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Potassium

It is not "quite similar" to sodium but it is a complete new category instead!

Safety measures

Potassium is gradually covered with deposits of peroxo compounds (K2O2 und KO2) even when it is stored in a protective fluid. These deposits are very reactive and may burn or even explode on little pressure for example if lumps are grabbed with a gripper or cut with a knife. There have been fatal accidents on handling old potassium! The same may happen if you try to separate the pure metal from the oxide by melting the metal as described for sodium. Avoid the formation of the deposits:

  • Only buy small quantities which are rapidly consumed.
  • Check all new bottles and reject all of them where you will find potassion covered with peroxide deposits.
  • Strictly exclude oxygen, for example by
    • fusing in glass ampoules
    • replenishing the protective fluid after removal of potassium lumps, so that the bottle remains free from air bubbles. Or flush with argon gas.
    • Only use tightly closing caps.

Disposing

On storing potassium the hazard will grow more and more. Deactivation with t-Butanol as described below will then not be without risk. Especially yellow or red deposits are very dangerous. The problem is that there is no disposal company which will take charge of the potassium. The only way out will be to burn the potassium - best in the closed bottle and watching the combustion gas and the flying splinters.

Deactivation

Potassium is much more reactive than sodium and will react with ethanol or isopropanol too vigorously.  Use 2-Methyl-2-propanol (tert-Butylalcohol) instead! Since the metal is covered with the oxide deposits the reaction may only start after a long induction period. Potassium tends to form clusters which may persist for a long period of time. If the reaction dies down you may carefully add isopropanol or ethanol.

  • Since even on most careful treatment spontaneous ignition may occur it is best to perform the reaction under an inert gas atmosphere. Never use large mouth containers like a beaker.

Important:

  • Do not cool the reaction container in an ice bath. If the container breaks - and this might happen because of the strong heat - the metal will get into contact with water - and you do not like what will happen then...
  • Unfortunately a big excess of the solvent is needed to deactivate the potassium. If the concentration of the potassium alcolate, formed by the reaction, is too high the mixture will become viscous and then cannot cool the metal any more. In the worst case a potassium cluster may heat up until it is glowing and then ignite the whole mixture. This is a second reason not to use an ice bath since the cold solution will become viscous more easily. Keep the mixture thin fluid! It is self-explanatory that the potassium has to be transfered into excessive alcohol. Never drop the alcohol on excessive potassium! If there are residues in a container which cannot be removed, cover with an inert solvent to ensure sufficient cooling and then drop the alcohol to that mixture.
  • Dispose the potassium without rushing! Ensure that there is enough time for the job! The weaker the reaction the more safe is it.

Leave the mixture standing alone over night. Next day add more ethanol and at the end add carefully water. All the time watch, if there is a reaction! Leave the mixture standing alone another night.

Even if you do all this very carefully the reaction still remains hazardous. Be prepared to fight a fire all the time (safety trough, extinguishing agents, exclusion of all flammable compounds in the immediate vicinity). Only dispose the mixture to the organic waste solvents, if it is absolutely free of any metal residues. Ensure this by filtrating the mixture. The filtrate must be a completely clear solution.

More hints see disposing of sodium. Especially take care to effectively draw off the developed hydrogen gas, and carfully watch all the used equipment, if there are residues of the potassium. Only regard equipment as metal free, if it has been immersed completely and air-bubble-free in water.

There are people who say that because of the hazardous potential it is more save to burn the potassium in open air. Concerning the work safety this seems to be argueable in this case, but doing so you should be experienced how to perform the burning safely. (Sandbox, splinter shield, for example using a tin bucket etc.) Furthermore you should have an idea how to dispose the residues.