Thought I’d share this having just found myself in the position of needing to disconnect two sections of track that I’d previously soldered ( If I had solder-wick I would have tried that first but…) : Get your iron hot and focus on only one rail. with the hot iron flow the soldered joint and gently flex the sections so this joint opens and closes slightly. Remove the iron but continue flexing the joint until the solder cools. Now with this “cold solder joint” all you need do is flow the solder in the remaining rail and gently pull the sections apart.