The item is permanent but it's also necessary to complete a mission of The Explorer Society Quest.
[Edit] Sorry for the lack of information haha.
Scale of Frozen Dragon can be obtained in the Explorer Society Quest in an Aditional Mission: The Island of Dragons.
To receive this mission your character must have: The Ice Island Quest until the final mission and rank IV at the Explorer Society.
This mission is necessary to complete the Explorer Society Quest and if you have the quest alredy completed, you can't pick up more Scales from a Frozen Dragon.
I don't have characters to test it but you can try this:
1. Start the mission.
2. Pick up your scale
3. Put the scale in your house or depot.
4. Return to the NPC Lurik (Who gave you the mission) and say "Lost"
4. Try to pick up again.
You can follow this spoiler: https://tibia.fandom.com/wiki/The_Explorer_Society_Quest#Additional_missions