Used coolant

I asked my tame chemist in the office next door. I'm told if you add a small amount of saturated salt solution, the oil should float to the surface. To make a sturated salt solution, dissolve as much salt possible into hot water and let it cool so the excess solidifies out. Let us know if it works.

John

That should work, though how much is a "small amount" I have some reservations. Could get expensive.

"Salting out", as it is known, is a familiar technique in organic chemistry for helping to separate water from organic liquids (which frequently are able to dissolve significant amounts of water. It relies on the fact that the solute reduces the free energy of the water - makes it more stable - so less likely to bunk off into a misalliance with the organic molecules.

Trouble is, to be really effective, it needs the salt to be present in fairly significant concentration, which would be expensive, and could only be done by putting the salt in the coolant, not by adding a little brine to a lot of coolant.

BTW, you wont get much more salt into water by heating it, the temperature coefficient of solubility of sodium chloride is very low. It will dissolve a bit quicker though.

You'll just have to try it; I don't use soluble (emulsified) oil myself, I am speaking from experience doing organic chemistry...

OTOH, wouldn't it be easier (and cheaper) just to leave it in an open container and let the water evaporate?

David

...and speed it up using one of those aquarium bubbly things (see other thread) maybe.

Regards, Tony

Try this as a starting point:

My thanks to all for the suggestions. Most of the flocculants appear to present a bigger disposal issue than the coolant. I'll try the salt. I have tried natural evaporation and that halved a 2 gallon bucket in 4 years :-) I'll give more thought to forced evaporation but volatiles might be an issue.

again my thanks Roland

Just a guess - maybe the oil forms a layer on top which prevents the water from evaporating?

A bubble stone should negate this behaviour and allow faster evaporation.

-- Peter Fairbrother

Peter,

An oil layer does indeed inhibit evaporation - markedly. I did a 3-month test a year or so ago with a 5mm layer of motor kerosene (diesel) above an open measuring cylinder of water. Evaporation of the water was reduced by a factor of about 60 compared with unshielded water.

David

Home made centrifuge ?. Then dispose of the water and reuse the oil...

Regards,

Chris