The Neurotoxin Vats are tall buildings used by the Scorpion Cell to store a special toxin that was supposed to be capable of countering Yuri's mind control technology.
In Obsidian Sands, multiple Neurotoxin Vats are scattered inside the Scorpion Cell's base. Yuri first thought that these vats were just another variation of the Bio Reactor that powers the Scorpion Cell's base. He later knew that it was filled with unidentified toxins that the Proselyte must be careful about.
During development of the mission Obsidian Sands, the Neurotoxin Vats near Rashidi's Palace were originally research modules (as seen in Foehn reveal trailer). It is currently unknown if the vats existed in the mission during its early development.