For purifying water in a survival kit I believe. 

 Nope used for thyroid according to wiki. 

 Used to block one's thyroid from absorbing radioactive iodine after a nuclear incident. Prevents various cancers which would result from said iodine being absorbed and used in the body.  Extremely useful in the first week or so after an incident where radioactive materials are ejected into the atmosphere and are falling out 👀 

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