Originally Posted by
janetdoe
...
I told them I understood that this was a questionable item, and I was prepared to throw the bag away. They said they wanted to call an expert over. I asked if I was free to dispose of the bag and go to my gate or if I needed to stay, and they indicated that I needed to stay there.
They paged someone who had a badge that said 'Explosives Expert' and he ran a battery of chemical tests. In the meantime, another TSO started filling out a form and asked for my boarding pass and ID. I handed him my BP and passport, and he wanted my driver's license. Then he needed my SSN. I said, "Isn't my passport number sufficient?" and he looked puzzled/reluctant, so I went ahead and gave him my SSN.
They asked why I had the salts, and I explained that my doctor instructed me to use them. They said I was free to go and could take the bag. I asked them if they wanted to keep a sample of the salts, and they declined.
All in all, not too bad, everyone was polite, except one TSO - when I said that I was prepared to throw the salts away because they might be questionable, he asked "So you're testing us?"

In short, you were detained, harassed, had your identity information recorded, and were accused of testing the system, because you were following medical advice and carrying a powdered substance. And as noted earlier by others, there are no restrictions on powders.
I'm not confident that keeping it in your checked bag on the return trip would have avoided trouble. There are reports of people's bags being searched for carrying soil samples and other powders.
Although I'm not sure how much notice would be taken, if you have the time and energy for it, I recommend that you file a complaint to the FSD of the airport where this happened. Calling an explosives "expert" when the ETD test was negative, taking down your SSN before they had completed their tests*, and accusing you of "testing the system" are all out of line. Maybe our legal experts here can advise, but I would also be finding out what other personal information they recorded and what they intend to do with it.
How absurd to receive such treatment for doing something that's really not that unusual, and certainly not illegal.
*Edited to add: They had no business taking your SSN or personal info under any circumstances, but doing it before they find anything wrong is outrageous!