Australia's Science Forum

Can anyone please advise me on how to dispose of a potassium permanganate/glycerol dem reaction. I have a bout 1/2 an evaporating dish left over. CSIS advises KMnO4 can be tipped down the sink. Chemwatch say definitely not, extremely harmful to aquatics. I'm tempted to just wrap it up in newspaper and bin it?

Put it on your flume cupboard and evaporate it. Cheapest way to go.

If you are talking about the solid that remains after the reaction between KMnO4 and glycerol have reacted I make sure that it is thoroughly cooled down (let it sit in the fume cupboard for a day or so) before disposing of it in the bin. Just make sure that the reaction has used up all the chemicals.

I set up a small mountain of sand on a metal base (large coffee tin lid or metal baking tray) then make a well in the sand and put about two teaspoons of potassium permanganate crystal in the depression in the sand, then make another small depression in the KMnO4 crystals before pouring the glycerine onto the KMnO4. The kids love the volcano fire that happens and the lava that flows down the side of the sand volcano. We do this prac outside in the open air and make sure that the students are away from any fumes or smoke generated by the reaction. The setup goes into the fume cupboard afterwards to dissipate any smell in the prep room.

I would be interested in knowing if my disposal method is correct or if I should be doing something else with the residue.
Lyn.

Hi all
Looking for updated advice on potassium permanganate disposal. I have followed the Science Assist recommendations of adding 2M sulfuric acid then 10% sodium bisulfate but the colour has hardly reduced. So now I have gone from having 250mls 0.1M pot. permanganate to having about 2L - still dark purple. Do I keep going adding more Sod bisulfate or adding more water to dilute it further? Will I ever be able to pour it down the sink or am I just creating more waste which we will have to pay for disposal?
Gone are the days where we can toss anything down the sink with little thought of the damage to our water systems!
Kathryn

Here's something from RiskAssess - "permanganate cation is highly toxic to aquatic life, but reacts in sewer with organic matter to form Mn(II) and MnO2".
So I just chuck it down the sink with some water!!

This is from Science Assist Chemical Handbook for Australian Schools. Great resource.

WASTE DISPOSAL
Solid potassium permanganate must not be disposed of with
general waste. Store surplus or waste solid in the original
container or other suitable labelled container. Arrange for
collection by licenced waste disposal contractor.
Small quantity of solution: Treat with a reducing agent
under acidic conditions to give a solution containing Mn(II).
To treat 500mL of 0.1M KMnO4 solution: Acidify by adding
10mL of 2M H2SO4. In a fume cupboard, slowly add 300mL
of 10% w/v sodium bisulfite or sodium metabisulfite solution.
The resulting solution should be colourless to faint pink. If
permanganate still remains, add a further portion of
bisulfite solution. Neutralise by addition of sodium carbonate
to within pH 6-8. Wash the solution down the sink

As I said, I have done that and the colour has not changed.

Morning my fellow colleagues,

I recently discovered that 1 part vinegar to 1 part 3% hydrogen peroxide cleans up potassium permanganate stains a treat!

This morning I tried putting some in a small beaker of potassium permanganate waste and it went clear.

Are there any chemists out there who could tell me what could the resulting liquid be? It certainly fizzes during its reaction, I am assuming oxygen given off but didn't have a taper on hand to check. Further to this, could it be a potassium hydroxide which could be neutralized and then washed down the sink?

Thanks in advance,

Googled this - MnO4−(aq)+H2O2(aq) = Mn2+(aq)+O2(g) It did say it needed to be an acidic environment, so the vinegar was important. I saw someone put vitamin C in KMnO4 and it went colourless. I think this is also the KMnO4 being reduced to Mn ions. I'm still not convinced I need to do anything other than what RiskAssess recommends - chuck it down the sink.

P.S. Maximum 10g per day of manganese salts down the drain.