Mélange (Soviet name for Inhibited Red Fuming Nitric Acid) is a liquid oxidant rocket propellant component that was "used during the Soviet era as one of two components to propel small and medium range missiles.
"[1] It is highly toxic and aggressive mixture of nitric acid (≥ 70%) and dinitrogen tetroxide (18-27%) and other additives and impurities (~ 3%) with very limited amount of water (≤ 4%).
Upon decomposition it produce red fumes of nitrogen tetroxide and nitric acid.
Most states are eliminating their mélange, either by neutralizing it or transferring it to specialized chemical facilities.
The substance can be processed into chemical products for civilian use, such as agricultural fertilizers.