calcium carbonate. That is just too complex when you could buy calcium carbonate to start with. $\endgroup$ – MaxW Apr 15 '16 at 22:57
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    $\begingroup$ Agricultural lime - So much is used that the egg shells would be a very small source of calcium carbonate (assuming that the product is fine enough and dry enough to be mixed directly...). So the plant that makes agricultural lime would be near a calcium carbonate mine. So the problem would at least be the shipping costs between the two plant locations. $\endgroup$ – MaxW Apr 15 '16 at 23:04
  • $\begingroup$ Thank you @aventurin. I accept your answer because in the end we are selling it 20% as feed lime and the rest of it as agricultural lime. $\endgroup$ – Marco Martinelli Apr 16 '16 at 14:03

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